Bertha Madras - US grants

The objectives of the proposed research are to develop improved molecular probes for specific cocaine recognition sites in primate brain and to provide fundamental information on the distribution and pharmacological properties of these sites in relation to cocaine abuse. The relatively low affinity and rapid dissociation of [3H]cocaine limited its suitability for these studies and a higher affinity cocaine congener [3H]CFT ([3H]WIN 35,428), which binds to virtually the same sites as [3H]cocaine, was developed. (3H]CFT was suitable for mapping high density cocaine recognition sites in brain, for monitoring dopamine nerve terminal degeneration in Parkinson's diseased brain and as a PET (positron emission tomography) imaging ligand. We propose to continue our ongoing studies with [3H]CFT to clarify the functional relevance of high- and low-affinity binding components for cocaine and to characterize cocaine binding sites in discrete brain regions revealed by autoradiographic mapping of [3H]CFT binding. Although [3H]CFT is an effective probe for cocaine recognition sites, its moderate affinity for the dopamine transporter, a principle target of cocaine in the brain, has prompted a search for higher affinity ligands. We will evaluate the higher affinity ligands [125I]RTI-55 and [3H]Lu 19-005, using techniques similar to those used in our initial studies with [3H]CFT. In addition, novel phenyltropane analogs (3-iodo, 4-chloro, 3,4-dichloro) will be synthesized or acquired, and evaluated in coordinated biochemical and behavioral studies. The relative potencies of these compounds for inhibiting [3H]CFT (dopamine transporter) and [3H]citalopram (serotonin transporter) binding, for producing cocaine-like discriminative stimulus effects and for maintaining i.v. self-administration will be measured. The results will be compared with data from RTI-55 and Lu 19-005. Based on our findings, we will select the highest affinity and most selective for the dopamine transporter for further development. The proposed research will provide needed information for defining the principal neurochemical targets of cocaine in the brain and for developing rational approaches to the pharmacological management of cocaine abuse.

The Society for Neuroscience Partnership in Science Literacy aims to form an enduring relationship between the Society for Neuroscience and the Boston Museum of Science. The first project will be an endeavor in adult science education, with the Division on Addictions at Harvard Medical School acting as the representative of the Society for Neuroscience. Phase one of the Partnership will consist of a 6 month development period, followed by a year-long program at the Museum of Science. During the second phase, the products of the Partnership will be widely disseminated by the Society for Neuroscience. The Partnership will plan a multidisciplinary program that will provide adults with an appreciation for the methods of scientific research, and teach them about the neurobiology of drug abuse, addiction, and a co-morbid disease, depression. The program will consist of a two-character multimedia play that will raise important scientific questions relating to drug abuse, addiction, and depression, and a CD-ROM-based exhibit that will teach the neurobiology underlying these issues. The play will be shown in a Museum theater 60-80 times during the year. It will promote audience participation, build a human context for scientific questions relating to drug use, and motivate viewers to explore the exhibit. The exhibit will consist of a large screen high-density TV monitor displaying a continuously running introduction to the exhibit (a photo-CD program having stills and animation). The exhibit will also have 10 stations, each of which will consist of a panel (artifacts and graphics) and a 14" color television monitor that will display CD-ROM,programs containing slides, videos, and animated films. Five of the monitors will present background information on the following topics: 1) Drugs (definitions, classes, sources, other uses); 2) Cellular Communication (neuronal structure, synaptic transmission, drug-receptor interactions); 3) Relevant Neuroanatomy (the dopaminergic midbrain reward system relevant to addiction, noradrenergic and serotonergic pathways relevant to depression); 4) Addiction (definitions, concepts, risk factors, co-morbidity, treatment approaches); and 5) Research (the scientific method and its role in public health). The remaining monitors will present information about the following drugs or classes of drug: alcohol, nicotine, cocaine, opiates, and cannabis/hallucinogens. The scientific information will also be presented in 4 lectures/slide presentations (involving audience participation) at the Museum. Two of the lectures will be for public audiences, and two for invited guests (educators, press, and community and religious leaders). Special interest groups having specific concerns about drug abuse and addiction will be identified. Their needs will be assessed, and then addressed in Special Interest Dinners at the Museum, that will include viewing of the play and exhibit, and a panel discussion with experts. Pamphlets, CDs, and slide/video sets will be produced. The programs and materials of the Partnership will serve as educational models, and will be disseminated by the Society for Neuroscience. All efforts will be evaluated.

The proposed research has two objectives, to define the molecular targets of cocaine in human brain and to use positron emission tomography (PET) in the preclinical evaluation of potential cocaine substitutes. Our first goal is to systematically characterize [3H]cocaine binding sites in human brain regions including the nucleus accumbens, striatum, locus coeruleus, hippocampus, and amygdala. The research motivated by three preliminary findings that merit further investigation; (1) Using ex vivo autoradiography, we identified a number of regions in nonhuman primate brain that accumulate high levels of {3H}cocaine after i.v. administration of trace or pharmacologically relevant doses. We will characterize sites in these regions with a view to determining their functional significance. (2) In human post-mortem control striata, cocaine binding sites labeled by [3H]WIN 35, 428 were associated with the dopamine transporter. In Parkinson's diseased striata, [3H]WIN 35,428 binding sites differed from the dopamine transporter. We will compare sites labeled by [3H]WIN 35, 438 in these populations, with a view to assessing their relevance to the reinforcing properties of cocaine. (3) Preliminary data suggest that cocaine is metabolized more rapidly in the substantia nigra/ventral tegmental area of nonhuman primate brain than the striatum and we will extend these studies to human brain. Our second goal is focused on developing PET imaging techniques in nonhuman primate brain (Macaca fascicularis) to identify potential cocaine therapeutic agents. We will use positron emission tomography (PET) to image in vivo the direct (monoamine transporters) and indirect (D1 dopamine receptors) targets of cocaine in brain. Our objectives are to identify and to synthesize cocaine congeners with a view to developing high affinity long-acting cocaine substitutes. Their occupancy of the dopamine transporter will be measured by PET using [11C]WIN 35, 428 and occupancy of a broader spectrum of cocaine binding sites will be detected by the relatively non-selective cocaine congener [11C]CDCT. Candidate compounds will include high affinity long-acting dopamine transport inhibitors, novel cocaine congeners synthesized as a component of this program, and D1 dopamine receptor agonists. Occupancy of the D1 receptor will be measured by [11C]SCH 39166. We will evaluate dopamine transporter ligands (indirect dopamine agonists) and extend these studies to potent dopamine agonist drugs targeted to D1 dopamine receptors. This approach will provide fundamental information on [3H]cocaine binding sites in human brain tissue and utilize brain imaging techniques for identifying potential cocaine therapeutic agents.

The Society for Neuroscience Partnership in Science Literacy aims to form an enduring relationship between the Society for Neuroscience and the Boston Museum of Science. The first project will be an endeavor in adult science education, with the Division on Addictions at Harvard Medical School acting as the representative of the Society for Neuroscience. Phase one of the Partnership will consist of a 6 month development period, followed by a year-long program at the Museum of Science. During the second phase, the products of the Partnership will be widely disseminated by the Society for Neuroscience. The Partnership will plan a multidisciplinary program that will provide adults with an appreciation for the methods of scientific research, and teach them about the neurobiology of drug abuse, addiction, and a co-morbid disease, depression. The program will consist of a two-character multimedia play that will raise important scientific questions relating to drug abuse, addiction, and depression, and a CD-ROM-based exhibit that will teach the neurobiology underlying these issues. The play will be shown in a Museum theater 60-80 times during the year. It will promote audience participation, build a human context for scientific questions relating to drug use, and motivate viewers to explore the exhibit. The exhibit will consist of a large screen high-density TV monitor displaying a continuously running introduction to the exhibit (a photo-CD program having stills and animation). The exhibit will also have 10 stations, each of which will consist of a panel (artifacts and graphics) and a 14" color television monitor that will display CD-ROM,programs containing slides, videos, and animated films. Five of the monitors will present background information on the following topics: 1) Drugs (definitions, classes, sources, other uses); 2) Cellular Communication (neuronal structure, synaptic transmission, drug-receptor interactions); 3) Relevant Neuroanatomy (the dopaminergic midbrain reward system relevant to addiction, noradrenergic and serotonergic pathways relevant to depression); 4) Addiction (definitions, concepts, risk factors, co-morbidity, treatment approaches); and 5) Research (the scientific method and its role in public health). The remaining monitors will present information about the following drugs or classes of drug: alcohol, nicotine, cocaine, opiates, and cannabis/hallucinogens. The scientific information will also be presented in 4 lectures/slide presentations (involving audience participation) at the Museum. Two of the lectures will be for public audiences, and two for invited guests (educators, press, and community and religious leaders). Special interest groups having specific concerns about drug abuse and addiction will be identified. Their needs will be assessed, and then addressed in Special Interest Dinners at the Museum, that will include viewing of the play and exhibit, and a panel discussion with experts. Pamphlets, CDs, and slide/video sets will be produced. The programs and materials of the Partnership will serve as educational models, and will be disseminated by the Society for Neuroscience. All efforts will be evaluated.

DESCRIPTION (Investigator's Abstract): Idiopathic Parkinson's disease (IP) is a progressive neurodegenerative disorder characterized by a severe depletion of nigrostriatal dopamine neurons and distinct neurological deficits. Management of the disease continues to pose major diagnostic and therapeutic challenges. The overall goals of this project are to develop improved markers and therapeutic approaches to IP. Preliminary studies in this laboratory have generated promising leads for each of these goals. We have identified CFT (WIN 35,428; 2beta carbomethoxy -3beta-4-(fluorophenyl) tropane) as a sensitive marker for the pathophysiological changes in Parkinson's disease. [3H] CTF binds to the dopamine transporter and binding is markedly reduced in postmortem Parkinson's diseased brains in vitro. In vivo, positron emission tomographic imaging (PET) with [11C] CTF suggests that it is an accurate indicator of dopamine neuron degeneration in MPTP-treated monkeys and in humans, as reported by others. Our first aim is to establish a quantitative assay of [11C] CFT in vivo with PET. Pilot studies with [11C] CFT have indicated the feasibility of quantifying the density of the dopaniine transporter with PET. We then will relate the density of [11C] CFT to progressive changes in motor in MPTP treated monkeys. Our second aim is to establish a quantitative assay of [11] CFT in humans. We will quantify [11C] CTT uptake in normal human subjects and utilize this information for imaging of patients with 1P. We will evaluate the efficacy of [11C] CFT as an in vivo imaging agent for the pathophysiology of 1P both to differentiate patients from age-matched controls and as a tool for monitoring the progression of the disease. Our third goal is to utilize PET imaging in monkeys to relate the therapeutic potential of D1 dopamine receptor agonists with the degree of dopamine neuron degeneration. A selective D1 agonist improved motor function in MPTP -treated cynomolgus monkeys and we will extend these studies to other drugs administered acutely and chronically. These results will be compared with findings using D2 agonists. These studies will provide fundamental information on the usefulness of the dopamine transporter as a marker for Parkinson's disease and clarify whether dopamine agonists targeted to D1 dopamine receptors represent important leads for the therapeutic management of Parkinson's disease.

substance abuse related disorder; mental disorders; nervous system; drug screening /evaluation; Primates; human tissue; behavioral /social science research tag;

This application for an Independent Scientist Award (K02) requests support to develop an integrated program of cocaine research. Cocaine abuse persists as a leading public health problem in the country and basic research can contribute to diminishing the national burden. A systematic approach to investigating the molecular targets of cocaine and consequences of cocaine abuse to the brain will provide information needed for the development of novel and effective treatments of cocaine abuse. The goals of the laboratory are to consolidate chemical, biochemical, imaging and behavioral approaches to cocaine research and provide a bridge for clinical applications. Studies are proposed to investigate the molecular targets of cocaine in nonhuman primate and human brain with a view to identifying potential sites for drug therapies. Although current evidence converges on basal ganglia doparnine systems as primary contributors to the reinforcing properties of cocaine, the profuse sequelae produced by cocaine supports the need to probe other neurochemical targets of cocaine in discrete brain regions. The investigator will continue a productive collaborative program to develop novel cocaine substitutes or antagonists and utilize neurochemical, behavioral and biochemical techniques to evaluate the suitability of these drugs for the treatment of cocaine abuse. She will develop and utilize ligands for PET or SPECT imaging of brain to identify long-acting cocafne substitutes and to quantify the targets of cocaine in living brain tissue. This pragmatic and integrated approach will provide fundamental information on the neurobiology of cocaine with direct relevance to clinical applications.

animal tissue; substance abuse related disorder; mental disorders; Primates; nervous system; behavioral /social science research tag;

animal tissue; substance abuse related disorder; mental disorders; nervous system; biological products; Primates; drug screening /evaluation; psychology; behavioral /social science research tag;

DESCRIPTION: (Applicant's Abstract) Cocaine addiction is a complex and multi-dimensional problem that has defied conventional medical, psychological and legal interventions. Although behavioral modification procedures that promote abstinence are optimal strategies, they have not been successful. Mounting evidence indicates that pharmacological agents are required to treat cocaine addiction. The long-term goals of this research are to develop medications for the management of cocaine addiction. The specific goals are to investigate promising novel compounds with strategies that can be applied directly to human studies. Although progress has been made in the use of animal models to study cocaine's effects on the brain, most animal studies cannot be repeated in human subjects. Positron emission tomography (PET) offers a unique opportunity for studying the cerebral biochemistry and pharmacology of candidate therapeutics for cocaine abuse at the preclinical level, and for applying the same techniques in the clinical phase of the research. The applicants propose to use PET imaging techniques to investigate whether dopaminergic compounds display pharmacokinetic and pharmacodynamic properties that may be appropriate for treating cocaine dependency. Two classes of compounds will be investigated, dopamine transporter inhibitors developed with a chemist-collaborator, Dr. Peter Meltzer, and D1 dopamine receptor agonists. The applicants will investigate the feasibility of identifying dopamine transporter drugs that bind to the dopamine transporter at sufficiently high levels to prevent access to [11C]cocaine. Such compounds may effectively serve as both cocaine replacements and as cocaine antagonists. Subsequently, these compounds will be administered chronically, with a view of determining whether transporter blockade persists. It is hypothesized that the D1 dopamine receptor, an indirect target of cocaine, is subject to profound regulatory processes which may contribute to or detract from the therapeutic potential of candidate drugs. Based on this theory, studies will investigate the effects of candidate compounds or D1 receptor availability using [11C]SCH23390 to image the sites. This approach will provide lead compounds for further assessment as cocaine medications and strategies directly applicable to human studies.

substance abuse related disorder; radiology; positron emission tomography; nervous system; biological products; Mammalia; Primates; drug screening /evaluation; mental disorders; behavioral /social science research tag;

animal tissue; substance abuse related disorder; mental disorders; human tissue; biological products; Primates; drug screening /evaluation; nervous system; behavioral /social science research tag;

animal tissue; substance abuse related disorder; mental disorders; Primates; Mammalia; nervous system; behavioral /social science research tag;

technology /technique development; substance abuse related disorder; male; radiology; human subject; spectrometry; Primates; aging; Mammalia; biological products; drug screening /evaluation; nervous system; female; behavioral /social science research tag;

radiology; nervous system; human tissue; spectrometry; Primates; aging;

technology /technique development; animal tissue; substance abuse related disorder; magnetic resonance imaging; drug screening /evaluation; Primates; aging; Mammalia; biological products; nervous system; radiology; behavioral /social science research tag;

animal tissue; substance abuse related disorder; psychology; drug screening /evaluation; Primates; biological products; nervous system; behavioral /social science research tag;

Increasing evidence suggests that the dopamine transporter is an important marker for pathological changes in dopamine neurons, including Parkinson's disease, aging and substance abuse. Potent dopamine transport inhibitors of the phenyltropane series (e.g. WIN 35,428 or CFT) are among the most effective candidates for PET (positron emission tomography) or SPECT (single photon emission computed tomography) imaging of the dopamine transporter in living brain. The goals of this project were to investigate whether altropane, an N-iodoallyl derivative of WIN 35,428 (IACFT:E-N-iodoallyl-2 -carbomethoxy-3 -(4-fluorophenyl)tropane), displays in vitro properties suitable for evaluation as a SPECT imaging agent. In cynomolgus monkey (Macaca fascicularis) striatum, the region containing the highest levels of dopamine in brain, the unlabeled E- isomer (IC50 6.62 q 0.78 nM) was more potent than the Z-isomer (IC50 52.6 q 0.3 nM) and displayed a relatively high dopamine:serotonin transporter selectivity (28-fold). In radiolabeled form, [125I]altropane bound to sites in the striatum with a single high affinity (KD 5.33 q 0.55 nM) and with a site density (BMAX 301 pmol/g original wet tissue weight) that was within the density range reported previously for the dopamine transporter in striatum. Saturation experiments revealed that [125I]altropane recognized a single affinity binding site, in contrast to the two binding components characteristically detected with [3H]WIN 35,428 or with other brain imaging agents, (e.g. [125I]RTI-55 ( -CIT) or [125I]RTI-121). This unanticipated property of altropane is advantageous because detection of a single affinity site allows for relative ease in quantifying the density of the transporter in vitro or in vivo. Drugs inhibited [125I]altropane binding with a rank order of potency that corresponded closely to their rank order for inhibiting [3H]WIN 35,428 binding (r2 0.99; p < 0.0001) and for blocking dopamine transport. These results indicate that the binding domain on the dopamine transporter can accommodate large groups in the region of the amine nitrogen of phenyltropanes. The selectivity of altropane for the dopamine over the serotonin transporter is also a favorable property of altropane because of the presence of the serotonin transporter in primate striatum, the possibility of serotonin fiber sprouting in the striatum, hyperinnervation of the host striatum by serotonin neurons from ventral mesencephalon grafts, and increased striatal contrast. Based on the high affinity and selectivity of altropane for the dopamine transporter, altropane is a candidate marker for imaging and monitoring the status of the dopamine transporter, and associated dopamine neurons in brain. Madras BK, Meltzer PC, Liang AY, Hanson R, Elmaleh DE, Babich J, Fischman AJ. [125I]Altropane, a SPECT Imaging Probe for

If neuron-specific, molecular targets for PET or SPECT brain imaging agents may also serve as a window on the status of associated neurons. The dopamine transporter is a particularly attractive target for imaging, as it is expressed uniquely on dopamine neurons. As dopamine neurons degenerate markedly in Parkinson's disease in tandem with the dopamine transporter, imaging agents targeted to the transporter can expedite the diagnosis and treatment of Parkinson's disease. SPECT or PET imaging of the transporter in brain requires selective imaging agents that display appropriate pharmacokinetic properties. We discovered that [125I]altropane ([125I]IACFT,2 -carbomethoxy-3 -(4-fluorophenyl)-n-(1-iodoprop-1-en-3-yl)nortropane) bound with high affinity 5 nM) to a single site on the dopamine transporter and was selective for the dopamine over the serotonin transporter in homogenates of monkey striatum. The goals of this project were to determine whether the selective binding of [125I]altropane is reflected in its brain distribution, the in vitro and ex vivo distribution of [125I]altropane in squirrel monkey (Saimiri sciureus) brain was determined by quantitative autoradiography of coronal brain sections. In vitro, [125I]altropane (2 nM) distribution was discrete and was detectable primarily in the dopamine-rich putamen, caudate nucleus and nucleus accumbens. The resulting putamen:cerebellum ratio exceeded 120:1 (n=3). The selective in vitro binding of [125I]altropane to the dopamine transporter, at concentrations approaching its Kd value highlight its suitability for investigating the density of the dopamine transporter in various brain regions in vitro. Ex vivo autoradiography was conducted in monkeys to determine whether the brain distribution of [125I]altropane in vitro was predictive of its brain distribution pattern after intravenous administration. Thirty minutes after intravenous injection, highest levels of [125I]altropane (0.3 nmol/kg) were detected in the caudate-putamen and nucleus accumbens and lowest levels in the cerebellum and cortex. The putamen or caudate:cerebellum ratio was 7. SPECT imaging of the brain within 30 min of i.v. injection confirmed the rapid and selective accumulation of [123I]altropane to the striatum. The selective binding of altropane to the dopamine-rich striatum within 30 minutes of intravenous administration indicates that it is uniquely suited for SPECT or PET imaging of the dopamine transporter and associated dopamine neurons. [125I]Altropane, a dopamine transporter probe, is a promising imaging agent for the dopamine transporter and associated dopamine neurons in brain. In vitro, [125I]altropane distribution in vitro is strikingly similar to the distribution of the dopamine transporter or transporter mRNA in brain. The resulting putamen:cerebellum ratio 100:1, a ratio not achieved previously, suggests that it is among the most selective probes for the dopamine transporter. The favorable binding properties of altropane in vitro are not necessarily predictive of the rate at which it may enter the brain, distribute or clear the brain in vivo. Ex vivo autoradiography is an effective procedure for gauging the appropriateness of a probe for imaging. It provides information on brain penetrance of a ligand, rate of entry and a detailed anatomical map of the distribution of a ligand. Administered intravenously, the paramount properties of [125I]altropane were rapid entry into brain, selective accumulation in striatum within 30 minutes and a similar distribution in vitro and in vivo. The rapid entry into brain and high degree of localization to striatum within 30 minutes anticipated that altropane was a promising SPECT candidate. SPECT imaging with [123I]altropane in human subjects and in monkeys fully support this expectation. The unique pharmacokinetic properties of [123I]altropane allow SPECT imaging sessions to be conducted within a short time period after administration of the probe, a substantial convenience for clinical studies. Conversion of altropane from a SPECT to a PET ligand without changing its molecular structure is feasible, by insertion of [11C] as a methyl group on the 2 -carbomethoxy position. PET and SPECT imaging with [11C] and [123I]altropane, conducted under virtually the same conditions and time frame, will permit detailed assessment of the relative advantages and disadvantages associated with the two imaging techniques. With emerging technologies targeted to neuroprotective and neuroregenerative agents, the capacity to view the status of dopamine neurons will offer objective information on the efficacy of these novel approaches. Imaging of the dopamine transporter in living brain in a longitudinal study can clarify the neuroadaptive processes that occur consequent to cocaine. From the medications development perspective, imaging of the transporter can provide important information of level of occupancy of candidate cocaine medications. By virtue of its favorable pharmacokinetic properties and rapid, selective accumulation in the striatum, altropane is a promising SPECT and PET imaging probe. The production of an identical PET and SPECT imaging agent will allow for meaningful comparisons to be made between the two imaging techniques. Finally, the close correspondence between in vitro and in vivo distribution of altropane supports the feasibility of comparing measures of dopamine neurons in living brain tissue and in post-mortem tissue with an identical probe. Madras BK, Gracz LM. Meltzer PC, Liang AY, Elmaleh DR, Fischman AJ. Altropane, a SPECT imaging probe for dopamine neurons II. In vitro and ex vivo distribution in primate brain, Synapse, in press, 1998. Madras BK, Gracz LM, Kaufman MJ, Meltzer PC, Elmaleh D, Fischman AJ. Altropane, a novel SPECT imaging agent for cocaine binding sites on the dopamine transporter, NIDA Res. Monograph, 176 1996. Fischman AJ, Babich JW, Elmaleh DE, Barrow SA, Meltzer PC, Madras BK. SPECT imaging of dopamine transporter sites in normal

Increasing evidence suggests that the dopamine transporter is situated almost exclusively on dopamine neurons. Accordingly, it is an excellent marker for Parkinson's disease, a neurodegenerative disease characterized by a severe loss of dopamine neurons. We previously demonstrated that the potent dopamine transport inhibitor [125I]altropane (IACFT:E-N-iodoallyl-2 -carbomethoxy-3 -(4-fluorophenyl)tropane) is a high affinity selective probe for the dopamine transporter in monkey brain and an effective SPECT imaging agent in nonhuman primate brain. This project had two objectives, to determine whether the favorable binding properties of altropane in nonhuman primates extends to human brain and to assess the suitability of altropane as a marker for Parkinson's diseased brain. In homogenates of human brain putamen, [125I]altropane bound to a single high affinity site (KD 4.96 q 0.38 nM, n = 4) and a site density (BMAX 212 q 41.1 pmol/g original wet tissue weight). The affinity was within the range of affinities reported for effective brain imaging agents and, equally significant, binding to a single affinity site increases the level of accuracy for density measurements. The density was within the density range reported previously for the dopamine transporter in this brain region. Drugs inhibited [125I]altropane binding with a rank order of potency that corresponded closely to their rank order for blocking dopamine transport (r 0.98, p <0.001). In post-mortem Parkinson's diseased brain, bound [125I]altropane (1 nM) was markedly reduced (89%, 99% in putamen, depending on measures of non-specific binding) compared with normal aged-matched controls (normal putamen 49.2 q 8.1 pmol/g ; Parkinson's diseased putamen 0.48q0.33 pmol/g; n = 4). In vitro autoradiography, conducted in tissue sections at a single plane of the basal ganglia, revealed high levels of [125I]altropane binding the caudate nucleus and putamen, but lower levels (73% of the caudate-putamen) in the nucleus accumbens (n = 7). In Parkinson's diseased brains (n = 4), [125I]altropane binding was 13% of the levels detected in normal putamen, 17% of normal values in the caudate nucleus and 25% of normal levels in nucleus accumbens. Accordingly, [125I]altropane detected losses of the dopamine transporter that are consistent with dopamine depletion reported previously. The association of [125I]altropane to the dopamine transporter in human post-mortem tissue, the marked reduction of [125I]altropane binding in Parkinson's diseased brains, its rapid entry into brain and highly localized distribution in dopamine-rich brain regions, support its use as a probe for monitoring the dopamine transporter and associated dopamine neurons in vitro and in vivo by SPECT or PET imaging technologies. As an in vivo imaging agent, altropane displays favorable pharmacokinetic properties, achieving equilibrium with the primate brain dopamine transporter within 30 - 60 minutes. These properties are well suited to both PET and SPECT imaging. In concert with this advantage is the feasibility of converting altropane into a chemically identical PET ([11C] or SPECT (123I]) imaging agent. A detailed assessment and comparison of PET vs SPECT imaging conducted under identical conditions with altropane is ongoing. Imaging of the dopamine transporter with WIN 35,428 and its congeners has been applied to the aging brain, Parkinson's disease, other neuropsychiatric disorders (e.g. Tourette's disorder, Lesch-Nyhan syndrome, and alcohol abuse. Investigation of the dopamine transporter as a target of psychostimulant drugs (e.g. cocaine, amphetamine) is another significant application of this class of probes. Cocaine induces neuroadaptive changes in the dopamine transporter and amphetamines are neurotoxic to dopamine neurons. Consequently, PET and SPECT imaging of the transporter can provide needed information on psychostimulant- induced addiction and toxicity in living brain and a useful strategy for investigating candidate cocaine medications. Notwithstanding these important applications, Parkinson's disease continues to be the dominant focus of dopamine transporter imaging research. Accurate imaging of dopamine nerve terminals will be useful in identifying subjects in the preclinical or early stages of the disease. This population may be candidates for emerging technologies designed to treat the disease by promoting regeneration of dopamine neurons. The effectiveness of agents that "rescue" and/or promote growth of dopamine neurons may be gauged by monitoring dopamine nerve terminals with altropane. Based on these and previous data from our laboratory a Phase I clinical trial is ongoing. Madras BK, Babich JW, Elmaleh DR, Meltzer PC, Fischman AJ. The SPECT ligand altropane effectively detects Parkinson's disease in human putamen. Soc Nucl. Med. 38 220, 1997. Madras BK, Gracz LM, Meltzer, PC, Babich J, Fischman AJ. [125I]Altropane, a SPECT imaging probe for dopamine neurons III. Human

The transporters for the monoamines dopamine, serotonin and norepinephrine are principal targets for the majority of antidepressant drugs, methylphenidate (Ritalin), the most frequently prescribed drug for treatment of Attention Deficit Hyperactivity Disorder, and the addictive drug cocaine. By blocking monoamine transporters and elevating monoamine levels, the drugs trigger a cascade of biochemical events, leading to therapeutic benefit or, in the case of cocaine, stimulant effects and abuse liability. Without exception, the molecular structure of therapeutic and other drugs that modulate monoamine transporters have been designed with an amine nitrogen in the molecular structure. We recently reported a unique series of compounds (aryloxatropanes) that bear no amine nitrogen in their structure (nonamines) yet are potent inhibitors of the dopamine transporter. The objective of the present study was to determine whether the brain distribution of a nonamine corresponds to the known distribution of the dopamine transporter in rhesus monkey brain (Macaca mulatta). Initially, parametric studies were conducted to establish appropriate pre-incubation, incubation, and buffer wash times. Subsequently, 20 mm coronal tissue sections were incubated with [3H]O-1059 (0.3 nM) to measure total binding, and cocaine (30 mM) to measure nonspecific binding. Autoradiographic analysis of the distribution of the [3H]O-1059 was subsequently performed in 9 distinct brain regions, of 6 anterior to posterior planes. Dense labelling was noted in the striatum and considerably lower levels were observed in other brain regions. The distribution pattern was similar to that obtained with the selective monoamine ligand ([3H]CFT or [3H]WIN 35,428), indicating that the absence of an amine nitrogen does affect brain distribution of potent dopamine transport inhibitors. Overall, these data support further development of nonamines, a new generation of transport inhibitors.

Monoamine transporters are the targets of brain imaging agents, antidepressant drugs, cocaine, and methylphenidate, the most effective drug for treating attention-deficit disorder. This Division has an ongoing program to develop novel therapeutic and imaging agents for neuropsychiatric disorders. To identify promising therapeutic or imaging agents that target transporters, it is necessary to first investigate the binding properties of the compounds in vitro and determine their affinity and transporter specificity. Based on data from these experiments, candidate drugs progress through a series of other in vivo tests in nonhuman primates, and if warranted into clinical trials. The goal of this pilot project is to develop stable cell lines that express non-human primate dopamine, norepinephrine and serotonin transporter cDNA. These stable cells lines will be used for at least three purposes. 1. to investigate novel drugs (designed as imaging agents or as therapeutics) in a preparation that is potentially less hazardous to human health than monkey brain tissue. 2. To compare the sequence homology of squirrel monkey dopamine transporter and human transporter. 3. to determine evolutionary changes monkey vs human transporters. In brain tissue, the squirrel monkey and the human transporters bind cocaine with higher affinity than the transporter of macaque monkeys and we will investigate whether amino acid sequences account for these differences. We will clone dopamine transporter cDNAs from old-world and new-world monkey using a reverse transcriptase-polymerase chain reaction strategy, based on the high degree of similarity between the cloned mammalian dopamine transporter sequences. RNA will be extracted from monkey substantia nigra using a Poly(A)Pure mRNA purification kit. These cell lines will provide a resource for screening potential imaging agents in vitro that is not dependent upon the availability of monkey brain tissue, have greater consistency from experiment to experiment, and are less

The D4 dopamine receptor, one of at least five subtypes of dopamine receptors, was recently cloned. Mounting evidence suggests that many variants of this receptor are found in human populations. One variant of the receptor occurs with high frequency in a population with attention deficit hyperactivity disorder. The D4 receptor is also relevant to schizophrenia, as the effective antipsychotic drug clozapine binds the receptor with high affinity. In cocaine addiction, the D4 receptor is implicated as an indirect target of cocaine. For each of these neuropsychiatric disorders, investigation of D4 dopamine receptor pharmacology, receptor expression and regulation is warranted. Although it is feasible to study the D4 receptor in cell lines expressing the cloned receptor. the functional significance, distribution, binding properties, expression and regulation of the D4 receptor in primate brain tissue has been difficult because of inadequate probes for this receptor subtype. The purpose of the present study was to investigate the brain distribution and pharmacological properties of the D4 receptor in primate brain, using two novel probes for the D4 dopamine receptor. Autoradiographic distribution of the receptor was determined in rhesus monkey brain (Macaca mulatta) with a D4-selective probe [3H]LU-85-295. Initial parametric studies were conducted to establish appropriate incubation and buffer wash times. Subsequently, coronal tissue sections were incubated with [3H]LU 85295 (3 nM) to measure total binding and with haloperidol (10 fM) to measure nonspecific binding. Autoradiography with [3H]LU 85295 revealed a brain distribution of the D4 receptor similar to the distribution of mRNA encoding the receptor, with highest levels in frontal and insular cortices and in hippocampus, amygdala, thalamus, and hypothalamus. Stability problems with [3H]LU 85295 prompted us to custom synthesize a novel probe [3H]U-101958 for the D4 receptor. Preliminary data in homogenates of hippocampus indicate that the binding properties of [3H]-LU 85295 are consistent with the D4 receptor. This research is the first to identify the D4 receptor in primate brain tissue with a D4-selective probe. Research to fully characterize and quantify the receptor in primate brain are ongoing. These studies may provide effective leads for investigating regulation of the receptor in living and in post-mortem human brain. DeLa Garza II, R and Madras BK. Autoradiographic distribution of dopamine D4 receptors in non-human primate brain. Soc. Neurosci.

Dopamine receptor agonists/antagonists are considered strong candidates for the treatment of cocaine addiction. However, as cocaine is likely to be used with other drugs, including marijuana, we investigated whether dopamine agonists modify the behavioral effects of cannabinoids in monkeys. The cannabinoid agonist l-nantradol was studied alone to establish a dose response relationship. High doses of l-nantradol reduced activity and induced sedation. For each subject, a dose of l-nantradol that did not produce sedation or reduced activity when administered was identified. This subthreshold dose was administered along with a full range of doses of the D2/D3 dopamine receptor agonist quinelorane. Paradoxically, this drug combination produced significant decreases in motor activity, general activity and marked sedation. These effects are unanticipated because D2/D3 agonists generally stimulate motor and other activity in nonhuman primates. These results indicate cannabinoid and dopamine agonist interactions warrant further investigation in light of the

Brain serotonin systems are implicated in psychiatric disorders, including depression, anxiety and schizophrenia. At least 14 subtypes of serotonin receptors have been identified by cloning techniques. Of these, the serotonin 5-HT1A receptor has been identified as the direct target of atypical anxiolytic drugs such as buspirone and the indirect target of antidepressant drugs. The primary objective of this project is to develop imaging agents to monitor the 5-HT1A receptor in living brain with SPECT. The most widely used radionuclide in nuclear medicine is 99mtechnetium (99mTc; T+ 6hr) because it can be generated in a laboratory from a kit. As an initial step in development, rhenium analogs of the final target technetium compounds are tested in vitro. The 5-HT1A receptor was detected in frontal cortex of rhesus monkey brain with the 5-HT1A receptor ligand [3H]-8-OH-DPAT (0.6 nM), incubated in the presence of clonidine and prazosin to mask other potential targets of the radioligand. Nonspecific binding was measured with buspirone (3 fM) or serotonin (10 fM). Pilot studies were conducted to determine whether two 5-HT1A receptor ligands, coupled to a rhenium chelate would retain high affinity binding to the 5-HT1A serotonin receptor. REO-1 displayed relatively high affinity for the 5-HT1A receptor (IC50 30 nM) whereas REO-2 was of lower affinity (IC50 200 nM). These studies indicate the feasibility of developing rhenium chelate analogs

The dopamine transporter is expressed almost exclusively on dopamine neurons and is an effective marker for the neurons. The transporter has been imaged in Parkinson's disease and other neurological diseases to determine the condition of dopamine neurons. The status of the dopamine transporter is also under investigation as the protein is a principal target of cocaine and methylphenidate (or Ritalin, a drug therapy for Attention Deficit Hyperactivity Disorder). Accordingly, imaging of the dopamine transporter in brain is one of the most rapidly growing fields of brain PET and SPECT imaging. Isotopes such as [11C] or [18F ] for PET or [123I] for SPECT imaging are generally incorporated into brain imaging probes. However, 99mtechnetium (99mTc) is widely used in imaging of peripheral tissues because it can be generated in the laboratory, obviating the need for producing [11C]) by a cyclotron or shipping [123I] long distances. However, progress in developing Tc-based probes for brain imaging has been slow because technetium chelates do not readily penetrate the brain. In our ongoing research to develop effective imaging agents for the transporter, we tested the feasibility of developing a technetium (99Tc) probe. We linked chelated rhenium to analogs of WIN 35,428, the ligands of choice for PET and SPECT imaging of the dopamine transporter. Previously, we reported the design and synthesis of a 99mTc imaging agent, technepine, that crossed the blood-brain barrier and selectively labeled dopamine-rich neurons. Technepine was the first reported technetium-labeled compound to cross the blood-brain barrier and accumulate in a selective target in brain. We are currently investigating other compounds which may increase the signal noise ratio in the brain. Using [3H]WIN 35,428 to label the dopamine transporter and [3H]citalopram to label the serotonin transporter in monkey striatum, we identified several novel rhenium analogs that are potent and selective for the transporter. O-1196 displayed high affinity (IC50 9.35 nM) and 65-fold selectivity for the dopamine over the serotonin transporter. To investigate brain penetrance of this compound, PET imaging of the dopamine transporter was conducted in adult rhesus monkeys using [11C]WIN 35,428 to label the transporter. Occupancy of the transporter by O-1196 was measured by the loss of [11C]WIN 35,428 labeled sites in the striatum. O-1196 crossed the blood-brain barrier and displaced [11C]WIN 35,428 in the striatum. This study further supports the feasibility of developing technetium-labeled compounds to image brain receptors and transporters. Research is planned to improve the synthetic steps, optimize other probes and develop methods to quantify brain images in rhesus monkeys of the technetium chelate. Madras BK, Jones AG, Mahmood A, Zimmerman RE, Holman BL, Davison A, Blundell P, Meltzer PC. Technepine A high affinity 99mtechnetium SPECT probe to label the dopamine transporter in brain, Synapse, 22:239-246, 1996. Jones AJ, Meltzer PC, Mahmood A, Zimmerman RE, Garada B, Holman BL, Davison A, Blundell P, Madras BK. Technepine a 99mtechnetium SPECT imaging agent to label the dopamine transporter in brain, Soc. Nucl. Med. Abst., 37:57, 1996. Meltzer PC, Madras BK. Imaging of dopamine transporters in humans with technetium-99m TRODAT-1. Eur. J. Nucl. Med. 24 462, 1997. Meltzer PC, Blundell P, Jones AG, Mahmood A, Garada B, Zimmerman RE, Davison A, Holman BL, Madras BK. A technetium- 99m SPECT imaging agent which targets the dopamine transporter in primate brain, J. Med. Chem., 40 1835-1844, 1997. Meltzer PC, Blundell P, Jones AG, Mahmood A, Zimmerman, RE, Garada B, Holman BL, Davison A, Madras BK. Design and synthesis of technepine the first in vivo 99mtechnetium SPECT probe which labels the dopamine transporter. NIDA Research Monograph, L. Harris

This laboratory has been actively pursuing the design and development of drugs targeted to monoamine transporters for over a decade. The novel drugs have been indispensable as imaging agents for brain dopamine systems in Parkinson's disease and in cocaine abuse research, as candidate medications for cocaine addiction and Parkinson's disease, and as probes to develop a model of transporter function. We have discovered that a novel class of tropanes that have oxygen or carbon substitutions for nitrogen (nonamines) bind to monoamine transporters with high affinity and are as effective as their amine counterparts at inhibiting monoamine transport in vitro. These data demonstrate that neither ionic nor hydrogen bonding between an amine nitrogen on the ligand and a transporter amine counterion is needed for high affinity binding and blockade of transport. This discovery offers a compelling reason to investigate how drugs bind to and block monoamine transporters. Pilot experiments are designed to determine the critical domains on monoamine transporter molecules that mediate ligand binding and transport using site-directed mutagenesis and chimeric transporters. Point mutations will be made using the GeneEditor Site Directed Mutagenesis System Expression of mutant transporter protein will be confirmed using immunocytochemistry and/or western blotting. We will use a range drugs to determine the effects of mutations on uptake of [3H]

Neurochemical signals in brain are rapidly terminated by several processes, including transporters. Neurotransporters on cell surface membranes decrease the availability of neurotransmitters by sequestering them into neurons or glia for storage processing or metabolism. Drugs that bind to transporters generally increase synaptic neurotransmitter availability by blocking transport. The transporters for the monoamines dopamine, serotonin and norepinephrine are principal targets for the majority of antidepressant drugs, methylphenidate (Ritalin), the most frequently prescribed drug for Attention Deficit Hyperactivity Disorder, and cocaine. By blocking monoamine transporters and elevating monoamine levels the drugs trigger a cascade of biochemical events, leading to therapeutic benefit, or in the case of cocaine, stimulate effects and abuse liability. Without exception, the molecular structure of therapeutic and other drugs that modulate monoamine transporters contains an amine nitrogen. Drug design has been guided by a prevailing but untested premise that drugs require an amine nitrogen, corresponding to the amine nitrogen of neurotransmitters, to bind a counterion on the transporter protein. We recently discovered several compounds without an amine nitrogen, aryloxatropanes (8-oxa-bicyclo-3-aryl-[3.2.1.]octanes), that are potent inhibitors of the dopamine serotonin and/or norepinephrine transporters in monkey brain. We extended this series to other novel nonamines in order to investigate structure-activity relationships. 1. In this series the oxytropane was linked to an aromatic ring in the position. We demonstrated stereoselective binding of the most potent representative compounds ((1R)O-1072 3.27 nM vs (1S)O-1114 47nM). 2. We demonstrated significant influence of halogens on the aromatic ring of these derivatives. In this regard the rank order of potency of halogenated derivatives was 3,4-Cl2 > I > Cl > Br > F >>H. 3. Selectivity of this series of compounds for the dopamine over the serotonin transporter was low. 4. If the aromatic ring was substituted in the 3 position, the compounds displayed similar stereoselectivity but greater selectivity for the dopamine over the serotonin transporter. These results indicate that a number of nonamines are potent inhibitors of the dopamine and serotonin transporters, and similar in potency to their amine nitrogen bearing counterparts. The results demonstrate that an amine nitrogen is not essential for blockade of monoamine transporters. Within this series, transporter affinity appears to be largely sustained by the aromatic ring. Orientation of the 3-aryl moiety influences transporter selectivity. Based on these results, transporter-inhibitor association may be guided by aromatic ring interactions. Future research will investigate the pharmacological activity of these compounds and structure-activity relationships with a view of developing a model of the monoamine transporter. This research will clarify the feasibility of developing cocaine antagonists for the dopamine transporter. Meltzer PC, Liang AY, Gonzalez MD, Blundell P, Madras BK. The first synthesis of 2-carbomethoxy-3-aryl-8-oxabicyclo[3.2.1]octanes;

The neurochemical mechanisms that mediate cocaine's effects are not fully understood. The dopamine transporter, located in the caudate nucleus and putamen, is considered an important mediator of cocaine's effects. These regions of primate brain region accumulate the highest levels of cocaine after i.v. administration. However, the other targets of cocaine may also contribute to the effects of the drug, particularly as cocaine maintains self-administration in the absence of the transporter. In order to fully investigate cocaine distribution in the brain, we conducted PET imaging with [11C]cocaine in primate brain. Analysis of the brain images revealed rapid transport of radioactivity into putamen, caudate, thalamus, frontal cortex and cerebellum. Anatomical regions accumulating [11C]cocaine were verified by magnetic resonance imaging (MRI). The caudate and putamen accumulated the highest levels of cocaine. The orbitofrontal cortex, a region not previously identified as a significant target of cocaine, accumulated [11C]cocaine within two minutes after i.v. administration. In contrast to the caudate or putamen, the time-activity curve was significantly different from that of other brain regions. Radioactivity plateaued and remained high for over 70 minutes in this brain region. These results are significant in view of reports by others that glucose metabolism is severely depressed in the orbitofrontal cortex of monkey brain after chronic cocaine administration. Equally compelling, the orbitofrontal cortex has also been identified as a brain region of significant activity in human subjects after cocaine administration. The binding sites for cocaine in this brain region will be actively investigated in primate and human brain in vitro. Brownell A-L, Livni E, Madras BK. Global approach in modeling of [N-(C-11-methyl] (-)-cocaine] pharmacokinetics in nonhuman

The development of neuroprotective and neuroregenerative agents for dopamine neurons is viewed as a plausible objective for treating Parkinson's disease. Brain imaging of the dopamine transporter, localized almost exclusively on dopamine neurons, offers a potential window on the effectiveness of these agents. In 5 adult cynomolgus monkeys, PET imaging with the dopamine transporter probe [11C]WIN 35,428 (CFT) yielded a binding potential of approximately 2. After MPTP (3 x 0.6 mg/kg), all animals showed profound signs of Parkinsonism and a reduction of the binding potential to 0.1. Within 3 months, two monkeys exhibited signs of recovery, including weight gain and improvement in motor function. Most significantly, PET imaging of the dopamine transporter reflected these changes, as the binding potential of [11C]WIN 35,428 increased. These results may indicate that synaptic or axonal sprouting occurred during the recovery phase, although the latter is more likely in view of the time course of recovery. This novel finding suggests that PET imaging of the transporter may be an effective noninvasive method for assessing the therapeutic efficacy of therapies designed to prevent further degeneration of, or to promote regeneration of dopamine neurons. Madras BK T. Brackett, N. Alpert, A. Bonab, AJ Fischman. PET imaging of the dopamine transporter in Parkinsonian monkeys a

The dopamine transporter is a principal target of cocaine in the brain. The overall objectives of the research are to investigate the therapeutic potential of novel drugs that bind the transporter with higher affinity than does cocaine. We recently reported a new series of compounds targeted to transporters, that unlike all current transporter drugs, contain no amine nitrogen in their structure. Among the most potent in this series was O-913, (2--carbomethoxy-3-(3,4dichlorophenyl)-8-oxabicyclo[3.2.1]octane) which bound with high affinity to the dopamine transporter in cynomolgus monkey striatum (IC50 3.08 q 0.07 nM) or human putamen (IC50 4.53 q1.58) and is a potent inhibitor of dopamine transport in COS-7 cells expressing the human dopamine transporter (IC50 5.9 q 0.9 nM). To investigate whether O-913 produces subjective effects similar to those produced by monoamine transporter inhibitors, O-913 was tested in squirrel monkeys trained to discriminate cocaine from vehicle under a two-lever choice procedure. O-913 engendered dose-related increases in the proportion of responses directed to the cocaine-associated lever, and full substitution for cocaine (> 90% cocaine-appropriate responding) was achieved at 1 mg/kg (n = 4). The results indicate that the aryloxatropane O-913 enters the brain and produces cocaine-like discriminative stimulus effects. These studies indicate that nonamine dopamine transport inhibitors cross the blood-brain barrier to produce behavioral effects similar to their amine nitrogen-bearing counterparts. Together with other biochemical, pharmacological and imaging data, these results suggest that nonamines have the same potential and drug therapies as do monoaminergic drugs. Further evaluation of this class of compounds is ongoing. Madras BK, Pristupa ZB, Niznik HB, Liang AY, Meltzer PC. Novel compounds reveal that nitrogen-based drugs are not essential for

The objective of this new initiative is to clone the dopamine and other monoamine transporters from monkey brain and develop stable cell lines that express non-human primate dopamine transporter cDNA's The monkey dopamine transporter coding sequences will provide information on the evolution of this critical brain transport system from monkey to human The cell lines expressing the monkey dopamine transporter clones will be used to screen novel drugs with diagnostic and therapeutic potential It will obviate the need to depend on availability of monkey brain tissue, reduce the hazard associated with fresh tissue, and provide consistency Finally, a cell line expressing the transporter will enable investigation of transporter regulation We have cloned dopamine transporter cDNAs from rhesus, cynomolgus and squirrel monkeys using a reverse transcriptase-polymerase chain reaction strategy, based on the high degree of similarity between the cloned mammalian dopamine transporte r sequences RNA was extracted from the substantia nigra and reverse transcribed into cDNA Oligonucleotides corresponding to highly conserved regions that are 5' and 3' to the dopamine transporter coding region were used to amplify the dopamine transporter coding region PCR products of the correct size were directly ligated into the expression vector pcDNA3 1/V5/His-TOPO and plus and minus strands were fully sequenced We are now expressing these monkey dopamine transporter expression constructs in HEK-293 cells The data demonstrate that 1 All monkey dopamine transporter coding regions differ from the human sequence; 2 At the protein level, all the monkey sequences contain a consensus cluster of amino acids in the second extracellular loop which differ from the human transporter; 3 Other differences are limited to single amino acid changes, none in transmembrane-spanning domains PUBLICATION Miller GM, Sajdel-Sulkowska EM, Madras BK Cloning of dopamine transporter coding regions from new and old world monkey Soc Neurosci Abst 24 609 1998

Cannabis is a widely used illicit drug and state referenda are sanctioning its use as a medicine Dopamine agonists are effective therapeutic agents for Parkinson's disease, endocrine diseases and are candidate medications for cocaine addiction Increasing evidence in rodents suggests that cannabinoids antagonize dopamine responses at the behavioral and cellular level Medicinal and illicit use of each drug class raises the potential for concomitant use and supports the need to investigate whether antagonism of cannabinoid effects by dopamine agonists, observed in rodents, extends to primates We investigated the effects of a CB1 cannabinoid agonist, dopamine receptor agonists and their interaction on unconditioned behaviors in cynomolgus monkeys Administration of the CB1 agonist levonantradol alone (0 01 - 0 3 mg/kg) significantly decreased locomotor, general activity and sedation, but did not induce rigidity When administered alone, the D2 agonist quineloran e (0 03 - 1 0 mg/kg) produced hyperactivity in two monkeys, whereas the D2 agonist pergolide and the D1 agonists SKF 81297 failed to produce marked changes in activity Administration of an ineffective dose of levonantradol (0 03 mg/kg, determined from a dose-response curve) followed by a D2 receptor agonist precipitated sedation and a decrease in general and locomotor activity In contrast, when an ineffective dose of levonantradol was administered prior to the D1 agonist SKF 81297, no significant changes in motor activity or sedation occurred D2 potentiation of CB1 agonist-induced sedation suggests a unique interaction between these two receptor systems in primate brain Four significant conclusions can be drawn from these results 1 The unconditioned behavioral effects of CB1 agonists in primates differ from those reported in rodents 2 The paradoxical D2-induced potentiation of a cannabinoid agonist differs markedly from what would be predicted based on the behavioral effects of the drugs given alone 3 Preliminiary data suggest that potentiation of cannabinoid-induced sedation appears to be restricted to D2 and not D1 agonists 4 These data have clinical implications, particularly if they generalize to marijuana PUBLICATION Meschler JP, Clarkson FA, Mathews PJ, Howlett AC, Madras BK Cannabinoid and dopamine agonists interact to produce paradoxical behavioral effects in non-human primates Naunyn-Schmiedeberg's Arch Pharmacol 358 R58, 1998

The dopamine transporter, expressed almost exclusively on dopamine neurons, is a sensitive marker for physiological and pathological changes in dopamine neurons In Parkinson's disease, a view of the status of dopamine neurons in living brain has contributed significantly to our understanding of the natural progression of the disease and the relationship between disease severity and dopamine neuron depletion Imaging of dopamine neurons can identify populations that will benefit from treatments designed to arrest disease progression or promote regeneration of dopamine neurons Dopamine transporter imaging has extended to other states with suspected abnormalities in dopamine neurons (e g Huntington's disease, methamphetamine abuse) In 1989-90, this laboratory first identified potent phenyltropane dopamine transport inhibitors (e g CFT or WIN 35,428) as promising imaging agents for PET (positron emission tomography) or SPECT (single photon emission computed to mogr aphy) imaging of the transporter [11C]CFT ([11C]WIN 35,428) and its analog [123I]or [11C]altropane have progressed to clinical trials 99mTechnetium (99mTc), is the most widely used for imaging of peripheral tissues as it is the least technical challenge However, Tc-based probes present a significant challenge for brain imaging because the metal chelate needed to attach the isotope to a probe results in low brain penetration of the probe We now report a novel99mTc imaging agent, O-1505-T which penetrates the brain at relatively high concentrations In vitro, the precursor O-1506 displayed high affinity for the dopamine transporter (IC50 2 05 nM) and low affinity for the serotonin transporter (IC50 497 nM), resulting in a selectivity ratio > 240 Four normal and two MPTP-treated monkeys were injected with 10-25 mCi of O-1505T and serial SPECT images were acquired over 2 h The images were reconstructed using a filtered back projection algorithm and striatal-cerebellar ratios we re calculated In normal animals, accumulation of O-1505T in the dopamine-rich striatum was rapid and peak levels were achieved within 30 min Accumulation was nearly completely displaceable with unlabeled CFT (1 mg/kg) but was not affected by a similar dose of the serotonin transporter-selective drug citalopram The striatal:cerebellar ratio fell from 2 5:1 to 1:1 in MPTP-treated monkeys Blood clearance of the probe was rapid and approached zero by 60 min The results demonstrate that O-1505T is superior to the previously reported agent technepine It is a suitable SPECT ligand for imaging dopamine neurons because it combines the critical characteristics of 1 Facile labeling with 99mTc; 2 High striatal:cerebellar ratio; 3 High selectivity for dopamine over serotonin transporters; 4 Favorable radiation dosimetry; 5 Pharmacokinetics well matched to the physical half-life of 99mTc This study provides further evidence of the feasibility of developing technetium-labeled compound s to image brain receptors and transporters PUBLICATION Madras BK Imaging the dopamine transporter a window on dopamine neurons Advances in Neurodegenerative Disorders 1998 (J Marwah and H Teitelbaum, eds ) Vol 1 Parkinson's disease, pp 229- 253 Prominent Press, Scottsdale, AZ

The use of stimulant medications for attention deficit hyperactivity, which is diagnosed in 2 - 6% of children in North America, has almost tripled since 1990 The increased usage presumably stems from wider recognition of this disorder, as well as the expanding knowledge that such stimulant medication continues to be effective over years, well into adulthood, without known production of adverse side effects There is yet no consensus on the mechanisms of the commonly used anti-hyperactivity medications, amphetamine and methylphenidate Both drugs promote psychomotor slowing of hyperactive children and adults, yet both raise extracellular dopamine levels Paradoxically, elevation of dopamine enhances motor activity, and forms the basis of medications for Parkinson's disease This apparent paradox is the focus of the pilot study The objective of the research is to investigate a novel hypothesis, that a the normal pulsatile supply of dopamine, with a broad range of c oncen trations, results in a different pattern of receptor availability and trafficking than a constant and high supply of the neurotransmitter, which may result with anti-hyperactivity medications To pursue this research, we are cloning the monkey D1 and D2 dopamine receptors and will investigate this hypothesis with the receptor expressed in vitro and in vivo with imaging PUBLICATION Seeman P and Madras BK Anti-hyperactivity medication methylphenidate and amphetamine Mol Psychiatry 3 386-396, 1998

The overall objectives of the research are to develop novel drugs with therapeutic potential for treating cocaine addiction, and dopamine-related diseases which would benefit from elevation of extracellular dopamine levels The drugs are inhibitors of dopamine and serotonin transporters, the targets of anti-depressant, anti-hyperactivity drugs and cocaine The biogenic amines transmitters led chemists to accept the need for an amine nitrogen in design of drugs targeted to transporters and receptors This premise was changed when we reported high affinity non-amines drugs targeted to dopamine and serotonin transporters (Madras et al , Synapse 24 340, 1996) We now report four novel findings with non-amines 1 It is feasible to develop highly selective non-amines as the 8-oxa non-amine O-1059 (IC50 4 59 nM ) was > 450-fold selective for the dopamine over the serotonin transporter; 2 Hydrogen bonding is not necessary for conferring high affinity as the 8-carba an a log of O-1059 displayed high affinity for the transporter (IC50 5 5 nM); 3 The binding domain of a non-amine [3H]O-1059 is virtually identical to that of the monoamine [3H]WIN 35,428 (CFT; 4 Non-amines can elevate extracellular dopamine levels above basal levels in rodent brain Non-amine dopamine transport inhibitors retain the properties of their amine nitrogen-bearing counterparts and represent a new class of drugs with therapeutic potential for neuropsychiatric disorders Further investigation of this class of compounds is warranted PUBLICATIONS Madras BK, Miller G , George S, O'Dowd B, Meltzer PC Non-amines a new generation of monoamine reuptake (dopamine, serotonin transporter) inhibitors Soc Neurosci Abstr 24; 278, 1998 Madras BK , Miller G, Fischman AJ, Bonab A, Meltzer PC Monoamine transporters; novel insights with novel nonamines Naunyn-Schmiedeberg's Arch Pharmacol 358 R 73, 1998

Transporters for the monoamines dopamine, serotonin and norepinephrine are principal targets for the majority of antidepressant drugs such as fluoxetine/Prozac (serotonin transporter), methylphenidate/Ritalin (dopamine transporter), the most frequently prescribed drug for Attention Deficit Hyperactivity Disorder, and cocaine Without exception, the molecular structure of therapeutic and other drugs that modulate monoamine transporters contains an amine nitrogen We recently reported that the amine nitrogen can be exchanged for oxygen (aryloxatropanes, 8-oxa-bicyclo-3-aryl-[3 2 1 ]octanes) and retain potent inhibition of the dopamine, serotonin and/or norepinephrine transporters in monkey brain Oxygen-induced hydrogen bonding to substitute for amine-induced ionic bond formation was proposed as a mechanism to account for high affinity of this class of non-amines To investigate whether even hydrogen bonding is necessary, we replaced the oxygen with a carbon atom We now repo rt that several carbon-based compounds displayed high affinity binding for the dopamine transporter, including O-1231 (IC50 7 1 q 1 7nM), O-1414 (IC50 9 6 q 1 8 nM), O-1442 (IC50 14 3 q 1 1 nM) O-1231, which contains a flattened 2,3-unsaturated bond in the ring structure, was > 700-fold selective for the dopamine (DAT) over the serotonin (SERT) transporter O-1414, a saturated analog of O1231 in the 3- form ("chair") was only 3-fold selective for the DAT over the SERT whereas its 3-` analog ("boat") was > 10-fold Five conclusions can be drawn from these data Conformation of a molecule plays a significant role in conferring DAT or SERT affinity Orientation of the 3-aryl ring and the orientation of the 2-carbomethoxy ring relative to the aromatic ring is critical for alignment with the transporter Development of transporter-selective drug therapies for neuropsychiatric diseases can be guided by appropriate orientation of the 3-aryl group 8-Carbatropanes display high affinity for monoamine transporters, indicating that a functionality corresponding to an amine nitrogen is not necessary for anchoring the molecule to its target protein and blockade of monoamine transporters Within this series, transporter affinity appears to be largely sustained by the aromatic ring The DAT may have multiple binding sites for tropanes, while the SERT may be less flexible Ongoing research with mutant forms of the DAT will explore this premise This research has several implications First, it will clarify the feasibility of developing cocaine antagonists targeted to the dopamine transporter Second, it will help to clarify the molecular mechanisms by which drugs block monoamine transport Finally, these compounds have created a new generation of transporter drugs

disease /disorder model; drug screening /evaluation; positron emission tomography

The human dopamine transporter is a target of cocaine, clinically relevant drugs used to treat attention deficit disorder, movement disorders, nicotine addiction and probes for imaging dopamine neurons in living brain The broad significance of the dopamine transporter offers a compelling reason to investigate the molecular mechanisms by which the transporter functions and is blocked by clinically relevant drugs We are investigating a hypothesis that aromatic amino acids in the human dopamine transporter are critical for drug binding and dopamine transport This hypothesis is based on recent findings from our laboratory that non-amines, which contain no amine nitrogen, retain high affinity binding and blockade of monoamine transport As non-amines do not participate in ionic or hydrogen bonding to the transporter, the aromatic ring of the drug and transporter may contribute to the formation of a drug-transporter complex This hypothesis is being investigated by site-dire cted mutagenesis of rationally selected aromatic amino acid residues on the human dopamine transporter We express the mutant transporter constructs in the HEK-293 cell line, and investigate their capacity to transport [3H]dopamine and ability to bind [3H]non-amines and their monoamine counterparts Our initial data demonstrates that mutation of specific aromatic amino acid residues to alanine in the dopamine transporter results in profound effects on the formation of drug-transporter complexes, and on dopamine transport The effects of certain mutations can be restored by replacing the mutated alanine residue with a different aromatic residue These studies will contribute to understanding the mechanisms by which therapeutic and addictive drugs block the dopamine transporter They will also provide needed information for our ongoing program of developing novel drugs for the diagnosis and treatment of dopamine-related neuropsychiatric diseases

Brain serotonin receptors are implicated in psychiatric disorders, particularly depression, anxiety and substance abuse Of the 14 subtypes of serotonin receptors identified in brain, the 5HT-1A receptor is a direct target of the atypical anti-anxiety drug buspirone and an indirect target of antidepressant drugs To determine the feasibility of monitoring this receptor in living brain by SPECT imaging, we investigated rhenium analogues of WAY 100635 WAY 100635 is an aryl piperazine that previously has been identified as a PET ligand for brain 5HT1A serotonin receptors In an effort to optimize the affinity and brain uptake of these metal-chelated analogues, several compounds were synthesized with various linkers between the receptor binding moiety and two N2S2 chelate systems In vitro assays of the complexes were conducted in frontal cortex of brain using [3H]8-OH-DPAT a 5HT1A ligand and [3H]7-OH-DPAT to label the D3 dopamine receptor Several compounds displa yed nanomolar affinity for the 5HT1A receptor and one compound was potent at the D3 dopamine receptor Further research on brain uptake and biodistribution is planned in small mammalian species Our successful imaging of the brain dopamine transporter with technetium-labeled probes may extend to other proteins of therapeutic or diagnostic relevance Alan J Fischman, MD, Ph D Department of Nuclear Medicine, Radiology, Massachusetts General Hospital, Boston, MA To develop and evaluate novel PET and SPECT imaging agents as markers for dopamine neurons in Parkinson's disease and other brain disorders To conduct clinical trials with altropane To determine brain occupancy of candidate cocaine medications To determine the effects of chronic administration of candidate medications on brain dopamine systems To evaluate the brain occupancy pf a novel candidate antiparkinsonian drug To develop novel technetium agents Ali Bonab, Ph D , Massachusetts General Hospital Boston, MA Nat Alpert, Ph D , Massachusetts General Hospital Boston, MA To develop methods for quantifying the dopamine transporter using PET imaging of brain Anna-Liisa Brownell, Ph D , Department of Radiology ,Massachusetts General Hospital ,Boston, MA To conduct PET imaging studies with novel and other compounds, for probing the targets of cocaine Peter C Meltzer, Ph D , Organix, Inc Paul Blundell, Ph D To synthesize and evaluate novel tropanes as probes for monoamine transporters, as imaging agents and as therapeutics for cocaine medications and Parkinson's disease To develop novel technetium agents Aloke Dutta, Ph D , Organix, Inc To develop potent and selective GBR analogs for the dopamine transporter Alun G Jones, Ph D , Harvard Medical School Ashfaq Mahmood, Ph D , Harvard Medical School To develop technetium imaging agents for brain dopamine and serotonin systems Alan Davison, Ph D , Massachusetts Institute of Technology To develop technetium imaging agents for brain dopamine and serotonin systems Jack Bergman, Ph D , McLean Hospital, Belmont, MA To measure the effects of chronic cocaine on dopamine systems in brain Allyn C Howlett, Ph D St Louis University, St Louis MO To investigate cannabinoid/dopamine agonists interaction To assess therapeutic potential of cannabinoid antagonists Susan Amara, Mark Sonders, Vollum Institute, Portland OR To determine effects of novel drugs on currents in cells transfected with transporters Susan George, M D , University of Toronto Brian O'Dowd, Ph D ,University of Toronto To measure effects of non-amines on extracellular dopamine levels in vivo Beth Hoffman, Ph D NIH To develop point mutations on the dopamine transporter Philip Seeman, M D , Ph D To develop novel hypotheses on mechanism of action of anti-hyperactivity medications

The dopamine transporter, expressed almost exclusively on dopamine neurons, is a sensitive marker for physiological and pathological changes in dopamine neurons In Parkinson's disease, a view of the status of dopamine neurons in living brain has contributed significantly to our understanding of the natural progression of the disease and the relationship between disease severity and dopamine neuron depletion Imaging of dopamine neurons can identify populations that will benefit from treatments designed to arrest disease progression or promote regeneration of dopamine neurons Dopamine transporter imaging has extended to other states with suspected abnormalities in dopamine neurons (e g Huntington's disease, methamphetamine abuse) In 1989-90, this laboratory first identified potent phenyltropane dopamine transport inhibitors (e g CFT or WIN 35,428) as promising imaging agents for PET (positron emission tomography) or SPECT (single photon emission computed to mogr aphy) imaging of the transporter [11C]CFT ([11C]WIN 35,428) and its analog [123I]or [11C]altropane have progressed to clinical trials 99mTechnetium (99mTc), is the most widely used for imaging of peripheral tissues as it is the least technical challenge However, Tc-based probes present a significant challenge for brain imaging because the metal chelate needed to attach the isotope to a probe results in low brain penetration of the probe We now report a novel99mTc imaging agent, O-1505-T which penetrates the brain at relatively high concentrations In vitro, the precursor O-1506 displayed high affinity for the dopamine transporter (IC50 2 05 nM) and low affinity for the serotonin transporter (IC50 497 nM), resulting in a selectivity ratio > 240 Four normal and two MPTP-treated monkeys were injected with 10-25 mCi of O-1505T and serial SPECT images were acquired over 2 h The images were reconstructed using a filtered back projection algorithm and striatal-cerebellar ratios we re calculated In normal animals, accumulation of O-1505T in the dopamine-rich striatum was rapid and peak levels were achieved within 30 min Accumulation was nearly completely displaceable with unlabeled CFT (1 mg/kg) but was not affected by a similar dose of the serotonin transporter-selective drug citalopram The striatal:cerebellar ratio fell from 2 5:1 to 1:1 in MPTP-treated monkeys Blood clearance of the probe was rapid and approached zero by 60 min The results demonstrate that O-1505T is superior to the previously reported agent technepine It is a suitable SPECT ligand for imaging dopamine neurons because it combines the critical characteristics of 1 Facile labeling with 99mTc; 2 High striatal:cerebellar ratio; 3 High selectivity for dopamine over serotonin transporters; 4 Favorable radiation dosimetry; 5 Pharmacokinetics well matched to the physical half-life of 99mTc This study provides further evidence of the feasibility of developing technetium-labeled compound s to image brain receptors and transporters PUBLICATION Madras BK Imaging the dopamine transporter a window on dopamine neurons Advances in Neurodegenerative Disorders 1998 (J Marwah and H Teitelbaum, eds ) Vol 1 Parkinson's disease, pp 229- 253 Prominent Press, Scottsdale, AZ

Cannabis is a widely used illicit drug and state referenda are sanctioning its use as a medicine Dopamine agonists are effective therapeutic agents for Parkinson's disease, endocrine diseases and are candidate medications for cocaine addiction Increasing evidence in rodents suggests that cannabinoids antagonize dopamine responses at the behavioral and cellular level Medicinal and illicit use of each drug class raises the potential for concomitant use and supports the need to investigate whether antagonism of cannabinoid effects by dopamine agonists, observed in rodents, extends to primates We investigated the effects of a CB1 cannabinoid agonist, dopamine receptor agonists and their interaction on unconditioned behaviors in cynomolgus monkeys Administration of the CB1 agonist levonantradol alone (0 01 - 0 3 mg/kg) significantly decreased locomotor, general activity and sedation, but did not induce rigidity When administered alone, the D2 agonist quineloran e (0 03 - 1 0 mg/kg) produced hyperactivity in two monkeys, whereas the D2 agonist pergolide and the D1 agonists SKF 81297 failed to produce marked changes in activity Administration of an ineffective dose of levonantradol (0 03 mg/kg, determined from a dose-response curve) followed by a D2 receptor agonist precipitated sedation and a decrease in general and locomotor activity In contrast, when an ineffective dose of levonantradol was administered prior to the D1 agonist SKF 81297, no significant changes in motor activity or sedation occurred D2 potentiation of CB1 agonist-induced sedation suggests a unique interaction between these two receptor systems in primate brain Four significant conclusions can be drawn from these results 1 The unconditioned behavioral effects of CB1 agonists in primates differ from those reported in rodents 2 The paradoxical D2-induced potentiation of a cannabinoid agonist differs markedly from what would be predicted based on the behavioral effects of the drugs given alone 3 Preliminiary data suggest that potentiation of cannabinoid-induced sedation appears to be restricted to D2 and not D1 agonists 4 These data have clinical implications, particularly if they generalize to marijuana PUBLICATION Meschler JP, Clarkson FA, Mathews PJ, Howlett AC, Madras BK Cannabinoid and dopamine agonists interact to produce paradoxical behavioral effects in non-human primates Naunyn-Schmiedeberg's Arch Pharmacol 358 R58, 1998

The objective of this new initiative is to clone the dopamine and other monoamine transporters from monkey brain and develop stable cell lines that express non-human primate dopamine transporter cDNA's The monkey dopamine transporter coding sequences will provide information on the evolution of this critical brain transport system from monkey to human The cell lines expressing the monkey dopamine transporter clones will be used to screen novel drugs with diagnostic and therapeutic potential It will obviate the need to depend on availability of monkey brain tissue, reduce the hazard associated with fresh tissue, and provide consistency Finally, a cell line expressing the transporter will enable investigation of transporter regulation We have cloned dopamine transporter cDNAs from rhesus, cynomolgus and squirrel monkeys using a reverse transcriptase-polymerase chain reaction strategy, based on the high degree of similarity between the cloned mammalian dopamine transporte r sequences RNA was extracted from the substantia nigra and reverse transcribed into cDNA Oligonucleotides corresponding to highly conserved regions that are 5' and 3' to the dopamine transporter coding region were used to amplify the dopamine transporter coding region PCR products of the correct size were directly ligated into the expression vector pcDNA3 1/V5/His-TOPO and plus and minus strands were fully sequenced We are now expressing these monkey dopamine transporter expression constructs in HEK-293 cells The data demonstrate that 1 All monkey dopamine transporter coding regions differ from the human sequence; 2 At the protein level, all the monkey sequences contain a consensus cluster of amino acids in the second extracellular loop which differ from the human transporter; 3 Other differences are limited to single amino acid changes, none in transmembrane-spanning domains PUBLICATION Miller GM, Sajdel-Sulkowska EM, Madras BK Cloning of dopamine transporter coding regions from new and old world monkey Soc Neurosci Abst 24 609 1998

The human dopamine transporter is a target of cocaine, clinically relevant drugs used to treat attention deficit disorder, movement disorders, nicotine addiction and probes for imaging dopamine neurons in living brain The broad significance of the dopamine transporter offers a compelling reason to investigate the molecular mechanisms by which the transporter functions and is blocked by clinically relevant drugs We are investigating a hypothesis that aromatic amino acids in the human dopamine transporter are critical for drug binding and dopamine transport This hypothesis is based on recent findings from our laboratory that non-amines, which contain no amine nitrogen, retain high affinity binding and blockade of monoamine transport As non-amines do not participate in ionic or hydrogen bonding to the transporter, the aromatic ring of the drug and transporter may contribute to the formation of a drug-transporter complex This hypothesis is being investigated by site-dire cted mutagenesis of rationally selected aromatic amino acid residues on the human dopamine transporter We express the mutant transporter constructs in the HEK-293 cell line, and investigate their capacity to transport [3H]dopamine and ability to bind [3H]non-amines and their monoamine counterparts Our initial data demonstrates that mutation of specific aromatic amino acid residues to alanine in the dopamine transporter results in profound effects on the formation of drug-transporter complexes, and on dopamine transport The effects of certain mutations can be restored by replacing the mutated alanine residue with a different aromatic residue These studies will contribute to understanding the mechanisms by which therapeutic and addictive drugs block the dopamine transporter They will also provide needed information for our ongoing program of developing novel drugs for the diagnosis and treatment of dopamine-related neuropsychiatric diseases

The overall objectives of the research are to develop novel drugs with therapeutic potential for treating cocaine addiction, and dopamine-related diseases which would benefit from elevation of extracellular dopamine levels The drugs are inhibitors of dopamine and serotonin transporters, the targets of anti-depressant, anti-hyperactivity drugs and cocaine The biogenic amines transmitters led chemists to accept the need for an amine nitrogen in design of drugs targeted to transporters and receptors This premise was changed when we reported high affinity non-amines drugs targeted to dopamine and serotonin transporters (Madras et al , Synapse 24 340, 1996) We now report four novel findings with non-amines 1 It is feasible to develop highly selective non-amines as the 8-oxa non-amine O-1059 (IC50 4 59 nM ) was > 450-fold selective for the dopamine over the serotonin transporter; 2 Hydrogen bonding is not necessary for conferring high affinity as the 8-carba an a log of O-1059 displayed high affinity for the transporter (IC50 5 5 nM); 3 The binding domain of a non-amine [3H]O-1059 is virtually identical to that of the monoamine [3H]WIN 35,428 (CFT; 4 Non-amines can elevate extracellular dopamine levels above basal levels in rodent brain Non-amine dopamine transport inhibitors retain the properties of their amine nitrogen-bearing counterparts and represent a new class of drugs with therapeutic potential for neuropsychiatric disorders Further investigation of this class of compounds is warranted PUBLICATIONS Madras BK, Miller G , George S, O'Dowd B, Meltzer PC Non-amines a new generation of monoamine reuptake (dopamine, serotonin transporter) inhibitors Soc Neurosci Abstr 24; 278, 1998 Madras BK , Miller G, Fischman AJ, Bonab A, Meltzer PC Monoamine transporters; novel insights with novel nonamines Naunyn-Schmiedeberg's Arch Pharmacol 358 R 73, 1998

The dopamine transporter is increasingly recognized as a window on the status of dopamine neurons Dopamine transporter levels decline in tandem with the loss of dopamine in Parkinson's disease and in experimentally produced parkinsonism The dopamine transporter is also a principal target of Ritalin , Zyban and cocaine in brain Although it is feasible to accurately measure the density of the transporter in post-mortem tissue, measures of transporter density in living brain by PET or SPECT imaging are more challenging With PET imaging in non-human primate brain, we measured transporter levels using a technique of three injections of [11C]CFT (WIN 35,428) followed by non-linear least-squares (NLSQ) fitting of all the dynamic data simultaneously The resulting data yielded a value for B'max which does not correspond closely to B'max/Kd The advantages of the three-injection model is the feasibility of measuring B'max and Kd (Koff/Kon) separately It is inadvisabl e to use B'max/Kd or distribution volume ratio (DVR) in all circumstances as an indicator of B'max as the underlying assumption for generating binding potential is the constancy of Kd For receptor imaging, agonist drugs can convert receptors from high to low affinity, thereby reducing the apparent Kd for PET imaging agents that are either agonists or partial agonists Kd may also differ as a function of other factors, including age, pathological states, mutations in receptors, or modifications of the membrane matrix of protein targets If feasible, it seems imprudent to sacrifice the possibility of obtaining accurate data with measures of Kd and B'max

Transporters for the monoamines dopamine, serotonin and norepinephrine are principal targets for the majority of antidepressant drugs such as fluoxetine/Prozac (serotonin transporter), methylphenidate/Ritalin (dopamine transporter), the most frequently prescribed drug for Attention Deficit Hyperactivity Disorder, and cocaine Without exception, the molecular structure of therapeutic and other drugs that modulate monoamine transporters contains an amine nitrogen We recently reported that the amine nitrogen can be exchanged for oxygen (aryloxatropanes, 8-oxa-bicyclo-3-aryl-[3 2 1 ]octanes) and retain potent inhibition of the dopamine, serotonin and/or norepinephrine transporters in monkey brain Oxygen-induced hydrogen bonding to substitute for amine-induced ionic bond formation was proposed as a mechanism to account for high affinity of this class of non-amines To investigate whether even hydrogen bonding is necessary, we replaced the oxygen with a carbon atom We now repo rt that several carbon-based compounds displayed high affinity binding for the dopamine transporter, including O-1231 (IC50 7 1 q 1 7nM), O-1414 (IC50 9 6 q 1 8 nM), O-1442 (IC50 14 3 q 1 1 nM) O-1231, which contains a flattened 2,3-unsaturated bond in the ring structure, was > 700-fold selective for the dopamine (DAT) over the serotonin (SERT) transporter O-1414, a saturated analog of O1231 in the 3- form ("chair") was only 3-fold selective for the DAT over the SERT whereas its 3-` analog ("boat") was > 10-fold Five conclusions can be drawn from these data Conformation of a molecule plays a significant role in conferring DAT or SERT affinity Orientation of the 3-aryl ring and the orientation of the 2-carbomethoxy ring relative to the aromatic ring is critical for alignment with the transporter Development of transporter-selective drug therapies for neuropsychiatric diseases can be guided by appropriate orientation of the 3-aryl group 8-Carbatropanes display high affinity for monoamine transporters, indicating that a functionality corresponding to an amine nitrogen is not necessary for anchoring the molecule to its target protein and blockade of monoamine transporters Within this series, transporter affinity appears to be largely sustained by the aromatic ring The DAT may have multiple binding sites for tropanes, while the SERT may be less flexible Ongoing research with mutant forms of the DAT will explore this premise This research has several implications First, it will clarify the feasibility of developing cocaine antagonists targeted to the dopamine transporter Second, it will help to clarify the molecular mechanisms by which drugs block monoamine transport Finally, these compounds have created a new generation of transporter drugs

DESCRIPTION: (Provided by Applicant): This application for a NIDA Senior Scientist Award (K05) requests support for the candidate to pursue a multidisciplinary program focused on drug abuse research. The candidate's overall objectives are to investigate the molecular targets of psychostimulant drugs of abuse, the neuroadaptive mechanisms consequent to chronic drug exposure and to develop novel and effective medications for cocaine addiction. The dopamine transporter, a principal target of cocaine and amphetamine, is the major focus of the research. The research program is based on exciting leads generated over the previous project period and is supported by two grants from NIDA and two subcontracts. An ongoing objective is to investigate the therapeutic potential of novel cocaine agonists targeted to the dopamine transporter, with molecular, biochemical, behavioral and brain imaging techniques. Non-amines, and "tropane horses" are a major focus of the medications development research. Non-amines bear no amine nitrogen in their structure yet retain the high affinity for the monoamine transporters and appropriate brain distribution, of their amine progenitors. "Tropane horses" are a new class of compounds designed as cocaine antagonists. PET imaging of brain dopamine transporters will monitor dopamine transporter occupancy of candidate medications to establish drug doses that fully block access of cocaine to the transporter. Cell and molecular biology approaches will provide a mechanistic platform in support of our research. We will investigate the relevance of dopamine transporter gene polymorphisms to behavioral responses elicited by psychostimulants and the influence of polymorphisms on dopamine transporter density. Substrate or inhibitor induction of immediate early gene expression in cells transfected with the dopamine transporter will guide parallel investigation of neuroadaptive processes in pre-synaptic dopamine neurons. The research will be conducted in cell lines transfected with primate transporters and in non-human primates. This integrated research program will provide fundamental information on the neurobiological mechanisms underlying the behavioral effects of psychostimulants and candidate medications to treat cocaine addiction.

transport inhibitor; analog; tropanes; Primates; animal colony; amines;

cell surface receptors; amphetamines; brain; Primates; animal colony;

psychological stressor; opioid receptor; aggression; animal colony; Primates; behavioral /social science research tag;

substance abuse related behavior; cocaine; Saimiri; animal colony; behavioral /social science research tag;

ephrins; gene expression; brain; Primates; animal colony;

neurotoxicology; membrane transport proteins; 3,4 methylenedioxymethamphetamine; Primates; animal colony;

analog; pharmacokinetics; benzene; Primates; animal colony;

transport inhibitor; neurotransmitter transport; dopamine; Primates; animal colony;

molecular probes; dopamine transporter; technetium; Primates; animal colony; gene expression; biotechnology;

cocaine; receptor; Primates; animal colony; amines;

cocaine; drug design /synthesis /production; inhibitor /antagonist; Primates; animal colony;

analog; tropanes; dopamine; Primates; animal colony;

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. AIMS: MDMA methylene-dioxymethamphetamine or ecstasy is a widely abused psychoactive drug, considered to produce its empathic effects primarily by modulating serotonin transporter SERT function and brain serotonin activity. MDMA is also a mild psychomotor stimulant in humans and nonhuman primates, an effect reportedly mediated by dopaminergic activity. We previously demonstrated that MDMA is an effective substrate for the dopamine DAT transporter. Based on these findings, we hypothesized that an acute dose of MDMA would occupy the DAT in vivo, as manifest by reduced DAT binding potential. METHODS: In rhesus monkeys n=5, we used PET imaging and the DAT ligand (11C)CFT to measure DAT binding potential. PET imaging was performed over 60 min, with regions of interest drawn over striatum and cerebellum and binding potential calculated using the SSRT method. Following generation of baseline DAT binding potential, MDMA (1.5 mg/kg was injected intravenously and imaging was repeated 1 hour after drug injection. RESULTS: Contrary to expectations, DAT binding potential measured with (11C)CFT was consistently higher, 121 percent (n=5, than baseline values, following an acute dose of MDMA. Intramuscular MDMA and the DAT ligand (11C)altropane yielded inconsistent changes, confirming our previous findings that METH effects are sensitive to route of administration and time. CONCLUSIONS: These unanticipated findings are conceivably attributable to neurochemical properties of METH or technical reasons. MDMA may alter DAT regulatory mechanisms acutely to increase DAT availability or alternately, MDMA blockade of striatal SERT could prevent SERT occupancy by (11C)CFT to increase PET ligand availability for the DAT.

DESCRIPTION (provided by applicant): Among psychostimulants, methamphetamine (METH) has one of the highest risks for progression to addiction. Although METH use is declining in the general population, use nevertheless persists among high school students and adults. Onset of use during adolescence significantly increases susceptibility to developing addiction to METH, and to other drugs, compared with initiation of drug use during adulthood. The mechanisms underlying the heightened vulnerability of adolescents to addiction are poorly understood. As the adolescent brain is not fully developed and undergoes extensive changes until the mid-twenties, we postulate that METH (and other drugs) alters the trajectory of normal neurodevelopment. Specifically, we will interrogate the hypothesis that METH will affect expression levels of mRNA encoding proteins critical for neurodevelopment, but these changes will differ in the adolescent and adult brain. Axonal guidance molecules (AGMs) are receptors and ligands that guide neurodevelopment (e.g. axon guidance and pruning), and are vital elements in neuroadaptive processes in the adult brain (neurogenesis, synaptic plasticity, dendritic morphology, axonal repair). Accumulating evidence directly and inferentially links psychostimulants (cocaine, amphetamine, methamphetamine) to modulation of AGM expression. Pilot or published research from our laboratory and others demonstrated that: (a) METH altered mRNA expression levels of specific AGMs in hippocampus and, (b) the indirect METH target, the D1 dopamine receptor, altered mRNA expression of specific AGMs in vitro. The hypothesis, that elevated potential for METH addiction in youth is associated with METH-induced alterations in AGMs in hippocampus during a crucial phase of neurodevelopment, resulting in reduced neurogenesis and enhanced drug reward, will be tested in 3 aims. Aim 1 will compare the effects of repeated exposure to a low fixed dose of METH on AGM mRNA expression in the hippocampus and on conditioned place preference in young adolescent or adult mice. Aim 2 will investigate the hypothesis that METH, acting via AGMs, affects hippocampal neurogenesis differently in adolescent and adult mice. Aim 3 will investigate whether ephrin B3, a regulator of neurogenesis, shapes drug-seeking behavior in mice, by comparing METH drug-seeking in wild-type and in null mutant mice in the two age cohorts. The research will fill a major void in neurodevelopmental processes that conceivably shape vulnerability to addiction in the adolescent brain, and guide parallel research with other drugs that engender heightened addictive potential in adolescents. With the advent of small molecules targeted to AGMs, the research may lead to novel probes to image and map these critical proteins in the course of human neurodevelopment, to new medication targets that may assist in reversing METH addiction, compromised cognition and affective states. The findings will furthermore provide information for public education on the biological risks associated with early drug use. PUBLIC HEALTH RELEVANCE: Young adolescents are at higher risk of becoming addicted to methamphetamine than adults, as they are to other drugs (cocaine, marijuana, opioids, alcohol, nicotine, inhalants), yet the effects of these drugs on brain development is largely unknown. The proposed research will investigate whether METH modifies expression of proteins that are critical for neurodevelopment, research that conceivably will provide new leads for medications and information germane to public education on biological consequences of early initiation of drug use.

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. AIMS: In brain, axon growth or attenuated growth is guided by diverse receptors and ligands, designated axonal guidance molecules (AGMs), during neurodevelopment. In the adult brain, AGMs influence cognition (neurogenesis, synaptic plasticity, dendritic morphology) and pathological processes (promotion/blockade of axonal repair). Users of the drug methamphetamine (METH) are at high risk for addiction, neurotoxicity and cognitive impairment, manifest by pruning or losses in monoaminergic axons combined with impaired hippocampal function and neurogenesis. Based on our research that dopamine receptor activity can alter AGM mRNA expression, we investigated whether METH alters mRNA expression of AGMs in hippocampus, a brain region critical for learning, memory, neurogenesis. METHODS: We compared AGM mRNA expression in hippocampus of 5 control and 5 METH (5.0 mg/kg) treated mice, administered daily for 6, followed by a no treatment day. RESULTS: Real-time PCR detected robust mRNA expression of AGMs in adult whole mouse brain: semaphorin3e, semaphorin5a, neuropilin-1, ephrinA2, ephrinB3, EphB3, EphA4, EphB4, EphB6. mRNA expression levels of two AGMs (semaphorin5a and EphB3) were reduced in hippocampus of METH treated mice compared with saline controls. Semaphorin5a is an AGM implicated in axonal guidance and development of brain vasculature, and EphB3 is implicated in maintaining mature neuronal connections, re-arrangement of synaptic connections, and in hippocampal axon defasciculation. CONCLUSIONS: METH may alter hippocampal morphology and function by changing expression levels of axonal guidance molecules. Conceivably, AGMs contribute to METH-induced neurotoxicity and reduced cognition, thereby highlighting new mechanisms of METH action and leads for medications development.

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. AIMS: All medications that treat attention deficit hyperactivity disorder (ADHD) attenuate the transport of dopamine (DA) and norepinephrine (NE), via the dopamine (DAT) and/or norepinephrine (NET) transporters. Trace amines have been implicated in ADHD, as the trace amine phenethylamine (PEA) is reduced in urines of ADHD male children and normalized by anti-ADHD medications, in some reports. With the underlying mechanisms unknown, we postulated that ADHD medications normalize PEA levels in ADHD children by blockade of PEA transport by the DAT or NET. METHODS: We determine whether ADHD medications (methylphenidate, (+)-amphetamine, atomoxetine, modafinil) affected (3H)PEA transport by the DAT and the NET. RESULTS: Methylphenidate was nearly 2-fold more potent at blocking (3H)PEA than (3H)DA transport by the DAT and also potently blocked (3H)PEA transport by the NET. (+)-Amphetamine was 3-fold less potent at blocking (3H)PEA than (3H)DA transport. Atomoxetine was a weak inhibitor of (3H)DA or (3H)PEA transport by the DAT and a potent inhibitor at the NET Modafinil, which occupies the DAT and the NET in vivo, was a relatively weak inhibitor of DAT transport, but was slightly more potent at blocking (3H)PEA than (3H)DA transport. Other therapeutic drugs, mazindol, nomifensine, benztropine bupropion, were 2-4 times more potent at blocking (3H)PEA than (3H)DA transport. CONCLUSIONS: Conceivably, blockade of PEA transport by anti-hyperactivity medications accounts for normalization of urinary PEA levels in ADHD male children. These results implicate trace amines, transporters and the trace amine receptor1 in the therapeutic response of ADHD medications which target DAT and NET.

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. AIMS: Monoamine transporters regulate neurotransmitter levels, which release or sequester them from and into neurons. Cocaine and other psychostimulants inhibit the dopamine (DAT) and norepinephrine (NET) transporters, with relative potencies that correlate with their potencies for producing stimulant effects and abuse liability. The trace amine phenylethylamine (PEA) is implicated in addiction, but the relationship between PEA, monoamine transporters and drugs is unknown. We postulated that PEA is a substrate for the DAT and NET, that drugs would potently inhibit [3H]PEA transport and that blockade of (3H)PEA transport by DAT inhibitors would be relevant to the stimulant and reinforcing properties of cocaine-like drugs. METHODS: We measured (3H)PEA transport kinetics, compared drug effects on (3H)PEA and (3H)dopamine transport in human DAT-HEK-293 cells, and compared relative drug potencies in vitro with reported drug potencies for producing behavioral effects in primates. RESULTS: (3H)PEA was actively transported, with DAT and NET affinities similar to (3H)dopamine or (3H)norepinephrine affinities. (-)-Cocaine and other drugs dose-dependently inhibited PEA transport by the DAT, at greater potencies than those that block (3H)dopamine transport. The relative potencies of drugs for blocking (3H)PEA transport correlated highly with their reported relative potencies for producing psychomotor stimulation and maintaining self-administration in primates. CONCLUSIONS: Drug inhibition of PEA transport by the DAT and NET conceivably elevates extracellular PEA levels in brain. These results implicate PEA and the trace amine receptor1 activation as contributors to the psychostimulant and reinforcing effects of DAT inhibitors.

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. AIMS: The stimulant modafinil and its active isomer r-modafinil (armodafinil) are approved for the treatment of narcolepsy and undergoing assessment to treat other neuropsychiatric disorders. Armodafinil is more potent, has a longer duration of action, and contains no inactive components. Both were designated atypical because of their unknown mechanism of action. In a PET imaging study in nonhuman primates, we reported that clinically relevant doses of modafinil occupied the dopamine (DAT) and norepinephrine (NET) transporters in living brain, conceivably elevating extracellular catecholamine levels in brain and nullifying its "atypical" designation. We now report whether these findings in primates extend to human brain with armodafinil. METHODS: Twelve human subjects were enrolled. Plasma armodafinil levels were obtained and in vivo armodafinil occupancy of the DAT in striatum was detected by (11C)altropane. Changes in extracellular dopamine were detected by indirect displacement of the D2 dopamine receptor agonist (11C)raclopride in human subjects. RESULTS: Armodafinil occupied striatal DAT (100 mg PO: 34 percent-40 percent, 1- 2.5 hrs, n=6;250 mg: 60 percent-percent, 1-2.5 hrs;n=6). Armodafinil resulted in modest increases in extracellular dopamine levels, at both doses. CONCLUSIONS: Armodafinil cccupancy of the DAT and elevation of extracellular dopamine in vivo further implicate the DAT as a therapeutic site of action. These findings validate our previous discovery in nonhuman primates, support evaluation of armodafinil for dopamine-related disorders, e.g. attention deficit hyperactivity disorder, highlight the therapeutic potential of low affinity DAT inhibitors, and possibly the abuse liability of this previously designated class of "atypical" drugs.

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. AIMS: Methamphetamine (METH) use increased 60 percent in 2009, even though users are at high risk for addiction, neurotoxicity and cognitive impairment. As adolescents are more susceptible to METH addiction and other these adverse consequences than adults, we hypothesized that METH affects behaviors and neurodevelopmental genes (axonal guidance molecules or AGMs) differently in adolescent and adults. We investigated the effects of METH on expression of genes implicated in neurodevelopment, neurogenesis, neuroadaptation in adolescent and adult brain. METHODS: We compared METH (5 mg/kg) with saline in 12 adolescent male (30 days) and 12 adult male mice (10 weeks), given i.p. daily for 6 days, by measuring locomotor activity, stereotypy and mRNA expression of AGMs in 3 brain regions. RESULTS: METH (5 mg/kg) increased locomotor activity in adolescent and adult mice, but in the adolescent mice: (1) peak effects were later;(2) locomotion was higher;(3) duration was longer. In the two age cohorts, expression levels of specific AGMs differed following METH treatment in hippocampus and striatum. CONCLUSIONS: METH affected locomotion and AGM gene expression differently in adolescent and adult mice. Altered mRNA expression levels of specific AGMs in hippocampus, striatum conceivably are associated with the cascade of METH-induced neurodevelopmental, morphological, behavioral, cognitive changes in brain. Combined with other strategies, this novel approach may clarify the mechanisms by which METH confers heightened susceptibility of the adolescent to addiction and to other adverse consequences.

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. AIMS: Compounds that affect dopamine transporter (DAT) function have therapeutic potential to treat cocaine addiction, and other CNS disorders. They also have abuse potential, depending on structure, potency, dose, pharmacokinetic properties and route of administration. The stimulant pyrovalerone is a relatively high affinity DAT inhibitor with limited therapeutic use because of abuse liability. To develop medications with reduced abuse liability, we designed pyrovalerone analogs and assessed in vitro potencies at monoamine transporters (dopamine, serotonin, norepinephrine) and in vivo occupancy of the DAT. METHODS: DAT affinity was determined in HEK-293 cells transfected with the human DAT. DAT occupancy (reduction in binding potential) was measured with PET imaging of the DAT probe (11C)CFT ((11C)WIN 35,428) and anesthetized rhesus monkeys. After acquisition of baseline DAT levels, the test compound was administered and PET imaging performed with a second injection of (11C)CFT one hour later. RESULTS: Novel pyrovalerone analogs exhibited high to moderate DAT potency (3.1 - 216 nM) and moderate to high DAT:SERT selectivity. All compounds (1 mg/kg) occupied 59 percent or more of DAT sites in the striatum. Several compounds with high affinity for the DAT in vitro showed lower DAT occupancy than lower affinity compounds, within the time frame of the PET session. DAT occupancy correlated with lipophilicity (logP values) and not with DAT affinity. CONCLUSIONS: For pyrovalerone analogs, lipophilicity, but not in vitro affinity, predicts in vivo DAT occupancy, Several compounds displayed rapid DAT onset, findings relevant both for therapeutic potential or abuse liability.

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. AIMS: MDMA methylene-dioxymethamphetamine or ecstasy is a widely abused psychoactive drug, considered to produce its empathic effects primarily by modulating serotonin transporter SERT function and brain serotonin activity. MDMA is also a mild psychomotor stimulant in humans and nonhuman primates, an effect reportedly mediated by dopaminergic activity. We previously demonstrated that MDMA is an effective substrate for the dopamine DAT transporter. Based on these findings, we hypothesized that an acute dose of MDMA would occupy the DAT in vivo, as manifest by reduced DAT binding potential. METHODS: In rhesus monkeys n=5, we used PET imaging and the DAT ligand (11C)CFT to measure DAT binding potential. PET imaging was performed over 60 min, with regions of interest drawn over striatum and cerebellum and binding potential calculated using the SSRT method. Following generation of baseline DAT binding potential, MDMA (1.5 mg/kg was injected intravenously and imaging was repeated 1 hour after drug injection. RESULTS: Contrary to expectations, DAT binding potential measured with (11C)CFT was consistently higher, 121 percent (n=5, than baseline values, following an acute dose of MDMA. Intramuscular MDMA and the DAT ligand (11C)altropane yielded inconsistent changes, confirming our previous findings that METH effects are sensitive to route of administration and time. CONCLUSIONS: These unanticipated findings are conceivably attributable to neurochemical properties of METH or technical reasons. MDMA may alter DAT regulatory mechanisms acutely to increase DAT availability or alternately, MDMA blockade of striatal SERT could prevent SERT occupancy by (11C)CFT to increase PET ligand availability for the DAT.AIMS: The undeveloped adolescent brain is particularly susceptible to addiction. Risk analyses show early onset of drug use results in a much higher prevalence of addiction to alcohol, nicotine, cocaine, opioids, and MDMA, than initiation of drug use in adulthood. Our focus on MDMA (3, 4-methylenedioxymethamphetamine, ecstasy) is driven by a recent surge in use among youth combined with declining perception of harm. We explored the hypothesis that MDMA exposure during brain development alters the trajectory of normal neurodevelopment by modifying expression of genes designated axonal guidance molecules (AGMs). AGMs are critical for neurodevelopment, neurogenesis and neuroadaptation. METHODS: 14 peri-adolescent mice and 14 adult mice were administered either a low dose of MDMA (3 mg/kg) daily for 6 non-sequential days, or saline, with locomotor activity measured daily. Real-time quantitative PCR measured mRNA expression of 22 genes implicated in MDMA effects in post-mortem brain regions. RESULTS: MDMA suppressed locomotor activity in adolescent mice and increased activity in adult mice. Locomotor effects occurred at earlier times and declined faster in adolescent than adult mice. In striatum and hippocampus, MDMA produced different changes in expression of genes implicated in activity, neurodevelopment and neuroadaptation. CONCLUSIONS: MDMA produces marked differences in adolescent and adult mice, in locomotor activity and in gene expression levels, conceivably contributing to the higher susceptibility of adolescents to MDMA-induced addiction and cognitive impairment. This novel approach may clarify the role of these and other critical genes in mediating the heightened adverse consequences of MDMA, other psychostimulant drugs of abuse in adolescents.

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. AIMS: The stimulant and reinforcing properties of cocaine, correlate with its ability to inhibit monoamine transporters, e.g. dopamine (DAT), and serotonin (SERT) transporters, in brain (e.g. striatum, nucleus accumbens). Cocaine blockade of monoamine transporters results in elevated extracellular concentrations of dopamine, resulting in enhanced stimulation medicated by dopamine receptor activity. The search for pharmacotherapies for cocaine addiction has focused on the design of compounds that bind selectively to the DAT but with slow onset of DAT occupancy and extended duration of action. Phenyltropane analogs of cocaine, of which CFT (WIN 35,428) is the prototype, have offered promising leads for the discovery of DAT selective inhibitors. Building on our previous studies indicating that an amine nitrogen in the 8-aza position is not a prerequisite for potent inhibition of monoamine inhibition, we discovered that 8-thiatropanes retain substantial DAT binding potency and DAT:SERT selectivity. Presently, we evaluate replacing the 2-carbomethoxy group with a 2-isoxazole. METHODS: Binding experiments initially were established using tissue homogenates from primate brain and then applied to cloned human transporters expressed in HEK-293 cells. RESULTS: This new class of 8-thiabicyclo(3.2.1)octanes displayed potent and selective DAT inhibition, with the 3b-aryl compounds particularly potent (IC50 = 7[unreadable]43 nM). In both the 3a-aryl and 3b-aryl series, the 3-methylisoxazole manifested superior DAT inhibitory potency and selectivity compared with the 3-phenylisoxazoles. CONCLUSIONS: The results with this new class of 8-thiatropanes suggests further evaluation is warranted.