Kirk A. Frey - US grants

This project will apply a newly-developed tracer kinetic method for estimation of regional brain benzodiazepine binding site ("benzodiazepine receptor";BZR) numbers to normal human subjects and to patients with anxiety disorders. It will employ positron emission tomography (PET) and the radiotracer [11C]flumazenil to image and quantify cerebral BZR in vivo. The project has three major divisions: the first is devoted to further model and method validation; the second concerns evaluation of benzodiazepine receptor occupancy following administration of pharmacologic doses of unlabeled benzodiazepines; the third will explore the possibility of altered benzodiazepine receptors in patients with anxiety disorders. The studies should yield new information on the central nervous system actions of benzodiazepines in humans, and will permit the direct testing of hypothesized psychiatric disease mechanism. Experiments are proposed to further investigate current modeling assumptions regarding the quantification of high-affinity ligand binding to the BZR. The initial experimental design will make use of test- retest receptor binding studies with distinct tracer input functions and analytic methods employed. Tracer kinetic estimation of receptor density, on the basis of the regional brain distribution volume of [11C]flumazenil following bolus intravenous injection, will be compared with the equilibrium tracer distribution achieved by intravenous infusion to establish steady-state levels in blood and brain. Subsequently, the precision of kinetic determinations of receptor availability will be investigated in subjects studied twice over several weeks. Analytic methods will be developed to quantify and display changes in BZR availability resulting from administration of pharmacologic doses of unlabeled benzodiazepines. The relationships between plasma levels of oxazepam, brain BZR occupancy, and behavioral and physiologic measure of drug action will be investigated in normal subjects following subacute administration of oxazepam. Evidence for dose-response relationships between plasma drug levels and PET BZR occupancy, power spectral changes in the EEG, and altered performance on neuropsychometric testing will be sought. Aspects of benzodiazepine receptor pharmacology will be evaluated in patients with anxiety disorders including those with generalized anxiety or with panic attacks. The possibility of primary alteration of BZR number will be examined in unmedicated patients. Subsequently, the possibility of altered agonist interaction with the BZR will be evaluated by determination of the BZR occupancy produced by pharmacologic doses of oxazepam.

This Program Project focuses on in vivo neurochemistry of human neurological disorders, emphasizing subcortical structures and their interactions in neurodegenerative and idiopathic functional disorders of movement. Studies in the proposal combine neurochemical phenotypes with functional measures, the latter including motor performance, blood flow activation, neurotransmitter release, ans aspects of sleep physiology. The Program consists of 4 Scientific Projects and 3 Cores. Project by Kilbourn, "New Radiotracers for Neurological PET", will introduce a novel functional approach to assessment of GABAA receptors through allosteric ligands of the chloride ionophore. GABAergic projects are critical components of striatal output and other extrapyrimidal sites. Assessment of GABAA function will complement glucose metabolism studies that may preferentially reflect excitatory glutamatergic pathways. Project by Frey, "Striatal Dopamine and Motor Performance in Aging and Parkinson's Disease" will determine functional motor correlates of nigrostriatal dopaminergic losses in aging and Parkinson's disease and will assess their reversal by acute dopaminergic challenge. Project by Gilman, "Neurochemical and Sleep Disorders in Multiple System Atrophy", will assess the relationships between disrupted sleep in extrapyrimidal neurodegeneration and brain stem cholinergic projections. Project by Albin, "Dopamine Synaptic Mechanisms in Tourette Syndrome", will assess striatal dopaminergic projects and their function from a multi-faceted approach, including measures of their density, their capacity for dopamine re-uptake, their capacity for dopamine release, and an assessment of ambient synaptic dopamine occupancy of D2-type dopamine receptors. Cyclotron/Radiochemistry, Tomography and Data Analysis, and Administrative Core functions support each Project. Overall , the disorders under study in this Program are of unknown pathogenesis and have only symptomatic therapies. The proposed studies will lead to enhanced insight into extrapyrimidal neurochemistry and will address important aspects of dysfunction and disability in these disorders. Novel and improved therapies and new pathophysiological mechanisms and insight may ultimately result.

CORE D: ADMINISTRATION The Administrative Core provides overall scientific and fiscal oversight for the entire Program Project. Several key, shared administrative services are provided for interface with oversight and regulatory agencies, both on a local and on a national level. The Scientific Advisory Committee will advise the Program Principal Investigator and the Project and Core Directors of scientific issues relating to the various clinical questions being addressed in the individual projects of the Program Project Grant.

PROJECT 1 COGNITIVE IMPAIRMENT AND DECLINE IN PARKINSON DISEASE One of the most frequent and disabling developments in the mid- and later stages of Parkinson disease (PD) is the development of cognitive impairment, leading to dementia. The specific mechanism(s) leading to dementia in PD are at present unknown. However, postmortem pathological examinations of PD brains reveal degenerative changes in the basal forebrain and cerebral cortex that may account for dementia in advanced disease. In addition, there are variable proportions of demented PD patients in whom some changes typical of Alzheimer disease (AD) are seen also. It will be important to better understand the mechanism(s) leading to dementia in PD as improved treatments for the motor symptoms and the progressive losses of brainstem dopaminergic neurons are developed. If these treatments do not address the processes leading to more widespread pathology in PD, overall morbidity and mortality in PD may not be improved. In the present project, we will recruit and characterize a cohort of PD patients with moderate motor PD severity, and who are at increased risk for the development of dementia. We will perform behavioral and cognitive testing at baseline, together with PET imaging of dopaminergic degeneration and basal forebrain cholinergic degeneration with the radiotracers [11C]DTBZ to map vesicular monoamine transporter binding sites and [11C]PMP to measure acetylcholinesterase hydrolysis rates, respectively. We will additionally perform imaging with [11C]PIB to detect pathological cerebrocortical deposition of fibrillary A3 amyloid protein (the senile plaques of AD). Patients will be followed prospectively over 2 years with repeat neuropsychometric measures to determine interval cognitive decline. We will assess the relationships between the PET neurodegenerative measures and the loss of cognitive function over time to address the neurochemical mechanism(s) that may be present. In addition, we will conduct a multivariate analysis of the PET measures to assess the possible presence of a global process linking the dopaminergic and cholinergic degenerations and the development of Af3 amyloid deposition.

Cognitive impairment and dementia are common and disabling problems in patients with neurodegenerations characterized by intraneuronal ?-synuclein (?-Syn) aggregates. These patients are classified clinically as either Parkinson disease with dementia (PDD) or as dementia with Lewy bodies (DLB). This labeling distinction is based on the order of presentation of parkinsonism versus dementia ? in PDD, the movement disorder occurs first, while in DLB, the cognitive impairment occurs first or within 1-year of parkinsonism onset. PDD and DLB exhibit virtually identical pathological findings at autopsy. Abnormalities found include pathological depositions of ?-Syn, A?-amyloid, and tau proteins, the latter as intraneuronal paired helical filaments or ?neurofibrillary tangles? (NFT). In individual brains, ?-Syn alone may be present in cell bodies (Lewy bodies) or in synaptic terminals (Lewy neurites). In other brains, ?-Syn deposits are present together with A?-amyloid plaques. In still other brains, ?-Syn, A?-amyloid and tau NFT pathologies are all present, often diagnosed neuropathologically as Alzheimer disease (AD) with PD. The neuropathologic findings do not, however, correlate substantially with subject clinical classification as PDD versus DLB. The future development of effective therapy for dementia in ?-synucleinopathy will likely require targeting of the pathologic pathways involved, and this in turn, necessitates ability to determine the type(s) of pathology present in individual patients and assessment of which pathologies most strongly drive progression of cognitive impairments. To be effective in disease modification, therapies will require testing and application in patients with only mild symptoms. In the present proposal, we will determine endophenotypes of mild dementia in patients with ?-synucleinopathy, employing multi-tracer molecular brain imaging with positron emission tomography (PET). We will determine the presence of ?- Syn neuropathology on the basis of [11C]dihydroteterabenazine (DTBZ) PET imaging of nigrostriatal projection integrity. We will identify the presence of A?-amyloid plaque deposition with [11C]Pittsburgh compound-B (PiB) PET imaging, and the presence of tau NFT pathology with [18F]AV1451 (formerly designated T807) PET imaging. Together, these imaging results will permit classification of each subject as: ?pure? synucleinopathy, or synucleinopathy with A?-amyloid, or as synucleinopathy with both A?-amyloid and tau. We will test the hypothesis that the progression of cognitive decline will be more rapid in the synucleinopathy with both A?-amyloid and tau endophenotype, and that the progression of cognitive impairment in subjects with this endophenotype will correlate with the progression of NFT pathology as determined in follow-up [18F]AV1451-PET. The development of reliable trait biomarkers of neurodegenerative pathologies in PDD and DLB will enable progress in the development and assessment of new therapeutic interventions desperately needed in these syndromes.

Activated monoamine oxidase-B (MAO-B) has been implicated in Alzheimer?s disease and related disorders (ADRD). In order to capitalize upon MAO-B dysfunction as a potential therapeutic target for ADRD, imaging agents for quantifying MAO-B enzymatic activity using positron emission tomography (PET) are required. Despite historical attempts at developing MAO-B imaging agents, key challenges remain for the widespread clinical application of MAO PET in ADRD. Prior research focused upon radiolabeled suicide inhibitors ([11C]L- deprenyl-D2) and reversible inhibitors ([11C]SL25.1188). However, imaging agents based on MAO-B inhibitors have limitations, as they may quantify MAO-B levels but provide no information on enzymatic activity. To address this critical gap in brain PET, the overall objective of this R21 proposal is to translate a first-in-class substrate- based imaging agent for clinical imaging of MAO-B dysfunction in ADRD. Our central hypothesis is that PET imaging with [11C]COU, an MAO-B substrate that forms a trapped metabolite, is uniquely positioned to quantify MAO-B activity with PET for the first time. The proposed research will complete preclinical experiments (pharm- tox, dosimetry, chemistry validation) and documentation (IND and IRB) necessary for clinical translation (Aim 1), conduct essential first-in-human (FIH) PET studies to establish human dosimetry, determine our kinetic modeling approach, and validate the PET signal is dependent on MAO-B activity in blocking studies (Aim 2), and carry out proof-of-concept MAO PET imaging in AD patients (Aim 3). The research is significant because [11C]COU PET could solve the problem of quantifying MAO-B activity in the brain that has been unfeasible since the earliest days of MAO PET imaging in the 1980s. Clinical translation of [11C]COU is justified by extensive preclinical results that provide groundwork for the exciting FIH studies proposed by this R21 grant. Our team at the University of Michigan has worked together for decades at the cutting edge of brain PET and has been collaborating for 8 years on preclinical proof-of-concept studies with [11C]COU. Our expertise in radiochemistry and preclinical imaging (Scott, Brooks, Kilbourn), kinetic modeling and PET image quantitation (Koeppe), as well as ADRD research and clinical nuclear medicine (Frey) uniquely positions us to accomplish the proposed research. The project goals will be realized through quantitation of MAO-B activity using PET via an innovative trapped metabolite approach. [11C]COU is CNS permeable and, once in the brain, gets oxidized by MAO-B and fragments to generate [11C]1-methyl-2,3-dihydropyridin-4(1H)-one ([11C]MDHP). Since [11C]MDHP cannot penetrate the blood-brain barrier, it is trapped in the CNS and we expect that evaluating kinetics using a standard two-tissue compartment model (with irreversible trapping of [11C]MDHP), will allow use of k3 rate constant estimates as an index of MAO activity. Overall, this project will deliver a new technique for quantitating MAO activity with PET that will improve our understanding of MAO-B function in aging as well as ADRD (and other diseases) and, ultimately, aid in utilizing MAO-B imaging for the detection and treatment of disease.