Richard M. Van Rijn, Ph.D. - US grants

Project summary/Abstract G-protein coupled receptors (GPCRs) have long been a favorite target of pharmaceutical companies for treatment of myriad diseases as they are easily accessible and ubiquitously expressed. The predominant signal transduction routes for GPCRs are through the namesake G-protein pathway and by interaction with ?-arrestin-linked scaffolds. Several research groups, including my own, have identified that G- proteins and ?-arrestins can each uniquely modulate types of behavior. The discovery that drugs acting at GPCRs can exhibit so-called functional selectivity [i.e. activate only one pathway and not the other] has provided new opportunities for development of signaling biased drugs with fewer adverse effects. While G-proteins and ?-arrestins mostly provide a divergence of signaling cascades, a small set of enzymes ambiguously play roles in both pathways. Of particular interest is the mitogen activated protein kinase `ERK' (extracellular signal-regulated kinase). ERK function and dysfunction has been linked to many diseases and disorders such as cancer, depression and drug addiction. Numerous studies have been conducted investigating how G-proteins and ?-arrestins regulate ERK activity in simple cellular models. However, due to a lack of specific tools it has been much harder to establish how G-protein- mediated and ?-arrestin-mediated ERK activation individually contribute to the modulation of behavior. Particularly it is of interest whether the total amount of ERK activation is the driving force behind the physiological effect, or whether the mechanism of activation (G-protein versus ?-arrestin) is important. Recent pharmacological advances are now allowing us to propose experiments that will enable the dissection of G-protein and ?-arrestin ERK activation in behavioral assays. For this proposal we will use G-protein and ?-arrestin-biased drugs acting on delta opioid receptors as well as utilize innovative chemogenetic approaches to address our research questions. Our prior studies investigating delta opioid receptors have revealed that G-protein-biased drugs at this receptor can reduce alcohol use, whereas those delta opioids that activate ERK reduce anxiety. Upon completion of this study we will be able to address fundamental questions regarding signaling biased ERK activation related to alcohol use and anxiety-like behavior. More importantly, we will be able to describe `how biased' a delta opioid receptor drug must be and how /how much ERK it should be able to activate in order to efficaciously reduce alcohol use and anxiety, simultaneously. Such a drug would be very valuable given that alcohol use disorders are highly co-morbid with general anxiety disorders and post-traumatic stress disorders. Additionally, alcohol withdrawal induced anxiety is a major contributor to relapse and thus a bi-functional delta opioid drug would be a significantly better therapeutic option for patients suffering from alcohol use disorders than the currently available treatment options.

Project summary Chronic pain is a debilitating and costly condition from which more than 25 million US citizens suffer on a daily basis. Current available analgesic drugs often do not provide complete pain relief and/or come with serious side effects, and thus, there is a need to develop novel painkillers, that won?t produce restrictive adverse effects. µ-opioid receptor (µOR) agonists are one of the most effective analgesics for moderate to severe acute pain. Yet, the currently available µOR agonists come with serious side effects including analgesic tolerance and dependence when used for prolonged periods of time limiting their use primarily to short-term pain treatment or terminal care. This is a major reason why the Center for Disease Prevention and Control created new guidelines recommending against using µOR agonists for chronic pain. Targeting ?-opioid receptor (?ORs) instead of µORs has a clear upside as ?OR selective agonists are less addictive, and do not cause problematic constipation and respiratory depression like µOR agonists, such as morphine and oxycodone do. Moreover, functional ?OR expression reportedly increases during chronic events, including nerve ligation and persistent inflammation. The µOR and ?OR are Gi-coupled receptor that inhibit cAMP production However, these and other G protein-coupled receptors can also signal in a G-protein-independent manner, via ?-arrestin proteins. For opioid receptors recruitment of ?-arrestin is associated with several debilitating adverse effects. Improved understanding of receptor-selective signaling, has made it possible to design pathway-selective agonists, primarily referred to as biased agonists that can avoid or reduce some of these side effects. In the case of ?ORs, strong ?-arrestin recruitment has been associated with seizures, increased alcohol use, hyperlocomotion and analgesic tolerance. Thus, G-protein-biased ?OR agonists hold great potential as novel pain treatment. In this proposal we will combine computational modelling, medicinal chemistry and cellular pharmacology to develop a novel, potent, selective, G-protein-biased ?OR agonist. This proposal is divided in two specific aims: In specific aim 1, we will run molecular dynamics studies on a homology model of an agonist-bound ?OR structure in order to predict binding of G-protein and ?-arrestin biased ?OR agonists. We will use a structure-based approach to rationally design and synthesize novel G-protein-biased ?OR agonists. To speed up the development of the compounds we will use a chemical scaffold that is based on the potent µOR agonist drug fentanyl, but importantly can be modified to create ?OR agonist selective agonists. In specific aim 2, we will characterize the synthesized drugs for receptor selectivity, drug potency and signaling bias using specific cellular assays. Analgesic effects of the drugs will be measured in a model of acute inflammatory pain. The obtained information will feed-back to aim 1, to further drive and improve the modelling and synthesis processes. This proposal fits the chemistry science track award for rapid transition R03 mechanism from the National Institute on Drug Abuse, to discover new drugs with low abuse potential.

Project summary Alcohol use disorders (AUD) cost the United States health system roughly $250 billion per year, and recent data suggests that alcohol use in the US is rising. Problematically, only three drugs have been FDA approved for treatment of AUD and less than 10% of patients are prescribed them. Increasingly, patients reach to the internet to find alternative treatment options for AUD without a necessary prescription. A pertinent example is Mitrayna speciosa (kratom), an opioid containing plant that is used extramedically to self-medicate chronic pain as well as opioid dependence. Unsurprisingly given the role of the opioid receptor system in alcohol use and craving, kratom is occasionally used to self-medicate AUD. However, currently no studies have investigated whether kratom or any of its major alkaloids effectively reduce alcohol use. Additionally, it is unknown if these alkaloids have rewarding properties in alcoholics. Kratom contains several alkaloids (including the main constituent mitragynine) that are known to bind to and activate opioid receptors. Interestingly, these opioids appear to act as so-called ?biased agonists? in vitro by activating only the G-protein signaling pathway of G protein-coupled receptors (GPCRs), such as the opioid receptor, but not those pathways associated with ?-arrestin proteins. We have recently found that G-protein biased agonists targeting ?-opioid receptor (?OR) can effectively reduce alcohol intake in mice. In this proposal, we hypothesize that those alkaloids in kratom that can activate ?ORs will contribute to reduced voluntary alcohol consumption in mice particularly by signaling in a G-protein biased manner. We further hypothesize that these alkaloids will not produce conditioned place preference, a measure of the rewarding properties of a drug, via ?ORs. To investigate our hypothesis we will identify six kratom-derived opioids with the strongest affinity for ?ORs. We will then assess whether kratom and these kratom-derived opioids can reduce alcohol use in a model of limited-access voluntary alcohol consumption in wild-type mice as well as in specific opioid receptor knockout animals. Thirdly, we will determine to what degree kratom and the kratom- derived opioids can induce a conditioned place preference response in naïve and alcohol exposed wild-type mice and in ?OR knockout mice. The information that will be gathered by successful completion of this proposal can jumpstart clinical studies into the use of kratom and the kratom-derived opioids for AUD treatment as well as educate the general public about the risks and benefits of kratom use. The aims of this proposal fit the larger goal of my research program which is geared toward development of novel therapeutics to treat AUD. This is in line with the major initiative of the National Institute on Alcohol Abuse and Alcoholism to ?offer effective intervention for problem alcohol use at all ages?.

Project Summary/Abstract Primary breast cancers systemically disseminate at very early stages of disease, often times even before the primary tumor is diagnosed. Therefore, patients that have surgery to remove primary tumors already harbor disseminated disease. Outgrowth of these disseminated micrometastases can be triggered years to decades after the primary lesion is removed, leading to inhibition of vital organ function and patient lethality. Currently, environmental stimuli that are responsible for triggering metastatic outgrowth are not well defined. In particular, population studies investigating alcohol consumption and breast cancer recurrence have yielded controversial results. A confounding factor for this disparage may be inaccurate reporting about the amount and duration of alcohol consumption. Therefore, the major OBJECTIVE of this proposal is to evaluate the ability of moderate, binge, and excessive alcohol consumption to break systemic breast cancer dormancy leading to progression of metastatic disease. To accomplish this objective, we will utilize controlled rodent models of differential alcohol intake together with an in vivo bioluminescent reporter system of epithelial-mesenchymal transition (EMT). EMT is strongly linked to breast cancer progression, including development of stem-like tumor cells that have an increased capacity to initiate metastatic tumors. Furthermore, previous in vitro studies suggest that alcohol stimulation can induce an EMT-associated transcriptional program. Therefore, in AIM1 of our proposal mice bearing systemically dormant EMT reporter tumor cells within the lungs and liver will be treated with our established moderate, excessive and binge alcohol consumption protocols. Our bioluminescent approach will allow us to longitudinally track these cohorts of control and alcohol drinking mice for induction of EMT in tumor cells harbored within these common organ sites of breast cancer metastasis. In addition to directly acting on tumor cells, alcohol can profoundly alter the fibrotic and immune makeup of metastatic organ sites. Maintenance of tissue compliance and immune surveillance are two critical mechanisms by which the lungs and liver resist metastatic colonization. In AIM2 of our proposal, postsurgical animals bearing matrix-sensitive and immune-sensitive dormant tumor cells will be treated with our differential alcohol consumption protocols. These animals will be evaluated for an impaired ability to maintain tumor cell dormancy within these critical vital organs. Results gained by our collaborative studies will result in new insight into the mechanisms by which alcohol may contribute the metastatic recurrence of breast and potentially other cancers. !