Emily M. Jutkiewicz, Ph.D. - US grants

Project Summary/Abstract There is a significant unmet clinical need to find effective analgesic drugs for the treatment of chronic pain that have fewer adverse effects, tolerance development, and abuse potential. We have identified a novel mixed efficacy opioid ligand (AAH8) that is highly effective for treating pain in animal models but does not produce tolerance or dependence when administered repeatedly. This compound appears to have minimal rewarding effects in an animal model. These data suggest that our candidate compound may be the ultimate opioid analgesic that produces significant pain relief with little risk of developing tolerance or addiction. AAH8 has equivalent affinity for mu and delta opioid receptors but it is a mu opioid receptor agonist and a delta opioid receptor antagonist and appears to cross the blood brain barrier. Blocking delta-opioid receptors has been proposed to alter the trafficking of mu-opioid receptors as related to desensitization, downregulation, and tolerance. While it is unusual to think that an effective mu-opioid analgesic would not have abuse potential, our preliminary data suggest that the mixed efficacy opioid ligand marks a significant improvement over current opioid analgesics, especially for treating chronic pain. Therefore, the long-term goal of the proposed work is to identify effective treatments for chronic pain with fewer adverse consequences associated with long term treatments. The objective here is to examine the effects of AAH8 in models of chronic pain, drug self- administration, and adverse side effects as compared with clinically used opioid analgesics. The overarching hypothesis is that AAH8 will have limited reinforcing effects in a drug self-administration assays and will retain efficacy in chronic pain assays. To accomplish this work, AAH8 will be evaluated in a chronic pain models and in drug self-administration assays in opioid-naïve and -experienced subjects to determine its reinforcing effects. Overall, this venture has the potential to identify a drug that would dramatically improve the treatment and management of chronic pain by reducing the hazards associated with long term opioid treatment.

Project Summary/Abstract There are fundamental gaps in our understanding of the neurobiological processes involved in addiction, in particular the complex changes produced by drug-paired cues (conditioned reinforcers) that increase drug-taking behavior and provoke relapse. Identifying novel mechanisms by which conditioned reinforcers modify behavior is essential for future efforts to design new treatments to control drug craving and prevent relapse to addiction. The long-term goal of this work is to further our understanding of the behavioral and neurobiological mechanisms mediating drug-paired stimuli that serve as conditioned reinforcers. The objective of this application is to identify the role of the endogenous enkephalinergic system in regulating the reinforcing properties of cocaine-associated stimuli that are an essential part of cocaine addiction. Enkephalins binds with high affinity to delta-opioid receptors (DOPRs), which are highly expressed within the reward pathway, and DOPR activation can alter responding for drug-paired cues without primary reinforcing effects. Our overarching hypothesis is that enkephalins acting at delta-opioid receptors (DOPRs) in the nucleus accumbens shell (NAc-S) play an essential role in the behavioral and neurochemical mechanisms mediating the conditioned reinforcing properties of cocaine-paired cues. This proposal will couple behavioral measurements of conditioned reinforcement with in vivo microdialysis and comprehensive mass spectrometry analysis to evaluate in real-time the role of the enkephalin and DOPRs in establishing and maintaining the salience of cocaine-associated cues. Through the innovative use of behavioral and neurochemical measurement techniques, this proposal will expand beyond the status quo to investigate novel mechanisms selectively mediating conditioned reinforcement but not necessarily the direct, primary reinforcing effects of cocaine. Ultimately, such knowledge has the potential to develop new treatments for preventing relapse.

This application proposes a novel approach to improving the safety of opioid analgesics by post-receptor pharmacological targeting of G protein ?? subunits to modify the actions of ?-opioid receptors (MORs). Our laboratory has identified small molecule inhibitors of G protein ?? subunits that demonstrate in vivo efficacy in various animal models of disease. Relevant to this application, we identified two related G?? inhibitors, M119 and gallein that increase MOR agonist analgesic potency in mice without potentiating side effects that include development of tolerance, respiratory depression, constipation or addiction. Thus co-administration of G?? inhibitors with opioid analgesics has the potential to improve their safety profile by opening up the therapeutic window between analgesic efficacy and deleterious side effects. We propose that gallein and M119 modify opioid action by blocking specific feedback pathways downstream of MORs while leaving pro-analgesic pathways intact. MORs couple to the Gi family of G proteins and promote analgesia through G protein-dependent inhibition of neurotransmitter release via G??-dependent regulation of K+ (GIRK) channels, N-type Ca2+ channels and inhibition of vesicle fusion with synaptic membranes. At the same time G?? activates feedback pathways including phospholipase C (PLC?) and G protein-coupled receptor kinases (GRKs), which limit opioid receptor activity. Gallein and M119 block G??-dependent regulation of PLC? and GRK2 without blocking GIRK or N-type Ca2+ channels and thereby biasing MORs toward pro-analgesic signaling. Gallein and M119 have been powerful probe compounds to validate the idea that pharmacological G?? blockade could improve the properties of opioid analgesics, but the chemical characteristics of the molecules makes them unsuitable for therapeutic development. Data with new chemical series? derived from our high throughput screening (HTS) campaign support a G?? on-target mechanism of action. The primary goal of this application is to develop and mechanistically characterize novel ?drug like? G?? inhibitors that can be utilized to improve the safety of opioid analgesics. This application is divided into 3 specific aims 1) We will diversify the chemistry of promising lead compounds derived from HTS with the goal of improving potency and ?drug like? characteristics. We expect that upon completion of this aim we will identify a high potency ?drug like? G?? inhibitor that can be a strong lead candidate for therapeutic development. 2) We will use whole animal PLC?? and ?-arrestin-2 knockout models, and brain slice electrophysiology to examine the roles of blocking feedback inhibition of MOR signaling by PLC, PKC and ?-arrestin pathways in the potentiating actions of G?? inhibitors. 3) There is a significant need to find an opioid analgesic for the treatment of chronic pain without abuse potential and adverse side effects. We will explore the utility of G?? inhibition in chronic opioid use in a mouse model of chronic inflammatory pain, with both chronic and acute administration and use a rat model of morphine self-administration.