Biased Kappa Opioid Agonists as Non-addictive Analgesics. Prescription opioid abuse has increased dramatically over the last decade and now comprises the largest growing substance abuse problem in the United States. These abused medications are mu opioid agonists, and alternatives for pain treatment are needed. Kappa opioid receptor (KOR) agonists are analgesic in humans and have low abuse liability, however the dysphoric and sedating properties of these compounds have precluded their clinical utility and development. Recently several groups have discovered that the analgesic properties are mediated through G- protein signaling, while the sedating and dysphoric effects are mediated through non-G-protein pathways, likely either arrestin2 or ERK1/2. Interestingly, several groups have described KOR agonists that preferentially activate G-protein pathways over arrestin or ERK1/2 pathways, termed biased KOR agonists. These compounds are promising candidates as non-addictive analgesics that will be devoid of the sedating and dysphoric effects of other typical KOR agonists. We have recently demonstrated that one such compound produces antinociception in mice and rats without evidence of sedation and dysphoria. Further this compound does not interfere with forebrain dopamine neurotransmission, thought to underlie the untoward effects of typical KOR agonists. The extent and nature of signaling bias is determined in vitro, using cell-based assays. As such, it is not readily apparent how this signaling bias in vitro translates into improved pharmacology in vivo. These compounds have been explored as analgesics primarily using non-clinically relevant pain assays, such as tail flick or hot plate tests in rodents, and these assays do not generally predict clinical efficacy. In this application we propose to assess a wide profile of signaling bias for KOR agonists developed using two distinct chemical scaffolds, and to determine the relationship between intracellular signaling bias across multiple pathways in native neuronal tissue (striatum and dorsal root ganglia) with in vivo efficacy in dysregulation of dopamine neurochemistry and production of antinociception, sedation/dysphoria, and abuse liability using clinically relevant rodent models of inflammatory, post-operative, and neuropathic pain, and drug self- administration. Additionally we will assess the role of gender in signaling bias efficacy, as females have been shown to be more sensitive to the analgesic effects of KOR agonists and less sensitive to the dysphoric effects. We hope to determine a profile of signaling bias in vitro that translates into an improved pharmacological profile for KOR agonists in vivo that can be used for further drug development and mechanistic studies.
Opioid addiction, whether by the use of heroin or prescription narcotics, has emerged as the fastest growing substance abuse problem in the United States with an estimated 5.5 million regular users of opioids for non- medical purposes. Biased kappa opioids, which are analgesic but devoid of troubling psychotomimetic effects, could be important alternatives for pain treatment that possess little to no abuse liability. This proposal is to develop an understanding of how biased agonism at kappa opioid receptors translates into improved analgesics with little to no abuse potential.
