The development of delta opioid receptor agonists for the treatment of opioid withdrawal associated behaviors

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Project Summary Chronic opioid use can lead to opioid induced hyperalgesia (OIH), which is a paradoxical increase in pain sensitivity. Currently, the only specific treatment for OIH is opioid cessation. However, during this abstinence period, patients suffer from their untreated pain as well as opioid withdrawal; and the majority of patients relapse within the first year. As a result, OIH patients are particularly vulnerable to the development of opioid use disorder. Novel targeted therapies that could alleviate OIH would result in decreased prescription opioid misuse and abuse. The Pradhan lab has recently shown that δ opioid receptor (δOR) agonists can reduce OIH in a mouse model. However, the development of δOR agonists has been limited by seizurogenic activity and tolerance. These adverse effects appear to be ligand biased, and δOR agonists which favor G protein signaling over β-arrestin recruitment have a reduced propensity to induce analgesic tolerance and pro-convulsant effects. PharmNovo has developed novel G protein biased δOR agonists. Their lead compound, PN6047, is pre-clinically safe and effective in animal models of chronic pain; does not produce convulsions and, shows little analgesic tolerance. The objective of this proposal is to form an academic-industry collaboration to evaluate novel biased δOR agonists for the treatment of OIH. In the UG3 phase, the Pradhan lab will test PN6047 and another lead compound, PN6041 which has higher G-protein bias, in their models of OIH. Dr. Jutkiewicz will test these lead agonists for adverse effects in models of seizurogenic activity and abuse liability. In parallel, PharmNovo will use the two lead compounds to design and synthesize a limited catalogue of novel ligands with the aim to obtain the optimal properties of high selectivity and potency, G protein bias, and good CNS penetrance. These compounds will be screened in vitro by the Kelly Lab. The critical Go/No-Go milestone necessary to progress to the UH3 phase will be the identification of at least one lead compound that is effective in models of OIH, is non-seizurogenic, lacks abuse liability, and has a promising ADME/ toxicity profile; and if we produce at least 10 follow up agonists with high selectivity and differential bias/efficacy. In the UH3 phase, approximately 12-15 compounds identified in the UG3 phase will be fully characterized in cellular and brain membrane assays, with 6-10 of these tested for efficacy in OIH models, for analgesic tolerance, potential development of opioid-induced hyperalgesia, seizurogenic activity, and abuse potential. The most promising compounds will undergo commercial in silico and in vitro ADME/PK and pre-regulatory toxicology testing. Finally, we expect that an emergent lead compound will be suitable for in vivo acute toxicology, dose range finding/maximum tolerated dose testing and, if possible within timescale and budget, repeated dose toxicity studies. If fully successful, the project will have generated a novel, optimized δOR agonist ready to enter Regulatory Toxicology, as a prelude for human testing as a treatment for OIH.