Exploring the Applicability of Potential Negative Allosteric Modulators at the Mu Opioid Receptor

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Project Summary/Abstract We are experiencing the third wave of opiates, a shift to powerful synthetics that is mirrored in other drugs of abuse such as cannabinoids (Spice) and cathinones (‘bath salts’). These potent drugs are preferred by dealers for economic reasons, but many of the new synthetic opiates bind so tightly to their target receptor, that the current treatment (naloxone/Narcan) for opioid overdose can prove ineffective. There are police reports of victims of synthetic opiate overdose found with multiple expended doses of naloxone, or who need IV administration. In the case of fentanyl-associated ‘wooden chest syndrome’, even a trained CPR provider cannot prevent death by asphyxiation. Where a competitive antagonist struggles against carfentanyl, a negative allosteric modulator may succeed. These molecules act via secondary sites on the receptor. Two candidate compounds have been identified; we hypothesize that negative allosteric modulators at the mu opioid receptors (µORs) can serve as an alternative strategy to overcome potent synthetic opiates, with the goal of alleviating the fatality of opioid toxicity. The project involves an iterative series of tests of structural analogues of these candidate negative allosteric modulators for their ability to reverse opiate signaling both in vitro and in vivo. The goal is to develop an optimized negative allosteric modulator at the µOR that would reverse opiate overdose in an emergency setting. Due to the nature of allosteric modulators, there is reason to expect that this would also avoid the strong withdrawal symptoms elicited by naloxone in opiate-dependent individuals, which is also an advantage in an emergency setting. Such a compound may also have superior pharmacological properties to naltrexone in places where methadone/buprenorphine are unavailable. With the current climate of the opioid crisis, it is crucial to explore the implications of the negative allosteric modulators, as it could lead to an alternative antidote to the increasingly powerful opiates that are being seen. Indiana University is a large university with a strength in biological research and particularly in drugs of abuse such as cannabinoids and opiates; the university also features many scientific resources (e.g. core facilities) to support research. The neuroscience program is highly interactive thanks in part to the Gill Center that sponsors an annual Symposium, visiting speakers, and a journal club. A training plan has been developed that covers techniques (in vitro and in vivo assays), coursework, training in the responsible conduct of research, as well as mentorship in some of the less tangible, but nonetheless essential, qualities that make for a successful scientist.