Developing small molecules to engage an analgesic gpcr in pain unpleasantness neural circuits - for millions of patients who suffer from a variety of painful conditions, opioid analgesics can…

Developing small molecules to engage an analgesic gpcr in pain unpleasantness neural circuits - for millions of patients who suffer from a variety of painful conditions, opioid analgesics can provide decisive pain relief in part by decreasing the aversion normally associated with pain perception (i.e., the characteristic unpleasant quality of pain experience, regardless of etiology). Mechanistically, this analgesia against pain unpleasantness is associated with the binding of opioids to specific g protein-coupled receptors (gpcrs), the MU opioid receptors, particularly in brain pathways that contribute to the affective-motivational dimension of pain. However, MU opioid receptors are also broadly expressed outside of pain circuits, where opioids produce unacceptably dangerous side effects including addiction and potentially fatal respiratory depression. Crucially, the human genome contains hundreds of other gpcrs with distinct expression profiles. Thus, because gpcrs are highly druggable proteins, developing small molecules that engage non-opioid, non-addictive gpcrs in affective-motivational pain circuits is an attractive strategy to develop safer analgesics that reduce pain unpleasantness more safely and across all pain conditions. We have assembled a multidisciplinary team comprising pain biologists, neuroscientists, physicians, gpcr pharmacologists, and medicinal chemists; advisors with pharmaceutical industry, drug development, intellectual property, and commercialization experience; and representatives from patient advocacy groups. In our previous work, we discovered an ensemble of neurons in the amygdala that encodes pain unpleasantness and demonstrated that interfering with amygdalar neural activity using artificially expressed gpcrs (dreadds) significantly diminished pain affective- motivational behaviors in mice. We next launched an analgesic target discovery project combining mouse genetic tools, single-cell RNA sequencing, and bioinformatics methods to catalog gpcrs present in the amygdalar neurons active during pain. After generating this catalog, we histologically validated expression of these gpcrs and conducted preliminary antinociceptive efficacy tests, using known gpcr ligands. This work identified an amygdalar gpcr with antinociceptive properties. Furthermore, engagement of this target is not reinforcing in rodents. Although existing ligands were sufficient to demonstrate the antinociceptive potential of this gpcr, our next objective is to develop small molecules with optimized physical, PD, and PK properties. Toward this aim, our team proposes to use medicinal chemistry and computational docking techniques as in our previous study based on the recent resolution of several cryo-EM structures. Further, given that translational efforts can fail due to insufficient understanding of the target biology and its conservation in humans, we will expand our understanding of this gpcr biology by investigating signaling and its distribution in human tissues.