PROJECT SUMMARY The use of DNA-encoded library (DEL) technology for the identification of therapeutic molecules to treat opioid use disorders (OUDs). This Phase I SBIR project aims at the identification, using a novel DEL drug discovery platform, of small molecular weight compounds that can bind to the receptor GPR26 belonging to the family of G-protein coupled receptors (GPCRs) with the goal of restoring brain functions associated with the reward system without affecting opioid receptors. Effects of opioids are mediated through GPCR μ-opioid receptors (MORs) and indirectly through dopaminergic pathways via dopamine receptors. Some of these pathways, and the basal ganglia signaling in general, were largely deciphered by us in the Greengard lab over the last three decades. Morphine perturbs the mesolimbic dopaminergic system which is triggered in conditions of dependence and withdrawal. Furthermore, morphine-dependency is associated with elevated cAMP levels, altering broad cAMP signaling, in the striatum especially. GPCRs represent one of the most important therapeutic classes and many of them remain largely understudied and without a known ligand (called orphan GPCRs or oGPCRs). We have identified several oGPCRs strongly and selectively expressed in brain regions highly relevant for substance use disorders (SUDs). Those represent a remarkable and unexploited opportunity to counteract OUDs in an innovative way, and without targeting the opioid receptors directly. We are proposing to focus this program on GPR26 that appears to be the strongest candidate, based on our knowledge and preliminary data, to modify cAMP signaling and potentially rebalance the basal ganglia signaling. GPCRs drug discovery is hampered by the need of large amounts of mostly non-physiological receptor protein (E. coli) for high-throughput screening (HTS) and the need for a clear biological activity to perform HTS drug screening. Our research strategy is to identify GPR26 binders addressing each of these limitations by using a DNA-encoded library (DEL) screening approach that will allow small amounts of a physiological/high quality target to be used with very large screening power (125 million entirely new and proprietary compounds) and a binding-based assay that is activity-independent. The central hypothesis is that due to the very large number of compounds available to be tested and the inherent diversity, it will be possible to identify efficiently, in a cost-effective way, compounds that are high-affinity binders (pre-optimization) of GPR26. DEL screening protocols have been generated and optimized focusing on minimizing the amount of protein to be used and on purifying protein targets from mammalian cells. These steps will ensure that a physiological GPR26 version is used for screening purposes and that screen duplicates will increase confidence and improve hits’ heuristic values determination. Aim 1 will be dedicated to DEL screening campaigns and 125 millions of DEL c...