KOR Agonist Functional Selectivity in Peripheral Sensory Neurons

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DESCRIPTION (provided by applicant): Functional selectivity, also known as "biased agonism", is a term used to describe the ability of drugs, acting at the same receptor subtype, to differentially regulate the activity of each of the multiple signaling cascades coupled to the receptor. The underlying mechanism for functional selectivity is based upon the formation of ligand-specific receptor conformations that are dependent upon ligand structure and that have differential ability to regulate various cellular signal transduction molecules. There is now tremendous excitement over the potential of functional selectivity to revitalize the drug discovery/development process. Ligands with high efficacy for specific signaling pathways (or specific patterns of signaling) that mediate beneficial effects, and with minimal activity at pathways that lead to adverse effects, are expected to have improved therapeutic efficacy. However, the pharmaceutical industry has been slow to incorporate ligand functional selectivity into the drug discovery process in large part because there have been few examples of ligand functional selectivity in physiologically relevant cell systems or in vivo. If successful, the work proposed here will help to establish the relevance of signaling specificity in a therapeutically relevant behavioral model of antinociception. We propose to demonstrate that ligand efficacy for specific signaling pathways associated with antinociception can be finely tuned by structural modifications to a ligand. In this application, we propose to use U50,488 and Salvinorin-A (Sal-A) as scaffolds to develop functionally selective analogs that maintain high efficacy for signaling pathways that lead to antinociception and minimize activity toward anti-antinociceptive signaling pathways. Our specific aims are to 1) modify the structure of the KOR agonist, Sal-A, and 2) modify the structure of the KOR agonist, U50,488, to minimize efficacy for MAPK (ERK and JNK) signaling while maintaining (or enhancing) efficacy for activation of Gai signaling. Analogs of Sal-A and U50,488 will be synthesized in an iterative cycle of synthesis/evaluation/redesign until compounds with the proposed pharmacological characteristics of high KOR affinity and efficacy for antinociception (Gai signaling) and low efficacy for MAPK signaling (anti-antinociceptive) are obtained. Initial efficacy evaluation will be done utilizing an ex vivo model (primary sensory neuron cultures) that provides high predictability of antinociceptive efficacy in vivo. Compounds that reach the efficacy criteria ex vivo will be further tested for antinociceptive efficacy in a complementary in vivo behavioral model of pain. This work will be the first to examine structure-activity relationships of functionally selective ligands using a physiologically- and therapeutically-relevant model system to guide compound development. If successful, this work will not only establish the importance of functional selectivity in physiological systems and thereby herald fundamental changes in drug development strategies, but also may lead to new drugs with improved therapeutic profiles for the treatment of pain.