Identification of Small Molecule Inhibitors Selective for Type 1 Adenylyl Cyclase

Abstract

Adenylyl cyclases (ACs) are important integrators of signaling through G protein‐coupled receptors. There are nine isoforms of membrane‐bound ACs that have unique regulatory properties and expression patterns. Adenylyl cyclase 1 (AC1) belongs to a group of ACs that are stimulated by calcium in a calmodulin‐dependent manner. Studies with AC1 knockout mice suggest that inhibitors of AC1 may be useful for treating neuropathic/inflammatory pain, opioid dependence, and preventing neuronal excitotoxicity. However, previous reports in mice lacking both AC1 and AC8 suggest that non‐selective inhibition of AC1 and AC8 would result in significant memory impairments and possibly depression. These observations suggest that AC1‐selective inhibitors have potential in a variety of neurological diseases. Accordingly, inhibition of AC1 with the small molecule NB001 had analgesic properties in animal models of chronic pain in the absence of alterations of hippocampal LTP and fear memory. Unfortunately, the mechanism of action of NB001 remains unknown as it failed to directly inhibit AC1. The present study identified several novel classes of AC1 inhibitors through both chemical library screening and structure‐activity relationship studies. Compounds were initially tested against forskolin and Ca2+ (i.e. A23187) stimulated cAMP accumulation in HEK‐AC1 cells. Robust inhibitors were also evaluated against members from other AC families (i.e. AC2 and AC5) revealing selective AC1 inhibitors. Further comparisons between AC1 and AC8 revealed ligands that showed selectivity for AC1. Subsequent studies determined the effect of these AC1 modulators on Gαi/o‐coupled receptor‐mediated inhibition of cAMP accumulation as well as heterologous sensitization of AC.