Pharmacological validation of adenylyl cyclase 1 as a drug target for chronic pain

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Chronic pain costs the US more than $635 billion per year, however, patients fail to receive adequate relief from the available drugs and often become drug-dependent. These observations highlight the importance for identifying new agents acting on unique targets to treat chronic pain. Genetic, neurobiological, and preclinical studies have suggested that adenylyl cyclase type 1 (AC1) may provide that new drug target. AC1 knock out mice (AC1-/-) show reduced or absent inflammatory and neuropathic pain when compared to littermate controls. Preclinical studies with a small molecule inhibitor of AC1, NB001 revealed that NB001 reduced chronic pain responses (i.e. inflammatory and neuropathic) in both mice and rats. Similarly, we have recently shown that a novel AC1 inhibitor, ST034307 also reduced inflammatory pain in a mouse model. These studies are consistent with the premise that AC1 is a new target for inhibitors of chronic pain. Unfortunately, both NB001 and ST034307 have significant issues and liabilities preventing further development. To that end, we have recently screened a chemical library collection that allowed us to identify a pyrimidinone scaffold for the development of novel AC1 inhibitors. This scaffold was prioritized for hit-to-lead optimization based on several promising criteria. Preliminary structure-activity relationship (SAR) studies have revealed for the first time compounds with sub-micromolar potency at AC1, as well as selectivity versus the closely-related AC8. Further, initial in vivo studies with a lead compound reveal activity in an animal model of chronic pain. Despite these promising observations, the lead compounds suffer from extremely low aqueous solubility. We propose medicinal chemistry optimization of this scaffold to develop potent and selective inhibitors of AC1 activity as novel probes under the following Specific Aims: Specific aim 1 will use medicinal chemistry optimization of the pyrimidinone scaffold to develop potent drug-like AC1-selective molecular probes. Specific aim 2 will establish the pharmacological specificity of the probe molecules using a set of in vitro model assays and explore the mechanisms for probe activity. Additionally, we will execute in vivo preclinical pharmacokinetic testing with iterative medicinal chemistry and pharmacology. Specific aim 3 will then use the best molecules to explore the in vivo pharmacological activity of the AC1 inhibitors in a mouse model of inflammatory pain, conditioned place preference, and opioid withdrawal. At the end of this study, we shall provide the research community with chemical probes with < 100 nM AC1 potency, > 30-fold selectivity vs other ACs and related CNS targets, and in vivo efficacy. These new probes will provide essential tools to validate AC1 as a new and safe drug target in the treatment of chronic pain.