Development of selective calpain-1 inhibitors for chronic pain

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PROJECT SUMMARY Never in the history of the United States has the unmet medical need to develop novel, non-opioid therapeutics for chronic pain been more urgent than it is today. More than 65 million US adults suffer from chronic pain, resulting in almost $635 billion in annual healthcare costs. Despite their limited efficacy, and potential for addiction, tolerance, and impaired motor performance, opioids have become a mainstay for chronic pain management, resulting in an opioid epidemic that is ravaging communities throughout the US. Thus, there is an urgent need to develop novel, non-opioid therapies for chronic pain management. This application addresses this unmet medical need by leveraging our novel artificial intelligence (AI)-driven drug discovery platform to develop selective inhibitors of calpain-1 as novel non-opioid therapeutics for chronic pain. Studies in chronic neuropathic pain animal models have shown that nerve injury overactivates calpain-1, which downregulates K+ Cl- cotransporter activity, resulting in diminished synaptic inhibition and neuropathic pain. Prior work by our group has also shown that both pharmacological inhibition and whole body genetic knockout of calpain-1 attenuates chronic pain behaviors in mouse models of sickle cell disease (SCD). Importantly, the analgesic effect of calpain-1 inhibition did not induce tolerance side effects, suggesting the potential for calpain-1 inhibitors to be non-addictive. By applying our innovative artificial intelligence (AI)-driven drug discovery platform to screen a virtual chemical library, we identified four (4) novel calpain-1 inhibitors, and validated them for efficacy in biochemical assays. Here, we propose to progress our most potent hit compound to a lead compound that is calpain-1 selective, cysteine protease family selective, non-opioid, and CNS penetrant with efficacy demonstrated in at least 1 of 3 chronic pain animal models tested, including chronic sickle cell disease pain, chronic inflammatory pain, and chronic neuropathic pain. Three aims are proposed, including Aim 1: Synthesize ~100 analogs of our most potent hit compound, and characterize in vitro activity and selectivity. Success criteria: Top 20 cell-permeable, calpain-1 inhibitors, moderately selective against calpain-2, and highly selective against cathepsins and caspase-1, Aim 2: Evaluate ADME-Tox and PK profile of our top 20 calpain-1 inhibitors from Aim 1. Success criteria: Top 2 CNS-penetrant selective calpain-1 inhibitors with favorable in vivo PK profile, and Aim 3: Determine the efficacy and PK/PD relationship of our top calpain-1 inhibitor in 3 chronic pain animal models. Success: at least 40% reduction in mechanical hyperalgesia in at least 1 of the 3 chronic pain animal models tested. Successful completion of this Phase I will yield a novel CNS-penetrant, selective calpain-1inhibitor with efficacy demonstrated in at least 1 chronic pain animal model. Our overall product would be the first, oral, CNS acting, selective calpain-1 inhibitor for chronic pain. Importantly, our product would reduce opioid usage in chronic pain patients, and help to stem the US opioid epidemic.