Development of caspase-6 inhibitors for treatment of NASH

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Abstract Hepatocellular death plays an essential role in the development of nonalcoholic steatohepatitis (NASH). The activity of the energy sensor AMP-activated kinase (AMPK) is repressed in NASH and nonalcoholic fatty liver disease (NAFLD). Recent studies from our laboratory demonstrate that AMPK normally phosphorylates the pro-apoptotic caspase-6 to inhibit its activation, keeping hepatocyte apoptosis in check. Steatosis-induced suppression of AMPK activity relieves this inhibition, rendering caspase-6 activated in both human and murine NASH. Activation of AMPK or inhibition of caspase-6, even after the onset of NASH, improves liver damage and fibrosis. Because caspase-6 is an attractive therapeutic target, we will develop high affinity and high specificity chemical inhibitors of caspase 6 for the treatment of NASH. We will pursue two series that are already well advanced, one that binds covalently to the enzyme with high affinity and specificity, and a second noncovalent series that stabilizes the inactive, zymogen state of caspase-6 and inhibits its activation. Selective inhibition of caspase-6 over other caspases has been difficult to achieve before now, but should be safe given the mild phenotype of caspase-6 knockout animals and patients with inactivating mutations. Using structure- based design, we will develop a clinical candidate based on affinity, specificity, ADME properties, bioavailability and in vivo activity in mouse models of NASH. We will also develop a biomarker for capsase-6 inhibition in vivo that will help guide future clinical trials. These efforts may lead to development of the first specific drug that directly attacks the pathogenic process underlying the development of human NASH.