ASK1/^p38 axis inhibition blocks the release of mitochondrial "danger signals" from hepatocytes and suppresses progression to cirrhosis and liver cancer

Background & Aims: Apoptosis Signal-regulating Kinase 1 (ASK1) is activated by various pathological stimuli and induce cell apoptosis via downstream p38 activation. We studied the effect of pharmacological ASK1 inhibition on cirrhosis and its sequalae using comprehensive preclinical in vivo and in vitro systems. Approach & Results: Short- (4-6 wk) and long-term (24-44 wk) ASK1 inhibition using small molecule GS-444217 was tested in thioacetamide-induced and BALB/c.Mdr2-/- murine models of cirrhosis and hepatocellular carcinoma (HCC), and in vitro using primary hepatocyte cell death assays. Short-term GS-444217 therapy in both models strongly reduced phosphorylated p38, hepatocyte death, and fibrosis by up to 50%. Profibrogenic release of mitochondrial DAMP mtDNA from dying hepatocytes was blocked by ASK1 or p38 inhibition. Long-term (24 wk) therapy in BALBc.Mdr2-/- model resulted in moderate 25% reduction in bridging fibrosis, but not in net collagen deposition. Despite this, development of cirrhosis was effectively prevented, with strongly reduced p21+ hepatocyte staining (by 72%), serum ammonia levels (by 46%) and portal pressure (average 6.07 vs 8.53 mmHg in controls). Extended ASK1 inhibition for 44 wk in aged BALB/c.Mdr2-/- mice resulted in markedly reduced tumor number and size by similar to 50% compared to control group. Conclusions: ASK1 inhibition suppresses profibrogenic release of mtDNA from dying hepatocytes in p38-dependent manner and protects from liver fibrosis. Long-term ASK1 targeting resulted in diminished net antifibrotic effect, but the progression to liver cirrhosis and cancer in BALBc/Mdr2 (-/-) mice was effectively inhibited. These data support the clinical evaluation of ASK1 inhibitors in fibrotic liver diseases.