Abstract 14894: Mst1 Mediates Doxorubicin-Induced Cardiomyopathy by Sirt3 Downregulation

INTRODUCTION: Heart failure is a major side effect of doxorubicin (DOX) treatment in patients with cancer. However, the mechanisms underlying the development of DOX-induced cardiomyopathy (DCM) need to be addressed. Here, we demonstrate that the serine/threonine kinase MST1, a major component of the Hippo pathway, contributes to the development of DOX-induced myocardial injury. HYPOTHESIS: The inhibition of MST1 protects from DCM by preserving SIRT3 expression METHODS: C57BL/6J WT mice and mice with cardiomyocyte-specific dominant-negative MST1 (kinase-dead, DN-MST1) overexpression received 3 weekly injections of DOX, reaching a final cumulative dose of 18 mg/kg. Echocardiographic, histological and biochemical analyses were performed 6 weeks after the first administration of DOX. RESULTS: MST1 signaling was significantly activated in cardiomyocytes in response to DOX treatment in vitro and in vivo. Wild-type (WT) mice treated with DOX had reduced fractional shortening (46,1±1,8 vs. 31,1±1,1, n=7-11, p<0.0001) and TEM mitochondrial abnormalities (3,7±0,9 vs. 10,2±1,5, n=12, p<0.0001). However, systolic dysfunction was abolished in mice with CM-specific overexpression of DN-MST1 (31,1±1,1 vs. 46,3±1,1, n=11, p>0.0001) or treated with the MST1 inhibitor ‘XMU-MP-1’ (37,5±1,8 vs. 46,6±1,9, n=8, p<0.01), indicating that MST1 inhibition attenuates DOX-induced cardiac dysfunction. DOX treatment also led to a significant downregulation of cardiac levels of SIRT3 (1±0,1 vs. 0,6±0,1, p<0.05), a deacetylase involved in mitochondrial protection, in WT mice, which was rescued by MST1 inhibition (0,6±0,1 vs. 1,3±0,04, p<0.001). Pharmacological inhibition of SIRT3 blunted the protective effects of MST1 inhibition (44,5±1,6 vs. 32,5±2,3, n=4, p<0.01), indicating that SIRT3 downregulation mediates the cytotoxic effects of MST1 activation in response to DOX treatment. Finally, we found a significant upregulation of MST1 levels in human myocardial tissue of cancer patients treated with DOX (1,5±0,23 vs. 2,4±0,12, N=81-123 cells from 3 different patients, p<0.001). CONCLUSION: MST1 contributes to DOX-induced cardiomyopathy by promoting mitochondrial damage through SIRT3 downregulation in cardiomyocytes.