Melanoma patient-derived xenografts accurately model the disease and develop fast enough to guide treatment decisions

Doxorubicin is among the essential medicines with a wide antitumor spectrum, but its clinical application is limited by its cardiotoxicity. We recently discovered that ROCK1 is a key molecule in mediating cardiac remodeling in response to various stresses. To determine the roles of ROCK1 in doxorubicin cardiotoxicity, we gave three doses of doxorubicin injections to wild type (WT) and ROCK1-/- mice with one week intervals between treatments, the cumulative dose being 24 mg/kg. ROCK1-/- mice exhibited preserved cardiac function, reduced apoptosis, autophagy and fibrosis compared to the WT mice. To further determine the cellular mechanisms, we have examined the role of ROCK1 in cardiomyocytes using cardiomyocyte-specific knockout mice, MHC-Cre/ ROCK1fl/fl , which partially reproduced the cardioprotective characteristics of ROCK1-/- mice, indicating that ROCK1 in both cardiomyocytes and non-cardiomyocytes mediates doxorubicin cardiotoxicity. To elucidate the molecular mechanisms, a detailed time course study after a single doxorubicin injection at 10 mg/kg was performed in ROCK1-/- and MHC-Cre/ROCK1fl/fl mice. The molecular analysis revealed that both ROCK1-/- and MHC-Cre/ROCK1fl/fl hearts exhibited significant reduction of doxorubicin-induced early responses including increased apoptotic (Bax) and autophagic (p62/SQSTM1 and LC3- II) markers, associated with reduced Beclin 1 phosphorylation on Thr119, supporting reduced Beclin 1-mediated autophagy initiation due to increased association of Beclin 1 with Bcl 2 or Bcl-XL in these hearts compared to the WT or ROCK1fl/fl mice. These results support that ROCK1 deficiency is cardioprotective against doxorubicin- induced cardiotoxicity at least in part through reducing Beclin 1-mediated autophagy initiation in cardiomyocytes and restoring autophagic flux to ameliorate doxorubicin cardiotoxicity.