Abstract 170: Mechanism of Cardiotoxicity of Tyrosine Kinase Inhibitors

Aim: It is becoming evident that many of the signaling elements driving cancer cell division, for which kinase inhibitors (KIs) are targeted, are the same as those necessary for cardiomyocyte viability. Adverse cardiac events have been reported for a number of KIs. Aim of this study was to identify KIs that induce toxicity to cardiomyocytes and to elucidate the central molecular mechanisms mediating the toxicity. Methods: 288 anti-cancer agents (123 are KIs) were screened for their ability to induce cardiotoxicity in cultured primary cardiomyocytes. Cell viability assay was done by measuring the ATP levels in cardiomyocytes after exposure of cells to a 3-log concentration range of each compound for 24 hours. Toxicity data was combined with kinase profiling data to identify protein kinases mediating the toxicity of KIs. In parallel, the molecular mechanism mediating the cardiomyocyte toxicity of dasatinib, a second generation Bcr-Abl and Src family tyrosine kinase inhibitor, was investigated. The role of Src kinase in regulation of cardiomyocyte viability was analyzed by siRNA-mediated Src knockdown. Overexpression of wild type Src and dasatinib- resistant Src in cardiomyocytes was performed to investigate the role of Src in regulating the cardiomyocyte toxicity of dasatinib. Western blotting was used to investigate for downstream signaling targets of Src. Results: Of the KIs, 70 compounds decreased the cardiomyocyte viability by 10-80 %. The kinase profiling data showed that IGF1R, MEK/ERK pathway, PI3K and Src kinases are the key kinases regulating cardiomyocyte viability. Dasatinib treatment dose-dependently increased cardiomyocyte death. Depletion of Src by siRNA also reduced cardiomyocyte viability. Dasatinib treatment attenuated FGF induced ERK phosphorylation. Overexpression of dasatinib-resistant mutant of Src, but not wild type Src, protected the cardiomyocyte from dasatinib toxicity and rescued the FGF-induced ERK phosphorylation. Conclusions: Cardiomyocyte toxicity of KIs can be attributed to inhibition of IGF1R, MEK/ERK pathway, PI3Ks and Src family kinases. Cardiomyocyte toxicity of dasatinib is mediated by Src kinase inhibition which in turn attenuates MEK/ERK pathway signalling.