A Novel Preclinical Strategy for Identifying Cardiotoxic Kinase Inhibitors and Mechanisms of Cardiotoxicity

Rationale: Despite intense interest in strategies to predict which kinase inhibitor (KI) cancer therapeutics may be associated with cardiotoxicity, current approaches are inadequate. Sorafenib is a KI of concern because it inhibits growth factor receptors and Raf-1/B-Raf, kinases that are upstream of extracellular signal-regulated kinases (ERKs) and signal cardiomyocyte survival in the setting of stress. Objectives: To explore the potential use of zebrafish as a preclinical model to predict cardiotoxicity and to determine whether sorafenib has associated cardiotoxicity, and, if so, define the mechanisms. Methods and Results: We find that the zebrafish model is readily able to discriminate a KI with little or no cardiotoxicity (gefitinib) from one with demonstrated cardiotoxicity (sunitinib). Sorafenib, like sunitinib, leads to cardiomyocyte apoptosis, a reduction in total myocyte number per heart, contractile dysfunction, and ventricular dilatation in zebrafish. In cultured rat cardiomyocytes, sorafenib induces cell death. This can be rescued by adenovirus-mediated gene transfer of constitutively active MEK1, which restores ERK activity even in the presence of sorafenib. Whereas growth factor induced activation of ERKs requires Raf, alpha-adrenergic agonist-induced activation of ERKs does not require it. Consequently, activation of alpha-adrenergic signaling markedly decreases sorafenib-induced cell death. Consistent with these in vitro data, inhibition of alpha-adrenergic signaling with the receptor antagonist prazosin worsens sorafenib-induced cardiomyopathy in zebrafish. Conclusions: Zebrafish may he a valuable preclinical tool to predict cardiotoxicity. The alpha-adrenergic signaling pathway is an important modulator of sorafenib cardiotoxicity in vitro and in vivo and appears to act through a here-to-fore unrecognized signaling pathway downstream of alpha-adrenergic activation that bypasses Raf to activate ERKs. (Circ Res. 2011;109:1401-1409.)