Abstract: Objective To investigate the protective effects of protein kinase C(PKC)inhibitors on the cardiotoxicity induced by sunitinib (SU) at the cellular and whole animal levels. 
Methods The neonatal rat ventricular myocytes (NRVMs) were cultured and incubated with different concentrations of SU (1, 5, 10 μmol/L). The intracellular adenosine triphosphate (ATP) level, lactate dehydrogenase (LDH) release and the mitochondrial membrane potential (MMP) were measured. Then the effects of non-selective PKC inhibitor bisindolylmaleimide 1 (Bis-1), selective novel PKC inhibitor Rotterlin, or inhibitory peptides on SU-induced cardiotoxicity were observed. Male C57 mice were randomly divided into four groups, including control group, SU group, SU combined with PKC inhibitor chelerythrine (CHE) at low dose (i.p. 0.375 mg·kg-1·d-1) and high dose (i.p. 0.75 mg·kg-1·d-1) groups. SU was administered continuously by gavage and intraperitoneal injection of CHE was given. At 3 weeks after administration, the heart tissues were harvested and mitochondria from ventricular myocardium were extracted to measure the activity of mitochondrial complexes Ⅳ and Ⅴ. The transmission electron microscopy (TEM) was used to observe the mitochondria microstructures. Western blot analysis was performed to detect the expression of phosphorylated PKC subtypes, including p-PKCε, p-PKCδ and p-PKCα in each group. 
Results SU significantly reduced ATP level, increased LDH release and decreased MMP in NRVMs in a concentration and time-dependent manner. TEM showed that SU-induced visible changes could be prevented by non-selective PKC inhibitor Bis-1, selective novel PKC inhibitor Rotterlin and selective PKCε inhibitory peptide. Administration of SU significantly reduced the activity of mitochondrial complexes Ⅳ and Ⅴ in mouse myocardium, and TEM showed significant morphological changes such as swelling and cristae fusion in myocardial cell mitochondria. Co-administration of different dose of CHE prevented the decrease of mitochondrial complexes Ⅳ and Ⅴ activities. Meanwhile, TEM showed that CHE significantly alleviated the mitochondrial morphological changes induced by SU. Western blot analysis showed that the expression level of p-PKCε was significantly increased in SU group compared with the control group, but p-PKCδ or p-PKCα had no significant change. High-dose CHE significantly inhibited the overexpression of p-PKCε, restoring it to the control group level. 
Conclusion PKC inhibitors have a significant protective effect against SU-induced cardiotoxicity, which may be due to the inhibition of excessive activation of novel PKC (mainly PKCε subtype). 

Key words: protein kinase C inhibitor, sunitinib, cardiotoxicity