Which sequence best protects the heart against trastuzumab and anthracycline toxicity? An electron microscopy study in rats.

BACKGROUND/AIM: Two effective cytotoxic agents, doxorubicin and trastuzumab, are associated with potentially life-threatening cardiotoxicity. The present study was designed to investigate cardiotoxicity aggravated by the timing of administration of trastuzumab and doxorubicin in rats. MATERIALS AND METHODS: Twenty-four rats were randomly assigned to one of four groups. These received one of the following treatment drug regimens administered via intraperitoneal injection: (i) 0.9% saline control (n=6); (ii) doxorubicin (5 mg/kg) on day 1 then trastuzumab 10 mg/kg on day 15 (n=6); (iii) trastuzumab 10 mg/ kg on day 1 then doxorubicin (5 mg/kg) on day 15 (n=6) or (iv) doxorubicin (5 mg/kg) on day 1 and trastuzumab 10 mg/ kg on day 1 (n=6). On the 30th day, the hearts were processed for pathological analysis by electron microscopy. RESULTS: Electron microscopy revealed an ultrastructurally normal heart tissue in the control group. At electron microscopic examination of the tissue samples in the second and fourth group, a mild degree of dilation was observed in the peri-nuclear cisternae of some heart muscle cells. In the third group, pathological changes were detected in mitochondria. These exhibited prominent cristae, which also showed a mild degree of ultrastructural pathology in mitochondria. CONCLUSION: Based on electron microscopy findings, sequential administration of anthracycline first, followed by trastuzumab is safer in terms of cardiotoxicity, while the most toxic schedule for the rat heart was trastuzumab first, followed by anthracycline.