Abstract 9710: Prevention of Doxorubicin-Induced Cardiotoxicity Through Targeted Degradation of Topoisomerase 2b

Introduction: Doxorubicin-induced cardiotoxicity is a serious complication of cancer therapy recognized 40 years ago and remains to be a major clinical challenge today. Doxorubicin poisons topoisomerase 2a to kill cancer cells, whereas doxorubicin induces cardiotoxicity through topoisomerase 2b. When topoisomerase 2b was genetically deleted in the cardiomyocytes of adult mice, doxorubicin-induced cardiomyopathy can be prevented. Hypothesis: Pharmacological depletion of topoisomerase 2b in cardiac tissue could prevent doxorubicin-induced cardiomyopathy. Methods: Cell lines were treated with dexrazoxane (100 μM) for different time intervals with or without the proteasome inhibitor MG132 (10 μM). Cell lysates were immunoblotted with anti-topoisomerase 2a or 2b antibodies or anti-actin. Mice were injected with dexrazoxane (100 mg/kg IP) and cardiac tissues were analyzed for expression of topoisomerase 2b over time using western blot analysis. To study the effect of dexrazoxane pre-treatment on doxorubicin-induced chronic heart failure, C57BL/6 mice (n=7) were pre-treated with dexrazoxane (100 mg/kg IP) 8 hours before doxorubicin (5 mg/kg IP). Single injection of dexrazoxane (n=6), doxorubicin (n=8), or saline control (n=6) were also administered to three different cohorts of mice. This protocol was repeated weekly for 5 weeks. Pre-treatment and post-treatment cardiac MRI were obtained to evaluate the change in left ventricular ejection fraction. Results: Dexrazoxane induced a ubiquitin-dependent degradation of topoisomerase 2b, but not 2a in cell lines. In dexrazoxane-treated mice, topoisomerase 2b was not detectable 8 hours after dexrazoxane administration, but gradually returned to normal levels by 48 hours. Dexrazoxane pre-treatment 8 hours before doxorubicin prevented doxorubicin-induced reduction in ejection fraction as determined by cardiac MRI in a chronic heart failure model. Conclusions: Targeted degradation of topoisomerase 2b by dexrazoxane prevented doxorubicin-induced cardiotoxicity. Through selective degradation of topoisomerase 2b, but not 2a, doxorubicin's tumoricidal activity is preserved. This preventive strategy will be tested in a prospective clinical trial in breast cancer patients.