In vitro activity: Dexrazoxane (10 mM), known clinically to limit anthracycline cardiac toxicity, prevents daunorubicin-induced myocyte apoptosis, but not necrosis induced by higher anthracycline concentrations in rat cardiac myocytes. Dexrazoxane presumably exerts its cardioprotective effects by either binding free or loosely bound iron, or iron complexed to doxorubicin, thus preventing or reducing site-specific oxygen radical production that damages cellular components. Dexrazoxane specifically abolishes the DNA damage signal gamma-H2AX induced by doxorubicin, but not camptothecin or hydrogen peroxide, in H9C2 cardiomyocytes. Dexrazoxane also induces rapid degradation of Top2beta, which paralleles the reduction of doxorubicin-induced DNA damage. Dexrazoxane antagonizes doxorubicin-induced DNA damage through its interference with Top2beta, which could implicate Top2beta in doxorubicin cardiotoxicity. Dexrazoxane is hydrolyzed to its active form intracellularly and binds iron to prevent the formation of superhydroxide radicals, thus preventing mitochondrial destruction.