Secondary Alcohol Metabolites

Introduction The cardiotoxicity of doxorubicin (DOX) and other quinone-containing antitumor anthracyclines has been tentatively attributed to the formation of drug semiquinones which generate superoxide anion and reduce ferritin-bound Fe(III), favoring the release of Fe(II) and its subsequent involvement in free radical reactions. In the present study NADPHand DOX-supplemented cytosolic fractions from human myocardial biopsies are shown to support a twostep reaction favoring an alternative mechanism of Fe(II) mobilization. The first step is an enzymatic two-electron reduction of the C-13 carbonyl group in the side chain of DOX, yielding a secondary alcohol metabolite which is called doxorubicinol (3.9±0.4 nmoles/mg protein per 4 h, mean±SEM). The second step is a nonenzymatic and superoxide anion-independent redox coupling of a large fraction of doxorubicinol (3.2±0.4 nmol/mg protein per 4 h) with Fe(III) -binding proteins distinct from ferritin, regenerating stoichiometric amounts of DOX, and mobilizing a twofold excess of Fe(ll) ions (6.1±0.7 nmol/mg protein per 4 h). The formation of secondary alcohol metabolites decreases significantly (P < 0.01) when DOX is replaced by less cardiotoxic anthracyclines such as daunorubicin, 4 '-epi DOX, and 4-demethoxy daunorubicin (2.1±0.1, 1.2±0.2, and 0.6±0.2 nmol/mg protein per 4 h, respectively). Therefore, daunorubicin, 4 '-epi DOX, and 4-demethoxy daunorubicin are significantly (P < 0.01) less effective than DOX in mobilizing Fe(II) (3.5±0.1, 1.8+0.2, and 0.9±0.3 nmol/mg protein per 4 h, respectively). These results highlight the formation of secondary alcohol metabolites and the availability of nonferritin sources of Fe(III) as novel and critical determinants of Fe(II) delocalization and cardiac damage by structurally distinct anthracyclines, thus providing alternative routes to the design of cardioprotectants for anthracyclinetreated patients. (J. Clin. Invest. 1995. 95:1595-1605.)