Redox Cycling of Anthracyclines by Cardiac Mitochondria

In the accompanying paper (Davies, K. J. A., and Doroshow, J. A. (1986) J. Biol. Chern. 261, 30603067), we have demonstrated that anthracycline antibiotics are reduced to the semiquinone form at Complex I of the mitochondrial electron transport chain. In the experiments presented in this study we examined the effects of doxorubicin (Adriamycin), daunorubicin, and related quinonoid anticancer agents on superoxide, hydrogen peroxide, and hydroxyl radical production by preparations of beef heart submitochondrial particles. Superoxide anion formation was stimulated from (mean f S.E.) 1.6 f 0.2 to 69.6 f 2.7 or 32.1 2 1.5 nmol.min"*mg-' by the addition of 90 PM doxorubicin or daunorubicin, respectively. However, the anthracycline 5-iminodaunorubicin, in which an imine group has been substituted in the C ring quinone moiety, did not increase superoxide production over control levels. In the presence of rotenone, initial rates of oxygen consumption and superoxide formation were identical under comparable experimental conditions. Furthermore, H202 production increased from undetectable control levels to 2.2 f 0.3 nmol*min-l*mg" after treatment of submitochondrial particles with doxorubicin (200 PM). The hydroxyl radical, or a related chemical oxidant, was also detected after the addition of an anthracycline to this system by both ESR spectroscopy using the spin trap 5,5-dimethylpyrroline-N-oxide and by gas chromatographic quantitation of CHa produced from dimethyl sulfoxide. Hydroxyl radical production, which was iron-dependent in this system, occurred in a nonlinear fashion with an initial lag phase due to a requirement for H202 accumulation. We also found that two quinonoid anti-cancer agents which produce less cardiotoxicity than the anthracyclines, mitomycin C, and mitoxantrone, stimulated significantly less or no hydroxyl radical production by submitochondrial particles. These experiments suggest that injury to cardiac mitochondria which is produced by anthracycline antibiotics may result from the generation of the hydroxyl radical during anthracycline metabolism by NADH dehydrogenase.