Abstract

Anthracyclines are potent antitumor agents that cause cardiotoxicity at high cumulative doses. Because anthracycline cardiotoxicity is attributed to their ability to avidly bind iron (Fe), we examined the effect of anthracyclines on intracellular Fe trafficking in neoplastic cells and differentiated cardiomyocytes. In both cell types, incubation with doxorubicin (DOX) resulted in a significant (p< 0.004) accumulation of Fe in the storage protein, ferritin. Pulse-chase experiments using control cells demonstrated that within 6 h, the majority of ⁵⁹Fe donated from transferrin was incorporated into ferritin. Over longer incubation periods up to 18 to 24 h, ⁵⁹Fe was subsequently mobilized from ferritin into other compartments in control cells. However, anthracyclines inhibited ferritin-⁵⁹Fe redistribution during the 18- to 24-h period, resulting in a significant (p < 0.0003) 3- to 5-fold accumulation of ferritin-⁵⁹Fe compared with control cells. The increase in ferritin-⁵⁹Fe after a 24-h incubation with DOX could not be correlated with increased ferritin expression, suggesting that ⁵⁹Fe accumulation occurred in pre-existing ferritin. In addition to DOX, other redox-cycling agents (i.e., menadione and paraquat) also increased ferritin-⁵⁹Fe levels. Moreover, the intracellular superoxide scavenger, Mn(III) tetrakis(4-benzoic acid)-porphyrin complex, partially prevented the ability of DOX and menadione at inducing this effect. Hence, superoxide generation by these compounds could play a role in causing ferritin-⁵⁹Fe accumulation. This study is the first to demonstrate the effect of anthracyclines at inhibiting Fe mobilization from ferritin, resulting in marked Fe accumulation within the molecule. This response may have consequences in terms of the cytotoxic effects of anthracyclines.