Doxorubicin irreversibly inactivates iron regulatory proteins 1 and 2 in cardiomyocytes: evidence for distinct metabolic pathways and implications for iron-mediated cardiotoxicity of antitumor therapy.

Changes in iron homeostasis have been implicated in cardiotoxicity induced by the anticancer anthracycline doxorubicin (DOX). Certain products of DOX metabolism, like the secondary alcohol doxorubicinol (DOXol) or reactive oxygen species (ROS), may contribute to cardiotoxicity by inactivating iron regulatory proteins (IRP) that modulate the fate of mRNAs for transferrin receptor and ferritin. It is important to know whether DOXol and ROS act by independent or combined mechanisms. Therefore, we monitored IRP activities in H9c2 rat embryo cardiomyocytes exposed to DOX or to analogues which were selected to achieve a higher formation of secondary alcohol metabolite (daunorubicin), a concomitant increase of alcohol metabolite and decrease of ROS (5-iminodaunorubicin), or a defective conversion to alcohol metabolite (mitoxantrone). On the basis of such multiple comparisons, we characterized that DOXol was able to remove iron from the catalytic Fe-S cluster of cytoplasmic aconitase, making this enzyme switch to the cluster-free IRP-1. ROS were not involved in this step, but they converted the IRP-1 produced by DOXol into a null protein which did not bind to mRNA, nor was it able to switch back to aconitase. DOX was also shown to inactivate IRP-2, which does not assemble or disassemble a Fe-S cluster. Comparisons between DOX and the analogues revealed that IRP-2 was inactivated only by ROS. Thus, DOX can inactivate both IRP through a sequential action of DOXol and ROS on IRP-1 or an independent action of ROS on IRP-2. This information serves guidelines for designing anthracyclines that spare iron homeostasis and induce less severe cardiotoxicity.