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 ox ygen species (ROS), may contribute to cardiotoxicity by inactivating iron r egulatory proteins (IRP) that modulate the fate of mRNAs for transferrin re ceptor and ferritin. It is important to know whether DOXol and ROS act by i ndependent or combined mechanisms. Therefore, we monitored IRP activities i n H9c2 rat embryo cardiomyocytes exposed to DOX or to analogues which were selected to achieve a higher formation of secondary alcohol metabolite (dau norubicin), a concomitant increase of alcohol metabolite and decrease of RO S (5-iminodaunorubicin), or a defective conversion to alcohol metabolite (m itoxantrone). On the basis of such multiple comparisons, we characterized t hat DOXol was able to remove iron from the catalytic Fe-S cluster of cytopl asmic aconitase, making this enzyme switch to the cluster-free IRP-1. ROS w ere not involved in this step, but they converted the IRP-1 produced by DOX ol into a null protein which did not bind to mRNA, nor was it able to switc h 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 an alogues revealed that IRP-2 was inactivated only by ROS. Thus, DOX can inac tivate 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 sever e cardiotoxicity.