Iron is not involved in oxidative stress-mediated cytotoxicity of doxorubicin and bleomycin

Background and purpose: The anticancer drugs doxorubicin and bleomycin are well-known for their oxidative stress-mediated side effects in heart and lung, respectively. It is frequently suggested that iron is involved in doxorubicin and bleomycin toxicity. We set out to elucidate whether iron chelation prevents the oxidative stress-mediated toxicity of doxorubicin and bleomycin and whether it affects their antiproliferative/proapoptotic effects. Experimental approach: Cell culture experiments were performed in A549 cells. Formation of hydroxyl radicals was measured in vitro by electron paramagnetic resonance (EPR). We investigated interactions between five iron chelators and the oxidative stress-inducing agents (doxorubicin, bleomycin and H2O2) by quantifying oxidative stress and cellular damage as TBARS formation, glutathione (GSH) consumption and lactic dehydrogenase (LDH) leakage. The antitumour/proapoptotic effects of doxorubicin and bleomycin were assessed by cell proliferation and caspase-3 activity assay. Key results: All the tested chelators, except for monohydroxyethylrutoside (monoHER), prevented hydroxyl radical formation induced by H2O2/Fe2+ in EPR studies. However, only salicylaldehyde isonicotinoyl hydrazone and deferoxamine protected intact A549 cells against H2O2/Fe2+. Conversely, the chelators that decreased doxorubicin and bleomycin-induced oxidative stress and cellular damage (dexrazoxane, monoHER) were not able to protect against H2O2/Fe2+. Conclusions and implications: We have shown that the ability to chelate iron as such is not the sole determinant of a compound protecting against doxorubicin or bleomycin-induced cytotoxicity. Our data challenge the putative role of iron and hydroxyl radicals in the oxidative stress-mediated cytotoxicity of doxorubicin and bleomycin and have implications for the development of new compounds to protects against this toxicity.