Diminished molecular response to doxorubicin and loss of cardioprotective effect of dexrazoxane in Egr-1 deficient female mice.

Doxorubicin (DOX) and VP16 are DNA topoisomerase II inhibitors yet only DOX induces an irreversible cardiotoxicity, likely through DOX-induced oxidative stress. Egr-1 is overexpressed after many stimuli that increase oxidative stress in vitro and after DOX-injection into adult mice in vivo. To investigate Egr-1 function in the heart, we compared the molecular and histological responses of wild type (+/+) and Egr-1 deficient (-/-) female mice to saline, DOX, VP16, the cardioprotectant dexrazoxane (DZR), or DOX+DZR injection. DOX, and to a lesser extent VP16, induced characteristic increases in cardiac muscle and non-muscle genes typical of cardiac damage in +/+ mice, whereas only beta-MHC and Sp1 were increased in -/- mice. DZR-alone treated +/+ mice showed increased cardiomyocyte transnuclear width without a change to the heart to body weight (HW/BW) ratio. However, DZR-alone treated -/- mice had an increased HW/BW, increased cardiomyocyte transnuclear width, and gene expression changes similar to DOX-injected +/+ mice. DZR pre-injection alleviated DOX-induced gene changes in +/+ mice; in DZR+DOX injected -/- mice the increases in cardiac and non-muscle gene expression were equal to, or exceeded that, detected after DOX-alone or DZR-alone injections. We conclude that Egr-1 is required for DOX-induced molecular changes and for DZR-mediated cardioprotection.