The importance of topoisomerase II beta in the anthracycline-induced heart failure and its prevention by dexrazoxane
Final Report Abstract
The clinical application of anthracyclines frequently results in heart failure. Although this is usually attributed to the oxidative stress resulting from redox cycling of anthracyclines, recent findings suggest that anthracycline-induced cardiotoxicity is mediated through TOP2β. In agreement, the only clinical remedy to DOX-induced cardiotoxicity dexrazoxane (DRZ) is capable of depleting TOP2β from cultured cells. However, DRZ is feared to interfere with anthracycline therapies and has been weakly implicated in secondary leukemia. This project focused on the cellular effect of DRZ, in particular on its interaction with TOP2β. Unexpectedly, permanent, genetic depletion of Top2β from cardiomyocytes resulted in a dilative heart failure accompanied by fibrosis. This was accompanied by expression changes of genes implicated in heart failure, but also of transcriptional factors, consistent with the emerging role of Top2β in transcriptional regulation. The transient depletion evoked by DRZ was protective against anthracycline-induced DNA damage both in tumor cells and in cardiomyocytes. This protection was mediated through TOP2α or TOP2β rather than iron chelation. DRZ causes TOP2β protein degradation acting most likely via bisdioxopiperazine binding site in the N-terminus of the enzyme. The protective effect of DRZ against anthracycline-induced DNA damage was attenuated in cells expressing TOP2β with mutations of the bisdioxopiperazine binding site. In tumor cells, DRZ caused direct DSB formation followed by DNA damage response, as revealed by the phosphorylation of ATM, ATR, Chk1, Chk2 and γH2AX. Additionally, with the participation of ATM/ATR and JNK, DRZ increased the expression of ATF3. ATF3 knockdown led to cellular apoptosis and delayed DSB recovery following DRZ exposure, indicating role in the prevention of apoptosis and in the processing of DSB. In summary, our findings suggest that TOP2β is indispensable for normal heart function, but that its depletion by DRZ may protect against anthracycline-induced DNA damage. In tumor cells triggers DNA damage followed by the activation of the DNA damage response pathway and ATF3 upregulation.
