Topoisomerase IIβ–Mediated DNA Double-Strand Breaks: Implications in Doxorubicin Cardiotoxicity and Prevention by Dexrazoxane

Abstract

Doxorubicin is among the most effective and widely used anticancer drugs in the clinic. However, cardiotoxicity is one of the life-threatening side effects of doxorubicin-based therapy. Dexrazoxane (Zinecard, also known as ICRF-187) has been used in the clinic as a cardioprotectant against doxorubicin cardiotoxicity. The molecular basis for doxorubicin cardiotoxicity and the cardioprotective effect of dexrazoxane, however, is not fully understood. In the present study, we showed that dexrazoxane specifically abolished the DNA damage signal ;-H2AX induced by doxorubicin, but not camptothecin or hydrogen peroxide, in H9C2 cardiomyocytes. Doxorubicin-induced DNA damage was also specifically abolished by the proteasome inhibitors bortezomib and MG132 and much reduced in top2B À/À mouse embryonic fibroblasts (MEF) compared with TOP2B +/+ MEFs, suggesting the involvement of proteasome and DNA topoisomerase IIB (Top2B). Furthermore, in addition to antagonizing Top2 cleavage complex formation, dexrazoxane also induced rapid degradation of Top2B, which paralleled the reduction of doxorubicin-induced DNA damage. Together, our results suggest that dexrazoxane antagonizes doxorubicin-induced DNA damage through its interference with Top2B, which could implicate Top2B in doxorubicin cardiotoxicity. The specific involvement of proteasome and Top2B in doxorubicininduced DNA damage is consistent with a model in which proteasomal processing of doxorubicin-induced Top2B-DNA covalent complexes exposes the Top2B-concealed DNA doublestrand breaks.

DNA damage response by single-strand breaks in terminally differentiated muscle cells and the control of muscle integrity

“…37 However, the lack of modulation of DOXO toxicity by NAC supports a model in which the proteosomal processing of DOXO-induced TOP2b-DNA cc exposes DSB that, if not repaired, are the major contributors to cell death. Similar data have been obtained in cardiomyocytes 26 in which DOXO-induced DNA damage was shown to involve the TOP2b isozyme that is the only TOP2 isoform expressed in adult heart as well as in our myotubes (data not shown).…”

“…Several studies suggest that the toxicity exerted by TOP2 inhibitors is due to proteasomal processing of TOP2-DNA adducts that exposes TOP2-concealed DSB. 25,26 In agreement with this model, the proteasome inhibitor MG132 attenuated (Po0.05) DOXOinduced lethality in myotubes (Figure 6d). Conversely, the radical oxygen species (ROS)-scavenger N-acetylcysteine (NAC) did not affect the cytotoxicity induced by DOXO (Figure 6d), indicating that in muscle cells, the redox cycling ability of DOXO does not have a major role in toxicity.…”

Cardiotoxicity From Human Epidermal Growth Factor Receptor‐2 (HER2) Targeted Therapies

“…Given the important protective role of ErbB2 in stress conditions, a “2‐hit” model has been postulated as being responsible for the synergism between anthracycline and trastuzumab in causing cardiac dysfunction. In this model, anthracyclines activate cardiac stress pathways through several mechanisms that include generation of reactive oxygen species and oxidative damage of cardiomyocytes,66 and inhibition of topoisomerase 2β leading to double‐stranded breaks in DNA 67. Concomitant ErbB2 inhibition disrupts cardioprotective and prosurvival signaling, diminishing the heart's ability to tolerate noxious stimuli and recover 68, 69, 70, 71.…”

Doxorubicin-induced chronic dilated cardiomyopathy—the apoptosis hypothesis revisited

“…Inhibition of TOP2 induces genotoxic stress and the activation of p53 [25,29]. Transcriptional activity of p53 biases the levels of pro-and anti-apoptotic proteins of the BCL2 family towards the prior by expressing the BCL2 family proteins PUMA and NOXA ( Figure 1A), leading to the process of Mitochondrial Outer Membrane Permeabilisation (MOMP; Figure 1B).…”