Ku70 and Rad51 vary in their importance for the repair of doxorubicin- versus etoposide-induced DNA damage

Abstract

For DNA targeting anticancer drugs, cellular DNA repair mechanisms may cause resistance and hamper the therapeutic outcome. DNA damage induced by topoisomerase IIα inhibitors like etoposide and anthracyclines, which are a mainstay of cancer therapy, is also repaired in many cell types, but the impact and precise mechanisms of this repair are still obscure. To investigate the DNA damage response of human adenocarcinoma HT29-cells to doxorubicin and to compare the involvement of Ku70 and Rad51 in the repair of doxorubicin- versus etoposide-induced DNA damage, we assessed cell cycle distribution and cell death, DNA damage, proteins relevant for repair by homologous recombination and non-homologous end-joining, and clonogenicity following exposure to doxorubicin at clinically achievable concentrations. Also, we assessed changes in the repair kinetics after siRNA-mediated attenuation of Ku70 or Rad51 expression. We found that exposure to doxorubicin for 24 h induced a substantial amount of DNA damage that was largely repaired when doxorubicin was removed and the cells were maintained in drug-free medium. Nevertheless, a pronounced G(2)/M arrest occurred at times when repair was maximal. This was followed by a distinct increase in cell death and loss of clonogenicity. In this regard, responses to doxorubicin and etoposide were similar. However, distinct differences in the repair process following doxorubicin versus etoposide were seen in concentration dependency, time-course and requirement of Ku70 and Rad51 proteins. In spite of the shared molecular target of doxorubicin and etoposide, DNA lesions induced by these compounds are repaired differently.

Cardiotoxicity of anticancer treatments

“…5 Myocyte injury can also be reversible to a certain extent; beyond that point, however, cell death ensues, resulting in permanent loss of contractile reserve. 6 Myocyte injury and cell death can be detected by the imaging of necrotic cells using electron microscopy, and by measuring plasma t roponin levels. 7,8 Myofibril dysfunction and cell injury leading to necrosis can be thought of as separate entities.…”

A Small Molecule Inhibitor of Human RAD51 Potentiates Breast Cancer Cell Killing by Therapeutic Agents in Mouse Xenografts

“…Similarly, it was shown that HR, but not NHEJ, dominates the repair of topotecan-induced DSBs in human immortalized fibroblasts, because inhibition of DNA-PK, one of the key NHEJ enzymes, does not sensitize cells to topotecan [40]. In contrast, DSBs induced by doxorubicin and etoposide are mainly repaired through NHEJ, although HR is also activated in response to etoposide [41].…”

The prognostic value of BRCA1 promoter methylation in early stage triple negative breast cancer

“…Though anthracycline agents induce double-strand breaks, repair of these lesions appears to require non-homologous end joining, an error-prone double strand break repair pathway that does not require BRCA1 , and preclinical data suggests that anthracyclines do not exhibit selective toxicity in BRCA1 -deficient cells [40-42]. Conversely, repair of platinum-induced interstrand crosslinks invokes BRCA1 -mediated homologous recombination, and there is abundant clinical and in vitro evidence that BRCA1 -deficient cells are hypersensitive to platinum agents [41-44].…”