BRCA1 and BRCA2 Deficient Cells Are Sensitive to Etoposide-induced DNA Double Strand Breaks via Topoisomerase II

Abstract

The function of BRCA1 and BRCA2 in DNA repair could affect the sensitivity of cells to cytotoxic agents, and would therefore be an important component of planning therapy for breast and ovarian cancers. Previously, both BRCA1-and BRCA2-deficient tumors were shown to be sensitive to mitomycin C, and the mechanism was presumed to be a defect in the repair of interstrand crosslinks by homologous recombination. Here, we show that both BRCA1 and BRCA2 determine the sensitivity to the cytotoxic drug, etoposide, using genetic complementation of BRCA-deficient cells. Etoposide is known to bind to topoisomerase II and prevent the resolution of the ''cleavable complex,'' in which one DNA duplex is passed through a second duplex. The specificity of this BRCAdependent sensitivity was confirmed by the use of aclarubicin, which is a catalytic inhibitor of topoisomerase II and prevents the formation of the cleavable complex. In the presence of aclarubicin, the differential sensitivity of BRCA-proficient and BRCA-deficient cells was lost. Thus, etoposide requires the presence of topoisomerase II to show specific sensitization in the absence of the function of BRCA1 or BRCA2. We conclude that homologous recombination is used in the repair of DNA damage caused by topoisomerase II poisons. Overall, these results suggest that etoposide is a potentially useful drug in the treatment of BRCA-deficient human cancers. [Cancer Res 2007;67(15):7078-81]

Premature senescence is a major response to DNA cross-linking agents in BRCA1-defective cells: implication for tailored treatments of BRCA1 mutation carriers

“…Although differential response was observed in a few clones, this was not correlated to BRCA1 expression levels. Contradictory results have been published on the role of BRCA1 in modulating the response to these compounds, both in vitro and in clinical trials (16)(17)(18)(25)(26)(27). Other genetic variables, different from BRCA1, may account for these conflicting results.…”

“…Most of our knowledge on the role of BRCA1 in the drug response of breast cancer cells comes from studies done on murine cell models or on a breast cancer cell line (HCC1937) obtained from a carrier of BRCA1 mutation (14)(15)(16)(17)(18)(19). The analysis of these BRCA1-defective models has suggested an increased sensitivity to specific categories of chemotherapeutic agents.…”

The electrochemistry of quinizarin revealed through its mediated reduction of oxygen

“…The main accepted mode of chemotherapeutic action for the anthracycline antibiotics is through intercalation of the quinonal moiety into dsDNA and subsequent inhibition of the topoisomerase II enzyme (24). To demonstrate the intercalative abilities of QZ, the voltammetric response of an oxygenated solution containing 60 nM QZ was measured, in the presence of increasing concentrations of solution-phase DNA (Fig.…”

The Effects of Topoisomerase Inhibition on Dna Repair and Apoptosis in L929 Fibroblasts

“…Kolorektal adenokarsinoma hücrelerinde etoposit varlığında RAD51 protein ifadesinin arttığı gözlenmiştir [32]. Bununla birlikte, BRCA2 ve RAD51 mutant Chinese hamster hücrelerinin topoizomeraz 2 inhibitörlerine daha duyarlı olduğu belirlenmiştir [33]. Çalışmamızda RAD51 düzeyleri istatistiksel olarak anlamlı bir azalış ya da artış göstermese de etoposit uygulanan gruplarda 3, 6, 9. saatlerde azalırken, 12 ve 24. saatte artması etoposite maruziyetin artmasıyla apoptozun artmasının diğer bir göstergesi olarak düşünülebilir.…”

“…Çalışmamızda RAD51 düzeyleri istatistiksel olarak anlamlı bir azalış ya da artış göstermese de etoposit uygulanan gruplarda 3, 6, 9. saatlerde azalırken, 12 ve 24. saatte artması etoposite maruziyetin artmasıyla apoptozun artmasının diğer bir göstergesi olarak düşünülebilir. Etoposit, topoizomeraz II varlığında görev yapmaktadır ve BRCA1, BRCA2 gibi DNA onarım enzimleri olmayan hücrelerin etoposite duyarlılığının arttığı gösterilmiştir [33]. Çalışmamızda BRCA2 mRNA ifade düzeyleri zaman ve konsantrasyonlar arasında farklılık göstermiştir.…”