Abstract
BackgroundMutations in the DNA damage response (DDR) factors, breast cancer 1 (BRCA1) and BRCA2, sensitize tumor cells to poly(ADP-ribose) polymerase (PARP) inhibitors. The ataxia telangiectasia mutated (ATM) kinase is a key DDR protein whose heterozygous germline mutation is a moderate–risk factor for developing breast cancer. In this study, we examined whether ATM inactivation in breast cancer cell lines confers sensitivity to PARP inhibitors.MethodsWild-type BRCA1/2 breast cancer cells (i.e., MCF-7 and ZR-75-1 lines) were genetically manipulated to downregulate ATM expression then assayed for cytostaticity/cytotoxicity upon treatment with PARP inhibitors, olaparib and iniparib.ResultsWhen ATM-depleted cells and their relative controls were treated with olaparib (a competitive PARP-1/2 inhibitor) and iniparib (a molecule originally described as a covalent PARP-1 inhibitor) a different response to the two compounds was observed. ATM-depletion sensitized both MCF-7 and ZR-75-1 cells to olaparib-treatment, as assessed by short and long survival assays and cell cycle profiles. In contrast, iniparib induced only a mild, ATM-dependent cytostatic effect in MCF-7 cells whereas ZR-75-1 cells were sensitive to this drug, independently of ATM inactivation. These latest results might be explained by recent observations indicating that iniparib acts with mechanisms other than PARP inhibition.ConclusionsThese data indicate that ATM-depletion can sensitize breast cancer cells to PARP inhibition, suggesting a potential in the treatment of breast cancers low in ATM protein expression/activity, such as those arising in mutant ATM heterozygous carriers.
Highlights
Mutations in the DNA damage response (DDR) factors, breast cancer 1 (BRCA1) and BRCA2, sensitize tumor cells to poly(ADP-ribose) polymerase (PARP) inhibitors
Effects of ataxia telangiectasia mutated (ATM)-depletion in breast cancer MCF-7 cell line To assess the influence of ATM in breast cancer susceptibility to PARP inhibitors, we genetically repressed ATM expression by RNA interference in MCF-7 cells
We chose the MCF-7 breast cancer cell line because it is ER positive, HER2 negative, and wild-type for the BRCA1, BRCA2, and TP53 genes [25], features we observed in breast tumors arising in our A-T heterozygotes [23]
Summary
Mutations in the DNA damage response (DDR) factors, breast cancer 1 (BRCA1) and BRCA2, sensitize tumor cells to poly(ADP-ribose) polymerase (PARP) inhibitors. In the past few years, much effort has been made towards identifying chemotherapeutic compounds targeting the core components of DDR and repair pathways, which are frequently altered in tumor cells The goal for these new anti cancer strategies would be to take advantage of the cancer cell defects in repairing their own DNA and use it as an Achille’s heel to enhance therapeutic indices, with limited normal tissue toxicity. BER inactivation by PARP inhibitors induces SSBs that during DNA replication cause lethal breaks in both DNA strands In normal cells, the latter breaks are repaired by HR, but in tumor cells in which HR is defective, such as in the presence of BRCA1/2 mutations, DSBs are not repaired and their accumulation causes cell death [1,2]. Though there might be various causes explaining the clinical performance of the different PARP inhibitors, one of the challenging issues remains on how to identify those patients most receptive to these treatments [13]
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