Antitumor Activity of ATR inhibitor AZD6738 in Breast Cancer Cells

Abstract

Background: The DNA repair system is critical for maintaining genomic integrity. Defects in the DNA damage repair (DDR) pathway can lead to chromosomal aberrations resulting in cancer with genetic instabilities. Recent findings suggest that competent DNA repair in the cancer cell induces resistance to therapeutic agents. Defects in the DDR pathway are common in high grade cancer patients. Therefore, the inhibition of DNA repair could lead to reduce the drug resistance and induce the accumulation of errors which is becoming an attractive strategy for cancer treatment. DNA damage response usually starts with the sensing or detection of the DNA damage to maintain genomic integrity. The ataxia telangiectasia and Rad3-related (ATR) can be activated by various types of DNA damage and it initiates DNA damage-induced signalling cascade. ATR is a master regulator of DDR, signaling to control cell cycle transitions, DNA replication, DNA repair, and apoptosis. Therefore, the ATR pathway might be useful target for new drug development and it is important that the effects of many current cancer treatments are modulated by DDR. Materials and Methods: We studied the growth inhibitory effects of AZD6738 on human breast cancer cell lines using MTT assay. Cell cycle analysis and western blotting were also performed to determine molecular changes induced by AZD6738. Immunofluorescence assay and comet assay were conducted to understand the action mechanisms of AZD6738 on breast cancer cells. Results: Anti-proliferative effects and the inhibition of DDR activity by ATR inhibitor, AZD6738 on human breast cancer cell lines were explored in this study. MTT assay resulted in the heterogenous response. AZD6738 induces cell cycle arrest and apoptosis in breast cancer cell lines. AZD6738 impaired DNA damage repair function and promoted cell death by damage accumulation in sensitive cells. In sensitive cell line, SKBR-3, the expression of phosphorylated CHK1 (S345) was downregulated with the other DNA repair molecules

RAD51, MRE11 and ERCC1 as opposed to less sensitive breast cancer cell BT-474. The number of RAD51 foci was significantly decreased at the sites of DNA damage in SKBR-3 after AZD6738 treatment. The decreased functional CHK1, which interacted with RAD51 foci, leads to the accumulation of DNA damage due to HR inactivation. And it was also identified that ATR inhibitor potentiate the efficacy of cytotoxic chemotherapeutic agents, cisplatin and paclitxel in breast cancer cell line. Conclusion: Understanding the antitumor efficacy and the mechanisms of ATR inhibitor in the breast cancer cell lines open up the possibility of future clinical trial targeting DNA damage repair in breast cancer.