Androgen Receptor Inhibitor Enhances The Antitumor Effect Of Parp Inhibitor In Breast Cancer Cells Via Modulation Of Dna Damage Response

Introduction: Olaparib, a PARP inhibitor has produced promising antitumor efficacy in patients with BRCA mutation. However, cancers with BRCAness represent only a small proportion of breast cancer cases. To make olaparib useful to the broader cancer population, the development of new combinational strategies are required. The androgen receptor (AR) is expressed in 60∼70% of breast cancers regardless of ER status and has been proposed as a therapeutic target in breast cancers that retain AR. AR signaling was recently demonstrated to be a key regulator of the DNA damage response (DDR) in prostate cancer cells. AR inhibition increased cell death induced by DNA damage from cytotoxic insults. Based on these evidence, we hypothesized that AR inhibition using AZD3514, a novel AR inhibitor, would enhance the anti-tumor effect of PARP inhibitor in breast cancer cells by blocking DNA repair pathway. Materials and Methods: The cytotoxic assay, cell cycle analysis and western blotting were conducted to determine whether AZD3514, an AR inhibitor could enhance the anti-tumor effects of olaparib on breast cancer cells. The regulation of DDR activity by AZD3514 was accessed by the comet and IFA analysis. The molecular mechanism of DDR regulation by AZD3514 was also determined through gene knockdown experiments. These in vitro data were validated in vivo model as well. Results: AR inhibition had a minimal anti-proliferative effect on most of the breast cancer cell lines irrespective of the degree of AR expression levels as a monotherapy. However, AZD3514 downregulated the expressions of DDR molecules, including ATM and chk2 in some breast cancer cell lines. Breast cancer cell lines exhibited a various level of response of the combination treatment irrespective of their subtype as well as their AR expression levels. Co-targeting AR and PARP suppressed the proliferation and induced G2/M cell cycle arrest and apoptosis in MDA-MB-468 cells, but not that of MDA-MB-453 cells. Furthermore, AZD3514 treatment decreased the activity of ATM-chk2 axis resulting in the accumulation of DNA damage via compromising DDR activity in MDA-MB-468 cells. The results indicated that the mechanism underlying that AZD3514 enhances cellular sensitivity to olaparib would be through abrogation of the DNA DSB repair pathway in MDA-MB-468 cells. We also found that down-regulation of NKX3.1 expression correlated with suppressed activation of ATM-chk2 axis in MDA-MB-468 cells. In addition, the suppressed levels of NKX3.1 following AZD3514 treatment were a result of that AZD3514 induced TOPORS expression resulting in acceleration of NKX3.1 degradation. Finally, these in vitro findings were validated in a MDA-MB-468 xenograft model. Conclusions: Our data revealed that post-translational regulation of NKX3.1 by modulation of TOPORS expression following AZD3514 treatment induced ATM inactivation which can increase olaparib sensitivity in AR positive and TOPORS expressed breast cancer cells. This study firstly demonstrated the anti-tumor effect of AZD3514 in a combination with olaparib via compromising DDR activity in breast cancer cell lines as well as in a xenograft model. Our results provide a rationale for the future clinical trials of olaparib combined with AR inhibition in the treatment of breast cancers. Citation Format: Ahrum Min, Seock-Ah Im, Hyemin Jang, Seongyeong Kim, So Hyeon Kim, Yu Jin Kim, Debora Keunyoung Kim, Yaewon Yang, Koung Jin Suh, Kyung-Hun Lee, Tae-Yong Kim, Do-Youn Oh, Yung-Jue Bang. Androgen receptor inhibitor enhances the antitumor effect of PARP inhibitor in breast cancer cells via modulation of DNA damage response. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-107.