Abstract 3077: Potent inhibition of bromodomain-containing BET family with ABBV-075 induces robust antitumor efficacy in preclinical models of breast cancer and exhibits in vitro synergy with doxorubicin

Abstract

Abstract Breast cancer diagnosisis highly prevalent in the US, with an estimated 231,840 new cases occurring in 2015. Targeted therapies, such as tamoxifen or Trastuzumab (herceptin) are available to woman whose tumors are estrogen receptor (ER) positive or HER2 positive, respectively. However, women with triple negative breast cancer or relapsed metastatic disease have limited treatment options. ABBV-075 is a novel BET family bromodomain inhibitor currently under phase I clinical investigation for a wide spectrum of cancer indications. Here we show that ABBV-075 exhibits broad anti-proliferative activity across cell lines representing ER positive, HER2+, and triple negative breast cancer. Notably, ABBV-075 induced G1 arrest and growth inhibition of breast cancer cell lines regardless of ER or RB status. This result suggests that ABBV-075 may provide therapeutic benefit to a broader patient population relative to the recently approved cdk4/6 inhibitor, palbociclib. The G1 arrest mechanism of ABBV-075 was efficacious in breast cancer xenograft studies, where significant tumor growth inhibition was observed. Additionally, ABBV-075 exhibited synergy in ER positive cell lines with doxorubicin, a TOPO2 inhibitor and DNA intercalating agent prescribed to ER positive patients refractory to hormone therapies. Intriguingly, the mechanism by which ABBV-075 and doxorubicin interact was independent of the TOP2-trapping activity of doxorubicin and instead required DNA intercalation. Together, these results demonstrate the potential of ABBV-075 as a treatment option across the different subtypes of breast cancer and in combination with doxorubicin in patients with ER positive disease Citation Format: Emily J. Faivre, Xiaoyu Lin, Denise M. Wilcox, Xiaoli Huang, Aparna Sarthy, Terry Magoc, Daniel H. Albert, Guowei Fang, Saul H. Rosenberg, Keith F. McDaniel, Warren M. Kati, Yu Shen. Potent inhibition of bromodomain-containing BET family with ABBV-075 induces robust antitumor efficacy in preclinical models of breast cancer and exhibits in vitro synergy with doxorubicin. [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 3077.