Abstract P6-13-06: Novel combination therapies for triple negative breast cancer identified by high-throughput screening
Authors: Wali VB , Langdon CG , Held MA , Platt JT , Safonov A , Aktas B , Stern DF , Pusztai L , Hatzis C 
Published: May 2016

Background: Finding effective novel therapies for triple negative breast cancer (TNBC) remains an unmet challenge. Our objective was to assess the sensitivity of TNBC to single drugs and to combinations using a systematic screen of existing FDA approved drugs combined with other approved or experimental agents and to characterize the mechanism of action of the most promising combinations.

Methods: We conducted a comprehensive high-throughput drug combination screen in six TNBC cell lines with different genetic backgrounds. We tested a panel of 128 agents with known targets for their growth inhibitory potential individually and in pairwise combinations with six FDA approved anticancer drugs in MDA-MB-231, MDA-MB-436, MDA-MB-468, BT-20, BT-549, and HCC-38 TNBC cell lines. High-throughput assays were performed in 384-well plates and dose response curves were generated using 5 concentrations of the secondary drug, while keeping the first drug at fixed dose. Cell viability was measured 72h after treatment exposure using CellTiter-Glo®. Drug combinations were assessed for overall inhibitory effect and also for superadditivity, assessed as deviations from non-interaction using Bliss model of synergy. Selected synergistic and effective drug combinations identified from the high-throughput screen were subsequently validated in a 96-well low-throughput format in all TNBC cell lines.

Results: Cell cycle and apoptosis regulators were more inhibitory as single agents across TNBC cell lines relative to other drug classes. Bortezomib, carfilzomib, YM155, Flavopiridol, KP372-1, and dactinomycin were highly toxic to all TNBC lines as single agents. Combinations with either everolimus or erlotinib were particularly effective in BT-20 and MDA-MB-468, and combinations with crizotinib in MDA-MB-231 cells. Bay-11-7082/erlotinib and MK-1775/everolimus were few of the promising combinations that elicited potentiated response in all the cell lines. ABT-263/crizotinib was one of the top synergistic combination most effective in MDA-MB-231 cells that express highest relative mRNA and protein levels of respective drug targets, Bcl-xL, and AXL. The combination treatment with ABT-263 and crizotinib also resulted in apoptosis in MDA-MB-231 cells, indicated by marked PARP cleavage in these cells, while MDA-MB-436 cells with lowest expression of Bcl-xL were resistant to apoptosis or growth inhibition, indicating a potential efficacy of this combination in a subset of TNBCs.

Conclusions: This study reveals novel combinations of cell cycle or apoptosis regulators and crizotinib, everolimus, or erlotinib with enhanced anticancer activity. Combinations of Bay-11-7082 and erlotinib; and MK-1775 and everolimus had mild synergistic activity in all TNBC lines, while ABT-263 and Crizotinib showed large synergistic antiproliferative activity in a subset of TNBCs. These promising drug combinations have great potential to improve cure rates in TNBC patients. Since crizotinib, everolimus, and erlotinib are US FDA-approved while ABT-263 and MK-1775 are in advanced clinical trials, there is a rapid path for clinical translation for these drug-combinations after validation in animal studies.

Citation Format: Wali VB, Langdon CG, Held MA, Platt JT, Safonov A, Aktas B, Stern DF, Pusztai L, Hatzis C. Novel combination therapies for triple negative breast cancer identified by high-throughput screening. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P6-13-06.