Abstract 2143: Identification of new molecular liabilities of a subset of triple-negative breast cancers through the investigation of englerin A

Identification of new molecular liabilities of a subset of triple-negative breast cancers through the investigation of englerin A There remains a need to identify targeted therapies for triple-negative breast cancers (TNBCs) but a major challenge has been the heterogeneity of these cancers. We initiated a screen to discover compounds that are selectively cytotoxic to cells representing distinct molecular subtypes of TNBC. The overall goal is to identify compounds with selective actions and new molecular liabilities for subtypes of TNBC. Englerin A was identified by cytotoxicity assay as a compound with a greater than 1,500-fold selectivity for BT-549 cells and 300-fold for Hs578T TNBC cells as compared to other TNBC cell lines. Interestingly, the treatment of Hs578T cells with englerin A produced a biphasic concentration response curve, which is unique among the TNBC cell lines but is seen in A-498 renal carcinoma cells where englerin A sensitivity was first noted.1 In renal cell carcinoma cell lines one strongly supported mechanism of action of englerin A is via activation of TRPC1/4/5 non-selective cation channels.2-4 In our assays, the TRPC1/4/5 antagonist Pico1455 decreases the potency of englerin A in BT-549 and Hs578T cells, but not more resistant TNBC cells, suggesting that the TRPC1/4/5 agonist activity of englerin A is likely responsible for the selective effects in the sensitive cell lines. BT-549 and Hs578T cells were found to have significantly higher expression of TRCP1 and TRPC4 subunit mRNA as compared to englerin A resistant cells. Furthermore, knockdown of TRPC4 expression in BT-549 cells decreased englerin A potency. Consistent with its function as an agonist of the TRPC1/4/5 cation channel, we found that englerin A caused a concentration-dependent increase in intracellular Ca2+ in BT-549 cells within 30 seconds of exposure, and this effect was inhibited by pre-treatment with Pico145. These studies led to the hypothesis that TNBC cells expressing high levels of TRPC4 might also be more sensitive to clinically approved classes of drugs that increase intracellular cation concentrations. Results show that BT-549 and Hs578T cells are more sensitive to digoxin than other TNBC cells. Overall, these studies suggest that a subgroup of TNBCs may be susceptible to treatments with selective targets of cation influx. Ongoing work is aimed at evaluating the sensitivity of these cell lines to other drugs that disrupt intracellular cation levels. 1. Ratnayake, R. et al. (2009). 2. Ludlow, M. J. et al. (2016). 3. Akbulut, Y. et al. (2015). 4. Carson, C. et al. (2015). 5. Rubaiy, H. N. et al. (2017). Citation Format: Corena V. Grant, Chase M. Carver, Shayne D. Hastings, April L. Risinger, John A. Beutler, Susan L. Mooberry. Identification of new molecular liabilities of a subset of triple-negative breast cancers through the investigation of englerin A [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2143.