Abstract P5-05-06: Umbelliferon derivatives for androgen receptor positive triple negative breast cancer
Authors: Saswati Bhattacharya, Pam Westmark, Noah Siegel, Yuanqi Cai, Sahar Kandil, Andrew D Westwell, Christopher McGuigan, Ruth O'Regan
Journal: Cancer Research (2020)

Abstract Purpose: Triple negative breast cancer (TNBC), which lacks hormone receptors and HER-2 over expression, has a poor prognosis due to the absence of targeted therapeutics. Gene expression profiling identified different subtypes of TNBC, several of which express androgen receptor (AR). AR inhibitors could provide a much-needed, less toxic, therapeutic intervention for patients with AR+ TNBC. However, clinical trials have shown modest activity of these agents in patients with metastatic AR+ TNBC to date. Conversion from AR antagonist to agonist is a well-recognized mechanism of resistance for AR inhibitors in the treatment of prostate cancer. To that end, we synthesized novel 7-substituted umbelliferon derivatives (UMBDs) with a distinct scaffold modified from available AR antagonists, designed to avoid such conversion. We have previously demonstrated that one of these agents, UMBD# 3 (compound 7a), demonstrates sub-micro molar inhibitory activity in a human prostate cancer with greater than 30 to 50 fold potency over the anti-androgens bicalutamide (Bica) and enzalutamide (Enza). In our current study, we tested the efficacy of UMBD# 3 in an AR+ TNBC cells that are sensitive or have acquired resistance to Bica. Methods: Bica-resistant cell lines were generated via multiple passaging of wild type (WT) MDA-MB-231 cells in media containing varying concentrations of Bica. Cell viability assays were conducted over a 72-hour period post seeding of AR+TNBC cell lines with AR antagonists Bica, Enza or UMBD#3. IC50 for respective drugs was determined via linear regression on normalized control values. Real time PCR and western blots were used to determine changes of AR at mRNA and protein level respectively, in response to the different agents. In order to isolate potential mechanistic pathway, we evaluated two proteins that are highly expressed in breast cancer, namely Poly (ADP-ribose) polymerase-1 (PARP-1) and Cadherin-11 (CAD-11) and assessed their expression in AR+ TNBC cells treated with UMBD#3. Results: The IC 50 for UMBD#3 was 6 and 4-fold lower than for Bica or Enza, respectively, in the WT AR+ TNBC cells (Bica, Enza and UMBD#3 IC50 were 136 ± 12.19, 91±12 and 20±7 µM respectively). The IC-50 for Bica in the Bica-resistant AR+ TNBC cells was 729 ± 42 µM, 6-fold higher than the WT cells. The IC50 for UMBD#3 in the Bica-resistant cells was 23.4±10 µM, similar to the WT cells. UMBD#3 caused a decrease in AR expression in the Wt and Bica-resistant calls. Expression of CAD-11 and PARP-1 were decreased in AR+ TNBC cells treated with UMBD#3 both at mRNA level and protein level. Conclusion: We show for the first time in vitro the anti-proliferative effect of a novel AR antagonist, UMBD#3, in WT and resistant AR+ TNBC. UMBD#3 appears to act via downregulation of AR with resultant decreased expression PARP and CAD-11. Given the apparent inherent resistance of AR+ TNBC to standard anti-androgens, further evaluation of this agent is warranted. Citation Format: Saswati Bhattacharya, Pam Westmark, Noah Siegel, Yuanqi Cai, Sahar Kandil, Andrew D Westwell, Christopher McGuigan, Ruth O'Regan. Umbelliferon derivatives for androgen receptor positive triple negative breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P5-05-06.