Inhibitory Effects of Coumestrol in Triple‐Negative Inflammatory Breast Cancer

Abstract

Breast cancer is the second leading cause of death in females in the United States, being Inflammatory Breast Cancer (IBC) the most aggressive subtype. Usually, this cancer is diagnosed in an advanced stage with metastasis. Experts in IBC pathogenesis think that IBC rapid metastasis is induces by tumor emboli formation, a hallmark of IBC. The poor prognosis for patients with IBC emphasizes the need to better understand the molecular signature of this disease to develop effective targeted therapeutics. To this date, there is no effective targeted therapeutics, especially for those patients that account for approximately 20-40% of IBC cases with triple-negative breast cancer (TNBC) classification. Importantly, several studies have shown that estrogen can exert non-genomic effects in IBC and non-IBC TNBC, mediated by the expression of an alternate isoform of estrogen receptor alpha-66, estrogen receptor alpha-36, and GPR30. In this context, estrogen can activate non-genomic signaling pathways involved in the acquisition of oncogenic phenotypes such as increased motility and invasion in IBC cells. Phytoestrogens, like coumestrol (Cou), are natural compounds found in plants, specifically soybeans or clover sprouts. Also, it is a polyphenolic compound that is structurally similar to estradiol (E2) and several studies have shown that coumestrol induces a cytotoxic effect in TNBC. We hypothesize (1) that estrogen non-genomic signaling has an active role in the aggressive metastatic phenotype of IBC, and (2) that Cou has anticancer activity by inhibiting estrogen non-genomic signaling in IBC. To test this hypothesis, IBC cells were treated with E2 or Cou, and activation of downstream kinases was analyzed by Western blot and using a Human Phospho-Kinase Array. A dose-response curve in 2D and 3D models were generated to determine the half-maximal inhibitory concentration (IC50) of Cou. Finally, treatment using the IC50 of Cou caused a decrease in cell viability in the TNBC cell line. Also, in comparison to E2, Cou decrease migration, proliferation, and tumor emboli formation in IBC cell line. In summary, IBC cells are responsive to E2 treatment making this signaling pathway attractive for the development of innovative therapeutic strategies. Importantly, these Cou preliminary studies show a potential anticancer activity in IBC cell lines.