Reversal of the ERα Negative Receptor in Human Breast Cancer Cells by Dichloro‐napthoquinone Analog
Authors: Robinson Anastasia GJ , Copeland Robert L 
Published: November 2023

Breast cancer can present as either estrogen receptor α (ERα) negative or positive. Further, the expression of estrogen receptor (ER), progesterone receptor (PR), and the HER2 receptor tyrosine kinase can subdivide breast cancers into clinically meaningful classes. Breast cancers lacking expression of all three of these receptors (triple negative breast cancers, or TNBC) are of particular interest for molecular research, because these tumors currently have no effective targets for therapy. Furthermore, TNBCs are relatively more prevalent among African American women and can account for some of the health disparities associated with breast cancer. It has been shown in studies that the loss of ERα expression is due to epigenetic regulation through histone deactylase (HDAC) inhibition and chromatin remodeling. ERα− breast cancers also frequently present with elevated growth factor receptor expression and/or signaling with resultant p42/44/ mitogen activated kinase (MAPK) signaling, and it has been discovered that hyperactivation of MAPK directly represses ERα expression in a reversible manner. The abrogation of the MAPK pathway by direct inhibition of hyper‐activated MAPK or possible upstream inhibition of over‐expressed EGFR, c‐erbB‐2, or epigenetic alterations of the ERα gene promoter region, may result in re‐expression of ERα. Our laboratory has reported the in‐house synthesis of a novel dichloro‐naphthoquinone analog (DCNQ). Our previous studies have shown that this compound possesses significant pharmacological effects associated with marked anti‐tumorigenic activities and significant inhibitory effects on MAPK signaling. Established ERα+ and ERα− breast cancer cell lines from Caucasian and African American were used in this study. MTT assay and flow cytometry were used to elucidate cell viability and cell cycle respectively. MAPK activity was examined using MAPK inhibitor kits comparing standard to DCNQ. RT_PCR assays were performed to show ER RNA expression. The in vitro effect of (DCNQ) was evaluated on ERα+ (MCF‐7) and ERα− (HCC1806 and HS‐578T). DCNQ inhibited the growth of the ERα+ and ERα− breast cancer cell lines dose‐dependently following treatment for 1, 3 and 5 days. These in vitro studies of DCNQ on human breast cancer cell lines revealed significant anti‐tumor activities with IC50s for MCF‐7, HCC1806 and HS‐578T of 1, 10 and 4.5 mM respectively. Furthermore, DCNQ induced apoptosis in both ERα+ and ERα− cell lines time‐dependently. DCNQ inhibited progression through the cell cycle in all three cell lines in the S‐phase with the greatest proportion of cells accumulating in the S‐ phase by day 5. Quantitative RT‐PCR arrays elucidated ERα gene re‐expression in HCC1806 and HS‐578T with treatment. Furthermore, these cells were reevaluated using lower concentrations (1μM) of DCNQ in combination with tamoxifen inducing cell death. The down‐regulation of the ERα expression by hyperactive MAPK is a direct mechanism which is potentially reversible through DCNQ. Therefore, this novel compound which targets the MAPK pathway may offer a model for treating ERα− breast cancers by reactivating ERα expression in these cancers and thus rendering them susceptible to anti‐estrogen therapy.Support or Funding InformationCharles and Mary Latham Foundation