Characterizing the effects of estrogen and G15 on triple-negative Inflammatory Breast Cancer

Abstract

Inflammatory breast cancer (IBC) remains the most aggressive and lethal form of breast cancer—reporting rapid progression, poor prognosis, and a unique clinical diagnosis. IBC is frequently classified as a hormone receptor-negative (HR-negative) breast cancer, where cancer cells test negative for estrogen and progesterone receptors and cannot be treated with current hormone therapies. Still, estrogen stimulation enhances cell migration and invasion phenotypes on IBC cells via activation of non-genomic (rapid) signaling cascades—which are known to be mediated by alternate ERs such as the G-protein coupled estrogen receptor (GPER). However, the estrogen-induced transcriptome on IBC cells remains unknown, and the involvement of GPER on estrogen-response signals remains unclear. An extensive understanding of the effects induced by estrogen and G15 (GPER-specific antagonist) on IBC cells provides a new opportunity to address the current need for alternative approaches against IBC patients. Here, RNA sequencing was performed on IBC cells SUM149 to characterize the transcriptome induced by 17β-estradiol (E2) at different time points. In addition, IBC cells SUM149 and SUM190 were treated with G15 alone and combined with E2 to identify the drug’s effects on estrogen-response signals and IBC’s aggressiveness—possibly elucidating GPER’s role. RNA-seq analysis on IBC SUM149 revealed an E2-induced enhancement in the expression of genes associated with transcription factors, signaling cascade mediators, and growth factor ligands—some of which G15 treatment was able to disrupt. Furthermore, G15 reduced the cell viability, growth rate, and colony size of IBC cell SUM149 and inhibited the cell viability and growth rate of IBC SUM190. G15 also inhibited the E2-induced expression of Cyclin-E1 (a cell cycle progression marker), inhibited the anti-apoptotic regulator B-cell lymphoma 2 (BCL-2), and increased the pro-apoptotic marker cleave caspase-3 on IBC SUM149. Regarding non-genomic signals, G15 disrupted the regulatory mechanism of the E2-induced ERK and AKT signaling on IBC cells SUM149, reporting a sustained activation of the ERK and AKT signals. These findings suggest a protective role of GPER on two IBC cell models and provide novel insight into the estrogen sensitivity of TN-IBC SUM149, which can guide future therapeutic efforts against GPER-positive IBC patients.