Targeting estrogen non‐genomic signaling in a three‐dimensional (3D) in vitro model of inflammatory breast cancer

Abstract

Inflammatory Breast Cancer (IBC) is the most aggressive form of breast cancer with a low overall 5‐year survival rate of ~30–60%. To this date the molecular signature associated with IBC is not completely characterized, which lead to a lack of effective targeted therapeutics, especially for those patients that account for the 20–40% of triple‐negative (TNBC) IBC cases. Several studies established that molecular signature of IBC shows important differences from the other breast cancer subtypes, such as overexpression of ErbB receptors, RhoC GTPase and Cox‐2, E‐cadherin aberrant expression, and loss of WISP3 among others. However, these molecular alterations do not explain completely the aggressive and rapid IBC phenotype. Recently, several studies have shown that estrogen can exert non‐genomic effects in triple‐negative IBC and other TNBCs, mediated by the expression of alternate estrogen receptors, including ERα36 and GPR30. Estrogen non‐genomic signaling refers to the rapid action of these alternate estrogen receptors that upon estrogen binding activates protein‐kinase cascades in the cytoplasm. We hypothesize that estrogen can elicit a specific non‐genomic signaling cascade that promotes the acquisition of aggressive oncogenic phenotypes in IBC and that targeting this pathway can be an effective anticancer therapy for IBC. To test this hypothesis, we are going to use pharmacological inhibition of ERα36 and GPR30 using antagonists against these receptors alone or in combination with EGFR inhibition. In parallel, we are going to use siRNA to down‐regulate the expression of these receptors. The first approach is to determine if inhibiting estrogen nongenomic signaling by targeting the alternate receptors affect cell proliferation in a 3D colony formation assay using Matrigel. Preliminary observations showed that cells treated with E2 develop larger colonies (increase proliferation) when compared to vehicle control. Inhibiting GPR30 alone have a slight reduction in cell proliferation compared to E2, but when combined with an EGFR inhibitor (Gefitinib) showed a synergistic effect by decreasing proliferation further that by Gefitinib alone. Ongoing experiments include the effects of Icaritin (modulator of ERα36) and the siRNA experiments to test the effects in cell proliferation, migration and invasion. This study will provide the foundation for further characterization of the role estrogen non‐genomic signaling in the progression of IBC and to test its potential as a therapeutic target.Support or Funding InformationSupport by RISE Program Grant number: 5R25GM061151‐18