Targeting Estrogen Non‐Genomic Signaling in a Three‐Dimensional (3D) in VitroModel of Inflammatory Breast Cancer

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 has not been fully 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 progression. Recently, several studies have shown that estrogen can exert non‐genomic effect 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 used pharmacological inhibitors of the Epidermal Growth Factor Receptor (EGFR) alone and GPR30 alone or in combination. The first approach was to determine if inhibiting estrogen non‐genomic signaling by targeting one of the alternate receptors, GPR30, affects cell proliferation in a 3D colony formation assay using Matrigel. Preliminary observations showed that after G15 treatment (GPR30 inhibitor), there was a slight reduction in cell proliferation compared to E2, but when combined with IRESSA (EGFR inhibitor) there was a further decreased on proliferation when compared to IRESSA alone. Ongoing experiments include the effects of Icaritin (modulator of ERα36) and knockdown of ERα36 using siRNA experiments to test the effects in cell proliferation, migration and invasion. Also, we are in the process of determining the half‐maximal inhibitory concentration (IC 50 ) of G15, IRESSA and IRESSA + G15 by performing a dose response curve (Alamar Blue cell viability assay) of SUM149 cell line, to observe if there is an additive effect when combined the pharmacological inhibitors of EGFR and GPR30. 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.