Glyceollin I Reverses Epithelial to Mesenchymal Transition in Letrozole Resistant Breast Cancer through ZEB1

• Main Authors: Patrick P. Carriere, Shawn D. Llopis, Anna C. Naiki, Gina Nguyen, Tina Phan, Mary M. Nguyen, Lynez C. Preyan, Letitia Yearby, Jamal Pratt, Hope Burks, Ian R. Davenport, Thu A. Nguyen, KiTani Parker-Lemieux, Florastina Payton-Stewart, Christopher C. Williams, Stephen M. Boué, Matthew E. Burow, Bridgette Collins-Burow, Aaron Hilliard, A. Michael Davidson, Syreeta L. Tilghman
• Format: Article
• Language: English
• Published: MDPI AG 2015-12-01
• Series: International Journal of Environmental Research and Public Health
• Subjects: letrozole resistance; epithelial mesenchymal transition; breast cancer; phytochemicals; aromatase inhibitors; metastasis
• Online Access: http://www.mdpi.com/1660-4601/13/1/10

Although aromatase inhibitors are standard endocrine therapy for postmenopausal women with early-stage metastatic estrogen-dependent breast cancer, they are limited by the development of drug resistance. A better understanding of this process is critical towards designing novel strategies for disease management. Previously, we demonstrated a global proteomic signature of letrozole-resistance associated with hormone-independence, enhanced cell motility and implications of epithelial mesenchymal transition (EMT). Letrozole-resistant breast cancer cells (LTLT-Ca) were treated with a novel phytoalexin, glyceollin I, and exhibited morphological characteristics synonymous with an epithelial phenotype and decreased proliferation. Letrozole-resistance increased Zinc Finger E-Box Binding Homeobox 1 (ZEB1) expression (4.51-fold), while glyceollin I treatment caused a −3.39-fold reduction. Immunofluorescence analyses resulted of glyceollin I-induced increase and decrease in E-cadherin and ZEB1, respectively. In vivo studies performed in ovariectomized, female nude mice indicated that glyceollin treated tumors stained weakly for ZEB1 and N-cadherin and strongly for E-cadherin. Compared to letrozole-sensitive cells, LTLT-Ca cells displayed enhanced motility, however in the presence of glyceollin I, exhibited a 68% and 83% decrease in invasion and migration, respectively. These effects of glyceollin I were mediated in part by inhibition of ZEB1, thus indicating therapeutic potential of glyceollin I in targeting EMT in letrozole resistant breast cancer.