Epithelial-Mesenchymal Transcription Factor Snail Contributes to Development of Embryonic Phenotype and Progression of Ovarian Epithelial Cancer Metastases

Objectives: Metastasis of epithelial ovarian carcinomas (EOC) involves epithelial-mesenchymal transition (EMT) mediated by transcription factors, such as Snail. Snail binds to the promoter region of tumor suppressor let-7 miRNAs. Low let-7 levels correlate with decreased survival in EOC. We aimed to describe the regulation of stemness as impacted by the Snail-let-7 axis in EOC with the use of cell lines; characterize the impact of Snail knock down (KD) on metastasis progression utilizing orthotopic patient-derived mouse xenograft (PDX) model. Methods: Cell lines: In OVSAHO (EOC cell line), Snail was overexpressed by estrogen receptor fusion, or cells were treated with epidermal growth factor (EGF) to induce EMT. Gene expression of Snail, Slug, E-cadherin (mesenchymal/epithelial factors), Nanog, Oct4, Lin28 (embryonic factors), and let-7 family miRNAs was analyzed by quantitative PCR (qPCR). Let-7i promoter luciferase with and without Snail were co-transfected into OVSAHO and 293T (human embryonic kidney) cell lines and followed by measurements of activity. Orthotopic xenografts: Six week old nude (J:NU) mice, 5-8 per experiment, underwent ovarian bursa injections of luciferized patient-derived EOC cells with control vs. Snail KD (500,000 cells). Bioluminescence was quantified (IVIS Lumina) over 21 days. Results: EOC cell lines: 1. OVSAHO: Overexpression of Snail-ER resulted in increased Nanog expression (transcription factor in embryonic stem cells). Increased Snail expression correlated with decreased let-7 expression. 2. Co-transfection of Snail significantly repressed let-7i promoter luciferase activity in OVSAHO and 293T cell lines (pb0.03; 2-tailed t-test). Orthotopic xenografts: EOC cell line xenograft and PDX reproducibly phenocopy EOC. Preliminary data demonstrate decreased tumor burden via bioluminescence quantification in Snail KD vs. control in PDX. Additional data is being analyzed. Conclusion: We are working on demonstrating that replacing let-7 microRNA or knocking down EMT transcription factor Snail disrupts cancer stem cell (CSC) state and impedes disease progression. Our cell line data supports the relationship between Snail overexpression and induction of CSC. Preliminary PDX data demonstrates decrease in metastatic disease with Snail KD. Delivery of SiRNA by mesoporous silica nanoparticles (MSN) to breast cancer metastases has been (Figure Presented) utilized by our collaborators to shut down EMT. Our PDX model can serve to test this mechanism in EOC.