S6-5: Obesity Drives Epithelial-to-Mesenchymal Transition and Tumor Progression in a Novel Claudin-Low Mammary Cancer Model.

Abstract

Abstract Background: Epidemiological evidence suggests a potential role of obesity in regulating clinical subtype, differentiation status, and prognosis of breast cancer. Specifically, an elevated waist-hip ratio is associated with increased risk and progression of basal-like breast cancer, an aggressive form characterized by heterogeneous tumors typically enriched in a putative tumor initiating cell (TIC) population. However, the exact mechanism of obesity-driven tumor progression remains unknown. Therefore, we hypothesized that obesity regulates a plastic population of multipotent malignant cells. Materials, Methods, and Results: To test this hypothesis, we generated and characterized two distinct murine mammary tumor cell lines derived from MMTV-Wnt-1 transgenic mice, designated M-Wnt and E-Wnt. M-Wnt cells displayed a mesenchymal morphology while E-Wnt cells had an epithelial morphology. M-Wnt cells harbored a large CD44+/CD24- putative TIC population (62% +/−7.8), had significant mammosphere forming capacity (>30% of cells form mammospheres, p<0.0001), and increased ALDH activity (7% are ALDH+, p=0.0004). M-Wnt cells have increased migration (scratch assay) and invasion in vitro (226-fold higher after 30h, p<0.0001). As few as 50 unsorted M-Wnt cells, injected into C57BL/6 mice were capable of forming a tumor. Microarray analysis revealed that M-Wnt cells display gene expression profiles virtually identical to human Claudin-low breast tumors, while E-Wnt cells clustered with basal-like tumors. EMT and stem cell gene expression patterns of M-Wnt cells were maintained in vivo, including decreased E-cadherin and increased N-cadherin, fibronectin, vimentin, SNAIL, TWIST, SLUG, FOXC2, and TGF-β (p<0.05 for all). Using these cell lines in vivo, we tested the hypothesis that energy balance modulation, through diet-induced obesity (DIO) and calorie restriction (CR), regulates the TIC population. We found that M-Wnt tumors, transplanted into ovariecomized syngeneic female C57BL/6 mice, grew at significantly different growth rates depending on the diet treatment (DIO > Control, p=0.011; CR < Control, p=0.012), while E-Wnt tumors were only affected by CR (CR < Control p=0.001; no difference between DIO and Control tumors). DIO enhanced M-Wnt tumor progression, adipocyte infiltration, and central necrosis and drove EMT (decreased E-Cadherin and increased fibronectin and N-Cadherin expression) through modulation of key TIC associated genes, including increased TGF-β, SNAIL, FOXC2, and Oct4 (p<0.05 for all). Discussion: In conclusion, we found that the mesenchymal M-Wnt cell line is highly responsive to changes in dietary energy balance status relative to the E-Wnt differentiated epithelial cell line, which demonstrates that clinical subtypes of breast cancer are differentially regulated by energy balance modulation. Additionally, our data demonstrates, for the first time, that energy balance modulation (ie, CR and obesity) directly regulates EMT, in response to local upregulation of TGF-β signaling. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr S6-5.