CONTRIBUTION OF THE GUT MICROBIOME TO OBESITY-DRIVEN TRIPLE-NEGATIVE BREAST CANCER

Breast cancer (BC) is the leading cause of death in women in the United States, where the triple-negative BC (TNBC) subtype is particularly fatal, partially due to its resistance to standard treatments. The global prevalence of obesity has tripled since 1975. As obesity is an established risk factor for BC, including the TNBC subtype, preclinical mouse models are crucial for elucidating mechanisms underlying the obesity-cancer link. Mounting evidence suggests gut microbial communities are implicated in obesity and cancer, with gut dysbiosis commonly observed in these conditions. Given its malleability, the gut microbiota is an appealing therapeutic target for obesity and cancer. Short-chain fatty acids (SCFAs), particularly butyrate, reduce obesity-associated adiposity and confer anti-cancer effects, making them promising for improving BC therapy. In Chapter 2, we sought to establish and characterize a new transplantable mouse model of TNBC on a C57BL/6 background. We successfully developed four readily tumorigenic claudin-low TNBC cell lines—B6TAg1.02, B6TAg2.03, B6TAg2.10, and B6TAg2.51— from tumors generated from C3-TAg transgenic C57BL/6 mice (B6TAg) and confirmed that the tumors that formed from the three most transcriptionally distinct B6TAg cell lines were enhanced by obesity. In Chapter 3, we characterized the gut microbiota from the same control and DIO mice from Chapter 2 and found that the gut microbiotas were compositionally distinct. Because SCFA-producing microbes support intestinal health, we tested whether SCFA supplementation influenced tumor progression in the B6TAg1.02 cell line. While butyrate supplementation increased cytotoxicity in vitro, our in vivo study revealed no statistically significant reductions in tumor volume and mass in our TNBC model. Finally, we tested whether butyrate supplementation could reduce body weight or tumor outcomes in DIO mice injected with the B6TAg1.02 cell line; however, we observed no statistically significant reduction in tumor volume and mass. The results from this dissertation provide researchers with new TNBC cell lines to investigate the complex interactions between obesity and TNBC in human-relevant cell lines of BC. Unsurprisingly, we demonstrate that diet had the biggest effect on the gut microbiota in our mouse model of TNBC. Future work is needed to understand how butyrate impacts tumor outcomes in TNBC.