Abstract 1405: Colorectal carcinogenesis in Smad4/SPTBN1 mutants alter the intestinal microbiome and resistance to 5FU

Background/Aims: Emerging data shows a rise in colorectal cancer (CRC) incidence in young men and women that is often chemoresistant, with potential new risk factors including alterations in the microbiome that remain understudied. We have recently observed altered microbiome with modulation of the gut immune response through crosstalk between sensors, microbes, and the TGF-β signaling pathway. Interestingly, we observed that human CRC cell lines with disruption of TGF-β had increased sensitivity to cisplatin and other DNA cross-linking agents. Yet at the same time, human CRC with loss of Smad4 portends poor prognosis and resistance to chemotherapy. Therefore, it was unclear whether the epithelial loss of Smad4 or stromal loss of Smad4 expression could be responsible for chemoresistance. Here, we investigated the role of chemotherapy with disruption of TGF-β signaling and an altered intestinal microbiome in colorectal carcinogenesis. Methods: CRCs induced by azoxymethane (AOM)/dextran sodium sulfate (DSS) in wild type (WT) and TGF-β signaling deficient mice (SKO: Smad4+/- and Smad4+/-/Sptbn1+/-) were treated with 5-Fluoro-Uracil (5FU). Shotgun metagenomic sequencing was performed in fecal samples from WT and SKO mice before and after treatment. Results: Our analyses revealed that SKO mice are more susceptible to AOM/DSS induced CRC as demonstrated by increased multiplicity (SKO vs WT: 10.25±1.5 vs 5.5±1.4, p=0.01) and tumor size (SKO vs WT: 3.63±0.7mm vs 2.17±0.3mm, p=0.02). CRC that develops in mice with disrupted TGF-β signaling is chemoresistance to 5FU and progress to liver metastasis confirmed by histological and immunohistochemical analysis. Interestingly, SKO mice display a unique gut microbiome signature compared to the WT mice. SKO mice had significantly reduced abundances of beneficial species of B. vulgutus (0.056±0.0078 vs 0.018±0.0052) and P. distasonis (0.007±0.001 vs 0.003±0.001). In addition to E. Boltae, and Mordavella sp., the relative abundance of Bacteroides was significantly reduced in AOM/DSS induced tumors and recovered to basal levels after 5FU treatment in WT mice but not in SKO mice with deficient TGF-β signaling (e.g. Bacteroides dorei: WT basal vs WT-CRC vs WT-CRC-5FU: 0.28±0.08 vs 0.05 ±0.01 vs 0.45±0.17; SKO basal vs SKO CRC vs SKO-CRC-5FU: 0.13±0.02 vs 0.06 ±0.007 vs 0.07±0.01). Conclusions: Our study identified unique gut microbiome species corresponding to 5FU resistance through interactions with key immune-related pathways such as TGF-β members that are implicated in CRC development and drug resistance. The in vivo studies suggest a cell non-autonomous role of the TGF-β pathway in CRC chemoresistance. Collectively, the altered microbiome composition from impaired TGF-β signaling could promote colorectal carcinogenesis and drug resistance. Manipulating these specific species associated with 5FU could potentially increase drug response. Citation Format: Shuyun Rao, Zhuanhuai Wang, Xiaochun Yang, Lindsay M. Hopson, Stephanie S. Singleton, Wilma Jogunoori, Raja Mazumder, Vincent Obias, Paul Lin, Bao-Ngoc Nguyen, Michael Yao, Larry Miller, Jon White, Lopa Mishra. Colorectal carcinogenesis in Smad4/SPTBN1 mutants alter the intestinal microbiome and resistance to 5FU [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1405.