Abstract 5128: Understanding the association of gut microbiota and tumor microenvironment in gastric and esophageal cancer
Authors: Thakkar Prashant V. , Zhang Chao , Sharma Prateek , Vennelaganti Sreekar , Betel Doron , Shah Manish A. 
Published: August 2018

Gastric and Esophageal cancers remain one of the leading causes of cancer related deaths. Dysbiosis of gut microbiome is a strong risk factor for gastrointestinal cancer, likely due to altered mucosal immunity and pro-inflammatory immune microenvironment. However, molecular interactions between host human cells and microbiome are poorly understood in context of gastric and esophageal cancer. Our main goal is to understand how altered mucosal microbiome alters tumor microenvironment, thus creating conditions conducive to tumorigenesis. Using a novel computational pipeline combined with low-pass (10-30x) whole genome sequencing (WGS), we examined microbiome composition of 15 gastric cancer (GC) and adjacent normal tissue (n=30). We found a higher overall bacterial content in tumor samples compared to that of matching normal tissues. Furthermore, we observed dysbiosis in H. pylori positive samples, consistent with previous findings. Among other microbes, we found specific enrichment of V. Parvula (12/15) and P. melaninogenica (10/15) in tumor tissues, both of which have been implicated in tumorigenicity. A subset of these samples (10 GC and 12 normal) underwent parallel RNAseq analysis. Using gene expression signature panel of 176 genes, we examined association of various immune cell types with tumor versus normal mucosa. We found an overall higher immune response, and higher association of Th1 and Th2 helper cells and macrophages, with tumors as compared to normal mucosa. We further corroborated these findings using single cell RNAseq approach. Using ELISA, we detected significantly increased expression of pro-inflammatory cytokines such as TNF-α, IL-8, GRO, MCP-1 and IL-1a in tumor samples than normal mucosa. Increased TNF-α and IL-8 expression has been directly correlated to tumor invasion and metastasis, and tumor vascularity respectively. Additionally, MCP-1 is known to recruit macrophages and is secreted by gastric epithelial cells in response to pro-inflammatory cytokines upon H. pylori infection. Using a similar approach, we performed WGS and RNAseq, on 9 normal squamous cell carcinoma (NSCC), 8 non-dysplastic Barrett's esophagus (BE) and 6 esophageal adenocarcinoma samples. WGS analysis revealed higher microbial diversity in NSCCs compared to BE samples with high abundance of V. Parvula, P. melaninogenica and S. parasanguinis. Unsupervised clustering analysis revealed high abundance of F. nucleatum in adenocarcinoma, which has been associated with shorter survival in esophageal cancer. Unsupervised clustering analysis of RNAseq data revealed high enrichment of CD4+ Th1 and Th2 helper cell and CD8+ T cell associated immune response in some adenocarcinoma and BE samples. Together our data suggest that both gastric and esophageal cancers display distinct microbial patterns associated with chronic inflammation and tumor-promoting pro-inflammatory microenvironment.

Citation Format: Prashant V. Thakkar, Chao Zhang, Prateek Sharma, Sreekar Vennelaganti, Doron Betel, Manish A. Shah. Understanding the association of gut microbiota and tumor microenvironment in gastric and esophageal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5128.