Abstract 2880: Modulating disease susceptibility in a model of human colon cancer by microbiome rederivation
Authors: Amos-Landgraf James , Busi Susheel , Ericsson Aaron , McCoy Marina , Parker Taybor , Schehr Rebecca , Hankins Miriam , Franklin Craig , Bryda Elizabeth 
Published: August 2015

Abstract
To understand the impact of differences in complex microbiota on colon cancer susceptibility, we utilized the Pirc (Polyposis In Rat Colon) model of familial human colon cancer to correlate the longitudinal changes of the gut microbiota with early adenoma development. Recent human epidemiologic studies have shown associations of gut microbiota differences in patients with colorectal cancer vs. controls.
To test if differences in the gut microbiota modulate susceptibility, we used the F344/NTac-ApcPirc/+ rat model and altered the microbiome through embryo rederivation using three distinct strains of surrogate dams: F344/NHsd, LEW/SsNHsd, and Crl:SD, all harboring different commensal microbiota. Fecal samples from the pups and dams were collected at various time points. Extracted DNA was sequenced using the Illumina MiSeq platform for the 16S rRNA gene V4 hypervariable region. Adenoma development was monitored periodically via colonoscopy and terminal tumor counts and histology were performed at 180 days. We found the complex microbiota of the surrogates to be distinct from one another and that the pups resembled their respective dams. At the terminal time-point, rats harboring the LEW microbiota had significantly reduced colonic tumor burden (number and size) compared to both F344 (p&lt;0.001) and SD (p&lt;0.05). Colonic tumors were also absent in 2 of the 15 rederived pups with the LEW microbiota reducing the Pirc phenotype penetrance from 100% to 87%.
At weaning, we found the LEW microbiota to be unique with a high percentage of Prevotella copri. Pups with the LEW microbiota also differed significantly from the other pups by an additional 8 operational taxonomic units (OTUs). At 6 months of age, the relative abundance of P. copri, and 5 additional OTUs correlated with decreased tumor burden in these pups (Spearman’s, p≤0.05). Conversely, higher prevalence of family Peptococcaceae and Akkermansia muciniphila were positively correlated (p&lt;0.05) with increased tumor number. Histological analysis of colons from the LEW and SD offspring showed significant goblet cell hyperplasia (p&lt;0.002) in the distal colon of the LEW pups. No aberrant crypt foci (ACF) or microadenomas were found in the two LEW pups that did not harbor colonic adenomas, indicating a possible inhibition of initiation. Immunohistochemical staining for Ki67 showed that the proliferation index of both the normal epithelium and tumors in the SD group was trending significantly higher compared to the LEW rats.
Our results indicate that microbial alteration through rederivation affects colon cancer susceptibility. The prevalence or lack of specific OTUs at weaning can potentially serve as predictors of tumor burden at later stages. More importantly, the study points towards differences in the microbiota of the offspring acting as modulators of disease phenotype affecting initiation or progression of colon cancer.
Citation Format: James Amos-Landgraf, Susheel Busi, Aaron Ericsson, Marina McCoy, Taybor Parker, Rebecca Schehr, Miriam Hankins, Craig Franklin, Elizabeth Bryda. Modulating disease susceptibility in a model of human colon cancer by microbiome rederivation. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2880. doi:10.1158/1538-7445.AM2015-2880