A Cohort Effect on AOM/DSS Colorectal Cancer Model Performance in C57BL/6 Mice

The azoxymethane/dextran sodium sulfate (AOM/DSS) murine model is widely used to study the pathogenetic mechanisms of colitis-associated colorectal cancer (CRC). However, the reproducibility of this model can be challenged in the long run due to several factors, specifically, the variability of the gut microbiota composition in laboratory mice. Here, we report the results of our three cohort study of C57BL/6 male mice with the AOM/DSS model of CRC, bred in the same vivarium facility. The experiments with cohorts 1 and 2 from different rooms were performed in parallel, while the experiment with cohort 3 was conducted 18 months later. The results demonstrate that mice of these cohorts developed colonic tumors with different efficiency: the percentage of animals with visible tumors was 37.5, 84.6, and 96.7% respectively. Notably, cohorts 2 and 3 also differed by the average number of tumors per animal and the area of affected colonic tissue. Gut microbiota analysis via 16S rRNA amplicon sequencing revealed significant cross-cohort differences in the species diversity, which might account for the variability in AOM/DSS model performance. Our experience shows that long-term working with murine models may engender problems with their reproducibility, specifically, with data heterogeneity. To minimize such a heterogeneity, special consideration should be given to mouse housing conditions, particularly to those factors that affect gut microbiota. A regular monitoring of specific pathogens according to FELASA recommendations, as well as the screening of the commensal microbiota using next generation sequencing techniques before the onset of experiments, are also highly reasonable.