Background Alterations of the gut virome has been associated with human colorectal cancer (CRC)1,2 , but the timing and mechanism of such alterations remain unknown. To answer this question, we performed a longitudinal study on an azoxymethane (AOM)-induced CRC murine model.
Method Four adult A/J mice per sex were intraperitoneally injected with 8mg/kg AOM or PBS weekly for 6 weeks, and the colons of the mice were monitored biweekly by colonoscopy until 24 weeks after the initial injection. At least a pair of endoscopically normal and tumour tissues were biopsied during colonoscopies of each mouse at different time points. Tissues were formalin-fixed, paraffin-embedded, stained with hematoxylin and eosin (H&E), and examined by a pathologist blindly. Stool samples from weeks 0, 10, 12, 14, 20, and 24 were subjected to DNA extraction and whole metagenomic analysis. The number of tumours was calculated by analysis of colonoscopic videos, and the tumour size was scored based on the diameter of the colon lumen occupied by a tumour.
Results The number and size of the tumours increased as the mice aged in the AOM-treated group, as compared to the control group. Tumours were first observed in the AOM group in week 12. Significantly lower alpha diversity and shift in viral profile were observed when tumours first appeared. Novel viruses from the genera Brunovirus, and Hpunavirus were identified to be positively associated with tumour growth and enriched at a late time point in the AOM group. On the other hand, members from Lubbockvirus were negatively correlated with the tumour growth. Network analysis revealed two clusters of bacteriophages in the AOM virome. While one cluster positively correlated with tumour growth, the other cluster negatively correlated with tumor growth.
Conclusion Our findings suggest that the gut virome alters along with colorectal tumour formation and provide strong evidence of a potential role for bacteriophage in the development of colorectal neoplasia.