Intestinal toll-like receptor 4 knockout alters the functional capacity of the gut microbiome following irinotecan treatment.

Purpose: Irinotecan can cause high levels of diarrhea caused by toxic injury to the gastrointestinal microenvironment. Toll-like receptor 4 (TLR4) and the gut microbiome have previously been implicated in gastrointestinal toxicity and diarrhea; however, the link between these two factors has not been definitively determined. We used a tumor-bearing, intestinal epithelial cell (IEC) TLR4 knockout model (Tlr4) to assess microbiome changes following irinotecan treatment. We then determined if a fecal microbiota transplant (FMT) between Tlr4 and wild-type (WT) mice altered irinotecan-induced gastrointestinal toxicity.

Methods: MC-38 colorectal cancer cells were injected into WT and Tlr4 mice. Fecal samples were collected prior to tumor inoculation, prior to irinotecan treatment and at cull. 16S rRNA gene sequencing was used to assess changes in the microbiome. Next, FMT was used to transfer the microbiome phenotype between Tlr4 and WT mice prior to irinotecan treatment. Gastrointestinal toxicity symptoms were assessed.

Results: In study 1, there were no compositional differences in the microbiome between Tlr4 and WT mice at baseline. However, predicted functional capacity of the microbiome was different between WT and Tlr4 at baseline and post-irinotecan. In study 2, Tlr4 mice were protected from grade 3 diarrhea. Additionally, WT mice who did not receive FMT had more colonic damage in the colon compared to controls (P = 0.013). This was not seen in Tlr4 mice or WT mice who received FMT (P > 0.05).

Conclusion: Tlr4 and WT had no baseline compositional microbiome differences, but functional differences at baseline and following irinotecan. FMT altered some aspects of irinotecan-induced gastrointestinal toxicity.