TLR4 deficiency upregulates TLR9 expression and enhances irinotecan‐related intestinal mucositis and late‐onset diarrhoea

BACKGROUND AND PURPOSE: Severe diarrhoea, a common gastrointestinal manifestation of anticancer treatment with irinotecan, might involve single nucleotide polymorphisms (SNPs) of toll-like receptors (TLRs), described as critical bacterial sensors in the gut. Here, colorectal cancer patients carrying missense TLR4 A896G (rs4986790) or C1,196T (rs4986791) SNPs and Tlr4 knockout (Tlr4-/-) mice were given irinotecan to investigate the severity of the induced diarrhoea. EXPERIMENTAL APPROACH: ). Diarrhoea severity was evaluated by measuring intestinal injury and inflammatory markers expression after animals were killed. KEY RESULTS: All patients with TLR4 SNPs chemotherapy-treated presented diarrhoea, whereas gastrointestinal toxicity was observed in 50% of the wild homozygous individuals. Mice injected with irinotecan presented systemic bacterial translocation and increased TLR4 immunostaining in the intestine. In line with the clinical findings, Tlr4 gene deficiency enhanced irinotecan-related diarrhoea and TLR9 expression in mice. An increased myeloperoxidase activity and Il-18 expression along with IL-10 decreased production in Tlr4-/- mice also indicated an intensified intestinal damage and inflammatory response. CONCLUSION AND IMPLICATIONS: TLR4 deficiency upregulates TLR9 expression and enhances intestinal damage and the severity of late-onset diarrhoea during irinotecan-based treatment. Identifying patients genetically predisposed to chemotherapy-associated diarrhoea is a strategy toward precision medicine.