Environmental triggers of early-onset colorectal cancer: interactions between microplastics and pks+ E coli in early-life gut colonization

SUMMARY Early-onset colorectal cancer (EOCRC) is rising at an alarming rate and is now the leading cause of cancer- related deaths in men and the second in women under 50 in the U.S. Despite growing awareness, the environmental drivers of this trend remain poorly understood. Genomic studies have identified a unique DNA mutation signature enriched in EOCRC linked to colibactin, a genotoxin produced by E. coli harboring the polyketide synthase (pks+) gene island. Notably, active pks+ E. coli colonization of tumors is not more common in EOCRC versus late-onset patients, suggesting that early-life exposure—potentially under conditions that compromise gut homeostasis—may be a critical risk factor. Micro- and nano-plastics (MNPs), now widespread in the environment and food chain, are known to disrupt intestinal barrier integrity and induce gut dysbiosis in animal models. Alarmingly, infants have been shown to carry the highest MNP levels in stool, potentially rendering them susceptible to early-life pks+ E. coli genotoxicity. We hypothesize that oral MNP exposure compromises the mucosal barrier of the gut, enabling pks+ E. coli to invade the underlying intestinal epithelia and induce tumor-initiating DNA mutations. In our preliminary studies, chronic MNP exposure in mice led to enlarged lymphoid aggregates in the colon and enhanced tumor burden in a chemical carcinogenesis model. These findings support the need to examine whether MNPs contribute to EOCRC initiation by facilitating genotoxic microbial invasion. Aim 1 will test whether MNPs potentiate epithelial invasion by pks+ E. coli in vivo. Mice will receive oral gavage of pks+ E. coli (with and without prior antibiotic suppression of the microbiome) followed by short-term and chronic MNP exposure in the drinking water, using a novel MNP formulation we have developed and previously tested in mice. Bacterial invasion will be assessed via quantitative PCR and RNA in situ hybridization. Aim 2 will test whether MNPs potentiate epithelial mutagenesis by pks+ E. coli in vivo. DNA from intestinal tissue in Aim 1 will be isolated and mutational signatures evaluated using ultradeep error-corrected sequencing of a custom hybrid-capture panel of CRC “driver” genes. High sequencing accuracy and depth will enable us to confidently call rare colibactin-induced mutations in the normal intestine. This pilot study leverages our institutional expertise in microbiome research and mouse models of mutagenic processes, as well as our preliminary data supporting MNP-driven immune disruption in the gut. This work will generate foundational evidence linking MNPs to bacterial genotoxicity and EOCRC risk, laying the groundwork for an R01. Our results will also provide proof-of-concept for feasibility of new screening approaches aimed at detecting mutational signatures that predict cancer risk in healthy individuals. Such future strategies, if successful, could scale to the entire population for early-life non-invasive screening to prevent EOCRC.