Abstract 2796: Colibactin mutation signatures are associated with younger age of onset in colorectal cancer

Abstract Escherichia coli (E. coli) strains carrying the polyketide synthase (pks) island produce the genotoxin colibactin associated with pathogenesis of colorectal cancer (CRC). Colibactin binds directly to DNA, causing alkylating damage leading to double stranded DNA breaks. Colibactin mutagenesis results in mutations in hexameric A-T rich DNA motifs that can be identified by whole genome sequencing (WGS) as mutation signatures SBS28 and SBS88 (SBS-pks). Since WGS is not routinely used clinically, we developed an approach to specifically identify SBS-pks using a clinical targeted exon capture assay, MSK-IMPACT. In an institutional pan-cancer clinical cohort of 78, 905 tumors we identified 15, 967 samples with 20 mutations detected by MSK-IMPACT. We identified 150/1, 884 samples with microsatellite stable CRC with 10% mutations attributable to SBS-pks. Examining clinicopathologic and genomic features of SBS-pks+ compared to SBS-pks- CRC tumors, we found that SBS-pks+ signatures are significantly enriched in younger age of onset compared to SBS-pks- CRC patients (median age 55 vs median age 59, p= 0. 0028). SBS-pks+ CRC exhibit similar driver mutations and tumor mutational burden (TMB) compared to SBS-pks- CRC but are associated with increased fraction of genome altered (FGA). To mechanistically investigate colibactin-associated damage we developed a novel long-term human colon organoid-microbe co-culture model system that takes advantage of reversal of polarity in suspension culture. WGS of human CRC organoids co-cultured for three months with pks+ and delta-pks E. coli NC101 confirmed induction of pks+ specific SBS-pks signatures, validating the model. Leveraging this model and a biobank of normal colon organoids from donors aged / 50 years, we are investigating the molecular mechanisms underlying the association of SBS-pks with younger age of onset CRC. Citation Format: Stefanie Gerstberger, Melissa Lumish, Saskia Hartner, Farheen Shah, Seongmin Choi, Anisha Luthra, Qingwen Jiang, Hyung Jun Woo, Ahmed Mahmoud, Henry Walch, Simran Asawa, Mark Donoghue, Andrea Cercek, Rona Yaeger, Andrew McPherson, Francisco Sanchez-Vega, Karuna Ganesh. Colibactin mutation signatures are associated with younger age of onset in colorectal cancer abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 2796.