Rapamycin rescues APC-mutated colon organoid differentiation.

Familial adenomatous polyposis (FAP) is an autosomal dominant disorder characterized by germline mutations in the adenomatous polyposis coli (APC) gene. This leads to numerous colorectal adenomas and a high risk of colorectal cancer (CRC). Our stem cell-derived colon organoid model revealed that a heterozygous APC mutation is sufficient to induce colorectal cancer formation. We found a link between APC mutation type, organoid maturation and FAP severity. Here, we show that severe germline mutations in hESCs employ diverse mechanisms of carcinogenesis. FAP1-hESCs expressing a truncated 332-amino acid protein exhibited a hyperactivated mTOR pathway, including PTEN inactivation and increased S6K1 and eIF4E activation. This affected oncogenic c-Myc expression and contributed to apoptosis resistance. Rapamycin treatment restored differentiation potential in FAP1 organoids but not FAP2 organoids, which expressed a larger truncated protein without mTOR pathway activation. Our in vitro colon organoids system findings were validated in human patients. Notably, a colon from a FAP1 patient exhibited high expression of mTOR pathway proteins. These findings highlight the potential of rapamycin for personalized therapy in FAP patients with distinct mTOR-mediated APC mutations. Our colon organoid model is valuable for studying CRC and developing new diagnostic, preventive, and therapeutic approaches to prevent or delay tumorigenesis in FAP patients.