Calcitriol Modulates Age-dependent Drug Response in Paired Patient-derived Normal and Tumor Colorectal Organoids

The incidence of early-onset colorectal cancer (EO-CRC, <50 years) is rising worldwide, highlighting the need to better understand the underlying causes of this age-related divergence. We used paired patient-derived normal and tumor colorectal organoids to investigate the therapeutic window of chemotherapeutic agents and its modulation by calcitriol (the most active vitamin D metabolite). Dose-response analyses revealed marked interpatient variability, with SN38 being more potent than 5-fluorouracil (5-FU) and oxaliplatin. Normal organoids were more resistant than paired tumor counterparts to 5-FU and oxaliplatin in both EO-CRC and late-onset CRC (LO-CRC, >50 years), indicating selective tumor cytotoxicity. In contrast, the therapeutic window for SN38 was preserved in LO-CRC but not in EO-CRC organoids, revealing age-dependent differences in drug sensitivity. Moreover, calcitriol reduced the cytotoxicity of 5-FU and SN38 in normal organoids regardless of patient age, while in tumor organoids this protective effect was restricted to EO-CRC. As a consequence, calcitriol treatment selectively expanded the therapeutic window for 5-FU and SN38 in LO-CRC organoids. Mechanistically, these effects correlated with calcitriol-induced antiproliferative action and transcriptional regulation of drug metabolism-related pathways. Overall, our findings identify age-dependent differences in chemotherapy response and support the importance of maintaining adequate vitamin D status to reduce chemotherapy-associated toxicity.