Abstract 1049: Modulating the polymorphic UGT1A1 gene to enhance camptothecin anti-colorectal effect

Abstract

Several semisynthetic analogs of camptothecin (CPT) are used clinically for the treatment of various types of cancers, including colorectal (CRC) cancer, despite their severe, potentially life-threatening toxicities. Studies defined key mutations in the UDP-glycosyltransferase 1 polypeptide A1 (UGT1A1) gene in CRC which play a role in the toxicity and resistance of a broad class of anti-cancer drugs that target DNA topoisomerases. UGT-1A1 is responsible for the glucuronidation and detoxification of the active/toxic metabolite of the topoisomerase I poison, CPT and its analogues, SN-38. Herein, we investigated the potential chemomodulatory effects of a UGT1A1-gene inducer, phenytoin, to the anticancer properties of CPT. The cytotoxic effects of CPT, phenytoin and their combination were evaluated against various colorectal cancer cell lines (SW620, HT29 and HCT116) using sulforhodamine-B assay under normoxic and hypoxic conditions. In HT29, CPT alone and after combination treatment had IC50’s of 0.1235 µM and 0.0269 µM, respectively, under normoxic conditions; and 0.1352 µM and 0.0476 µM, respectively, under hypoxic conditions. In SW620, CPT alone and after combination treatment had IC50’s of 1.9861 µM and 0.0087 µM, respectively, under normoxic conditions; and 1.9549 µM and 0.0024 µM, respectively, under hypoxic conditions. In HCT116, CPT alone and after combination treatment had IC50’s of 0.163 µM and 0.0157 µM, respectively, under normoxic conditions; and 0.1013 µM and 0.0766 µM, respectively, under hypoxic conditions. Flow cytometric analysis after annexin-V/FITC staining showed that the combination treatment significantly induced total apoptosis in all cell lines under investigation. In both HT29 and SW620, the combination treatment significantly suppressed the autophagy compared to CPT treatment alone using acridine orange staining coupled with flowcytometry. Cell cycle analysis using DNA content flowcytometry after PI staining showed significant S-phase arrest in the combination treatment when compared to the control across all cell lines under investigation. This indicates that sub-molecular mechanisms of phenytoin induced chemomodulatory effect to CPT anticancer properties is oxygen tension dependent. Further investigation for the intratumoral metabolism of CPT under hypoxic as well as normoxic conditions and particularly those attributed to UGT-1A1 is currently undergoing. Citation Format: Dalia Al Saeedy, Reham K. Abuhijjleh, Ahmed Gouda, Sherif F. El-Khamisy, Ahmed M. Al-Abd. Modulating the polymorphic UGT1A1 gene to enhance camptothecin anti-colorectal effect [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1049.