Abstract 5420: The effect of folate deficiency on chemosensitivity of colon cancer cells to 5-Fluorouracil

Abstract

Abstract Background: Folate is an essential cofactor in one-carbon transfer reactions including nucleotide biosynthesis, thereby playing an important role in DNA replication and repair. In cancer cells, folate depletion interrupts DNA synthesis, thereby causing cancer cell death. This has been the basis for chemotherapy using antifolates and 5-Fluorouracil (5FU). We determined the effect of folate deficiency on the sensitivity of colon cancer cells to 5FU in a well established in vitro model of folate deficiency. Methods: Three human colon cancer cell lines (HCT116, Caco-2, HT29) were grown in RPMI1640 medium containing 0 (deficient) and 2.3 μM (replete) of folic acid. Proliferation was measured with growth curves every 3 days for 12 days and intracellular folate concentrations were determined at day 0, 6 and 12. Functional folate depletion was determined by the deoxyuridine suppression test. In vitro chemosensitivity of these colon cancer cell lines to 5FU with leucovorin (LV; 5 μM) was determined using a modified SRB protein assay. In HCT116 and Caco-2, thymidylate synthase (TS) activity was measured and TS, p53 and p21 protein expression was determined by immunoblotting. Results: All three colon cancer cell lines grown in the folate-deficient medium exhibited significantly slower growth rates than the corresponding cell lines grown in the folate-replete medium (p<0.05). Intracellular folate concentrations were significantly lower in all three cell lines grown in the folate-deficient medium than those grown in the folate-replete medium (p<0.05). Intracellular folate depletion induced in these cells was functionally significant as indicated by the deoxyuridine suppression test (p<0.05). All cells grown in the folate-deficient medium showed progressively lower intracellular folate concentrations over time (p<0.05). All three cell lines grown in the folate-deficient medium exhibited significantly higher chemosensitivity to 5FU+LV, albeit to a different degree, compared with those grown in the folate-replete medium (p<0.05). Caco-2, but not HCT116, cells grown in the folate-deficient medium showed significantly lower TS activity (p<0.05). Caco-2 cells grown in the folate-deficient medium had significantly lower protein expression of p53 and p21 but not TS. No differences in protein expression of TS, p53, and p21 were observed in HCT116 cells. Conclusion: Our data suggest that folate deficiency significantly enhances the sensitivity of colon cancer cells to 5FU based chemotherapy. Dietary or other strategies to deplete intracellular folate concentrations in colon cancer cells to enhance chemosensitivity to 5FU are worthy of further investigation. Given the dramatically increased dietary intake and blood levels of folate in North America resulting from folic acid fortification and supplementation, whether or not high folate status would affect chemotherapy for colon cancer also warrants future studies. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5420. doi:1538-7445.AM2012-5420