Methylenetetrahydrofolate reductase polymorphism is associated with folate pool in gastrointestinal cancer tissue

The folate pool in cancer tissue is a critical factor for the effect of 5-FU-based chemotherapy. Methylenetetrahydrofolate reductase (MTHFR) plays a role in the metabolism of folate. The gene of MTHFR is polymorphic (C667T, alanine-to-valine), and this is related to the activity of the enzyme. We analyzed the association between MTHFR genotype and the folate pool in gastrointestinal cancer tissues. MTHFR genotypes were determined in 67 surgically-resected gastrointestinal cancer tissues by PCR-RFLP analysis. Forty-five patients received no treatment and 22 patients received oral administration of UFT, a combination of Uridine and Tegafur, before surgery. 5,10-Methylenetetrahydrofolate (CH2FH4) and tetrahydrofolate (FH4) were measured by fluoro-dUMP (FdUMP) binding assay as representative values of the folate pool. The number of FdUMP binding sites on Thymidylate synthase (TS) was quantified in the samples from UFT-administered patients. The incidences of MTHFR genotype were as follows: Ala/Ala, 27; Ala/Val, 30; Val/Val, 10. In the UFT(-) group, the amount of FH4 in Ala/Val-type cancer tissue was higher than that in Ala/Ala-type (1.50 +/- 1.13 versus 0.72 +/- 0.64, p < 0.05). This relationship was also observed on the sum of CH2FH4 and FH4 (2.88 +/- 1.85 versus 1.75 +/- 1.06, p < 0.05). Val/Val-type cancer tissue had higher amount of either CH2FH4 and FH4 than Ala/Ala-type, although this finding did not reach statistical significance. In the UFT(+) group, no relationship between MTHFR genotype and the free folate pool was observed, presumably due to the influence of the amounts of FdUMP and TS in the tissue. The calculation of total CH2FH4 from the value of free CH2FH4, free TS and total TS showed a weak genotype-dependent difference in total CH2FH4. The TS inhibition rate also showed a weak genotype-dependent difference. These results suggest a link between MTHFR genotype and the folate pool in gastrointestinal cancer, leading to the association of MTHFR genotype with TS inhibition rate upon 5-FU exposure. The MTHFR genotype might be considered in the design of 5-FU-based chemotherapy, especially in patient-specific strategies with leucovorin supplementation.