5,10-Methylenetetrahydrofolate (N5,N10-Methylenetetrahydrofolate; 5,10-CH2-THF) is cofactor in several biochemical reactions. It exists in nature as the diastereoisomer [6R]-5,10-methylene-THF.
As an intermediate in one-carbon metabolism, 5,10-CH2-THF converts to 5-methyltetrahydrofolate, 5-formyltetrahydrofolate, and methenyltetrahydrofolate. It is substrate for the enzyme methylenetetrahydrofolate reductase (MTHFR)[1] [2] It is mainly produced by the reaction of tetrahydrofolate with serine, catalyzed by the enzyme serine hydroxymethyltransferase.
Methylenetetrahydrofolate is a source of the equivalent of formaldehyde or CH22+ in biosyntheses.
Methylenetetrahydrofolate is also an intermediate in the detoxification of formaldehyde.[3]
It is the one-carbon donor for thymidylate synthase, for methylation of 2-deoxy-uridine-5-monophosphate (dUMP) to 2-deoxy-thymidine-5-monophosphate (dTMP). The coenzyme is necessary for the biosynthesis of thymidine and is the C1-donor in the reactions catalyzed by TS and thymidylate synthase (FAD).
[6R]-5,10-methylene-THF is a biomodulator that has proven to enhance the desired cytotoxic antitumor effect of Fluorouracil (5-FU) and can bypass the metabolic pathway required by other folates (such as leucovorin) to achieve necessary activation.[4] The active metabolite is being evaluated in clinical trials for patients with colorectal cancer in combination with 5-FU.