 Raltitrexed is fully active after polyglutamylation, which allows cellular retention of the drug.By inhibiting Thymidylate synthase (TS), thus formation of precursor pyrimidine nucleotides, raltitrexed prevents the formation of DNA and RNA, which are required for the growth and survival of both normal cells and cancer cells.Inhibition of L1210 cell growth in culture IC50 = 9 nM, is one of the strongest antimetabolites in use.