Pemetrexed-13C5 is intended for use as an internal standard for the quantification of pemetrexed by GC- or LC-MS. Pemetrexed is an antifolate with anticancer activity.1,2,3 It is an inhibitor of folate-dependent enzymes involved in purine synthesis, including thymidylate synthase and dihydrofolate reductase (Kis = 109 and 7 nM, respectively, for the human recombinant enzymes), and the potency for thymidylate kinase is increased following polyglutamination of pemetrexed (Ki = 1.3 nM for pemetrexed-glu5).1,2 Pemetrexed is an inhibitor of other nucleotide metabolism enzymes in a polyglutamination-dependent manner, including glycinamide ribonucleotide formyltransferase, with Ki values of 9,300 and 65 nM for the non-glutaminated and polyglutaminated mouse recombinant enzyme, respectively, and aminoimidazole carboxamide ribonucleotide formyltransferase, with Ki values of 3,600 and 265 nM for the non-glutaminated and polyglutaminated human enzyme, respectively. It inhibits proliferation of CCRF-CEM cells but not 5,10-dideazatetrahydrofolate-resistant CR15 cells (IC50s = 0.254 and 200 µM, respectively).1 Pemetrexed (100 mg/kg, i.p.) reduces tumor growth in A549, H1299, and PC-9 non-small cell lung cancer cell (NSCLC) mouse xenograft models but not in models using the same cell lines overexpressing thymidylate kinase.3
1.Shih, C., Chen, V.J., Gossett, L.S., et al.LY231514, a pyrrolo[2,3-d]pyrimidine-based antifolate that inhibits multiple folate-requiring enzymesCancer Res.57(6)1116-1123(1997) 2.Hanauske, A.R., Chen, V., Paoletti, P., et al.Pemetrexed disodium: A novel antifolate clinically active against multiple solid tumorsOncologist6(4)363-373(2001) 3.Takezawa, K., Okamoto, I., Okamoto, W., et al.Thymidylate synthase as a determinant of pemetrexed sensitivity in non-small cell lung cancerBr. J. Cancer104(10)1594-1601(2011)