lometrexol and glycineamide-ribonucleotide

We recently described the syntheses of 12a-c, 4-amino-7-oxo substituted analogues of 5-deaza-5,6,7,8-tetrahydrofolic acid (5-DATHF), and 5,10-dideaza-5,6,7,8-tetrahydrofolic acid (DDATHF), in six steps from commercially available p-substituted methyl benzoates in 20-27% overall yields. Such analogues were tested in vitro against CCRF-CEM leukemia cells and showed that they are completely devoid of any activity, the IC(50) being higher than 20 microg/mL for all cases. To clarify if the presence of the carbonyl group in position C7, the distinctive feature of our synthetic methodology, is the reason for this lack of activity, we have now obtained the 7-oxo substituted analogues of 5-DATHF and DDATHF, 18a-c, in 10-30% overall yield. Testing of 18a-c in vitro against CCRF-CEM leukemia cells revealed that these compounds are totally inactive. A molecular modeling study of 18b inside the active site of the complex E. coliGARTFase-5-DATHF-GAR pointed to an electronic repulsion between the atoms of the 7-oxo group and the carbonyl group of Arg90 as a possible explanation for the inactivity of 18a-c.

Topics: Antineoplastic Agents; Crystallography, X-Ray; Drug Screening Assays, Antitumor; Escherichia coli; Folic Acid Antagonists; Humans; Hydroxymethyl and Formyl Transferases; Models, Molecular; Phosphoribosylglycinamide Formyltransferase; Ribonucleotides; Structure-Activity Relationship; Tetrahydrofolates; Tumor Cells, Cultured

Tight-binding inhibition of recombinant human monofunctional glycinamide ribonucleotide formyltransferase by Lometrexol (6R-5,10-dideazatetrahydrofolate) requires polyglutamation. LY254155 and LY222306 differ from 5,10-dideazatetrahydrofolate in the replacement of the 1',4'- phenylene moiety by a 2',5'-thiophene and a 2',5'-furan, respectively. Compared to Lometrexol, the thiophene and furan analogues had 25- and 75-fold greater inhibitory potencies against human monofunctional glycinamides ribonucleotide formyltransferase (Ki = 2.1 and 0.77 nM, respectively). The binding affinities of the thiophene and furan analogues for membrane folate-binding protein from human KB cells were 6- and 350-fold weaker than Lometrexol, respectively. Both the thiophene analogue and 5,10-dideazatetrahydrofolate inhibited the in vivo growth of murine 6C3HED lymphosarcoma, murine C3H mammary carcinoma, and human xenograft HXGC3, HC1, and VRC5 colon carcinomas by 95-100%. The thiophene analogue was efficacious against human xenograft PANC-1, a pancreatic carcinoma which was completely resistant to 5,10- dideazatetrahydrofolate. These novel antifolates represent the first monoglutamated tight-binding inhibitors of glycinamide ribonucleotide formyltransferase. By eliminating the need for polyglutamation, this class of antifolates may have clinical activity in the treatment of solid tumors expressing low levels of folylpolyglutamate synthetase or tumors resistant to antifolate therapy due to increased gamma-glutamyl hydrolase activity.

Topics: Acyltransferases; Animals; Antineoplastic Agents; Carrier Proteins; Female; Folate Receptors, GPI-Anchored; Folic Acid Antagonists; Humans; Hydroxymethyl and Formyl Transferases; Leukemia; Mice; Mice, Inbred C3H; Mice, Inbred C57BL; Phosphoribosylglycinamide Formyltransferase; Receptors, Cell Surface; Ribonucleotides; Stereoisomerism; Structure-Activity Relationship; Tetrahydrofolates