Abstract
Tight-binding inhibition of recombinant human monofunctional glycinamide ribonucleotide formyltransferase by Lometrexol (6R-5,10-didea-zatetrahydrofolate) 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 glycinamide 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 γ-glutamyl hydrolase activity.
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The authors dedicate this study to our colleague, the late Dr. Gerald Grindey, who recently succumbed to the disease he dedicated his life to cure. His contributions and leadership in cancer therapy development will be greatly missed.
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