In vitro and in vivo properties of novel nucleoside transport inhibitors with improved pharmacological properties that potentiate antifolate activity

The activity of antimetaholite inhibitors of de novo deoxyribonucleotide bi osynthesis can be compromised by the salvage of extracellular preformed nuc leosides and nucleobases, Dipyridamole (DP) is a nucleoside transport inhib itor that has been used clinically in an attempt to increase antimetabolite activity; however, DP binds tightly to the serum protein alpha (1)-acid gl ycoprotein (AGP) thereby rendering this therapeutic strategy largely ineffe ctive. Four novel Dr analogues (NU3076, NU3084, NU3108, and NU3121) have be en developed with substitutions at the 2,6- and 4,8-positions of the pyrimi dopyrimidine ring. The novel Dr analogues inhibit thymidine (dThd) uptake i nto L1210 cells in vitro (NU3076 IC50, 0.25 muM; NU3084 IC50, 0.27 muM; NU3 108 IC50, 0.31 muM; NU3121 IC50, 0.26 muM; and DP IC50, 0.37 muM), but, unl ike DP, their activity remains largely unaffected in the presence of 5 mg/m l AGP, The four DP analogues inhibit dThd and hypoxanthine rescue from Al-i mta (multitargeted antifolate)-induced growth inhibition in A549 and COR L2 3 human lung carcinoma cell lines in the presence of 2.5 mg/ml AGP, whereas the activity of DP is completely abolished. i.p. administration of 10 mg/k g NU3108, NU3121, and Dr produced peak plasma concentrations of 4.4, 2.1, a nd 6.7 muM, respectively, and levels were sustained above 1 muM for similar to 45 min (DP) and 120 min (NU3108 and NU3121). [H-3]thymidine incorporati on into COR L23 xenografts grown in CD1 nude mice was reduced by 64% (NU310 8), 44% (NU3121), and 65% (DP)2 h after administration of the nucleoside tr ansport inhibitors. In conclusion, two novel DP analogues (NU3108 and NU312 1) have been identified that do not bind to AGP and that display superior p harmacokinetic profiles in comparison to DP and inhibit [H-3]thymidine inco rporation into human tumor xenografts in vivo.