ATP-binding domain of NTPase/helicase as a target for hepatitis C antiviral therapy

To enhance the inhibitory potentiaI of 1-beta-D-ribofuranosyl-1,2,4-triazol e-3-carboxamide (ribavirin) vs hepatitis C virus (HCV) NTPase/helicase, rib avirin-5'-triphosphate (ribavirin-TP) was synthesized and investigated. Rib avirin-TP was prepared with the use of modified Yoshikawa-Ludwig-Mishra-Bro om procedure (cf. Mishra & Broom, 1991, J. Chem. Sec., Chem. Commun, 1276-1 277) involving phosphorylation of unprotected nucleoside. Kinetic analysis revealed enhanced inhibitory potential of ribavirin-TP (IC 50=40 mu M) as compared to ribavirin (IC50 > 500 mu M). Analysis of the inh ibition type by means of graphical methods showed a competitive type of inh ibition with respect to ATP. In view of the relatively low specificity towa rds nucleoside-5'-triphosphates (NTP) of the viral NTPase/helicases, it cou ld not be ruled out that the investigated enzyme hydrolyzed the ribavirin-T P to less potent products. Investigations on non- hydrolysable analogs of r ibavirin-TP or ribavirin-5'-diphosphate (ribavirin-DP) are currently under way.