Synthesis, biological properties and anti-HIV-1 activity of new pyrimidine P1,P2-dinucleotides.

New homo- and hetero-P(1),P(2)-dinucleotides were prepared with the use of multistep procedures starting from the monophosphates of 3'-fluoro-2-thiothymidine, 3'-fluoro-4-thiothymidine, AZT and 1-[(2-hydroxyethoxy)-methyl-5-propyl-6-phenylselenenyl]uracil. Anti-HIV properties of the synthesized P(1),P(2)-dinucleotides were evaluated against laboratory syncytia inducing strain HIV-1 in CEM-T4 cells. Anti-HIV activities were in the range of 5-45 nM, and therapeutic indexes were higher than 4666-14000. Interactions of the above mentioned compounds with recombinant HIV-1 reverse transcriptase were also investigated. The obtained results point to reverse transcriptase inhibition, with somewhat lower inhibitory activity than that of their parental nucleoside-5'-triphosphates. Compound 6 may be regarded as a potent anti-HIV/AIDS drug.

Inhibition of the helicase activity of HCV NTPase/helicase by 1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide-5 '-triphosphate (ribavirin-TP).

In the presented study the ribavirin-TP--an established inhibitor of the NTPase activity of the superfamily NTPase/helicases II--was investigated as an inhibitor of the unwinding activity of the hepatitis C virus (HCV) NTPase/helicase. The kinetics of the reaction revealed that ribavirin-TP reduces the turnover number of the helicase reaction by a mechanism that does not correspond to that of the inhibition of the NTPase activity. Our results suggest that derivatives of ribavirin-TP with enhanced stability towards hydrolytic attack may be effective inhibitors of the enzyme.

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

To enhance the inhibitory potential of 1-beta-D-ribofuranosyl-1,2,4-triazole-3-carboxamide (ribavirin) vs hepatitis C virus (HCV) NTPase/helicase, ribavirin-5'-triphosphate (ribavirin-TP) was synthesized and investigated. Ribavirin-TP was prepared with the use of modified Yoshikawa-Ludwig-Mishra-Broom procedure (cf. Mishra & Broom, 1991, J. Chem. Soc., Chem. Commun, 1276-1277) involving phosphorylation of unprotected nucleoside. Kinetic analysis revealed enhanced inhibitory potential of ribavirin-TP (IC50=40 microM) as compared to ribavirin (IC50 > 500 microM). Analysis of the inhibition type by means of graphical methods showed a competitive type of inhibition with respect to ATP. In view of the relatively low specificity towards nucleoside-5'-triphosphates (NTP) of the viral NTPase/helicases, it could not be ruled out that the investigated enzyme hydrolyzed the ribavirin-TP to less potent products. Investigations on non- hydrolysable analogs of ribavirin-TP or ribavirin-5'-diphosphate (ribavirin-DP) are currently under way.

Purification and some properties of a novel dsRNA degrading nuclease bound to rye germ ribosomes.

A two-step procedure including affinity chromatography for purification of rye germ ribosomal nuclease that degrades double-stranded RNA from a virus of Penicillium chrysogenum and the poly(I).poly(C) complex was developed. The specific activity towards poly(I).poly(C) of the obtained nuclease preparations was 30 times as high as that of ribosomes. The recovery of activity was 3.4% when the Octyl-Sepharose column was used, and 2.0% in the case of the Phenyl-Sepharose column. On polyacrylamide/SDS gel electrophoresis the nuclease was resolved into two proteins of molecular mass 62 kDa and 57 kDa, respectively. 2-Mercaptoehanol and Mn2+ stimulated the activity of the purified enzyme. Glycerol (20%-50% concentration) stabilized enzyme. In addition to activity towards dsRNA and ssRNA the enzyme cleaves native and denatured DNA. It is suggested that this type of a nuclease takes part in regulation of the mRNA level in cytoplasm.

Purification and characterization of nuclease I associated with rye germ ribosomes.

A nuclease has been purified about 100-fold from ammonium chloride wash of rye germ ribosomes. The enzyme was electrophoretically homogeneous. Its M, was 20,000 and pl 4.8. The neclease hydrolyzed endonuclelytically DNA and RNA and was accompanied by 3-nucleotidase activity. The enzyme degraded RNA to oligonucleotides with a phosphomonoester bond at position 5', and both denatured and native DNA to 5'-OH and 3'-phosphate-terminated fragments. Zinc ions and 2-mercaptoethanol stimulated deoxyribonucleolytic activity. EDTA, polyamines and heparin had only little or no effect. The enzyme is a glycoprotein containing 28% of carbohydrate which consists of fucose, mannose and glucosamine. The nuclease isolated is classified as nuclease I.

The presence of deoxyribonucleolytic activity in cytoplasmic ribosomes of rye (Secale cereale L) germs.

Deoxyribonucleolytic activity was found to be associated with cytoplasmic ribosomes and ribosomal subunits of rye germs. The activity has the pH optimum at 5.0. Treatment of ribosomes and 60S subunits with 0.5 M-ammonium chloride released a considerable part of deoxyribonucleolytic and ribonucleolytic activity; treatment of 40S subunits resulted in a complete release of deoxyribonucleolytic activity and partial release of ribonucleolytic activity. This suggests the presence in ribosomes of rye germs of two types of nucleolytic enzymes: an enzyme of the nuclease I type with deoxyribonuclease and ribonuclease activities, and typical ribonucleases hydrolysing RNA only.