Application of real-time PCR for testing antiviral compounds against Lassa virus, SARS coronavirus and Ebola virus in vitro.

This report describes the application of real-time PCR for testing antivirals against highly pathogenic viruses such as Lassa virus, SARS coronavirus and Ebola virus. The test combines classical cell culture with a quantitative real-time PCR read-out. The assay for Lassa virus was validated with ribavirin, which showed an IC(50) of 9 micrograms/ml. Small-scale screening identified a class of imidazole nucleoside/nucleotide analogues with antiviral activity against Lassa virus. The analogues contained either dinitrile or diester groups at the imidazole 4,5-positions, and many of which possessed an acyclic sugar or sugar phosphonate moiety at the imidazole 1-position. The IC(50) values of the most active compounds ranged from 5 to 21 micrograms/ml. The compounds also inhibited replication of SARS coronavirus and Ebola virus in analogous assays, although to a lesser extent than Lassa virus.

[Hemostatic and analgesic effect of Gonghuan Zhixue Tablet on mice].

OBJECTIVE: To explore the hemostatic and analgesic effect of Gonghuan Zhixue Tablet (GHZXT) on mice and to produce experimental evidence for exploiting new drug for endometrorrhagia caused by Cu-intrauterine contraceptive device (Cu-IUD). METHODS: Compared with 6-aminocaproic acid and notoginseng, the effects of GHZXT on clotting and bleeding time of mice with capillary method and severed tail were investigated; and compared with aspirin, the analgesic effects of GHZXT on mice were investigated with hot plate and torsive body method. RESULTS: The clotting time of mice was remarkably shortened with a rising of the dosage of GHZXT and the difference between each therapeutic group and distilled water group was remarkable. As compared with distilled water group, the bleeding time of each dosage group of GHZXT was obviously shortened; and each dosage of GHZXT could prolong the time of pain reaction to hot plate and decrease the degree of torsive body of the mice. CONCLUSION: Pharmacological experiment has proved that GHZXT has evident hemostatic and analgesic function.

Potent inhibition of NTPase/helicase of the West Nile Virus by ring-expanded ("fat") nucleoside analogues.

A series of ring-expanded ("fat") nucleoside analogues (RENs) containing the 6-aminoimidazo[4,5-e][1,3]diazepine-4,8-dione ring system have been synthesized and screened for inhibition of NTPase/helicase of the West Nile Virus (WNV). To assess the selectivity of RENs against the viral enzymes, a truncated form of human enzyme Suv3((Delta)(1)(-)(159)) was also included in the study. Ring-expanded nucleosides 16, 17, and 19, which possess the long C(12), C(14), and C(18) side-chains, respectively, at position 6, as well as the ring-expanded heterocycle 39, which contains aralkyl substitution at position 1, were all found to have excellent profiles of activity and selectivity toward the viral versus human enzymes against the West Nile Virus (IC(50) ranging 1-10 muM). Compound 30, while being an equally potent inhibitor of WNV, was found to be somewhat less selective, whereas compound 36, which is an alpha-anomeric counterpart of 30, exhibited potent and selective inhibition of WNV (IC(50) 1-3 muM). The same compounds that showed potent inhibition of viral helicase activity completely failed to show any activity against the viral NTPase reaction even up to 500 muM. However, at concentrations >500 muM of RENs and the ATP concentrations >10 times the K(m) value of the enzyme, a significant activation of NTPase activity was observed. This activating effect underwent further dramatic enhancement (>1000%) by further increases in ATP concentration in the reaction mixture, suggesting that the viral helicase and NTPase reactions are not coupled. A tentative mechanistic model has been proposed to explain the observed results.

Ring-expanded ("fat") nucleoside and nucleotide analogues exhibit potent in vitro activity against flaviviridae NTPases/helicases, including those of the West Nile virus, hepatitis C virus, and Japanese encephalitis virus.

A series of ring-expanded ("fat") heterocycles, nucleoside and nucleotide analogues (RENs) containing the imidazo[4,5-e][1,3]diazepine ring system (9, 14, 15, 18, 24-26, 28, 31, and 33) and imidazo[4,5-e][1,2,4]triazepine ring systems (30b, 30c, 32, and 34), have been synthesized as potential inhibitors of NTPases/helicases of Flaviviridae, including the West Nile virus (WNV), hepatitis C virus (HCV), and Japanese encephalitis virus (JEV). An amino-terminal truncated form of human enzyme Suv3(delta1-159) was also included in the study so as to assess the selectivity of RENs against the viral enzymes. The analogues of RENs included structural variations at position 1 of the heterocyclic base and contained changes in both the type of sugar moieties (ribo, 2'-deoxyribo, and acyclic sugars) and the mode of attachment (alpha versus beta anomeric configuration) of those sugars to the heterocyclic base. The target RENs were biochemically screened separately against the helicase and ATPase activities of the viral NTPases/helicases. A number of RENs inhibited the viral helicase activity with IC50 values that ranged in micromolar concentrations and exhibited differential selectivity between the viral enzymes. In view of the observed tight complex between some nucleosides and RNA and/or DNA substrates of a helicase, the mechanism of action of RENs might involve their interaction with the appropriate substrate through binding to the major or minor groove of the double helix. The REN-5'-triphosphates, on the other hand, did not influence the above unwinding reaction, but instead exerted the inhibitory effect on the ATPase activity of the enzymes. The activity was found to be highly dependent upon the low concentration levels of the substrate ATP. At concentrations >500 microM of RENs and the ATP concentrations >10 times the Km value of the enzyme, a significant activation of NTPase activity was observed. This activating effect underwent further dramatic enhancement (>1000%) by further increases in ATP concentration in the reaction mixture. A tentative mechanistic model has been proposed to explain the observed results, which includes an additional allosteric binding site on the viral NTPases/helicases that can be occupied by nucleoside/nucleotide-type molecules such as RENs.

in vitro inhibition of the measles virus by novel ring-expanded ('fat') nucleoside analogues containing the imidazo[4,5-e]diazepine ring system.

The synthesis and in vitro anti-measles virus (anti-MV) activity of a class of ring-expanded ('fat') nucleoside analogues (1-4) containing the title heterocyclic ring system are reported. The target compounds were synthesized by base-catalyzed condensations of 4,5-dicarboxylic acid esters of the appropriately substituted imidazole-1-ribosides with suitably substituted guanidine derivatives. Compounds were screened for anti-MV activity in African green monkey kidney cells (CV-1), employing ribavirin as the control standard. While the parent compound 1 itself failed to show any significant antiviral activity against MV, its analogues containing hydrophobic substituents at the 2-position (2) or the 6-position (4) showed promising antiviral activity at submicromolar or micromolar concentration levels with no apparent toxicity to the host cell line. Both compounds showed higher anti-MV activity than the control drug ribavirin.

Characterization of imidazo[4,5-d]pyridazine nucleosides as modulators of unwinding reaction mediated by West Nile virus nucleoside triphosphatase/helicase: evidence for activity on the level of substrate and/or enzyme.

Compounds that interact with DNA or RNA generally act as inhibitors of enzymes that unwind DNA or RNA. In the present study we describe the synthesis and properties of some nucleoside analogues that interact with double-stranded DNA but that, in contrast, facilitate the unwinding reaction mediated by West Nile (WN) virus nucleoside triphosphatase (NTPase)/helicase. The nucleoside analogues described, 1-(2'-O-methyl-beta-D-ribofuranosyl)imidazo[4,5-d]pyridazine-4,7(5H,6H)-dione (HMC-HO4), 1-(beta-D-ribofuranosyl)imidazo[4,5-d]pyridazine-4,7(5H,6H)-dione, and 1-(2'-deoxy-alpha-D-ribofuranosyl)imidazo[4,5-d]pyridazine-4,7(5H,6H)dione, all contain the imidazo[4,5-d]pyridazine ring system. The extent of the enhancing effect on helicase activity was found to be dependent on the time of exposure of the DNA substrate to the compounds and their concentrations. The nucleoside analogues were nevertheless found to be capable of uncoupling the ATPase and helicase activities of the enzyme by a mechanism operating on the level of the enzyme. Thus, in the case of HMC-HO4, the direct interaction with the enzyme caused inhibition of its helicase activity, with a half-maximal inhibitory concentration of 30 microM. The similar potency of the compound against replication of WN virus in cell culture suggests that inhibition of the helicase activity of the viral enzyme is responsible for the observed antiviral activity of HMC-HO4 and may indeed represent an important mode of action of antiviral drugs in general. Comparative studies performed with the related NTPase/helicase from hepatitis C virus revealed that the extent of the effects mediated by imidazo[4,5-d]pyridazine nucleosides is enzyme specific. The substances described may represent a starting point for the development of a new class of helicase-specific antivirals.

Novel ring-expanded nucleoside analogs exhibit potent and selective inhibition of hepatitis B virus replication in cultured human hepatoblastoma cells.

Novel ring-expanded nucleoside (REN) analogs (1-3) containing 5:7 fused ring systems as the heterocyclic base were found to be potent and selective inhibitors of hepatitis B virus (HBV) replication in cultured human hepatoblastoma 2.2.15 cells. The most active compound, 6-amino-4,5-dihydro-8H-1-(beta-D-ribofuranosyl)imidazo[4,5-e][1,3]diazepine-4,8-dione (1), inhibited the synthesis of intracellular HBV replication intermediates and extracellular virion release in 2.2.15 cells with 50% effective concentration (EC50) of 0.604 and 0.131 microM, respectively. All three compounds had no effect on the synthesis of viral ribonucleic acids (RNA) in 2.2.15 cells. These compounds also exhibited low cellular toxicity in stationary and rapidly growing cell systems.