Molecular docking analysis of HSV-1 proteins models with synthetic and plant derived compounds

The atomic resolution model of US9, UL20, and gH protein of HSV is known. Hence, the ligand protein interaction of the US9, UL20, and gH protein models were carried out with synthetic drugs like acyclovir, bexarotene, vinorelbine, foscarnet, famciclovir, cidofovir and two plant derived natural drug acacetin and anthraquinone. Based on structure and docking study, it is predicted that protein US20 and gH binds with particular anti-HSV drug i.e. acyclovir, cidofovir, acacetin and famciclovir, acacetin respectively, while interaction of different protein is different with drugs.

[Evaluation and application of natural products for viral infections]

The limited efficacy and significant clinical toxicity of combination interferone and ribavirin therapy have generated strong interest in developing novel inhibitors of hepatitis C virus (HCV) replication. Recently, a growing understanding of the structure and function of critical viral enzymes and the development of HCV replicons have accelerated the development of highly specific candidate antiviral agents. In the life cycle of HCV, enveloped virions bind and penetrate into host cell using viral envelope glycoproteins. In the cytoplasm, the viral RNA genome serves as mRNA, and produces viral protein as a long polyprotein that is cleaved by both host and viral proteases. Progeny virions assemble by budding into ER/Golgi apparatus, where the glycoproteins maturate, and are released at the cell surface. All stages of replication cycle from the attachment of virus to the release of progeny should be antiviral targets. We have searched for antiviral candidates from natural resources for about 20 years. So far, we have found several classes of compounds with unique antiviral action. Among them, anionic substances interfere with virus attachment and/or entry, several substances inhibit the maturation of virus-specific glycoproteins, low molecules can inhibit the virus release from infected cells, glycerol derivatives reduce the pathogenicity of virus, and some compounds exert virucidal action that impairs the ability of virus to infect host cells. These substances might be worthy to be evaluated as novel anti-HCV agents by using HCV replication systems in cultured cell lines.

[Studies on evaluation of natural products for antiviral effects and their applications]

In the search for novel antiviral molecules from natural products, we have discovered various antiviral molecules with characteristic mechanisms of action. Scopadulciol (SDC), isolated from the tropical medicinal plant Scoparia dulcis L., showed stimulatory effects on the antiviral potency of acyclovir (ACV) or ganciclovir (GCV). This effect of SDC was exerted via the activation of viral thymidine kinase (HSV-1 TK) and, as a result, an increase in the cellular concentration of the active form of ACV/GCV, i.e., the triphosphate of ACV or GCV. On the basis of these experimental results, cancer gene therapy using the HSV-1 tk gene and ACV/GCV together with SDC was found to be effective in suppressing the growth of cancer cells in animals. Acidic polysaccharides such as calcium spirulan (Ca-SP) from Spirulina platensis, nostoflan from Nostoc flagelliforme, and a fucoidan from the sporophyll of Undaria pinnatifida (mekabu fucoidan) were also found to be potent inhibitors against several enveloped viruses. Their antiviral potency was dependent on molecular weight and content of the sulfate or carboxyl group as well as counterion species chelating with sulfate groups, indicating the importance of the three-dimensional structure of the molecules. In addition, unlike dextran sulfate, Ca-SP was shown to target not only viral absorption/penetration stages but also some replication stages of progeny viruses after penetration into cells. When mekabu fucoidan or nostoflan was administered with oseltamivir phosphate, their synergistic antiviral effects on influenza A virus were confirmed in vitro as well as in vivo.

The role of a HSV thymidine kinase stimulating substance, scopadulciol, in improving the efficacy of cancer gene therapy

BACKGROUND

The most extensively investigated strategy of suicide gene therapy for treatment of cancer is the transfer of the herpes simplex virus thymidine kinase (HSV-TK) gene followed by administration of antiviral prodrugs such as acyclovir (ACV) and ganciclovir (GCV). The choice of the agent that can stimulate HSV-TK enzymatic activity is one of the determinants of the usefulness of this strategy. Previously, we found that a diterpenoid, scopadulciol (SDC), produced a significant increase in the active metabolite of ACV. This suggests that SDC may play a role in the HSV-TK/prodrug administration system.

METHODS

The anticancer effect of SDC was evaluated in HSV-TK-expressing (TK+) cancer cells and nude mice bearing TK+ tumors. In vitro and in vivo enzyme assays were performed using TK+ cells and tumors. The phosphorylation of ACV monophosphate (ACV-MP) was measured in TK- cell lysates. The pharmacokinetics of prodrugs was evaluated by calculating area-under-the-concentration-time-curve values.

RESULTS

SDC stimulated HSV-TK activity in TK+ cells and tumors, and increased GCV-TP levels, while no effect of SDC was observed on the phosphorylation of ACV-MP to ACV-TP by cellular kinases. The SDC/prodrug combination altered the pharmacokinetics of the prodrugs. In accord with these findings, SDC enhanced significantly the cell-killing activity of prodrugs. The bystander effect was also significantly augmented by the combined treatment of ACV/GCV and SDC.

CONCLUSIONS

SDC was shown to be effective in the HSV-TK/prodrug administration system and improved the efficiency of the bystander effect of ACV and GCV. The findings will be considerably valuable with respect to the use of GCV in lower doses and less toxic ACV. This novel strategy of drug combination could provide benefit to HSV-TK/prodrug gene therapy.

Selective enhancement of scopadulcic acid B production in the cultured tissues of Scoparia dulcis by methyl jasmonate

The effects of methyl jasmonate (MeJA) on isoprenoid production were evaluated in cultured tissues of Scoparia dulcis. It was found that MeJA suppressed the accumulation of chlorophylls, carotenoids, phytol and beta-sitosterol in the tissues. MeJA, however, remarkably enhanced the production of scopadulcic acid B (SDB), with 10 microM being optimal observed concentration for stimulation of SDB production. The maximum concentration of SDB was observed 6 d after MeJA treatment.

Evaluation of scopadulciol-related molecules for their stimulatory effect on the cytotoxicity of acyclovir and ganciclovir against Herpes simplex virus type 1 thymidine kinase gene-transfected HeLa cells

Herpes simplex virus type 1 thymidine kinase (HSV TK) is involved in both antiherpetic therapy and cancer gene therapy with acyclovir (ACV) and ganciclovir (GCV). Enhanced sensitivity to these drugs is advantageous in their clinical use. In the present study, scopadulciol (SDC) and its related compounds were evaluated for their stimulatory effect on the cytotoxicity of ACV and GCV by determination of selective toxicities against HSV TK-expressing HeLa cells. Although SDC remarkably potenciated the cytotoxicity of ACV and GCV, the other tested compounds showed only weak selectivity, except for compound 34.

Structure-activity relationship of in vitro antiviral and cytotoxic activity of semisynthetic analogues of scopadulane diterpenes

Fourteen semisynthetic compounds derived from the natural scopadulane-type diterpenes thyrsiflorin A (4), B (5), and C (6), including several precursors, have been examined in vitro for their antiherpetic activity against Herpes simplex virus type II (HSV-2) and cytotoxicity against two human tumor cell lines. Four of these compounds showed moderate antiherpetic activity, but none of them exhibited a significant cytotoxicity against the cell lines used. Some structure-activity relationships have been identified for the antiviral activity in these scopadulane derivatives as well as important structural features for the cytotoxic activity.