New type of interferon inducer

Photodynamic Inactivation of Bovine Coronavirus with the Photosensitizer Toluidine Blue O

Coronaviruses (CoVs) belong to the group of enveloped positive-sense single-strand RNA viruses and are causative agents of respiratory, gastro-intestinal, and central nervous systems diseases in many host species, i.e., birds, mammals, and humans. Beta-CoVs revealed a great potential to cross the barrier between species by causing three epidemics/pandemics among humans in the 21st century. Considering the urgent need for powerful antiviral agents for decontamination, prevention, and treatment of BCoV infections, we turned our attention to the possibility of photodynamic inactivation with photosensitizers in combination with light irradiation. In the present study, we evaluated, for the first time, the antiviral activity of toluidine blue O (TBO) against Beta-coronavirus 1 (BCoV) in comparison to methylene blue (MB). First, we determined the in vitro cytotoxicity of MB and TBO on the Madin-Darby bovine kidney (MDBK) cell line with ISO10993-5/Annex C. Thereafter, BCoV was propagated in MDBK cells, and the virus titer was measured with digital droplet PCR, TCID50 assay and plaque assay. The antiviral activity of non-toxic concentrations of TBO was estimated using the direct inactivation approach. All effects were calculated in MAPLE 15® mathematical software by developing programs for non-linear modeling and response surface analysis. The median inhibitory concentration (IC50) of TBO after 72 h of incubation in MDBK cells was 0.85 µM. The antiviral activity of TBO after the direct inactivation of BCoV (MOI = 1) was significantly stronger than that of MB. The median effective concentration (EC50) of TBO was 0.005 µM. The cytopathic effect decreased in a concentration-dependent manner, from 0.0025 to 0.01 µM, and disappeared fully at concentrations between 0.02 and 0.3 µM of TBO. The number of virus particles also decreased, depending on the concentration applied, as proven by ddPCR analysis. In conclusion, TBO exhibits significant potential for direct inactivation of BCoV in vitro, with a very high selectivity index, and should be subjected to further investigation, aiming at its application in veterinary and/or human medical practice.

Modulation of the Antiviral Activity of Poly (A-U) by Ethidium Bromide and Propidium Iodide

The role of ethidium bromide (EB) and propidium iodide (PI) in modulating the antiviral and interferon-inducing activities of poly(adenylate-uridylate) (poly (A-U)) was examined using the human foreskin fibroblast-vesicular stomatitis virus (HSF-VSV) bioassay system in which the concentration of poly (A-U) was fixed at 0.05 mM or 0.2 mM while the EB or PI concentration was varied to produce variable EB (or PI)/ribonucleotide ratios ranging from 1:16 to 2:1. EB, PI and poly (A-U) tested individually were not efficacious antiviral agents. When poly (A-U) was combined with the ethidium bromide or propidium iodide the antiviral activity was potentiated 15- to 22-fold at EB (or PI)/ribonucleotide ratios in the region of 1/4. The interferon-inducing activity of the EB (or PI)/poly (A-U) combinations were equal to the sum of the interferon-inducing activity of the poly (A-U) and the EB or (PI). These results indicate that the EB and PI potentiate the antiviral activity of the poly (A-U) without superinduction of interferon. The direct viral inactivation study demonstrated that EB, PI, poly (A-U) and the EB (or PI)/poly (A-U) combinations did not inactivate the VSV at concentrations near the 50% viral inhibitory dose.

Enhancement of the Antiviral Activity of Poly (A-U) by Adriamycin and Daunomycin

The role of adriamycin (ADR) and daunomycin (DMN) in modulating the antiviral activity of poly (adeylate-uridylate) (poly (A-U)) was examined using a human foreskin fibroblast – vesicular stomatitis virus (HSF-VSV) bioassay in which the concentration of poly (A-U) was fixed at 0.05 mm or 0.2 mm while the ADR or DMN concentration was varied to produce ADR (or DMN)/ribonucleotide ratios ranging from 1:16 to 2:1. Poly (A-U), ADR and DMN were not efficacious antiviral agents when tested individually at the concentrations employed in the ADR (or DMN)/poly (A-U) combinations. When the ADR or DMN was combined with the poly (A-U) to produce ADR (or DMN)/poly (A-U) ratios of 1/6, the 50% effective doses (ED50) of the poly (A-U), ADR and DMN decreased 18, 104, and 185-fold, respectively. However, when ADR or DMN was combined with polyriboinosinic-polyribocytidylic acid [poly (I) · poly (C)], the ED50 of the ADR, DMN and the poly (I) · poly (C) were not affected. Interferon neutralization studies indicated that ADR, DMN, poly (A-U) and the ADR (or DMN)/poly (A-U) combination induced the production of interferon-beta (IFN-β). The amount of IFN produced by the ADR (or DMN)/poly (A-U) combinations was equal to the sum of the IFN prduced by their constituents. These results indicate that the ADR and DMN potentiate the antiviral activity of the poly (A-U) without affecting the amount of IFN induced. The direct viral inactivation study demonstrated that ADR, DMN, poly (A-U) and the ADR (or DMN)/poly (A-U) combinations do not inactivate the VSV at concentrations near the ED50.

RNA–Intercalating Agent Interactions: in vitro Antiviral Activity Studies

Twenty intercalating agents were tested to examine the effects of intercalating dye-induced perturbations upon the antiviral activity of poly (adenylate–uridylate) [poly (A-U)]. Neither poly (A-U) alone nor each intercalative dye was an efficacious antiviral agent. When poly (A-U) was combined with major groove intercalating dyes (acridine orange or proflavine), no synergism was observed. When poly (A-U) was combined with minor groove intercalating dyes [ethidium (EB), propidium (PI), adriamycin (ADR) or daunomycin (DMN)] or minor/major groove intercalating dyes [9-aminoacridine (9-AA), N2-methyl-9-hydroxy-ellipticine (NMHE) or N2,N6-dimethyl-9-hydroxy-ellipticine (DMHE)] the 50% effective doses (ED50) of the poly (A-U), 9-AA, ADR, DMHE, DMN, EB, NMHE and PI decreased 18-, 22-, 60-, 274-, 61-, 154-, 113- and 299-fold, respectively. When poly (A-U) was combined individually with 11 dyes whose mode of intercalation was not known, the ED50 of ametantrone (HAQ), chloroquine (CHL), mitoxantrone (DHAQ) and quinine (QUI) decreased 125-, 65-, 251- and 32-fold, respectively. These results suggest that the four dyes may intercalate into poly (A-U) from the minor groove. Ten (ADR, CHL, DMN, DHAQ, DMHE, EB, HAQ, NMHE, PI, QUI) of the 20 dyes evaluated exhibited significant synergism with poly (A-U), as quantified by the fractional inhibitory concentration index. Interferon (IFN) neutralization assays demonstrated that the IFN-inducing capability of the dye/poly (A-U) combinations approximated the sum of the capabilities of the poly (A-U) and the dyes employed. These results suggest that the majority of the dyes tested potentiate the antiviral activity of poly (A-U) without affecting the amount of IFN induced.

In vitro antiviral activity of poly (A-U) and ellipticines

The role of N2-methyl-9-hydroxy-ellipticine (NMHE) and N2,N6-dimethyl-9-hydroxy-ellipticine (DMHE) in modulating the antiviral activity of poly (A-U) was examined using a human foreskin fibroblast-vesicular stomatitis virus (HSF-VSV) bioassay in which the concentration of poly (A-U) was fixed at 0.05 mM or 0.2 mM while the NMHE or DMHE concentration was varied to produce variable NMHE (or DMHE)/ribonucleotide ratios ranging from 1:16 to 2:1. Poly (A-U), NMHE and DMHE tested individually were not efficacious antiviral agents. When the poly (A-U) was combined with the NMHE or DMHE, the antiviral activity of the poly (A-U) was potentiated 16- to 20-fold a NMHE (or DMHE)/ribonucleotide ratios in the region of 1/4. Poly (A-U), NMHE and DMHE induce beta-IFN. The interferon-inducing activity of the NMHE (or DMHE)/poly (A-U) combination was equal to the sum of the interferon-inducing activity of the poly (A-U) alone and the NMHE (or DMHE) alone. The direct viral inactivation study demonstrated that NMHE, DMHE, poly (A-U) and the NMHE (or DMHE)/poly (A-U) combinations did not inactivate VSV at concentrations near the 50% viral inhibitory dose. Photomicrographs of HSF cells incubated with NMHE alone or with a NMHE/poly (A-U) combination suggest that poly (A-U) affects the subcellular distribution of the NMHE by steering the NMHE to the nucleolus. These observations suggest that modulation of a nuclear process may be responsible for the enhanced antiviral activity.

Enhancement of the antiviral activity of poly r(A-U) by ametantrone and mitoxantrone

The role of ametantrone (HAQ) and mitoxantrone (DHAQ) in modulating the antiviral and interferon-inducing activities of poly r(A-U) was examined using the human foreskin fibroblast-vesicular stomatitis virus (HSF-VSV) bioassay system in which the concentration of poly r(A-U) was fixed at 0.05 mM or 0.2 mM while the HAQ or DHAQ concentration was varied to produce variable HAQ (or DHAQ)/ribonucleotide ratios ranging from 1:16 to 2:1. HAQ, DHAQ and poly r(A-U) tested individually were not efficacious antiviral agents. When poly r(A-U) was combined with the ametantrone or mitoxantrone the antiviral activity was potentiated 10-fold at HAQ (or DHAQ)/ribonucleotide ratios in the region of 1/4 to 1/6. The interferon-inducing activity of the HAQ (or DHAQ)/poly r(A-U) combinations were equal to the sum of the interferon-inducing activity of the poly r(A-U) and the HAQ (or DHAQ). These results indicate that the HAQ and DHAQ potentiate the antiviral activity of the poly r(A-U) without the superinduction of interferon. The direct viral inactivation study demonstrated that HAQ, DHAQ, poly r(A-U) and the HAQ (or DHAQ)/poly r(A-U) combinations did not inactivate the VSV at concentrations near the viral 50% inhibitory dose.

Enhancement of the antiviral and interferon-inducing activities of poly r(A-U) by carminic acid

Experiments have been designed to systematically examine the effects of carminic acid (CAR) on the antiviral/interferon-inducing activity of poly r(A-U), using the human foreskin fibroblast-vesicular stomatitis virus bioassay system. Modulation of the antiviral/interferon-inducing activity of poly r(A-U) by carminic acid was examined at fixed poly r(A-U) concentrations of 0.05 mM or 0.2 mM while varying the carminic acid concentrations to produce variable CAR/ribonucleotide ratios ranging from 1:16 to 2:1. Carminic acid and poly r(A-U) were tested individually at the concentrations employed in the CAR/poly r(A-U) combinations. Neither the carminic acid alone nor poly r(A-U) alone were effective antiviral agents/interferon inducers. The antiviral/interferon-inducing activity of poly r(A-U) was potentiated twelve-fold at CAR/ribonucleotide ratios in the region of 1/6 to 1/4. These results suggest a synergism between the poly r(A-U) and the carminic acid at the concentrations employed in this study.

[Interferons--research, effects and importance]

Interferons are a family of proteins synthesized by the cells of higher organisms as a first reaction to viral infections, preceding the immune response. They are also involved in the regulation of the immune system and therefore included among the lymphokines. Since they had been shown to have antitumor activity in vitro and in experimental animals, they were suggested to be powerful drugs in cancer therapy.