Inhibition of virus-cell interactions, which are required for virus replication, constitutes an exciting area of research for the discovery of novel antiviral agents. RNA based drugs are in clinical use for treatment of infectious diseases as immunomodulators, anti-inflammatory and antiviral agents. Nuclex, a low molecular weight exogenous yeast RNA, consists of a pure, homogeneous 25-membered oligonucleotide. The preventive and therapeutic effects of Nuclex were demonstrated against pandemic strains of influenza virus, parainfluenza virus, Hepatitis C, Herpes simplex virus types 1 and 2, cytomegalovirus, and HIV on experimental models in vitro and in vivo. The mechanism of the antiviral action of the drug relies on its ability to change conformations of cell regulatory proteins and viral coat proteins. An antiviral effect of Nuclex against Epstein-Barr virus (EBV) etiological agent of infectious mononucleosis associated with a number of lymphoproliferative and autoimmune diseases was studied in this work.
The study was performed with EBV-positive human B-cells (Raji) – latently infected with EBV, and EBV-producing tamarin (Saguinus oedipus) B-cell line (B95-8). The drug cytotoxicity was assessed by MTT-method. As a result of investigations it was found that the drug has low toxicity relative to both lymphoblastoid cell cultures. The inhibitory concentrations suppressing 10% of cell viability (IC10) were 2000 µg/ml and IC50s (50% inhibited cell viability) were 5000 µg/ml for both cell lines. An antiviral activity of Nuclex was measured by PCR in EBV infected cells Raji, as a model of acute infection and in non-induced B95-8 cells as a model of chronic EBV infection after 48 hours incubation. The drug effectively inhibited viral replication in the studied concentration range from 10 to 500 µg/ml in EBV-infected Raji cells and B95-8 cells. Effective concentration of Nuclex that inhibited 90% level of the viral DNA accumulation (EC90) was 50 µg/ml for in both cell lines. A virucidal activity of the drug was investigated considering the ability of Nuclex to influence the conformation of the viral surface proteins. The levels of inhibition of the EBV DNA accumulation were 30% after incubation of the drug at the concentration 100 µg/ml with the EBV for the 30 and 60 min exposures and the subsequent infection of Raji cells incubated for 48 hours, while 50% inhibition of viral DNA accumulation was observed at the drug concentration 200 µg/ml under 30 min exposure and 30% at 60 min exposure.
Thus Nuclex showed a strong antiviral effect against EBV. Considering an antiviral activity of the drug (EC90) at 50 µg/ml, and a virucidal action EC50 at 200 µg/ml, determination of its mechanism of action, which could be related to siRNA properties, will constitute the next stage of our research.
