In vitro methods for testing antiviral drugs.

Despite successful vaccination programs and effective treatments for some viral infections, humans are still losing the battle with viruses. Persisting human pandemics, emerging and re-emerging viruses, and evolution of drug-resistant strains impose continuous search for new antiviral drugs. A combination of detailed information about the molecular organization of viruses and progress in molecular biology and computer technologies has enabled rational antivirals design. Initial step in establishing efficacy of new antivirals is based on simple methods assessing inhibition of the intended target. We provide here an overview of biochemical and cell-based assays evaluating the activity of inhibitors of clinically important viruses.

Scutellaria polysaccharide inhibits the infectivity of Newcastle disease virus to chicken embryo fibroblast.

BACKGROUND: To select the antiviral active site of Scutellaria polysaccharide (SPS), safe concentrations of crude total Scutellaria polysaccharide (SPS(t)) and fractional polysaccharide SPS50, SPS60, SPS70 and SPS80 on chicken embryo fibroblast (CEF) were first compared using the MTT method. Then, SPS(t), SPS50, SPS60, SPS70, and SPS80 at five concentrations within the safe concentration, together with Newcastle disease virus (NDV), were added to the cultivating system of CEF in three models: pre-addition of polysaccharide, post-addition of polysaccharide, and simultaneous addition of polysaccharides and NDV after mixing. The effects of SPS on the cellular infectivity of NDV (A570 value and the highest viral inhibitory rate) were compared using the MTT method. RESULTS: At appropriate concentrations, the five polysaccharides could significantly inhibit the infectivity of NDV on CEF. Among the five polysaccharide groups, the SPS80 group exhibited the highest viral inhibitory rate in the three sample-addition modes. CONCLUSION: This finding indicates that SPS80 possesses the best efficacy as a component of antiviral polysaccharide drug.

Anti-tumor and anti-viral activities of Galanthus nivalis agglutinin (GNA)-related lectins.

Galanthus nivalis agglutinin (GNA)-related lectin family, a superfamily of strictly mannose-binding specific lectins widespread among monocotyledonous plants, is well-known to possess a broad range of biological functions such as anti-tumor, anti-viral and anti-fungal activities. Herein, we mainly focused on exploring the precise molecular mechanisms by which GNA-related lectins induce cancer cell apoptotic and autophagic death targeting mitochondria-mediated ROS-p38-p53 apoptotic or autophagic pathway, Ras-Raf and PI3K-Akt anti-apoptotic or anti-autophagic pathways. In addition, we further discussed the molecular mechanisms of GNA-related lectins exerting anti-viral activities by blocking the entry of the virus into its target cells, preventing transmission of the virus as well as forcing virus to delete glycan in its envelope protein and triggering neutralizing antibody. In conclusion, these findings may provide a new perspective of GNA-related lectins as potential drugs for cancer and virus therapeutics in the future.

Reverse genetics approaches to combat pathogenic arenaviruses.

Several arenaviruses cause hemorrhagic fever (HF) in humans, and evidence indicates that the worldwide-distributed prototypic arenavirus lymphocytic choriomeningitis virus (LCMV) is a neglected human pathogen of clinical significance. Moreover, arenaviruses pose a biodefense threat. No licensed anti-arenavirus vaccines are available, and current anti-arenavirus therapy is limited to the use of ribavirin, which is only partially effective and is associated with anemia and other side effects. Therefore, it is important to develop effective vaccines and better antiviral drugs to combat the dual threats of naturally occurring and intentionally introduced arenavirus infections. The development of arenavirus reverse genetic systems is allowing investigators to conduct a detailed molecular characterization of the viral cis-acting signals and trans-acting factors that control each of the steps of the arenavirus life cycle, including RNA synthesis, packaging and budding. Knowledge derived from these studies is uncovering potential novel targets for therapeutic intervention, as well as facilitating the establishment of assays to identify and characterize candidate antiviral drugs capable of interfering with specific steps of the virus life cycle. Likewise, the ability to generate predetermined specific mutations within the arenavirus genome and analyze their phenotypic expression would significantly contribute to the elucidation of arenavirus-host interactions, including the basis of their ability to cause severe HF. This, in turn, could lead to the development of novel, potent and safe arenavirus vaccines.

New targets and new drugs in the treatment of HIV.

Antiretroviral treatment has modified the course of human immunodeficiency virus (HIV) infection transforming it into a chronic disease. However, as treatment is conceived "for life", more effective and safety drugs, overcoming the growing resistance of the virus are required. New molecules may block the known viral targets or other new ones. The mechanism of the virus union and entrance to the cell includes the new therapeutic targets that are studied more frequently. Although studies with substances that efficiently block the virus-CD4 receptors union are in very early phases, other studies of molecules capable to block the entrance co-receptors are in more advanced phases (II or III), and enfuvirtide, a substance that blocks membrane fusion, the last phase of virus entrance, has been recently marketed. Another very promising pharmacological target is the integration of the proviral DNA as we know some substances that in vitro block HIV integrase. Besides this, new drugs are increasing the three classic antiretroviral families. Among nucleoside analogs emtricitabine (recently marketed) and amdoxovir are the more prominent. Capravirine and TMC-125 are the non-nucleoside analogs whose studies are more advanced. And atazanavir, fos-amprenavir, tipranavir and TMC-114 are the new protease inhibitors recently marketed or near to be.