Coronavirus derived expression systems. Progress and problems

Host Defence RNases as Antiviral Agents against Enveloped Single Stranded RNA Viruses

Owing to the recent outbreak of Coronavirus Disease of 2019 (COVID-19), it is urgent to develop effective and safe drugs to treat the present pandemic and prevent other viral infections that might come in the future. Proteins from our own innate immune system can serve as ideal sources of novel drug candidates thanks to their safety and immune regulation versatility. Some host defense RNases equipped with antiviral activity have been reported over time. Here, we try to summarize the currently available information on human RNases that can target viral pathogens, with special focus on enveloped single-stranded RNA (ssRNA) viruses. Overall, host RNases can fight viruses by a combined multifaceted strategy, including the enzymatic target of the viral genome, recognition of virus unique patterns, immune modulation, control of stress granule formation, and induction of autophagy/apoptosis pathways. The review also includes a detailed description of representative enveloped ssRNA viruses and their strategies to interact with the host and evade immune recognition. For comparative purposes, we also provide an exhaustive revision of the currently approved or experimental antiviral drugs. Finally, we sum up the current perspectives of drug development to achieve successful eradication of viral infections.

Transmissible gastroenteritis virus (TGEV)-based vectors with engineered murine tropism express the rotavirus VP7 protein and immunize mice against rotavirus

A coronavirus vector based on the genome of the porcine transmissible gastroenteritis virus (TGEV) expressing the rotavirus VP7 protein was constructed to immunize and protect against rotavirus infections in a murine model. The tropism of this TGEV-derived vector was modified by replacing the spike S protein with the homologous protein from mouse hepatitis virus (MHV). The rotavirus gene encoding the VP7 protein was cloned into the coronavirus cDNA. BALB/c and STAT1-deficient mice were inoculated with the recombinant viral vector rTGEV_S-MHV–VP7, which replicates in the intestine and spreads to other organs such as liver, spleen and lungs. TGEV-specific antibodies were detected in all the inoculated BALB/c mice, while rotavirus-specific antibodies were found only after immunization by the intraperitoneal route. Partial protection against rotavirus-induced diarrhea was achieved in suckling BALB/c mice born to dams immunized with the recombinant virus expressing VP7 when they were orally challenged with the homotypic rotavirus strain.

Anti-SARS coronavirus 3C-like protease effects of Isatis indigotica root and plant-derived phenolic compounds

The 3C-like protease (3CLpro) of SARS-coronavirus mediates the proteolytic processing of replicase polypeptides 1a and 1ab into functional proteins, becoming an important target for the drug development. In this study, Isatis indigotica root extract, five major compounds of I. indigotica root, and seven plant-derived phenolic compounds were tested for anti-SARS-CoV 3CLpro effects using cell-free and cell-based cleavage assays. Cleavage assays with the 3CLpro demonstrated that IC50 values were in micromolar ranges for I. indigotica root extract, indigo, sinigrin, aloe emodin and hesperetin. Sinigrin (IC50: 217 microM) was more efficient in blocking the cleavage processing of the 3CLpro than indigo (IC50: 752 microM) and beta-sitosterol (IC50: 1210 microM) in the cell-based assay. Only two phenolic compounds aloe emodin and hesperetin dose-dependently inhibited cleavage activity of the 3CLpro, in which the IC50 was 366 microM for aloe emodin and 8.3 microM for hesperetin in the cell-based assay.