One of the key stages in the development of mRNA vaccines is their delivery. Along with liposome, other materials are being developed for mRNA delivery that can ensure both the safety and effectiveness of the vaccine, and also facilitate its storage and transportation. In this study, we investigated the polyglucin:spermidine conjugate as a carrier of an mRNA-RBD vaccine encoding the receptor binding domain (RBD) of the SARS-CoV-2 spike protein. The conditions for the self-assembling of mRNA-PGS complexes were optimized, including the selection of the mRNA:PGS charge ratios. Using dynamic and electrophoretic light scattering it was shown that the most monodisperse suspension of nanoparticles was formed at the mRNA:PGS charge ratio equal to 1:5. The average hydrodynamic particles diameter was determined, and it was confirmed by electron microscopy. The evaluation of the zeta potential of the investigated complexes showed that the particles surface charge was close to the zero point. This may indicate that the positively charged PGS conjugate has completely packed the negatively charged mRNA molecules. It has been shown that the packaging of mRNA-RBD into the PGS envelope leads to increased production of specific antibodies with virus-neutralizing activity in immunized BALB/c mice. Our results showed that the proposed polycationic polyglucin:spermidine conjugate can be considered a promising and safe means to the delivery of mRNA vaccines, in particular mRNA vaccines against SARS-CoV-2.

In the present work we studied the antiviral activity of the home library of monoterpenoid derivatives using the pseudoviral systems of our development, which have glycoproteins of the SARS-CoV-2 virus strains Wuhan and Delta on their surface. We found that borneol derivatives with a tertiary nitrogen atom can exhibit activity at the early stages of viral replication. In order to search for potential binding sites of ligands with glycoprotein, we carried out additional biological tests to study the inhibition of the re-receptor-binding domain of protein S. For the compounds that showed activity on the pseudoviral system, a study using three strains of the infectious SARS-CoV-2 virus was carried out. As a result, two leader compounds were found that showed activity on the Wuhan, Delta, and Omicron strains. Based on the biological results, we searched for the potential binding site of the leader compounds using molecular dynamics and molecular docking methods. We suggested that the compounds can bind in conserved regions of the central helices and/or heptad repeats of glycoprotein S of SARS-CoV-2 viruses.

Nucleic acid-based influenza vaccines are a promising platform that have recently and rapidly developed. We previously demonstrated the immunogenicity of DNA vaccines encoding artificial immunogens AgH1, AgH3, and AgM2, which contained conserved fragments of the hemagglutinin stem of two subtypes of influenza A—H1N1 and H3N2—and conserved protein M2. Thus, the aim of this study was to design and characterize modified mRNA obtained using the above plasmid DNA vaccines as a template. To select the most promising protocol for creating highly immunogenic mRNA vaccines, we performed a comparative analysis of mRNA modifications aimed at increasing its translational activity and decreasing toxicity. We used mRNA encoding a green fluorescent protein (GFP) as a model. Eight mRNA-GFP variants with different modifications (M0–M7) were obtained using the classic cap(1), its chemical analog ARCA (anti-reverse cap analog), pseudouridine (Ψ), N6-methyladenosine (m6A), and 5-methylcytosine (m5C) in different ratios. Modifications M2, M6, and M7, which provided the most intensive fluorescence of transfected HEK293FT cells were used for template synthesis when mRNA encoded influenza immunogens AgH1, AgH3, and AgM2. Virus specific antibodies were registered in groups of animals immunized with a mix of mRNAs encoding AgH1, AgH3, and AgM2, which contained either ARCA (with inclusions of 100% Ψ and 20% m6A (M6)) or a classic cap(1) (with 100% substitution of U with Ψ (M7)). M6 modification was the least toxic when compared with other mRNA variants. M6 and M7 RNA modifications can therefore be considered as promising protocols for designing mRNA vaccines.

In order to test the antiviral activity, a series of usnic acid derivatives were synthesized, including new, previously undescribed compounds. The activity of the derivatives against three strains of SARS-CoV-2 virus was studied. To understand the mechanism of antiviral action, the inhibitory activity of the main protease of SARS-CoV-2 virus was studied using the developed model as well as the antiviral activity against the pseudoviral system with glycoprotein S of SARS-CoV-2 virus on its surface. It was shown that usnic acid exhibits activity against three strains of SARS-CoV-2 virus: Wuhan, Delta, and Omicron. Compounds 10 and 13 also showed high activity against the three strains. The performed biological studies and molecular modeling allowed us to assume that the derivatives of usnic acid bind in the N-terminal domain of the surface glycoprotein S at the binding site of the hemoglobin decay metabolite.

In this work, we evaluated the antiviral activity of Arbidol (Umifenovir) against SARS-CoV-2 using a pseudoviral system with the glycoprotein S of the SARS-CoV-2 virus on its surface. In order to search for binding sites to protein S of the virus, we described alternative binding sites of Arbidol in RBD and in the ACE-2-RBD complex. As a result of our molecular dynamics simulations combined with molecular docking data, we note the following fact: wherever the molecules of Arbidol bind, the interaction of the latter affects the structural flexibility of the protein. This interaction may result both in a change in the shape of the domain–enzyme binding interface and simply in a change in the structural flexibility of the domain, which can subsequently affect its affinity to the enzyme. In addition, we examined the possibility of Arbidol binding in the stem part of the surface protein. The possibility of Arbidol binding in different parts of the protein is not excluded. This may explain the antiviral activity of Arbidol. Our results could be useful for researchers searching for effective SARS-CoV-2 virus inhibitors targeting the viral entry stage.

When developing drugs against SARS-CoV-2, it is important to consider the characteristics of patients with different co-morbidities. People infected with HIV-1 are a particularly vulnerable group, as they may be at a higher risk than the general population of contracting COVID-19 with clinical complications. For such patients, drugs with a broad spectrum of antiviral activity are of paramount importance. Glycyrrhizinic acid (Glyc) and its derivatives are promising biologically active compounds for the development of such broad-spectrum antiviral agents. In this work, derivatives of Glyc obtained by acylation with nicotinic acid were investigated. The resulting preparation, Glycyvir, is a multi-component mixture containing mainly mono-, di-, tri- and tetranicotinates. The composition of Glycyvir was characterized by HPLC-MS/MS and its toxicity assessed in cell culture. Antiviral activity against three strains of SARS-CoV-2 was tested in vitro on Vero E6 cells by MTT assay. Glycyvir was shown to inhibit SARS-CoV-2 replication in vitro (IC₅₀2–8 μM) with an antiviral activity comparable to the control drug Remdesivir. In addition, Glycyvir exhibited marked inhibitory activity against HIV pseudoviruses of subtypes B, A6 and the recombinant form CRF63_02A (IC₅₀ range 3.9–27.5 µM). The time-dependence of Glycyvir inhibitory activity on HIV pseudovirus infection of TZM-bl cells suggested that the compound interfered with virus entry into the target cell. Glycyvir is a promising candidate as an agent with low toxicity and a broad spectrum of antiviral action.