The development of preventive vaccines became the first order task in the COVID-19 pandemic caused by SARS-CoV-2. This paper reports the construction of the pVAX-RBD plasmid containing the Receptor-Binding Domain (RBD) of the S protein and a unique signal sequence 176 which promotes target protein secretion into the extracellular space thereby increasing the efficiency of humoral immune response activation. A polyglucine-spermidine conjugate (PGS) was used to deliver pVAX-RBD into the cells. The comparative immunogenicity study of the naked pVAX-RBD and pVAX-RBD enclosed in the PGS envelope showed that the latter was more efficient in inducing an immune response in the immunized mice. In particular, RBD-specific antibody titers were shown in ELISA to be no higher than 1 : 1000 in the animals from the pVAX-RBD group and 1 : 42000, in the pVAX-RBD-PGS group. The pVAX-RBD-PGS construct effectively induced cellular immune response. Using ELISpot, it has been demonstrated that splenocytes obtained from the immunized animals effectively produced INF-y in response to stimulation with the S protein-derived peptide pool. The results suggest that the polyglucine-spermidine conjugate-enveloped pVAX-RBD construct may be considered as a promising DNA vaccine against COVID-19.

Angiotensin-converting enzyme 2 (ACE2), the functional receptor of SARS-CoV-2, plays a crucial role in the pathogenesis of COVID-19. ACE2 targeting holds the promise for preventing and inhibiting SARS-CoV-2 infection. In this work, we describe the development and use of a test system based on competitive ELISA for the primary screening of potential antiviral compounds. We studied the activity of the library of dyes of different groups. Several dyes (ortho-cresolphthalein, eosin (free acid), eosin (Na salt)) that inhibited the interaction of ACE2 with the spike proteins of SARS-CoV-2 have been identified among the candidates. A potential antiviral drug, methylene blue, did not show activity in our study. We believe that our results can help in the further search for inhibitors of interaction between the coronavirus spike protein and ACE2 receptor.

Antibodies are complex protein structures, and producing them using eukaryotic expression systems presents significant challenges. One frequently overlooked aspect of expression vectors is the nucleotide sequence encoding the signal peptide, which plays a pivotal role in facilitating the secretion of recombinant proteins. This study presents the development of an integrative vector, pVEAL3, for expressing full-length recombinant monoclonal antibodies in mammalian cells. The vector features a distinctive nucleotide sequence that encodes an artificial chimeric signal peptide with the following amino acid sequence: MMRTLILAVLLVYFCATVHC. Additionally, the vector incorporates several regulatory elements to enhance antibody expression, including the Gaussia luciferase signal sequence, internal ribosome entry site (IRES), P2A peptide, and a furin cleavage site. These elements coordinate to regulate the synthesis levels of the antibody chains. The analysis of clones obtained via transfection with the developed vector showed that over 95% of them secreted antibodies at levels significantly higher than those of the control. The immunochemical analysis of the chimeric antibody produced by the CHO-K1-10H10ch cell line confirmed the preservation of its functional activity.

The hexane extract of Psoralea drupacea Bunge fruits was initially evaluated for antivi-ral activity against SARS-CoV-2 based on GC-MS data indicating high bakuchiol con-tent (87.74%). Unexpectedly, the extract showed no antiviral effect in Vero E6 cells due to cytotoxicity (CC₅₀ = 7.5 μg/mL), while purified bakuchiol demonstrated moderate antiviral activity (IC₅₀ = 6.2 ± 0.8 μg/mL; SI = 2.9). Quantitative NMR revealed that the actual bakuchiol content in the extract was 44.3% — approximately half the GC-MS value — explaining the lack of efficacy at non-cytotoxic concentrations. Both the ex-tract and purified bakuchiol effectively blocked the RBD-ACE2 interaction in a com-petitive ELISA (71.3% inhibition at 50 μM for bakuchiol; IC₅₀ = 18.5 μM). Notably, the extract also inhibited the viral main protease 3CLpro (IC₅₀ = 32.0 ± 3.5 μg/mL), while purified bakuchiol showed no such activity. These findings reveal a dual mechanism: bakuchiol inhibits viral entry via RBD-ACE2 blockade, while other extract components (e.g., angelicin, psoralen) suppress viral replication via 3CLpro inhibition.