In Vitro Antiviral Activity of a New Indol-3-carboxylic Acid Derivative Against SARS-CoV-2.

The coronavirus disease (COVID-19) pandemic has brought into sharp relief the threat posed by coronaviruses and laid the foundation for a fundamental analysis of this viral family, as well as a search for effective anti-COVID drugs. Work is underway to update existent vaccines against COVID-19, and screening for low-molecular-weight anti-COVID drug candidates for outpatient medicine continues. The opportunities and ways to accelerate the development of antiviral drugs against other pathogens are being discussed in the context of preparing for the next pandemic. In 2012-2015, Tsyshkova et al. synthesized a group of water-soluble low-molecular-weight compounds exhibiting an antiviral activity, whose chemical structure was similar to that of arbidol. Among those, there were a number of water-soluble compounds based on 5-methoxyindole-3-carboxylic acid aminoalkyl esters. Only one member of this rather extensive group of compounds, dihydrochloride of 6-bromo-5-methoxy-1-methyl-2-(1-piperidinomethyl)-3-(2-diethylaminoethoxy) carbonylindole, exhibited a reliable antiviral effect against SARS-CoV-2 in vitro. At a concentration of 52.0 µM, this compound completely inhibited the replication of the SARS-CoV-2 virus with an infectious activity of 106 TCID50/mL. The concentration curves of the analyzed compound indicate the specificity of its action. Interferon-inducing activity, as well as suppression of syncytium formation induced by the spike protein (S-glycoprotein) of SARS-CoV-2 by 89%, were also revealed. In view of its synthetic accessibility - high activity (IC50 = 1.06 µg/mL) and high selectivity index (SI = 78.6) - this compound appears to meets the requirements for the development of antiviral drugs for COVID-19 prevention and treatment.

Influenza virus uncoating in infected cells and effect of rimantadine.

Uncoating of influenza virus (strain WSN) in MDCK cells was studied by following the fate of the virus labelled with radioactive precursors. The accumulation of subviral components of input virus was observed in nuclear-associated cytoplasm (NAC) obtained by treatment of the nuclei with citric acid. Two types of subviral components were found there, ribonucleoproteins (RNPs) and larger subviral particles (SVP) containing RNPs in association with M protein. SVP, with different relative amounts of M protein, were revealed in NAC, suggesting that M protein was gradually released from RNPs. The released RNPs entered the nuclei while M protein accumulated within perinuclear membranes. Thus, SVP could be regarded as probable intermediates in virus uncoating. Rimantadine prevented the release of M protein from RNPs and their penetration into the nuclei provoking the accumulation of subviral components in NAC.