Antiviral activity of oligonucleotides targeting the SARS-CoV-2 genomic RNA stem-loop sequences within the 3’-end of the ORF1b.

Increased evidence shows vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) exhibited no long-term efficacy and limited worldwide availability, while existing antivirals and treatment options have only limited efficacy. In this study, the main objective was the development of antiviral strategies using nucleic acid-based molecules. To this purpose, partially overlapped 6-19-mer phosphorothioate deoxyoligonucleotides (S-ONs) designed on the SARS-CoV-2 genomic RNA stem-loop packaging sequences within the 3' end of the ORF1b were synthetized using the direct and complementary sequence. Among the S-ONs tested, several oligonucleotides exhibited a fifty percent inhibitory concentration antiviral activity ranging from 0.27 to 34 μM, in the absence of cytotoxicity. The S-ON with a scrambled sequence used in the same conditions was not active. Moreover, selected 10-mer S-ONs were tested using different infectious doses and against different SARS-CoV-2 variants, showing comparable antiviral activity that was abrogated when the central sequence was mutated. Experiments to evaluate the intracellular functional target localization of the S-ON inhibitory activity were also performed. Collectively the data indicate that the SARS-CoV-2 packaging region in the 3' end of the ORF1b may be a promising target candidate for further investigation to develop innovative nucleic-acid-based antiviral therapy.