# Evaluation of RNA Secondary Stem-Loop Structures in the UTRs of Mouse Hepatitis Virus as New Therapeutic Targets

## TL;DR

This study explores RNA structures in the UTRs of MHV-A59 as potential targets for antiviral drugs, showing that siRNAs targeting these structures can significantly inhibit virus replication.

## Contribution

The study identifies novel RNA secondary structures in MHV-A59 UTRs as promising targets for RNAi-based antiviral therapies.

## Key findings

- siRNAs targeting SL1 and MIN structures significantly reduced MHV-A59 replication and plaque size.
- The combination of siSL1 and siMIN showed a stronger inhibitory effect than monotherapy.
- SL1 structure is conserved in SARS-CoV-2, suggesting it as a potential new target for antiviral drugs.

## Abstract

MHV-A59 is a beta-coronavirus that causes demyelinating encephalitis and hepatitis in mice. Recently, the mouse infection model of MHV-A59 has been used as an alternative animal infection model for SARS-CoV and SARS-CoV-2, aiding the development of new antiviral drugs. In this study, the MHV-A59 model was employed to investigate the potential of SARS-CoV-2 UTRs as new targets for antiviral drugs. Optimal targets within the MHV-A59 UTRs were identified using a shRNA and siRNA design tool, focusing on RNA secondary stem-loop (SL) structures in the UTRs. We then examined whether the designed RNAi constructs could inhibit MHV-A59 replication. In the 5′UTR, the stem-loop 1 (SL1) was identified as the most effective target, while in the 3′UTR, the minimal element for the initiation of negative-strand RNA synthesis (MIN) proved to be the most effective. Importantly, siRNAs targeting SL1 and MIN structures significantly reduced total RNA synthesis, negative-strand genomic RNA synthesis, subgenomic (sg) RNA synthesis, viral titer, and the plaque size of MHV-A59 compared to the control. Although not statistically significant, the combination of siSL1 and siMIN had a stronger effect on inhibiting MHV-A59 replication than either siRNA monotherapy. Interestingly, while the SL1 structure is present in both MHV and SARS-CoV-2, the MIN structure is unique to MHV. Thus, the SL1 of SARS-CoV-2 may represent a novel and promising target for RNAi-based antiviral drugs.