Investigating the antiviral activity of bioactive Swertia chirayita compounds against coronaviruses.

Aim: The emergence of three pandemic coronaviruses in the last two decades combined with numerous coronaviruses circulating in bats suggest that spillover of new coronaviruses into humans is likely in the future. The development of broad-spectrum antivirals is vital to allow rapid deployment to patients in the absence of a pan-coronavirus vaccine. This project aims to employ a model coronavirus system as an initial screening tool to identify novel natural product-derived antivirals. Methods: Antiviral activity of a panel of natural compounds and synthetic xanthones based on bioactive compounds from the medicinal plant Swertia chirayita were tested against a model seasonal human coronavirus (HCoV) OC43. Infected baby hamster kidney (BHK-21) cells were treated with compounds and impact on infectivity determined by quantifying viral titres. Alongside, cytotoxicity of the compounds was also determined. Results: Our initial screen identified six compounds that indicated antiviral activity, with synthetic xanthones showing a significant reduction in viral infectivity of HCoV-OC43 at non-cytotoxic concentrations. Preliminary experiments suggest that these inhibit the virus at early stages of the viral life cycle. Conclusions: We have identified bioactive compounds derived from Swertia chirayita, which show significant antiviral efficacy in a human coronavirus. Further work to evaluate their pan-coronavirus activity, as well as to understand the mechanism of action are on-going.