[Can Coronavirus HCoV-229E be Used as a Model Virus Instead of SARS-CoV-2 in Antiviral Efficacy Studies?]

In recent years, due to the pandemic, many in vitro studies have been conducted to develop therapeutic methods for the diagnosis and treatment of viruses and to test antivirals. Studies examining whether the use of HCoV-229E for modeling SARS-CoV-2 is safe and sufficient are limited in the literature. Therefore, in this study, we aimed to investigate whether HCoV-229E culture and quantitation studies, which can be performed under BSL-2 conditions, can be a preliminary model for SARS-CoV-2 experiments requiring BSL-3 conditions through antiviral efficacy assays. In our study, MRC5 cells were used for HCoV-229E propagation and analysis and Vero-E6 cells were used for SARS-CoV-2 propagation and analysis. During propagation, cell morphology and cytopathic effects (CPE) were examined daily with an inverted microscope and the logarithmic increase in viral RNA loads in the cultures was confirmed by real-time reverse transcriptase polymerase chain reaction (RT-PCR) using samples taken from the culture supernatants. Subsequently, the plaque assay (PFU/ml), which is frequently used in the literature for virus quantitation and the revised tissue culture infectious dose 50% assay (TCID50/ml) quantitation test with crystal violet staining, a new method developed in our laboratory, were performed. For antiviral assays, remdesivir, molnupiravir and oseltamivir, which have been used clinically against SARS-CoV-2 infection, were used and the efficacies of these drugs tested on HCoV-229E and SARS-CoV-2 were studied in parallel cultures before and after virus inoculation. Viral RNA suppression in the groups as a result of the drug treatments was analyzed by quantitative PCR method. It was found that the antiviral effect of remdesivir on SARS-CoV-2 lasted at least 12 hours longer than its effect on HCoV-229E and that the drug was more effective in suppressing viral load in the first 24 hours when applied prophylactically in cultures inoculated with HCoV-229E. For SARS-CoV-2, no difference was observed in the timing of remdesivir administration (24 hours or 48 hours). Molnupiravir and oseltamivir administered prophylactically in the first 24 hours had higher antiviral efficacy against both viruses than after virus inoculation. Furthermore, molnupiravir and remdesivir had no cytotoxic effect on cell morphology in virus inoculated cultures, while the negative effects of oseltamivir on cell viability were detected by inverted microscopy. In conclusion, remdesivir and molnupiravir prophylactically administered at a dose of 10 μM to cells inoculated with SARS-CoV-2 and HCoV-229E in vitro showed the highest antiviral activity in the first 24 hours and remdesivir caused the least cytotoxicity on cell viability. In this study, standardized versions of HCoV-229E production, quantitation and drug administration protocols were performed in comparison with SARS-CoV-2. The suppression of viral RNA loads at 12 and 24 hours by all prophylactically administered drugs was similar in both viruses as assessed at 48 hours. This study concluded that antiviral drug candidates developed for SARS-CoV-2 had similar effects on HCoV-229E, suggesting that HCoV-229E could be a model for SARSCoV-2 studies. For this reason, it was decided that HCoV-229E, which can be produced and tested under BSL-2 conditions in laboratories without BSL-3 conditions, could be used safely in studies on SARS-CoV-2.