August 2022 EMM Editor's Choice Article

The August 2022 EMM Editor’s Choice article is “Evaluation of the mutagenic effects of Molnupiravir and N4-hydroxycytidine in bacterial and mammalian cells by HiFi sequencing,” ( by Jaime A. Miranda, Page B. McKinzie, Vasily N. Dobrovolsky, and Javier R. Revollo.

During the COVID-19 pandemic, the SARS-CoV-2 variants continue to emerge and spread around the world, resulting in an urgent demand for antiviral drugs to treat COVID-19. Molnupiravir (MOV; EIDD-2801) is a prodrug of the ribonucleoside analog β-D-N(4)-hydroxycytidine (NHC; EIDD1931) used as a broad-spectrum antiviral agent. After oral administration, MOV is converted into active NHC (NHC triphosphate), which is incorporated into the viral RNA genome during its replication. This leads to an accumulation of RNA mutations that ultimately inhibits SARS-CoV-2 propagation. Due to the oral bioavailability and potent antiviral activity against SARS-CoV-2, MOV has been authorized as an antiviral COVID-19 treatment for emergency use. Based on in vitro and in vivo genotoxicity studies, MOV is considered to have a low risk for genotoxicity in clinical use. However, safety concerns still remain that MOV/NHC can cause mutations in host cells as well.

Thus, in this study, Miranda and colleagues evaluated the mutagenic effects of MOV in E. coli and of MOV and NHC in mouse lymphoma L5178Y cells and human lymphoblastoid TK6 cells by HiFi sequencing. HiFi sequencing is a technique that can generate nearly error-free consensus reads by repeatedly sequencing both strands of circular DNA molecules. They used HiFi sequencing to detect ultralow-frequency (10−8 mutations per base pair) substitution mutations of MOV/NHC in the whole genomes. In E. coli, MOV increased genome-wide mutation frequencies (MFs) in a dose-dependent manner. MOV mainly induced A:T → G:C transitions, which was consistent with the previous Ames test results showing that MOV was mutagenic to bacteria, particularly to A:T-sensitive strains. Like in E coli, MOV and NHC dose-dependently increased MFs in L5178Y and TK6 cells and the vast majority of both MOV- and NHC-induced mutations were A:T → G:C transitions. These results suggest that MOV and NHC have the same mechanisms of mutagenesis across both types of mammalian cells, as DNA mutagens.

Treatment with MOV reduces the high risk of progression to severe COVID-19, including hospitalization or death. Nonetheless, the potential harm coming from the risk of mutagenicity in humans is a matter of concern. The results of this study provide strong evidence that MOV and NHC are mutagenic to mammalian cells. It should be noted that the NHC exposure concentrations used for mammalian cells were comparable to those observed in the plasma of humans who received clinical doses of MOV. Therefore, further detailed studies and long-term observations are needed to clarify the potential mutagenic effects associated with the clinical use of MOV.

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