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bioRxiv · 10.1101/2021.05.11.443555

Mechanism of molnupiravir-induced SARS-CoV-2 mutagenesis

Kabinger, F.·Stiller, C.·Schmitzova, J.·Dienemann, C.·Hillen, H. S.·Höbartner, C.·Cramer, P.
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Abstract

Molnupiravir is an orally available antiviral drug candidate that is in phase III trials for the treatment of COVID-19 patients1,2. Molnupiravir increases the frequency of viral RNA mutations3,4 and impairs SARS-CoV-2 replication in animal models4-6 and in patients2. Here we establish the molecular mechanisms that underlie molnupiravir-induced RNA mutagenesis by the RNA-dependent RNA polymerase (RdRp) of the coronavirus SARS-CoV-2. Biochemical assays show that the RdRp readily uses the active form of molnupiravir, {beta}-D-N4-hydroxycytidine (NHC) triphosphate, as a substrate instead of CTP or UTP. Incorporation of NHC monophosphate into nascent RNA does not impair further RdRp progression. When the RdRp uses the resulting RNA as a template, NHC directs incorporation of either G or A, leading to mutated RNA products. Structural analysis of RdRp-RNA complexes containing mutagenesis products shows that NHC can form stable base pairs with either G or A in the RdRp active center, explaining how the polymerase escapes proofreading and synthesizes mutated RNA. This two-step mutagenesis mechanism likely applies to various viral polymerases and can explain the broad-spectrum antiviral activity of molnupiravir.

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Kabinger, F., Stiller, C., Schmitzova, J., Dienemann, C., Hillen, H. S., Höbartner, C., Cramer, P.. 2021-05-11. Mechanism of molnupiravir-induced SARS-CoV-2 mutagenesis. https://doi.org/10.1101/2021.05.11.443555

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