The adenosine analog prodrug ATV006 is orally bioavailable and has preclinical efficacy against parental SARS-CoV-2 and variants.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus driving the ongoing coronavirus disease 2019 (COVID-19) pandemic, continues to rapidly evolve. Because of the limited efficacy of vaccination in prevention of SARS-CoV-2 transmission and continuous emergence of variants of concern (VOCs), orally bioavailable and broadly efficacious antiviral drugs are urgently needed. Previously, we showed that the parent nucleoside of remdesivir, GS-441524, has potent anti-SARS-CoV-2 activity. Here, we report that esterification of the 5'-hydroxyl moieties of GS-441524 markedly improved antiviral potency. This 5'-hydroxyl-isobutyryl prodrug, ATV006, demonstrated excellent oral bioavailability in rats and cynomolgus monkeys and exhibited potent antiviral efficacy against different SARS-CoV-2 VOCs in vitro and in three mouse models. Oral administration of ATV006 reduced viral loads and alleviated lung damage when administered prophylactically and therapeutically to K18-hACE2 mice challenged with the Delta variant of SARS-CoV-2. These data indicate that ATV006 represents a promising oral antiviral drug candidate for SARS-CoV-2.

Remdesivir Metabolite GS-441524 Effectively Inhibits SARS-CoV-2 Infection in Mouse Models.

The outbreak of coronavirus disease 2019 (COVID-19) has resulted in a global pandemic due to the rapid spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). At the time of this manuscript's publication, remdesivir is the only COVID-19 treatment approved by the United States Food and Drug Administration. However, its effectiveness is still under question due to the results of the large Solidarity Trial conducted by the World Health Organization. Herein, we report that the parent nucleoside of remdesivir, GS-441524, potently inhibits the replication of SARS-CoV-2 in Vero E6 and other cell lines. Challenge studies in both an AAV-hACE2 mouse model of SARS-CoV-2 and in mice infected with murine hepatitis virus, a closely related coronavirus, showed that GS-441524 was highly efficacious in reducing the viral titers in CoV-infected organs without notable toxicity. Our results support that GS-441524 is a promising and inexpensive drug candidate for treating of COVID-19 and other CoV diseases.

The N-terminal ubiquitin-associated domain of Cezanne is crucial for its function to suppress NF-κB pathway.

Cezanne, a deubiquitinating cysteine protease (DUB) belonging to A20 subgroup of ovarian tumor (OTU) protein superfamily, functions as a negative regulator of NF-κB to attenuate NF-κB activation and to restrain pro-inflammatory transcription in response to TNF receptor (TNFR) signaling. It is the first documented OTU DUB that preferably disassembles Lys11-linked polyubiquitin chains and has been shown to regulate multiple cellular events including immune signaling, cell survival and tumor progression. Previous studies showed that in response to TNF stimulation, Cezanne is recruited to the activated TNFR complex to suppress the build-up of polyubiquitinated RIP1 signal by removing Lys63 polyubiquitin from RIP1. However, how is Cezanne recognized and recruited to TNFR complex is not clear yet. In this study, we characterized a ubiquitin-associated (UBA) domain in the N-terminal region of Cezanne and proved its activity to bind Lys63 polyubiquitin chain. By constructing a series of truncated and site-specific point mutants, we further localized the crucial binding sites for Lys63 polyubiquitin chains at Leu9 and Ser10 sites of Cezanne UBA domain. Mutation at these sites disrupted the recruitment of Cezanne to activated TNFR complex and dramatically reduced the inhibition of NF-κB activation by Cezanne. Our study demonstrated that the N-terminal UBA domain is crucial for the function of Cezanne during NF-κB activation. Cezanne is recognized and recruited into activated TNFR complex by specifically binding to polyubiquitinated signaling proteins after TNF stimulation through its N-terminal polyubiquitin binding site. This study sheds light on the molecular mechanism of negative regulation of NF-κB activation by Cezanne.