An Oral Combination therapy against SARS-CoV-2 based on Synergistic Action of Auranofin and Remdesivir

Summary The combination of direct-acting and host-directed antivirals targeting SARS-CoV-2 represents an attractive treatment strategy to combat COVID-19. In our previous work, we showed that the FDA-approved anti-arthritis drug Auranofin restricts SARS-CoV-2 replication and pathology in an animal model. Here, we report that Auranofin inhibits SARS-CoV-2 by targeting viral entry and main protease (Mpro) activity without affecting viral transcription. Time-of-addition studies combined with functional assays of viral entry, protease activity, and cell–cell fusion delineated its inhibitory effects at both early and late stages of the viral life cycle. Molecular docking and isothermal titration calorimetry analyses of Auranofin and the known Mpro inhibitor Nirmatrelvir indicated competitive binding within the Mpro active-site pocket. In addition, Auranofin attenuated NF-κB-dependent signalling and suppressed proinflammatory cytokine production. Combination studies with SARS-CoV-2 targeting nucleoside analogues, revealed the strongest synergistic antiviral activity with remdesivir in vitro. Comparable synergy was observed between auranofin and GS-621763, the orally bioavailable derivative of remdesivir, and was further validated in a preclinical animal model. Collectively, these findings provide a rationale for the further development of auranofin-nucleoside analog combinations targeting SARS-CoV-2. Funding This research has been supported by ICMR (IIRPIG-2023-0000978) and BIRAC grant (BT/CS0070/06/22) to ST. We acknowledge the infrastructure and research support provided to IISc by the Crypto Relief Fund, L&T Trust, DST-FIST program, Institute of Eminence Fund, Ministry of Education, and the DBT-IISc partnership program (Phase II). RN acknowledges DBT-RA fellowship, SK acknowledges PMRF fellowship, and RS acknowledges FICCI-PMRF fellowship. Research in context Evidence before this study Multiple previous studies have provided evidence showing that auranofin is an antiviral agent targeting SARS-CoV-2 through a host-targeting mechanism, involving the inhibition of thioredoxin reductase and redox homeostasis. Mixed results have been reported regarding the effect of this drug on inhibiting virus-induced syncytia. A prior study from our lab demonstrated the drug’s effectiveness in reducing SARS-CoV-2 viral loads in both cell and animal models. Added value of the study Our study firmly establishes the synergistic use of Auranofin and Remdesivir GS 621763 in the treatment of SARS-CoV-2 infection.