Furin Inhibitors Block SARS-CoV-2 Spike Protein Cleavage to Suppress Virus Production and Cytopathic Effects

Cheng, Ya-Wen; Chao, Tai-Ling; Li, Chiao-Ling; Chiu, Mu-Fan; Kao, Han-Chieh; Wang, Sheng-Han; Pang, Yu-Hao; Lin, Chih-Hui; Tsai, Ya-Min; Lee, Wen-Hau; Tao, Mi-Hua; Ho, Tung-Ching; Wu, Ping-Yi; Jang, Li-Ting; Chen, Pei-Jer; Chang, Sui-Yuan; Yeh, Shiou-Hwei

Development of specific antivirals is an urgent unmet need for SARS-coronavirus 2 (SARS-CoV-2) infections. This study focuses on host proteases that proteolytically activate the SARS-CoV-2 spike protein, critical for its fusion after binding to angiotensin-converting enzyme 2 (ACE2), as antiviral targets. We first validated cleavage at a putative furin substrate motif at SARS-CoV-2 spike by expressing it in VeroE6 cells and found prominent syncytium formation. Both cleavage and syncytium were abolished by treatment with furin inhibitors decanoyl-RVKR-chloromethylketone (CMK) and naphthofluorescein but not by transmembrane protease serine 2 (TMPRSS2) inhibitor camostat. CMK and naphthofluorescein showed antiviral effects in SARS-CoV-2-infected cells by decreasing viral production and cytopathic effects. Further analysis revealed that, similar to camostat, CMK blocks virus entry, but it further suppresses the cleavage of spike and syncytium. Naphthofluorescein instead acts primarily by suppressing viral RNA transcription. Therefore, furin inhibitors may become promising antivirals for prevention and treatment of SARS-CoV-2 infections.