Cysteine protease inhibitor blocks SARS-CoV-2 infection of human and monkey cells

Drake Mellott, Chien-Te Tseng, Aleksandra Drelich, Pavla Fajtova, Bala C Chenna, Demetrios Kostomiris, Jason C Hsu, Jiyun Zhu, Zane Taylor, Vivian Tat, Ardala Katzfuss, Linfeng Li, Miriam A Giardini, Danielle Skinner, Ken Hirata, Sungjun Beck, Aaron F Carlin, Alex E. Clark, Laura Berreta, Daniel Maneval, Felix Frueh, Brett L Hurst, Hong Wang, Klaudia I Kocurek, Frank M Raushel, Anthony O'Donoghue, Jair L. Siqueira-Neto, Thomas D Meek, James H McKerrow

doi: https://doi.org/10.1101/2020.10.23.347534

This article is a preprint and has not been certified by peer review [what does this mean?].

PDF: https://www.biorxiv.org/content/10.1101/2020.10.23.347534v1.full.pdf

Abstract

K777 is a di-peptide analog that contains an electrophilic vinyl-sulfone moiety and is a potent, covalent inactivator of cathepsins. Vero E6, HeLa/ACE2, Caco-2, A549/ACE2, and Calu-3, cells were exposed to SARS-CoV-2, and then treated with K777. K777 reduced viral infectivity with EC50 values of inhibition of viral infection of: 74 nM for Vero E6, <80 nM for A549/ACE2, and 4 nM for HeLa/ACE2 cells. In contrast, Calu-3 and Caco-2 cells had EC50 values in the low micromolar range. No toxicity of K777 was observed for any of the host cells at 10-100 μM inhibitor. K777 did not inhibit activity of the papain-like cysteine protease and 3CL cysteine protease, encoded by SARS-CoV-2 at concentrations of ≤ 100 μM. These results suggested that K777 exerts its potent anti-viral activity by inactivation of mammalian cysteine proteases which are essential to viral infectivity. Using a propargyl derivative of K777 as an activity-based probe, K777 selectively targeted cathepsin B and cathepsin L in Vero E6 cells. However only cathepsin L cleaved the SARS-CoV-2 spike protein and K777 blocked this proteolysis. The site of spike protein cleavage by cathepsin L was in the S1 domain of SARS-CoV-2 , differing from the cleavage site observed in the SARS CoV-1 spike protein. These data support the hypothesis that the antiviral activity of K777 is mediated through inhibition of the activity of host cathepsin L and subsequent loss of viral spike protein processing.

Competing Interest Statement

The authors have declared no competing interest.

https://www.biorxiv.org/content/10.1101/2020.10.23.347534v1