TMPRSS2 and viral infectious disease: We further demonstrated that FBP could not significantly inhibit SARS-CoV-2 replication in Calu-3 cells, in which SARS-CoV-2 relied on TMPRSS2 but not on endocytosis for viral infection (Figure S11), which was consistent with the activity of FBP against SARS-CoV-2 by inhibiting endosomal acidification.