Fig. 1: 4H30 showed antiviral activity against SARS-CoV-2 before and after virus challenge.

a Peptide sequences of H23, H26, H30, 2H30, 4H30, and reference HBD2. Peptide 2H30 and 4H30 were 2-branched and 4-branched H30 cross-linked by lysine at the C terminal of H30. b The antiviral activity of these peptides in the high salt concentration (150 mM, PBS) was determined by plaque reduction assay (n = 3). c The antiviral activity of these peptides against SARS-CoV-2 in the low salt concentration (30 mM, PBS/5) was determined by plaque reduction assay (n = 3). P values were generated by comparison with an untreated virus (0). d The antiviral activity of 2-branched H30 (2H30) and 4-branched H30 (4H30) against SARS-CoV-2 (HKU001a) in PBS was determined by plaque reduction assay (n = 4). e The cytotoxicity of 4H30 in VeroE6 and Calu-3 cells was measured by MTT assay (n = 3). f The antiviral activity of 4H30 was determined by anti-nucleocapsid (NP) immunofluorescent staining. SARS-CoV-2 with or without 4H30 treatment was added to cells for infection. Representative images were taken at 18 h post-infection (hpi) in VeroE6 cells. Scale bar, 20 μm. g The post-infection antiviral activity of 4H30 against SARS-CoV-2 (B.1.1.63, D614G) in VeroE6 and Calu-3 cells (n = 6). At 6 hpi, 4H30 (50 μg/mL) was added to infected cells and viral titers in cell supernatants were measured at 24 hpi (for VeroE6 cells) or 30 hpi (for Calu-3 cells). h The broad-spectrum antiviral activities of 4H30 against SARS-CoV-2 variants and MERS-CoV (MERS) in VeroE6 cells were determined by plaque reduction assay (n = 4). *P < 0.05 and **P < 0.01 when compared with DMEM. P values were calculated by the two-tailed Student’s t-test. Data were presented as means ± SD of indicated biological samples with more than two independent experiments.