Non-Toxic Dimeric Peptides Derived from the Bothropstoxin-I Are Potent SARS-CoV-2 and Papain-like Protease Inhibitors

The COVID-19 outbreak has rapidly spread on a global scale, affecting the economy and public health systems throughout the world. In recent years, peptide-based therapeutics have been widely studied and developed to treat infectious diseases, including viral infections. Herein, the antiviral effects of the lysine linked dimer des-Cys(11), Lys(12),Lys(13)-(pBthTX-I)(2)K ((pBthTX-I)(2)K)) and derivatives against SARS-CoV-2 are reported. The lead peptide (pBthTX-I)(2)K and derivatives showed attractive inhibitory activities against SARS-CoV-2 (EC(50) = 28–65 µM) and mostly low cytotoxic effect (CC(50) > 100 µM). To shed light on the mechanism of action underlying the peptides’ antiviral activity, the Main Protease (M(pro)) and Papain-Like protease (PL(pro)) inhibitory activities of the peptides were assessed. The synthetic peptides showed PL(pro) inhibition potencies (IC(50)s = 1.0–3.5 µM) and binding affinities (K(d) = 0.9–7 µM) at the low micromolar range but poor inhibitory activity against M(pro) (IC(50) > 10 µM). The modeled binding mode of a representative peptide of the series indicated that the compound blocked the entry of the PL(pro) substrate toward the protease catalytic cleft. Our findings indicated that non-toxic dimeric peptides derived from the Bothropstoxin-I have attractive cellular and enzymatic inhibitory activities, thereby suggesting that they are promising prototypes for the discovery and development of new drugs against SARS-CoV-2 infection.