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-Cys11, Lys12,Lys13-(pBthTX-I)2K ((pBthTX-I)2K)) and derivatives against SARS-CoV-2 are reported. The lead peptide (pBthTX-I)2K and derivatives showed attractive inhibitory activities against SARS-CoV-2 (EC50 = 28-65 µM) and mostly low cytotoxic effect (CC50 > 100 µM). To shed light on the mechanism of action underlying the peptides' antiviral activity, the Main Protease (Mpro) and Papain-Like protease (PLpro) inhibitory activities of the peptides were assessed. The synthetic peptides showed PLpro inhibition potencies (IC50s = 1.0-3.5 µM) and binding affinities (Kd = 0.9-7 µM) at the low micromolar range but poor inhibitory activity against Mpro (IC50 > 10 µM). The modeled binding mode of a representative peptide of the series indicated that the compound blocked the entry of the PLpro 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.

Synthesis and structure-activity relationship of nitrile-based cruzain inhibitors incorporating a trifluoroethylamine-based P2 amide replacement.

The structure-activity relationship for nitrile-based cruzain inhibitors incorporating a P2 amide replacement based on trifluoroethylamine was explored by deconstruction of a published series of inhibitors. It was demonstrated that the P3 biphenyl substituent present in the published inhibitor structures could be truncated to phenyl with only a small loss of affinity. The effects of inverting the configuration of the P2 amide replacement and linking a benzyl substituent at P1 were observed to be strongly nonadditive. We show that plotting affinity against molecular size provides a means to visualize both the molecular size efficiency of structural transformations and the nonadditivity in the structure-activity relationship. We also show how the relationship between affinity and lipophilicity, measured by high-performance liquid chromatography with an immobilized artificial membrane stationary phase, may be used to normalize affinity with respect to lipophilicity.

Antiviral Action against SARS-CoV-2 of a Synthetic Peptide Based on a Novel Defensin Present in the Transcriptome of the Fire Salamander (Salamandra salamandra).

The potential emergence of zoonotic diseases has raised significant concerns, particularly in light of the recent pandemic, emphasizing the urgent need for scientific preparedness. The bioprospection and characterization of new molecules are strategically relevant to the research and development of innovative drugs for viral and bacterial treatment and disease management. Amphibian species possess a diverse array of compounds, including antimicrobial peptides. This study identified the first bioactive peptide from Salamandra salamandra in a transcriptome analysis. The synthetic peptide sequence, which belongs to the defensin family, was characterized through MALDI TOF/TOF mass spectrometry. Molecular docking assays hypothesized the interaction between the identified peptide and the active binding site of the spike WT RBD/hACE2 complex. Although additional studies are required, the preliminary evaluation of the antiviral potential of synthetic SS-I was conducted through an in vitro cell-based SARS-CoV-2 infection assay. Additionally, the cytotoxic and hemolytic effects of the synthesized peptide were assessed. These preliminary findings highlighted the potential of SS-I as a chemical scaffold for drug development against COVID-19, hindering viral infection. The peptide demonstrated hemolytic activity while not exhibiting cytotoxicity at the antiviral concentration.