Calpeptin is a potent cathepsin inhibitor and drug candidate for SARS-CoV-2 infections (preprint)

Several drug screening campaigns identified Calpeptin as a drug candidate against SARS-CoV-2. Initially reported to target the viral main protease (Mpro), its moderate activity in Mpro inhibition assays hints at a second target. Indeed, we show that Calpeptin is an extremely potent cysteine cathepsin inhibitor, a finding additionally supported by X-ray crystallography. Cell infection assays proved Calpeptin’s efficacy against SARS-CoV-2. Treatment of SARS-CoV-2-infected Golden Syrian hamsters with sulfonated Calpeptin at a dose of 1 mg/kg body weight significantly reduces the viral load in the trachea. Our results show that the inhibition of cathepsins, a protein family of the host organism, is a promising approach for the treatment of SARS-CoV-2 and potentially other viral infections. An intrinsic advantage in targeting host proteins is their mutational stability in contrast to highly mutable viral targets.

A novel insight on SARS-CoV-2 S-derived fragments in the control of the host immunity (preprint)

Despite all efforts to combat the pandemic of COVID-19, we are still living with high numbers of infected persons, an overburdened health care system, and the lack of an effective and definitive treatment. Understanding the pathophysiology of the disease is crucial for the development of new technologies and therapies for the best clinical management of patients. Since the manipulation of the whole virus requires a structure with an adequate level of biosafety, the development of alternative technologies, such as the synthesis of peptides from viral proteins, is a possible solution to circumvent this problem. In addition, the use and validation of animal models is of extreme importance to screen new drugs and to compress the organism's response to the disease. Peptides derived from recombinant S protein from SARS-CoV-2 were synthesized and validated by in silico, in vitro and in vivo methodologies. Macrophages and neutrophils were challenged with the peptides and the production of inflammatory mediators and activation profile were evaluated. These peptides were also inoculated into the swim bladder of transgenic zebrafish larvae at 6 days post fertilization to mimic the inflammatory process triggered by the virus, which was evaluated by confocal microscopy. In addition, toxicity and oxidative stress assays were also developed. In silico and molecular dynamics assays revealed that the peptides bind to the ACE2 receptor stably and interact with receptors and adhesion molecules, such as MHC and TCR, from humans and zebrafish. Macrophages stimulated with one of the peptides showed increased production of NO, TNF-α and CXCL2. Inoculation of the peptides in zebrafish larvae triggered an inflammatory process marked by macrophage recruitment and increased mortality, as well as histopathological changes, similarly to what is observed in individuals with COVID-19. The use of peptides is a valuable alternative for the study of host immune response in the context of COVID-19. The use of zebrafish as an animal model also proved to be appropriate and effective in evaluating the inflammatory process, comparable to humans.

Photobiomodulation reduces the cytokine storm syndrome associated with Covid-19 in the zebrafish model (preprint)

This work presents the first study showing how photobiomodulation (PBM) significantly increases cellular and tissue repair and elucidating the role of PBM with low-level laser as a possible new therapy in pathologies in COVID-19-associated cytokine storm syndrome from a zebrafish model. Our results demonstrate new strategies for treating SARS-COV-2 using PBM to modulate the expression of the genes and metabolites involved in inflammatory processes. These metabolic alterations show that the r-Spike led to disturbance in the energetic and inflammatory system, corroborating with the severe clinical conditions of human patients. Furthermore, PBM decreased the gene expression levels of pro-inflammatory cytokines such as il1b, il6, tnfa, and nfkbiab, and of factors involved in oxidative stress (romo1) and energy metabolism (slc2a1a, coa1), in various tissues, promoting an anti-inflammatory response. In summary, our study suggests that PBM may have a positive role in treating cytokine storm syndrome associated with COVID-19. PBM can significantly regulate the inflammatory response promoting cellular and tissue repair of injured tissues. This work suggests that PBM may have a positive role in treating COVID-19-associated cytokine storm syndrome. Nevertheless, the need for more clinical trials remains, and there is a significant gap to overcome before clinical trials.