Molecule proves effective against Covid virus – 10/25/2023 – Science

The promising effects of a molecule called calpeptin S in combating Sars-CoV-2 infection were described by researchers from ICB-USP (Institute of Biomedical Sciences of the University of São Paulo) and collaborators in an article published this month in the journal Communications Biology.

In tests with hamsters, the treatment reduced the production of viral particles in the animal’s trachea after the fifth day of infection. In Vero cells (a line originating from monkey kidney and widely used as an experimental model), low concentrations of the compound (in the nanomolar range) were able to eliminate the viral load. In human cells, there was a reduction of up to 80% in the changes caused by viral invasion.

Calpeptin S is a variation of calpeptin – a calpain inhibitor molecule, a protein that uses calcium in the human body to accelerate the breakdown of water molecules, promoting chemical reactions. Calpeptin had already been studied for the treatment of various cancers and chronic diseases.

“In the case of Covid-19, the difference in relation to other drugs already approved or in a more advanced stage of development is that calpeptin not only attacks Mpro [proteína importante para a replicação do coronavírus] but also acts more intensely on cathepsin-L, one of the ways the coronavirus accesses human cells”, explained to the ICB-USP press office Edmarcia Elisa de Souza, researcher at the Unit for Drug Discovery laboratory, coordinated by professor Carsten Wrenger in the Department of Parasitology.

As Souza explains, cathepsin-L is one of the proteases responsible for the work of the lysosome – an organelle that digests and eliminates molecules that should not be used by the cell, such as virus molecules, for example. However, in the case of Covid-19, the effect is reversed. Viral particles that enter the cell are processed by cathepsin-L present in lysosomes, which ends up increasing the release of the virus, spreading it throughout the cells.

“As cathepsin-L is little subject to mutations, unlike the proteins of Sars-CoV-2 itself, this increases the inhibitory potential of the compound compared to other drugs.”

Based on the results of tests with Vero and human cells, validated by genetic and fluorescence microscopy assays, the researchers estimate that calpeptin S is even more potent in the human body.

Also according to Souza, the compound did not cause toxic effects in the cells tested. “There was doubt as to whether calpeptin could alter the structure of cathepsin-L and produce effects that could impair cell functionality, but this hypothesis was ruled out in our trials, which explains why the compound only proved toxic at much higher doses than than those necessary to eliminate viruses.”

In the next stage of the investigation, the researchers intend to evaluate whether calpeptin S maintains good performance against the omicron variant – as is expected to happen.

International project

Calpeptin was selected by German researchers based on a study published in 2021 in the journal Science. Among 35 competitors, it was the molecule that achieved the best performance in a screening carried out using X-ray crystallography tests. In the process, calpeptin was fused to the Mpro protein.

Despite showing good results, the molecule remained in organisms for a short time, which reduced its effectiveness. From this, to enhance the drug’s action, the researchers developed a new molecule, calpeptin S, which is fused with a molecule originating from sulfur. “We compared calpeptin S with the original calpeptin in ICB and confirmed that the new molecule was effective in combating the virus”, said the researcher.

Next, several enzymatic and X-ray crystallography assays were carried out to evaluate which of the seven cathepsin variations (which exist in the human body and are responsible for spreading the virus in cells) calpeptin S interacted with best and how the interaction would work. between them and Mpro.

The investigation received funding from Fapesp through six projects (15/26722-8, 20/12277-0, 20/07251-2, 20/09149-0, 22/01812-8 and 21/02736-0) and was carried out in collaboration with researchers from the University of Hamburg and Desy (Deutsches Elektronen-Synchrotron), both in Germany. Research groups from the Cellular and Developmental Biology and Microbiology departments at ICB-USP also participated.

The potential of the drug against Sars-CoV-2 was identified by German scientists. The tests to validate the action of the compound against the virus in animal models and cells were carried out in the BSL3 Cell Culture Facility for Vector and Animal Research laboratory at ICB-USP, which has biosafety level three (NB3).

The human cell was provided by the Laboratory of Cellular and Molecular Biology, coordinated by professor Glaucia Maria Machado-Santelli, from the Department of Cellular and Developmental Biology; the viruses were provided by the Clinical and Molecular Virology Laboratory, coordinated by professor Edison Durigon, professor of Microbiology; and the animal tests were carried out in conjunction with LaPam (Laboratory for Applied Research on Mycobacteria), coordinated by professor Ana Marcia de Sá Guimarães, also from Microbiology.

The article Calpeptin is a potent cathepsin inhibitor and drug candidate for Sars-CoV-2 infections can be read here.