In preclinical in vitro and in vivo experiments, RB4 caused the necrosis of mouse melanoma cells and reduced the viability of human cancer cells. The tumor cells in the experiment lost the integrity of the plasma membrane, mitochondria (energy producing organelles) expanded, and even in the absence of chromatin condensation, which is a morphological marker of apoptosis. The researchers acknowledge that they still do not fully understand the cause of this necrosis.
The peptide also reduced lung metastasis and the development of subcutaneous melanoma in mice. The results showed that RB4 directly acted on the tumor, induced the expression of two damage related molecular patterns (damps), and led to the apoptosis of immune melanoma cells.
“In the search for new molecules, RB4 derived from protein lipoprotein 2[plp2] shows a preference for causing necrosis, which is a specific type of cell death, especially in melanoma, but how this necrosis occurs and develops is not clear. This article discusses some aspects of the morphological composition of the peptide and the final effect of contact with it,” the co-author Fabr í CIO Castro Machado told Ag ê ncia FAPESP.
Machado was a member of the experimental cancer group of the Department of Microbiology, immunology and Parasitology of the Federal University of Sao Paulo (unifesp) in Brazil. At present, Machado is a researcher of recepta biopharma (receptabio), a Brazilian biotechnology company that develops cancer drugs (hence “RB” in the polypeptide name).
With the support of FAPESP, a team led by Luiz rodolpho travassos, an honorary professor of unifesp, began the research. The author of this article pays tribute to travassos, who died in 2020. The latter has published more than 230 articles in authoritative scientific journals, many of which are about the research of peptides and peptidases (enzymes that decompose proteins into peptides and eventually into single amino acids) in infectious diseases and cancer. Because of this interest, he contacted receptabio in 2008. The CEO of the company is Jos é Fernando Perez, who is the former scientific director of FAPESP (1993-2005).
“Professor travassos identified the sequence and small molecules of several bioactive peptides based on the antibody developed by receptabio. RB4 was also found in the process of searching for new molecules, although it did not come from the antibody.” Alice Santana Morais, R & D analyst of receptabio and corresponding author of the article, said: “we have another rb9, which is in a more advanced research stage. There are several papers and patents, but it is still in the preclinical stage.
In 2016, scientists described the structure of rb9 and its mechanism of action as an inhibitor of melanoma cells. A recent article published in 2020 showed that rb9, as an immunomodulator, can be used to control tumor progression.
“Whether in academia or in companies like receptabio, we need to work together to conduct research.” “We are looking for partners to facilitate the drug development process, which is long and arduous and requires discussion, details and experience exchange,” Morais said
New cancer therapies developed in recent years include peptide based chemotherapy. Peptides have attracted more and more attention, not only because they can bind to the membrane of tumor cells, but also because of their low molecular weight, good permeability of cell tissues and low toxicity to normal tissues. They can be used as carriers of cellular reagents, ligands, vaccines and cytotoxic drugs, and as materials for peptide therapy alone or peptide binding.
In the study on the antitumor effect of RB4, the team found that the peptide interfered with the morphology, replication and association of b16f10-nex2 melanoma cells cultured in the laboratory. Compared with the control group, RB4 treated cells did not replicate and form clusters, and lost their natural morphology after up to 24 hours of culture.
In addition, RB4 reduced the number of lung metastatic nodules in a synthetic melanoma model involving tumor tissue from mice with the same genetic composition. This result was detected after melanoma cells were injected intravenously into mice. They were intraperitoneally injected with the peptide five times the next day (300 micrograms per animal), delaying tumor growth by 40 days. The survival rate of mice treated with RB4 was significantly higher than that of the control group, and the population survival rate increased by more than 25%, up to 10 days.
Melanoma originates from cells that produce melanin, the pigment that gives skin color. It can appear in all parts of the body. Although skin cancer is the most common form of cancer in Brazil, accounting for 30% of all cases, melanoma accounts for only 3% of malignant tumors. However, it is the most life-threatening because it is likely to spread to other organs (metastasis).
According to the National Cancer Institute (Inca), there are about 8400 melanoma cases in Brazil every year. The disease caused 1978 deaths in 2019.