Study reveals strategy for novel treatment of aggressive type of breast cancer

Triple-negative breast cancer grows rapidly and is highly likely to metastasize. Experiments with mice identified a molecule that binds to a defense cell receptor and activates an immune response against the tumor.

By Luciana Constantino  |  Agência FAPESP – The findings of a study involving mouse cells point to a promising line of research to develop a treatment for triple-negative breast cancer (TNBC), an aggressive tumor with a high probability of metastasis.

A group of researchers led by Brazilians Renata Pasqualini, a biochemist, and Wadih Arap, an oncologist, have identified a peptide (CSSTRESAC) capable of binding to an alternative vitamin D receptor (PDIA3) found in the membranes of macrophages, an important type of immune cell that can infiltrate TNBC tumors and cause immunosuppression.

According to an article on the study published in the journal eLife, systemic administration of CSSTRESAC to mice with TNBC led to intense expression of anti-tumor cytokines and cell response modulation, both of which activated the immune system and reduced tumor growth. 

“Our strategy is different, and undoubtedly complements more conventional approaches. Instead of treating tumor cells directly, we use CSSTRESAC to modulate and induce a more efficient immune response. This strategy, in conjunction with surgery, chemotherapy and radiation therapy, could offer a more robust alternative for treating TNBC, which is usually very aggressive and hard to control locally and systemically,” Pasqualini told Agência FAPESP.

The conclusions are based on an experimental murine model, she notes, but the results are promising. “We still have a long way to go until we get to phase I clinical trials in human patients, but the published results are promising and justify advancement of this research line toward clinical translation studies in the next phase,” she said.

Pasqualini and Arap are currently leading a laboratory at Rutgers University in New Jersey (USA). A third of the article’s authors are Brazilian, including first author Fernanda Iamassaki Staquicini, who was awarded a scholarship by FAPESP in the early 2000s.

The research was also supported by FAPESP via two projects (12/24105-3 and 20/13562-0) for which the principal investigator is Mauro Javier Cortez Véliz, a professor in the Department of Parasitology at the University of São Paulo’s Biomedical Sciences Institute (ICB-USP) in Brazil.

Breast cancer

Breast cancer is the second most common type of cancer worldwide, with an estimated 2.3 million new cases per year. It accounts for almost 25% of cancer cases in women and is the most frequent cause of death from cancer among women, causing an estimated 684,000 deaths per year. Between 10% and 20% of breast cancers are triple-negative depending on the diagnostic criteria.

In Brazil, breast cancer is the most common type of cancer among women in all regions, except non-melanoma skin cancer. Its frequency is highest in the South and Southeast, according to the National Cancer Institute. In 2021, the number of new cases nationwide was estimated to be 66,280 (43.7 per 100,000 women). It is also the leading cause of death from cancer among Brazilian women.

TNBC is considered aggressive, typically large in size at onset and tending to grow rapidly, with strong chances of metastasis. Recurrence is more likely than for most other types of breast cancer, even after treatment. It is diagnosed by means of tests to detect cancer cells. It is termed triple-negative because the cancer cells lack estrogen and progesterone receptors, and test negative for the protein HER2.

Metastatic spread usually occurs by means of the elimination of tumor-infiltrating lymphocytes (immune cells) and secretion of immunoinhibitory cytokines, mainly by tumor-associated macrophages. Because of the larger number of tumor-infiltrating lymphocytes, TNBC is more likely to respond to immunotherapy, and this led the researchers to investigate the immunoregulatory functions mediated by the peptide CSSTRESAC.

Novel technique

In the study, the group used a technique known as in vivo phage display to isolate peptides found in the tumor as a strategy for non-malignant target discovery. The technique captures proteins or protein fractions that interact with target molecules.

In this manner, they identified the cyclic peptide CSSTRESAC, which binds to protein disulfide-isomerase A3 (PDIA3), a vitamin D receptor expressed on the surface of tumor-associated macrophages (TAM).

“Systemic administration of CSSTRESAC in TNBC-bearing mice shifted the cytokine profile toward an anti-tumor immune response and delayed tumor growth. Moreover, CSSTRESAC enabled ligand-directed theranostic delivery to tumors, and a mathematical model confirmed our experimental findings,” the researchers write in the article.

Theranostics – a portmanteau of therapeutics and diagnostics – is a novel approach that combines the use of a radioactive drug to identify diagnose a tumor and a second radioactive drug to deliver therapy.

“Our next step will be to investigate the integration of this strategy with approved therapies already used to treat TNBC,” Staquicini said. “Radiation therapy, for example, is effective in the near term but remains frustrating because of frequent local recurrence or metastasis in other organs. Radiation therapy combined with our peptide seems likely to improve the prognosis of patients by means of local tumor control.”

The members of the group began collaborating several years ago. In a project conducted at ICB-USP, for example, they showed how Leishmania exploits signaling pathways of endosomal toll-like receptors via TLR9 (which recognizes unmethylated DNA of pathogens such as bacteria, viruses and parasites) to inhibit the microbicidal function of macrophages, fostering their intracellular proliferation in the host. An article on the study was published in 2019 in The Journal of Clinical Investigation Insight. 

The laboratory headed by Pasqualini and Arap is internationally recognized for its work on vascular biology, progression mechanisms in various types of cancer, and development of innovative therapeutic approaches. A particularly significant point is the potential clinical relevance of molecules with therapeutic effect delivered to target cells, heightening biological activity and reducing side-effects.

The ability to map molecular markers in accordance with the concept of “postcodes” in blood vessels throughout the human body has been developed for two decades by the group and by scientists in other research centers. These “postcodes” are part of a molecular mapping technology that assures drug delivery solely to target cells without affecting neighboring tissue.

The article “Targeting a cell surface vitamin D receptor on tumor-associated macrophages in triple-negative breast cancer” is at: elifesciences.org/articles/65145.