Abstract Breast cancer is the most frequently diagnosed cancer and the leading cause of cancer death in females worldwide. Early cancer detection and tumors molecular characterization are the key measures for effective therapy. Molecular changes associated with tumor development are detected by the immune system and reflected with specific antibody production. We used microarrays containing 120K of peptides with random amino acid sequences to analyze the repertoire of circulating antibodies in the blood plasma of patients with early stages of breast cancer (BC). Previously we have shown that healthy donors and BC patients have distinct circulating antibody repertoires. Further analysis reviled that BC patients with various progesterone receptor (PR) expression levels also have circulating antibodies reacting with different peptides (mimotopes) on microarrays. In this study we selected 61 peptides from 120K peptides presented on microarrays that show statistically significant difference for the interaction with the circulating antibodies of blood plasma from PR+ and PR- BC patients. Peptides interacting with PR+ and PR- patients plasma have common amino acid motifs suggesting that patients with tumors expressing different PR levels mount specific immune response reflecting molecular changes associated with various tumor subtype. Therefore, the panel of peptides that specifically interact with the immunoglobulins of patients with different PR expression can be used for the development of non-invasive test systems. Thus, peptide microarrays can be used to create a new tool for studying the repertoire of circulating antibodies for different diseases evaluation. Supported by grant FZMW-2020-0007. Supported by grants from the Ministry of Science and Higher Education of the Russian Federation (FZMW-2020-0007)

Discovery of the B7 family immune checkpoints such as CTLA-4 (CD152), PD-1 (CD279), as well as their ligands B7-1 (CD80), B7-2 (CD86), B7-H1 (PD-L1, CD274), and B7-DC (PD-L2, CD273), has opened new possibilities for cancer immunotherapy using monoclonal antibodies (mAb). The blockade of inhibitory receptors (CTLA-4 and PD-1) with specific mAb results in the activation of cancer patients' T lymphocytes and tumor rejection. However, the use of mAb in clinics has several limitations including side effects and cost of treatment. The development of new low-molecular compounds that block immune checkpoints' functional activity can help to overcome some of these limitations. In this paper, we describe a synthetic peptide (p344) containing 14 amino acids that specifically interact with CTLA-4 protein. A 3D computer model suggests that this peptide binds to the 99MYPPPY104 loop of CTLA-4 protein and potentially blocks the contact of CTLA-4 receptor with B7-1 ligand. Experimental data confirm the peptide-specific interaction with CTLA-4 and its ability to partially block CTLA-4/B7-1 binding. The identified synthetic peptide can be used for the development of novel immune checkpoint inhibitors that can block CTLA-4 functional activity for cancer immunotherapy.

Changes in the repertoire of circulating antibodies is a promising biomarker for various diseases. We have developed microarrays containing more than thousands of peptides with random amino acid sequences that can be used to analyze the entire repertoire of circulating antibodies. Using these peptide microarrays, we have shown that in the blood of patients diagnosed with breast cancer (BC) antibodies interacting with certain peptides are found. Moreover, circulating antibodies of patients with different molecular subtypes of BC (luminal A, luminal B and Basal-like) interact with different, but overlapping, panels of peptides. We have selected 634 peptides from 120K peptides presented on microarrays that specifically interact with circulating antibodies of blood plasma from patients with various subtypes of BC. This panel of peptides that specifically interact with the blood plasma immunoglobulins of patients with various molecular BC subtypes can be used for the development of non-invasive diagnostic test systems. Microchips containing thousands of peptides can be used as a tool for molecular screening populations at risk for various diseases. Thus, peptide microarrays can be used to create a new tool for studying the repertoire of circulating antibodies for different diseases evaluation, as well as for studying and evaluating protein-protein interactions.

Current advances in research of immune checkpoints CTLA-4, PD-1, PD-L1, opened new possibilities for effective cancer immunotherapy using monoclonal antibodies. However, antibodies have a number of limitations for clinical use, which provides a basis for the search for low molecular weight compounds capable of regulating (blocking) molecules that inhibit the immune response. This paper presents the results of molecular docking and evaluation of synthetic peptide interaction with a CTLA-4 molecule. Using mathematical modeling, it was shown that peptides interacted with the 99MYPPPY104 loop of the CTLA-4 protein and could potentially block the interaction of the CTLA-4 receptor with its natural ligand B7-1. The specificity of the interaction between the identified peptide and recombinant chimeric CTLA-4 protein was evaluated. The detected synthetic peptide can be used for the development of immunomodulatory drugs for therapy of cancer or autoimmune diseases.

Current strategy for the blockade of molecules inhibiting T-cell immunity, the immune checkpoints (ICP), such as CTLA-4, PD-1, and B7-H1(PD-L1), using monoclonal antibodies (mAbs), showed significant clinical effects in cancer immunotherapy. In this kind of therapy, antibodies do not kill tumor cells directly, but block inhibitory signals for T lymphocytes, resulting in activation of the immune response cascade that eliminate malignant cells and lead to tumor degradation. However, the mAb preparations have some limitations, and the development of new low-molecular-weight antagonists (for example, peptides) is an important issue. In this study, we used peptide microarrays and phage display libraries to search for peptides that interact with the immune checkpoints. We found peptides that specifically bind CTLA-4, PD-1, B7-1, B7-2 and B7-H1(PD-L1) which play important role in the regulation of the immune responses. These synthetic peptides can be applied to the development of new immunomodulating drugs for cancer immunotherapy.

Members of B7-CD28 family ligands and receptors play the important role in the co-stimulation and inhibition of the T-cell mediated immune response. Blocking of the B7 family molecules inhibiting the immune response (also called immunological checkpoints), CTLA4 and PD-1 / PD-L1 promoted to important therapeutic achievements in cancer immunotherapy and improved survival of cancer patient. The recent discovery of new B7 family molecules (such as B7-H3 [CD276], B7-H4 [B7S1 / B7x / Vtcn1], B7-H5 [VISTA / PD-1H / GI24], B7-H6 and B7-H7 [HHLA2]) has expanded therapeutic possibilities for the management of cancer patients. In this article, we discuss the clinical application of known blockers of immunological checkpoints and the prospects for the use of newly discovered molecules.

The blood serum of tumor patients contains antibodies recognizing tumor-associated antigens and other molecular products of tumor growth. We studied the interaction of blood antibodies from breast cancer patients with synthetic peptides that were applied on the microchip surface. The serum from healthy volunteers and breast cancer patients was shown to contain antibodies that interact with various peptides. Statistically significant between-group differences were observed in the level of binding with 122 informative peptides (0.01% of the total number of peptides on a microchip). Analysis of antibodies that interact with the peptide panel holds much promise for the diagnostics of breast cancer.