Abstract 6371: Identification of a lymphocyte activation gene-3-binding peptides using phage displayed-peptide libraries for cancer immunotherapy

Abstract

Abstract Treatment with immune checkpoint blockades against CTLA-4, PD-1, and PD-L1 is currently giving improved results to many cancer patients. Nevertheless, a significant proportion of cancer patients treated with immune checkpoint blockades are still largely unsatisfied with the benefits of these drugs. One of the reasons is that cancer cells also use other immune checkpoints such as lymphocyte activation gene-3 (LAG-3), T cell immunoreceptor with Ig and ITIM domains, and T-cell immunoglobulin and mucin-domain containing-3. In this study, we screened phage displayed-peptide libraries for peptides that selectively bind to LAG-3. After five rounds of screening, we selected a candidate peptide and named it LAG3Pep. LAG3Pep preferentially bound to human LAG-3-transfected HEK 293T cells over mock-transfected cells and phorbol myristate acetate/ionomycin/chloroquine-stimulated Jurkat T cells over unstimulated cells. LAG3Pep also bound to splenocytes isolated from tumor-bearing mice, suggesting the reactivity across human and mouse LAG-3. Pull-down assay of human recombinant LAG-3 protein using biotin-labeled LAG3Pep yielded a protein band of LAG-3. LAG3Pep showed a high-affinity binding to the LAG-3 protein in SPR assays. Pre-treatment of a LAG-3-blocking antibody competed the binding of LAG3Pep to stimulated Jurkat T cells. LAG3Pep inhibited the binding of the LAG-3 protein to THP-1 cells expressing HLA-DR, a well-known LAG-3 ligand. In addition, treatment of T-cells with LAG3Pep in combination with a PD-L1-blocking antibody recovered the secretion of IL-2 by T-cells which was suppressed by FGL-1, another ligand of LAG-3, secreted from HepG2 tumor cells in co-culture. Intravenous administration of LAG3Pep in combination with a PD-L1-blocking peptide showed an anti-tumor growth activity in the MC38 syngeneic mouse colon tumor model. These results show that LAG3Pep acts as LAG-3 blockade and, in combination with a PD-L1-blockade, could be a promising tool for cancer immunotherapy. Citation Format: Seok-Min Lee, Byungheon Lee. Identification of a lymphocyte activation gene-3-binding peptides using phage displayed-peptide libraries for cancer immunotherapy. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6371.