LAUSR

Lymphocyte activation gene-3 (LAG-3) has emerged as a promising target for cancer immunotherapy. It is expressed on activated CD4+ and CD8+ T cells, and on the surface of B cells, natural killer cells, and dendritic cells (DC). It has also been found to be highly expressed on activated T cells upon treatment with monoclonal antibodies targeting the PD-1/PD-L1 pathway, which may explain the resistance mechanism of monotherapy. Several anti-LAG-3 antibodies are being examined in clinical trials to treat different types of cancers. Despite their specificity and affinity, antibody-based checkpoint inhibitors are hampered by poor tumor permeability and high production costs. In this study, we aimed to discover a small peptide-based anti-LAG-3 inhibitor using a novel biopanning technique developed in our laboratory. We discovered several anti-LAG-3 inhibitor peptides, and the CMA16 peptide showed the highest stability and blocking efficacy. The peptides were synthesized by the solid-phase peptide synthesis using PurePepTM Chorus synthesizer (Gyros Protein Technologies, Tucson, AZ). The molecular weights and purity were confirmed by mass spectrometry and HPLC, respectively. To evaluate the function of the CMA16 peptide, a series of in vitro functional assays including binding ELISA, serum stability and cell viability assays were performed. In vivo anti-tumor activity of the peptides was examined in five-week-old C57BL/6 mice bearing MC38 cells. CMA16 significantly inhibited the growth of MC38 tumors. Quantification of CD8+ tumor-infiltrating cells revealed a significant increase in this type of immune cells in the group of mice treated with CMA16. These findings support the further development of the CMA16 peptide as potential anti-LAG-3 inhibitor for cancer immunotherapy. Citation Format: Mohammed Alahmari, Umar-Farouk Mamani, Yuhan Guo, Chien-Yu Lin, Mohammed Nurudeen Ibrahim, Yongren Li, Kun Cheng. A small molecular-weight anti-lag-3 peptide inhibits colon tumor growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB194.