Abstract
The clinical efficacy of immune checkpoint inhibitors (ICIs) in colorectal cancer (CRC) remains limited. Modulation of the glucagon-like peptide-1 receptor (GLP-1R) may enhance T-cell-mediated antitumor responses. The present study aimed to evaluate the antitumor effects of the GLP-1R antagonist Exendin 9-39 (Exe-9) combined with anti-programmed cell death protein-1 (PD-1) treatment in preclinical CRC models. Using in vitro co-culture assays, ELISA and in vivo murine models, alongside immunohistochemical and molecular analyses of clinical samples, HT-29 and MC38-OVA colon cancer cell lines were co-cultured in vitro with activated T cells in the presence of Exe-9. In vivo, male BALB/c mice were injected with MC38 to establish a CRC model and nude mice were used to assess T-cell dependency. To evaluate this synergistic effect, BALB/c mice with CRC were treated with Exe-9, anti-PD-1 or a combination. Additionally, clinical CRC samples were analyzed to assess the association of GLP-1R expression with the immunotherapy response. Exe-9 significantly enhanced T-cell-mediated cytotoxicity in CRC cell lines and reduced tumor growth in immunocompetent CRC mice; however, this effect was not observed in nude mice. Furthermore, combination therapy with the GLP-1R antagonist and anti-PD-1 yielded an improved antitumor effect compared with either treatment alone, and high GLP-1R ex2pression in clinical samples correlated with poor ICI response. These findings suggest that GLP-1R antagonism potentiates T-cell-mediated antitumor immunity and may provide a promising adjunctive therapeutic strategy for patients with CRC when combined with ICIs in the future.