Abstract

Colorectal cancer (CRC) remains one of the most prevalent and malignant cancers worldwide. Although various therapeutic strategies have been developed, CRC patients often exhibit poor responses. The combination of chemotherapy with immune checkpoint inhibitors represents a promising new treatment approach. However, pervasive drug resistance and significant interindividual variability in treatment efficacy remain major challenges, highlighting the urgent need to elucidate the underlying molecular mechanisms for improved therapy. In this study, we demonstrated that gemcitabine (GEM) exerts therapeutic effects against CRC. Notably, when combined with an anti-PD-L1 immune checkpoint inhibitor, GEM synergistically enhanced antitumor immunity, as evidenced by an increased infiltration of CD8+ T cells. Additionally, the population of anti-tumor IFN-γ and TNF-α-producing CD8+ T cells was elevated. We also observed significantly upregulated PD-L1 expression in both human and mouse CRC cell lines (HCT116, MC38, and CT26) following GEM treatment, which was further confirmed at the cell surface level. Mechanistically, GEM was found to stimulate lactate metabolism and promote lactylation of the PD-L1 protein, which could be reversed by inhibiting lactate dehydrogenase or pyruvate kinase. Furthermore, GEM delayed the degradation of PD-L1 protein confirmed by cycloheximide treatment. In addition, we also identified increased lactylation of H3 upon GEM treatment, suggesting transcriptional activation of PD-L1. Together, our findings provide novel insights into the mechanism of GEM in CRC treatment and support the future development of combined chemo-immunotherapeutic strategies.