Lactate, as a critical byproduct of tumor metabolic reprogramming, plays an important role in DNA damage repair and tumor immune infiltration. This work aims to elucidate the molecular mechanisms by which lactate promotes tumor DNA damage repair (DDR) and subsequent immune evasion.

Hepatocellular carcinoma (HCC), lung adenocarcinoma (LUAD), and ovarian cancer (OC) cells with cisplatin-induced DNA damage were treated with lactate at a concentration gradient, Endothelial cell-specific molecule 1 (ESM1) shRNA, ESM1 overexpression plasmid, or the Protein Kinase B (AKT) Serine/Threonine Kinase 1 (Akt1) inhibitor LY294002. Proliferation, apoptosis, and DNA damage levels were assessed using 5-ethynyl-2^′-deoxyuridine (EdU) staining, flow cytometry-based apoptosis assay, and comet assay. Western blot (WB), Polymerase Chain Reaction (PCR), and immunofluorescence (IF) were employed to evaluate the effects of lactate on the expression of ESM1, Akt1, and Cyclic GMP-AMP Synthase (cGAS) pathway-related proteins in cancer cells. Xenograft tumor models were established using ESM1 whole-gene knockout mice, and Cluster of Differentiation 8 Positive (CD8+) T cell infiltration and apoptotic levels in tumors were detected via flow cytometry. Immunohistochemistry (IHC) was performed to examine the expression of ESM1, double-stranded DNA (dsDNA), and CD8 in tumor patient samples, followed by correlation analysis.

This study demonstrates that lactate increases ESM1 mRNA and protein expression in a concentration-dependent manner and reduces DNA damage in tumor cells. Lactate suppresses DDR by activating the Akt1 signaling pathway via ESM1 and further inhibits the cGAS pathway, thereby downregulating the transcription of chemokines and pro-inflammatory factors. In vivo experiments confirm that ESM1 knockout promotes CD8+ T cell infiltration into tumors and induces apoptosis. Analysis of tumor patient samples further validates the negative correlation between ESM1 and CD8+ T cell levels in cancer patients.

In summary, lactate activates the Akt1-Murine Double Minute 2 (MDM2)-p53 pathway via ESM1 to suppress DDR, while the reduction of DDR-generated dsDNA inactivates the cyclic GMP-AMP synthase–Stimulator of Interferon Genes (cGAS-STING) pathway, thereby inhibiting CD8+ T cell immune infiltration.