α-ketoglutarate/succinate ratio imbalance impairs thymine DNA glycosylase function and base excision repair process increasing susceptibility to pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal cancer, with chronic metabolic disorders increasing risk and severity. Prolonged exposure to altered metabolism changes specific metabolite levels, impacting epigenetic landscape contributing neoplastic lesion acquisition. This study examines the interplay between metabolism and epigenetics in dysmetabolic-driven PDAC tumorigenesis, exploiting LSL-KrasG12D;PDX-1-Cre mice (KC mice) exposed to high-fat diet (HFD) and KRAS-mutated human pancreatic ductal epithelial (HPDE) cells. Untargeted metabolomics of HFD-fed KC pancreata reveals altered free fatty acid and elevated S-adenosyl methionine levels during tumorigenesis. Targeted metabolomics shows increased succinate alongside reduced α-ketoglutarate levels. This imbalance suggests an epigenetic derangement, targeting DNA methylation. In KRAS-mutated HPDE cells exposed to altered metabolism, the DNA demethylation complex of ten-to-eleven-translocation methylcytosine 1 and thymine DNA glycosylase (TDG) is disrupted, leading to iterative cytosine modification and apurinic/apyrimidinic (AP) site accumulation. Succinate directly binds TDG at arginine 275, hyperactivating it and increasing AP site formation. This alteration combined with the methylation-prone metabolic environment, impairs the base excision repair pathway by hypermethylating and downmodulating DNA ligases LIG1 and LIG3. This predisposes to genomic instability and pancreatic preneoplastic lesion development. These findings uncover a metabolic-epigenetic axis in dysmetabolic PDAC, highlighting how metabolite-driven epigenetic changes compromise DNA repair and drive tumorigenesis.