Dysmetabolic-dependent α-ketoglutarate/succinate ratio imbalance impairs TDG function and base excision repair process increasing susceptibility to pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is a high lethal cancer with poor prognosis and lack of effective therapeutic options. Chronic metabolic disorders, including obesity and type 2 diabetes, are established risk factors for PDAC and contribute to its unfavorable prognosis. Prolonged exposure to altered metabolic states induces aberrant fluctuations in specific metabolites, which can impact the epigenetic landscape and facilitate the acquisition of neoplastic lesions. Indeed, certain metabolites function as cofactors for epigenetic enzymes, modulating their activity. In this study, we explored the interplay between metabolism and epigenetics in PDAC tumorigenesis under dysmetabolic conditions, aiming to uncover novel vulnerabilities in pancreatic cancer. The link between dysmetabolism and PDAC was examined in LSL-KrasG12D; PDX-1-Cre mice (KC mice) exposed to high-fat diet (HFD). Untargeted metabolomic analysis of pancreatic tissue revealed altered free fatty acid levels and elevated S-adenosyl methionine (SAM) during tumor development in HFD-fed mice. Targeted metabolomics further showed increased succinate (SA) levels alongside reduced α-ketoglutarate (αKG) levels, indicating dysregulation of the DNA methylation pathway. Given these findings, the DNA demethylation complex of ten-to-eleven-translocation methylcytosine 1 (TET1) and thymine DNA glycosylase (TDG) was further investigated in human pancreatic ductal epithelial cells bearing KRAS mutation exposed to dysmetabolic mimicking culture conditions. We demonstrated that dysmetabolic stress disrupts quickly TET1/TDG function, leading to accumulation of iterative cytosine modifications, including 5-formylcytosine (5fC), and increased apurinic/apyrimidinic (AP) sites. Specifically, AP site accumulation was a consequence of TDG hyperactivation induced by direct binding of SA on its arginine residue 275. This TDG alteration, together with the methylation-prone metabolic environment, impairs the base excision repair (BER) pathway by hypermethylation of the promoters of DNA ligases 1 (LIG1) and 3 (LIG3) and thus inducing their downregulation. The resulting inhibition of single-strand break repair predisposes to genomic instability and promotes pancreatic preneoplastic lesion development. Our results reveal an unprecedented role of metabolic-epigenetic crosstalk in dysmetabolism-driven PDAC tumorigenesis. These findings highlight TDG as a novel therapeutic target and propose 5fC and AP sites as potential biomarkers for pancreatic cancer.