Abstract

Purpose: Clinical studies have suggested a therapeutic synergy between EGFR-TKIs and radiotherapy; however, the underlying mechanisms remain incompletely understood, particularly in tumors harboring the acquired resistance mutation EGFR T790M. Methods: Using EGFR T790M-positive cell lines, patient-derived organoids (PDOs), and patient-derived xenograft (PDX) models, we systematically investigated radiation responses in EGFR T790M-mutant tumors. Metabolic profiling, protein interaction and phosphorylation analyses, enzyme activity assays, chromatin immunoprecipitation sequencing (ChIP-seq), and DNA damage repair assessments were performed to elucidate the molecular mechanisms of therapeutic synergy between EGFR-TKIs and radiotherapy. Results: We show that EGFR T790M drives a radiation-amplified glycolytic program characterized by enhanced intracellular lactate accumulation. Radiation induces EGFR-dependent tyrosine phosphorylation and activation of lactate dehydrogenase A (LDHA), sustaining lactate production. Rather than being rapidly exported or oxidized, lactate is retained intracellularly and promotes histone H3 lysine lactylation (H3Kla) at promoter regions of DNA repair genes, establishing a repair-permissive chromatin state. This epigenetic priming enhances repair complex assembly, accelerates recruitment of repair factors to DNA double-strand breaks, and facilitates efficient DNA damage resolution. Genetic or pharmacological disruption of the LDHA-lactate axis impairs DNA repair and restores radiosensitivity. In EGFR T790M PDX models, targeting this metabolic pathway significantly enhances radiotherapy efficacy with acceptable toxicity. Conclusions: Our findings identify a previously unrecognized metabolic-epigenetic-repair axis through which EGFR T790M promotes radiotherapy resistance. This study redefines the functional role of EGFR T790M in radiation biology, provides mechanistic insight into the clinical synergy between EGFR inhibition and radiotherapy,