Repurposing cepharanthine as a radiosensitizer in esophageal squamous cell carcinoma through dual metabolic intervention and direct targeting of p70s6K.

BACKGROUND

Metabolic reprogramming underpins the acquisition of radioresistance in esophageal squamous cell carcinoma (ESCC); however, the specific bioenergetic vulnerabilities and direct pharmacological targets remain to be fully elucidated. This study defines a distinct metabolic phenotype conferring radioresistance and evaluates the natural alkaloid Cepharanthine (CEP) as a mechanism-driven radiosensitizer.

METHODS

Matched clinical cohorts of radiosensitive and radioresistant ESCC patients were analyzed using widely-targeted and targeted metabolomics. Bioenergetic profiling (ECAR/OCR) was performed on established isogenic radioresistant cells. The mechanistic interactions between CEP and its target were mapped via network pharmacology, surface plasmon resonance (SPR), cellular thermal shift assays (CETSA), ubiquitin-proteasomal degradation assays, and Q347A site-directed mutagenesis. In vivo efficacy was validated across human cell-derived xenografts (CDX) and immunocompetent syngeneic (AKR/C57BL/6) mouse models.

RESULTS

Clinical multi-omics revealed a "metabolic duality" in radioresistant ESCC, characterized by the concurrent hyperactivation of glycolysis and oxidative phosphorylation (OXPHOS). CEP administration disrupted this metabolic network, significantly sensitizing ESCC cells to irradiation [Dose-modifying factor at 37% survival (DMF37) > 1]. Mechanistically, CEP directly engages the kinase domain of p70S6K-a structural interaction dependent on the Q347 residue-and triggers its ubiquitin-proteasomal degradation. This targeted clearance disrupts the upstream PI3K/Akt/mTOR survival axis. Genetic overexpression of wild-type p70S6K, but not the Q347A mutant, rescued the dual hypermetabolic phenotype and reinstated radioresistance. Clinically, elevated p70S6K expression correlated with poor disease-free survival and therapeutic failure. In vivo, CEP synergized with radiotherapy to suppress tumor kinetics in both CDX and syngeneic models, while concurrently enhancing CD8+ T cell infiltration in the immunocompetent microenvironment, with no observable systemic toxicity.

CONCLUSIONS

Radioresistant ESCC relies on a dual hypermetabolic state driven by the PI3K/Akt/mTOR/p70S6K cascade. CEP overcomes this radioresistance by physically binding to and degrading p70S6K, thereby inducing bioenergetic exhaustion and reshaping the anti-tumor microenvironment. These findings provide a solid mechanistic rationale for translating CEP into clinical radiotherapeutic regimens.