Cucurbitacin B targets PPAT to suppress de novo purine biosynthesis in esophageal squamous cell carcinoma

Background: The de novo purine biosynthesis (DNPB) pathway is increasingly recognized as a key driver of tumor progression. Nevertheless, its precise role in regulating esophageal squamous cell carcinoma (ESCC) growth, radiosensitivity, and therapeutic response has not been fully elucidated.

Purpose: This study aimed to determine contribution of phosphoribosyl pyrophosphate amidotransferase (PPAT), the rate-limiting enzyme of the DNPB pathway, in ESCC progression and potential therapeutic benefit of PPAT-targeted intervention.

Methods: Single-cell RNA Sequencing and untargeted metabolomics analyses were used to characterize PPAT-associated metabolic changes in ESCC. Structure-based virtual screening was performed to identify potential PPAT inhibitors. The interaction and degradation of PPAT by Cucurbitacin B (CuB) were investigated using docking, pull-down, CETSA, and ubiquitination assays, and its anti-tumor and radiosensitizing effects were evaluated in vitro and in vivo.

Results: We identified PPAT as a critical modulator of ESCC malignancy. PPAT promoted the production of energy-related nucleotides, including AMP, GMP, ADP, GDP, ATP, and GTP, thereby fueling ESCC tumor growth in vitro and in vivo. Moreover, CuB specifically targeted PPAT and induced its polyubiquitin-mediated degradation via TRIM38, thereby suppressing the DNPB pathway and inhibiting tumor growth. Importantly, CuB also functioned as a radiosensitizer, significantly enhancing the therapeutic efficacy of radiotherapy in ESCC.

Conclusion: In conclusion, our findings reveal that targeting PPAT is a promising therapeutic strategy to suppress ESCC progression and enhance the efficacy of radiotherapy.