Harnessing tumor-associated exosomal aminopeptidase N as a dual-function tool for monitoring and tackling chemoresistance in gastric cancer.

Chemoresistance remains a major obstacle to effective treatment in gastric cancer (GC), with a notable scarcity of clinically applicable biomarkers and therapeutic targets. In this study, we employed an integrated proteomic approach analyzing paired serum samples from GC patients at disease control and progressive disease stages during chemotherapy, exosomes from chemoresistant and chemosensitive GC cells, and corresponding whole-cell proteomes to identify tumor-associated exosomal drivers of chemoresistance. Cross-dataset integration identified aminopeptidase N (APN/CD13) as selectively enriched under chemoresistant conditions. Functional validation demonstrated that APN depletion via shRNA or CRISPR restored cisplatin sensitivity in refractory cells, whereas APN overexpression conferred chemoprotection. A neutralizing anti-APN monoclonal antibody resensitized resistant cells and showed superior efficacy compared with the broad-spectrum peptidase inhibitor bestatin in vivo. Mechanistically, APN sustained a ferroptosis-suppressive state: its inhibition increased ROS and lipid peroxidation, shifted transcriptomic profiles toward pro-ferroptotic pathways, and downregulated the lipid peroxide detoxifier AKR1C2, which correlated with poor prognosis and APN expression in the TCGA-STAD cohort. Exosomal transfer assays confirmed that APN-enriched vesicles disseminated chemoresistance and ferroptosis evasion to sensitive cells, accelerating tumor progression during chemotherapy, whereas APN-deficient exosomes lacked this capacity. Clinically, serum exosomal APN levels robustly distinguished progressive disease from disease control in a cohort of 105 patients (AUC = 0.85; optimal cutoff 0.936 ng/mL). Collectively, these findings position exosomal APN as a dual-function tool, serving both as a dynamic liquid biopsy biomarker and an antibody-targetable node for monitoring and overcoming chemoresistance in gastric cancer.