Elevated ANXA5 and ANXA6 in Urinary Exosomes Predict Poor Response to First-Line Therapy in Small Cell Lung Cancer

Abstract Background Small cell lung cancer (SCLC) exhibits high heterogeneity and primary therapeutic resistance leading to an unfavorable prognosis. Recognizing the significant roles of Annexin (ANXA) family proteins in cancer development and drug resistance, this study aimed to evaluate urinary exosomal ANXA proteins as non-invasive biomarkers for predicting therapeutic response in SCLC patients. Methods Urine samples were prospectively collected from 50 male SCLC patients receiving first-line platinum-based chemotherapy with or without immunotherapy. Patients were classified as responders (CR/PR) or non-responders (SD/PD) based on RECIST v1.1. Urinary exosomes were isolated via ultracentrifugation and profiled using data-independent acquisition mass spectrometry (DIA-LC-MS/MS), followed by targeted parallel reaction monitoring (PRM) validation. Results Proteomic analysis identified seven ANXA family members (ANXA2, ANXA3, ANXA4, ANXA5, ANXA6, ANXA7, and ANXA11) in urinary exosomes of SCLC patients. Differential expression analysis revealed significant upregulation of ANXA5 (p = 0.0295) and ANXA6 (p = 0.0191) in non-responders compared to responders in the discovery cohort. PRM validation confirmed these findings, demonstrating significantly elevated levels of ANXA5 (p = 0.0006) and ANXA6 (p = 0.0027) in non-responders. A strong positive correlation was observed between ANXA5 and ANXA6 expression. Receiver Operating Characteristic (ROC) curve analysis showed promising diagnostic performance for both ANXA5 (AUC = 0.76) and ANXA6 (AUC = 0.85) in the validation cohort for discriminating between responders and non-responders. Conclusion Elevated urinary exosomal ANXA5 and ANXA6 are promising non-invasive biomarkers for predicting primary treatment non-response in male SCLC, potentially aiding personalized therapy. These findings could facilitate personalized treatment strategies and improve clinical outcomes.