Proteomic analysis of urinary and tissue‐exudative extracellular vesicles to discover novel bladder cancer biomarkers

Proteomic analysis of urinary extracellular vesicles (EVs) is a powerful approach to discover potential bladder cancer (BCa) biomarkers, however urine contains numerous EVs derived from the kidney and normal urothelial epithelium, which can obfuscate information related to BCa cell‐derived EVs. In this study, we combined proteomic analysis of urinary EVs and tissue‐exudative EVs (Te‐EVs), which were isolated from culture medium of freshly resected viable BCa tissues. Urinary EVs were isolated from urine samples of 11 individuals (7 BCa patients and 4 healthy individuals), and Te‐EVs were isolated from 7 BCa tissues. We performed tandem mass tag (TMT)‐labeling liquid chromatography (LC‐MS/MS) analysis for both urinary EVs and Te‐EVs and identified 1960 proteins in urinary EVs and 1538 proteins in Te‐EVs. Most of the proteins identified in Te‐EVs were also present in urinary EVs (82.4%), with 55 of these proteins showing upregulated levels in the urine of BCa patients (fold change > 2.0; P < .1). Among them, we selected 22 membrane proteins as BCa biomarker candidates for validation using selected reaction monitoring/multiple reaction monitoring (SRM/MRM) analysis on urine samples from 70 individuals (40 BCa patients and 30 healthy individuals). Six urinary EV proteins (heat‐shock protein 90, syndecan‐1, myristoylated alanine‐rich C‐kinase substrate (MARCKS), MARCKS‐related protein, tight junction protein ZO‐2, and complement decay‐accelerating factor) were quantified using SRM/MRM analysis and validated as significantly upregulated in BCa patients (P < .05). In conclusion, the novel strategy that combined proteomic analysis of urinary EVs and Te‐EVs enabled selective detection of urinary BCa biomarkers.