Circulating extracellular vesicle PTPRO methylation: an exploratory biomarker for minimally invasive diagnosis of early-stage lung adenocarcinoma

Protein tyrosine phosphatase receptor-type O (PTPRO), a member of the PTP family, has garnered attention for its diagnostic and prognostic potential through the methylation of circulating tumor DNA (ctDNA). However, the utility of ctDNA has shown limited sensitivity and specificity, particularly in early-stage lung adenocarcinoma (LUAD). Given the enhanced stability of tumor-derived DNA in small extracellular vesicles (sEVs) from cancer cells, this research investigates the feasibility of using PTPRO methylation in saliva-derived sEVs as a non-invasive and easily accessible biomarker for the early detection of LUAD. To explore the relationship between PTPRO methylation and prognosis in early-stage LUAD, we conducted Kaplan-Meier survival analyses and assessed the methylation status of the PTPRO promoter using methylation-specific PCR (MSP) and q-MSP. Saliva samples were collected from 60 early-stage LUAD patients, 30 pneumonia patients, and 21 healthy controls, with isolation and characterization of salivary sEVs through transmission electron microscopy (TEM), nanoparticle tracking analysis (NTA), and immunoblotting. Kaplan-Meier analysis revealed hypermethylation of PTPRO was linked to poorer overall survival in early-stage LUAD patients. PTPRO methylation was detected in salivary sEVs of 73.3% of early-stage LUAD patients, compared to only 35% in plasma sEVs. Receiver operating characteristic (ROC) analysis confirmed that PTPRO methylation in salivary sEVs effectively distinguished early-stage LUAD patients from both pneumonia patients and healthy individuals. This suggests that PTPRO hypermethylation is associated with adverse prognosis in early-stage LUAD. The detection of PTPRO methylation in salivary sEVs demonstrates high sensitivity and specificity, indicating its potential as an epigenetic biomarker for the non-invasive diagnosis of early-stage LUAD.