Proteomic Profiling of Extracellular Vesicles Distinguishes Prostate Cancer Molecular Subtypes

Prostate cancer is the most common non-cutaneous cancer among men in the United States. Most prostate cancers are driven by androgen receptor (AR) signalling, but there are an increasing number of cases that lose AR and gain neuroendocrine (NE) features (AR-/NE+) or lack both (AR-/NE-). These latter subtypes are particularly aggressive and lethal. Extracellular vesicles (EVs) have shown great potential as biomarkers for non-invasive liquid biopsy assays, as EVs contain biomolecules from their cells of origin. Here, we used a shotgun proteomics approach with mass spectrometry to interrogate the global proteome of EVs isolated from prostate cancer cell lines reflecting diverse clinical subtypes, including AR-/NE+ and AR-/NE- models. We identified 3952 EV proteins, which clustered largely by tumour subtype and provided enough proteomic coverage to derive classic gene signatures of AR or NE identity that are of high relevance for prostate cancer prognostication. EVs isolated from AR+ cells displayed high levels of proteins regulated by AR and mTOR signalling. EVs isolated from AR-/NE+ cells contained known NE markers such as SYP and CHGA, whereas EVs from AR-/NE- models were enriched in basal cell markers and proteins that regulate epithelial-to-mesenchymal transition (EMT). We integrated our cell line data with recently published EV proteomics data from 27 advanced prostate cancer patients and found 2733 overlapping proteins, including cell surface markers relevant to prostate cancer, AR activity indicators, and proteins enriched in specific subtypes (AR+, AR-/NE-, AR-/NE+). This approach may be useful for rare cancer subtypes, such as prostate cancers that lose AR-related features and gain NE features, to optimise the use of these liquid biopsy samples for clinical decision making.