Abstract 6965: Characterizing the proteome landscape of extracellular vesicles from prostate cancer cell lines by mass spectrometry

Abstract Multiple subtypes of prostate cancer can emerge in advanced stages of disease, such as tumors that maintain androgen receptor features (AR+), those without AR but with neuroendocrine features (AR-/NE+), and those without AR or NE features (AR-/NE-). These latter subtypes are particularly aggressive and incredibly lethal. Extracellular vesicles (EVs) are small particles that are mediators of cell-cell communication and have been nominated as potential biomarkers of disease state. We hypothesized that the proteome of EVs contains information about their originating cell that can distinguish between prostate cancer subtypes. To address this, we isolated EVs from cell lines of differing subtypes – AR+ (LNCaP, LNCaP95, C4-2, 22RV1), AR-/NE+ (NCI-H660, EF1, LASCPC-01), and AR-/NE- (PC3, DU145) – and prepared the EV proteome for quantitative, label-free mass spectrometry analysis. This identified 2, 000+ proteins in the EVs for each cell line where EVs from similar subtypes clustered together. Interestingly, we also found that EVs contained enough protein information to utilize developed gene signatures for AR or NE activity. EVs isolated from AR-/NE+ cells contained known NE signature proteins such as SYP, CHGA, and UCHL1. EVs from the AR+ cell lines displayed 50% AR activity driven by PSA and STEAP1 proteins in addition to other significant distinguishing protein markers. This supports the potential for using the proteome of tumor-derived EVs to identify novel signature molecular markers besides those already known to the field for developing liquid-based biomarker assays. In addition, our work characterizes the EV surfaceome which is critical for enriching signals from tumor-derived EVs feasible for clinical diagnostics assay development. While PSMA has been a reliable marker for cells reliant on AR signaling, less is known about protein markers in the AR- subset. Our work highlights TROP2 as especially enriched in the EVs from AR-/NE- cell lines, supporting its relevance as a target in patients without treatment options. To evaluate disease outcomes, further clinical studies are needed to develop specific and sensitive tests based on the EV proteome derived from advanced prostate cancer patients. Citation Format: Megan L. Ludwig, Abderrahman Day, Hannah E. Bergom, Zoi Sychev, Alec Horrmann, Justin Hwang, Justin M. Drake. Characterizing the proteome landscape of extracellular vesicles from prostate cancer cell lines by mass spectrometry abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 6965.