Abstract PR013: Unlocking the proteome of metastatic prostate cancer circulating tumor cells

Abstract In recent years, liquid biopsies have emerged to provide improved insights on the current disease state of a patient, but they generally rely on a small number of protein markers from immunofluorescent staining or cell-free DNA, which provides limited information especially around drug targets. As more targeted therapies and immunotherapies enter the market, selecting the optimal drug target could improve patient outcomes drastically. One way to achieve this goal is to generate multi-omic datasets from the cancer cells in circulation, known as circulating tumor cells (CTCs). In this study, we collaborated with Astrin Biosciences and used their patented isolation technology to enrich CTCs with high purity from the blood of 15 metastatic castration resistant prostate cancer (mCRPC) patients. The enriched CTCs and a patient matched control sample consisting primarily of white blood cells were divided such that RNA and protein could be interrogated from the same patient. Label free unbiased mass spectrometry-based proteomics was used to identify the CTC-enriched proteins and marks the first time a global proteomic assessment has been performed on CTCs from cancer patients. Initial analysis identified over 1,500 peptides corresponding to greater than 500 proteins from each patients’ CTCs; including increased epithelial cell markers in the CTC-enriched sample and increased WBC markers in the control sample. Hallmarks of androgen response and detection of the androgen receptor were also identified in the CTC-enriched proteome. Overall, this study was designed to show the feasibility of obtaining large scale proteomic data from a liquid biopsy and future studies will provide more insight into the clinical utility of such data with a focus on cancer signaling mechanisms and biomarkers. Importantly, as we analyze more patients, we plan to compare the proteomic data with future RNA signatures across mCRPC patients to eventually be able to correlate them with drug response with the overall goal to improve treatment selection and patient outcomes. Citation Format: Justin M. Drake, Zoi Sychev, Alec Horrmann, Kaylee Judith Smith, Catalina Galeano-Garces, Ali Arafa, Nicholas Heller, Mahdi Ahmadi, Jiarong Hong, Megan Ludwig, Justin Hwang, Emmanuel S. Antonarakis, Jayant Parthasarathy. Unlocking the proteome of metastatic prostate cancer circulating tumor cells [abstract]. In: Proceedings of the AACR Special Conference: Advances in Prostate Cancer Research; 2023 Mar 15-18; Denver, Colorado. Philadelphia (PA): AACR; Cancer Res 2023;83(11 Suppl):Abstract nr PR013.