Proteome Profiling of 1 to 5 Spiked Circulating Tumor Cells Isolated from Whole Blood Using Immunodensity Enrichment, Laser Capture Microdissection, Nanodroplet Sample Processing, and Ultrasensitive nanoLC-MS.

Proteome profiling of circulating tumor cells (CTCs) can provide crucial insight into disease progression and the role of CTCs in tumor metastasis. We describe an integrated workflow to measure global protein expression in 1-5 spiked CTCs enriched from whole blood by immunodensity gradient centrifugation. Enriched CTCs were purified and collected by laser capture microdissection, prepared using a recently developed nanodroplet-based processing platform (nanoPOTS), and finally analyzed by ultrasensitive nanoLC-MS/MS. The workflow was capable of identifying an average of 164 and 607 protein groups from samples comprising 1 and 5 LNCaP cells, respectively, that were isolated from human whole blood. A panel of prostate cancer-specific proteins were identified and quantified, which was used to differentiate between spiked CTCs and white blood cells.