Microparticles from ovarian carcinomas are shed into ascites and promote cell migration

Objective: Microparticles are cellular-derived vesicles (0.5-1.0 Km) composed of cell membrane components, which are actively shed from the surface of various cells, including epithelial cells. We compared microparticles in ascites between women with ovarian carcinoma and women with benign ovarian pathology, and isolated tumor-derived (epithelial cell adhesion molecule [EpCAM]-positive) microparticles for functional analysis and proteomics. Materials and Methods: Cases included 8 patients with benign ovarian neoplasms and 41 with ovarian carcinoma. Ascites from a high-grade stage III serous carcinoma was used for functional and proteomic analysis. Cancer cells were isolated using EpCAM-coated beads, microparticles were isolated by ultracentrifugation/flow cytometry, and sorting was achieved using markers (eg, EpCAM). Binding and migrations assays were performed with 3 ovarian cancer cell lines. Proteomic analysis of EpCAM-positive microparticles and ascites cancer cells was performed by mass spectrometry. Results: Microparticles in benign pelvic fluid were similar to early and advanced-stage ascites (2.4 vs 2.8 vs 2.0 × 10 ⁶ microparticles/mL). Advanced stage had a greater proportion of EpCAM-positive microparticles than early or benign disease (13.3% vs 2.5% vs 2.1%; P = 0.001), and serous histology had more than endometrioid (13.2% vs 1.8%; P = 0.01). Microparticles bound to the surface of 3 cultured cell lines, and were internalized into the EpCAM-positive microparticles, resulting in more cell migration than buffer alone or EpCAM-negative microparticles (P = 0.007). A dose-dependent increase was seen with increasing numbers of EpCAM-positive microparticles. Proteomics revealed that most proteins in EPCAM-positive microparticles were shared with cancer cells, and many are associated with cell motility and invasion, such as fibronectin, filamin A, vimentin, myosin-9, and fibrinogen. Conclusions: Ascites from advanced-stage and serous ovarian carcinomas contain large numbers of tumor-derived microparticles. In vitro, these microparticles bind to cancer cells and stimulate migration. Tumor-derived microparticles in ascites could mediate the predilection for peritoneal spread in serous ovarian carcinomas.