Abstract LB-242: Oncosomes: Large bioactive particles secreted by prostate cancer cells

Abstract

Abstract Purpose of the study: Human prostate tumor cells were recently shown by our group to secrete large (0.5-10 m diameter) bioactive microvesicles capable of activating signal transduction and inducing proliferation and migration in cells in the tumor microenvironment (Di Vizio, et al. Cancer Res. 2009 69: 5601-9). These secreted particles, termed oncosomes, were shown to be vehicles for numerous signaling proteins involved in cell growth and motility. They also contain the membrane protein caveolin-1 (Cav-1), a mediator of prostate cancer (PCa) metastasis and a circulating PCa biomarker. The purpose of this study was to develop the tools to identify, isolate, sort and characterize PCa-derived oncosomes. Experimental procedures: Secreted particles from PCa cells were ultracentrifuged at 100,000xg and the pelleted material processed on a Moflo High-Speed Cell Sorter (Beckman-Coulter) and analyzed using Summit V4.3 software (Dako Colorado, Inc.). 1, 3 and 10 m bead standards (Spherotech Inc.) were used to set size gates. To avoid capturing aggregated material, forward scatter and pulse width were set at a linear scale and only single events were gated and analyzed. Sorted particles were visualized by confocal and electron microscopy. Results: Using the above procedure, we were able to retrieve intact particles of 1-10 m in diameter secreted by LNCaP cells overexpressing the oncoprotein MyrAkt1. The nontumorigenic prostate stromal cell line WPMY-1 secreted > 10-fold fewer particles in this size range. We confirmed that these were membrane-derived particles by showing that they contained MyrAkt1, which localizes to the plasma membrane. Particles in a similar size range were also sorted after purification from LNCaP cells stably expressing a Cav-1/GFP fusion protein. Sorted particles visualized microscopically appeared to be surrounded by a lipid bilayer and to have intrinsic structure that made them resistant to collapse. Particles isolated by these methods evoked degradation of FITC-labeled collagen and contained active MMP9 and MMP2, two key proteases involved in tumor cell invasion. Conclusions: The specific type of large bioactive particle we have isolated has not been previously described in any tumor system. Studies are ongoing to detect these particles in animal models of cancer and in human patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-242.