MR-IMAGING OF PHAGOCYTOSIS IN EXPERIMENTAL GLIOMAS

PURPOSE: To determine whether phagocytosis can be observed in vivo in glioma cells. MATERIALS AND METHODS: Rat C6 glioma cells were studied in culture and after intracerebral implantation into 13 rats. Monocrystalline iron oxide nanoparticles (MION), a model marker of phagocytosis, was administered intravenously to tumor-bearing rats at 2-20 mg of iron per kilogram. Magnetic resonance (MR) imaging was performed at multiple time points. RESULTS: Glioma cells in culture showed uptake of MION in amounts of up to 10 ng of iron per 10(6) cells, corresponding to approximately 50,000 particles per cell. Fluorescently labeled MION was found to be located primarily in tubular lysosomes. Intracerebral gliomas showed characteristic changes in signal intensity at MR imaging that peaked 12 hours after administration of MION and lasted up to 5 days; these changes corresponded to uptake and subsequent biodegradation of MION by tumor cells. CONCLUSION: Phagocytosis of glioma cells can be detected in vivo with iron oxide-enhanced MR imaging, and this may permit accurate delineation of tumor margins.