Magnetic Resonance Imaging of Human Glioma Cells by means of an Interleukin-6 Receptor-Targeted Contrast Agent

The interleukin 6 receptor (IL-6R) and its ligand interleukin 6 (IL-6) play a crucial role in glioma growth and development accomplished by autocrine growth promotion and induction of angiogenesis via activation of vascular epithelial growth factor A (VEGF-A). Therefore, IL-6R represents a target for both therapy (preventing VEGF-A activation by blocking the receptor) and imaging (higher receptor density on tumor cells). A short heptapeptide that selectively binds to IL-6R and which inhibits the effect of IL-6 was coupled to the magnetic resonance imaging (MRI) contrast agent gadolinium (Gd)-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) and the fluorescent dye rhodamine. MRI, confocal laser scanning microscopy, and flow cytometry showed that our IL-6-DOTA-rhodamine conjugate was taken up into the cytoplasm of human U373 glioma cells without any cytotoxic effects. Competition experiments indicate that this uptake was receptor-mediated. This conjugate might be used for future MRI studies of brain tumors after systemic or intraoperative local application. The cytoplasm specificity of the conjugate also makes it a potential building block for the design of future cytoplasm-directed imaging and therapeutic conjugates.