Neovascularization Induced Growth of Implanted Co Glioma Multicellular Spheroids: Magnetic Resonance Microimaging1

Magnetic resonance imaging has been used to follow noninvasively tumor neovascularization and tumor growth in a model system of multicellular C6 rat glioma spheroids implanted s.c. in nude mice. By position ing a single spheroid approximately 1 cm from the site of incision both the vascularization of the tumor and the wound healing processes were spa tially separated and could be simultaneously followed. The model pro posed here provides defined initial conditions of tumor geometry and cell proliferative status and separation of initial tumor growth from neovas cularization. Magnetic susceptibility relaxation provided an intrinsic marker for blood containing vessels. The implanted spheroid induced vessel growth within 4 days after implantation that was geometrically oriented toward the spheroid and distinct from wound healing at the site of incision. Volume measurements showed a corresponding 4-day lag in growth followed by Comperi/ progression. Sham implantation of agarose beads of similar diameter showed no induction of vessel growth, ruling out a direct effect of wound healing. The new vessels penetrating the tumor were highly permeable to the contrast reagent gadolinium-diet hvlenetriaminepentaacetic acid. This permeability may be due to the action of vascular endothelial growth factor, a major angiogenic growth factor in this system, and a potent permeability factor.