CHARACTERIZATION OF ANGIOGENESIS AND MICROCIRCULATION OF HIGH-GRADE GLIOMA - AN INTRAVITAL MULTIFLUORESCENCE MICROSCOPIC APPROACH IN THE ATHYMIC NUDE-MOUSE

The current study follows angiogenesis and microcirculatory changes as sociated with malignant glioma growth by means of an intravital fluore scence microscopic approach, which allows for the direct and continuou s visualization of the glioma microvasculature and its quantitative an alysis. Fluorescently labeled C-6, rat glioma cells (5 x 10(5)) were i mplanted into dorsal skinfold chamber preparations of athymic nude mic e. Glioma growth, vascularization, microhemodynamics, vascular permeab ility, and leukocyte-endothelial cell interactions were simultaneously followed over a 22-day observation period using intravital epiillumin ation microscopy and a multifluorescent labeling technique. Analysis o f the process of glioma vascularization revealed three stages with dis tinct microvascular characteristics: avascular stage (days 0 to 6), la g of glioma growth but initial glioma-induced angiogenesis within the host tissue in peritumoral areas; early vascular stage (days 6 to 14), glioma cell proliferation associated with a spatially homogeneous dev elopment of a glioma microvasculature; and late vascular stage (days 1 4 to 22), exponential tumor growth and expansion (> 400 mm(3)) with hi gh vascular densities in the peritumoral region and reduced vasculariz ation (microvascular perfusion) in the glioma center. Within the cente r, the functional vessel length per area correlated inversely with gli oma size (P < 0.01). In the peritumoral region, functional vessel leng th per area was independent of glioma size, indicating persistent, hig h angiogenic activity throughout the observation period. Thus, the mic rovasculature of mature gliomas revealed a microvascular zonal divisio n with a progressive reduction of the functional vessel length per are a within the tumor center. The perfusion failure of individual microve ssels within the glioma center was partly compensated by an increase o f diameters (P < 0.05), and thus by an increase of blood flow in these functional microvessels (P < 0.05) over time. Histologic analysis dem onstrated both expanding and infiltrating growth patterns, as well as focal necroses on day 22. These are the first data from repeated in vi vo analysis of glioma growth, vascularization, and microcirculation.