Absence of host-site influence on angiogenesis, blood flow, and permeability in transplanted RG-2 gliomas

The host site is believed to regulate tumor angiogenesis, which could resul t in site-dependent drug delivery parameters, greatly affecting experimenta l tumor research. In RG-2 rat gliomas we measured cellular proliferation; c ell cycle time was the same for RG-2 cells in brain and s.c. tumors (25 h), and was the same for endothelial cells in these tumors (46 h). We measured the transcapillary transfer constant (K) of alpha-aminoisobutyric acid and blood flow (F) with iodoantipyrine in RG-2 gliomas transplanted into brain , liver, kidney, muscle, s.c. tissue, and into the abdominal cavity. Data w as evaluated by quantitative autoradiography and direct tissue sampling. Th e variation of F (12.6-84.0 ml/g/min) and K (26.1-49.2 mu l/g/min) in RG-2 tumors in the different host sites was less than in surrounding tumor-free tissue (F = 20-1500 ml/g/min and K = 1.6-700 mu l/g/min). In contrast to ot her models, RG-2 does not result in tumors with host site-dependent behavio r. The RG-2 tumor cells appear to participate in, if not dominate, the angi ogenesis process regardless of the host site. Values of F and K were more d ependent on tumor topography (center versus periphery) and local histologic al features (necrosis versus viable tumor) than host site. We believe that the methods used for data acquisition may introduce as much variability in Results as the tumors themselves and that to better understand how tumor an giogenesis affects the vascular phenotype, comparative studies are needed t o validate the results obtained with newer methodologies.