Modulation of angiogenesis by human glioma xenograft models that differentially express vascular endothelial growth factor

To evaluate the potential actions of vascular endothelial growth factor (VEGF) on capillary permeability and drug transport, tumorigenic human glioma cell lines were developed that expressed different levels of VEGF. Three human glioma cell lines (i.e. U373, SF126, SF188) were screened for VEGF under normoxic and hypoxic (i.e. induced by CoCl₂) conditions by Western blot analysis. Subsequent to these results, sense and antisense VEGF₁₆₄ cDNA transfections were conducted. It was found that parental SF188 (SF188/V- ) and SF188/V+ (sense transfected) cells could serve as an appropriate in vivo model based on their divergent levels of VEGF expression. Media derived from SF188/V+ cells stimulated endothelial cell growth by 30-60%, and enhanced endothelial cell clonogenicity by 5-10-fold compared to SF188/V- or empty vector transfected cells. Nude rats implanted with either SF188/V- or SF188/V+ cells subcutaneously and intracerebrally formed tumors, with those derived from SF188/V+ cells growing at a faster rate. Immunohistochemistry analysis indicated that the expression of VEGF and number of capillaries (factor viii assay) were approximately 3-fold greater in SF188/V+ tumors compared to SF188/V- tumors. Pharmacological assays, such as measurements of cytotoxicity and DNA adducts, in SF188/V- and SF188/V+ cells treated with carmustine or temozolomide were similar. Therefore, other than differences in VEGF expression and growth in vivo, SF188/V- and SF188/V+ cells possess a similar phenotype, and can serve as models to evaluate the influence of VEGF on drug transport.