The oxygenation status of
tumors derived from wild-type C6
glioma cells and clone D27 cells overexpressing
dimethylarginine dimethylaminohydrolase (DDAH) was assessed in vivo using a variety of direct and indirect assays of
hypoxia. Clone D27
tumors exhibit a more aggressive and better-vascularized phenotype compared to wild-type C6
gliomas. Immunohistochemical analyses using the
2-nitroimidazole hypoxia marker
pimonidazole, fiber optic OxyLite measurements of
tumor pO2, and localized 31P magnetic resonance spectroscopy measurements of
tumor bioenergetic status and pH clearly demonstrated that the D27
tumors were more hypoxic compared to C6 wild type. In the
tumor extracts, only
glucose concentrations were significantly lower in the D27
tumors. Elevated Glut-1 expression, a reliable functional marker for
hypoxia-inducible factor-1-mediated metabolic adaptation, was observed in the D27
tumors. Together, the data show that overexpression of DDAH results in C6
gliomas that are more hypoxic compared to wild-type
tumors, and point strongly to an inverse relationship of
tumor oxygenation and angiogenesis in vivo--a concept now being supported by the enhanced understanding of
oxygen sensing at the molecular level.