Uncoupling of hexose transport and phosphorylation in human gliomas demonstrated by PET

Tumor uptake of [18F]2-fluoro-2-deoxy-glucose (FDG) was studied in 20 patients with histologically classified gliomas, using dynamic positron emission tomography (PET). Parametric images of local blood volume, glucose metabolic rate, transport and phosphorylation rate constants were generated by weighted non-linear least-squares fits on a pixel-by-pixel basis. Tumor metabolism, i.e. ratios of tumor peak metabolism to contralateral brain metabolism, corresponded with histological grade. Approximately half of the tumors showed considerable metabolic heterogeneity, and metabolically active areas were found in the periphery of seven tumors. Rate constants of FDG transport and phosphorylation were significantly correlated and were inversely coupled to plasma glucose levels in contralateral brain. In contrast, tumor transport and phosphorylation rate constants varied independently of each other and of plasma glucose concentration. In some tumors large alterations of FDG phosphorylation were observed in presence of nearly normal FDG transport.