Rat prostate adenocarcinoma cells were used to evaluate different incubation procedures for the measurement of fluorodeoxyglucose (FDG) uptake and to measure the effects on chemotherapy.
Methods: The cells were incubated for 10 or 60 min in media with different glucose concentrations. Furthermore, the cells were treated for 4 hr with different doses of gemcitabine. FDG uptake was measured immediately and 4 hr after treatment. The FDG transport was determined with a zero-trans assay, as well as the messenger RNA (mRNA) content of the glucose transporter type 1 (GLUT1) and the hexokinase assay (HK).
Results: A decrease in FDG uptake with increasing cell number after 60 min of incubation in all media was found. The shorter incubation time yielded more stable uptake data. The glucose content in the medium decreased with increasing cell number and incubation time, which showed that the glucose-to-FDG ratio is not constant in assays that use glucose-containing media. Treatment with gemcitabine resulted in an increase in FDG uptake with increasing dose and time after the end of therapy. Incubation experiments with 3H-inulin revealed that the changes were not caused by unspecific membrane alterations. The affinity (Km) of the transport system remained unchanged, whereas the maximum velocity (Vmax) increased. However, the mRNA content for GLUT1 and HK was unchanged.
Conclusion: With these data in mind, an uptake procedure was suggested in a glucose-free medium with an end concentration of 0.1 mM FDG or a zero-trans assay to determine Vmax and Km of the transport system. In FDG-PET studies on patients with tumors, these in vitro data may be helpful to monitor and optimize the therapeutic outcome by combining the chemotherapeutic agent with low doses of deoxyglucose.