In vitro 2-deoxy-2-[18F]fluoro-D-glucose uptake: practical considerations.

In oncology 2-deoxy-2-[(18)F]fluoro-D-glucose ([(18)F]-FDG), a glucose analogue, is the most used positron emission tomography (PET) tracer. There are however some limitations due to low metabolic activity or high surrounding physiological uptake in several tumors or regions. Investigating new tracers or methods is expensive and elaborative when animal experiments or phase I clinical trials are used. In vitro experiments can overcome these limitations. We analyzed the influence of incubation time, cell medium conditions, administered activity, and cell density on [(18)F]-FDG uptake in six different cell cultures. Glucose transporter 1 (GLUT1)- and hexokinase 2 (HK2)-expression at high and low cell density was analyzed using immunocytochemistry. FDG-uptake increases over time and absence of glucose in the incubation medium increases uptake. By increasing the administered activity, uptake per protein also increases and tracer uptake per protein is lower at higher cell densities. Immunocytochemical analysis reveals a lower expression of both GLUT1 and HK2 at higher cell concentrations. All investigated parameters influenced FDG uptake and therefore we can conclude it is of utmost importance to keep administered activity, incubation medium, and time constant and to correct uptake when cell density changes due to environmental conditions, such as therapy.