A cell-culture reactor for the on-line evaluation of radiopharmaceuticals:Evaluation of the lumped constant of FDG in human glioma cells

A fluidized-bed cell-culture reactor with on-line radioactivity detection w as developed for the in vitro evaluation of radiopharmaceuticals. The techn ique was applied to measure the dependency of the lumped constant (LC) of F DG on the glucose concentration in the culture medium in a human glioma cel l line. Methods: Human glioblastoma cells (86HG39) immobilized in open poro us microcarriers were cultivated in a continuously operating fluidized-bed bioreactor. At different glucose concentrations in the culture medium, step inputs (0.1 MBq/mL) of FDG were performed and the cellular uptake of FDG w as measured on-line and compared with analyzed samples. From these results, the LC of FDG and its dependency on the glucose concentration were calcula ted. Results: This fluidized-bed technique enabled precise and reproducible adjustment of all relevant experimental parameters, including radiotracer time-concentration course, medium composition. pH, dissolved oxygen and tem perature under steady-state conditions, and an on-line determination of the intracellular radiotracer uptake. The immobilized glioma cells formed stab le, 9-dimensional, tumor-like spheroids and were continuously proliferating , as proven by an S-phase portion of 25%-40%. For further examination of th e cells, an enzymatic method for detachment from the carriers without cellu lar destruction was introduced. In the FDG experiments, a significant depen dency of the LC on the glucose level was found. For normoglycemic glucose c oncentrations, the LC was determined to be in the range of 0.7 +/- 0.1, whe reas in hypoglycemia LC increased progressively up to a value of 1.22 +/- 0 .01 at a glucose concentration of 3 mmol/L. Conclusion: The bioreactor repr esents an improved in vitro model for the on-line evaluation of radiotracer s and combines a wide range of experimental setups and S-dimensional, tissu e-like cell cultivation with a technique for on-line radioactivity detectio n.