Fig. (3) Sensitivity of TK-expressing rat C6 constructs to GCV. Pools of stable transfectants containing vector only (pUB), wild-type TK, A168F, A168Y, Mutant 30 and SR39 were constructed and transfected in rat C6 glioma cells and evaluated for prodrug sensitivity as described in Materials and Methods. After six days of prodrug treatment, the growth inhibition was determined by staining with Alamar Blue and fluorescence recorded at 530/590 nm. Each data point (mean ± SEM, n=3 performed with at least fifteen replicates) is expressed as a percentage of the value for control wells with no prodrug treatment.