Mouse glioma cells (CT-2A and GL261) as well as human glioblastoma cells U373, U251 and U87 were cultured in Dulbecco's Modified Eagle's medium (DMEM; Sigma-Aldrich, St. Louis, USA) (high glucose) supplemented with 10 % fetal bovine serum (FBS). In the case of CT-2A, U373 and GL261, 1 % penicillin/streptomycin (P/S) was added. For U373, Gibco® MEM non-essential amino acids were added as well. For the determination of IC 50 , cells were seeded at 3 x 10