Time-dependent inhibition of glioblastoma cell proliferation by Dexamethasone

Because of the outstanding importance of the glucocorticoid Dexamethasone ( DEX) as supportive therapy in the management of brain tumours, the direct e ffect of DEX on tumour cell proliferation is of particular interest. Previo us in vitro studies led to contradictory results. To characterise more prec isely the influence of DEX, we investigated the glioblastoma multiforme (GM ) cell lines A172, T98G and 86HG39. Cells were treated with DEX concentrati ons ranging from 5 x 10(-9) to 5 x 10(-5) M from 24 to 240 h under differen t treatment conditions. Influence of DEX on glioma cell viability was asses sed daily for 5 days by MTT-assay: (I) with continuous DEX incubation (acut e treatment), (II) in a recultivation period without DEX after 5 days of DE X pre-incubation (pre-treatment), (III) with continuous DEX incubation afte r 5 days of DEX pre-incubation (combination treatment). DEX acute treatment led to strongly decreased proliferation of A172 cells, whereas T98G and 86 HG39 cells remained uninfluenced. In opposite, a time-delayed inhibition of cell proliferation was observed in all three cell lines after DEX pre-trea tment. Combination treatment induced a significant increase of the inhibito ry effect in A172 and T98G cells. These data show a variable, partial time- dependent inhibitory effect of DEX on the proliferation of GM cells and may open new treatment strategies for malignant brain tumours.