Dexamethasone induced partial resistance to methotrexate in C6-glioma cells.

Chemotherapy results in glioma are poor. In addition to chemotherapy most patients are treated with dexamethasone (Dex) to reduce brain edema. Therefore we examined the influence of Dex on the sensitivity of C6 glioma cells to methotrexate (MTX) using MTT-tests. The LD50 of MTX was 3*10(-8)M, 10(-7)M, 4*10(-6)M and 4*10(-4)M after 72, 24, 6 and 1 hour treatment, respectively. After incubations with combinations of Dex and MTX, twice as many cells survived high MTX concentrations. This protection could be overcome by addition of 10 to 100 fold more MTX. It was not species-specific since the effect was also found in human TE671 cells.