Survival of human glioma cells treated with various combination of temozolomide and X-rays

Purpose: To investigate the effect of temozolomide, a 3-methyl derivative of mitozolomide in combination with X-rays in human glioma-derived cell lines. Methods and Materials: Glioma cell lines D384 and U251 were treated with temozolomide for various periods of time in combinations with X-rays. Temozolomide administration was repeated every 24 h for exposures up to 96 h. Cytotoxicity was determined with a clonogenic assay. Results: Incubation of D384 cells with temozolomide during 24 h prior to or following irradiation results in a moderate enhancement of the cytotoxicity. Prolonged treatment with temozolomide, i.e., 48-96 h before X-rays, causes a stronger potentiation. In contrast, no enhancement is observed in irradiated U251 cells in combination with 24-96 h temozolomide treatment. In addition to single-dose irradiation, rye investigated the effect of temozolomide in D384 cells with concomitant fractionated irradiation. A 96-h exposure to temozolomide with simultaneous doses of 2 Gy X-rays at 24-h intervals, causes a significant further reduction in cell survival as compared to fractionated irradiation only. Conclusion: Depending on the cell line, treatment of glioma cells with temozolomide and X-rays can have either an additional effect or potentiate cell killing. (C) 2000 Elsevier Science Inc.