Expression of ABC-1 transporter is elevated in human glioma cells under irradiation and temozolomide treatment

Abstract

Objective: Chemo-therapeutic treatment of glioma patients has minor success. Little is known about mechanisms of a pronounced resistance of gliomas towards actual therapies, yet. ABC-1 belongs to the group of transporters known to be involved in the export of hydrophobic substances and vascular regulation. This study investigates an effect of both temozolomide (TMZ) treatment and/or irradiation on the expression of the ABC-1 transporter in human U87-MG glioma cells. Material and methods: In parallel experiments U87-MG cells underwent either irradiation (RT), chemo-treatment (CT) using TMZ, and combined chemo/radiation-treatment (CT/RT). After each treatment the cells were incubated either 2 or 24 hours at 37°C and counted before protein analysis using Western-Blot technique. Results and conclusions: An exponential growth of cellular density was observed for both untreated and irradiated cells being, however, about 2-times slower in irradiated compared to untreated cells. In contrast the density increase of chemo-treated cells as well as that of cells, which underwent the combined CT/RT treatment was of linear nature. ABC-1 expression was detected in untreated as well as treated cells. Increasing cell density and all kinds of treatment resulted in a considerably enhanced ABC-1 expression. CT treatment resulted in highly up-regulated ABC-1 expression especially in non-confluent cultures compared to untreated cells. Irradiation had a comparable or even higher inducible effect on the ABC-1 expression rates depending, however, on cell density. The highest expression rates were observed in cultures with high cellular density 2 hours after application of the combined treatment. Strong up-regulation of ABC-1 expression under both irradiation and chemo-treatment might be a clue to multidrug and irradiation cross-resistance mechanisms of malignant glioma cells converting the ABC-1 transporter into an attractive pharmacological target for a clinical breakthrough in the therapy of malignant gliomas.