Enhanced MDR1 expression and chemoresistance of cancer stem cells derived from glioblastoma.

We established a cancer stem (CS) cell line, U87CS, by means of spheroid culture of U87MG cells derived from glioblastoma (GBM) in neuronal stem cell medium. U87CS cells presented positive immunohistochemical staining for multidrug resistance (MDR)1 and CD133, a marker for a subset of leukemia and GBM CS cells. The gene expression of MDR1 and CD133 on U87CS cells increased by an average of 8.51 and 47.18 times, respectively, compared to the levels on U87MG cells by real-time quantitative RT-PCR. U87CS cells possessed stronger drug-resistance to conventional anti-cancer drugs, such as doxorubicin (Dox), etoposide (VP-16), carboplastin, and BCNU than U87MG cells. Double immunofluoresence staining showed co-expression of MDR1 and CD133 on U87CS cells transplanted into nude mice brains. In addition, we identified the crossreactivity of CD133 and MDR1 in a surgical specimen of GBM. Our results suggest that CS cells may be resistant to current chemotherapy and represent a novel target for GBM therapeutics.