Targeting the androgen receptor as a novel therapeutic strategy for high-grade gliomas by suppressing glioma cancer stem cells.

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e13504 Background: Glioblastoma (GBM) is the most aggressive and most common type of primary brain malignancies with median overall survival being only 20.9 months. The incidence of GBM is 50% greater in men than in women, and GBM transplanted into animals grow at a slower rate in females compared with males. Gender difference in GBM indicates that sex hormones such as androgen receptor (AR) may be involved in the tumorigenesis of GBM. A newer generation of AR antagonist, Enzalutamide, is available for prostate cancer treatment in clinic and can pass the blood-brain barrier, thus a good candidate for GBM treatment. Methods: Cell proliferation assay, cell cycle analysis, and cell apoptosis assay were performed on different GBM cell lines after Enzalutamide treatment. After treating GBM cells with or without Enzalutamide in mono-layer cell culturing or tumor spheres, cancer stem cell sub-population (CD133+ cells) in different groups was compared using flow cytometry. After enriching GBM cancer stem cells by sorting CD133+ U87MG cells out, cell proliferation assay was performed on CD133+ U87MG cells. Western blotting was performed comparing marker gene expression levels including CD133 and c-Myc with total protein isolated from GBM cells treated with Enzalutamide at different time points. A syngeneic orthotopic GBM mouse model was used for in vivo study. The size of tumors in the brain was monitored weekly with and without Enzalutamide treatment by in vivo imaging system for the luciferase activities. Results: Enzalutamide inhibited the proliferation of GBM cells both in vitro and in vivo. Enzalutamide induced apoptosis of GBM cells as well as arrested the cell cycle at G2/M phase in a cell cycle that has a potential of radio-sensitizing effect. Enzalutamide decreased the cancer stem cells population both in cultured mono-layer cells and in tumor spheres. Enzalutamide inhibited the proliferation of CD133+ U87MG cells after four days’ treatment. c-Myc is a proto-oncogene and required for maintenance of GBM cancer stem cells. Both CD133 and c-Myc expression levels decreased in GBM cell lines after Enzalutamide treatment in a time-dependent manner. Conclusions: Enzalutamide targets cancer stem cells and inhibits the proliferation of GBM.