Preclinical Development Targeting Radiation-Induced G2 Checkpoint Activation with the Wee-1 Inhibitor MK-1775 in Glioblastoma Cell Lines

Thepurpose of this studywas todetermine the capacity ofMK-1775, apotentWee-1 inhibitor, to abrogate the radiation-induced G2 checkpoint arrest andmodulate radiosensitivity in glioblastoma cell models and normal human astrocytes. The radiation-induced checkpoint response of established glioblastoma cell lines, glioblastoma neural stem (GNS) cells, and astrocytes were determined in vitro by flow cytometry and in vivo by mitosis-specific staining using immunohistochemistry. Mechanisms underlying MK-1775 radiosensitization were determined by mitotic catastrophe and gH2AX expression. Radiosensitivity was determined in vitro by the clonogenic assay and in vivo by tumor growth delay. MK-1775 abrogated the radiation-induced G2 checkpoint and enhanced radiosensitivity in established glioblastoma cell lines in vitro and in vivo, without modulating radiation response in normal human astrocytes.MK-1775 appeared to attenuate the early-phase of the G2 checkpoint arrest in GNS cell lines, although the arrest was not sustained and did not lead to increased radiosensitivity. These results show that MK-1775 can selectively enhance radiosensitivity in established glioblastoma cell lines. Further work is required to determine the role Wee-1 plays in checkpoint activation of GNS cells. Mol Cancer Ther; 10(12); 2405–14. 2011 AACR.