Wee1 Kinase Inhibition Enhances Pi3k Inhibitor Response In P53 Deficient Gliomas

Glioblastoma multiforme (GBM) is an aggressive brain tumor that is resistant to chemotherapy and radiation, and is almost always fatal. Oncogenic activation of the PI3K signaling pathway plays a pivotal role in the development of GBM and is a major molecular target for therapeutic development. However, clinical results of single-agent PI3K inhibitors have been modest to date. PI3K inhibitors have led to tumor stabilization and some disease responses; however, dramatic tumor regressions are not typical. Multiple recent reports have described mechanisms of resistance to PI3K inhibitors. The goal of the present study was to identify ways to improve the efficacy of PI3K inhibitor-based therapy by overcoming adaptive resistance. In this study we show that PI3K inhibitor BKM induces G2/M cell cycle arrest and inhibits GBM cell proliferation. We identified WEE1 as a putative treatment target of resistance to PI3K inhibition based on its potential function as a mitotic gatekeeper and its specific overexpression in GBM. WEE1 kinase is a key molecule in maintaining G2-cell-cycle checkpoint arrest for premitotic DNA repair. We show that that BKM treatment activates WEE1, which in turn phosphorylates CDC2 at Tyr15, inactivates CDC2 and inhibits CDC2 activity, leading to G2/M arrest in glioma initiating cells (GICs). We show that treatment with WEE1 inhibitor MK1775 inhibited BKM-induced Cdc2 Tyr15 phosphorylation, and forced GICs to enter into the mitotic phase of the cell cycle. Using a panel of GICs, we show that MK1775 synergizes with BKM to inhibit GBM cell proliferation. Further, MK1775 and BKM as a single agent alone partially blocks proliferation, however, combination of MK1775 and BKM induces apoptosis as evaluated by Annexin V positive cells, cleaved PARP and caspase 3, and TUNEL staining. This effect was observed specifically in p53 mutant cells. Finally we show that depletion of WEE1 by shRNAs synergizes with BKM to inhibit GBM cell proliferation and induce apoptosis. These results indicate that WEE1 inhibition potentiated the effectiveness of PI3K targeted inhibition in GBM, and suggest a combinational inhibition of WEE1 and PI3K might allow successful targeted therapy in p53 mutant GBM. Citation Format: Shaofang Wu, Siyuan Zheng, Shuzhen Wang, W.K.Alfred Yung, Dimpy Koul. WEE1 kinase inhibition enhances PI3K inhibitor response in p53 deficient gliomas. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 31. doi:10.1158/1538-7445.AM2015-31