Potential Therapeutic Effect of Glycogen Synthase Kinase 3β Inhibition against Human Glioblastoma

Katsuyoshi Miyashita,Yutaka Hayashi,Toshinari Minamoto,Wei Mai,Hironori Fujisawa,Kazuyuki Kawakami,Abbas Shakoori,Mitsutoshi Nakada,Jun-Ichiro Hamada

doi:10.1158/1078-0432.ccr-08-0760

Abstract

Glioblastoma represents the malignant brain tumor that is most refractory to treatment and in which the identification of molecular target(s) is urgently required. We investigated the expression, activity, and putative pathologic role of glycogen synthase kinase 3beta (GSK3beta), an emerging therapeutic target for neurodegenerative diseases, in human glioblastoma. The active fraction of GSK3beta that is phosphorylated at the tyrosine 216 residue (pGSK3betaY216) was identified in glioblastoma cell lines. GSK3beta activity for phosphorylating its substrate was detected in these cells by nonradioisotopic in vitro kinase assay. Higher expression levels of GSK3beta and pGSK3betaY216 were frequently detected in glioblastomas compared with nonneoplastic brain tissues. Inhibition of GSK3beta activity by escalating doses of a small-molecule inhibitor (AR-A014418) or inhibition of its expression by RNA interference induced the apoptosis and attenuated the survival and proliferation of glioblastoma cells in vitro. Inhibition of GSK3beta was associated with increased expression of p53 and p21 in glioblastoma cells with wild-type p53 and with decreased Rb phosphorylation and expression of cyclin-dependent kinase 6 in all glioblastoma cell lines. Administration of AR-A014418 at a low dose significantly sensitized glioblastoma cells to temozolomide and 1-(4-amino-2-methyl-5-pyrimidinyl)methyl-3-(2-chloroethyl)-3-nitrosourea, chemotherapeutic agents used in the clinical setting, as well as to ionizing radiation. These results indicate that GSK3beta exerts a pathologic role by promoting the survival and proliferation of glioblastoma cells and by protecting them from apoptosis via the inactivation of p53- and/or Rb-mediated pathways. Consequently, we propose that GSK3beta provides a potential therapeutic target in glioblastoma.

Highlights

Glioblastoma represents the malignant brain tumor that is most refractory to treatment and in which the identification of molecular target(s) is urgently required
Because of the highly invasive properties of the tumor, we expect that glycogen synthase kinase 3h (GSK3h) inhibition provides dual benefits for the treatment of glioblastoma by attenuating tumor proliferation and by protecting host brain tissue from degradation and allowing its repair
nonradioisotopic in vitro kinase assay (NRIKA) [22] showed that GSK3h derived from these cells was able to phosphorylate its substrate, h-catenin (Fig. 1B, top panels). These results indicate that glioblastoma cells contain constitutively active GSK3h and that its activity is thought to be decontrolled by phosphorylationdependent regulation

Summary

Introduction

Glioblastoma represents the malignant brain tumor that is most refractory to treatment and in which the identification of molecular target(s) is urgently required. The majority of small-molecule inhibitors currently under development for cancer treatment target a family of protein tyrosine kinases that include epidermal growth factor receptor (EGFR) and platelet-derived growth factor receptor [4, 5]. Based on the demonstration of a frequent deregulation of EGFR and/or platelet-derived growth factor receptor in glioblastomas [6, 7], several clinical trials have tested the efficacy of small-molecule inhibitors of these tyrosine kinases on glioblastoma patients. These include the use of gefitinib and erlotinib targeting EGFR and imatinib mesylate targeting platelet-derived growth factor receptor, bcr-abl, and c-kit [8, 9]. We have subsequently shown similar properties for GSK3h in gastrointestinal, pancreas, and liver cancer cells [22]

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