Receptor Tyrosine Kinases: Principles and Functions in Glioma Invasion.

Protein tyrosine kinases are enzymes that are capable of adding a phosphate group to specific tyrosines on target proteins. A receptor tyrosine kinase (RTK) is a tyrosine kinase located at the cellular membrane and is activated by binding of a ligand via its extracellular domain. Protein phosphorylation by kinases is an important mechanism for communicating signals within a cell and regulating cellular activity; furthermore, this mechanism functions as an "on" or "off" switch in many cellular functions. Ninety unique tyrosine kinase genes, including 58 RTKs, were identified in the human genome; the products of these genes regulate cellular proliferation, survival, differentiation, function, and motility. Tyrosine kinases play a critical role in the development and progression of many types of cancer, in addition to their roles as key regulators of normal cellular processes. Recent studies have revealed that RTKs such as epidermal growth factor receptor (EGFR), platelet-derived growth factor receptor (PDGFR), c-Met, Tie, Axl, discoidin domain receptor 1 (DDR1), and erythropoietin-producing human hepatocellular carcinoma (Eph) play a major role in glioma invasion. Herein, we summarize recent advances in understanding the role of RTKs in glioma pathobiology, especially the invasive phenotype, and present the perspective that RTKs are a potential target of glioma therapy.

Strong therapeutic potential of γ-secretase inhibitor MRK003 for CD44-high and CD133-low glioblastoma initiating cells.

The Notch signal regulates both cell viability and apoptosis, and maintains stemness of various cancers including glioblastoma (GBM). Although Notch signal inhibition may be an effective strategy in treating GBM initiating cells (GICs), its applicability to the different subtypes of GBM remains unclear. Here, we analyzed the effectiveness of MRK003, a preclinical γ-secretase inhibitor, on GICs. Nine patient-derived GICs were treated by MRK003, and its efficacy on cell viability, apoptosis, sphere forming ability and Akt expression level which might be related to Notch downstream and be greatly important signals in GBM was evaluated. MRK003 suppressed viability and sphere-formation ability, and induced apoptosis in all GICs in varying doses of MRK003. Based on their sensitivities to MRK003, the nine GICs were divided into "relatively sensitive" and "relatively resistant" GICs. Sensitivity to MRK003 was associated with its inhibitory effect on Akt pathway. Transgenic expression of the myristoylated Akt vector in relatively sensitive GICs partially rescued the effect of MRK003, suggesting that the effect of MRK003 was, at least in part, mediated through inhibition of the Akt pathway. These GICs were differentiated by the expression of CD44 and CD133 with flow cytometric analysis. The relatively sensitive GICs are CD44-high and CD133-low. The IC50 of MRK003 in a set of GICs exhibited a negative correlation with CD44 and positive correlation with CD133. Collectively, MRK003 is partially mediated by the Akt pathway and has strong therapeutic potential for CD44-high and CD133-low GICs.

Prognostic paradox: brain damage around the glioblastoma resection cavity.

Hyperintense lesions around the resection cavity on magnetic resonance diffusion-weighted imaging (MR-DWI) frequently appear after brain tumor surgery due to the damage of surrounding brain. The putative connection between the lesion and the prognosis for patients with glioblastoma (GBM) was explored. This retrospective study reviewed consecutive sixty-one patients with newly diagnosed GBM. Postoperative MRI was performed within 2 weeks after the initial surgery. We classified the cases into two groups depending on whether DWI hyperintense lesions were observed or not [DWI(+) group and DWI(-) group]. Progression-free survival (PFS) and overall survival (OS) were compared between the two groups. Forty-two patients were identified. The various extents of hyperintense lesions around the resection cavity were observed in 28/42 (66.7%) cases. In the DWI(+) and DWI(-) groups, median PFS was 10.0 [95% confidence interval (CI) 8.4-11.5] and 6.7 (95% CI 4.9-8.5) months, respectively (p = 0.042), and median OS was 18.0 (95% CI 12.2-23.8) and 17.0 (95% CI 15.7-18.3) months, respectively (p = 0.254). On multivariate analysis, the presence of DWI hyperintense lesion was more likely to be an independent predictor for 6-month PFS (p = 0.019; HR, 0.038; 95% CI 0.002-0.582). Tumor recurrence appeared outside the former DWI hyperintense lesion. Hyperintense lesions surrounding the resected GBM on MR-DWI might be a favorable prognostic factor in patients with GBM.

Detection of the development of late-onset idiopathic aqueductal stenosis (LIAS) by chronological magnetic resonance imaging: a case report.

Late-onset idiopathic aqueductal stenosis (LIAS) has been recognized as one of the clinical entities of adulthood hydrocephalus for decades, although there have been no radiological reports that show normal ventricular systems before the development of LIAS. We present here an adolescent case of LIAS with a previously normal ventricular system on magnetic resonance imaging (MRI). A 17-year-old boy had been suffering from chronic headaches and mild intellectual disability (MID) since he became a teenager, and this had prevented him from leading an ordinary school life. MRIs on admission showed triventriculomegaly from the aqueductal stenosis that had not been detected on previous MRIs, at least until the age of 6. An endoscopic third ventriculostomy was successfully performed, which improved both the headache and the MID. The developmental mechanism of LIAS remains unclear, although the membranous ependymal-like tissue observed in the aqueduct suggested the preceding existence of an inflammatory process around this region. To the best of our knowledge, this case was noteworthy because the development of LIAS was clearly demonstrated on MRI for the first time.

Reversible acute bilateral blindness resulting from a frontal brain tumor: a case report.

We experienced an unusual case of a 15-year-old girl who suffered acute bilateral blindness caused by a frontal lobe tumour. She underwent emergent operation, after which her vision recovered. This case emphasizes that a brain mass can cause sudden onset blindness and an emergency intervention might save the patient's sight.

Glycogen synthase kinase 3ß inhibition sensitizes human glioblastoma cells to temozolomide by affecting O6-methylguanine DNA methyltransferase promoter methylation via c-Myc signaling.

Glycogen synthase kinase 3ß (GSK3ß) is a serine/threonine protein kinase involved in human cancers including glioblastoma. We have previously demonstrated that GSK3ß inhibition enhances temozolomide effect in glioma cells. In this report, we investigated the molecular mechanisms of sensitization of glioblastoma cells to temozolomide by GSK3ß inhibition, focusing on O(6)-methylguanine DNA methyltransferase (MGMT) gene silencing. Glioblastoma tissues from patients treated with the GSK3ß-inhibiting drugs were subjected to immunohistochemistry and methylation-specific PCR assay. Human glioblastoma cell lines T98G, U138, U251 and U87 were treated with a small-molecule GSK3ß inhibitor, AR-A014418 or GSK3ß-specific small interfering RNA. The combined effect of temozolomide and AR-A014418 on cell proliferation was determined by AlamarBlue assay and an isobologram method. MGMT promoter methylation was estimated by methylation-specific PCR and MethyLight assay. MGMT gene expression was evaluated by real-time quantitative reverse transcriptase-PCR. c-Myc and DNA (cytosine-5)-methyltransferase 3A binding to the MGMT promoter was estimated by chromatin immunoprecipitation assay. GSK3ß inhibition decreased phosphorylation of glycogen synthase and reduced MGMT expression and increased MGMT promoter methylation in clinical tumors. In glioblastoma cell lines, GSK3ß inhibition decreased cell viability, enhanced temozolomide effect and downregulated MGMT expression with relevant changes in the methylation levels of the MGMT promoter. Here, we showed for the first time that c-Myc binds to the MGMT promoter with consequent recruitment of DNA (cytosine-5)-methyltransferase 3A, regulating the levels of MGMT promoter methylation. The results of this study suggest that GSK3ß inhibition enhances temozolomide effect by silencing MGMT expression via c-Myc-mediated promoter methylation.

Receptor tyrosine kinases: principles and functions in glioma invasion.

Protein tyrosine kinases are enzymes that are capable of adding a phosphate group to specific tyrosines on target proteins. A receptor tyrosine kinase (RTK) is a tyrosine kinase located at the cellular membrane and is activated by binding of a ligand via its extracellular domain. Protein phosphorylation by kinases is an important mechanism for communicating signals within a cell and regulating cellular activity; furthermore, this mechanism functions as an "on" or "off" switch in many cellular functions. Ninety unique tyrosine kinase genes, including 58 RTKs, were identified in the human genome; the products of these genes regulate cellular proliferation, survival, differentiation, function, and motility. Tyrosine kinases play a critical role in the development and progression of many types of cancer, in addition to their roles as key regulators of normal cellular processes. Recent studies have revealed that RTKs such as epidermal growth factor receptor (EGFR), platelet-derived growth factor receptor (PDGFR), c-Met, Tie, Axl, discoidin domain receptor 1 (DDR1), and erythropoietin-producing human hepatocellular carcinoma (Eph) play a major role in glioma invasion. Herein, we summarize recent advances in understanding the role of RTKs in glioma pathobiology, especially the invasive phenotype, and present the perspective that RTKs are a potential target of glioma therapy.

Prediction of high-grade meningioma by preoperative MRI assessment.

High-grade (World Health Organization grades II and III) meningiomas grow aggressively and recur frequently, resulting in a poor prognosis. Assessment of tumor malignancy before treatment initiation is important. We attempted to determine predictive factors for high-grade meningioma on magnetic resonance (MR) imaging before surgery. We reviewed 65 meningiomas (39 cases, benign; 26 cases, high-grade) and assessed four factors: (1) tumor-brain interface (TBI) on T1-weighted imaging (T1WI), (2) capsular enhancement (CapE), i.e., the layer of the tumor-brain interface on gadolinium-enhanced T1WI (T1Gd), (3) heterogeneity on T1Gd, and (4) tumoral margin on T1Gd. All four factors were useful in distinguishing high-grade from benign meningiomas, according to univariate analysis. On multivariate regression analysis, unclear TBI and heterogeneous enhancement were independent predictive factors for high-grade meningioma. In meningiomas with an unclear TBI and heterogeneous enhancement, the probability of high-grade meningioma was 98%. Our data suggest that this combination of factors obtained from conventional sequences on MR imaging may be useful to predict high-grade meningioma.

Association between carotid plaque composition assessed by multidetector computed tomography and cerebral embolism after carotid stenting.

INTRODUCTION: We aimed to assess the relationship between atherosclerotic carotid plaque composition analyzed using multidetector computed tomography (MDCT) and the appearance of new ischemic lesions detected by diffusion-weighted images (DWI) after carotid artery stenting (CAS). METHODS: We quantitatively and qualitatively analyzed plaque characteristics in carotid arteries using MDCT before CAS in 19 patients. Carotid plaques were expediently subdivided into four components with Hounsfield unit (HU) values of <0, 0-60, 60-130, and >600. The incidence of distal embolism was evaluated with DWI. Pearson's correlation analyses were used to assess the association between plaque composition and the incidence of cerebral embolization. RESULTS: Fifteen patients (79%) demonstrated new DWI lesions after CAS. High-signal DWIs were noted as follows: one in six patients, 2 ~ 5 in five patients, 6 ~ 10 in two patients, and >10 in two patients. The mean volumes of the plaque components for HU < 0, 0-60, 60-130, and >600 were 5.4, 200, 260, and 59 mm(3), respectively. There was a strong correlation between the number of high-signal DWI lesions in the ipsilateral side and the plaque volume of HU < 0 (r = 0.927; P < 0.0001). There was a moderate correlation between the number of high-signal DWI lesions and the plaque volume of HU 0-60 (r = 0.568; P = 0.0099) and the sum total of HU < 0 and HU 0-60 (r = 0.609; P = 0.0047). CONCLUSIONS: Quantitative and qualitative tissue characterization of carotid plaques using MDCT might be a useful predictor for silent ischemic lesions after CAS.

Dissecting aneurysms of the vertebral artery--angiographic patterns at the dissecting site on balloon test occlusion.

INTRODUCTION: At present, the risk of future hemorrhage or ischemic insult from vertebral artery (VA) dissection cannot be estimated from available imaging data. We investigated the relationship between symptoms and the angiographic patterns of the dissecting site on balloon test occlusion (BTO) to develop guidelines for clinical decision-making. METHODS: We retrospectively reviewed 18 patients with unilateral VA dissection who presented with subarachnoid hemorrhage (SAH) or cerebral infarction. We analyzed the angiographic findings at the dissecting site on contralateral VA angiograms during BTO of the affected VA, classified the angiographic patterns into two types, and compared the symptoms they presented. RESULTS: Patients with dissection opacified from the distal to the proximal side are more likely to present with cerebral infarction than SAH. Conversely, patients with dissection opacified from the proximal to the distal side had a significantly higher incidence of SAH. CONCLUSIONS: Angiographic findings at the dissecting site on contralateral VA angiograms during BTO of the affected VA are helpful for considering the treatment and prognosis of patients with VA dissecting aneurysms.

Identification of tumor-initiating cells in a highly aggressive brain tumor using promoter activity of nucleostemin.

Controversy remains over whether the cancer stem cell (CSC) theory applies to all tumors. To determine whether cells within a highly aggressive solid tumor are stochastically or hierarchically organized, we combined a reporter system where the nucleostemin (NS) promoter drives GFP expression (termed NS-GFP) with a mouse brain tumor model induced by retroviral Ras expression on a p16(Ink4a)/p19(Arf)-deficient background. The NS-GFP system allowed us to monitor the differentiation process of normal neural stem/precursor cells by analyzing GFP fluorescence intensity. In tumor-bearing mice, despite the very high frequency of tumorigenic cells, we successfully identified the NS-GFP(+) cells as tumor-initiating cells (T-ICs). The clonal studies conclusively established that phenotypical heterogeneity can exist among the cells comprising a genetically homogeneous tumor, suggesting that this aggressive brain tumor follows the CSC model. Detailed analyses of the NS-GFP(+) brain tumor cells revealed that T-ICs showed activation of the receptor tyrosine kinase c-Met, which functions in tumor invasiveness. Thus, the NS-GFP system provides a powerful tool to elucidate stem cell biology in normal and malignant tissues.

Postoperative diabetes insipidus associated with pituitary apoplexy during pregnancy.

BACKGROUND: Pituitary apoplexy during pregnancy is so rare that only 15 cases (12 pituitary adenomas, 2 lymphocytic neurohypophysitis, and 1 normal pituitary gland) have been published to date. Here, we report the case of a pregnant woman presenting with pituitary apoplexy from a nonfunctioning pituitary adenoma and provide a possible mechanism and management option for postoperative diabetes insipidus (DI). CASE PRESENTATION: A 26-year-old woman presented with sudden onset of headache and bitemporal hemianopsia in the 26th week of her first pregnancy. Magnetic resonance imaging clearly revealed an 18 mm pituitary mass with a fluid-fluid level component displacing the optic chiasma upward. Endonasal endoscopic transsphenoidal surgery was successfully carried out 7 days after the onset of symptoms. DI became apparent immediately after the operation and was not controllable by arginine vasopressin (AVP) but by 1-desamino-8-D-arginine vasopressin (DDAVP) instead. This finding suggests an association between DI and vasopressinase secretion from the placenta, because vasopressinase can degrade AVP but not DDAVP. DI had diminished by the time the patient delivered a healthy girl at the 40th week of gestation. CONCLUSION: Postoperative DI associated with pituitary apoplexy during pregnancy should be treated by DDAVP, which is not affected by placental vasopressinase secretion.

[Awake surgery with line bisection task for two cases of parietal glioma in the non-dominant hemisphere].

Awake surgery for lesions in the non-dominant parietal lobe is rare. We report two cases of right parietal lobe glioma for which awake surgery was performed in order to avoid ataxie optique and hemispatial neglect due to injury in the superior and inferior parietal lobule, respectively. Among several tests to assess the dysfunction of spatial recognition, line bisection test was selected for the task during awake surgery because of its simplicity, easy repetition, and utility. The tumor was successfully removed without any neurological deficit in both the cases. The line bisection test is simple and useful for preserving spatial recognition during an awake surgery.

The correlation between promoter methylation status and the expression level of O6-methylguanine-DNA methyltransferase in recurrent glioma.

BACKGROUND: The DNA repair protein O(6)-methylguanine-DNA methyltransferase is a drug-resistant protein, which protects the tumors from chemotherapeutic alkylating agents, such as temozolomide. The methylation status of O(6)-methylguanine-DNA methyltransferase promoter has been shown to be a major predictive factor for clinical outcome in glioma patients when treated by alkylating agents. Thereby, there were many reports on O(6)-methylguanine-DNA methyltransferase promoter methylation and mRNA expression in primary glioma, in contrast, there were only a few studies in recurrent glioma. METHODS: We evaluated the O(6)-methylguanine-DNA methyltransferase mRNA expression and promoter methylation status in glioma patients before and after recurrence by quantitative real-time PCR and methylation-specific PCR assay. Thirteen paired primary and recurrent glioma patients were analyzed, including four patients in whom malignant transformation occurred from Grade II to Grade III. RESULTS: Methylation-specific PCR assay demonstrated that the status of O(6)-methylguanine-DNA methyltransferase promoter changed from methylated to unmethylated in 10 of 13 samples when the tumor relapsed. Moreover, intra-individual O(6)-methylguanine-DNA methyltransferase mRNA level increased in recurrent gliomas than in primary ones (P = 0.016). O(6)-methylguanine-DNA methyltransferase mRNA level was correlated with the methylation status (P = 0.012). CONCLUSIONS: Our results give the evidence that the increase of O(6)-methylguanine-DNA methyltransferase mRNA expression caused by methylation changes in recurrence may be associated with chemoresistance in the recurrent glioma.

Transcrusal approach to the retrochiasmatic region with special reference to temporal lobe retraction: an anatomical study.

BACKGROUND: The retrochiasmatic region is one of the most challenging areas to surgically expose. The authors evaluated the transcrusal approach, which involves removal of the superior and posterior semicircular canal from the ampulla to the common crus, to expose the retrochiasmatic region and compared it with the retrolabyrinthine approach, both of which are a variation of the posterior petrosal approach with hearing preservation, with a special emphasis on the influence of temporal lobe retraction. METHODS: Six sides of silicone-injected cadaveric heads were dissected using two approaches: the transcrusal approach and the retrolabyrinthine approach. For each craniotomy, 3 exposure parameters in the retrochiasmatic region were measured: (1) horizontal distance, (2) vertical distance, and (3) triangular area of exposure, at three different levels of temporal lobe retractions: 0, 5, and 10 mm of retraction from the level of the tentorial incisura. RESULTS: Without temporal lobe retraction, only the transcrusal and not the retrolabyrinthine approach provided a direct exposure of the retrochiasmatic region, especially in the horizontal distance (p < 0.001). At all levels of temporal lobe retraction, the transcrusal approach provided greater exposure in the horizontal and vertical distances and in the area of exposure. Nonetheless, in the horizontal distance, the difference between the transcrusal and retrolabyrinthine approaches decreased along with increased temporal lobe retraction, and almost no difference was obtained at 10 mm of retraction. CONCLUSIONS: Posterior petrosal approaches can provide an excellent exposure of the retrochiasmatic region. Of these two approaches, namely, transcrusal and retrolabyrinthine with hearing preservation, the transcrusal approach offers greater exposure than the retrolabyrinthine approach. The beneficial effect of partial labyrinthectomy of the transcrusal approach to the retrochiasmatic region is accentuated in the exposure of the horizontal distance with less temporal lobe retraction.

Ganglioglioma of the thoracolumbar spinal cord in a patient with neurofibromatosis type 1: a case report and literature review.

Gangliogliomas of the spinal cord are rare, and the conus medullaris is an extremely rare site for their occurrence. The authors present a case in which a ganglioglioma was found in the thoracolumbar spinal cord, including the conus medullaris, of a 5-year-old female patient with neurofibromatosis type 1 (NF1) who presented with paraparesis and urinary disturbance. MRI revealed an intramedullary lesion within the thoracolumbar spinal cord, including the conus medullaris, which was surgically removed. Pathological investigation showed a ganglioglioma consisting of glioneuronal tumor cells. This is the first report to provide a pathological description of a spinal cord ganglioglioma in a patient with NF1. Because gangliogliomas usually have a good prognosis following resection, it is important to clearly distinguish them from other NF1-associated lesions, even though ganglioglioma of the thoracolumbar spinal cord, including the conus medullaris, is an extremely rare condition.

Sphingosine-1-phosphate receptor type 1 regulates glioma cell proliferation and correlates with patient survival.

Sphingosine-1-phosphate (S1P) is a bioactive lipid that signals through a family of G protein-coupled receptors consisting of 5 members termed S1P(1-5), and it regulates cellular proliferation, migration and survival. We investigated the expression and role of S1P receptors in glioma. Human glioma expressed S1P(1), S1P(2), S1P(3), and S1P(5) by quantitative real-time PCR analysis. Expression of the S1P(1) was significantly lower in glioblastoma than in the normal brain (p < 0.01) and diffuse astrocytoma (p < 0.05). Immunoblotting showed that normal brain expressed more S1P(1) protein than did glioblastoma. Immunohistochemistry showed that S1P(1) was localized predominantly in the astrocytes in the normal brain, but no staining was observed in glioblastoma. Downregulation of S1P(1) expression correlated with poor survival of patients with glioblastoma (p < 0.05). S1P(1) small interfering RNA promoted cell proliferation in high-expressor glioma cell lines (T98G, G112). Cell proliferation was promoted by the pertussis toxin, which deactivates G(i/o) type of G proteins; the S1P(1) is exclusively coupled to these proteins. Forced expression of the S1P(1) in low-expressor cell lines (U87, U251) resulted in decreased cell growth and led to suppressed tumor growth in transplanted gliomas in vivo. Furthermore, we found a significant association between the S1P(1) expression and early growth response-1, a transcriptional factor that exhibits tumor suppression in glioblastoma cells (p < 0.05). These data indicate that the downregulation of S1P(1) expression enhances the malignancy of glioblastoma by increasing cell proliferation and correlates with the shorter survival of patients with glioblastoma.

The expression level of sphingosine-1-phosphate receptor type 1 is related to MIB-1 labeling index and predicts survival of glioblastoma patients.

Although there are many reports on the clinical use of the MIB-1 labeling index (LI), which is a measure of proliferative activity in astrocytomas; its significance varies between studies. There are no known molecules that are directly linked to the MIB-1 LI in astrocytomas. We evaluated the clinical value of the MIB-1 LI in our human glioblastoma cases and determined the molecules that possibly influenced the MIB-1 LI. An immunohistochemical study of the MIB-1 protein was performed and MIB-1 LIs of 38 glioblastomas were determined. In the same cases, epidermal growth factor receptor (EGFR), platelet-derived growth factor receptor-alpha (PDGFRA), and sphingosine-1-phosphate receptor type 1 (S1P(1)), which are known regulators of glioma cell proliferation, were detected and quantified by quantitative real-time-PCR or western blotting. Kaplan-Meier survival curves for 38 patients with glioblastomas showed that a high MIB-1 LI correlated with poor survival (P < 0.05). Among the molecules tested, only the low expression of S1P(1) was significantly correlated with the high MIB-1 LI in glioblastomas (P < 0.05). Multivariate analysis revealed that the S1P(1) expression level was a significant prognostic factor. Our results indicate that the MIB-1 LI is an important prognostic factor in human glioblastomas. Furthermore, downregulation of S1P(1) expression increases proliferative activity, and thus enhances the malignancy of glioblastomas, resulting in a poor survival.

Radiation-induced cerebellar high-grade glioma accompanied by meningioma and cavernoma 29 years after the treatment of medulloblastoma: a case report.

Here, we report the case of a patient with cerebellar high-grade glioma that developed after the patient underwent treatment for medulloblastoma. A 34-year-old man visited our hospital with complaints of dizziness and truncal ataxia. Magnetic resonance image showed a cerebellar tumor with multiple cavernomas and two lesions that were suspected to be meningiomas. The cerebellar tumor was surgically removed. According to pathological examination, the tumor was a high-grade glioma that was positive for methylated O-6-methylguanine-DNA methyltransferase promoter. In the past, he had received radiotherapy at the age of 5, after which he was operated for desmoplastic medulloblastoma in his right cerebellar hemisphere. Seven years after the initial therapy, cavernoma-induced intracerebral hemorrhage of the right temporal lobe was noted. To our knowledge, this is the first case of radiation-induced double intracranial tumors accompanied by symptomatic cavernoma.

Potential therapeutic effect of glycogen synthase kinase 3beta inhibition against human glioblastoma.

PURPOSE: 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. EXPERIMENTAL DESIGN: 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. RESULTS: 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. CONCLUSION: 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.