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.

Massive Hemorrhage from the Posterior Ethmoidal Artery during Transsphenoidal Surgery: Report of 2 Cases.

Nasal bleeding is a major complication that can occur during and after transsphenoidal surgery (TSS) for intra- and suprasellar tumors. In most cases, the cause of this bleeding can be attributed to a branch of the maxillary artery called the sphenopalatine artery, injury to which can lead to life-threatening situations. Upon exposure of the suprasellar region and planum sphenoidale during surgery, it is also important to avoid damaging the posterior ethmoidal artery (PEA), a branch of the ophthalmic artery. While recent advancement in endoscopic techniques enables the performance of extended TSS, the chances of PEA injury seem to be increasing. In the current report, we present two cases that showed massive PEA bleeding during regular (not extended) TSS. The total blood loss was 2280 ml and 2150 ml, and endoscopic views disturbed by the massive hemorrhages remarkably delayed accurate stanching of the responsive artery. Therefore, anatomical recognition of the PEA is required to avoid fatal hemorrhaging during even regular TSS, especially for the beginners of this surgery.

Symptomatic foramen of Magendie arachnoid cyst in an elderly patient.

BACKGROUND: Arachnoid cysts (ACs) are congenital anomalies of the central nervous system and arise in virtually all locations where the arachnoid membrane exists. Posterior fossa ACs are considered to develop in the posterior aspect of the rhombencephalic roof plate and do not communicate freely with the fourth ventricle or perimedullary subarachnoid space. Although posterior fossa ACs have been reported a number of times, ACs arising from the foramen of Magendie are very rare. CASE DESCRIPTION: We report here on a 76-year-old female who presented with progressive gait disturbance. Magnetic resonance imaging of the head showed a large AC in the foramen of Magendie that was compressing the inferior vermis and medial aspects of the cerebellar hemisphere without causing hydrocephalus. Neurological examination revealed cerebellar ataxia without Romberg's sign. A nearly total excision of the cyst was safely performed via a median suboccipital approach. The patient's postoperative course was excellent and her neurological recovery was remarkable. CONCLUSION: Most cases of ACs located in the foramen of Magendie are reported in children, and it is extremely rare to observe such ACs in the elderly. In fact, to our knowledge, a symptomatic foramen Magendie AC has never been reported previously in an elderly person. Our results indicate that proper surgical intervention can yield highly positive outcomes in such cases.

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.

Adenoid cystic carcinoma in the cavernous sinus diagnosed with the endoscopic endonasal approach.

A 42-year-old woman presented with right oculomotor, abducens, and trigeminal palsy. Neuroimaging revealed a small lesion in the right cavernous sinus mimicking meningioma. Because the symptoms gradually worsened, the patient underwent an endoscopic endonasal transsphenoidal surgery for tumor biopsy. Histological examination of the surgical specimen revealed adenoid cystic carcinoma (ACC). Before and after the operation, no evidence of other primary lesions could be detected. The patient was treated with stereotactic radiosurgery (SRS). ACC in the cavernous sinus can be difficult to diagnosis before histological confirmation, because it is extremely rare as a primary lesion and resembles a cavernous sinus meningioma on neuroimaging studies. Two years after the first SRS, the tumor recurred along the trigeminal nerve and SRS was performed again. Our study illustrates that in case in which a lesion in the cavernous sinus progresses on neurological and neuroimaging studies, a biopsy should be taken to provide most accurate diagnosis and treatment.

Endoscopic removal of subgaleal hematoma in a 7-year-old patient treated with anticoagulant and antiplatelet agents.

BACKGROUND: Subgaleal hematomas frequently occur in children after head trauma and extend over the cranial sutures. Although conservative treatment suffices in most cases, surgical removal of a subgaleal hematoma is indicated when the patient presents with anemia and headache associated with its progressive enlargement. CASE DESCRIPTION: We present the case of a 7-year-old boy who was medicated with warfarin and aspirin due to a hypoplastic left ventricle and fell from a rock wherein he hit his head in the frontal region. Although a computed tomography scan of the head revealed no intracranial lesion, an extracranial hematoma was found to extend over the cranial sutures, leading to the diagnosis of subgaleal hematoma. The hematoma continued to grow gradually despite the cessation of warfarin and aspirin therapy immediately after the head trauma. Since the patient's headache and anemia were progressing as the hematoma enlarged, removal of the hematoma was performed 3 days after admission. Endoscopic hematoma removal was planned to enable accurate coagulation of the sites of bleeding and removal of the maximal amount of hematoma through minimal incision. The hematoma was completely removed, and the patient's postoperative course was excellent with alleviation of both the anemia and the headache. No sign of hematoma recurrence could be detected during 2 years follow-up. CONCLUSION: An angled endoscope can allow visualization of the deep subgaleal space, and this technique enabled direct visualization of the bleeding sites and accurate coagulation to prevent recurrence of hematoma. Endoscopic techniques, such as minimally invasive techniques, can allow sufficient removal of subgaleal hematoma with minimal morbidity, especially in patients such as ours.

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.

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.

Characterizing invading glioma cells based on IDH1-R132H and Ki-67 immunofluorescence.

Glioma, the most common primary brain tumor, is characterized by proliferative-invasive growth. However, the detailed biological characteristics of invading glioma cells remain to be elucidated. A monoclonal antibody (clone HMab-1) that specifically and sensitively recognizes the isocitrate dehydrogenase-1 (IDH1) protein carrying the R132H mutation can identify invading glioma cells by immunostaining. To investigate the degree of invasion in gliomas of distinct grades and the proliferative capacity of the invading cells, immunofluorescent staining was conducted using antibodies against IDH1-R132H and Ki-67 on 11 surgical and autopsy specimens of the tumor core and the invading area. Higher numbers of IDH1-R132H-positive cells in the invading area correlated with a higher tumor grade. Double staining for IDH1-R132H and Ki-67 demonstrated that most invading cells that expressed IDH1-R132H were not stained by the Ki-67 antibody, and the ratio of Ki-67-positive cells among IDH1-R132H-positive cells was significantly lower in the invasion area than in the tumor core in all grades of glioma. These data suggest that higher grade gliomas have a greater invasive potential and that invading cells possess low proliferative capacity.

Mechanism of chemoresistance against tyrosine kinase inhibitors in malignant glioma.

Glioblastoma (GBM) is one of the most lethal malignancies in humans, and novel therapeutic strategies are urgently required for its treatment. Tyrosine kinases (TKs) play a pivotal role in intercellular signal transduction and regulate crucial processes of tumor cell biological activities in GBM. This information provides the basis for the molecular target therapies for GBMs. TK inhibitors (TKIs) are expected to be effective therapeutic strategies. However, one important limitation is that GBMs exhibit marked resistance to the TKIs currently available, yet the mechanisms underlying TKI resistance have not been fully characterized. In the current review, we will address the varieties of chemoresistance mechanisms against TKIs in GBM. The mechanisms responsible for TKI refractoriness in GBMs are divided into 2 aspects. The first includes tumor-related concerns, such as a lack of target expression, the multiplicity of targets, redundancy, the appearance of resistant cells, and tumor changes in characteristics. The second includes drug-related concerns, such as inefficient drug effects, delivery, pharmacokinetics, and intolerable side effects. A better understanding of these mechanisms is needed to develop accurate tests to predict the lack of response to TKIs and for developing novel approaches aimed at overcoming the resistance to TKIs.

Predictive value of fractional anisotropy of the arcuate fasciculus for the functional recovery of language after brain tumor resection: a preliminary study.

OBJECTIVE: The arcuate fasciculus has been recognized as an important pathway for language processing. Brain tumors located in proximity to the fasciculus frequently cause preoperative language impairment, and in some cases, no language recovery occurs after tumor resection. No predictive value has been presented for possible postoperative language recovery after tumor resection. The aim of this study is to analyze the preoperative state of the arcuate fasciculus in the patients with brain tumor from the perspective of its usefulness as a predictive factor for postoperative recovery of language functions. METHODS: For 12 right-handed patients with brain tumors in the left hemisphere, preoperative arcuate fasciculi were analyzed with fractional anisotropy (FA) of the diffusion tensor imaging (DTI) tractography. Language functions were evaluated pre- and postoperatively by using the Western Aphasia Battery (WAB). The preoperative value of the FA of the arcuate fasciculus on the lesion side was examined in relation with the language recovery. RESULTS: There was a positive relationship between preoperative increasing values of the FA of the left arcuate fasciculus and improvement of the postoperative total WAB score (p=0.0056), and the scores of the naming (p=0.018), reading (p=0.029), and writing subcategories (p=0.012) CONCLUSION: The preoperative increasing value of the FA of the arcuate fasciculus in the dominant hemisphere could be a predictor for postoperative language recovery following tumor resection. Meticulous procedure should be performed especially in the cases with higher FA of the arcuate fasciculus harboring high possibility of language recovery.

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.

Functional reorganization in the patient with progressing glioma of the pure primary motor cortex: a case report with special reference to the topographic central sulcus defined by somatosensory-evoked potential.

BACKGROUND: The concept of human brain reorganization due to slow-growing lesions, including low-grade glioma, has been gradually and generally accepted. However, few cases have been reported in which the reorganization, especially in the topographic pure primary motor cortex, was observed during brain surgery. We report a case of slow-growing oligodendroglioma located in the pure primary motor cortex, as detected by magnetic resonance imaging that could be resected in part thanks to the brain plasticity. In addition, we describe a pitfall of topographic guidance using somatosensory-evoked potential (SEP) monitoring. CASE DESCRIPTION: A 36-year-old right-handed patient underwent resection of a gradually growing oligodendroglioma located in the right primary motor cortex, with no other adjacent lesions, 8 years after the initial biopsy. The central sulcus was defined with intraoperative SEP monitoring in both operations. Based on the findings of the intraoperative direct electrical stimulation under awake craniotomy, we suspect that motor function shifted posteriorly and reorganized beyond the central sulcus. CONCLUSIONS: Pure primary motor cortex could be reorganized by its own lesion. In reorganized brain, topographic central sulcus defined based on SEP findings may be an inappropriate guidance to estimate true functional area. In such a condition, intraoperative direct electrical stimulation under awake craniotomy makes it feasible to resect pure primary motor cortex invaded by tumors.

Molecular analysis of a recurrent glioblastoma treated with bevacizumab.

We treated a case of recurrent glioblastoma (GBM) with bevacizumab and assessed its effect biologically. A 55-year-old man with a left frontal lobe GBM was experiencing recurrence 7 months postoperation. We administered bevacizumab concomitant with temozolomide (TMZ). Follow-up magnetic resonance imaging (MRI) showed dramatic but temporal tumor reduction; however, the patient died of re-recurrent disease 6 months after beginning bevacizumab. We obtained an autopsy and analyzed the detailed molecular change. In the autopsy specimen, the quantity of microvessels was significantly reduced. Vascular endothelial growth factor receptor (VEGFR) 1 and VEGFR2 were downregulated, most likely due to a negative feedback mechanism by blocking of VEGF signaling. Matrix metalloproteinase (MMP)-2 and membrane-type 1 MMP were upregulated, resulting in the higher activation of MMP-2 in the autopsy specimen. MIB-1 staining index and phosphorylation levels of p44/42-mitogen-activated protein kinase did not change, whereas phosphorylated protein kinase B (Akt) was decreased in the autopsy specimen, suggesting compensation and/or amplification of other proliferative signaling pathways such as suppression of apoptosis signaling. Consequently, bevacizumab might inhibit the VEGF autocrine loop, which then causes a change in molecular expression related not only to enhancement of tumor invasion but also maintenance of tumor proliferation.

Regression of cerebellar tonsillar descent and hydrocephalus after endoscopic third ventriculostomy in a patient with a quadrigeminal arachnoid cyst.

BACKGROUND: Posterior fossa arachnoid cysts, including quadrigeminal cistern arachnoid cysts, can occasionally cause compression of the quadrigeminal plate, leading to Sylvian aqueduct stenosis and induction of cerebellar tonsillar descent into the foramen magnum. This, in turn, can result in obstructive hydrocephalus. In such cases, the characteristic of hydrocephalus is generally considered to be hypertensive. CASE DESCRIPTION: We present the case of a 28-year-old female complaining of chronic and progressively worsening headaches following the delivery of her first child. Magnetic resonance imaging revealed marked tri-ventriculomegaly, the arachnoid cyst located in the quadrigeminal cistern, and cerebellar tonsillar descent. Ophthalmoscopy revealed bilateral papilledema indicating a long-standing elevation of intracranial pressure. Endoscopic third ventriculostomy (ETV) was performed successfully and resulted in complete recovery from her headaches and papilledema. Postoperative MRI revealed resolution of ventriculomegaly and cerebellar tonsillar descent, suggesting that the fourth ventricle outlet obstruction was associated with the development of the hydrocephalus in this patient. CONCLUSION: Our case is the first report that a quadrigeminal arachnoid cyst associated with both cerebellar tonsillar descent and hydrocephalus was well treated with ETV. It was indicated that the patient's hydrocephalus and cerebellar tonsillar descent were secondary and synergistic events, caused by the arachnoid cyst located in the quadrigeminal cistern.

Ligand-dependent EphB1 signaling suppresses glioma invasion and correlates with patient survival.

BACKGROUND: Extensive evidence implicates the Eph receptor family of tyrosine kinases and its ligand, ephrin, in glioma invasion, but it remains incompletely understood how these receptors affect chemotactic behavior of glioma. We sought to identify the Eph family members that correlate with patients' survival and to reveal the function of Eph in glioma invasion. METHODS: Clinical relevance of EphB genes was confirmed in a clinically annotated expression data set of 195 brain biopsy specimens. The function of EphB was analyzed in vitro and in vivo. RESULTS: Levels of mRNA of certain EphB members were significantly different in histological grades of glioma. According to Kaplan-Meier analysis, only the EphB1 level among 5 members of EphB emerged to be a powerful predictor of favorable survival in malignant glioma (n = 97, P = .0048), although the levels of EphB1 expression did not vary across the tumor grades. Immunoprecipitation showed that tyrosine phosphorylated EphB1 was not detected in all glioma cells tested. Forced overexpression and autophosphorylation of EphB1 in low expressor cell lines (U251, U87) did not affect cell migration or invasion in vitro, whereas EphB1 phosphorylation induced by ephrin-B2/Fc significantly decreased migration and invasion. Cells expressing ephrin-B2 showed noteworthy morphological changes consistent with migration induction; this alteration was negated by EphB1 overexpression. Concomitantly, overexpression of EphB1 abrogated the increased migration and invasion induced by ephrin-B2 in vitro and in vivo. CONCLUSIONS: These data suggest that ligand-dependent EphB1 signaling negatively regulates glioma cell invasion, identifying EphB1 as a favorable prognostic factor in malignant glioma.

Surgical strategies for nonenhancing slow-growing gliomas with special reference to functional reorganization: review with own experience.

Nonenhancing intrinsic brain tumors have been empirically treated with a strategy that has been adopted for World Health Organization (WHO) grade II gliomas (low-grade gliomas: LGGs), even though small parts of the tumors might have been diagnosed as WHO grade III gliomas after surgery. However, the best surgical strategy for nonenhancing gliomas, including LGGs, is still debatable. LGGs have the following features: slow growth, high possibility of histologically malignant transformation, and no clear border between the tumor and adjacent normal brain. We retrospectively examined 26 consecutive patients with nonenhancing gliomas who were surgically treated at Kanazawa University Hospital between January 2006 and May 2012, with special reference to functional reorganization, extent of resection (EOR), and functional mapping during awake surgery. These categories are closely related with the features of LGG, i.e. functional reorganization due to slow-growing nature, EOR with related malignant transformation, and functional mapping for delineating the unclear tumor border. Finally, we discuss surgical strategies for slow-growing gliomas that are represented by LGGs and nonenhancing gliomas. In conclusion, slow-growing gliomas tend to undergo functional reorganization, and the functional reorganization affects the presurgical evaluation for resectability based on tumor location related to eloquence. In the clinical setting, to definitely identify the reorganized functional regions, awake surgery is recommended. Therefore, awake surgery could increase the extent of the resection of the tumor without deficits, resulting in the delay of malignant transformation and increase in overall survival.

Rapidly progressing monoparesis caused by Chiari malformation type I without syringomyelia.

BACKGROUND: Patients with Chiari malformation type I (CM-I) can manifest neurological symptoms, such as headache, neck pain, dysesthesia, swallowing disturbance, and paresis, which are usually stable or slowly progressive even if syringomyelia is coexistent. In some instances, however, acute onset of neurological symptoms has been reported but the pathogenetic mechanism and subsequent clinical course have not been explained. In those cases, it was reported that urgent treatment of foramen magnum decompression (FMD) was very effective. This work reports that an 11-year-old girl with CM-I subacutely developed unique symptoms and that urgent treatment of FMD was very effective. CASE DESCRIPTION: We present here an 11-year-old girl with CM-I who subacutely developed dysphagia, left upper extremity monoparesis and sensory dysesthesia, with the limb assuming a peculiar posture at rest, with the wrist in extension and the elbow joint in flexion. Although her symptoms were assumed to be due to previously diagnosed CM-I without syringomyelia, no differences on magnetic resonance imaging (MRI) could be found except for slight change in the shape of tonsils compared with the previous ones. FMD and C1 removal with duraplasty was performed and resulted in an excellent neurological recovery. CONCLUSION: This case is a reminder that the presence of a new neurological deficit referable to nuclei within, or tracts that traverse, the cerebromedullary junction is a firm surgical indication for FMD in a patient with CM-I. MRI was nearly identical during the asymptomatic and symptomatic periods in this case, and did not explain the timing of symptom onset.

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.