Usefulness of Serum Soluble Interleukin-2 Receptor Levels for Differentiating between PCNSL and SCNSL.

Serum soluble interleukin-2 receptor (sIL-2R) is a practical tumor marker that is elevated in hematogenous tumors. The purpose of this study was to determine the usefulness of serum sIL-2R for differentiating among malignant brain tumors, including primary central nervous system lymphoma (PCNSL) and secondary central nervous system lymphoma (SCNSL). This study retrospectively investigated the sIL-2R levels in 130 patients with various types of malignant brain tumors, including PCNSL patients (n = 48) and SCNSL (n = 8); metastatic brain tumors (MTs, n = 16); and glioblastoma (GBM, n = 58). The median sIL-2R level (U/mL) of the PCNSL, SCNSL, MTs, and GBM groups were 489.7, 1024.8, 413.3, and 332.7 respectively. The sIL-2R level was significantly higher in the SCNSL group than in the PCNSL or other groups. The area under the ROC curve generated from the sIL-2R level was 0.826 (sensitivity: 0.875, specificity: 0.667, cutoff value: 521 U/mL) for differentiating SCNSL from PCNSL and 0.685 (sensitivity: 0.667, specificity: 0.707, cutoff value: 342 U/mL) for differentiating PCNSL from GBM. Measurement of sIL-2R level was convenient and useful to differentiate between SCNSL and PCSNL, both of which demand different treatment strategies.

CEP-1347 Targets MDM4 Protein Expression to Activate p53 and Inhibit the Growth of Glioma Cells.

BACKGROUND/AIM: The development of pharmacological inhibitors targeting negative regulators of p53, such as murine double minute (MDM) 2 and, more recently, MDM4, has been actively pursued as a potential strategy to treat cancers with wild-type p53. We previously showed that CEP-1347, a small molecule kinase inhibitor originally developed for the treatment of Parkinson's disease, suppressed MDM4 expression and activated wild-type p53 in retinoblastoma cells. However, it remains unknown whether CEP-1347 acts as an MDM4 inhibitor and as such activates p53 in other types of human cancer cells. MATERIALS AND METHODS: The effects of CEP-1347 and MDM4 knockdown on the mRNA and protein expression of components of the p53 pathway, including MDM4, in human glioma cell lines with and without p53 mutation were examined by RT-PCR and western blot analyses. Trypan blue dye exclusion was used to examine the effect of CEP-1347 on cell growth. RESULTS: CEP-1347 decreased the expression of MDM4, increase that of p53, and activated the p53 pathway in glioma cells with wild-type p53. Knockdown-mediated inhibition of MDM4 expression in a glioma cell line with wild-type p53 that overexpresses MDM4 resulted in increased p53 expression and activation of the p53 pathway. CEP-1347 preferentially inhibited the growth of glioma cells with wild-type p53 without showing toxicity to normal cells at clinically relevant concentrations. CONCLUSION: Our findings suggest CEP-1347 is a novel inhibitor of MDM4 protein expression and as such activates p53 to inhibit the growth of cancer cells with wild-type p53, including retinoblastoma and glioblastoma.

A surgical case of pediatric spinal medulloepithelioma.

Embryonal tumor with multilayered rosettes (ETMR), C19MC-altered was introduced to the World Health Organization classification of central nervous system tumors in 2016. It is characterized by amplification or fusion of the chromosome 19 microRNA cluster (C19MC) locus at 19q13.42. Medulloepithelioma also an ETMR but lacks C19MC alteration. We report a rare case of spinal medulloepithelioma in a 2-year-old boy and review the literature.

Necessity for craniospinal irradiation of germinoma with positive cytology without spinal lesion on MR imaging-A controversy.

BACKGROUND: Cerebrospinal fluid (CSF) cytology and spinal MR imaging are routinely performed for staging before treatment of intracranial germinoma. However, the interpretation of the results of CSF cytology poses 2 unresolved clinical questions: (1) Does positive CSF cytology correlate with the presence of spinal lesion before treatment? and (2) Is craniospinal irradiation (CSI) necessary for patients with positive CSF cytology in the absence of spinal lesion? METHODS: Multicenter retrospective analyses were performed based on a questionnaire on clinical features, spinal MR imaging finding, results of CSF cytology, treatments, and outcomes which was sent to 86 neurosurgical and 35 pediatrics departments in Japan. Pretreatment frequencies of spinal lesion on MR imaging were compared between the patients with positive and negative cytology. Progression-free survival (PFS) rates were compared between patients with positive CSF cytology without spinal lesion on MR imaging treated with CSI and with whole brain or whole ventricular irradiation (non-CSI). RESULTS: A total of 92 germinoma patients from 45 institutes were evaluated by both CSF cytology and spinal MR images, but 26 patients were excluded because of tumor markers, the timing of CSF sampling or incomplete estimation of spinal lesion. Of the remaining 66 germinoma patients, spinal lesions were equally identified in patients with negative CSF cytology and positive cytology (4.9% and 8.0%, respectively). Eleven patients treated with non-CSI had excellent PFS comparable to 11 patients treated with CSI. CONCLUSION: CSI is unnecessary for germinoma patients with positive CSF cytology without spinal lesions on MR imaging.

Malignant Progression of an IDH Mutant Brainstem Glioma in Adult.

Brain stem gliomas (BSG) in adults are rare and less aggressive than those in children. However, the molecular profile of adult BSG cases has not been well characterized. We report a case of adult BSG with isocitrate dehydrogenase (IDH) mutation. A 43-year-old male was admitted to our hospital with diplopia and right-sided hypesthesia. An open biopsy led to the tumor being diagnosed as a diffuse astrocytoma. Immunohistochemically, the tumor was positive for IDH1 R132H, but negative for H3K27M. The patient received 54 Gy of local radiotherapy and adjuvant temozolomide, which resulted in the size of the lesion decreasing significantly. At 56 months after the initial diagnosis, the patient was referred to our hospital with a severe headache and ataxia. Magnetic resonance imaging (MRI) revealed a contrast-enhanced lesion in the brain stem, which extended into the left cerebellar hemisphere and brainstem. Partial tumor removal was performed, and a pathological examination revealed the features of glioblastoma. Immunohistochemically, the tumor was positive for IDH1 R132H and p53 and negative for ATRX. To the best of our knowledge, there are few reports about adult case of brain stem astrocytoma to be confirmed via histological and molecular examinations of the primary and recurrent tumor. We exhibit detailed pathological and molecular findings which resembles to IDH mutant supratentorial diffuse astrocytic tumors.

So-called bifocal tumors with diabetes insipidus and negative tumor markers: are they all germinoma?

BACKGROUND: The Delphi consensus statements on the management of germ cell tumors (GCTs) failed to reach agreements on the statement that the cases with (i) pineal and neurohypophyseal bifocal lesion, (ii) with diabetes insipidus, and (iii) with negative tumor markers can be diagnosed as germinoma without histological verification. To answer this, multicenter retrospective analysis was performed. METHODS: A questionnaire on clinical findings, histological diagnosis, and details of surgical procedures was sent to 86 neurosurgical and 35 pediatrics departments in Japan. RESULTS: Fifty-one institutes reported 132 cases that fulfilled the 3 criteria. Tissue sampling was performed in 91 cases from pineal (n = 44), neurohypophyseal (n = 32), both (n = 6), and distant (n = 9) lesions. Histological diagnosis was established in 89 cases: pure germinoma or germinoma with syncytiotrophoblastic giant cells in 82 (92.1%) cases, germinoma and mature teratoma in 2 cases, and granulomatous inflammation in 2 cases. Histological diagnosis was not established in 2 cases. Although no tumors other than GCTs were identified, 3 (3.4%) patients had non-germinomatous GCTs (NGGCTs). None of the patients developed permanent complications after endoscopic or stereotactic biopsy. Thirty-nine patients underwent simultaneous procedure for acute hydrocephalus without permanent complications, and hydrocephalus was controlled in 94.9% of them. CONCLUSION: All patients who fulfilled the 3 criteria had GCTs or granulomatous inflammation, but not other types of tumors. However, no fewer than 3.4% of the patients had NGGCTs. Considering the safety and the effects of simultaneous procedures for acute hydrocephalus, biopsy was recommended in such patients.

TERT promoter mutation associated with multifocal phenotype and poor prognosis in patients with IDH wild-type glioblastoma.

BACKGROUND: Although mutations in the promoter region of the telomerase reverse transcriptase (TERTp) gene are the most common alterations in glioblastoma (GBM), their clinical significance remains unclear. Therefore, we investigated the impact of TERTp status on patient outcome and clinicopathological features in patients with GBM over a long period of follow-up. METHODS: We retrospectively analyzed 153 cases of GBM. Six patients with isocitrate dehydrogenase 1 (IDH1) or H3F3A gene mutations were excluded from this study. Among the 147 cases of IDH wild-type GBM, 92 (62.6%) had the TERTp mutation. Clinical, immunohistochemical, and genetic factors (BRAF, TP53 gene mutation, CD133, ATRX expression, O 6-methylguanine-DNA methyltransferase [MGMT] promoter methylation) and copy number alterations (CNAs) were investigated. RESULTS: GBM patients with the TERTp mutation were older at first diagnosis versus those with TERTp wild type (66.0 vs. 60.0 years, respectively, P = .034), and had shorter progression-free survival (7 vs. 10 months, respectively, P = .015) and overall survival (16 vs. 24 months, respectively, P = .017). Notably, magnetic resonance imaging performed showed that TERTp-mutant GBM was strongly associated with multifocal/distant lesions (P = .004). According to the CNA analysis, TERTp mutations were positively correlated with EGFR amp/gain, CDKN2A deletion, and PTEN deletion; however, these mutations were negatively correlated with PDGFR amp/gain, CDK4 gain, and TP53 deletion. CONCLUSIONS: TERTp mutations were strongly correlated with multifocal/distant lesions and poor prognosis in patients with IDH wild-type GBM. Less aggressive GBM with TERTp wild type may be a distinct clinical and molecular subtype of IDH wild-type GBM.

TERT promoter mutation confers favorable prognosis regardless of 1p/19q status in adult diffuse gliomas with IDH1/2 mutations.

TERT promoter mutations are commonly associated with 1p/19q codeletion in IDH-mutated gliomas. However, whether these mutations have an impact on patient survival independent of 1p/19q codeletion is unknown. In this study, we investigated the impact of TERT promoter mutations on survival in IDH-mutated glioma cases. Detailed clinical information and molecular status data were collected for a cohort of 560 adult patients with IDH-mutated gliomas. Among these patients, 279 had both TERT promoter mutation and 1p/19q codeletion, while 30 had either TERT promoter mutation (n = 24) or 1p/19q codeletion (n = 6) alone. A univariable Cox proportional hazard analysis for survival using clinical and genetic factors indicated that a Karnofsky performance status score (KPS) of 90 or 100, WHO grade II or III, TERT promoter mutation, 1p/19q codeletion, radiation therapy, and extent of resection (90-100%) were associated with favorable prognosis (p < 0.05). A multivariable Cox regression model revealed that TERT promoter mutation had a significantly favorable prognostic impact (hazard ratio = 0.421, p = 0.049), while 1p/19q codeletion did not have a significant impact (hazard ratio = 0.648, p = 0.349). Analyses incorporating patient clinical and genetic information were further conducted to identify subgroups showing the favorable prognostic impact of TERT promoter mutation. Among the grade II-III glioma patients with a KPS score of 90 or 100, those with IDH-TERT co-mutation and intact 1p/19q (n = 17) showed significantly longer survival than those with IDH mutation, wild-type TERT, and intact 1p/19q (n = 185) (5-year overall survival, 94% and 77%, respectively; p = 0.032). Our results demonstrate that TERT promoter mutation predicts favorable prognosis independent of 1p/19q codeletion in IDH-mutated gliomas. Combined with its adverse effect on survival among IDH-wild glioma cases, the bivalent prognostic impact of TERT promoter mutation may help further refine the molecular diagnosis and prognostication of diffuse gliomas.

[Diffuse Leptomeningeal Glioneuronal Tumor with Subarachnoid Hemorrhage:A Case Report].

Diffuse leptomeningeal glioneuronal tumor(DLGNT)is a rare primary neoplasm of the central nervous system, and is a condition that is newly listed in the 2016 World Health Organization(WHO)classification of tumors of the central nervous system. We report an adult case of DLGNT that was characteristically merged with subarachnoid hemorrhage. A 46-year-old woman reported persistent dizziness upon walking. MRI of the brain revealed a diffuse, infiltrating lesion with high intensity on FLAIR around the cerebellopontine angle to the lateral ventricle and in the leptomeninges of the spinal cord. The lesion on the cerebellopontine angle showed high intensity on T1 weighted images with contrast enhancement. Since diffuse glioma and meningeal carcinomatosis were suspected, we performed an endoscopic biopsy for the lesion in the right lateral ventricle. Although the tumor was tentatively diagnosed as WHO grade II diffuse astrocytoma, a definitive diagnosis could not be obtained. One month after surgery, the patient presented with acute headache and dizziness. CT showed subarachnoid hemorrhage in the cerebellopontine angle. To decompress the intracranial pressure and prevent re-bleeding, and to obtain enough tissue samples for definitive diagnosis, we removed the enhanced lesion and hematoma at the cerebellopontine angle. Tumor tissue was composed of oligodendroglial-like cells and was positive for GFAP, Olig2, synaptophysin, and S100 protein, although it was negative for IDH1R132H. Fluorescent in situ hybridization showed KIAA1566-BRAF fusion; however, neither 1p loss nor 1p19q co-deletion was observed. Together with histological and radiological findings, the tumor was ultimately diagnosed as DLGNT. The patient received maintenance chemotherapy with temozolomide, and the tumor was stable at 18 months after surgery.

Relationships between recurrence patterns and subventricular zone involvement or CD133 expression in glioblastoma.

INTRODUCTION: We previously reported that CD133 expression correlated with the recurrence pattern of glioblastoma (GBM). Subventricular zone (SVZ) involvement may also be associated with distant recurrence in GBM. Therefore, we herein investigated whether the combined analysis of SVZ involvement and CD133 expression is useful for predicting the pattern of GBM recurrence. MATERIALS AND METHODS: We retrospectively analyzed 167 cases of GBM. Tumors were divided into four groups based on spatial relationships between contrast-enhanced lesions (CEL) and the SVZ or cortex (Ctx) on MRI. The initial recurrence pattern (local/distant) was obtained from medical records. To identify factors predictive of recurrence, we examined CD133 expression by immunohistochemical, clinical (age, sex, KPS, Ki-67 labeling index, surgery, and MRI characteristics), and genetic (IDH1, MGMT, and BRAF) factors. RESULTS: The CD133 expression rate was higher in SVZ-positive tumors than in SVZ-negative tumors (P = 0.046). Distant recurrence was observed in 21% of patients, and no significant difference was noted in recurrence patterns among the four groups. However, strong CD133 expression was associated with a shorter time to distant recurrence in univariate, multivariate, and propensity-matched scoring analyses (P < 0.0001, P = 0.001, and P = 0.0084, respectively). In the combined analysis, distant recurrence was the most frequent (70%) in group III (SVZ-negative, Ctx-positive) GBM and those with high CD133 expression rates (≥ 15%). CONCLUSION: An integrated analysis of CD133 expression and MRI-based tumor classification may be useful for predicting the recurrence pattern of GBM.

Treatment outcomes of hypofractionated radiotherapy combined with temozolomide followed by bevacizumab salvage therapy in glioblastoma patients aged > 75 years.

BACKGROUND: The optimal treatment for elderly patients with glioblastoma has not been established. METHODS: We retrospectively analyzed the safety and efficacy of hypofractionated radiotherapy (45 Gy/15 fr) combined with temozolomide (TMZ) followed by bevacizumab (BEV) salvage treatment in 18 glioblastoma patients aged > 75 years. RESULTS: All of the patients received safe hypofractionated radiotherapy and concomitant TMZ (75 mg/m2), and 14 of 18 patients received maintenance TMZ. We administered BEV to 17 of 18 patients because their Karnofsky Performance Status scores declined and/or recurrence was detected. During the follow-up period (median duration: 17.5 months, range 3-33 months), 12 patients died of their disease. While the median progression-free survival period was 2.5 months, the median overall survival period was 20 months. Adverse events (National Cancer Institute Common Terminology Criteria for Adverse Events grade 3 or 4) occurred in 5 patients. CONCLUSION: Hypofractionated radiotherapy combined with TMZ and BEV salvage treatment was found to be safe and effective in glioblastoma patients aged > 75 years.

The Likelihood of Remnant Nonfunctioning Pituitary Adenomas Shrinking Is Associated with the Lesion's Blood Supply Pattern.

OBJECTIVE: Nonfunctioning pituitary adenomas (NFPA) often shrink after transsphenoidal surgery. However, little is known about the predictors of spontaneous NFPA regression. The aim of this study was to determine whether the blood supply pattern of remnant NFPA lesions was associated with the likelihood of such lesions shrinking. METHODS: A total of 37 remnant tumors in 31 patients who were treated at the Department of Neurosurgery, Yamagata University Hospital, were included in this study. All patients underwent preoperative dynamic 3.0T magnetic resonance imaging (MRI) to evaluate their tumors' arterial blood supplies, followed by endoscopic transsphenoidal surgery and intraoperative 1.5T MRI. Follow-up MRI scans were obtained at 1-2 weeks and 3-6 postoperative months. RESULTS: We detected tumor shrinkage in 15 of 37 (40.5%) remnant tumors on follow-up MRI scans obtained at 3-6 postoperative months. Remnant tumors were found in rostral and caudal locations in 21 and 16 cases, respectively. Rostral remnant tumors were significantly more likely to shrink (P < 0.0001). The tumors were classified into 3 groups according to their blood supply patterns (23 ascending, 6 descending, and 2 monophasic). The ascending blood supply pattern was found to be a positive predictor of tumor shrinkage (P = 0.002). Furthermore, no remnant tumors with rich blood supplies underwent spontaneous regression (P < 0.0001). CONCLUSIONS: Evaluations of the blood supplies of remnant NFPA via preoperative dynamic MRI and the locations of the remnant tumors could be useful for predicting postoperative tumor shrinkage.

Opening the ventricle during surgery diminishes survival among patients with newly diagnosed glioblastoma treated with carmustine wafers: a multi-center retrospective study.

Carmustine wafers (CW) were approved in Japan for newly diagnosed and recurrent malignant gliomas during 2013. The ventricle is often opened during surgery to achieve maximum resection. While not generally recommended in such situations, CW might be safely achieved by occluding an opened ventricle using gelform or collagen sheets. However, whether CW implantation actually confers a survival benefit for patients who undergo surgery with an open ventricle to treat glioblastoma remains unclear. Clinical, imaging, and survival data were collected in this multicenter retrospective study of 122 consecutive patients with newly diagnosed glioblastoma to determine adverse events and efficacy. Overall, 54 adverse events of all grades developed in 35 (28.6%) patients, with the most common being new seizures (16%). Adverse events did not significantly differ between patients with opened and closed ventricles during surgery. The 10- and 21.7-month, median, progression-free (PFS) and overall survival (OS), respectively did not significantly differ according to resection rates. However, median PFS and OS were significantly longer among patients with closed, than open ventricles (12.8 vs. 7.4 months; p = 0.0039 and 26.9 vs. 18.6 months; p = 0.011, respectively). Implanting CW into the resection cavity during concomitant radiochemotherapy with temozolomide seems to yield better survival rates without increased adverse events. Occlusion of the ventricular opening during surgery might be safe for CW implantation, but less so for treating patients with newly diagnosed glioblastoma.

Targeting JNK for therapeutic depletion of stem-like glioblastoma cells.

Control of the stem-like tumour cell population is considered key to realizing the long-term survival of patients with glioblastoma, one of the most devastating human malignancies. To date, possible therapeutic targets and targeting methods have been described, but none has yet proven to target stem-like glioblastoma cells in the brain to the extent necessary to provide a survival benefit. Here we show that targeting JNK in vivo, the activity of which is required for the maintenance of stem-like glioblastoma cells, via transient, systemic administration of a small-molecule JNK inhibitor depletes the self-renewing and tumour-initiating populations within established tumours, inhibits tumour formation by stem-like glioblastoma cells in the brain, and provide substantial survival benefit without evidence of adverse events. Our findings not only implicate JNK in the maintenance of stem-like glioblastoma cells but also demonstrate that JNK is a viable, clinically relevant therapeutic target in the control of stem-like glioblastoma cells.

MEK-ERK signaling dictates DNA-repair gene MGMT expression and temozolomide resistance of stem-like glioblastoma cells via the MDM2-p53 axis.

Overcoming the resistance of glioblastoma cells against temozolomide, the first-line chemotherapeutic agent of choice for newly diagnosed glioblastoma, is a major therapeutic challenge in the management of this deadly brain tumor. The gene encoding O(6) -methylguanine DNA methyltransferase (MGMT), which removes the methyl group attached by temozolomide, is often silenced by promoter methylation in glioblastoma but is nevertheless expressed in a significant fraction of cases and is therefore regarded as one of the most clinically relevant mechanisms of resistance against temozolomide. However, to date, signaling pathways regulating MGMT in MGMT-expressing glioblastoma cells have been poorly delineated. Here in this study, we provide lines of evidence that the mitogen-activated protein/extracellular signal-regulated kinase kinase (MEK)-extracellular signal-regulated kinase (ERK)-murine double minute 2 (MDM2)-p53 pathway plays a critical role in the regulation of MGMT expression, using stem-like glioblastoma cells directly derived from patient tumor samples and maintained in the absence of serum, which not only possess stem-like properties but are also known to phenocopy the characteristics of the original tumors from which they are derived. We show that, in stem-like glioblastoma cells, MEK inhibition reduced MDM2 expression and that inhibition of either MEK or MDM2 resulted in p53 activation accompanied by p53-dependent downregulation of MGMT expression. MEK inhibition rendered otherwise resistant stem-like glioblastoma cells sensitive to temozolomide, and combination of MEK inhibitor and temozolomide treatments effectively deprived stem-like glioblastoma cells of their tumorigenic potential. Our findings suggest that targeting of the MEK-ERK-MDM2-p53 pathway in combination with temozolomide could be a novel and promising therapeutic strategy in the treatment of glioblastoma.

FoxO3a functions as a key integrator of cellular signals that control glioblastoma stem-like cell differentiation and tumorigenicity.

Glioblastoma is one of the most aggressive types of human cancer, with invariable and fatal recurrence even after multimodal intervention, for which cancer stem-like cells (CSLCs) are now being held responsible. Our recent findings indicated that combinational inhibition of phosphoinositide-3-kinase/Akt/mammalian target of rapamycin (mTOR) and mitogen-activated protein/extracellular signal-regulated kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) pathways effectively promotes the commitment of glioblastoma CSLCs to differentiation and thereby suppresses their tumorigenicity. However, the mechanism by which these two signaling pathways are coordinated to regulate differentiation and tumorigenicity remains unknown. Here, we identified FoxO3a, a common phosphorylation target for Akt and ERK, as a key transcription factor that integrates the signals from these pathways. Combinational blockade of both the pathways caused nuclear accumulation and activation of FoxO3a more efficiently than blockade of either alone, and promoted differentiation of glioblastoma CSLCs in a FoxO3a expression-dependent manner. Furthermore, the expression of a constitutively active FoxO3a mutant lacking phosphorylation sites for both Akt and ERK was sufficient to induce differentiation and reduce tumorigenicity of glioblastoma CSLCs. These findings suggest that FoxO3a may play a pivotal role in the control of differentiation and tumorigenicity of glioblastoma CSLCs by the PI3K/Akt/mTOR and MEK/ERK signaling pathways, and also imply that developing methods targeting effective FoxO3a activation could be a potential approach to the treatment of glioblastoma.

Crosstalk between the PI3K/mTOR and MEK/ERK pathways involved in the maintenance of self-renewal and tumorigenicity of glioblastoma stem-like cells.

The molecular signaling pathways orchestrating the biology of cancer stem-like cells (CSLCs), including glioblastoma, remain to be elucidated. We investigated in this study the role of the MEK/extracellular signal-regulated kinase (ERK) pathway in the control of self-renewal and tumorigenicity of glioblastoma CSLCs, particularly in relation to the PI3K/mTOR (mammalian target of rapamycin) pathway. Targeted inactivation of MEK alone using pharmacological inhibitors or siRNAs resulted in reduced sphere formation of both cell line- and patient-derived glioblastoma CSLCs, accompanied by their differentiation into neuronal and glial lineages. Interestingly, this effect of MEK inactivation was apparently augmented in the presence of NVP-BEZ235, a dual inhibitor of PI3K and mTOR. As a potential explanation for this observed synergy, we found that inactivation of either the MEK/ERK or PI3K/mTOR pathway triggered activation of the other, suggesting that there may be mutually inhibitory crosstalk between these two pathways. Significantly, inactivation of either pathway led to the reduced activation of p70S6K, and siRNA-mediated knockdown of p70S6K resulted in the activation of both pathways, which no longer maintained the cross-inhibitory relationship. Finally, combinational blockade of both pathways in glioblastoma CSLCs suppressed their tumorigenicity, whether transplanted subcutaneously or intracranially, more efficiently than blockade of either alone. Our findings suggest that there is p70S6K-mediated, cross-inhibitory regulation between the MEK/ERK and PI3K/mTOR pathways, in which each contribute to the maintenance of the self-renewal and tumorigenic capacity of glioblastoma CSLCs. Thus, combinational disruption of these pathways would be a rational and effective strategy in the treatment of glioblastoma.

Dual blocking of mTor and PI3K elicits a prodifferentiation effect on glioblastoma stem-like cells.

Glioblastoma, the most intractable cerebral tumor, is highly lethal. Recent studies suggest that cancer stem-like cells (CSLCs) have the capacity to repopulate tumors and mediate radio- and chemoresistance, implying that future therapies may need to turn from the elimination of rapidly dividing, but differentiated, tumor cells to specifically targeting the minority of tumor cells that repopulate the tumor. However, the mechanism by which glioblastoma CSLCs maintain their immature stem-like state or, alternatively, become committed to differentiation is poorly understood. Here, we show that the inactivation of mammalian target of rapamycin (mTor) by the mTor inhibitor rapamycin or knockdown of mTor reduced sphere formation and the expression of neural stem cell (NSC)/progenitor markers in CSLCs of the A172 glioblastoma cell line. Interestingly, combination treatment with rapamycin and LY294002, a phosphatidylinositol 3-kinase (PI3K) inhibitor, not only reduced the expression of NSC/progenitor markers more efficiently than single-agent treatment, but also increased the expression of ßIII-tubulin, a neuronal differentiation marker. Consistent with these results, a dual PI3K/mTor inhibitor, NVP-BEZ235, elicited a prodifferentiation effect on A172 CSLCs. Moreover, A172 CSLCs, which were induced to undergo differentiation by pretreatment with NVP-BEZ235, exhibited a significant decrease in their tumorigenicity when transplanted either subcutaneously or intracranially. Importantly, similar results were obtained when patient-derived glioblastoma CSLCs were used. These findings suggest that the PI3K/mTor signaling pathway is critical for the maintenance of glioblastoma CSLC properties, and targeting both mTor and PI3K of CSLCs may be an effective therapeutic strategy in glioblastoma.

Regulation of neural stem/progenitor cell maintenance by PI3K and mTOR.

Control of stem cell state and differentiation of neural stem/progenitor cells is essential for proper development of the nervous system. EGF and FGF2 play important roles in the control of neural stem/progenitor cells, but the underlying mechanism still remains unclear. Here we show, using in vitro primary cultures of mouse neural stem/progenitor cells, that both PI3K and mTOR are activated by EGF/FGF2 but that inhibiting the activation of either PI3K or mTOR alone results in only reduced proliferation of neural stem/progenitor cells without affecting their stem cell state, namely, the capacity to self-renew. However, significantly, concurrent inhibition of PI3K and mTOR promoted exit from the stem cell state together with astrocytic differentiation of neural stem/progenitor cells. These findings suggest that PI3K and mTOR are involved in the EGF/FGF2-mediated maintenance of neural stem/progenitor cells and that they may act in parallel and independent pathways, complementing and backing up each other to maintain the stem cell state.