There has been increasing awareness that glioblastoma, which may seem histopathologically similar across many tumors, actually represents a group of molecularly distinct tumors. Emerging evidence suggests that cells even within the same tumor exhibit wide-ranging molecular diversity. Parallel to the discoveries of molecular heterogeneity among tumors and their individual cells, intense investigation of the cellular biology of glioblastoma has revealed that not all cancer cells within a given tumor behave the same. The identification of a subpopulation of brain tumor cells termed “glioblastoma cancer stem cells” or “tumor-initiating cells” has implications for the management of glioblastoma. This focused review will therefore summarize emerging concepts on the molecular and cellular heterogeneity of glioblastoma and emphasize that we should begin to consider each individual glioblastoma to be an ensemble of molecularly distinct subclones that reflect a spectrum of dynamic cell states.

Accumulating evidence suggests cancer cells exhibit a dependency on metabolic pathways regulated by nicotinamide adenine dinucleotide (NAD + ). Nevertheless, how the regulation of this metabolic cofactor interfaces with signal transduction networks remains poorly understood in glioblastoma. Here, we report nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting step in NAD + synthesis, is highly expressed in glioblastoma tumors and patient-derived glioblastoma stem-like cells (GSCs). High NAMPT expression in tumors correlates with decreased patient survival. Pharmacological and genetic inhibition of NAMPT decreased NAD + levels and GSC self-renewal capacity, and NAMPT knockdown inhibited the in vivo tumorigenicity of GSCs. Regulatory network analysis of RNA sequencing data using GSCs treated with NAMPT inhibitor identified transcription factor E2F2 as the center of a transcriptional hub in the NAD + -dependent network. Accordingly, we demonstrate E2F2 is required for GSC selfrenewal. Downstream, E2F2 drives the transcription of members of the inhibitor of differentiation (ID) helix-loop-helix gene family. Finally, we find NAMPT mediates GSC radiation resistance. The identification of a NAMPT-E2F2-ID axis establishes a link between NAD + metabolism and a self-renewal transcriptional program in glioblastoma, with therapeutic implications for this formidable cancer.T he prognosis for glioblastoma, the most common malignant intrinsic brain tumor in adults, remains poor despite aggressive multidisciplinary therapy, including maximal safe surgical resection, radiation therapy, and temozolomide (1, 2). The failure of these interventions to generate a durable response stems in part from inadequate understanding of the metabolic and molecular mechanisms underlying malignant behavior and therapeutic resistance (3, 4). Nicotinamide adenine dinucleotide (NAD + ) has a well-known role in cellular metabolism and is an important cofactor for signaling pathways that regulate aging, inflammation, diabetes mellitus, axonal injury, and cancer (5, 6). Nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme in mammalian NAD + synthesis, produces NAD + precursor nicotinamide mononucleotide (NMN) to drive NAD + -dependent processes. Interestingly, NAMPT expression is extremely low in the mammalian brain compared with other organs (7,8). However, NAMPT is highly expressed in several cancers, and features of cancer cells, including proliferation, invasion, and tumor growth, exhibit a dependence on NAD + (9-11). In noncancer cells, NAD + plays a critical role in transcriptional control, providing a metabolic basis for epigenetic reprogramming (12-16). Enzymes using NAD + as a cofactor, including the sirtuins and poly-ADP ribosyl transferases, regulate transcription factor activity and chromatin structure (13-15). Additionally, NAD + can control transcription by altering DNA methylation in neurons (12). However, in glioblastoma, little is known about NAD + -dependent transcriptional events and whether these even...

ObjectiveDelayed cerebral ischemia (DCI) is an independent risk factor for poor outcome after aneurysmal subarachnoid hemorrhage (SAH) and is multifactorial in etiology. While prior studies have suggested a role for matrix metalloproteinase‐9 (MMP‐9) in early brain injury after SAH, its contribution to the pathophysiology of DCI is unclear.MethodsIn the first experiment, wild‐type (WT) and MMP‐9−/− mice were subjected to sham or endovascular perforation SAH surgery. In separate experiments, WT and MMP‐9−/−mice were administered vehicle or minocycline either pre‐ or post‐SAH. All mice underwent assessment of multiple components of DCI including vasospasm, neurobehavioral function, and microvessel thrombosis. In another experiment, rabbits were subjected to sham or cisterna magna injection SAH surgery, and administered vehicle or minocycline followed by vasospasm assessment.Results MMP‐9 expression and activity was increased after SAH. Genetic (MMP‐9−/− mice) and pharmacological (pre‐SAH minocycline administration) inhibition of MMP‐9 resulted in decreased vasospasm and neurobehavioral deficits. A therapeutically feasible strategy of post‐SAH administration of minocycline resulted in attenuation of multiple components of DCI. Minocycline administration to MMP‐9−/− mice did not yield additional protection. Consistent with experiments in mice, both pre‐ and post‐SAH administration of minocycline attenuated SAH‐induced vasospasm in rabbits.Interpretation MMP‐9 is a key player in the pathogenesis of DCI. The consistent attenuation of multiple components of DCI with both pre‐ and post‐SAH administration of minocycline across different species and experimental models of SAH, combined with the excellent safety profile of minocycline in humans suggest that a clinical trial in SAH patients is warranted.

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OBJECTIVEDelayed cerebral ischemia (DCI) after aneurysmal subarachnoid hemorrhage (SAH) is characterized by large-artery vasospasm, distal autoregulatory dysfunction, cortical spreading depression, and microvessel thrombi. Large-artery vasospasm has been identified as an independent predictor of poor outcome in numerous studies. Recently, several animal studies have identified a strong protective role for inhalational anesthetics against secondary brain injury after SAH including DCI—a phenomenon referred to as anesthetic conditioning. The aim of the present study was to assess the potential role of inhalational anesthetics against cerebral vasospasm and DCI in patients suffering from an SAH.METHODSAfter IRB approval, data were collected retrospectively for all SAH patients admitted to the authors’ hospital between January 1, 2010, and December 31, 2013, who received general anesthesia with either inhalational anesthetics only (sevoflurane or desflurane) or combined inhalational (sevoflurane or desflurane) and intravenous (propofol) anesthetics during aneurysm treatment. The primary outcomes were development of angiographic vasospasm and development of DCI during hospitalization. Univariate and logistic regression analyses were performed to identify independent predictors of these endpoints.RESULTSThe cohort included 157 SAH patients whose mean age was 56 ± 14 (± SD). An inhalational anesthetic–only technique was employed in 119 patients (76%), while a combination of inhalational and intravenous anesthetics was employed in 34 patients (22%). As expected, patients in the inhalational anesthetic–only group were exposed to significantly more inhalational agent than patients in the combination anesthetic group (p < 0.05). Multivariate logistic regression analysis identified inhalational anesthetic–only technique (OR 0.35, 95% CI 0.14–0.89), Hunt and Hess grade (OR 1.51, 95% CI 1.03–2.22), and diabetes (OR 0.19, 95% CI 0.06–0.55) as significant predictors of angiographic vasospasm. In contradistinction, the inhalational anesthetic–only technique had no significant impact on the incidence of DCI or functional outcome at discharge, though greater exposure to desflurane (as measured by end-tidal concentration) was associated with a lower incidence of DCI.CONCLUSIONSThese data represent the first evidence in humans that inhalational anesthetics may exert a conditioning protective effect against angiographic vasospasm in SAH patients. Future studies will be needed to determine whether optimized inhalational anesthetic paradigms produce definitive protection against angiographic vasospasm; whether they protect against other events leading to secondary brain injury after SAH, including microvascular thrombi, autoregulatory dysfunction, blood-brain barrier breakdown, neuroinflammation, and neuronal cell death; and, if so, whether this protection ultimately improves patient outcome.