Alessandro Della Puppa

Intratumoral Hypoxic Gradient Drives Stem Cells Distribution and MGMT Expression in Glioblastoma

Glioblastoma multiforme (GBM) are highly proliferative tumors currently treated by surgical removal, followed by radiotherapy and chemotherapy, which are counteracted by intratumoral hypoxia. Here we exploited image guided surgery to sample multiple intratumoral areas to define potential cellular heterogeneity in correlation to the oxygen tension gradient within the GBM mass. Our results indicate that more immature cells are localized in the inner core and in the intermediate layer of the tumor mass, whereas more committed cells, expressing glial fibrillary acidic protein and β‐III‐tubulin, are distributed along the peripheral and neo‐vascularized area, where Smad1/5/8 and Stat3 result to be activated. Moreover, GBM stem cells, identified with the stem cell marker CD133, express high level of DNA repair protein O6‐methylguanine‐DNA‐methyltransferase (MGMT) known to be involved in chemotherapy resistance and highly expressed in the inner core of the tumor mass. Importantly, these cells and, particularly, CD133+ cells result to be resistant to temozolomide (TMZ), the most used oral alkylating agent for the treatment of GBM, which specifically causes apoptosis only in GBM cells derived from the peripheral layer of the tumor mass. These results indicate a correlation between the intratumoral hypoxic gradient, the tumor cell phenotype, and the tumor resistance to chemotherapy leading to a novel concentric model of tumor stem cell niche, which may be useful to define the real localization of the chemoresistant GBM tumor cells in order to design more effective treatment strategies. STEM CELLS 2010;28:851–862

Interaction of Hypoxia‐Inducible Factor‐1α and Notch Signaling Regulates Medulloblastoma Precursor Proliferation and Fate

Medulloblastoma (MDB) is the most common brain malignancy of childhood. It is currently thought that MDB arises from aberrantly functioning stem cells in the cerebellum that fail to maintain proper control of self‐renewal. Additionally, it has been reported that MDB cells display higher endogenous Notch signaling activation, known to promote the survival and proliferation of neoplastic neural stem cells and to inhibit their differentiation. Although interaction between hypoxia‐inducible factor‐1α (HIF‐1α) and Notch signaling is required to maintain normal neural precursors in an undifferentiated state, an interaction has not been identified in MDB. Here, we investigate whether hypoxia, through HIF‐1α stabilization, modulates Notch1 signaling in primary MDB‐derived cells. Our results indicate that MDB‐derived precursor cells require hypoxic conditions for in vitro expansion, whereas acute exposure to 20% oxygen induces tumor cell differentiation and death through inhibition of Notch signaling. Importantly, stimulating Notch1 activation with its ligand Dll4 under hypoxic conditions leads to expansion of MDB‐derived CD133+ and nestin+ precursors, suggesting a regulatory effect on stem cells. In contrast, MDB cells undergo neuronal differentiation when treated with γ‐secretase inhibitor, which prevents Notch activation. These results suggest that hypoxia, by maintaining Notch1 in its active form, preserves MDB stem cell viability and expansion. STEM CELLS 2010;28:1918–1929

The Three-Layer Concentric Model of Glioblastoma: Cancer Stem Cells, Microenvironmental Regulation, and Therapeutic Implications

Tumors arising in the central nervous system are thought to originate from a sub-population of cells named cancer stem cells (CSCs) or tumor initiating cells (TICs) that possess an immature phenotype, combined with self-renewal and chemotherapy resistance capacity. Moreover, in the last years, these cells have been identified in particular brain tumor niches fundamental for supporting their characteristics. In this paper, we report studies from many authors demonstrating that hypoxia or the so called “hypoxic niche” plays a crucial role in controlling CSC molecular and phenotypic profile. We recently investigated the relationship existing between Glioblastoma (GBM) stem cells and their niche, defining the theory of three-concentric layers model for GBM mass. According to this model, GBM stem cells reside preferentially within the hypoxic core of the tumour mass, while more differentiated cells are mainly localized along the peripheral and vascularized part of the tumour. This GBM model provides explanation of the effects mediated by the tumour microenvironment on the phenotypic and molecular regulation of GBM stem cells, describing their spatial distribution in the tumor bulk. Moreover, we discuss the possible clinical implications of the creation of this model for future GBM patient management and novel therapeutic strategies development.

Hypoxia and succinate antagonize 2-deoxyglucose effects on glioblastoma.

Glioblastoma multiforme (GBM) are highly proliferative brain tumors characterized by a hypoxic microenvironment which controls GBM stem cell maintenance. Tumor hypoxia promotes also elevated glycolytic rate; thus, limiting glucose metabolism is a potential approach to inhibit tumor growth. Here we investigate the effects mediated by 2-deoxyglucose (2-DG), a glucose analogue, on primary GBM-derived cells maintained under hypoxia. Our results indicate that hypoxia protects GBM cells from the apoptotic effect elicited by 2-DG, which raises succinate dehydrogenase activity thus promoting succinate level decrease. As a consequence hypoxia inducible factor-1α (HIF-1α) degradation occurs and this induces GBM cells to acquire a neuronal committed phenotype. By adding succinate these effects are reverted, as succinate stabilizes HIF-1α and increases GBM stem cell fraction particularly under hypoxia, thus preserving the tumor stem cell niche. 2-DG inhibits anaerobic glycolysis altering GBM cell phenotype by forcing tumor cells into mitochondrial metabolism and by inducing differentiation.

Neural potential of a stem cell population in the adipose and cutaneous tissues

Abstract Objective: A significant amount of recent interest has been focused on the possibility that adult human stem cells are a realistic therapeutic alternative to embryonic stem cells. Multipotent stem cells that have characteristics reminiscent of embryonic neural crest stem cells have been isolated from several postnatal tissues, including skin, gut, dental pulp and the heart, and are potentially useful for research and therapeutic purposes. However, their neurogenic potential, including their ability to produce electrophysiologically active neurons, is largely unexplored. In the present work, we investigated this issue with regard to skin-derived precursors (SKPs) and adipose-derived stem cells (ADSc) Methods: Adult stem cells isolated from skin and from adipose tissue derived from the same adult donor were treated with epidermal growth factor (EGF) and fibroblast growth factor 2 (FGF2). Neurospheres obtained were first expanded and evaluated in term of proliferative ability, and then their neuronal differentiation potential was analysed. Results: Adipose- and skin-derived neurospheres grew in suspension as spheres in the presence of the mitogens FGF2 and EGF. With this protocols, the spheres have been able to proliferate and to originate Schwann and glial-like cells. Discussion: In summary, we have demonstrated in this work that multipotent adult precursor cell can be isolated and expanded from two accessible adult tissue sources: skin and adipose tissue. The work described in this paper provides the framework for our attempts to use SKPs or ADSc as autologous adult stem cell population for cell replacement and discovery research.

5-Aminolevulinic Acid Fluorescence in High Grade Glioma Surgery: Surgical Outcome, Intraoperative Findings, and Fluorescence Patterns

Background. 5-Aminolevulinic acid (5-ALA) fluorescence is a validated technique for resection of high grade gliomas (HGG); the aim of this study was to evaluate the surgical outcome and the intraoperative findings in a consecutive series of patients. Methods. Clinical and surgical data from patients affected by HGG who underwent surgery guided by 5-ALA fluorescence at our Department between June 2011 and February 2014 were retrospectively evaluated. Surgical outcome was evaluated by assessing the resection rate as gross total resection (GTR) > 98% and GTR > 90%. We finally stratified data for recurrent surgery, tumor location, tumor size, and tumor grade (IV versus III grade sec. WHO). Results. 94 patients were finally enrolled. Overall GTR > 98% and GTR > 90% was achieved in 93% and 100% of patients. Extent of resection (GTR > 98%) was dependent on tumor location, tumor grade (P < 0.05), and tumor size (P < 0.05). In 43% of patients the boundaries of fluorescent tissue exceeded those of tumoral tissue detected by neuronavigation, more frequently in larger (57%) (P < 0.01) and recurrent (60%) tumors. Conclusions. 5-ALA fluorescence in HGG surgery enables a GTR in 100% of cases even if selection of patients remains a main bias. Recurrent surgery, and location, size, and tumor grade can predict both the surgical outcome and the intraoperative findings.

Molecular Mechanisms of HIF-1α Modulation Induced by Oxygen Tension and BMP2 in Glioblastoma Derived Cells

Background Glioblastoma multiforme (GBM) is one of most common and still poorly treated primary brain tumors. In search for new therapeutic approaches, Bone Morphogenetic Proteins (BMPs) induce astroglial commitment in GBM-derived cells in vitro. However, we recently suggested that hypoxia, which is characteristic of the brain niche where GBM reside, strongly counter-acts BMP effects. It seems apparent that a more complete understanding of the biology of GBM cells is needed, in particular considering the role played by hypoxia as a signaling pathways regulator. HIF-1α is controlled at the transcriptional and translational level by mTOR and, alike BMP, also mTOR pathway modulates glial differentiation in central nervous system (CNS) stem cells. Methodology/Principal Findings Here, we investigate the role of mTOR signaling in the regulation of HIF-1α stability in primary GBM-derived cells maintained under hypoxia (2% oxygen). We found that GBM cells, when acutely exposed to high oxygen tension, undergo Akt/mTOR pathway activation and that BMP2 acts in an analogous way. Importantly, repression of Akt/mTOR signaling is maintained by HIF-1α through REDD1 upregulation. On the other hand, BMP2 counter-acts HIF-1α stability by modulating intracellular succinate and by controlling proline hydroxylase 2 (PHD2) protein through inhibition of FKBP38, a PHD2 protein regulator. Conclusions/Significance In this study we elucidate the molecular mechanisms by which two pro-differentiating stimuli, BMP2 and acute high oxygen exposure, control HIF-1α stability. We previously reported that both these stimuli, by inducing astroglial differentiation, affect GBM cells growth. We also found differences in high oxygen and BMP2 sensitivity between GBM cells and normal cells that should be further investigated to better define tumor cell biology.

Predictive value of intraoperative 5-aminolevulinic acid–induced fluorescence for detecting bone invasion in meningioma surgery

OBJECT Bone invasion is a major concern in meningioma surgery, since it is predictive of the recurrence of cranial involvement, morbidity, and mortality. Bone invasion has been reported in 20%-68% of studies with histopathologically confirmed data. Unfortunately, radical resection of bone invasion remains challenging. The aim of this study was to assess the role of 5-aminolevulinic acid (5-ALA) fluorescence in guiding the resection of bone-invading meningiomas. To this purpose, the sensitivity, specificity, and positive and negative predictive values of 5-ALA in detecting meningioma bone invasion were evaluated. METHODS Data from 12 patients affected by bone-invading meningiomas (7 with skull base and 5 with convexity meningiomas) who had undergone surgery with the assistance of 5-ALA fluorescence and neuronavigation between July 2012 and March 2013 at the Department of Neurosurgery of Padua were retrospectively analyzed. To evaluate the sensitivity and specificity of 5-ALA fluorescence in detecting meningioma tissue, a pathologist analyzed 98 surgical bone samples under blue light, according to different fluorescence patterns. Magnetic resonance images and CT scans were obtained pre- and postoperatively to determine the extent of bone invasion resection. RESULTS The rate of 5-ALA-induced fluorescence of both tumor and bone invasion was 100%. Based on the pathological examination of bone specimens, 5-ALA presented a sensitivity of 89.06% (95% CI 81.41%-96.71%) and a specificity of 100% in detecting meningioma bone invasion, while the positive and negative predictive values were 100% and 82.93% (95% CI 71.41%-94.45%), respectively. At the postoperative stage, MRI did not detect cases of meningioma bone invasion, whereas CT scans revealed residual hyperostosis in 2 cases. CONCLUSIONS In summary, 5-ALA fluorescence represents a suitable and reliable technique for identifying and removing bone infiltration by meningiomas. However, further studies are needed to prove the clinical consequences of this promising technique in a larger population.

Right parietal cortex and calculation processing: intraoperative functional mapping of multiplication and addition in patients affected by a brain tumor

OBJECT The role of parietal areas in number processing is well known. The significance of intraoperative functional mapping of these areas has been only partially explored, however, and only a few discordant data are available in the surgical literature with regard to the right parietal lobe. The purpose of this study was to evaluate the clinical impact of simple calculation in cortical electrostimulation of right-handed patients affected by a right parietal brain tumor. METHODS Calculation mapping in awake surgery was performed in 3 right-handed patients affected by high-grade gliomas located in the right parietal lobe. Preoperatively, none of the patients presented with calculation deficits. In all 3 cases, after sensorimotor and language mapping, cortical and intraparietal sulcus areas involved in single-digit multiplication and addition calculations were mapped using bipolar electrostimulation. RESULTS In all patients, different sites of the right parietal cortex, mainly in the inferior lobule, were detected as being specifically related to calculation (multiplication or addition). In 2 patients the intraparietal sulcus was functionally specific for multiplication. No functional sites for language were detected. All sites functional for calculation were spared during tumor resection, which was complete in all cases without postoperative neurological deficits. CONCLUSIONS These findings provide intraoperative data in support of an anatomofunctional organization for multiplication and addition within the right parietal area. Furthermore, the study shows the potential clinical relevance of intraoperative mapping of calculation in patients undergoing surgery in the right parietal area. Further and larger studies are needed to confirm these data and assess whether mapped areas are effectively essential for function.

Hypertension as a biomarker in patients with recurrent glioblastoma treated with antiangiogenic drugs: a single-center experience and a critical review of the literature.

Treatment with angiogenesis inhibitors is becoming a cornerstone of modern anticancer therapy. Hypertension (HTN) is a common adverse event during antiangiogenic treatment and might represent a cancer biomarker in patients with recurrent glioblastoma treated with angiogenesis inhibitors. In a retrospective study, we analyzed 53 patients with recurrent glioblastoma treated with antiangiogenic drugs. Thirty patients were treated with sorafenib and 23 patients were treated with bevacizumab. All patients underwent brain gadolinium-enhanced MRI assessments according to the Radiologic Assessment in Neuro-Oncology criteria every 2 months or when clinically indicated. Blood pressure was measured before and during the treatment. We investigated whether treatment-related HTN may be associated with outcome in patients treated with antiangiogenic drugs. After 2 months of treatment, 24 patients (45%) achieved disease control: stable disease (17 patients) or a partial response (seven patients). The median overall survival from the start of antiangiogenic treatment was 7.3 months [95% confidence interval (CI) 6.02–8.5]; the median progression-free survival (PFS) was 2.7 months (95% CI 1.5–3.5); and the 6-month PFS was 32%. Twenty patients (38%) developed grades 2–3 HTN within 2 months of treatment. A significant association was found between HTN and disease control rate, and HTN and 6-month PFS; no significant association was found between HTN and the median PFS. According to univariate and multivariate analyses, HTN was related to a longer survival from antiangiogenic drug administration: 9.8 versus 4.8 months (P=0.001; hazard ratio=3.5, 95% CI 1.6–7.6). Our data indicate that HTN may be an effective biomarker in patients with recurrent glioblastoma treated with antiangiogenic drugs; in particular, it may be associated with a favorable effect on disease control, 6-month PFS, and the median overall survival.