Paola Brescia

CD133 Is Essential for Glioblastoma Stem Cell Maintenance

The role of the cell surface CD133 as a cancer stem cell marker in glioblastoma (GBM) has been widely investigated, since it identifies cells that are able to initiate neurosphere growth and form heterogeneous tumors when transplanted in immune‐compromised mice. However, evidences of CD133‐negative cells exhibiting similar properties have also been reported. Moreover, the functional role of CD133 in cancer stem/progenitor cells remains poorly understood. We studied the biological effects of CD133 downregulation in GBM patient‐derived neurospheres. Our results indicate that there is not a hierarchical relation between CD133‐positive and CD133‐negative cells composing the neurospheres. Indeed, CD133 appears in an interconvertible state, changing its subcellular localization between the cytoplasm and the plasmamembrane of neurosphere cells. Silencing of CD133 in human GBM neurospheres using lentivirus‐mediated short hairpin RNA impairs the self‐renewal and tumorigenic capacity of neurosphere cells. These results imply that CD133 could be used as a therapeutic target in GBMs. STEM CELLS 2013;31:857–869

Current Strategies for Identification of Glioma Stem Cells: Adequate or Unsatisfactory?

Cancer stem cells (CSCs) were isolated in multiple tumor types, including human glioblastomas, and although the presence of surface markers selectively expressed on CSCs can be used to isolate them, no marker/pattern of markers are sufficiently robust to definitively identify stem cells in tumors. Several markers were evaluated for their prognostic value with promising early results, however none of them was proven to be clinically useful in large-scale studies, leading to outstanding efforts to identify new markers. Given the heterogeneity of human glioblastomas further investigations are necessary to identify both cancer stem cell-specific markers and the molecular mechanisms sustaining the tumorigenic potential of these cells to develop tailored treatments. Markers for glioblastoma stem cells such as CD133, CD15, integrin-α6, L1CAM might be informative to identify these cells but cannot be conclusively linked to a stem cell phenotype. Overlap of expression, functional state and morphology of different subpopulations lead to carefully consider the techniques employed so far to isolate these cells. Due to a dearth of methods and markers reliably identifying the candidate cancer stem cells, the isolation/enrichment of cancer stem cells to be therapeutically targeted remains a major challenge.

Human glioblastoma tumours and neural cancer stem cells express the chemokine CX3CL1 and its receptor CX3CR1

Human gliomas represent an unmet clinical challenge as nearly two-thirds of them are highly malignant lesions with fast progression, resistance to treatment and poor prognosis. The most severe form, the glioblastoma multiforme, is characterised by a marked and diffuse infiltration through the normal brain parenchyma. Given the multiple effects of chemokines on tumour progression, aim of this study was to analyse the expression of the chemokine CX3CL1 and of its specific receptor CX3CR1 in 36 human surgical glioma samples, with different degrees of histological malignancy and in glioblastoma-derived neurospheres. Herein we show that both ligand and receptor are expressed at the mRNA and protein levels in most specimens (31/36). While receptor expression was similarly detected in low or high grade tumours, the uppermost scores of CX3CL1 were found in grades III-IV tumours: oligodendrogliomas, anaplastic astrocytomas and glioblastomas. Accordingly, the expression of CX3CL1 was inversely correlated with patient overall survival (p = 0.01). Glioblastoma-derived neurospheres, containing a mixed population of stem and progenitor cells, were positive for both CX3CR1 and for the membrane-bound chemokine, which was further up-regulated and secreted after TNF-IFNγ stimulation. Confocal microscopy of 3D neurospheres showed that the ligand was primarily expressed in the outer layer cells, with points of co-localisation with CX3CR1, indicating that this ligand-receptor pair may have important intercellular adhesive functions. The high expression of CXC3L1 in the most severe forms of gliomas suggests the involvement of this chemokine and its receptor in the malignant behaviour of these tumours.

Rai is a new regulator of neural progenitor migration and glioblastoma invasion.

The invasive nature of glioblastoma (GBM) is one important reason for treatment failure. GBM stem/progenitor cells retain the migratory ability of normal neural stem/progenitor cells and infiltrate the brain parenchyma. Here, we identify Rai (ShcC/N‐Shc), a member of the family of Shc‐like adaptor proteins, as a new regulator of migration of normal and cancer stem/progenitor cells. Rai is expressed in neurogenic areas of the brain and its knockdown impairs progenitor migration to the olfactory bulb. Its expression is retained in GBM stem/progenitor cells where it exerts the same promigratory activity. Rai silencing in cancer stem/progenitor cells isolated from different patients causes significant decrease in cell migration and invasion, both in vitro and in vivo, providing survival benefit. Rai depletion is associated with alteration of multiple‐signaling pathways, yet it always leads to reduced expression of proinvasive genes. STEM CELLS 2012;30:817–832

Functional Role of CLIC1 Ion Channel in Glioblastoma-Derived Stem/Progenitor Cells

Background Chloride channels are physiologically involved in cell division and motility. Chloride intracellular channel 1 (CLIC1) is overexpressed in a variety of human solid tumors compared with normal tissues, suggesting a potential involvement of CLIC1 in the regulation of tumorigenesis. This led us to investigate the role of CLIC1 in gliomagenesis. Methods We used the neurosphere system to isolate stem/progenitor cells from human glioblastomas (GBMs). CLIC1 targeting in GBM neurospheres was achieved by both lentiviral-mediated short-hairpin RNA transduction and CLIC1 antibody treatment, and its effect on stem-like properties was analyzed in vitro by proliferation and clonogenic assays and in vivo by orthotopic injection in immunocompromised mice. Channel activity was studied by perforated patch clamp technique. Differences in expression were analyzed by analysis of variance with Tamhane’s multiple comparison test. Kaplan–Meier analyses and log-rank test were used to assess survival. All statistical tests were two-sided. Results CLIC1 was statistically significantly overexpressed in GBMs compared with normal brain tissues (P < .001) with a better survival of patients with CLIC1 low-expressing tumors (CLIC1low vs CLIC1high survival: χ2 = 74.35; degrees of freedom = 1; log-rank P < .001). CLIC1 was variably expressed in patient-derived GBM neurospheres and was found enriched in the stem/progenitor compartment. CLIC1 silencing reduced proliferative (P < .01), clonogenic (P < .01), and tumorigenic capacity (P < .05) of stem/progenitor cells. The reduction of CLIC1 chloride currents with a specific CLIC1 antibody mirrored the biological effects of CLIC1 silencing in GBM patient–derived neurospheres. Conclusions Reduced gliomagenesis after CLIC1 targeting in tumoral stem/progenitor cells and the finding that CLIC1 expression is inversely associated with patient survival suggest CLIC1 as a potential target and prognostic biomarker.

Identification of Glioma Stem Cells: What is Already Known and How Far do We Still Need to Go? The Biomarkers Dilemma

Cancer stem cells (CSCs) have been isolated in multiple tumour types and although the presence of surface markers selectively expressed on CSCs can be used to isolate these cells, no marker or pattern of markers are sufficiently robust to definitively identify CSCs. Several markers have been evaluated for their prognostic value with promising early results, however to date none has been proven to be clinically useful in large-scale studies. A major need exists to identify markers of CSCs for glioblastoma (GBM), which would yield new therapeutic interventions. Given the complex genetic and epigenetic heterogeneity of human GBMs, it is unlikely that the expression of a single marker will define CSCs in every tumour, hence a combination of markers will probably best define glioma tumour stem cells. The studies reported in the literature regarding the identification of specific cell surface markers involved in tumourigenic processes of the GBM tumour-initiating cells have been inconclusive. Further investigations are necessary to identify both CSC-specific markers and the molecular mechanism sustaining the tumourigenic potential of these cells in order to develop novel treatments to target this group of cells. Markers for GBM stem cells such as CD133, CD15, integrin α6, L1CAM, are available and might be informative to identify these cells but cannot be conclusively linked to a stem cell phenotype. Overlap of expression, functional state and morphology of different subpopulations lead us to reconsider, or carefully consider, the techniques employed so far to characterize cancer stem cells. Major effort might be exploited to look for alternative methods, to isolate CSCs independently from markers. Due to a dearth of methods and markers that reliably assay the function of candidate stem cells, the isolation/enrichment of tumoural stem cells to be therapeutically targeted remains a major challenge.

Outcome and clinico-biological characteristics of advanced breast cancer patients with surgically resected brain metastases: A multidisciplinary approach

Background: Despite improvements in brain surgery and radiotherapy, patients with brain metastases (BM) from breast cancer still have a poor prognosis. The aim of the present study is to evaluate the outcome of a multimodal therapeutic strategy in an unselected cohort of patients. Methods: We retrospectively reviewed 24 breast cancer patients who developed BM and were treated with brain surgery, radiotherapy, and/or systemic therapy in the same institutions. Results: Primary treatment for BM was surgery in the whole cohort, radiotherapy in 11 patients, radiotherapy combined with systemic therapy in nine patients, and systemic therapy as single treatment in six patients (chemo/targeted therapy n= 4; hormonal therapy n=2). The median time from breast cancer diagnosis to brain surgery was 57.6 months (range 1.8–130.7 months). The overall survival from surgery for BM was 22 months and the overall survival from BM surgery by presence of other metastatic sites at surgery was 25 months for patients with BM only and 11 months for patients with other metastatic sites (p=0.046). Conclusion: Although this study is retrospective and limited by the small number of patients, the overall survival of 22 months from the time of brain surgery represents an excellent outcome. The multidisciplinary approach that combines the efforts of specialists from different disciplines leads to satisfactory results for patients in terms of survival in the current clinical practice and prospective subtype-oriented trials are urgently required in this category of patients.

Mutations targeting the coagulation pathway are enriched in brain metastases

Brain metastases (BMs) are the most common malignancy of the central nervous system. Recently it has been demonstrated that plasminogen activator inhibitor serpins promote brain metastatic colonization, suggesting that mutations in serpins or other members of the coagulation cascade can provide critical advantages during BM formation. We performed whole-exome sequencing on matched samples of breast cancer and BMs and found mutations in the coagulation pathway genes in 5 out of 10 BM samples. We then investigated the mutational status of 33 genes belonging to the coagulation cascade in a panel of 29 BMs and we identified 56 Single Nucleotide Variants (SNVs). The frequency of gene mutations of the pathway was significantly higher in BMs than in primary tumours, and SERPINI1 was the most frequently mutated gene in BMs. These findings provide direction in the development of new strategies for the treatment of BMs.