HMGA1 silencing reduces stemness and temozolomide resistance in glioblastoma stem cells

Objective: Glioblastoma multiforme (GBM) develops from a small subpopulation of stem-like cells, which are endowed with the ability to self-renew, proliferate and give rise to progeny of multiple neuroepithelial lineages. These cells are resistant to conventional chemo- and radiotherapy and are hence also responsible for tumor recurrence.

HMGA1 overexpression has been shown to correlate with proliferation, invasion, and angiogenesis of GBMs and to affect self-renewal of cancer stem cells from colon cancer. The role of HMGA1 in GBM tumor stem cells is not completely understood.

Research design and methods: We have investigated the role of HMGA1 in brain tumor stem cell (BTSC) self-renewal, stemness and resistance to temozolomide by shRNA- mediated HMGA1 silencing.

Results: We first report that HMGA1 is overexpressed in a subset of BTSC lines from human GBMs. Then, we show that HMGA1 knockdown reduces self-renewal, sphere forming efficiency and stemness, and sensitizes BTSCs to temozolomide. Interestingly, HMGA1 silencing also leads to reduced tumor initiation ability in vivo.

Conclusions: These results demonstrate a pivotal role of HMGA1 in cancer stem cell gliomagenesis and endorse HMGA1 as a suitable target for CSC-specific GBM therapy.     

苯妥英钠逆转胶质母细胞瘤多药耐药实验研究

目的研究不同浓度苯妥英钠(PHT)对化疗耐药胶质母细胞瘤细胞系(8-MG-BA)化疗耐药逆转的影响。方法用不同浓度苯妥英钠对8-MG-BA及H4细胞系处理后,以MTT法检测其对上述两种细胞系化疗耐药逆转的影响,并与维拉帕米(VRP)处理组进行对照。结果用PHT 5、10μg/mL和VRP 5μg/mL处理后,8-MG-BA细胞对卡莫司汀(BCNU)的逆转倍数分别为:25.34、34.97和14.27,对替尼泊苷(VM-26)的逆转倍数分别为:13.44、21.71和11.10。结论 PHT逆转作用大于VRP,且呈现剂量依赖关系。     

DJ‐1 expression in glioblastomas shows positive correlation with p53 expression and negative correlation with epidermal growth factor receptor amplification

DJ‐1, a protein that promotes the action of multiple anti‐apoptotic/pro‐survival pathways, is expressed prominently in human reactive astrocytes and in many human cancers. Glioblastomas (GBMs) are the most common adult primary brain tumor, and most show either abnormalities in p53 or epidermal growth factor receptor (EGFR) amplification, but not both. In this retrospective study of 40 surgically resected GBMs, we compared the immunohistochemical intensity of DJ‐1 expression (based on blinded scoring by independent examiners) to these and other molecular factors associated with GBM oncogenesis. We report here that: (i) most of the GBMs that we studied expressed DJ‐1 protein at significant levels, and typically in a cytoplasmic, non‐nuclear fashion; (ii) DJ‐1 staining intensity varied directly with strong nuclear p53 expression (assessed by immunostaining); and (iii) DJ‐1 staining intensity varied inversely with EGFR amplification (assessed by fluorescent in situ hybridization). Since the anti‐apoptotic/pro‐survival actions of DJ‐1 have been clearly linked in in vitro systems to p53 and receptor tyrosine kinase (i.e. EGFR) pathways that are hypothesized to be critical to GBM genesis, these observations indicate that DJ‐1 expression may play a role in the biology of some types of GBMs. Therefore, given the new associations presented here between DJ‐1, p53 and EGFR amplification in GBMs, future investigations of these tumors should include an analysis of DJ‐1 to determine whether its expression pattern is important for tumor progression, prognosis and responsiveness to therapy.     

Early versus late GD-DTPA MRI enhancement in experimental glioblastomas

Purpose:

To compare early versus late enhancement in two glioblastoma models characterized by different infiltrative/edematous patterns.

Materials and Methods:

Three weeks after inoculation into nude mice of U87MG and U251 cells, T1‐weighted images were acquired early (10.5 min), intermediate (21 min) and late (30.5 min) after a bolus injection of Gd‐DTPA at 300 μ mol/kg dosage. EARLY_TH and LATE_TH were the corresponding volumes with an enhancement higher than a threshold TH, defined by the mean (μ) and standard deviation (σ) on a contralateral healthy area. ADD_TH was the enhancing volume found in LATE_TH but not in EARLY_TH. T2 imaging of both tumors was performed, and T2 mapping of U251.

Results:

In all tumors, LATE_TH was significantly higher than EARLY_TH for TH ranging from μ+σ to μ+5σ. The ADD_TH/EARLY_TH ratio was not significantly different when U251 and U87MG tumors were compared. In the U87MG tumors, some enhancement was observed outside the regularly demarcated T2‐hyperintense area. In the U251 tumors, irregularly T2 demarcated, a large portion of ADD_μ+3σ had normal T2 values. At histology, U251 showed a higher infiltrative pattern than U87MG.

Conclusion:

In these models, the increase over time in the enhancing volume did not depend on the different infiltrative/edematous patterns and was not closely related with edema. J. Magn. Reson. Imaging 2011;33:550–556. © 2011 Wiley‐Liss, Inc.     

Measurement of glycine in the human brain in vivo by 1H‐MRS at 3 T: application in brain tumors

Glycine is a key metabolic intermediate required for the synthesis of proteins, nucleic acids, and other molecules, and its detection in cancer could, therefore, provide biologically relevant information about the growth of the tumor. Here, we report measurement of glycine in human brain and gliomas by an optimized point‐resolved spectroscopy sequence at 3 T. Echo time dependence of the major obstacle, myo‐inositol (mI) multiplet, was investigated with numerical simulations, incorporating the 3D volume localization. The simulations indicated that a subecho pair (TE₁, TE₂) = (60, 100) ms permits detection of both glycine and mI with optimum selectivity. In vivo validation of the optimized point‐resolved spectroscopy was conducted on the right parietal cortex of five healthy volunteers. Metabolite signals estimated from LCModel were normalized with respect to the brain water signal, and the concentrations were evaluated assuming the total creatine concentration at 8 mM. The glycine concentration was estimated as 0.6 ± 0.1 mM (mean ± SD, n = 5), with a mean Cramér‐Rao lower bound of 9 ± 1%. The point‐resolved spectroscopy sequence was applied to measure the glycine levels in patients with glioblastoma multiforme. Metabolite concentrations were obtained using the water signal from the tumor mass. The study revealed that a subset of human gliomas contains glycine levels elevated 1.5–8 fold relative to normal. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Ultra‐small gadolinium oxide nanoparticles to image brain cancer cells in vivo with MRI

The majority of contrast agents used in magnetic resonance imaging (MRI) is based on the rare‐earth element gadolinium. Gadolinium‐based nanoparticles could find promising applications in pre‐clinical diagnostic procedures of certain types of cancer, such as glioblastoma multiforme. This is one of the most malignant, lethal and poorly accessible forms of cancer. Recent advances in colloidal nanocrystal synthesis have led to the development of ultra‐small crystals of gadolinium oxide (US‐Gd₂O₃, 2–3 nm diameter). As of today, this is the smallest and the densest of all Gd‐containing nanoparticles. Cancer cells labeled with a sufficient quantity of this compound appear bright in T₁‐weighted MRI images. Here we demonstrate that US‐Gd₂O₃ can be used to label GL‐261 glioblastoma multiforme cells, followed by localization and visualization in vivo using MRI. Very high amounts of Gd are efficiently internalized and retained in cells, as confirmed with TEM and ICP‐MS. Labeled cells were visualized in vivo at 1.5 T using the chicken embryo model. This is one more step toward the development of “positively contrasted” cell tracking procedures with MRI. Copyright © 2010 John Wiley & Sons, Ltd.