Progress on antiangiogenic therapy for patients with malignant glioma

Pathophysiological roles of integrins in gliomas from the perspective of glioma stem cells

Glioblastoma is the most common primary intracranial tumor and is also one of the most malignant central nervous system tumors. Its characteristics, such as high malignancy, abundant tumor vasculature, drug resistance, and recurrence-prone nature, cause great suffering to glioma patients. Furthermore, glioma stem cells are the primordial cells of the glioma and play a central role in the development of glioma. Integrins—heterodimers composed of noncovalently bound a and ß subunits—are highly expressed in glioma stem cells and play an essential role in the self-renewal, differentiation, high drug resistance, and chemo-radiotherapy resistance of glioma stem cells through cell adhesion and signaling. However, there are various types of integrins, and their mechanisms of function on glioma stem cells are complex. Therefore, this article reviews the feasibility of treating gliomas by targeting integrins on glioma stem cells.

Role of Polymeric Local Drug Delivery in Multimodal Treatment of Malignant Glioma: A Review

Malignant gliomas (MGs) are the most common and devastating primary brain tumor. At present, surgical interventions, radiotherapy, and chemotherapy are only marginally effective in prolonging the life expectancy of patients with MGs. Inherent heterogeneity, aggressive invasion and infiltration, intact physical barriers, and the numerous mechanisms underlying chemotherapy and radiotherapy resistance contribute to the poor prognosis for patients with MGs. Various studies have investigated methods to overcome these obstacles in MG treatment. In this review, we address difficulties in MG treatment and focus on promising polymeric local drug delivery systems. In contrast to most local delivery systems, which are directly implanted into the residual cavity after intratumoral injection or the surgical removal of a tumor, some rapidly developing and promising nanotechnological methods—including surface-decorated nanoparticles, magnetic nanoparticles, and focused ultrasound assist transport—are administered through (systemic) intravascular injection. We also discuss further synergistic and multimodal strategies for heightening therapeutic efficacy. Finally, we outline the challenges and therapeutic potential of these polymeric drug delivery systems.

Glioblastoma: Targeting Angiogenesis and Tyrosine Kinase Pathways

Angiogenesis is a hallmark of glioblastoma (GBM) and remains an important therapeutic target in its treatment, especially for recurrent GBM. GBMs are characterized by the release of vascular endothelial growth factor (VEGF), an important regulator and promoter of angiogenesis. Therefore, antiangiogenic therapies (AATs) targeting VEGF or VEGF receptors (VEGFRs) were designed and thought to be an effective tool for controlling the growth of GBM. However, recent results of different clinical trials using humanized monoclonal antibodies against VEGF (bevacizumab), as well as tyrosine kinase inhibitors (TKIs) that target different VEGFRs alone or in combination with other therapeutic agents demonstrated mixed results, with the majority of reports indicating that GBM developed resistance against antiangiogenic treatments.

MRI Monitoring of Cerebral Blood Flow after the Delivery of Nanocombretastatin across the Blood Brain Tumor Barrier

Introduction of polymeric nanoparticles in cancer therapeutics is widely investigated since nanomedicine often enables the intratumoral delivery of drugs with increased efficacy with minimal side effects. In this study MRI monitoring was employed to study the therapeutic effect of nanocombretastatin (G3-CA4) in an orthotopic glioma model. Water insoluble combretastatin (CA4) was conjugated to a small-sized water soluble G3-succinamic acid PAMAM dendrimer. Nanoconstruct sizes were determined by TEM to be 3 to 5 nm. Intravenous (i.v.) delivery of G3-CA4 in an orthotopic glioma model produced a long-lived ischemia accompanied by necrosis at the core of the tumor but leaving a rim of viable tissue. In contrast, delivery of CA4 alone has no therapeutic effect in an experimental rat model of glioma.

Electrospun nanofibers for local anticancer therapy: Review of in vivo activity

Currently, chemotherapy is the most common treatment for oncological diseases. Systemic administration of chemotherapeutics provides an easy and effective distribution of the active agents throughout the patient's body, however organs may be severely impaired by serious life-threatening side effects. In many oncological diseases, particularly solid tumors, the local application of chemotherapeutics would be advantageous. Recently, nanofibrous materials as local drug delivery systems have attracted much attention. They have considerable potential in the treatment of various cancers as they can provide a high concentration of the drug at the target site for a prolonged time, thereby lowering total exposure and adverse effects. The present review describes the specifics of drug delivery to the tumor microenvironment, basic characteristics of nanofibrous materials and their preparation, and comprehensively summarizes recent scientific reports concerning in vivo experiments with drug-loaded electrospun nanofibrous systems designed for local anticancer therapy.

Human Glioma Migration and Infiltration Properties as a Target for Personalized Radiation Medicine

Gliomas are primary brain tumors that present the majority of malignant adult brain tumors. Gliomas are subdivided into low- and high-grade tumors. Despite extensive research in recent years, the prognosis of malignant glioma patients remains poor. This is caused by naturally highly infiltrative capacities as well as high levels of radio- and chemoresistance. Additionally, it was shown that low linear energy transfer (LET) irradiation enhances migration and invasion of several glioma entities which might counteract today’s treatment concepts. However, this finding is discussed controversially. In the era of personalized medicine, this controversial data might be attributed to the patient-specific heterogeneity that ultimately could be used for treatment. Thus, current developments in glioma therapy should be seen in the context of intrinsic and radiation-enhanced migration and invasion. Due to the natural heterogeneity of glioma cells and different radiation responses, a personalized radiation treatment concept is suggested and alternative radiation concepts are discussed.

Advanced interstitial chemotherapy combined with targeted treatment of malignant glioma in rats by using drug-loaded nanofibrous membranes

Glioblastoma multiforme (GBM), the most prevalent and malignant form of a primary brain tumour, is resistant to chemotherapy. In this study, we concurrently loaded three chemotherapeutic agents [bis-chloroethylnitrosourea, irinotecan, and cisplatin; BIC] into 50:50 poly[(d,l)-lactide-co-glycolide] (PLGA) nanofibres and an antiangiogenic agent (combretastatin) into 75:25 PLGA nanofibres [BIC and combretastatin (BICC)/PLGA]. The BICC/PLGA nanofibrous membranes were surgically implanted onto the brain surfaces of healthy rats for conducting pharmacodynamic studies and onto C6 glioma-bearing rats for estimating the therapeutic efficacy.

The chemotherapeutic agents were rapidly released from the 50:50 PLGA nanofibres after implantation, followed by the release of combretastatin (approximately 2 weeks later) from the 75:25 PLGA nanofibres. All drug concentrations remained higher in brain tissues than in the blood for more than 8 weeks. The experimental results, including attenuated malignancy, retarded tumour growth, and prolonged survival in tumour-bearing rats, demonstrated the efficacy of the BICC/PLGA nanofibrous membranes. Furthermore, the efficacy of BIC/PLGA and BICC/PLGA nanofibrous membranes was compared. The BICC/PLGA nanofibrous membranes more efficiently retarded the tumour growth and attenuated the malignancy of C6 glioma-bearing rats. Moreover, the addition of combretastatin did not significantly change the drug release behaviour of the BIC/PLGA nanofibrous membranes. The present advanced and novel interstitial chemotherapy and targeted treatment provide a potential strategy and regimen for treating GBM.

Direct contact with perivascular tumor cells enhances integrin αvβ3 signaling and migration of endothelial cells

The secretion of soluble pro-angiogenic factors by tumor cells and stromal cells in the perivascular niche promotes the aggressive angiogenesis that is typical of glioblastoma (GBM). Here, we show that angiogenesis also can be promoted by a direct interaction between brain tumor cells, including tumor cells with cancer stem-like properties (CSCs), and endothelial cells (ECs). As shown in vitro, this direct interaction is mediated by binding of integrin αvβ3 expressed on ECs to the RGD-peptide in L1CAM expressed on CSCs. It promotes both EC network formation and enhances directed migration toward basic fibroblast growth factor. Activation of αvβ3 and bone marrow tyrosine kinase on chromosome X (BMX) is required for migration stimulated by direct binding but not for migration stimulated by soluble factors. RGD-peptide treatment of mice with established intracerebral GBM xenografts significantly reduced the percentage of Sox2-positive tumor cells and CSCs in close proximity to ECs, decreased integrin αvβ3 and BMX activation and p130CAS phosphorylation in the ECs, and reduced the vessel surface area. These results reveal a previously unrecognized aspect of the regulation of angiogenesis in GBM that can impact therapeutic anti-angiogenic targeting.

Lactoferrin functionalized PEG-PLGA nanoparticles of shikonin for brain targeting therapy of glioma

Shikonin (SHK) is a highly liposoluble naphthoquinone pigment has recently been investigated as a potential antiglioma agent. However, shikonin shows several limitations like poor aqueous solubility, short half-life and non-selective biodistribution. Herein, we have developed a nanoparticles (NPs) prepared from PEG-PLGA using an emulsion solvent evaporation method. Nanoparticle surfaces were modified by coating with lactoferrin (Lf) to improve the crossing of the blood brain barrier and targeting of glioma cells via receptor-mediated path-ways. X-ray powder diffraction and differential scanning calorimetry analysis revealed the amorphous nature of SHK encapsulated within the NPs. Moreover, the drug-loaded NPs exhibit narrow size distribution and high encapsulation efficiency. The in vitro release experiments of the NPs exhibited sustained release for more than 72h. When compared to free SHK and SHK/NPs, in vivo study demonstrated higher brain concentration of SHK, indicating a significant effect of Lf coated NPs on brain targeting. Accordingly, these findings provide evidence for the potential of Lf-modified NPs as a targeted delivery system for brain glioblastomas treatment.

Bevacizumab combined with chemotherapy for glioblastoma: a meta-analysis of randomized controlled trials

Bevacizumab, as antibodies, were applied to inhibit tumor angiogenesis by preventing activation of vascular endothelial growth factor receptor. We analyzed four clinical trials, including 607 patients, to investigate the efficacy and safety of bevacizumab when combined with chemotherapy for the treatment of glioblastomas. Results demonstrated that bevacizumab when combined with chemotherapy improved progression-free survival (HR = 0.66; 95% CI 0.56-0.78; p < 0.00001) compared with bevacizumab or chemotherapy alone. Furthermore, overall survival showed insignificant difference between two arms (HR 0.99; 95% CI 0.8-1.21; p = 0.92). However, we found that patients treated with bevacizumab-containing therapy reported increased objective response rate (OR 1.85, 95% CI 1.17-2.93; p = 0.009), but more treatment-related adverse events (OR 1.75; 95% CI 1.09-2.83; p = 0.02).

Targeted concurrent and sequential delivery of chemotherapeutic and antiangiogenic agents to the brain by using drug-loaded nanofibrous membranes

Glioblastoma is the most frequent and devastating primary brain tumor. Surgery followed by radiotherapy with concomitant and adjuvant chemotherapy is the standard of care for patients with glioblastoma. Chemotherapy is ineffective, because of the low therapeutic levels of pharmaceuticals in tumor tissues and the well-known tumor-cell resistance to chemotherapy. Therefore, we developed bilayered poly(d,l)-lactide-co-glycolide nanofibrous membranes that enabled the sequential and sustained release of chemotherapeutic and antiangiogenic agents by employing an electrospinning technique. The release characteristics of embedded drugs were determined by employing an in vitro elution technique and high-performance liquid chromatography. The experimental results showed that the fabricated nanofibers showed a sequential drug-eluting behavior, with the release of high drug levels of chemotherapeutic carmustine, irinotecan, and cisplatin from day 3, followed by the release of high concentrations of the antiangiogenic combretastatin from day 21. Biodegradable multidrug-eluting nanofibrous membranes were then dispersed into the cerebral cavity of rats by craniectomy, and the in vivo release characteristics of the pharmaceuticals from the membranes were investigated. The results suggested that the nanofibrous membranes released high concentrations of pharmaceuticals for more than 8 weeks in the cerebral parenchyma of rats. The result of histological analysis demonstrated developmental atrophy of brains with no inflammation. Biodegradable nanofibrous membranes can be manufactured for long-term sequential transport of different chemotherapeutic and anti-angiogenic agents in the brain, which can potentially improve the treatment of glioblastoma multiforme and prevent toxic effects due to systemic administration.

Correlation of higher levels of soluble TNF-R1 with a shorter survival, independent of age, in recurrent glioblastoma

The circulating levels of soluble tumor necrosis factor receptor-1 (sTNF-R1) and sTNF-R2 are altered in numerous diseases, including several types of cancer. Correlations with the risk of progression in some cancers, as well as systemic manifestations of the disease and therapeutic side-effects, have been described. However, there is very little information on the levels of these soluble receptors in glioblastoma (GBM). Here, we report on an exploratory retrospective study of the levels of sTNF-Rs in the vascular circulation of patients with GBM. Banked samples were obtained from 112 GBM patients (66 untreated, newly-diagnosed patients and 46 with recurrent disease) from two institutions. The levels of sTNF-R1 in the plasma were significantly lower in patients with newly-diagnosed or recurrent GBM than apparently healthy individuals and correlated with the intensity of expression of TNF-R1 on the tumor-associated endothelial cells (ECs) in the corresponding biopsies. Elevated levels of sTNF-R1 in patients with recurrent, but not newly-diagnosed GBM, were significantly associated with a shorter survival, independent of age (p = 0.02) or steroid medication. In contrast, the levels of circulating sTNF-R2 were significantly higher in recurrent GBM than healthy individuals and there was no significant correlation with expression of TNF-R2 on the tumor-associated ECs or survival time. The results indicate that larger, prospective studies are warranted to determine the predictive value of the levels of sTNF-R1 in patients with recurrent GBM and the factors that regulate the levels of sTNF-Rs in the circulation in GBM patients.

Bevacizumab treatment for newly diagnosed glioblastoma: Systematic review and meta-analysis of clinical trials

High-grade glioma is a richly neovascularized brain solid tumor with a poor prognosis. Bevacizumab is a recombinant humanized monoclonal antibody that inhibits vascular endothelial cell proliferation and angiogenesis, which has shown clinical efficacy in recurrent glioblastoma. MEDLINE/PubMed, EMBASE and Web of Science databases were searched for relevant studies that compared bevacizumab plus combined radiotherapy/temozolomide (RT/TMZ) with RT/TMZ alone in newly diagnosed glioblastoma (GBM). Of all the studies identified, three comparative trials were included in the systematic review. All three enrolling trials, including a total of 1,738 patients, investigated bevacizumab or placebo plus combined RT/TMZ treatment in glioblastoma. The result showed no increased overall survival (OS) (pooled hazard ratio (HR), 1.04; 95% confidence interval (CI), 0.84-1.29; P=0.71) but increased progression-free survival (HR, 0.74; 95% CI, 0.62-0.88; P=0.0009). However, the two randomized double-blind placebo-control trials exemplified a high rate of adverse events of the bevacizumab compared with the placebo group while discrepant points were noted in term of quality-of-life outcome. Additionally, bevacizumab plus RT/TMZ did not increase the 6-month survival rate [odd ratios (ORs), 0.65; 95% CI, 0.37-1.13; P=0.13). Overall, addition of bevacizumab to radiotherapy-temozolomide treatment may be an effective therapy strategy for improving progression-free survival. OS and the 6-month survival rate was not prolonged and there was questionable efficacy of bevacizumab on the quality-of-life of glioblastoma patients, thus further clinical trials should be performed.

Current medical treatment of glioblastoma

Glioblastoma is the most common adult malignant primary brain tumor. Despite the advances in therapeutic options, survival of patients with glioblastoma remains dismal at 15-18 months. Current standard of care for newly diagnosed glioblastoma is maximal possible safe resection consistent with the preservation of neurologic function followed by concurrent temozolomide with radiation and adjuvant. Treatment options at recurrence include surgical resection with or without the placement of carmustine wafers, re-irradiation and chemotherapeutics such as nitrosoureas (lomustine, carmustine) or bevacizumab, a monoclonal antibody targeting vascular endothelial growth factor (VEGF).

Diagnostic and prognostic value of a disintegrin and metalloproteinase-17 in patients with gliomas

A disintegrin and metalloproteinase-17 (ADAM17) has been shown to regulate numerous proteins involved in the cell cycle, as well as tumor oncogenes. The expression pattern of ADAM17 in glioma patients, however, is unclear. In the present study, the expression pattern and prognostic significance of ADAM17 was investigated in patients with glioma. A total of 60 glioma specimens and eight normal control samples were obtained. Immunohistochemical and western blot analyses were used to examine the expression of ADAM17. In addition, the association of ADAM17 expression with the clinicopathological parameters and the survival rates of the glioma patients was analyzed. The results showed that ADAM17 was upregulated in the high-grade glioma tissues compared with that in the low-grade and normal brain tissues of the glioma patients, and that the level increased with ascending World Health Organization tumor grade (P<0.05). Furthermore, the survival rate of the patients with ADAM17-positive tumors was lower compared with the patients with ADAM17-negative tumors. These results indicated that the overexpression of ADAM17 was correlated with a high tumor grade and a poor prognosis in patients with glioma. ADAM17 may have an important oncogenic function in glioma progression, and is a potential diagnostic and therapeutic target.

Collagen IV and CXC chemokine-derived antiangiogenic peptides suppress glioma xenograft growth

Peptides are receiving increasing attention as therapeutic agents due to their high binding specificity and versatility to be modified as targeting or carrier molecules. Particularly, peptides with antiangiogenic activity are of high interest because of their applicability to a wide range of cancers. In this study, we investigate the biological activity of two novel antiangiogenic peptides in preclinical glioma models. One peptide SP2000 is derived from collagen IV and the other peptide SP3019 belongs to the CXC family. We have previously characterized the capacity of SP2000 and SP3019 to inhibit multiple biological endpoints linked to angiogenesis in human endothelial cells in several assays. Here, we report additional studies using endothelial cells and focus on the activity of these peptides against human glioma cell growth, migration and adhesion in vitro, and growth as tumor xenografts in vivo. We found that SP2000 completely inhibits migration of the glioma cells at 50 µmol/l and SP3019 produced 50% inhibition at 100 µmol/l. Their relative antiadhesion activities were similar, with SP2000 and SP3019 generating 50% adhesion inhibition at 4.9 ± 0.82 and 21.3 ± 5.92 µmol/l, respectively. In-vivo glioma growth inhibition was 63% for SP2000 and 76% for SP3019 after 2 weeks of administration at daily doses of 10 and 20 mg/kg, respectively. The direct activity of these peptides against glioma cells in conjunction with their antiangiogenic activities warrants their further development as either stand-alone agents or in combination with standard cytotoxic or emerging targeted therapies in malignant brain tumors.

Glioblastoma cell-secreted interleukin-8 induces brain endothelial cell permeability via CXCR2

Glioblastoma constitutes the most aggressive and deadly of brain tumors. As yet, both conventional and molecular-based therapies have met with limited success in treatment of this cancer. Among other explanations, the heterogeneity of glioblastoma and the associated microenvironment contribute to its development, as well as resistance and recurrence in response to treatments. Increased vascularity suggests that tumor angiogenesis plays an important role in glioblastoma progression. However, the molecular crosstalk between endothelial and glioblastoma cells requires further investigation. To examine the effects of glioblastoma-derived signals on endothelial homeostasis, glioblastoma cell secretions were collected and used to treat brain endothelial cells. Here, we present evidence that the glioblastoma secretome provides pro-angiogenic signals sufficient to disrupt VE-cadherin-mediated cell-cell junctions and promote endothelial permeability in brain microvascular endothelial cells. An unbiased angiogenesis-specific antibody array screen identified the chemokine, interleukin-8, which was further demonstrated to function as a key factor involved in glioblastoma-induced permeability, mediated through its receptor CXCR2 on brain endothelia. This underappreciated interface between glioblastoma cells and associated endothelium may inspire the development of novel therapeutic strategies to induce tumor regression by preventing vascular permeability and inhibiting angiogenesis.

A microRNA Link to Glioblastoma Heterogeneity

Glioblastomas (GBM) are one of the most malignant adult primary brain tumors. Through decades of research using various model systems and GBM patients, we have gained considerable insights into the mechanisms regulating GBM pathogenesis, but have mostly failed to significantly improve clinical outcome. For the most part GBM heterogeneity is responsible for this lack of progress. Here, we have discussed sources of cellular and microenvironmental heterogeneity in GBMs and their potential regulation through microRNA mediated mechanisms. We have focused on the role of individual microRNAs (miRNA) through their specific targets and miRNA mediated RNA-RNA interaction networks with the potential to influence various aspects of GBM heterogeneity including tumor neo-vascularization. We believe a better understanding of such mechanisms for regulation of GBM pathogenesis will be instrumental for future therapeutic options.

Activation of alternative pathways of angiogenesis and involvement of stem cells following anti-angiogenesis treatment in glioma

Malignant gliomas are hypervascular tumors that are highly resistant to all the currently available multimodal treatments. Therefore, anti-angiogenic therapies targeting VEGF or VEGF receptors (VEGFRs) were designed and thought to be an effective tool for controlling the growth of malignant gliomas. However, recent results of early clinical trials using humanized monoclonal antibodies against VEGF (Bevacizumab), as well as small-molecule tyrosine kinase inhibitors that target different VEGF receptors (VEGFRs) (Vatalanib, Vandetanib, Sunitinib, Sorafenib, etc) alone or in combination with other therapeutic agents demonstrated differing outcomes, with the majority of reports indicating that glioma developed resistance to the employed anti-angiogenic treatments. It has been noted that continued anti-angiogenic therapy targeting only the VEGF-VEGFR system might affect pro-angiogenic factors other than VEGF, such as basic fibroblast growth factor (bFGF), stromal derived factor 1 (SDF-1) and Tie-2. These factors may in turn stimulate angiogenesis by mobilizing bone marrow derived precursor cells, such as endothelial progenitor cells (EPCs), which are known to promote angiogenesis and vasculogenesis. In this short review, the current antiangiogenic treatments, possible mechanisms of activation of alternative pathways of angiogenesis, and possible involvement of bone marrow derived progenitor cells in the failure of anti-angiogenic treatments are discussed.

Glioblastoma: therapeutic challenges, what lies ahead

Glioblastoma (GBM) is one of the most aggressive human cancers. Despite current advances in multimodality therapies, such as surgery, radiotherapy and chemotherapy, the outcome for patients with high grade glioma remains fatal. The knowledge of how glioma cells develop and depend on the tumor environment might open opportunities for new therapies. There is now a growing awareness that the main limitations in understanding and successfully treating GBM might be bypassed by the identification of a distinct cell type that has defining properties of somatic stem cells, as well as cancer-initiating capacity - brain tumor stem cells, which could represent a therapeutic target. In addition, experimental studies have demonstrated that the combination of antiangiogenic therapy, based on the disruption of tumor blood vessels, with conventional chemotherapy generates encouraging results. Emerging reports have also shown that microglial cells can be used as therapeutic vectors to transport genes and/or substances to the tumor site, which opens up new perspectives for the development of GBM therapies targeting microglial cells. Finally, recent studies have shown that natural toxins can be conjugated to drugs that bind to overexpressed receptors in cancer cells, generating targeted-toxins to selectively kill cancer cells. These targeted-toxins are highly effective against radiation- and chemotherapy-resistant cancer cells, making them good candidates for clinical trials in GBM patients. In this review, we discuss recent studies that reveal new possibilities of GBM treatment taking into account cancer stem cells, angiogenesis, microglial cells and drug delivery in the development of new targeted-therapies.

Endothelial expression of TNF receptor-1 generates a proapoptotic signal inhibited by integrin α6β1 in glioblastoma

Activation of TNF receptor 1 (TNF-R1) can generate signals that promote either apoptosis or survival. In this study, we show that these signals can be determined by the character of the extracellular matrix in the tumor microenvironment. Specifically, through studies of glioblastoma, we showed that TNFα stimulation induced apoptosis of primary brain endothelial cells (EC) attached to collagen or fibronectin (which engage integrins α2β1/α3β1 and α5β1, respectively), but did not induce apoptosis of ECs attached to laminin (which engages integrins α6β1 and α3β1). TNF-R1 expression was significantly higher in ECs in glioblastoma (GBM) tumors compared with ECs in normal brain specimens. TNFα was also expressed in GBM tumor-associated ECs, which was associated with longer patient survival. ECs plated on anti-integrin α2 or α3 antibody were susceptible to TNFα-induced apoptosis, whereas those plated on anti-integrin α6 antibody were not. Moreover, the ECs plated on laminin, but not collagen, expressed cellular FLICE inhibitory protein (cFLIP) and TNFα stimulation of laminin-attached cells in which cFLIP had been downregulated resulted in the induction of apoptosis. In contrast, attachment to laminin did not induce cFLIP expression in GBM tumor stem cells. Together, our findings indicate that the laminin receptor integrin α6β1 promotes the survival of brain ECs by inhibiting prodeath signaling by TNF-R1, in part by inducing cFLIP expression.

Heterogeneity in malignant gliomas: a magnetic resonance analysis of spatial distribution of metabolite changes and regional blood volume

First-pass contrast-enhanced dynamic perfusion imaging provides information about the regional cerebral blood volume (rCBV), an increase of which indicates neovascularization. MR spectroscopic imaging informs about metabolite changes in brain tumors, with elevated choline (Cho) values revealing cell proliferation and density, and the glial metabolite creatine (Cr) representing high-energy storage. This study investigates metabolite changes within the tumor voxel of maximal rCBV value (rCBVmax). Anatomically coregistered parameter maps of rCBV, Cho and Cr were evaluated in 36 patients with primary or recurrent WHO grade III or IV gliomas. Apart from Cho and Cr values within the voxel of rCBVmax (Choperf, Crperf), the maximal Cho and Cr values of the tumor tissue were recorded (Chomax, Crmax). The correlation between these parameters was analyzed with Spearman’s rho test while a binomial test was performed to check whether Chomax = Choperf and Crmax = Crperf. We found that, in 29 of the 36 patients, neither Cho nor Cr had their maxima in the voxel of rCBVmax (Choperf, Crperf < Chomax, Crmax, P < 0.001). However, Choperf was highly correlated with Chomax (r = 0.76, P < 0.001) and Crperf with Crmax (r = 0.47, P < 0.001). Further Choperf correlated with Crperf (r = 0.55, P < 0.001). Neither of the spectroscopic parameters (Chomax, Crmax, Choperf, Crperf,) correlated with rCBVmax. In conclusion, in WHO grade III and IV gliomas the voxel with maximal rCBV often differs from the voxel with the maximal Cho and Cr, indicating the spatial divergence between neovascularization and tumor cell proliferation, cell density and glial processes. However, tCho and tCr changes within the area of neovascularization are positively correlated with the maximal increase within the tumor tissue. These results demonstrate aspects of regional tumor heterogeneity as characterized by different MR modalities that, apart from histopathological grading might be crucial for neurosurgical biopsy as well as for antiangiogenetic and future molecular therapies.

Recent advancements in multimodality treatment of gliomas

Gliomas account for the vast majority of malignant adult brain tumors. Even though tremendous effort has been made to optimize treatment of patients with high-grade glioma, the prognosis remains poor, especially for patients with glioblastoma. The dismal prognosis conferred by these tumors is in part caused by the tendency to diffusely infiltrate into neighboring brain tissue, but also by the inherent resistance of these tumors to both chemotherapy and radiation. This article reviews the recent advancements in multimodality treatment of patients with gliomas, both in the primary and recurrent setting, with an emphasis on the emerging targeted therapies. Moreover, the external beam radiotherapy options, including intensity modulated radiotherapy and particle (proton and carbon ion) radiotherapy are reviewed.

Antiangiogenic therapy for patients with recurrent and newly diagnosed malignant gliomas

Malignant gliomas have a poor prognosis despite advances in diagnosis and therapy. Although postoperative temozolomide and radiotherapy improve overall survival in glioblastoma patients, most patients experience a recurrence. The prognosis of recurrent malignant gliomas is dismal, and more effective therapeutic strategies are clearly needed. Antiangiogenesis is currently considered an attractive targeting therapy for malignant gliomas due to its important role in tumor growth. Clinical trials using bevacizumab have been performed for recurrent glioblastoma, and these studies have shown promising response rates along with progression-free survival. Based on the encouraging results, bevacizumab was approved by the FDA for the treatment of recurrent glioblastoma. In addition, bevacizumab has shown to be effective for recurrent anaplastic gliomas. Large phase III studies are currently ongoing to demonstrate the efficacy and safety of the addition of bevacizumab to temozolomide and radiotherapy for newly diagnosed glioblastoma. In contrast, several other antiangiogenic drugs have also been used in clinical trials. However, previous studies have not shown whether antiangiogenesis improves the overall survival of malignant gliomas. Specific severe side effects, difficult assessment of response, and lack of rational predictive markers are challenging problems. Further studies are warranted to establish the optimized antiangiogenesis therapy for malignant gliomas.

Molecular heterogeneity in glioblastoma: therapeutic opportunities and challenges

Glioblastoma (GBM) has been recognized as a clinical and pathologic entity for more than a century. Throughout its history, its cells of origin have been in question. Its behavior is aggressive and despite decades of effort, median survival is just beginning to improve. Surgical techniques and radiotherapy schemas continue to be refined, but the most recent progress has been achieved through improved medical therapies. These are the result of both pharmacological advances and a deeper understanding of the biological characteristics of GBM. Due to a combination of its complex phenotype and organ-specific clinical manifestations, efforts to refine GBM treatment with targeted therapies largely have been frustrated. In this review, we discuss recent attempts to exploit new molecular insights, consider the reasons for slow progress in developing better treatments, and examine future therapeutic options.

Glioblastoma-dependent differentiation and angiogenic potential of human mesenchymal stem cells in vitro

Tumor angiogenesis is of central importance in the malignancy of glioblastoma multiforme (GBM). As previously shown, human mesenchymal stem cells (hMSC) migrate towards GBM and are incorporated into tumor microvessels. However, phenotype and function of recruited hMSC remain unclear. We evaluated the differentiation and angiogenic potential of hMSC after stimulation with glioblastoma-conditioned medium in vitro. Immunostaining with endothelial, smooth muscle cell and pericyte markers was used to analyze hMSC differentiation in different concentrations of tumor-conditioned medium (CM), and the angiogenic potential was evaluated by matrigel-based tube-formation assay (TFA). Immunofluorescence staining revealed that tumor-conditioned hMSC (CM-hMSC) expressed CD 151, VE-cadherin, desmin, α-smooth muscle actin, nestin, and nerval/glial antigen 2 (NG2) in a CM concentration-dependent manner, whereas no expression of von-Willebrand factor (vWF) and smooth myosin could be detected. These findings are indicative of GBM-dependent differentiation of hMSC into pericyte-like cells, rather than endothelial or smooth muscle cells. Furthermore, TFA of hMSC and CM-hMSC revealed CM-dependent formation of capillary-like networks, which differed substantially from those formed by human endothelial cells (HUVEC), also implying pericyte-like tube formation. These results are indicative of GBM-derived differentiation of hMSC into pericyte-like mural cells, which might contribute to the neovascularization and stabilization of tumor vessels.

CD133+ niches and single cells in glioblastoma have different phenotypes

Putative CD133(+) brain tumor stem cells have been shown to be located in niches and as single cells. This is the first study providing insight into the different phenotypes of CD133(+) cells in glioblastoma according to localization. Paraffin sections were stained by double immunofluorescence with CD133 and the candidate stem cell markers Sox2, Bmi-1, EGFR, podoplanin and nestin, the proliferation marker Ki67 and the endothelial cell markers CD31, CD34, and VWF. Cell counting showed that the CD133(+) cells in the niches had a significantly higher expression of Sox2, EGFR and nestin compared to CD133(+) single cells, but only a 3% Ki67 labeling index versus 14% found for CD133(+) single cells. Only low endothelial cell marker expression was found in the niches or the CD133(-) tumor areas, while 43% CD133(+)/CD31(+) and 25% CD133(+)/CD34(+) single cells were found. CD133(+) blood vessels within CD133(+) niches were less proliferative and more often Bmi-1(+) than CD133(+) blood vessels outside niches. In conclusion, different CD133(+) cell phenotypes exist according to the in situ localization, and also the phenotype of CD133(+) blood vessels vary according to the localization. CD133(+) niches contain stem-like cells with a lower proliferation index than CD133(+) single cells, which have an endothelial differentiation profile suggesting a role in angiogenesis.

Phase II study of bevacizumab plus temozolomide during and after radiation therapy for patients with newly diagnosed glioblastoma multiforme

PURPOSE

This open-label, prospective, multicenter single-arm phase II study combined bevacizumab (BV) with radiation therapy (RT) and temozolomide (TMZ) for the treatment of newly diagnosed glioblastoma (GBM). The objectives were to determine the efficacy of this treatment combination and the associated toxicity.

PATIENTS AND METHODS

Seventy patients with newly diagnosed GBM were enrolled between August 2006 and November 2008. Patients received standard RT starting within 3 to 6 weeks after surgery with concurrent administration of daily TMZ and biweekly BV. After completion of RT, patients resumed TMZ for 5 days every 4 weeks and continued biweekly BV. MGMT promoter methylation was assessed on patient tumor tissue. A University of California, Los Angeles/Kaiser Permanente Los Angeles (KPLA) control cohort of newly diagnosed patients treated with first-line RT and TMZ who had mostly received BV at recurrence was derived for comparison.

RESULTS

The overall survival (OS) and progression-free survival (PFS) were 19.6 and 13.6 months, respectively, compared to 21.1 and 7.6 months in the University of California, Los Angeles/KPLA control cohort, and 14.6 and 6.9 months in the European Organisation for Research and Treatment of Cancer-National Cancer Institute of Canada cohort. Correlation of MGMT promoter methylation and improved OS and PFS was retained in the study group. Comparative subset analysis showed that poor prognosis patients (recursive partitioning analysis class V/VI) may derive an early benefit from the use of first-line BV. Toxicity attributable to RT/TMZ was similar, and additional toxicities were consistent with those reported in other BV trials.

CONCLUSION

Patients treated with BV and TMZ during and after RT showed improved PFS without improved OS compared to the University of California, Los Angeles/KPLA control group. Additional studies are warranted to determine if BV administered first-line improves survival compared to BV at recurrence.