Tumour angiogenesis: its mechanism and therapeutic implications in malignant gliomas

Vasorin Exocytosed from Glioma Cells Facilitates Angiogenesis via VEGFR2/AKT Signaling Pathway

Glioma is a highly vascularized tumor of the central nervous system. Angiogenesis plays a predominant role in glioma progression and is considered an important therapeutic target. Our previous study showed that vasorin (VASN), a transmembrane protein, is overexpressed in glioma and promotes angiogenesis; however, the potential mechanism remains unclear. In this study, we found that human vascular endothelial cells (hEC) co-cultured with VASN-overexpressing glioma cells exhibited accelerated migration ability and increased expression of VASN originated from glioma cells. VASN was found in exosomes secreted by glioma cells and could be taken up by hECs. hECs showed more edge filopodia and significantly upregulated expression of endothelial tip cell marker gene and protein levels after co-culture with VASN-overexpressing glioma cells. In clinical glioma tissue and orthotopic transplantation glioma tissue, the vascular density and the number of vascular endothelial cells with a tip cell phenotype in VASN-overexpressed tissues were significantly higher than in tissues with low expression. At the molecular level, VASN interacted with VEGFR2 and caused internalization and autophosphorylation of VEGFR2 protein, and then activated the AKT signaling pathway. Our study collectively reveals the function and mechanism of VASN in facilitating angiogenesis in glioma, providing a new therapeutic target for glioma.

IMPLICATIONS

These findings demonstrate that VASN exocytosed from glioma cells enhanced the migration of vascular endothelial cells by VEGFR2/AKT signaling pathway.

Application of Nanoparticles for Efficient Delivery of Quercetin in Cancer Cells

Quercetin (Qu, 3,5,7,3', 4'-pentahydroxyflavanone) is a natural polyphenol compound abundantly found in health food or plant-based products. In recent decades, Qu has gained significant attention in the food, cosmetic, and pharmaceutic industries owning to its wide beneficial therapeutic properties such as antioxidant, anti-inflammatory and anticancer activities. Despite the favorable roles of Qu in cancer therapy due to its numerous impacts on the cell signaling axis, its poor chemical stability and bioavailability, low aqueous solubility as well as short biological half-life have limited its clinical application. Recently, drug delivery systems based on nanotechnology have been developed to overcome such limitations and enhance the Qu biodistribution following administration. Several investigations have indicated that the nano-formulation of Qu enjoys more remarkable anticancer effects than its free form. Furthermore, incorporating Qu in various nano-delivery systems improved its sustained release and stability, extended its circulation time, enhanced its accumulation at target sites, and increased its therapeutic efficiency. The purpose of this study was to provide a comprehensive review of the anticancer properties of various Qu nano-formulation to augment their effects on different malignancies. Various targeting strategies for improving Qu delivery, including nanoliposomes, lipids, polymeric, micelle, and inorganic nanoparticle NPs, have been discussed in this review. The results of the current study illustrated that a combination of appropriate nano encapsulation approaches with tumor-oriented targeting delivery might lead to establishing QU nanoparticles that can be a promising technique for cancer treatment.

Safety and Efficacy of Anlotinib Hydrochloride Plus Temozolomide in Patients with Recurrent Glioblastoma

PURPOSE

Glioblastoma (GBM) is a highly vascularized tumor with few treatment options after disease recurrence. Here, we report the efficacy and safety of anlotinib hydrochloride plus temozolomide in patients with recurrent GBM.

PATIENTS AND METHODS

Patients with first definite postsurgical progression of histologically confirmed GBM preceded by standard radiotherapy and temozolomide chemotherapy were eligible for inclusion. All patients received temozolomide (150-200 mg/m2, orally, every day (QD) d1-5/4 wk) and anlotinib (10 mg, orally, QD, d1-14/3 wk) until disease progression or unacceptable toxicity. The primary endpoint was investigator-assessed 6-month progression-free survival (PFS) rate by the Response Assessment in Neuro-Oncology (RANO) criteria.

RESULTS

Twenty-one patients were enrolled between May 2020 and July 2021, with a median age of 55 (range 27-68) years old. According to the Response Assessment in Neuro-Oncology (RANO) criteria, tumor response occurred in 17 patients, of which 9 patients had a complete response, and the objective response rate was 81.0% [95% confidence interval (CI), 62.6-99.3]. The disease control rate was 95.2% (95% CI, 76.2-99.9), with three additional patients achieving a stable disease without tumor progression. The median PFS was 7.3 months (95% CI, 4.9-9.7), and the 6-month PFS rate was 61.9% (95% CI, 39.3-84.6). The median overall survival was 16.9 months (95% CI, 7.8-26.0). The most common adverse events were leukocytopenia (66.7%), thrombocytopenia (38.1%), and hypertriglyceridemia (38.1%). Five patients had nine grade 3 adverse events, with a 23.8% incidence rate. Two patients discontinued therapy due to ischemic stroke (grade 3) and wound dehiscence (grade 1), respectively. No grade 4 or treatment-related deaths occurred in this study.

CONCLUSIONS

Anlotinib combined with temozolomide is efficacious and tolerated in patients with recurrent GBM.

Advances in the Anti-Tumor Activity of Biflavonoids in Selaginella

Despite the many strategies employed to slow the spread of cancer, the development of new anti-tumor drugs and the minimization of side effects have been major research hotspots in the anti-tumor field. Natural drugs are a huge treasure trove of drug development, and they have been widely used in the clinic as anti-tumor drugs. Selaginella species in the family Selaginellaceae are widely distributed worldwide, and they have been well-documented in clinical practice for the prevention and treatment of cancer. Biflavonoids are the main active ingredients in Selaginella, and they have good biological and anti-tumor activities, which warrant extensive research. The promise of biflavonoids from Selaginella (SFB) in the field of cancer therapy is being realized thanks to new research that offers insights into the multi-targeting therapeutic mechanisms and key signaling pathways. The pharmacological effects of SFB against various cancers in vitro and in vivo are reviewed in this review. In addition, the types and characteristics of biflavonoid structures are described in detail; we also provide a brief summary of the efforts to develop drug delivery systems or combinations to enhance the bioavailability of SFB monomers. In conclusion, SFB species have great potential to be developed as adjuvant or even primary therapeutic agents for cancer, with promising applications.

The potential anti-cancer effects of quercetin on blood, prostate and lung cancers: An update

Cancer is caused by abnormal proliferation of cells and aberrant recognition of the immune system. According to recent studies, natural products are most likely to be effective at preventing cancer without causing any noticeable complications. Among the bioactive flavonoids found in fruits and vegetables, quercetin is known for its anti-inflammatory, antioxidant, and anticancer properties. This review aims to highlight the potential therapeutic effects of quercetin on some different types of cancers including blood, lung and prostate cancers.

Integrative analysis of a novel 5 methylated snoRNA genes prognostic signature in patients with glioma

Aim: To explore the prognostic value of methylated snoRNA genes in glioma and construct a prognostic risk signature. Materials & methods: We retrieved clinical information and 450K methylation data from The Cancer Genome Atlas and obtained five methylated snoRNA genes. Then we established a risk signature and verified the effect of SNORA71B on glioma cells with functional assays. Results: A risk signature containing five methylated snoRNA genes was constructed and demonstrated to be an independent predictor of glioma prognosis. Silencing SNORA71B restrained the proliferation, migration and invasion of glioma cells and reduced the expression of mesenchymal and cell cycle marker proteins. Conclusion: This study constructed a methylated snoRNA gene risk signature, which may provide a reference for glioma patients' prognosis assessment.

Plants as a Source of Anticancer Agents: From Bench to Bedside

Cancer is the second leading cause of death after cardiovascular diseases. Conventional anticancer therapies are associated with lack of selectivity and serious side effects. Cancer hallmarks are biological capabilities acquired by cancer cells during neoplastic transformation. Targeting multiple cancer hallmarks is a promising strategy to treat cancer. The diversity in chemical structure and the relatively low toxicity make plant-derived natural products a promising source for the development of new and more effective anticancer therapies that have the capacity to target multiple hallmarks in cancer. In this review, we discussed the anticancer activities of ten natural products extracted from plants. The majority of these products inhibit cancer by targeting multiple cancer hallmarks, and many of these chemicals have reached clinical applications. Studies discussed in this review provide a solid ground for researchers and physicians to design more effective combination anticancer therapies using plant-derived natural products.

MicroRNA-22 represses glioma development via activation of macrophage-mediated innate and adaptive immune responses

Macrophage-mediated tumor cell phagocytosis and subsequent neoantigen presentation are critical for generating anti-tumor immunity. This study aimed to uncover the potential clinical value and molecular mechanisms of miRNA-22 (miR-22) in tumor cell phagocytosis via macrophages and more efficient T cell priming. We found that miR-22 expression was markedly downregulated in primary macrophages from glioma tissue samples compared to adjacent tissues. miR-22-overexpressing macrophages inhibited glioma cell proliferation and migration, respectively. miR-22 upregulation stimulated the phagocytic ability of macrophages, enhanced tumor cell phagocytosis, antigen presentation, and efficient T cell priming. Additionally, our data revealed that miR-22-overexpressing macrophages inhibited glioma formation in vivo, HDAC6 was a target, and NF-κB signaling was a pathway closely associated with miR-22 in tumor-associated macrophages (TAMs) of glioma. Our findings revealed the essential roles of miR-22 in tumor cell phagocytosis by macrophages and more efficient T cell priming, facilitating further research on phagocytic regulation to enhance the response to tumor immunotherapy.

Ionizing Radiation-Induced GDF15 Promotes Angiogenesis in Human Glioblastoma Models by Promoting VEGFA Expression Through p-MAPK1/SP1 Signaling

Glioblastoma multiforme (GBM), the most aggressive cancer type that has a poor prognosis, is characterized by enhanced and aberrant angiogenesis. In addition to surgical resection and chemotherapy, radiotherapy is commonly used to treat GBM. However, radiation-induced angiogenesis in GBM remains unexplored. This study examined the role of radiation-induced growth/differentiation factor-15 (GDF15) in regulating tumor angiogenesis by promoting intercellular cross-talk between brain endothelial cells (ECs) and glioblastoma cells. Radiation promoted GDF15 secretion from human brain microvascular endothelial cells (HBMVECs). Subsequently, GDF15 activated the transcriptional promoter VEGFA in the human glioblastoma cell line U373 through p-MAPK1/SP1 signaling. Upregulation of vascular endothelial growth factor (VEGF) expression in U373 cells resulted in the activation of angiogenic activity in HBMVECs via KDR phosphorylation. Wound healing, tube formation, and invasion assay results revealed that the conditioned medium of recombinant human GDF15 (rhGDF15)-stimulated U373 cell cultures promoted the angiogenic activity of HBMVECs. In the HBMVEC-U373 cell co-culture, GDF15 knockdown mitigated radiation-induced VEGFA upregulation in U373 cells and enhanced angiogenic activity of HBMVECs. Moreover, injecting rhGDF15-stimulated U373 cells into orthotopic brain tumors in mice promoted angiogenesis in the tumors. Thus, radiation-induced GDF15 is essential for the cross-talk between ECs and GBM cells and promotes angiogenesis. These findings indicate that GDF15 is a putative therapeutic target for patients with GBM undergoing radio-chemotherapy.

3D tumor angiogenesis models: recent advances and challenges

The development of blood vessels, referred to as angiogenesis, is an intricate process regulated spatially and temporally through a delicate balance between the qualitative and quantitative expression of pro and anti-angiogenic molecules. As angiogenesis is a prerequisite for solid tumors to grow and metastasize, a variety of tumor angiogenesis models have been formulated to better understand the underlying mechanisms and associated clinical applications. Studies have demonstrated independent mechanisms inducing angiogenesis in tumors such as (a) HIF-1/VEGF mediated paracrine interactions between a cancer cell and endothelial cells, (b) recruitment of progenitor endothelial cells, and (c) vasculogenic mimicry. Moreover, single-cell sequencing technologies have indicated endothelial cell heterogeneity among organ systems including tumor tissues. However, existing angiogenesis models often rely upon normal endothelial cells which significantly differ from tumor endothelial cells exhibiting distinct (epi)genetic and metabolic signatures. Besides, the existence of intra-individual variations necessitates the development of improved tumor vascular model systems for personalized medicine. In the present review, we summarize recent advancements of 3D tumor vascular model systems which include (a) tissue engineering-based tumor models; (b) vascular organoid models, and (c) organ-on-chips and their importance in replicating the tumor angiogenesis along with the associated challenges to design improved models.

Optical Imaging in the Second Near Infrared Window for Vascular Bioimaging

Optical imaging in the second near infrared region (NIR-II, 1000-1700 nm) provides higher resolution and deeper penetration depth for accurate and real-time vascular anatomy, blood dynamics, and function information, effectively contributing to the early diagnosis and curative effect assessment of vascular anomalies. Currently, NIR-II optical imaging demonstrates encouraging results including long-term monitoring of vascular injury and regeneration, real-time feedback of blood perfusion, tracking of lymphatic metastases, and imaging-guided surgery. This review summarizes the latest progresses of NIR-II optical imaging for angiography including fluorescence imaging, photoacoustic (PA) imaging, and optical coherence tomography (OCT). The development of current NIR-II fluorescence, PA, and OCT probes (i.e., single-walled carbon nanotubes, quantum dots, rare earth doped nanoparticles, noble metal-based nanostructures, organic dye-based probes, and semiconductor polymer nanoparticles), highlighting probe optimization regarding high brightness, longwave emission, and biocompatibility through chemical modification or nanotechnology, is first introduced. The application of NIR-II probes in angiography based on the classification of peripheral vascular, cerebrovascular, tumor vessel, and cardiovascular, is then reviewed. Major challenges and opportunities in the NIR-II optical imaging for vascular imaging are finally discussed.

Pro- and Antiangiogenic Factors in Gliomas: Implications for Novel Therapeutic Possibilities

Angiogenesis, a complex, multistep process of forming new blood vessels, plays crucial role in normal development, embryogenesis, and wound healing. Malignant tumors characterized by increased proliferation also require new vasculature to provide an adequate supply of oxygen and nutrients for developing tumor. Gliomas are among the most frequent primary tumors of the central nervous system (CNS), characterized by increased new vessel formation. The processes of neoangiogenesis, necessary for glioma development, are mediated by numerous growth factors, cytokines, chemokines and other proteins. In contrast to other solid tumors, some biological conditions, such as the blood–brain barrier and the unique interplay between immune microenvironment and tumor, represent significant challenges in glioma therapy. Therefore, the objective of the study was to present the role of various proangiogenic factors in glioma angiogenesis as well as the differences between normal and tumoral angiogenesis. Another goal was to present novel therapeutic options in oncology approaches. We performed a thorough search via the PubMed database. In this paper we describe various proangiogenic factors in glioma vasculature development. The presented paper also reviews various antiangiogenic factors necessary in maintaining equilibrium between pro- and antiangiogenic processes. Furthermore, we present some novel possibilities of antiangiogenic therapy in this type of tumors.

Dichotomy in Growth and Invasion from Low- to High-Grade Glioma Cellular Variants

Glial dysfunction outraging CNS plasticity and integrity results in one of the most dangerous cancers, namely glioma, featuring little median survival period and high recurrence. The hallmark properties of proliferation, invasion and angiogenesis with the infiltrated macrophages in glioma are expected to be tightly coupled or cross-linked, but not properly related so far. The present study is aimed to find a relationship between this featured quadrangle from lower to higher grades (HG) of post-operative glioma tissues and their invading subsets. Elevated Ki67-associated proliferation in lower grades (LG) was supported with VEGF dependent angiogenic maintenance which found a decrease unlikely in HG. In contrast, MMP 2 and 9-associated invasions augmented high in HG with the dominant presence of CD204⁺ M2 polarized macrophages and a general increase in global DNMT1-associated methylation. Marked differences found in ECM invading cellular subsets of HG showing high proliferative capacity indicating rationally for recurrence, contrasting the nature of gross tumor tissue of the same grade. Thus in LG, the neoplastic lesion is more inclined to its growth while in higher grade more disposed towards tissue wreckage in support with cellular environmental milieu whereas the cellular variants and subsets of invaded cells showed different trends. Therefore, some operational dichotomy or coupling among cellular variants in glioma is active in determining its low- to high-grade transition and aggressive progression.

Potential Therapeutic Targets of Quercetin, a Plant Flavonol, and Its Role in the Therapy of Various Types of Cancer through the Modulation of Various Cell Signaling Pathways

Polyphenolic flavonoids are considered natural, non-toxic chemopreventers, which are most commonly derived from plants, fruits, and vegetables. Most of these polyphenolics exhibit remarkable antioxidant, anti-inflammatory, and anticancer properties. Quercetin (Qu) is a chief representative of these polyphenolic compounds, which exhibits excellent antioxidant and anticancer potential, and has attracted the attention of researchers working in the area of cancer biology. Qu can regulate numerous tumor-related activities, such as oxidative stress, angiogenesis, cell cycle, tumor necrosis factor, proliferation, apoptosis, and metastasis. The anticancer properties of Qu mainly occur through the modulation of vascular endothelial growth factor (VEGF), apoptosis, phosphatidyl inositol-3-kinase (P13K)/Akt (proteinase-kinase B)/mTOR (mammalian target of rapamycin), MAPK (mitogen activated protein kinase)/ERK1/2 (extracellular signal-regulated kinase 1/2), and Wnt/β-catenin signaling pathways. The anticancer potential of Qu is documented in numerous in vivo and in vitro studies, involving several animal models and cell lines. Remarkably, this phytochemical possesses toxic activities against cancerous cells only, with limited toxic effects on normal cells. In this review, we present extensive research investigations aimed to discuss the therapeutic potential of Qu in the management of different types of cancers. The anticancer potential of Qu is specifically discussed by focusing its ability to target specific molecular signaling, such as p53, epidermal growth factor receptor (EGFR), VEGF, signal transducer and activator of transcription (STAT), PI3K/Akt, and nuclear factor kappa B (NF-κB) pathways. The anticancer potential of Qu has gained remarkable interest, but the exact mechanism of its action remains unclear. However, this natural compound has great pharmacological potential; it is now believed to be a complementary—or alternative—medicine for the prevention and treatment of different cancers.

Activation of nuclear factor-κB in the angiogenesis of glioma: Insights into the associated molecular mechanisms and targeted therapies

Glioma is the most commonly observed primary intracranial tumour and is associated with massive angiogenesis. Glioma neovascularization provides nutrients for the growth and metabolism of tumour tissues, promotes tumour cell division and proliferation, and provides conditions ideal for the infiltration and migration of tumour cells to distant places. Growing evidence suggests that there is a correlation between the activation of nuclear factor (NF)‐κB and the angiogenesis of glioma. In this review article, we highlighted the functions of NF‐κB in the angiogenesis of glioma, showing that NF‐κB activation plays a pivotal role in the growth and progression of glioma angiogenesis and is a rational therapeutic target for antiangiogenic strategies aimed at glioma.

Pharmacological basis and new insights of quercetin action in respect to its anti-cancer effects

Quercetin is a kind of flavonoid compounds that comes from nature and is widely existed in the daily diet. Previous studies have found that quercetin has many effects such as anti-inflammatory, anti-oxidation and anti-cancer. Both in vivo and in vitro experiments have demonstrated that quercetin can exert anti-tumor effects by altering cell cycle progression, inhibiting cell proliferation, promoting apoptosis, inhibiting angiogenesis and metastasis progression, and affecting autophagy. This review summarizes the evidence for the pharmacological potential and inhibition of quercetin on cancers, supporting the viewpoint that quercetin should be adequately considered as a therapeutic agent against various cancers.

High gene expression levels of VEGFA and CXCL8 in the peritumoral brain zone are associated with the recurrence of glioblastoma: A bioinformatics analysis

The present study aimed to identify differentially regulated genes between the peritumoral brain zone (PBZ) and tumor core (TC) of glioblastoma (GBM), to elucidate the underlying molecular mechanisms and provide a target for the treatment of tumors. The GSE13276 and GSE116520 datasets were downloaded from the Gene Expression Omnibus (GEO) database. Differentially expressed genes (DEGs) for the PBZ and TC were obtained using the GEO2R tool. The bioinformatics and evolutionary genomics online tool Venn was used to identify common DEGs between the two datasets. The Database for Annotation, Visualization, and Integrated Discovery online tool was used to analyze enriched pathways of the Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases. The Search Tool for the Retrieval of Interacting Genes/Proteins online tool was used to construct a protein-protein interaction (PPI) network of DEGs. Hub genes were identified using Cytohubba, a plug-in for Cytoscape. The Gene Expression Profiling Interactive Analysis (GEPIA) database was utilized to perform survival analysis. In total, 75 DEGs, including 12 upregulated and 63 downregulated genes, were identified. In the GO term analysis, these DEGs were mainly enriched in ‘regulation of angiogenesis’ and ‘central nervous system development’. Furthermore, in the KEGG pathway analysis, the DEGs were mainly enriched in ‘bladder cancer’ and ‘endocytosis’. When filtering the results of the PPI network analysis using Cytohubba, a total of 10 hub genes, including proteolipid protein 1, myelin associated oligodendrocyte basic protein, contactin 2, myelin oligodendrocyte glycoprotein, myelin basic protein, myelin associated glycoprotein, SRY-box transcription factor 10, C-X-C motif chemokine ligand 8 (CXCL8), vascular endothelial growth factor A (VEGFA) and plasmolipin, were identified. These hub genes were further subjected to GO term and KEGG pathway analysis, and were revealed to be enriched in ‘central nervous system development’, ‘bladder cancer’ and ‘rheumatoid arthritis’. These hub genes were used to perform survival analysis using the GEPIA database, and it was determined that VEGFA and CXCL8 were significantly associated with a reduction in the overall survival of patients with GBM. In conclusion, the results suggest that the recurrence of GBM is associated with high gene expression levels VEGFA and CXCL8, and the development of the central nervous system.

Ardisia crispa root hexane fraction suppressed angiogenesis in human umbilical vein endothelial cells (HUVECs) and in vivo zebrafish embryo model

Ardisia crispa Thunb. A. DC. (Primulaceae) has been used extensively as folk-lore medicine in South East Asia including China and Japan to treat various inflammatory related diseases. Ardisia crispa root hexane fraction (ACRH) has been thoroughly studied by our group and it has been shown to exhibit anti-inflammatory, anti-hyperalgesic, anti-arthritic, anti-ulcer, chemoprevention and suppression against inflammation-induced angiogenesis in various animal model. Nevertheless, its effect against human endothelial cells in vitro has not been reported yet. Hence, the aim of the study is to investigate the potential antiangiogenic property of ACRH in human umbilical vein endothelial cells (HUVECs) and zebrafish embryo model. ACRH was separated from the crude ethanolic extract of the plant's root in prior to experimental studies. MTT assay revealed that ACRH exerted a concentration-dependent antiproliferative effect on HUVEC with the IC₅₀ of 2.49 ± 0.04 μg/mL. At higher concentration (10 μg/mL), apoptosis was induced without affecting the cell cycle distribution. Angiogenic properties including migration, invasion and differentiation of HUVECs, evaluated via wound healing, trans-well invasion and tube formation assay respectively, were significantly suppressed by ACRH in a concentration-dependent manner. Noteworthily, significant antiangiogenic effects were observed even at the lowest concentration used (0.1 μg/mL). Expression of proMMP-2, vascular endothelial growth factor (VEGF)-C, VEGF-D, Angiopoietin-2, fibroblast growth factor (FGF)-1, FGF-2, Follistatin, and hepatocyte growth factor (HGF) were significantly reduced in various degrees by ACRH. The ISV formation in zebrafish embryo was significantly suppressed by ACRH at the concentration of 5 μg/mL. These findings revealed the potential of ACRH as antiangiogenic agent by suppressing multiple proangiogenic proteins. Thus, it can be further verified via the transcription of these proteins from their respective DNA, in elucidating their exact pathways.

Vasorin stimulates malignant progression and angiogenesis in glioma

Glioma, the most common human primary brain tumor, is characterized by invasive capabilities and angiogenesis. Vasorin (VASN), a transmembrane protein, is reported to be associated with vascular injury repair and is overexpressed in some human tumors. However, its role in tumor progression and angiogenesis in glioma is unknown. In this study, VASN was shown to be overexpressed in high‐grade gliomas, and the expression level correlated with tumor grade and microvessel density in glioma specimens. Glioma patients with high VASN expression had a shorter overall survival time. Knockdown of VASN in glioma cells by shRNA significantly inhibited the malignancy of glioma, including cell proliferation, colony formation, invasion, and sphere formation. Ectopic expression of VASN increased glioma progression in vitro. The expression of VASN correlated with the mesenchymal type of glioblastoma multiforme (GBM) subtyped by gene set enrichment analysis (GSEA). Our results showed that the concentration of VASN was increased in the conditioned medium (CM) from glioma cells with VASN overexpression, and the CM from glioma cells with knockdown or overexpressed VASN inhibited or promoted HUVEC migration and tubulogenesis in vitro, respectively. Glioma growth and angiogenesis were stimulated upon ectopic expression of VASN in vivo. The STAT3 and NOTCH pathways were found to be activated and inhibited by VASN overexpression. Our findings suggest that VASN stimulates tumor progression and angiogenesis in glioma, and, as such, represents a novel therapeutic target for glioma.

Roles of Extracellular Vesicles in High-Grade Gliomas: Tiny Particles with Outsized Influence

High-grade gliomas, particularly glioblastomas (grade IV), are devastating diseases with dismal prognoses; afflicted patients seldom live longer than 15 months, and their quality of life suffers immensely. Our current standard-of-care therapy has remained essentially unchanged for almost 15 years, with little new therapeutic progress. We desperately need a better biologic understanding of these complicated tumors in a complicated organ. One area of rejuvenated study relates to extracellular vesicles (EVs)-membrane-enclosed nano- or microsized particles that originate from the endosomal system or are shed from the plasma membrane. EVs contribute to tumor heterogeneity (including the maintenance of glioma stem cells or their differentiation), the impacts of hypoxia (angiogenesis and coagulopathies), interactions amid the tumor microenvironment (concerning the survival of astrocytes, neurons, endothelial cells, blood vessels, the blood-brain barrier, and the ensuing inflammation), and influences on the immune system (both stimulatory and suppressive). This article reviews glioma EVs and the ways that EVs manifest themselves as autocrine, paracrine, and endocrine factors in proximal and distal intra- and intercellular communications. The reader should note that there is much controversy, and indeed confusion, in the field over the exact roles for EVs in many biological processes, and we will engage some of these difficulties herein.

Nanocarriers and nonviral methods for delivering antiangiogenic factors for glioblastoma therapy: the story so far

Angiogenesis, the formation of new blood vessels, is an essential component of glioblastoma (GB) progression. The development of angiogenesis inhibitor therapy, including treatments targeting vascular endothelial growth factor (VEGF) in particular, raised new hopes for the treatment of GB, but no Phase III clinical trial to date has reported survival benefits relative to standard treatment. There are several possible reasons for this limited efficacy, including VEGF-independent angiogenesis, induction of tumor invasion, and inefficient antiangiogenic factor delivery to the tumor. Efforts have been made to overcome these limitations by identifying new angiogenesis inhibitors that target angiogenesis through different mechanisms of action without inducing tumor invasion, and through the development of viral and nonviral delivery methods to improve antiangiogenic activity. Herein, we describe the nonviral methods, including convection-enhanced delivery devices, implantable polymer devices, nanocarriers, and cellular vehicles, to deliver antiangiogenic factors. We focus on those evaluated in intracranial (orthotopic) animal models of GB, the most relevant models of this disease, as they reproduce the clinical scenario of tumor progression and therapy response encountered in GB patients.

Exploratory Study of the Effect of IMA950/Poly-ICLC Vaccination on Response to Bevacizumab in Relapsing High-Grade Glioma Patients

Immunotherapy, including therapeutic vaccines, is increasingly being developed for patients with high-grade glioma, and combinations of immunotherapies and synergy with standard of care are being investigated. In this regard, bevacizumab (BEV) has been shown to synergize with immunotherapy in preclinical studies of glioma and in other tumour entities. Here, we conducted a post-hoc exploratory study to evaluate the effect of the IMA950/poly-ICLC peptide vaccine on subsequent BEV administration in high-grade glioma patients. 16 IMA950-vaccinated and 40 non-vaccinated patients were included. At initial diagnosis, patients benefited from surgery and chemoradiation. At first or subsequent recurrence, patients received 10mg/kg of BEV every 2-3 weeks. Primary endpoints were overall survival (OS) and progression-free survival (PFS) from BEV initiation. IMA950-vaccinated patients did not show improved response to BEV as compared to non-vaccinated patients: there was no difference in median PFS (2.6 vs. 4.2 months for vaccinated and control patients, respectively, p = 0.50) nor in median OS (7.8 vs. 10.0 months for vaccinated and control patients, respectively, p = 0.69). In conclusion, potential synergy of BEV and therapeutic vaccines, when administered sequentially, has yet to be established in the clinical setting of GBM recurrence. Potential synergy of concomitant administration should be tested in future trials.

Identification of hub genes and pathways in glioblastoma by bioinformatics analysis

Glioblastoma (GBM) is the most common type of malignant brain tumor, and is associated with poor patient prognosis. A comprehensive understanding of the molecular mechanism underlying GBM may help to guide the identification of novel diagnoses and treatment targets. The gene expression profile of the GSE4290 GBM dataset was analyzed in order to identify differentially expressed genes (DEGs). Enriched pathways were identified through Gene Ontology and the Kyoto Encyclopedia of Genes and Genomes analyses. A protein-protein interaction network was constructed in order to identify hub genes and for module analysis. Expression and survival analyses were conducted in order to screen and validate critical genes. A total of 1,801 DEGs were recorded, including 620 upregulated and 1,181 downregulated genes. Upregulated DEGs were enriched in the terms ‘mitotic cell cycle process’, ‘mitotic cell cycle’ and ‘cell cycle process’. Downregulated genes were enriched in ‘transsynaptic signaling’, ‘anterograde transsynaptic signaling’ and ‘synaptic signaling’. A total of 15 hub genes, which displayed a high degree of connectivity, were selected. These genes included vascular endothelial growth factor A, cyclin-dependent kinase 1 (CDK1), cell-division cycle protein 20 (CDC20), aurora kinase A (AURKA), and budding uninhibited by benzimidazoles 1 (BUB1). The identified DEGs and hub genes may help guide investigations on the mechanisms underlying the development and progression of GBM. CDK1, CDC20, AURKA and BUB1, which are involved in cell cycle pathways, may be potential targets in the diagnosis and therapy of GBM.

circ-SHKBP1 Regulates the Angiogenesis of U87 Glioma-Exposed Endothelial Cells through miR-544a/FOXP1 and miR-379/FOXP2 Pathways

Circular RNAs (circRNAs) are a type of endogenous non-coding RNAs, which have been considered to mediate diverse tumorigenesis including angiogenesis. The present study aims to elucidate the potential role and molecular mechanism of circ-SHKBP1 in regulating the angiogenesis of U87 glioma-exposed endothelial cells (GECs). The expression of circ-SHKBP1, but not linear SHKBP1, was significantly upregulated in GECs compared with astrocyte-exposed endothelial cells (AECs). circ-SHKBP1 knockdown inhibited the viability, migration, and tube formation of GECs dramatically. The expressions of miR-379/miR-544a were downregulated in GECs, and circ-SHKBP1 functionally targeted miR-544a/miR-379 in an RNA-induced silencing complex (RISC) manner. Dual-luciferase reporter assay demonstrated that forkhead box P1/P2 (FOXP1/FOXP2) were targets of miR-544a/miR-379. The expressions of FOXP1/FOXP2 were upregulated in GECs, and silencing of FOXP1/FOXP2 inhibited the viability, migration, and tube formation of GECs. Meanwhile, FOXP1/FOXP2 promoted angiogenic factor with G patch and FHA domains 1 (AGGF1) expression at the transcriptional level. Furthermore, knockdown of AGGF1 suppressed the viability, migration, and tube formation of GECs via phosphatidylinositol 3-kinase (PI3K)/AKT and extracellular signal-regulated kinase (ERK)1/2 pathways. Taken together, the present study demonstrated that circ-SHKBP1 regulated the angiogenesis of GECs through miR-544a/FOXP1 and miR-379/FOXP2 pathways, and these findings might provide a potential target and effective strategy for combined therapy of gliomas.

Gold nanoparticles attenuate metastasis by tumor vasculature normalization and epithelial-mesenchymal transition inhibition

Angiogenesis is a process by which vessels are formed through preexisting ones, and this plays a key role in the progression of solid tumors. However, tumor vessels are influenced by excessive pro-angiogenic factors, resulting in deformed structures that facilitate the intravasation of tumor cells into the circulation and subsequent metastasis. Moreover, abnormal tumor vessels have low blood perfusion and thereby decreased oxygen infusion into tumors. This results in a hostile microenvironment that promotes epithelial-mesenchymal transition (EMT), a process in which epithelial cells lose their polarity and gain increased motility, which is associated with metastasis and invasion. Here, we demonstrate that gold nanoparticles (AuNPs) facilitate tumor vasculature normalization, increase blood perfusion and alleviate hypoxia in melanoma tumors. Additionally, AuNPs were observed to reverse EMT in tumors, accompanied by the alleviation of lung metastasis. These AuNPs inhibited the migration of B16F10 cells and reversed EMT in B16F10 cells, indicating that AuNPs could directly regulate EMT independent of improvements in hypoxia. Taken together, our data demonstrated that AuNPs could induce tumor vasculature normalization and reverse EMT, resulting in decreased melanoma tumor metastasis.

Effectiveness of antiangiogenic drugs in glioblastoma patients: A systematic review and meta-analysis of randomized clinical trials

BACKGROUND

glioblastomas are highly vascularized tumors and various antiangiogenic drugs have been investigated in clinical trials showing unclear results. We performed a systematic review and a meta-analysis to clarify and evaluate their effectiveness in glioblastoma patients.

PATIENTS AND METHODS

we searched relevant published and unpublished randomized clinical trials analyzing antiangiogenic drugs versus chemotherapy in glioblastoma patients from January 2006 to January 2016 in MEDLINE, WEB of SCIENCE, ASCO, ESMO and SNO databases.

RESULTS

fourteen randomized clinical trials were identified (7 with bevacizumab, 2 cilengitide, 1 enzastaurin, 1 dasatinib, 1 vandetanib, 1 temsirolimus, 1 cediranib) including 4330 patients. Antiangiogenic drugs showed no improvement in overall survival with a pooled HR of 1.00, a trend for an inferior outcome, in terms of overall survival, was observed in the group of patients receiving antiangiogenic drug alone compared to cytotoxic drug alone (HR=1.24, p=0.056). Bevacizumab did not improve overall survival. Twelve trials (4113 patients) were analyzed for progression-free survival. Among antiangiogenic drugs, only bevacizumab demonstrated an improvement of progression-free survival (HR=0.63, p<0.001), both alone (HR=0.60, p=0.003) or in combination to chemotherapy (HR=0.63; p<0.001), both as first-line treatment (HR=0.70, p<0.001) or in recurrent disease (HR=0.52, p<0.001).

CONCLUSIONS

antiangiogenic drugs did not improve overall survival in glioblastoma patients, either as first or second-line treatment, and either as single agent or in combination with chemotherapy. Among antiangiogenic drugs, only bevacizumab improved progression-free survival regardless of treatment line, both as single agent or in combination with chemotherapy.

Lymphangiogenesis in Classical Hodgkin Lymphoma - Preliminary Study with Clinicopathological Correlations

A role for lymphangiogenesis in metastatic breast and prostate cancers has been suggested recently. The relevance of lymphangiogenesis in cancer as a rule, and more specifically in classical Hodgkin lymphoma, is poorly understood in comparison with that of angiogenesis. In a preliminary (pilot) study we have investigated the role of lymphatic vessels growth in 19 cases of classical Hodgkin lymphoma stained with the D2-40 (podoplanin) antibody. In each case, three lymphatic vessels hot spots were scrutinized twice. Of the 57 hot spots thus identified, we chose 15 at random for photography, microvessel counting and image analysis. We determined the mean perimeter, surface area, major axis length and complexity factor for each hot spot and correlated them with clinical and biological features of classical Hodgkin lymphoma. No correlations were found with clinical features. No associations were noted with the standard immuno-markers of classical Hodgkin lymphoma. However, significant inverse correlations were shown with pRb, BAX and IκB-α expression. The mean lymphatic major axis length was inversely correlated with the complexity factor. Last, we carried out an additional clinicopathological correlation of the expression of pRb, BAX and IκB-α in a cohort of classical Hodgkin lymphoma patients previously published.

Synthesis and Evaluation of Novel Carbocyclic Oxetanocin A (COA-Cl) Derivatives as Potential Tube Formation Agents

Six novel carbocyclic oxetanocin A analogs (2-chloro-C.OXT-A; COA-Cl) with various hydroxymethylated or spiro-conjugated cyclobutane rings at the N(9)-position of the 2-chloropurine moiety were synthesized and evaluated using human umbilical vein endothelial cells. All prepared compounds (2a-f) showed good to moderate activity with angiogenic potency. Among these compounds, 100 µM cis-trans-2',3'-bis(hydroxymethyl)cyclobutyl derivative (2b), trans-3'-hydroxymethylcyclobutyl analog (2d), and 3',3'-bis(hydroxymethyl)cyclobutyl derivative (2e) had greater angiogenic activity, with relative tube areas of 3.43±0.44, 3.32±0.53, and 3.59±0.83 (mean±standard deviation (S.D.)), respectively, which was comparable to COA-Cl (3.91±0.78). These data may be important for further development of this class of compounds as potential tube formation agents.

RGD peptide conjugation results in enhanced antitumor activity of PD0325901 against glioblastoma by both tumor-targeting delivery and combination therapy

Glioblastoma (GBM) is the most aggressive tumor type in the central nervous system. Both tumor-targeting drug delivery and combination therapy of multiple therapeutic agents with distinct mechanisms are important for GBM treatment. We combined these two strategies and developed a new platform of peptide-drug conjugate (RGD-PEG-Suc-PD0325901, W22) for tumor-targeting delivery using a combination of PD0325901 (a MEK1/2 inhibitor) and RGD peptide. In the present study, the combination of PD0325901 and RGD peptide strongly inhibited U87MG model in vitro and in vivo. This inhibition contributed to synergistic suppression of cell proliferation by blocking ERK pathway activity and cell migration. Modified by conjugation strategy, their conjugate W22 enhanced PD0325901 delivery to GBM cells by receptor mediated cellular internalization. W22 showed great superiority in targeting to U87MG xenografted tumors and strong anti-tumor efficacy based on ERK pathway inhibition and tumor-targeted delivery in vitro and in vivo. Moreover, W22 was stable in serum and able to release PD0325901 in the enzymatic environment. These data indicated that the RGD-PEG-Suc-PD0325901 conjugate provided a strategy for effective delivery of PD0325901 and RGD peptide into the GBM cells and inhibition of tumor growth in a synergistic manner.

Adhesion molecules and the extracellular matrix as drug targets for glioma

The formation of tumor vasculature and cell invasion along white matter tracts have pivotal roles in the development and progression of glioma. A better understanding of the mechanisms of angiogenesis and invasion in glioma will aid the development of novel therapeutic strategies. The processes of angiogenesis and invasion cause the production of an array of adhesion molecules and extracellular matrix (ECM) components. This review focuses on the role of adhesion molecules and the ECM in malignant glioma. The results of clinical trials using drugs targeted against adhesion molecules and the ECM for glioma are also discussed.

Chronic arterial hypertension impedes glioma growth: a multiparametric MRI study in the rat

Glioblastoma is the most aggressive brain tumor and is almost always fatal. These tumors are highly vascularized and angiogenesis is one of the pre-eminent mechanisms underlying their growth. Chronic arterial hypertension (CAH) is a common and worldwide pathology that markedlly alters the structure and function of the vasculature. Yet, essential hypertension is associated in the brain with potential locally impaired vasoreactivity, disturbed perfusion supply and hypoxia phenomena. Even though CAH is a global burden and has an important impact on brain function, nothing is known about the way this frequent pathology would interact with the evolution of glioma. We sought to determine if arterial hypertension influences gliobastoma growth. In the present study, rat glioma C6 tumor cells were implanted in the caudate-putamen of spontaneously hypertensive rats (SHR) or their normotensive controls, the Wistar-Kyoto (WKY) rats. The evolution of the tumor was sequentially analyzed by multiparametric magnetic resonance imaging and the inflammatory response was examined by histochemistry. We found that CAH significantly attenuates the growth of the tumor as, at 21 days, the volume of the tumor was 85.4±34.7 and 126.1±28.8 mm(3), respectively, in hypertensive and normotensive rats (P<0.02). Moreover, cerebral blood volume and cerebral blood flow were greater in the tumors of hypertensive rats (P<0.05). The lesser growth of the tumor observed in normotensive animals was not due to an enhanced rejection of the tumor cells in WKY rats, the inflammatory response being similar in both groups. For the first time, these results show that CAH impedes the growth of glioblastoma and illustrate the need to further study the impact of hypertension on the evolution of brain tumors.

Tumor vasculature and glioma stem cells: Contributions to glioma progression

Glioblastoma multiforme (GBM), the most malignant of brain tumors, is characterized by extensive vascularization and a high degree of invasion. The current standard of care is not very effective, resulting in tumor recurrence with patients rarely surviving over 2 years. This tumor recurrence is attributed to the presence of chemo and radiation resistant glioma stem cells (GSCs). These cells are associated with vascular niches which regulate GSC self-renewal and survival. Recent studies suggest that while blood vessels support glioma stem cells, these tumor cells in turn may regulate and contribute to the tumor vasculature by transdifferentiating into endothelial cells directly or through the secretion of regulatory growth factors such as vascular endothelial growth factor (VEGF) and hepatoma derived growth factor (HDGF). The relationship between the tumor vasculature and the glioma stem cells is the subject of this review.

Fully human VEGFR2 monoclonal antibody BC001 attenuates tumor angiogenesis and inhibits tumor growth

The critical role of VEGFR2 in tumor neovascularization and progression has allowed the design of clinically beneficial therapies based on it. Here we show that BC001, a new fully human anti-VEGFR2 monoclonal antibody, inhibits VEGF-stimulated endothelial cell migration, tube formation, and effectively suppressed the transdifferentiation of cancer stem cells into endothelial cells in vitro. Since BC001 exhibited no activity against the mouse VEGFR2 and mouse based study was required to confirm its efficacy in vivo, BC101, the mouse analogue of BC001, was developed. BC101 significantly attenuated angiogenesis according to Matrigel plug assay and resulted in ~80% growth inhibition of mouse B16F10 homograft tumors relative to vehicle control. Similarly, human analogue BC001 suppressed the growth of human xenograft tumors HCT116 and BGC823. Furthermore, immunohistochemical results showed reduced expression of CD31, VEGFR2 and Ki-67, as well as increased expression of Caspase 3 in BC001-treated tumor, which indicated BC001 was able to significantly decrease microvessel density, suppress proliferation and promote apoptosis. These results demonstrate the fully human VEGFR2 monoclonal antibody BC001 can work as an effective inhibitor of tumor angiogenesis and tumor growth both in vitro and in vivo.

Repair mechanisms help glioblastoma resist treatment

Glioblastoma multiforme (GBM) is a malignant and incurable glial brain tumour. The current best treatment for GBM includes maximal safe surgical resection followed by concomitant radiotherapy and adjuvant temozolomide. Despite this, median survival is still only 14-16 months. Mechanisms that lead to chemo- and radio-resistance underpin treatment failure. Insights into the DNA repair mechanisms that permit resistance to chemoradiotherapy in GBM may help improve patient responses to currently available therapies.

Update on anti-angiogenic treatment for malignant gliomas

Malignant gliomas are the most common primary brain tumor found in adults. Unfortunately, the prognosis for these type of tumors remains dismal despite aggressive treatment with surgical resection, radiation and chemotherapy. Therefore, therapeutics aimed at disrupting the angiogenesis of these tumors is being utilized in to improve survival outcomes and quality of life. This paper reviews the history of antiangiogenic agents in malignant gliomas, discusses the FDA approval of bevacizumab as monotherapy in recurrent glioblastoma and the subsequent controversy, and analyzes the most recent newly diagnosed trials of RTOG 0825 and AVAglio. Additionally, the results of the latest trials with antiangiogenic agents and possible biomarkers are reviewed. Multiple questions remain regarding the potential benefit of antiangiogenic treatments in patients with glioblastoma. Future clinical trials should be designed to learn more about these drugs, to optimize their future use.

Single agent efficacy of the VEGFR kinase inhibitor axitinib in preclinical models of glioblastoma

Anti-angiogenic therapy is a promising therapeutic strategy for the highly vascular and malignant brain tumor, glioblastoma (GBM), although current clinical trials have failed to demonstrate an extension in overall survival. The small molecule tyrosine kinase inhibitor axitinib that targets vascular endothelial growth factor receptor, potently inhibits angiogenesis and has single-agent clinical activity in non-small cell lung, thyroid, and advanced renal cell cancer. Here we show that axitinib exerts direct cytotoxic activity against a number of patient-derived GBM stem cell (GSCs) and an endothelial cell line, and inhibits endothelial tube formation in vitro. Axitinib treatment of mice bearing hypervascular intracranial tumors generated from human U87 glioma cells, MGG4 GSCs and mouse 005 GSCs significantly extended survival that was associated with decreases in tumor-associated vascularity. We thus show for the first time the anti-angiogenic effect and survival prolongation provided by systemic single agent treatment with axitinib in preclinical orthotopic GBM models including clinically relevant GSC models. These results support further investigation of axitinib as an anti-angiogenic agent for GBM.

Anti-angiogenic effect of auranofin on HUVECs in vitro and zebrafish in vivo

Angiogenesis plays an essential role in many physiological and pathological processes. Auranofin (Ridaura®), an important gold(I) complex, is used to treat rheumatoid arthritis. However, the effect of auranofin on blood vessel formation is still unclear. In this study, we investigated the anti-angiogenic activity of auranofin on human umbilical vein endothelial cells (HUVEC) in vitro and zebrafish in vivo. Our results showed that auranofin could inhibit the proliferation, migration and tube formation of HUVECs and disrupted the formation of intersegmental vessels and the subintestinal vessels of zebrafish embryos. Auranofin inhibited the phosphorylation of vascular endothelial growth factor 2 (p-VEGFR2) on HUVECs and suppressed the vascular endothelial growth factor (VEGF) signaling pathway (vegfa, flt-1, kdr) but not thioredoxin reductase (TrxR) on zebrafish. Our study suggested that auranofin might serve as a potential anti-angiogenic compound candidate.

P14ARF suppresses tumor-induced thrombosis by regulating the tissue factor pathway

How necrotic areas develop in tumors is incompletely understood but can impact progression. Recent findings suggest that the formation of vascular microthrombi contributes to tumor necrosis, prompting investigation of coagulation cascades. Here, we report that loss of tumor suppressor P14ARF can contribute to activating the clotting cascade in glioblastoma. P14ARF transcriptionally upregulated TFPI2, a Kunitz-type serine protease in the tissue factor pathway that inhibits the initiation of thrombosis reactions. P14ARF activation in tumor cells delayed their ability to activate plasma clotting. Mechanistically, P14ARF activated the TFPI2 promoter in a p53-independent manner that relied upon c-JUN, SP1, and JNK activity. Taken together, our results identify the critical signaling pathways activated by P14ARF to prevent vascular microthrombosis triggered by glioma cells. Stimulation of this pathway might be used as a therapeutic strategy to reduce aggressive phenotypes associated with necrotic tumors, including glioblastoma.

Mechanisms of tumor development and anti-angiogenic therapy in glioblastoma multiforme

Despite advances in surgical and medical therapy, glioblastoma multiforme (GBM) remains a fatal disease. There has been no significant increase in survival for patients with this disease over the last 20 years. Tumor vasculature formation and glioma cell invasion along the white matter tracts both play a pivotal role in glioma development. Angiogenesis and invasion are the major factors believed to be responsible for treatment resistance in tumors, and a better understanding of the glioma invasion and angiogenesis mechanisms will lead to the development of potential new treatments. In this review, we focus on the molecular characteristics of angiogenesis and invasion in human malignant glioma. We discuss bevacizumab and cilengitide, which are used to inhibit angiogenesis in GBM.

Pharmacokinetic assessment of efflux transport in sunitinib distribution to the brain

This study quantitatively assessed transport mechanisms that limit the brain distribution of sunitinib and investigated adjuvant strategies to improve its brain delivery for the treatment of glioblastoma multiforme (GBM). Sunitinib has not shown significant activity in GBM clinical trials, despite positive results seen in preclinical xenograft studies. We performed in vivo studies in transgenic Friend leukemia virus strain B mice: wild-type, Mdr1a/b(-/-), Bcrp1(-/-), and Mdr1a/b(-/-)Bcrp1(-/-) genotypes were examined. The brain-to-plasma area under the curve ratio after an oral dose (20 mg/kg) was similar to the steady-state tissue distribution coefficient, indicating linear distribution kinetics in mice over this concentration range. Furthermore, the distribution of sunitinib to the brain increased after administration of selective P-glycoprotein (P-gp) or breast cancer resistance protein (Bcrp) pharmacological inhibitors and a dual inhibitor, elacridar, comparable to that of the corresponding transgenic genotype. The brain-to-plasma ratio after coadministration of elacridar in wild-type mice was ≈ 12 compared with ≈ 17.3 in Mdr1a/b(-/-)Bcrp1(-/-) mice. Overall, these findings indicate that there is a cooperation at the blood-brain barrier (BBB) in restricting the brain penetration of sunitinib, and brain delivery can be enhanced by administration of a dual inhibitor. These data indicate that the presence of cooperative efflux transporters, P-gp and Bcrp, in an intact BBB can protect invasive glioma cells from chemotherapy. Thus, one may consider the use of transporter inhibition as a powerful adjuvant in the design of future clinical trials for the targeted delivery of sunitinib in GBM.