Artificial Cells, Nanomedicine, and Biotechnology, 2015; Early Online: 1–9 Copyright © 2015 Informa Healthcare USA, Inc. ISSN: 2169-1401 print / 2169-141X online DOI: 10.3109/21691401.2015.1052467

Drug delivery approaches for the treatment of glioblastoma multiforme Marc Fakhoury Artificial Cells, Nanomedicine, and Biotechnology Downloaded from informahealthcare.com by Nyu Medical Center on 06/17/15 For personal use only.

Department of Neurosciences, University of Montreal, Montreal, QC, Canada

Abstract Context: Glioblastoma multiforme (GBM) is by far the most common and aggressive form of glial tumor. It is characterized by a highly proliferative population of cells that invade surrounding tissue and that frequently recur after surgical resection and chemotherapy. Over the last decades, a number of promising novel pharmacological approaches have been investigated, but most of them have failed clinical trials due to some side-effects such as toxicity and poor drug delivery to the brain. The major obstacle in the treatment of GBM is the presence of the blood–brain barrier (BBB). Due to their relatively high molecular weight, most therapeutic drugs fail to cross the BBB from the blood circulation. Objective: This paper sheds light on the characteristics of GBM and the challenges of current pharmacological treatments. A closer look is given to the role of nanotechnology in the field of drug delivery, and its application in the treatment of brain tumors such as GBM. Method: For this purpose, effort was made to select the most recent studies using predefined search criteria that included at least one of the following keywords in the PubMed and Medline databases: glioblastoma, drug delivery, blood–brain barrier, nanotechnology, and nanoparticle. Conclusion: Breakthrough in nanotechnology offers promising applications in cancer therapy and targeted drug delivery. However, more efforts need to be devoted to the development of novel therapeutic strategies that enable the delivery of drugs to desired areas of the brain with limited side-effects and higher therapeutic efficiency.

rise (Adamson et al. 2009). It is estimated that approximately 10.82 per 100,000 individuals will develop a brain tumor of some kind in one year (de Robles et al. 2014). Glioblastoma multiforme (GBM) is the most common form of primary CNS gliomas, with an annual incidence close to 3 per 100,000 individuals (Adamson et  al. 2009, Kushnir and Tzuk-Shina 2011). This disease, which is characterized by small areas of necrotic tissue surrounded by anaplastic cells, primarily affects patients between 45 and 70 years old (Kushnir and Tzuk-Shina 2011). The brain is protected by the blood–brain barrier (BBB), which restricts the passage of potentially harmful molecules (Patel et al. 2009). The BBB acts as a frontier that isolates brain tissues from the blood vascular system. While water and small lipophilic molecules are able to freely diffuse through the BBB, most drugs and large molecules fail to cross its capillary walls, making it difficult to exert their therapeutic effects (Bernacki et al. 2008, Fakhoury et al. 2015). Although recent advances in molecular neuroscience have shaped our understanding of the physiology of the BBB and its relationship with pathological brain conditions, treatment of brain tumors still remains a big challenge. This is mostly due to the inability of drugs to cross the BBB and reach a specific part of the brain (Bernacki et al. 2008, Patel et al. 2009). Drug delivery to the brain relies on several mechanisms, the most common ones being the pharmacological and neurosurgical-based approaches (Serwer and James 2012). The pharmacological-based approach involves the use of polymeric delivery platforms such as nanotechnology-based systems, whereas neurosurgical-based delivery to the brain involves the use of more invasive methods such as intraventricular infusion, intracerebral delivery, and convection-enhanced diffusion (CED) (Serwer and James 2012). Although neurosurgical-based delivery is technically more difficult to achieve, it allows the drug to be administered to specific regions of the brain, leading to increased drug bioavailability and efficiency. This paper begins by giving an overview of the main characteristics of GBM (illustrated in Table I) and the challenges of current pharmacological treatments, and finally discusses new approaches for enhanced drug delivery and targeting to the brain.

Keywords: blood–brain barrier, drug delivery, glioblasoma multiforme, nanomaterial, nanotechnology

Introduction Disorders of the brain and central nervous system (CNS) are among the most severe and frequent causes of disability, and are often very difficult to treat (Misra et al. 2003). More particularly, primary brain tumors constitute an important cause of morbidity and mortality in both adults and children (de Robles et al. 2014). Despite several decades of research, the incidence of brain tumors has been reported to be on the

Correspondence: Marc Fakhoury, Department of Neurosciences, University of Montreal, Montreal, QC, Canada H3C3J7. Tel:  1 (514) 710-7060. E-mail: [email protected] (Received 25 February 2015; revised 1 April 2015; accepted 24 April 2015)

1

2  M. Fakhoury

Glioblastoma multiforme: a debilitating disease with poor prognosis

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Characteristics, Etiology, and Pathological features Despite several decades of research in the field of brain tumor therapy, GBM remains one of the most challenging diseases, particularly because of its highly invasive nature (Martinez-Quintanilla et al. 2013, Sathornsumetee and Rich 2006). It is classified into two subtypes: primary glioblastoma and secondary glioblastoma. Primary glioblastoma develops spontaneously in elderly patients without prior clinical evidence of lesions, whereas secondary glioblastoma develops from low-grade glioma (Ohgaki and Kleihues 2013). Although most GBM tumors appear to be sporadic, there are a variety of factors governing susceptibility to brain tumor disease (Reilly 2009). Known environmental factors, such as exposure to ionizing radiation and chemical carcinogens, have been shown to increase the risk of developing brain tumors like GBM (Adamson et al. 2009). Other risk factors for glioblastoma include high cholesterol level, hypertension, and smoking (Kushnir and Tzuk-Shina 2011). Also noteworthy are reports indicating genetic susceptibility to GBM. Studies of genetic syndromes and familial aggregation have shown that brain tumors like GBM are associated with inherited syndromes including neurofibromatosis 1 and 2, tuberous sclerosis, retinoblastoma, Li–Fraumeni syndrome, and Turcot’s syndrome (Reilly 2009, Schwartzbaum et al. 2006). Because most of these syndromes are associated with mutations in genes involved in DNA repair and in the regulation of cell growth, individuals with these syndromes are at higher risk of developing malignant brain tumors such as GBM (Reilly 2009). Histopathological studies have given some insights into the mechanisms of tumor invasion and development. GBM is classified as a grade IV brain tumor, and is characterized by a heterogeneous set of cells that are genetically unstable and resistant to chemotherapy (Ramirez et al. 2013, Wen and Kesari 2008). The histopathological characteristics of GBM include vascular proliferation and necrosis with pseudopalisading features, as well as increased blood vessel diameter and proliferation of endothelial cells (Sathornsumetee and Rich 2006, Onishi et al. 2013). One of the key events mediating the development of GBM tumors is angiogenesis (Folkman 2002, Onishi et al. 2013, Tate and Aghi 2009). Angiogenesis is the formation of new capillary blood from existing vasculature (Onishi et al. 2013, Tate and Aghi 2009). Among all brain tumors, GBM is the most angiogenic because it displays the highest degree of endothelial cell hyperplasia and vascular proliferation (Onishi et al. 2013). As a result, antiangiogenic therapies are being increasingly utilized for the treatment of GBM (Wong and Brem 2008).

Symptoms, diagnosis, and management The most common symptoms for individuals with GBM are focal neurological deficits, headaches, and seizures (Adamson et  al. 2009). Complications such as confusion, drowsiness, dysphagia, and nausea are also very frequently observed (Shahideh et al. 2012, Sizoo et al. 2010). However it is important to point out that the symptoms can vary depending on the

location of the tumor in the brain. For instance, patients with glioblastoma disseminated to the spinal cord present neurological symptoms that are different from those observed in other malignant brain tumors. These primarily include tetraplegia, paraplegia, sensory dysfunction, and gait ataxia (Singh et  al. 2009, Shahideh et  al. 2012). While the vast majority of GBM tumors are found in the frontal, temporal, and parietal lobes of the cerebral cortex, they also occur in the cerebellum and brainstem in a small proportion of patients (Stark et al. 2010). Patients with primary cerebellar GBM typically present signs such as headache, vomiting, and ataxia, whereas patients with GBM located at the brainstem present signs such as hemiparesis, vertigo, facial palsy, and difficulty in swallowing (Mishra et al. 2014, Stark et al. 2010). The use of diagnostic imaging techniques have significantly increased the availability of medical care and have made substantial improvement in the approaches to the treatment of GBM (Schwartzbaum et  al. 2006, Nelson and Cha 2003). Diagnosis of GBM typically begins with findings from magnetic resonance imaging (MRI), which enables the visualization of irregular nodular ring-enhancing lesions (Adamson et  al. 2009, Sathornsumetee et  al. 2007). Computed tomography (CT) can also be used to demonstrate the presence of a tumor, but because of its relatively lower resolution, CT scanning may cause small tumors to be missed (Park et al. 2011, Sathornsumetee et al. 2007). Other imaging tools employed in the diagnosis of GBM are magnetic resonance spectroscopy (MRS), MRI perfusion, and positron emission tomography (PET) scanning (Adamson et al. 2009). They can help differentiate tumor recurrence from benign necrosis, and could be used to provide quantitative measurements related to the biological properties of the tumor (Adamson et al. 2009, Nelson and Cha 2003). Even with the development of preoperative and intraoperative neuroimaging techniques, along with the recent advances in anticancer drug therapies, the prognosis of patients with GBM remains poor, with a median survival of 10–14 months (Adamson et  al. 2009, Sathornsumetee and Rich 2006). Standard care of GBM includes surgical removal of brain tumors coupled with radiotherapy and chemotherapy in order to slow tumor growth (Ramirez et al. 2013). However, despite surgical resection of cancer tissue, nearly 80% of tumors have been shown to recur at the primary site (Ramirez et  al. 2013, Wen and Kesari 2008). Moreover, the presence of the BBB makes it difficult for anticancer drugs, such as chemotherapeutic agents, to gain access to the brain, which further limits the efficacy of the treatment (Kesari 2011, Ramirez et al. 2013). There is therefore an urgent need for a more comprehensive understanding of the molecular underpinnings of drug delivery for brain cancer. This could open up avenues for the development of more efficient targeted molecular therapies offering enhanced recovery and reduced side-effects.

Drug delivery across the BBB: current challenges and limitations There is an enormous challenge faced by pharmaceutical companies to design and develop targeted therapies that

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Drug delivery approaches for the treatment of glioblastoma multiforme  3 could effectively reach the brain and treat brain diseases such as GBM (Fakhoury et al. 2015, Wong and Brem 2008). A lot of effort is being devoted to better understand the molecular properties of the BBB and the drug transport mechanisms across this barrier. The biochemical components of the BBB play a crucial role in preserving brain homeostasis and in protecting the brain from exposure to exogenous molecules (Figure 1). The BBB, which separates the circulating blood from the CNS, is primarily composed of endothelial cells linked by tight junctions (Serwer and James 2012). By closing the gap between contacting adjacent endothelial cells, tight junctions generate a barrier to the extracellular fluid, which helps regulate the passage of molecules across the BBB (Bazzoni and Dejana 2004, Fakhoury et  al. 2015). The structural bases of the BBB also comprise pericytes and astrocyte foot processes, which provide enhanced protection of the CNS by wrapping around endothelial cells (Figure 1). The absence of paracellular or transcellular channels within the BBB means that molecules in the circulation gain access to the brain interstitial fluid either though simple/facilitated diffusion or carrier/receptor-mediated transport (Fakhoury et  al. 2015, Pardridge 2012). However, these modes of transport mostly favor the passage of small lipid-soluble molecules, water, amino acids, and peptides (Fakhoury et  al. 2015). As a result, approximately 98% of small-molecule drugs and almost all large-molecule drugs do not get transported across the BBB (Pardridge 2005, Zhou et al. 2013). The structure and physiological function of the BBB have been extensively studied in patients with brain tumors (Serwer and James 2012). It has been shown that individuals with disseminated brain tumors such as GBM often have a disrupted and highly permeable BBB (Agarwal et  al. 2011, Benny and Pakneshan 2009). Despite the fact that the BBB may be disrupted at some levels, it remains intact near the growing part of the tumor, where most of the tumor cells reside (Agarwal et  al. 2013). Pro-angiogenic factors are often overexpressed in brain tumors, leading to increased

cerebral microvascular perfusion and leakage through the BBB (Argaw et  al. 2006, Benny and Pakneshan 2009). With respect to drug permeation, increased cerebral flow leads to increased interstitial fluid pressure, which limits the passage of small-molecule drugs through the BBB and towards the site of the tumor (Benny and Pakneshan 2009). Clearly, this field of research would benefit from the use of alternative routes of delivery to the brain that could help increase the bioavailability and therapeutic efficacy of drugs. Overcoming the BBB will provide a means for selectively targeting tumors for drug delivery, and may offer new hopes for patients with GBM.

Strategies for bypassing the BBB BBB disruption Many innovative approaches have been developed in order to improve the beneficial effects of drugs and their targeted delivery to the brain. One such strategy is to biochemically disrupt the membrane of the BBB (Blanchette and Fortin 2011, Misra et  al. 2003). Weakening the BBB typically improves the extravasation rates of drugs in the cerebral endothelium and significantly increases the parenchymal drug concentration (Misra et  al. 2003). This could be done through the use of a variety of techniques, including the infusion of solvents and vasoactive substances (Misra et al. 2003). However, although physiologically interesting, most of these methods are not practically used because of their associated toxic effects on brain microvascular endothelial cells and tight junctions (Misra et al. 2003). Another way of disrupting the BBB is through the use of high-intensity focused ultrasound (Chen et al. 2010, Liu et al. 2010). In one study, burst-tone ultrasound energy was delivered in the brain of rats with induced-GBM tumors (Liu et  al. 2010). The rats were then treated with a chemotherapeutic drug, and tumor growth was monitored using MRI (Liu et  al. 2010). It was shown that treated animals subjected to focused ultrasound energy had reduced tumor progression and higher survival rate, suggesting that disruption of the BBB could have beneficial effects for the treatment of brain tumors like GBM (Liu et al. 2010). However, continued research is needed for the development of more precise and effective ways of optimizing drug delivery to the brain, and more in vivo studies are needed prior to conducting clinical trials.

Intraventricular delivery

Figure 1. Schematic representation of the BBB. The morphology of the BBB consists of a layer of endothelial cells that form tight junctions, to restrict the passage of most therapeutic molecules to the brain. The functional integrity of the BBB also depends on the basal lamina, pericytes, and astrocyte foot processes. (Taken with permission from Anderson et al. 2011).

Another strategy for bypassing the BBB is to deliver the drug directly within the ventricular system of the brain (Fleischhack et  al. 2001). In this approach, drugs are injected into the cerebrospinal fluid (CSF) through the use of reservoirs implanted subcutaneously and connected to the ventricles via a catheter (Misra et al. 2003). One advantage of using intraventricular delivery is that the bioavailability of the drug is significantly increased within the CSF (Misra et al. 2003). Also, because the CSF provides an environment where there is minimal protein binding and relatively low enzymatic activity, the half-life of the drug is much longer when injected intraventricularly. However, intraventricular delivery of drugs is not

4  M. Fakhoury

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without its challenges. One limitation of this approach is that it is often associated with clinical hemorrhage, neurotoxicity, and infection, and as such, has not proven to be very effective in treating GBM (Misra et  al. 2003). Moreover, the delivery of drugs to the tumor is limited by its poor distribution into the brain parenchyma, and as a result, higher concentration of drug might be needed to achieve a therapeutic efficacy (Pardridge 2012, Buchwald and Bodor 2001). Clearly, further studies need to be done to investigate the safety and feasibility of intraventricular delivery in animal models of GBM.

Intrathecal delivery Intrathecal delivery is a promising approach for targeting specific areas of the brain and for achieving improved outcomes in patients with malignant tumors (Serwer and James 2012). By bypassing the BBB, it allows for the use of many agents that do not enter the brain from systemic circulation, such as drugs, cells, and DNA molecules (Serwer and James 2012). One study has shown that rats with disseminated brain tumors treated by intrathecal injection of an oncolytic recombinant poliovirus had a significantly higher rate of survival compared to non-treated animals, suggesting that intrathecal delivery could be used as an efficient approach for the treatment of patients with GBM (Ochiai et al. 2006). The beneficial effects of intrathecal delivery using antineoplastic drugs was also validated in clinical trials for other types of brain cancers, and this method has proven successful in reducing tumor growth without causing any apparent neurotoxicity (Gururangan et  al. 2006). Another advantage of this approach is that it could be used to help reduce pain in patients with brain tumors (Hayek et al. 2011). Moreover, since delivering therapeutic agents by intrathecal administration often results in higher CSF concentration, reduced amount of medication could be used to achieve equipotent doses (Hayek et al. 2011). The only known limitation is that the intrathecal route of administration cannot be used for all therapeutic drugs, as some have been shown to cause inflammation of the brain meninges (Clayton et  al. 2008, Serwer and James 2012). Therefore, cautious care must be taken while evaluating the feasibility of a drug prior to conducting clinical trials.

Convection-Enhanced Diffusion In attempts to overcome the problem of slow drug diffusion from the ependymal surface of the brain, CED is being extensively used in animal studies and clinical trials (Bruce et al. 2011, Pardridge 2012). CED is used for the treatment of neurological disorders such as GBM, as it enables the distribution of drugs throughout the interstitium via positivepressure infusion (Lopez et al. 2006). Since most malignant brain tumors are locally invasive, their progression could be more easily influenced by local drug delivery approaches such as CED (Bruce et al. 2011). In this approach, the drug is placed in a peripheral reservoir connected to a pump, and is delivered continuously to brain tissues via a catheter (Pardridge 2012, Perlstein et  al. 2008). In order to minimize the influence of therapeutic molecular weight on distribution, CED uses positive pressure to increase the drug

circulation throughout the tumor (Serwer and James 2012). Moreover, prolonged drug infusion could be achieved through the direct implantation of an osmotic pump (Serwer and James 2012). The advantage of using CED compared to other delivery approaches is that it enables high local drug concentrations in tumor tissue, while avoiding systemic toxicity (Bruce et al. 2011). This approach was already tested in a clinical trial, and it was shown that administration of a chemotherapeutic agent by CED in patients with GBM is associated with antitumor activity and prolonged survival (Bruce et al. 2011). Although CED provides a method of local delivery of antitumor agents directly to the site of the tumor, administration of therapeutics via this approach is not without its risks (Yun et al. 2013). The main limitations of using CED is that this technique remains technically challenging and is often associated with leakage of refluxed drug along the catheter, as well as a local infection (Yun et al. 2013). As a result, this delivery approach is still subject of ongoing preclinical investigations (Serwer and James 2012).

Intranasal delivery Intranasal delivery is a practical and non-invasive technique used for the delivery of therapeutic agents to the brain (Hashizume and Gupta 2010, Kaur et al. 2015). It has been proven useful in the treatment of brain tumors and other neurological conditions, and could provide an alternative to intravenous injection and CED (Hashizume et  al. 2008, Hashizume and Gupta 2010). The olfactory nerves innervating the epithelium represent a viable route between the external environment and the brain (Serwer and James 2012, Vyas et al. 2005). As a result, intranasal drug administration leads to direct release into the CSF, which makes it an ideal approach for fast delivery of therapeutic compounds to the brain. Given the simplicity of intranasal delivery, this route of administration has received a lot of attention for its application in the treatment of GBM and other neurological disorders (Hashizume et al. 2008, Sood et al. 2014). It was shown in one study that administration of a therapeutic compound via intranasal delivery in rats with GBM could result in its accumulation in brain tissues as quickly as 4 h after delivery (Hashizume et al. 2008). Another study has shown that intranasal delivery of methotrexate, an anticancer drug, leads to a marked reduction in brain tumor size in vivo, with minimal side-effects (Shingaki et  al. 2010). While encouraging, still more work is needed to fully evaluate the feasibility of this approach in clinical trials and compare its efficiency with other methods of delivery.

Nanotechnology-based systems for targeted delivery to the brain Most of the drugs fail in achieving a therapeutic effect because they are unable to access the brain and kill the cells responsible of the tumor development (Zhou et  al. 2013). In attempts to overcome this issue, nanotechnologybased devices are being extensively employed for brain tumor therapy (Benny and Pakneshan 2009, Ferrari 2005, Hosseini et  al. 2015). These nanovectors have proven successful for targeted drug delivery, and they primarily include nanoparticles, carbon nanotubes (CNTs), microcapsules,

Drug delivery approaches for the treatment of glioblastoma multiforme  5 Table I. Main characteristics of GBM. Characteristics of GBM Survival rate Age of recognition Sex ratio Incidence

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Pathological features Symptoms and signs

Brain areas affected Diagnosis tools Environmental factors Associated genetic syndromes

The mean survival rate is 10–12 months with therapy. 90% of the patients die within 18 months from diagnosis. Without therapy, survival is less than 6 months The mean age of primary GBM patients is about 62, whereas the mean age of secondary GBM is about 45 GBM develops more frequently in males than in females with a M:F ratio of 3:1 GBM accounts for 51.2% of all primary CNS gliomas. It affects approximately 3 per 100 000 individuals annually Most GBM are characterized by the presence of necrotic areas, vascular proliferation, unorganized blood vessels, and variable mitotic activity Symptoms such as drowsiness (87%), dysphagia (71%), gradual neurological deficits (51%), seizures (45%), gradual cognitive deficits (33%), and headaches (33%) are very frequently observed in patients with GBM GBM mostly affects the temporal lobe (31%), the parietal lobe (24%) and the frontal lobe (23%) of the cerebral cortex. It is less common (1–5%) in the cerebellum, the brainstem, and the spinal cord. Imaging techniques commonly employed for the diagnosis of GBM are MRS, MRI, MRI diffusion, PET and CT Factors known to increase the risk to GBM include ionizing radiation, chemical carcinogens, high cholesterol level, hypertension, and smoking GBM is associated with syndromes such as neurofibromatosis 1 and 2, tuberous sclerosis, retinoblastoma, Li–Fraumeni syndrome, and Turcot’s syndrome

liposomes, micelles, and dendrimers (Benny and Pakneshan 2009, Daraee et al. 2014). The main characteristics of nanotechnology-based devices and their application in the treatment of brain tumors like GBM are described in the following paragraphs and summarized in Table II.

Nanoparticles and Liposomes A wide variety of anticancer drugs has already been conjugated to nanomaterials for local administration and has

References Sathornsumetee and Rich (2006) Adamson et al. (2009), Kushnir and Tzuk-Shina (2011) Adamson et al. (2009) Adamson et al. (2009), Molenaar (2011) Ramirez et al. (2013), Sathornsumetee and Rich (2006) Adamson et al. (2009), Sizoo et al. (2010) Singh et al. (2009), Shahideh et al. (2012), Stark et al. (2010) Adamson et al. (2009), Park et al. (2011), Sathornsumetee et al. (2007) Adamson et al. (2009), Kushnir and Tzuk-Shina (2011) Reilly (2009), Schwartzbaum et al. (2006)

shown great promise in the treatment of malignant brain tumors such as GBM (Koziara et al. 2004, Inoue et al. 2009, Tripathi et  al. 2014). Using PET imaging of nanoparticles, it was shown that nanoparticles could penetrate the brain of rodents by CED and be successfully distributed to large intracranial volumes (Zhou et  al. 2013). Moreover, it was shown that CED administration of anticancer agents loaded into nanoparticles significantly increases the survival rate of animals with GBM, suggesting the potential use of this

Table II. Examples of nanotechnology-based delivery systems for the treatment of GBM. Delivery systems Characteristics Advantage for the treatment of GBM Nanoparticles ∼20–200 nm in diameter

They are made up of biodegradable polymers that can be conjugated to drugs and antibodies.

Liposomes ∼100–400 nm in diameter

They are small artificial vesicles made up of lipid bilayers. Their surface can be easily modified to increase the circulation half-life.

CNTs ∼1–4 nm in diameter

They are single or multi-layered sheets of self-assembling carbon atoms having the form of cylindrical large molecules. They are small structures of spherical shape with a semipermeable membrane made of polymers having the ability to resist chemical and enzymatic degradation. They are self-assembled particles made of surfactant molecules with a hydrophobic head and a hydrophilic tail. They are monodisperse macromolecules with a tree-like architecture. They are made of several branched molecule which adopt a symmetrical threedimensional morphology.

Microcapsules ∼10–1000 nm in diameter

Polymeric micelles ∼10–100 nm in diameter Dendrimers ∼3–20 nm in diameter

References

They have the ability to deliver therapeutic agents into cancer cells. They also provide enhanced drug efficacy and neuroprotection. They can be conjugated with some proteins or drugs to recognize cancer cells. They also have the potential to deliver higher therapeutic doses with minimally toxicity. Due to their relatively high inner volume and external surface, they could load a large amount of drug and induce apoptosis of cancer cells. They have the ability to encapsulate large amount of drugs and their surface could be modified to control the kinetics of drug release.

Hernández-Pedro et al. (2013), Upadhyay (2014), Xu et al. (2013)

Ligands could be easily incorporated into their structure offering the ability to target specific compartments in the brain. They can be conjugated to ligands that could serve as detecting agents. They also display low toxicity and increased diffusion in brain tissue.

Morshed et al. (2013), Xu et al. (2013)

Huwyler et al. (2008), Laquintana et al. (2009)

Hernández-Pedro et al. (2013), Rastogi et al. (2014), Zhang et al. (2011) Bhujbal et al. (2014), Fakhoury et al. (2014), Scott et al. (2011)

Albertazzi et al. (2013), Hernández-Pedro et al. (2013)

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6  M. Fakhoury approach in controlled delivery to the brain and its impact on the treatment of GBM (Zhou et al. 2013). However, one challenge faced in using nanoparticles for targeted drug delivery is that these polymeric devices degrade quickly and are rapidly cleared from the blood if administered by intravenous injection (Laquintana et al. 2009). Liposomes, which are small artificial vesicles made up of lipid bilayers, also have a short half-life in the blood (Laquintana et  al. 2009). However, increased circulation time can be accomplished by designing particles of smaller size or by coating the external membrane with specific ligands or proteins (Laquintana et  al. 2009). Surface-modified liposomes and nanoparticles have shown great promise in the treatment of brain tumor due to their ability to effectively cross the BBB and deliver therapeutic agents to the brain (Huwyler et al. 2008, Jin et al. 2005).

property makes them potentially toxic to the brain and to other organs in the body since they are capable of crossing membrane barriers (Kolosnjaj et  al. 2007). Nonetheless, CNTs are widely used in biomedical research for anticancer drug delivery due to their unique chemical and physical properties (Madani et al. 2011, Ren et al. 2012, Tavakolifard et  al. 2015). The advantage of using CNTs, as well as other nanomaterials, is that they can be conjugated to ligands that allow targeted delivery of chemotherapeutic drugs to brain glioma (Ren et al. 2012, Xin et al. 2011). Once CNTs are delivered to the tumor, they can penetrate cancer cells through direct diffusion or endocytosis without causing any damage to non-cancerous cells (Figure 2). In this context, CNTs constitute an ideal carrier for the delivery of therapeutic molecules to the brain and will continue to have a significant impact in the treatment of patients with GBM.

CNTs

Microcapsules

CNTs are another class of nanotechnology-based devices that have been extensively used for the treatment of brain tumors. CNTs have the form of cylindrical large molecules consisting of a hexagonal arrangement of carbon atoms (Zhang et al. 2011). CNTs are made up of either a single or a multi-graphene layer wrapped into a hexagonal closepacked cylindrical structure, and as such, they can be classified either as single-walled CNT (SWCNTs) or multi-walled CNTs (MWCNTs) (Rastogi et al. 2014, Zhang et al. 2011). As opposed to other nanomaterials, CNTs persist in the brain for several months, thus enabling the continuous release of drugs (Jain et al. 2011, Rastogi et al. 2014). However, this

Another promising technology for the targeted delivery of drugs and therapeutic molecules is the use of cell encapsulation (Orive et  al. 2009, Scott et  al. 2011). Cell encapsulation involves the formation of small microcapsules of spherical shape that could be loaded with drugs, proteins, or even living cells (Bhujbal et al. 2014, Murua et al. 2008, Negrulj et al. 2015). Microcapsules typically have a semipermeable membrane made of polymers that enable the protection of the encapsulated material from the harsh extracellular environment, while at the same time allowing the release of therapeutic molecules to the outside of the cell (Bhujbal et al. 2014, Fakhoury et al. 2014). The

Figure 2. Pathways for the penetration of CNTs into the cancer cell. (a) Non-receptor-mediated endocytosis: (1) The drug-loaded functionalized CNT is trapped into an endosome, (2) the CNT gets released from the endosome and the drug is delivered to the inside of the cell, and (3) the CNT is released from the cell by exocytosis; (b) Receptor-mediated endocytosis: (4) a membrane surrounds the CNT–receptor conjugate by forming endosomes, (5) the drug is released from the CNT, (6, 7, 8) the receptor is recycled back to the surface of the cell membrane; (c) Endocytosisindependent pathway: (9) drug-loaded functionalized CNTs directly penetrate into the cell, (10) the drug is released from the CNT, (11) the CNT is released from the cell (Taken with permission from Rastogi et al. 2014).

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Drug delivery approaches for the treatment of glioblastoma multiforme  7 coating of the microcapsule can be made of a wide variety of polymers, the most commonly used being sodium alginate and poly-L-lysine (Fakhoury et al. 2014, Farhana et  al. 2010). A study has demonstrated that microcapsules made of alginate and poly-L-lysine could successfully encapsulate and deliver endostatin, an angiogenic inhibitor, to brain tumor cells (Joki et al. 2001). In another study, it was shown that localized intracranial delivery of temozolomide, a chemotherapeutic drug, delivered using microcapsule devices, was able to significantly prolong the survival of animals with brain glioma (Scott et  al. 2011). Considered together, these studies suggest that the use of cell encapsulation offers the possibility of releasing therapeutic agents to targeted areas of the brain, which could provide new directions for the treatment of neurological diseases such as GBM.

Polymeric micelles and dendrimers Polymeric micelles are another group of nanotechnologybased devices that are making their way into the clinical arena (Gong et  al. 2012, Morshed et  al. 2013). They have recently emerged as a promising tool for the delivery of therapeutic compounds to the brain because of their ability to cross the BBB and persist for a longer time in brain tissues (Chen and Liu 2012). Moreover, their nano-size and coreshell structure make them useful for various therapeutic applications (Kim et al. 2013). Another advantage of using polymeric micelles is that they are very flexible in terms of design modification, allowing for the incorporation of a wide variety of ligands into their structure (Morshed et al. 2013). When injected intravenously in a mouse model of GBM, polymeric micelles conjugated with specific ligand molecules have been shown to efficiently deliver anticancer drugs, and have displayed superior ability to cross the BBB compared to non-conjugated polymeric micelles (Miura et al. 2013). Dendrimers provide another avenue for delivering drugs to specific cellular compartments. Their unique tree-like architecture confers them with desirable characteristics, such as reduced toxicity, low immune response, and the ability to diffuse in tissue for a long period of time (Albertazzi et al. 2013, Hernández-Pedro et al. 2013, Emerich and Thanos 2007). Approaches for delivering anticancer drugs to the brain using dendrimers are of widespread interest, and have mostly focused on the use of polyamidoamine (PAMAM) dendrimers (Fakhoury et  al. 2015). The advantage of using PMAM dendrimers is that they present lower cytotoxicity and have a higher density of functional groups compared to other types of dendrimers (Bai et al. 2013, Wu et al. 2006). They have been extensively used for the delivery of anticancer drugs and therapeutic genes for the treatment of GBM and other malignant brain tumors (Bai et al. 2013, Ren et  al. 2010). However, one challenge faced with the use of dendrimers is that it is relatively difficult to control the amount of drugs they release (Singh and Lillard 2009, Xu et  al. 2014). Clearly, more work needs to be done for the development of optimized delivery systems that could achieve favorable drug pharmacokinetics and high therapeutic efficacy.

Conclusion Despite enormous advances in drug therapy, GBM remains one of the most severe forms of malignant brain tumors in humans. It is characterized by a heterogeneous population of cells that are highly proliferative and genetically unstable. Even after surgical resection and chemotherapy, the probability of recurrence is very high among GBM patients. During the past few years, several approaches have been developed in attempts to overcome the BBB and improve the efficiency of pharmacological treatments. Among these approaches, the use of nanotechnology-based systems has revolutionized the field of drug delivery, offering the possibility to deliver therapeutic agents to local areas in the brain. Nonetheless, continued research is needed before nanomaterials could be fully used in clinical trials involving GBM. More particularly, the biological safety of nanomaterials needs to be better addressed by conducting toxicological studies in clinical settings. There is also an urgent need for the development of more efficient ways of controlling the release of drug from nanomaterials and their delivery to desired areas of the brain. Hopefully, insights arising from future experimental studies will lead to the development of better therapeutic interventions that could improve the quality of life of patients with GBM.­­­

Acknowledgments The author is the recipient of an award from the Natural Sciences and Engineering Research Council (NSERC) of Canada.

Declaration of interest The author report no declarations of interest. The author alone is responsible for the content and writing of the paper.

References Adamson C, Kanu OO, Mehta AI, Di C, Lin N, Mattox AK, Bigner DD. 2009. Glioblastoma multiforme: a review of where we have been and where we are going. Expert Opin Investig Drugs. 18:1061–1083. Albertazzi L, Gherardini L, Brondi M, Sulis Sato S, Bifone A, Pizzorusso T, et al. 2013. In vivo distribution and toxicity of PAMAM dendrimers in the central nervous system depend on their surface chemistry. Mol Pharm. 10:249–260. Anderson VC, Lenar DP, Quinn JF, Rooney WD. 2011. The blood-brain barrier and microvascular water exchange in Alzheimer’s disease. Cardiovasc Psychiatry Neurol. 2011:615829. Agarwal S, Manchanda P, Vogelbaum MA, Ohlfest JR, Elmquist WF. 2013. Function of the blood-brain barrier and restriction of drug delivery to invasive glioma cells: findings in an orthotopic rat xenograft model of glioma. Drug Metab Dispos. 41:33–39. Agarwal S, Sane R, Oberoi R, Ohlfest JR, Elmquist WF. 2011. Delivery of molecularly targeted therapy to malignant glioma, a disease of the whole brain. Expert Rev Mol Med. 13:e17. Argaw AT, Zhang Y, Snyder BJ, Zhao ML, Kopp N, Lee SC, et al. 2006. IL-1beta regulates blood-brain barrier permeability via reactivation of the hypoxia-angiogenesis program. J Immunol. 177:5574–5584. Bai CZ, Choi S, Nam K, An S, Park JS. 2013. Arginine modified PAMAM dendrimer for interferon beta gene delivery to malignant glioma. Int J Pharm. 445:79–87. Bazzoni G, Dejana E. 2004. Endothelial cell-to- cell junctions: Molecular organization and role in vascular homeostasis. Physiol Rev. 84:869–901.

Artificial Cells, Nanomedicine, and Biotechnology Downloaded from informahealthcare.com by Nyu Medical Center on 06/17/15 For personal use only.

8  M. Fakhoury Benny O, Pakneshan P. 2009. Novel technologies for antiangiogenic drug delivery in the brain. Cell Adh Migr. 3:224–229. Bernacki J, Dobrowolska A, Nierwinska K, Malecki A. 2008. Physiology and pharmacological role of the blood-brain barrier. Pharmacol Rep. 60:600–622. Bhujbal SV, de Vos P, Niclou SP. 2014. Drug and cell encapsulation: alternative delivery options for the treatment of malignant brain tumors. Adv Drug Deliv Rev. 67–68:142–153. Blanchette M, Fortin D. 2011. Blood-brain barrier disruption in the treatment of brain tumors. Methods Mol Biol. 686:447–463. Bruce JN, Fine RL, Canoll P, Yun J, Kennedy BC, Rosenfeld SS, et  al. 2011. Regression of recurrent malignant gliomas with convectionenhanced delivery of topotecan. Neurosurgery. 69:1272–1279 Buchwald P, Bodor N. 2001. A simple, predictive, structure-based skin permeability model. J Pharm Pharmacol. 53:1087–1098. Chen PY, Liu HL, Hua MY, Yang HW, Huang CY, Chu PC, et al. 2010. Novel magnetic/ultrasound focusing system enhances nanoparticle drug delivery for glioma treatment. Neuro Oncol. 12:1050–1060. Chen Y, Liu L. 2012. Modern methods for delivery of drugs across the blood-brain barrier. Adv Drug Deliv Rev. 64:640–665. Clayton J, Vloeberghs M, Jaspan T, Walker D, MacArthur D, Grundy R. 2008. Intrathecal chemotherapy delivered by a lumbar-thecal catheter in metastatic medulloblastoma: a case illustration. Acta Neurochir (Wien). 150:709–712. Daraee H, Eatemadi A, Abbasi E, Fekri Aval S, Kouhi M, Akbarzadeh A. 2014. Application of gold nanoparticles in biomedical and drug delivery. Artif Cells Nanomed Biotechnol. 1–13. de Robles P, Fiest KM, Frolkis AD, Pringsheim T, Atta C, St GermaineSmith C, et al. 2014. The worldwide incidence and prevalence of primary brain tumors: a systematic review and meta-analysis. Neuro Oncol. pii: nou283. Emerich DF, Thanos CG. 2007. Targeted nanoparticle-based drug delivery and diagnosis. J Drug Target. 15:163–183. Liu HL, Hua MY, Chen PY, Chu PC, Pan CH, Yang HW, et  al. 2010. Blood-brain barrier disruption with focused ultrasound enhances delivery of chemotherapeutic drugs for glioblastoma treatment. Radiology. 255:415–425. Fakhoury M, Coussa-Charley M, Al-Salami H, Kahouli I, Prakash S. 2014. Use of artificial cell microcapsule containing thalidomide for treating TNBS-induced Crohn’s disease in mice. Curr Drug Deliv. 11:146–153. Fakhoury M, Takechi R, Al-Salami H. 2015. Drug permeation across the blood-brain barrier: applications of nanotechnology. Br J Med Med Res. 6:547–556. Farhana SA, Shantakumar SM, Shyale S, Shalam M, Narasu L. 2010. Sustained release of verapamil hydrochloride from sodium alginate microcapsules. Curr Drug Deliv. 7:98–108. Ferrari M. 2005. Cancer nanotechnology: opportunities and challenges. Nat Rev Cancer. 5:161–171. Fleischhack G, Reif S, Hasan C, Jaehde U, Hettmer S, Bode U. 2001. Feasibility of intraventricular administration of etoposide in patients with metastatic brain tumours. Br J Cancer. 84:1453–1459. Folkman J. 2002. Role of angiogenesis in tumor growth and metastasis. Semin Oncol. 29:15–18. Gong J, Chen M, Zheng Y, Wang S, Wang Y. 2012. Polymeric micelles drug delivery system in oncology. J Control Release. 159:312–323. Gururangan S, Petros WP, Poussaint TY, Hancock ML, Phillips PC, Friedman HS, et  al. 2006. Phase I trial of intrathecal spartaject busulfan in children with neoplastic meningitis: a Pediatric Brain Tumor Consortium Study (PBTC-004). Clin Cancer Res. 12: 1540–1546. Hashizume R, Gupta N. 2010. Telomerase inhibitors for the treatment of brain tumors and the potential of intranasal delivery. Curr Opin Mol Ther. 12:168–175. Hashizume R, Ozawa T, Gryaznov SM, Bollen AW, Lamborn KR, Frey WH 2nd, Deen DF. 2008. New therapeutic approach for brain tumors: Intranasal delivery of telomerase inhibitor GRN163. Neuro Oncol. 10:112–20. Hayek SM, Deer TR, Pope JE, Panchal SJ, Patel VB. 2011. Intrathecal therapy for cancer and non-cancer pain. Pain Physician. 14:219–248. Hernández-Pedro NY, Rangel-López E, Magaña-Maldonado R, de la Cruz VP, del Angel AS, Pineda B, Sotelo J. 2013. Application of nanoparticles on diagnosis and therapy in gliomas. Biomed Res Int. 2013:351031. Hosseini M, Haji-Fatahaliha M, Jadidi-Niaragh F, Majidi J, Yousefi M. 2015. The use of nanoparticles as a promising therapeutic approach in cancer immunotherapy. Artif Cells Nanomed Biotechnol. 1–11.

Huwyler J, Drewe J, Krähenbuhl S. 2008. Tumor targeting using liposomal antineoplastic drugs. Int J Nanomedicine. 3:21–29. Inoue T, Yamashita Y, Nishihara M, Sugiyama S, Sonoda Y, Kumabe T, et al. 2009. Therapeutic efficacy of a polymeric micellar doxorubicin infused by convection-enhanced delivery against intracranial 9L brain tumor models. Neuro Oncol. 11:151–157. Jain AK, Das M, Swarnakar NK, Jain S. 2011. Engineered PLGA nanoparticles: an emerging delivery tool in cancer therapeutics. Crit Rev Ther Drug Carrier Syst. 28:1–45. Jin Y, Li J, Rong LF, Lü XW, Huang Y, Xu SY. 2005. Pharmacokinetics and tissue distribution of 5-fluorouracil encapsulated by galactosylceramide liposomes in mice. Acta Pharmacol Sin. 26:250–256. Joki T, Machluf M, Atala A, Zhu J, Seyfried NT, Dunn IF, et  al. 2001. Continuous release of endostatin from microencapsulated engineered cells for tumor therapy. Nat Biotechnol. 19:35–39. Kaur P, Garg T, Rath G, Goyal AK. 2015. In situ nasal gel drug delivery: A novel approach for brain targeting through the mucosal membrane. Artif Cells Nanomed Biotechnol. 1–10. Kesari S. 2011. Understanding glioblastoma tumor biology: the potential to improve current diagnosis and treatments. Semin Oncol. 38:2–10. Kim MS, Kim JS, Cho WK, Hwang SJ. 2013. Enhanced solubility and oral absorption of sirolimus using D-a-tocopheryl polyethylene glycol succinate micelles. Artif Cells Nanomed Biotechnol. 41:85–91. Kolosnjaj J, Szwarc H, Moussa F. 2007. Toxicity studies of carbon nanotubes. Adv Exp Med Biol. 620:181–204. Koziara JM, Lockman PR, Allen DD, Mumper RJ. 2004. Paclitaxel nanoparticles for the potential treatment of brain tumors. J Control Release. 99:259–269. Kushnir I, Tzuk-Shina T. 2011. Efficacy of treatment for glioblastoma multiforme in eldery patients (65+): a retrospective analysis. Isr Med Assoc.13:290–294. Laquintana V, Trapani A, Denora N, Wang F, Gallo JM, Trapani G. 2009. New strategies to deliver anticancer drugs to brain tumors. Expert Opin Drug Deliv. 6:1017–1032. Lopez KA, Waziri AE, Canoll PD, Bruce JN. 2006. Convection-enhanced delivery in the treatment of malignant glioma. Neurol Res. 28:542–548. Madani SY, Naderi N, Dissanayake O, Tan A, Seifalian AM. 2011. A new era of cancer treatment: carbon nanotubes as drug delivery tools. Int J Nanomedicine. 6:2963–2979. Martinez-Quintanilla J, Bhere D, Heidari P, He D, Mahmood U, Shah K. 2013. Therapeutic efficacy and fate of bimodal engineered stem cells in malignant brain tumors. Stem Cells. 31:1706–1714. Mishra SS, Behera SK, Dhir MK, Senapati SB. 2014. Cerebellar giant cell glioblastoma multiforme in an adult. J Neurosci Rural Pract. 5:295–297 Misra A, Ganesh S, Shahiwala A, Shah SP. 2003. Drug delivery to the central nervous system: a review. J Pharm Pharm Sci. 6: 252–273. Miura Y, Takenaka T, Toh K, Wu S, Nishihara H, Kano MR, et al. 2013. Cyclic RGD-linked polymeric micelles for targeted delivery of platinum anticancer drugs to glioblastoma through the blood-brain tumor barrier. ACS Nano. 7:8583–8592. Molenaar RJ. 2011. Ion channels in glioblastoma. ISRN Neurol. 2011:590249. Morshed RA, Cheng Y, Auffinger B, Wegscheid ML, Lesniak MS. 2013. The potential of polymeric micelles in the context of glioblastoma therapy. Front Pharmacol. 4:157. Murua A, Portero A, Orive G, Hernández RM, de Castro M, Pedraz JL. 2008. Cell microencapsulation technology: towards clinical application. J Control Release. 132:76–83. Negrulj R, Mooranian A, Chen-Tan N, Al-Sallami HS, Mikov M, Golocorbin-Kon S, et  al. 2015. Swelling, mechanical strength, and release properties of probucol microcapsules with and without a bile acid, and their potential oral delivery in diabetes. Artif Cells Nanomed Biotechnol. 1–8. Nelson SJ, Cha S. 2003. Imaging glioblastoma multiforme. Cancer J. 9:134–145. Ochiai H, Campbell SA, Archer GE, Chewning TA, Dragunsky E, Ivanov A, et al. 2006. Targeted therapy for glioblastoma multiforme neoplastic meningitis with intrathecal delivery of an oncolytic recombinant poliovirus. Clin Cancer Res. 12:1349–1354. Ohgaki H, Kleihues P. 2013. The definition of primary and secondary glioblastoma. Clin Cancer Res. 19:764–772. Onishi M, Kurozumi K, Ichikawa T, Date I. 2013. Mechanisms of tumor development and anti-angiogenic therapy in glioblastoma multiforme. Neurol Med Chir (Tokyo). 53:755–763.

Artificial Cells, Nanomedicine, and Biotechnology Downloaded from informahealthcare.com by Nyu Medical Center on 06/17/15 For personal use only.

Drug delivery approaches for the treatment of glioblastoma multiforme  9 Orive G, Anitua E, Pedraz JL, Emerich DF. 2009. Biomaterials for promoting brain protection, repair and regeneration. Nat Rev Neurosci. 10:682–692. Pardridge WM. 2005. The blood-brain barrier and neurotherapeutics. NeuroRx. 2:1–2. Pardridge WM. 2012. Drug transport across the blood-brain barrier. J Cereb Blood Flow Metab. 32:1959–1972 Park SS, Chunta JL, Robertson JM, Martinez AA, Oliver Wong CY, Amin M, et al. 2011. MicroPET/CT imaging of an orthotopic model of human glioblastoma multiforme and evaluation of pulsed lowdose irradiation. Int J Radiat Oncol Biol Phys. 80:885–892. Patel MM, Goyal BR, Bhadada SV, Bhatt JS, Amin AF. 2009. Getting into the brain: approaches to enhance brain drug delivery. CNS Drugs. 23:35–58. Perlstein B, Ram Z, Daniels D, Ocherashvilli A, Roth Y, Margel S, Mardor Y. 2008. Convection-enhanced delivery of maghemite nanoparticles: Increased efficacy and MRI monitoring. Neuro Oncol. 10:153–161. Ramirez YP, Weatherbee JL, Wheelhouse RT, Ross AH. 2013. Glioblastoma multiforme therapy and mechanisms of resistance. Pharmaceuticals (Basel). 6:1475–506. Rastogi V, Yadav P, Bhattacharya SS, Mishra AK, Verma N, Verma A, Pandit JK. 2014. Carbon nanotubes: an emerging drug carrier for targeting cancer cells. J Drug Deliv. 2014:670815. Reilly KM. 2009. Brain tumor susceptibility: the role of genetic factors and uses of mouse models to unravel risk. Brain Pathol. 19:121– 131. Ren J, Shen S, Wang D, Xi Z, Guo L, Pang Z, et al. 2012. The targeted delivery of anticancer drugs to brain glioma by PEGylated oxidized multi-walled carbon nanotubes modified with angiopep-2. Biomaterials. 33:3324–3333. Ren Y, Zhou X, Mei M, Yuan XB, Han L, Wang GX, et  al. 2010. MicroRNA-21 inhibitor sensitizes human glioblastoma cells U251 (PTEN-mutant) and LN229 (PTEN-wild type) to taxol. BMC Cancer. 10:27. Sathornsumetee S, Rich JN. 2006. New approaches to primary brain tumor treatment. Anticancer Drugs. 17:1003–1006. Sathornsumetee S, Rich JN, Reardon DA. 2007. Diagnosis and treatment of high-grade astrocytoma. Neurol Clin. 25:1111–1139 Schwartzbaum JA, Fisher JL, Aldape KD, Wrensch M. 2006. Epidemiology and molecular pathology of glioma. Nat Clin Pract Neurol. 2:494–503. Scott AW, Tyler BM, Masi BC, Upadhyay UM, Patta YR, Grossman R, et  al. 2011. Intracranial microcapsule drug delivery device for the treatment of an experimental gliosarcoma model. Biomaterials. 32:2532–2539. Serwer LP, James CD. 2012. Challenges in drug delivery to tumors of the central nervous system: an overview of pharmacological and surgical considerations. Adv Drug Deliv Rev. 64:590–597. Shingaki T, Inoue D, Furubayashi T, Sakane T, Katsumi H, Yamamoto A, Yamashita S. 2010. Transnasal delivery of methotrexate to brain tumors in rats: a new strategy for brain tumor chemotherapy. Mol Pharm. 7:1561–1568.

Shahideh M, Fallah A, Munoz DG, Loch Macdonald R. 2012. Systematic review of primary intracranial glioblastoma multiforme with symptomatic spinal metastases, with two illustrative patients. J Clin Neurosci. 219:1080–1086. Singh PK, Singh VK, Tomar J, Azam A, Gupta S, Kumar S. 2009. Spinal glioblastoma multiforme: unusual cause of post-traumatic tetraparesis. J Spinal Cord Med. 32:583–586. Singh R, Lillard JW Jr. 2009. Nanoparticle-based targeted drug delivery. Exp Mol Pathol. 86:215–223. Sizoo EM, Braam L, Postma TJ, Pasman HR, Heimans JJ, Klein M, et al. 2010. Symptoms and problems in the end-of-life phase of highgrade glioma patients. Neuro Oncol. 12:1162–1166. Sood S, Jain K, Gowthamarajan K. 2014. Intranasal therapeutic strategies for management of Alzheimer’s disease. J Drug Target. 22: 279–294. Stark AM, Maslehaty H, Hugo HH, Mahvash M, Mehdorn HM. 2010. Glioblastoma of the cerebellum and brainstem. J Clin Neurosci. 17:1248–1251. Tate MC, Aghi MK. 2009. Biology of angiogenesis and invasion in glioma. Neurotherapeutics. 6:447–457. Tavakolifard S, Biazar E, Pourshamsian K, Moslemin MH. 2015. Synthesis and evaluation of single-wall carbon nanotube-paclitaxelfolic acid conjugate as an anti-cancer targeting agent. Artif Cells Nanomed Biotechnol. 1–7. Tripathi RM, Shrivastav A, Shrivastav BR. 2014. Biogenic gold nanoparticles: As a potential candidate for brain tumor directed drug delivery. Artif Cells Nanomed Biotechnol. 1–7. Upadhyay RK. 2014. Drug delivery systems, CNS protection, and the blood brain barrier. Biomed Res Int. 2014:869269. Vyas TK, Shahiwala A, Marathe S, Misra A. 2005. Intranasal drug delivery for brain targeting. Curr Drug Deliv. 2:165–175. Wen PY, Kesari S. 2008. Malignant gliomas in adults. N Engl J Med. 359:492–507. Wong ET, Brem S. 2008. Antiangiogenesis treatment for glioblastoma multiforme: challenges and opportunities. J Natl Compr Canc Netw. 6:515–522. Wu G, Barth RF, Yang W, Kawabata S, Zhang L, Green-Church K. 2006. Targeted delivery of methotrexate to epidermal growth factor receptor-positive brain tumors by means of cetuximab (IMC-C225) dendrimer bioconjugates. Mol Cancer Ther. 5:52–59. Xin H, Jiang X, Gu J, Sha X, Chen L, Law K, et  al. 2011. Angiopepconjugated poly(ethylene glycol)-co-poly(e-caprolactone) nanoparticles as dual-targeting drug delivery system for brain glioma. Biomaterials. 32:4293–4305. Yun J, Rothrock RJ, Canoll P, Bruce JN. 2013. Convection-enhanced delivery for targeted delivery of antiglioma agents: the translational experience. J Drug Deliv. 2013:107573. Zhang W, Zhang Z, Zhang Y. 2011. The application of carbon nanotubes in target drug delivery systems for cancer therapies. Nanoscale Res Lett. 6:555. Zhou J, Patel TR, Sirianni RW, Strohbehn G, Zheng MQ, Duong N, et al. 2013. Highly penetrative, drug-loaded nanocarriers improve treatment of glioblastoma. Proc Natl Acad Sci USA. 110:11751–11756.