Recent progress towards development of effective systemic chemotherapy for the treatment of malignant brain tumors

Progress and Challenges in the Diagnosis and Treatment of Brain Cancer Using Nanotechnology

Primary brain cancer or brain cancer is the overgrowth of abnormal or malignant cells in the brain or its nearby tissues that form unwanted masses called brain tumors. People with malignant brain tumors suffer a lot, and the expected life span of the patients after diagnosis is often only around 14 months, even with the most vigorous therapies. The blood-brain barrier (BBB) is the main barrier in the body that restricts the entry of potential chemotherapeutic agents into the brain. The chances of treatment failure or low therapeutic effects are some significant drawbacks of conventional treatment methods. However, recent advancements in nanotechnology have generated hope in cancer treatment. Nanotechnology has shown a vital role starting from the early detection, diagnosis, and treatment of cancer. These tiny nanomaterials have great potential to deliver drugs across the BBB. Beyond just drug delivery, nanomaterials can be simulated to generate fluorescence to detect tumors. The current Review discusses in detail the challenges of brain cancer treatment and the application of nanotechnology to overcome those challenges. The success of chemotherapeutic treatment or the surgical removal of tumors requires proper imaging. Nanomaterials can provide imaging and therapeutic benefits for cancer. The application of nanomaterials in the diagnosis and treatment of brain cancer is discussed in detail by reviewing past studies.

Drug Permeability: From the Blood-Brain Barrier to the Peripheral Nerve Barriers

Drug delivery into the peripheral nerves and nerve roots has important implications for effective local anesthesia and treatment of peripheral neuropathies and chronic neuropathic pain. Similar to drugs that need to cross the blood-brain barrier (BBB) and blood-spinal cord barrier (BSCB) to gain access to the central nervous system (CNS), drugs must cross the peripheral nerve barriers (PNB), formed by the perineurium and blood-nerve barrier (BNB) to modulate peripheral axons. Despite significant progress made to develop effective strategies to enhance BBB permeability in therapeutic drug design, efforts to enhance drug permeability and retention in peripheral nerves and nerve roots are relatively understudied. Guided by knowledge describing structural, molecular and functional similarities between restrictive neural barriers in the CNS and peripheral nervous system (PNS), we hypothesize that certain CNS drug delivery strategies are adaptable for peripheral nerve drug delivery. In this review, we describe the molecular, structural and functional similarities and differences between the BBB and PNB, summarize and compare existing CNS and peripheral nerve drug delivery strategies, and discuss the potential application of selected CNS delivery strategies to improve efficacious drug entry for peripheral nerve disorders.

Surface Engineered Dendrimers: A Potential Nanocarrier for the Effective Management of Glioblastoma Multiforme

Gliomas are the most prevailing intracranial tumors, which account for approximately 36% of the primary brain tumors of glial cells. Glioblastoma multiforme (GBM) possesses a higher degree of malignancy among different gliomas. The blood-brain barrier (BBB) protects the brain against infections and toxic substances by preventing foreign molecules or unwanted cells from entering the brain parenchyma. Nano-carriers such as liposomes, nanoparticles, dendrimers, etc. boost the brain permeability of various anticancer drugs or other drugs. The favorable properties like small size, better solubility, and the modifiable surface of dendrimers have proven their broad applicability in the better management of GBM. However, in vitro and in vivo toxicities caused by dendrimers have been a significant concern. The presence of multiple functionalities on the surface of dendrimers enables the grafting of target ligand and/or therapeutic moieties. Surface engineering improves certain properties like targeting efficiency, pharmacokinetic profile, therapeutic effect, and toxicity reduction. This review will be focused on the role of different surface-modified dendrimers in the effective management of GBM.

Current Strategies to Enhance Delivery of Drugs across the Blood–Brain Barrier

The blood–brain barrier (BBB) has shown to be a significant obstacle to brain medication delivery. The BBB in a healthy brain is a diffusion barrier that prevents most substances from passing from the blood to the brain; only tiny molecules can pass across the BBB. The BBB is disturbed in specific pathological illnesses such as stroke, diabetes, seizures, multiple sclerosis, Parkinson’s disease, and Alzheimer’s disease. The goal of this study is to offer a general overview of current brain medication delivery techniques and associated topics from the last five years. It is anticipated that this review will stimulate readers to look into new ways to deliver medications to the brain. Following an introduction of the construction and function of the BBB in both healthy and pathological conditions, this review revisits certain contested questions, such as whether nanoparticles may cross the BBB on their own and if medications are selectively delivered to the brain by deliberately targeted nanoparticles. Current non-nanoparticle options are also discussed, including drug delivery via the permeable BBB under pathological circumstances and the use of non-invasive approaches to improve brain medication absorption.

Nanotechnology-based drug delivery for the treatment of CNS disorders

Approximately 6.8 million people die annually because of problems related to the central nervous system (CNS), and out of them, approximately 1 million people are affected by neurodegenerative diseases that include Alzheimer's disease, multiple sclerosis, epilepsy, and Parkinson's disease. CNS problems are a primary concern because of the complexity of the brain. There are various drugs available to treat CNS disorders and overcome problems with toxicity, specificity, and delivery. Barriers like the blood-brain barrier (BBB) are a challenge, as they do not allow therapeutic drugs to cross and reach their target. Researchers have been searching for ways to allow drugs to pass through the BBB and reach the target sites. These problems highlight the need of nanotechnology to alter or manipulate various processes at the cellular level to achieve the desired attributes. Due to their nanosize, nanoparticles are able to pass through the BBB and are an effective alternative to drug administration and other approaches. Nanotechnology has the potential to improve treatment and diagnostic techniques for CNS disorders and facilitate effective drug transfer. With the aid of nanoengineering, drugs could be modified to perform functions like transference across the BBB, altering signaling pathways, targeting specific cells, effective gene transfer, and promoting regeneration and preservation of nerve cells. The involvement of a nanocarrier framework inside the delivery of several neurotherapeutic agents used in the treatment of neurological diseases is reviewed in this study.

Modulation of Blood-Brain Barrier Permeability by Activating Adenosine A2 Receptors in Oncological Treatment

The blood–brain barrier (BBB) plays an important protective role in the central nervous system and maintains its homeostasis. It regulates transport into brain tissue and protects neurons against the toxic effects of substances circulating in the blood. However, in the case of neurological diseases or primary brain tumors, i.e., gliomas, the higher permeability of the blood-derived substances in the brain tissue is necessary. Currently applied methods of treatment for the primary brain neoplasms include surgical removal of the tumor, radiation therapy, and chemotherapy. Despite the abovementioned treatment methods, the prognosis of primary brain tumors remains bad. Moreover, chemotherapy options seem to be limited due to low drug penetration into the cancerous tissue. Modulation of the blood–brain barrier permeability may contribute to an increase in the concentration of the drug in the CNS and thus increase the effectiveness of therapy. Interestingly, endothelial cells in cerebral vessels are characterized by the presence of adenosine 2A receptors (A2AR). It has been shown that substances affecting these receptors regulate the permeability of the BBB. The mechanism of increasing the BBB permeability by A2AR agonists is the actin-cytoskeletal reorganization and acting on the tight junctions. In this case, the A2AR seems to be a promising therapy target. This article aims to assess the possibility of increasing the BBB permeability through A2AR agonists to increase the effectiveness of chemotherapy and to improve the results of cancer therapy.

Panax quinquefolium saponins protect against cisplatin evoked intestinal injury via ROS-mediated multiple mechanisms

BACKGROUND

Cisplatin is one of the most common chemotherapeutic drugs. Cisplatin-induced toxicity gives rise to gastrointestinal cell damage, subsequent diarrhea and vomiting, leading to the discontinuation of its clinical application in long-term cancer chemotherapy. Panax quinquefolium L., also known as American ginseng, has many pharmacological activities such as improving immunity, anti-tumor, anti-radiation and blood sugar lowering.

PURPOSE

Previously, our laboratory reported that American ginseng berry extract could alleviate chemotherapeutic agents-induced renal damage caused by cisplatin. Hence, this study further explored the protective effect of P. quinquefolium saponins (PQS) on cisplatin-induced intestinal injury in mice and the possible molecular mechanisms.

METHODS

Biochemical markers, levels of inflammatory factors, histopathological staining and western blotting were used to analyze intestinal injury based on various molecular mechanisms.

RESULTS

We demonstrated the destruction of the intestinal barrier caused by cisplatin exposure by detecting the activity of diamine oxidase (DAO) and the expression of tight junction proteins zonula occludens-1 (ZO-1) and occludin. Meanwhile, cisplatin exposure changed SOD and MDA levels in the small intestine, causing oxidative damage to the intestinal mucosa. The inflammation associated-intestinal damage was further explored by the measurement of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and analysis of nuclear factor-kappa B (NF-κB) inflammatory pathway protein expression. Moreover, apoptotic cells labeled with TUNEL staining-positive cells and activated caspase family proteins suggest that cisplatin induces intestinal apoptosis. Interestingly, PQS pretreatment significantly reversed these situations.

CONCLUSION

These evidences clearly suggest that PQS can alleviate cisplatin-induced intestinal damage by inhibiting oxidative stress, reducing the occurrence of inflammation and apoptosis, and improving intestinal barrier function.

Intranasal Delivery of Nanoformulations: A Potential Way of Treatment for Neurological Disorders

Although the global prevalence of neurological disorders such as Parkinson’s disease, Alzheimer’s disease, glioblastoma, epilepsy, and multiple sclerosis is steadily increasing, effective delivery of drug molecules in therapeutic quantities to the central nervous system (CNS) is still lacking. The blood brain barrier (BBB) is the major obstacle for the entry of drugs into the brain, as it comprises a tight layer of endothelial cells surrounded by astrocyte foot processes that limit drugs’ entry. In recent times, intranasal drug delivery has emerged as a reliable method to bypass the BBB and treat neurological diseases. The intranasal route for drug delivery to the brain with both solution and particulate formulations has been demonstrated repeatedly in preclinical models, including in human trials. The key features determining the efficacy of drug delivery via the intranasal route include delivery to the olfactory area of the nares, a longer retention time at the nasal mucosal surface, enhanced penetration of the drugs through the nasal epithelia, and reduced drug metabolism in the nasal cavity. This review describes important neurological disorders, challenges in drug delivery to the disordered CNS, and new nasal delivery techniques designed to overcome these challenges and facilitate more efficient and targeted drug delivery. The potential for treatment possibilities with intranasal transfer of drugs will increase with the development of more effective formulations and delivery devices.

Multifunctional Polymeric Nanoplatforms for Brain Diseases Diagnosis, Therapy and Theranostics

The blood-brain barrier (BBB) acts as a barrier to prevent the central nervous system (CNS) from damage by substances that originate from the blood circulation. The BBB limits drug penetration into the brain and is one of the major clinical obstacles to the treatment of CNS diseases. Nanotechnology-based delivery systems have been tested for overcoming this barrier and releasing related drugs into the brain matrix. In this review, nanoparticles (NPs) from simple to developed delivery systems are discussed for the delivery of a drug to the brain. This review particularly focuses on polymeric nanomaterials that have been used for CNS treatment. Polymeric NPs such as polylactide (PLA), poly (D, L-lactide-co-glycolide) (PLGA), poly (ε-caprolactone) (PCL), poly (alkyl cyanoacrylate) (PACA), human serum albumin (HSA), gelatin, and chitosan are discussed in detail.

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

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

Current Strategies for Brain Drug Delivery

The blood-brain barrier (BBB) has been a great hurdle for brain drug delivery. The BBB in healthy brain is a diffusion barrier essential for protecting normal brain function by impeding most compounds from transiting from the blood to the brain; only small molecules can cross the BBB. Under certain pathological conditions of diseases such as stroke, diabetes, seizures, multiple sclerosis, Parkinson's disease and Alzheimer disease, the BBB is disrupted. The objective of this review is to provide a broad overview on current strategies for brain drug delivery and related subjects from the past five years. It is hoped that this review could inspire readers to discover possible approaches to deliver drugs into the brain. After an initial overview of the BBB structure and function in both healthy and pathological conditions, this review re-visits, according to recent publications, some questions that are controversial, such as whether nanoparticles by themselves could cross the BBB and whether drugs are specifically transferred to the brain by actively targeted nanoparticles. Current non-nanoparticle strategies are also reviewed, such as delivery of drugs through the permeable BBB under pathological conditions and using non-invasive techniques to enhance brain drug uptake. Finally, one particular area that is often neglected in brain drug delivery is the influence of aging on the BBB, which is captured in this review based on the limited studies in the literature.

Nanotheranostics: Emerging Strategies for Early Diagnosis and Therapy of Brain Cancer

Nanotheranostics have demonstrated the development of advanced platforms that can diagnose brain cancer at early stages, initiate first-line therapy, monitor it, and if needed, rapidly start subsequent treatments. In brain nanotheranostics, therapeutic as well as diagnostic entities are loaded in a single nanoplatform, which can be further developed as a clinical formulation for targeting various modes of brain cancer. In the present review, we concerned about theranostic nanosystems established till now in the research field. These include gold nanoparticles, carbon nanotubes, magnetic nanoparticles, mesoporous silica nanoparticles, quantum dots, polymeric nanoparticles, upconversion nanoparticles, polymeric micelles, solid lipid nanoparticles and dendrimers for the advanced detection and treatment of brain cancer with advanced features. Also, we included the role of three-dimensional models of the BBB and cancer stem cell concept for the advanced characterization of nanotheranostic systems for the unification of diagnosis and treatment of brain cancer. In future, brain nanotheranostics will be able to provide personalized treatment which can make brain cancer even remediable or at least treatable at the primary stages.

Dual-targeting immunoliposomes using angiopep-2 and CD133 antibody for glioblastoma stem cells

Glioblastoma stem cells (GSCs), which are identified as subpopulation of CD133⁺/ALDH1⁺, are known to show resistance to the most of chemotherapy and radiation therapy, leading to the recurrence of tumor in glioblastoma multiforme (GBM) patients. Also, delivery of temozolomide (TMZ), a mainline treatment of GBM, to the GBM site is hampered by various barriers including the blood-brain barrier (BBB). A dual-targeting immunoliposome encapsulating TMZ (Dual-LP-TMZ) was developed by using angiopep-2 (An2) and anti-CD133 monoclonal antibody (CD133 mAb) for BBB transcytosis and specific delivery to GSCs, respectively. The size, zeta potential and drug encapsulation efficiency of Dual-LP-TMZ were 203.4nm in diameter, -1.6mV and 99.2%, respectively. The in vitro cytotoxicity of Dual-LP-TMZ against U87MG GSCs was increased by 425- and 181-folds when compared with that of free TMZ and non-targeted TMZ liposome (LP-TMZ) (10.3μM vs. 4380μM and 1869μM in IC₅₀, respectively). Apoptosis and anti-migration ability of Dual-LP-TMZ in U87MG GSCs were also significantly enhanced comparing with those of free TMZ or LP-TMZ. In vivo study clearly showed a significant reduction in tumor size after intravenous administrations of Dual-LP-TMZ to the orthotopically-implanted brain tumor mice when compared with free TMZ or LP-TMZ. Increased life span (ILS) and median survival time (MST) of tumor-bearing mice were also increased when treated with Dual-LP-TMZ (211.2% in ILS and 49.2days in MST) than with free TMZ (0% in ILS and 23.3day in MST). These data indicate that conjugation of both An2 peptide and CD133 mAb to TMZ-encapsulating liposome is very effective in delivering the TMZ to GSCs via BBB, suggesting a potential use of Dual-LP-TMZ as a therapeutic modality for GBM.

Intranasal administration of carbamazepine-loaded carboxymethyl chitosan nanoparticles for drug delivery to the brain

Epilepsy is considered as a common and diverse set of chronic neurological disorders and its symptoms can be controlled by antiepileptic drugs (AEDs). The presence of p-glycoprotein and multi-drug resistance transporters in the blood-brain barrier could prevent the entry of AEDs into the brain, causing drug resistant epilepsy. To overcome this problem, we propose using carboxymethyl chitosan nanoparticles as a carrier to deliver carbamazepine (CBZ) intra-nasally with the purpose to bypass the blood-brain barrier thus to enhance the brain drug concentration and the treatment efficacy. Results so far indicate that the developed CBZ-NPs have small particle size (218.76 ± 2.41 nm) with high drug loading (around 35%) and high entrapment efficiency (around 80%). The in vitro release profiles of CBZ from the NPs are in accordance with the Korsmeyer-peppas model. The in vivo results show that both encapsulation of CBZ in nanoparticles and the nasal route determined the enhancement of the drug bioavailability and brain targeting characteristics.

RETRACTED: Overexpression of FADD and Caspase-8 inhibits proliferation and promotes apoptosis of human glioblastoma cells

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief. An Expression of Concern for this article was previously published while an investigation was conducted (see related editorial: https://doi.org/10.1016/j.biopha.2022.113812). This retraction notice supersedes the Expression of Concern published earlier. Concern was raised about the reliability of the Western blot data in Figure 1B, which appear to represent a distinct phenotype found in many other publications, as detailed here: https://pubpeer.com/publications/52B13D77036B8927AFCF19CEFA0991; and here: https://docs.google.com/spreadsheets/d/1r0MyIYpagBc58BRF9c3luWNlCX8VUvUuPyYYXzxWvgY/edit#gid=262337249. Concerns were also expressed over the unusual flow cytometry plots in Figure 3A, and the provenance of these data. The journal requested the corresponding author comment on these concerns and provide the associated raw data. The authors did not respond to this request and therefore the Editor-in-Chief decided to retract the article.

Apoferritin Nanocage for Brain Targeted Doxorubicin Delivery

An ideal brain-targeted nanocarrier must be sufficiently potent to penetrate the blood-brain barrier (BBB) and sufficiently competent to target the cells of interest with adequate optimized physiochemical features and biocompatibility. However, it is an enormous challenge to the researchers to organize the above-mentioned properties into a single nanocarrier particle. New frontiers in nanomedicine are advancing the research of new biomaterials. Herein, we demonstrate a straightforward strategy for brain targeting by encapsulating doxorubicin (DOX) into a naturally available and unmodified apoferritin nanocage (DOX-loaded APO). APO can specifically bind to cells expressing transferrin receptor 1 (TfR1). Because of the high expression of TfR1 in both brain endothelial and glioma cells, DOX-loaded APO can cross the BBB and deliver drugs to the glioma with TfR1. Subsequent research demonstrated that the DOX-loaded APO had good physicochemical properties (particle size of 12.03 ± 0.42 nm, drug encapsulation efficiency of 81.8 ± 1.1%) and significant penetrating and targeting effects in the coculture model of bEnd.3 and C6 cells in vitro. In vivo imaging revealed that DOX-loaded APO accumulated specifically in brain tumor tissues. Additionally, in vivo tumor therapy experiments (at a dosage of 1 mg/kg DOX) demonstrated that a longer survival period was observed in mice that had been treated with DOX-loaded APO (30 days) compared with mice receiving free DOX solution (19 days).

Application of Dendrimer-based Nanoparticles in Glioma Imaging

Dendritic polymers or dendrimers present an alternate template for the development of nanoparticulate-based drug delivery and imaging systems. The smaller size (~7-12 nm) of dendrimers have the advantage over the other particles, because its smaller size can possibly improve tumor penetration and the inclusion of tumor specific drug release mechanisms. A Paramagnetic Chemical Exchange Saturation Transfer (PARACEST) MRI contrast agent, Eu-DOTA-Gly4 or a clinical relevant Gd-DOTA was conjugated on the surface of a G5 PAMAM dendrimer. To create a dual mode MRI-optical imaging nanoparticle, Dylight680 was also incorporated on the amines surface of a G5 dendrimer. The particle was detected with in vivo MRI in preclinical glioma animal model. Furthermore, noninvasive imaging results were validated with in vivo and ex-vivo optical imaging.

Immune microenvironment of gliomas

High-grade gliomas are rapidly progressing tumors of the central nervous system (CNS) with a very poor prognosis despite extensive resection combined with radiation and/or chemotherapy. Histopathological and flow cytometry analyses of human and rodent experimental gliomas revealed heterogeneity of a tumor and its niche, composed of reactive astrocytes, endothelial cells, and numerous immune cells. Infiltrating immune cells consist of CNS resident (microglia) and peripheral macrophages, granulocytes, myeloid-derived suppressor cells (MDSCs), and T lymphocytes. Intratumoral density of glioma-associated microglia/macrophages (GAMs) and MDSCs is the highest in malignant gliomas and inversely correlates with patient survival. Although GAMs have a few innate immune functions intact, their ability to be stimulated via TLRs, secrete cytokines, and upregulate co-stimulatory molecules is not sufficient to initiate antitumor immune responses. Moreover, tumor-reprogrammed GAMs release immunosuppressive cytokines and chemokines shaping antitumor responses. Both GAMs and MDSCs have ability to attract T regulatory lymphocytes to the tumor, but MDSCs inhibit cytotoxic responses mediated by natural killer cells, and block the activation of tumor-reactive CD4⁺ T helper cells and cytotoxic CD8⁺ T cells. The presence of regulatory T cells may further contribute to the lack of effective immune activation against malignant gliomas. We review the immunological aspects of glioma microenvironment, in particular composition and various roles of the immune cells infiltrating malignant human gliomas and experimental rodent gliomas. We describe tumor-derived signals and mechanisms driving myeloid cell accumulation and reprogramming. Although, understanding the complexity of cell-cell interactions in glioma microenvironment is far from being achieved, recent studies demonstrated several glioma-derived factors that trigger migration, accumulation, and reprogramming of immune cells. Identification of these factors may facilitate development of immunotherapy for gliomas as immunomodulatory and immune evasion mechanisms employed by malignant gliomas pose an appalling challenge to brain tumor immunotherapy.

Peptide-22 and Cyclic RGD Functionalized Liposomes for Glioma Targeting Drug Delivery Overcoming BBB and BBTB

Chemotherapy outcomes for the treatment of glioma remain unsatisfied due to the inefficient drug transport across BBB/BBTB and poor drug accumulation in the tumor site. Nanocarriers functionalized with different targeting ligands are considered as one of the most promising alternatives. However, few studies were reported to compare the targeting efficiency of the ligands and develop nanoparticles to realize BBB/BBTB crossing and brain tumor targeting simultaneously. In this study, six peptide-based ligands (Angiopep-2, T7, Peptide-22, c(RGDfK), D-SP5 and Pep-1), widely used for brain delivery, were selected to decorate liposomes, respectively, so as to compare their targeting ability to BBB or BBTB. Based on the in vitro cellular uptake results on BCECs and HUVECs, Peptide-22 and c(RGDfK) were picked to construct a BBB/BBTB dual-crossing, glioma-targeting liposomal drug delivery system c(RGDfK)/Pep-22-DOX-LP. In vitro cellular uptake demonstrated that the synergetic effect of c(RGDfK) and Peptide-22 could significantly increase the internalization of liposomes on U87 cells. In vivo imaging further verified that c(RGDfK)/Pep-22-LP exhibited higher brain tumor distribution than single ligand modified liposomes. The median survival time of glioma-bearing mice treated with c(RGDfK)/Pep-22-DOX-LP (39.5 days) was significantly prolonged than those treated with free doxorubicin or other controls. In conclusion, the c(RGDfK) and Peptide-22 dual-modified liposome was constructed based on the targeting ability screening of various ligands. The system could effectively overcome BBB/BBTB barriers, target to tumor cells and inhibit the growth of glioma, which proved its potential for improving the efficacy of chemotherapeutics for glioma therapy.

Myeloid-derived suppressor cells in gliomas

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of early myeloid progenitors and precursors at different stages of differentiation into granulocytes, macrophages, and dendritic cells. Blockade of their differentiation into mature myeloid cells in cancer results in an expansion of this population. High-grade gliomas are the most common malignant tumours of the central nervous system (CNS), with a poor prognosis despite intensive radiation and chemotherapy. Histopathological and flow cytometry analyses of human and rodent experimental gliomas revealed the extensive heterogeneity of immune cells infiltrating gliomas and their microenvironment. Immune cell infiltrates consist of: resident (microglia) and peripheral macrophages, granulocytes, myeloid-derived suppressor cells, and T lymphocytes. Intratumoural density of glioma-associated MDSCs correlates positively with the histological grade of gliomas and patient’s survival. MDSCs have the ability to attract T regulatory lymphocytes to the tumour, but block the activation of tumour-reactive CD4⁺ T helper cells and cytotoxic CD8⁺ T cells. Immunomodulatory mechanisms employed by malignant gliomas pose an appalling challenge to brain tumour immunotherapy. In this mini-review we describe phenotypic and functional characteristics of MDSCs in humans and rodents, and their occurrence and potential roles in glioma progression. While understanding the complexity of immune cell interactions in the glioma microenvironment is far from being accomplished, there is significant progress that may lead to the development of immunotherapy for gliomas.

Targeting Glioma with a Dual Mode Optical and Paramagnetic Nanoprobe across the Blood-brain Tumor Barrier

In brain tumors, delivering nanoparticles across the blood-tumor barrier presents major hurdles. A clinically relevant MRI contrast agent, GdDOTA and a near-infrared (NIR) fluorescent dye, DL680 were conjugated to a G5 PAMAM dendrimer, thus producing a dual-mode MRI and NIR imaging agent. Systemic delivery of the subsequent nano-sized agent demonstrated glioma-specific accumulation, probably due to the enhanced permeability and retention effect. In vivo MRI detected the agent in glioma tissue, but not in normal contralateral tissue; this observation was validated with in vivo and ex vivo fluorescence imaging. A biodistribution study showed the agent to have accumulated in the glioma tumor and the liver, the latter being the excretion path for a G5 dendrimer-based agent.

Conserved molecular mechanisms underlying the effects of small molecule xenobiotic chemotherapeutics on cells

For proper determination of the apoptotic potential of chemoxenobiotics in synergism, it is important to understand the modes, levels and character of interactions of chemoxenobiotics with cells in the context of predicted conserved biophysical properties. Chemoxenobiotic structures are studied with respect to atom distribution over molecular space, the predicted overall octanol-to-water partition coefficient (Log OWPC; unitless) and molecular size viz a viz van der Waals diameter (vdWD). The Log OWPC-to-vdWD (nm^-1 ) parameter is determined, and where applicable, hydrophilic interacting moiety/core-to-vdWD (nm^-1 ) and lipophilic incorporating hydrophobic moiety/core-to-vdWD (nm^-1 ) parameters of their part-structures are determined. The cellular and sub-cellular level interactions of the spectrum of xenobiotic chemotherapies have been characterized, for which a classification system has been developed based on predicted conserved biophysical properties with respect to the mode of chemotherapeutic effect. The findings of this study are applicable towards improving the effectiveness of existing combination chemotherapy regimens and the predictive accuracy of personalized cancer treatment algorithms as well as towards the selection of appropriate novel xenobiotics with the potential to be potent chemotherapeutics for dendrimer nanoparticle-based effective transvascular delivery.

Deregulation of histone-modifying enzymes and chromatin structure modifiers contributes to glioma development

The epigenetic landscape is deregulated in cancer due to aberrant activation or inactivation of enzymes maintaining and modifying the epigenome. Histone modifications and global aberrations at the histone level may result in distorted patterns of gene expression, and malfunction of proteins that regulate chromatin modification and remodeling. Recent whole genome studies demonstrated that histones and chaperone proteins harbor mutations that may result in gross alterations of the epigenome leading to genome instability. Glioma development is a multistep process, involving genetic and epigenetic alterations. This review summarizes newly identified mechanisms affecting expression/functions of histone-modifying enzymes and chromatin modifiers in gliomas. We discuss recent approaches to overcome epigenetic alterations with histone-modifying enzyme inhibitors and their prospects for glioma therapy.

Uniform brain tumor distribution and tumor associated macrophage targeting of systemically administered dendrimers

Effective blood-brain tumor barrier penetration and uniform solid tumor distribution can significantly enhance therapeutic delivery to brain tumors. Hydroxyl-functionalized, generation-4 poly(amidoamine) (PAMAM) dendrimers, with their small size, near-neutral surface charge, and the ability to selectively localize in cells associated with neuroinflammation may offer new opportunities to address these challenges. In this study we characterized the intracranial tumor biodistribution of systemically delivered PAMAM dendrimers in an intracranial rodent gliosarcoma model using fluorescence-based quantification methods and high resolution confocal microscopy. We observed selective and homogeneous distribution of dendrimer throughout the solid tumor (∼6 mm) and peritumoral area within fifteen minutes after systemic administration, with subsequent accumulation and retention in tumor associated microglia/macrophages (TAMs). Neuroinflammation and TAMs have important growth promoting and pro-invasive effects in brain tumors. The rapid clearance of systemically administered dendrimers from major organs promises minimal off-target adverse effects of conjugated drugs. Therefore, selective delivery of immunomodulatory molecules to TAM, using hydroxyl PAMAM dendrimers, may hold promise for therapy of glioblastoma.

Efficient delivery of docetaxel for the treatment of brain tumors by cyclic RGD-tagged polymeric micelles

The treatment of glioblastoma, and other types of brain cancer, is limited due to the poor transport of drugs across the blood brain barrier and poor penetration of the blood‑brain‑tumor barrier. In the present study, cyclic Arginine‑Glycine‑Aspartic acid‑D‑Tyrosine‑Lysine [c(RGDyK)], that has a high binding affinity to integrin αvβ3 receptors, that are overexpressed in glioblastoma cancers, was employed as a novel approach to target cancer by delivering therapeutic molecules intracellularly. The c(RGDyK)/docetaxel polylactic acid‑polyethylene glycol (DTX‑PLA‑PEG) micelle was prepared and characterized for various in vitro and in vivo parameters. The specific binding affinity of the Arginine‑Glycine‑Aspartic acid (RGD) micelles, to the integrin receptor, enhanced the intracellular accumulation of DTX, and markedly increased its cytotoxic efficacy. The effect of microtubule stabilization was evident in the inhibition of glioma spheroid volume. Upon intravenous administration, c(RGDyK)/DTX‑PLA‑PEG showed enhanced accumulation in brain tumor tissues through active internalization, whereas non‑targeted micelles showed limited transport ability. Furthermore, RGD‑linked micelles showed marked anti‑glioma activity in U87MG malignant glioma tumor xenografts, and significantly suppressed the growth of tumors without signs of systemic toxicity. In conclusion, the results of the present study suggest that ligand‑mediated drug delivery may improve the efficacy of brain cancer chemotherapy.

The effects of selected inhibitors of histone modifying enzyme on C6 glioma cells

BACKGROUND

Aberrant epigenetic histone modifications are implicated in cancer pathobiology, therefore histone modifying enzymes are emerging targets for anti-cancer therapy. There is a few evidence for deregulation of the histone modifying enzymes in glioblastomas. Glioma treatment is a clinical challenge due to its resistance to current therapies.

METHODS

The effect of selected inhibitors on epigenetic modifications and viability of glioma C6 cells were studied using immunofluorescence and MTT metabolism test.

RESULTS

We found that VPA and TSA increase histone H4 acetylation in glioma cells, while chaetocin and BIX01294 at low concentrations reduce H3K9me3, and 3DZNep decreases H3K27me3. Long-term treatment with some epigenetic inhibitors affects viability of glioma cells.

CONCLUSIONS

We established the concentrations of selected inhibitors which in C6 glioma cells inhibit the enzyme activity, but do not decrease cell viability, hence allow to study the role of histone modifications in C6 glioma biology.

Cyclic RGD-linked polymeric micelles for targeted delivery of platinum anticancer drugs to glioblastoma through the blood-brain tumor barrier

Ligand-mediated drug delivery systems have enormous potential for improving the efficacy of cancer treatment. In particular, Arg-Gly-Asp peptides are promising ligand molecules for targeting αvβ3/αvβ5 integrins, which are overexpressed in angiogenic sites and tumors, such as intractable human glioblastoma (U87MG). We here achieved highly efficient drug delivery to U87MG tumors by using a platinum anticancer drug-incorporating polymeric micelle (PM) with cyclic Arg-Gly-Asp (cRGD) ligand molecules. Intravital confocal laser scanning microscopy revealed that the cRGD-linked polymeric micelles (cRGD/m) accumulated rapidly and had high permeability from vessels into the tumor parenchyma compared with the PM having nontargeted ligand, "cyclic-Arg-Ala-Asp" (cRAD). As both cRGD/m- and cRAD-linked polymeric micelles have similar characteristics, including their size, surface charge, and the amount of incorporated drugs, it is likely that the selective and accelerated accumulation of cRGD/m into tumors occurred via an active internalization pathway, possibly transcytosis, thereby producing significant antitumor effects in an orthotopic mouse model of U87MG human glioblastoma.

Is glioblastoma an epigenetic malignancy?

Epigenetic modifications control gene expression by regulating the access of nuclear proteins to their target DNA and have been implicated in both normal cell differentiation and oncogenic transformation. Epigenetic abnormalities can occur both as a cause and as a consequence of cancer. Oncogenic transformation can deeply alter the epigenetic information enclosed in the pattern of DNA methylation or histone modifications. In addition, in some cancers epigenetic dysfunctions can drive oncogenic transformation. Growing evidence emphasizes the interplay between metabolic disturbances, epigenomic changes and cancer, i.e., mutations in the metabolic enzymes SDH, FH, and IDH may contribute to cancer development. Epigenetic-based mechanisms are reversible and the possibility of “resetting” the abnormal cancer epigenome by applying pharmacological or genetic strategies is an attractive, novel approach. Gliomas are incurable with all current therapeutic approaches and new strategies are urgently needed. Increasing evidence suggests the role of epigenetic events in development and/or progression of gliomas. In this review, we summarize current data on the occurrence and significance of mutations in the epigenetic and metabolic enzymes in pathobiology of gliomas. We discuss emerging therapies targeting specific epigenetic modifications or chromatin modifying enzymes either alone or in combination with other treatment regimens.

Encapsulated therapeutic stem cells implanted in the tumor resection cavity induce cell death in gliomas

Therapeutically engineered stem cells have shown promise for glioblastoma multiforme (GBM) therapy; however, key preclinical studies are urgently needed for their clinical translation. In this study, we investigated a new approach to GBM treatment using therapeutic stem cells encapsulated in biodegradable, synthetic extracellular matrix (sECM) in mouse models of human GBM resection. Using multimodal imaging, we first showed quantitative surgical debulking of human GBM tumors in mice, which resulted in increased survival. Next, sECM encapsulation of engineered stem cells increased their retention in the tumor resection cavity, permitted tumor-selective migration and release of diagnostic and therapeutic proteins in vivo. Simulating the clinical scenario of GBM treatment, the release of tumor-selective S-TRAIL (secretable tumor necrosis factor apoptosis inducing ligand) from sECM-encapsulated stem cells in the resection cavity eradicated residual tumor cells by inducing caspase-mediated apoptosis, delayed tumor regrowth and significantly increased survival of mice. This study demonstrates the efficacy of encapsulated therapeutic stem cells in mouse models of GBM resection and may have implications for developing effective therapies for GBM.

Characteristics of the alternative phenotype of microglia/macrophages and its modulation in experimental gliomas

Microglia (brain resident macrophages) accumulate in malignant gliomas and instead of initiating the anti-tumor response, they switch to a pro-invasive phenotype, support tumor growth, invasion, angiogenesis and immunosuppression by release of cytokines/chemokines and extracellular matrix proteases. Using immunofluorescence and flow cytometry, we demonstrate an early accumulation of activated microglia followed by accumulation of macrophages in experimental murine EGFP-GL261 gliomas. Those cells acquire the alternative phenotype, as evidenced by evaluation of the production of ten pro/anti-inflammatory cytokines and expression profiling of 28 genes in magnetically-sorted CD11b⁺ cells from tumor tissues. Furthermore, we show that infiltration of implanted gliomas by amoeboid, Iba1-positive cells can be reduced by a systematically injected cyclosporine A (CsA) two or eight days after cell inoculation. The up-regulated levels of IL-10 and GM-CSF, increased expression of genes characteristic for the alternative and pro-invasive phenotype (arg-1, mt1-mmp, cxcl14) in glioma-derived CD11b⁺ cells as well as enhanced angiogenesis and tumor growth were reduced in CsA-treated mice. Our findings define for the first time kinetics and biochemical characteristics of glioma-infiltrating microglia/macrophages. Inhibition of the alternative activation of tumor-infiltrating macrophages significantly reduced tumor growth. Thus, blockade of microglia/macrophage infiltration and their pro-invasive functions could be a novel therapeutic strategy in malignant gliomas.

Cotransfected sodium iodide symporter and human tyroperoxidase genes following human telomerase reverse transcriptase promoter for targeted radioiodine therapy of malignant glioma cells

INTRODUCTION

Radioiodine is a routine therapy for differentiated thyroid cancers. In principle, undifferentiated thyroid cancers as well as nonthyroid cancers can concentrate and, thus, be treated with radioiodine after transfection with the human sodium iodide symporter (hNIS) gene. The human telomerase reverse transcriptase (hTERT) promoter is an effective tumor-specific promoter of gene expression and, thus, may be useful in targeted gene therapy of cancer.

METHODS

We used hTERT promoter-modulated expression of the hNIS and human thyroperoxidase (hTPO) genes in an experimental model of radioiodine-based treatment of malignant glioma. Cells were cotransfected by adenovirus in which the hNIS gene had been coupled to the hTERT promoter and the hTPO gene had been coupled to the human cytomegalovirus (CMV) promoter (Ad-hTERT-hNIS and Ad-CMV-hTPO, respectively), and they were evaluated in cells thus transfecting transgene expression by western blots, (125)I uptake and influx, and clonogenecity after (131)I treatment.

RESULTS

After cotransfection with two adenovirus, cells showed about 31-34 times higher (125)I uptake than the control cells transfected with Ad-CMV-EGFP (enhanced green fluorescent protein) and almost 1.3-1.4 times higher (125)I uptake than cells only transfected with Ad-hTERT-hNIS. Western blots revealed two bands of ∼70 and 110 kDa, respectively. The in vitro clonogenic assay indicated that, after exposure to 100-1000 μCi of (131)I-iodide for 12 hours, 91%-94% of cells cotransfected with the hNIS and hTPO genes, 88%-93% of cells transfected with the hNIS gene, and only 62%-68% of control (nontransfected) cells were killed.

CONCLUSIONS

The experiments demonstrated that an effective therapy of (131)I was achieved in malignant glioma cell lines after induction of tumor-specific iodide uptake activity by the hTERT promoter-directed NIS expression in vitro. Cotransfection of the hNIS and hTPO genes can lead to longer retention of radioiodide, but did not increase cell killing over that achieved with transfection with the hNIS gene alone.

Nanoscale materials for tackling brain cancer: recent progress and outlook

This article reports on recent progress in the development of advanced nanoscale photoreactive, magnetic and multifunctional materials applicable to brain cancer diagnostics, imaging, and therapy, with an emphasis on the latest contributions and the novelty of the approach, along with the most promising emergent trends.

Molecular targeting of glioblastoma: Drug discovery and therapies

Despite advances in treatment for glioblastoma multiforme (GBM), patient prognosis remains poor. Although there is growing evidence that molecular targeting could translate into better survival for GBM, current clinical data show limited impact on survival. Recent progress in GBM genomics implicate several activated pathways and numerous mutated genes. This molecular diversity can partially explain therapeutic resistance and several approaches have been postulated to target molecular changes. Furthermore, most drugs are unable to reach effective concentrations within the tumor owing to elevated intratumoral pressure, restrictive vasculature and other limiting factors. Here, we describe the preclinical and clinical developments in treatment strategies of GBM. We review the current clinical trials for GBM and discuss the challenges and future directions of targeted therapies.

Tissue concentration of systemically administered antineoplastic agents in human brain tumors

The blood-brain-barrier (BBB) limits the penetration of many systemic antineoplastic therapies. Consequently, many agents may be used in clinical studies and clinical practice though they may not achieve therapeutic levels within the tumor. We sought to compile the currently available human data on antineoplastic drug concentrations in brain and tumor tissue according to BBB status. A review of the literature was conducted for human studies providing concentrations of antineoplastic agents in blood and metastatic brain tumors or high-grade gliomas. Studies were considered optimal if they reported simultaneous tissue and blood concentration, multiple sampling times and locations, MRI localization, BBB status at sampling site, tumor histology, and individual subject data. Twenty-Four studies of 19 compounds were included. These examined 18 agents in contrast-enhancing regions of high-grade gliomas, with optimal data for 2. For metastatic brain tumors, adequate data was found for 9 agents. Considerable heterogeneity was found in the measurement value, tumor type, measurement timing, and sampling location within and among studies, limiting the applicability of the results. Tissue to blood ratios ranged from 0.054 for carboplatin to 34 for mitoxantrone in high-grade gliomas, and were lowest for temozolomide (0.118) and etoposide (0.116), and highest for mitoxantrone (32.02) in metastatic tumors. The available data examining the concentration of antineoplastic agents in brain and tumor tissue is sparse and limited by considerable heterogeneity. More studies with careful quantification of antineoplastic agents in brain and tumor tissue is required for the rational development of therapeutic regimens.

Regulation of KEAP1 expression by promoter methylation in malignant gliomas and association with patient's outcome

In light with the view that KEAP1 loss of function may impact tumour behavior and modify response to chemotherapeutical agents, we sought to determine whether KEAP1 gene is epigenetically regulated in malignant gliomas. We developed a Quantitative Methylation Specific PCR (QMSP) assay to analyze 86 malignant gliomas and 20 normal brain tissues. The discriminatory power of the assay was assessed by Receiving Operating Characteristics (ROC) curve analysis. The AUC value of the curve was 0.823 (95%CI: 0.764-0.883) with an optimal cut off value of 0.133 yielding a 74% sensitivity (95%CI: 63%-82%) and an 85% specificity (95%CI: 64%-95%). Bisulfite sequencing analysis confirmed QMSP results and demonstrated a direct correlation between percentage of methylated CpGs and methylation levels (Spearman's Rho 0.929, P=0.003). Remarkably, a strong inverse correlation was observed between methylation levels and KEAP1 mRNA transcript in tumour tissue (Spearman's Rho -0.656 P=0.0001) and in a cell line before and after treatment with 5-azacytidine (P=0.003). RECPAM multivariate statistical analysis studying the interaction between MGMT and KEAP1 methylation in subjects treated with radiotherapy and temozolomide (n=70), identified three prognostic classes of glioma patients at different risk to progress. While simultaneous methylation of MGMT and KEAP1 promoters was associated with the lowest risk to progress, patients showing only MGMT methylation were the subgroup at the higher risk (HR 5.54, 95% CI 1.35-22.74). Our results further suggest that KEAP1 expression is epigenetically regulated. In addition we demonstrated that KEAP1 is frequently methylated in malignant gliomas and a predictor of patient's outcome.