Convection-enhanced drug delivery for gliomas

The Influence of Size on the Intracranial Distribution of Biomedical Nanoparticles Administered by Convection-enhanced Delivery in Minipigs

Because of the blood-brain barrier (BBB), successful drug delivery to the brain has long been a key objective for the medical community, calling for pioneering technologies to overcome this challenge. Convection-enhanced delivery (CED), a form of direct intraparenchymal microinfusion, shows promise but requires optimal infusate design and real-time distribution monitoring. The size of the infused substances appears to be especially critical, with current knowledge being limited. Herein, we examined the intracranial administration of polyethylene glycol (PEG)-coated nanoparticles (NPs) of various sizes using CED in groups of healthy minipigs (n = 3). We employed stealth liposomes (LIPs, 130 nm) and two gold nanoparticle designs (AuNPs) of different diameters (8 and 40 nm). All were labeled with copper-64 for quantitative and real-time monitoring of the infusion via positron emission tomography (PET). NPs were infused via two catheters inserted bilaterally in the putaminal regions of the animals. Our results suggest CED with NPs holds promise for precise brain drug delivery, with larger LIPs exhibiting superior distribution volumes and intracranial retention over smaller AuNPs. PET imaging alongside CED enabled dynamic visualization of the process, target coverage, timely detection of suboptimal infusion, and quantification of distribution volumes and concentration gradients. These findings may augment the therapeutic efficacy of the delivery procedure while mitigating unwarranted side effects associated with nonvisually monitored delivery approaches. This is of vital importance, especially for chronic intermittent infusions through implanted catheters, as this information enables informed decisions for modulating targeted infusion volumes on a catheter-by-catheter, patient-by-patient basis.

Convection-Enhanced Drug Delivery: Experimental and Analytical Studies of Infusion Behavior in an In Vitro Brain Surrogate

Convection-enhanced drug delivery (CED) directly infuses drugs with a large molecular weight toward target cells as a therapeutic strategy for neurodegenerative diseases and brain cancers. Despite the success of many previous in vitro experiments on CED, challenges still remain. In particular, a theoretical predictive model is needed to form a basis for treatment planning, and developing such a model requires well-controlled injection tests that can rigorously capture the convective (advective) and diffusive transport of an infusate. For this purpose, we investigated the advection-diffusion transport of an infusate (bromophenol blue solution) in the brain surrogate (0.2% w/w agarose gel) at different injection rates, ranging from 0.25 to 4 μL/min, by closely monitoring changes in the color intensity, propagation distance, and injection pressures. One dimensional closed-form solution was examined with two variable sets, such as the mathematically calculated coefficient of molecular diffusion and average velocity, and the hydraulic dispersion coefficient and seepage velocity by the least squared method. As a result, the seepage velocity was greater than the average velocity to some extent, particularly for the later infusion times. The poroelastic deformation in the brain surrogate might lead to changes in porosity, and consequently, slight increases in the actual flow velocity as infusion continues. The limitation of efficiency of the single catheter was analyzed by dimensionless analysis. Lastly, this study suggests a simple but robust approach that can properly capture the convective (advective) and diffusive transport of an infusate in an in vitro brain surrogate via well-controlled injection tests.

Targeting the IL4 receptor with MDNA55 in patients with recurrent glioblastoma: Results of a phase IIb trial

BACKGROUND

MDNA55 is an interleukin 4 receptor (IL4R)-targeting toxin in development for recurrent GBM, a universally fatal disease. IL4R is overexpressed in GBM as well as cells of the tumor microenvironment. High expression of IL4R is associated with poor clinical outcomes.

METHODS

MDNA55-05 is an open-label, single-arm phase IIb study of MDNA55 in recurrent GBM (rGBM) patients with an aggressive form of GBM (de novo GBM, IDH wild-type, and nonresectable at recurrence) on their 1st or 2nd recurrence. MDNA55 was administered intratumorally as a single dose treatment (dose range of 18 to 240 ug) using convection-enhanced delivery (CED) with up to 4 stereo-tactically placed catheters. It was co-infused with a contrast agent (Gd-DTPA, Magnevist®) to assess distribution in and around the tumor margins. The flow rate of each catheter did not exceed 10μL/min to ensure that the infusion duration did not exceed 48 h. The primary endpoint was mOS, with secondary endpoints determining the effects of IL4R status on mOS and PFS.

RESULTS

MDNA55 showed an acceptable safety profile at doses up to 240 μg. In all evaluable patients (n = 44) mOS was 11.64 months (80% one-sided CI 8.62, 15.02) and OS-12 was 46%. A subgroup (n = 32) consisting of IL4R High and IL4R Low patients treated with high-dose MDNA55 (>180 ug) showed the best benefit with mOS of 15 months, OS-12 of 55%. Based on mRANO criteria, tumor control was observed in 81% (26/32), including those patients who exhibited pseudo-progression (15/26).

CONCLUSIONS

MDNA55 demonstrated tumor control and promising survival and may benefit rGBM patients when treated at high-dose irrespective of IL4R expression level.Trial Registration: Clinicaltrials.gov NCT02858895.

H3K27-altered diffuse midline glioma: a paradigm shifting opportunity in direct delivery of targeted therapeutics

INTRODUCTION

Despite much progress, the prognosis for H3K27-altered diffuse midline glioma (DMG), previously known as diffuse intrinsic pontine glioma when located in the brainstem, remains dark and dismal.

AREAS COVERED

A wealth of research over the past decade has revolutionized our understanding of the molecular basis of DMG, revealing potential targetable vulnerabilities for treatment of this lethal childhood cancer. However, obstacles to successful clinical implementation of novel therapies remain, including effective delivery across the blood-brain barrier (BBB) to the tumor site. Here, we review relevant literature and clinical trials and discuss direct drug delivery via convection-enhanced delivery (CED) as a promising treatment modality for DMG. We outline a comprehensive molecular, pharmacological, and procedural approach that may offer hope for afflicted patients and their families.

EXPERT OPINION

Challenges remain in successful drug delivery to DMG. While CED and other techniques offer a chance to bypass the BBB, the variables influencing successful intratumoral targeting are numerous and complex. We discuss these variables and potential solutions that could lead to the successful clinical implementation of preclinically promising therapeutic agents.

Oncolytic Viral Therapy for Malignant Glioma and Their Application in Clinical Practice

Glioblastoma is the most common primary malignant brain tumor in adults and outcomes remain poor despite the current standard of care multimodal therapy. Oncolytic virotherapy utilizes engineered viruses to exert an anti-tumor effect via both direct oncolysis and stimulation of an immune response within the tumor microenvironment, turning tumors from "cold" to "hot." This has shown promise as a novel therapeutic modality and attempts to circumvent the challenges associated with traditional treatments. Many oncolytic viruses have been investigated in completed and ongoing clinical trials and while safety has been demonstrated, clinical outcomes have been variable, often with only a subgroup of patients showing a significant response. This review summarizes these studies, addresses relevant technical aspects of oncolytic virus administration, and highlights practical considerations to assist providers in appropriately caring for patients treated with oncolytic virotherapy. Additionally, future directions within the field that may help to maximize efficacy of this modality are discussed.

Polymeric Nanoparticles in Brain Cancer Therapy: A Review of Current Approaches

Translation of novel therapies for brain cancer into clinical practice is of the utmost importance as primary brain tumors are responsible for more than 200,000 deaths worldwide each year. While many research efforts have been aimed at improving survival rates over the years, prognosis for patients with glioblastoma and other primary brain tumors remains poor. Safely delivering chemotherapeutic drugs and other anti-cancer compounds across the blood-brain barrier and directly to tumor cells is perhaps the greatest challenge in treating brain cancer. Polymeric nanoparticles (NPs) are powerful, highly tunable carrier systems that may be able to overcome those obstacles. Several studies have shown appropriately-constructed polymeric NPs cross the blood-brain barrier, increase drug bioavailability, reduce systemic toxicity, and selectively target central nervous system cancer cells. While no studies relating to their use in treating brain cancer are in clinical trials, there is mounting preclinical evidence that polymeric NPs could be beneficial for brain tumor therapy. This review includes a variety of polymeric NPs and how their associated composition, surface modifications, and method of delivery impact their capacity to improve brain tumor therapy.

Blood-brain barrier: emerging trends on transport models and new-age strategies for therapeutics intervention against neurological disorders

The integrity of the blood–brain barrier (BBB) is essential for normal central nervous system (CNS) functioning. Considering the significance of BBB in maintaining homeostasis and the neural environment, we aim to provide an overview of significant aspects of BBB. Worldwide, the treatment of neurological diseases caused by BBB disruption has been a major challenge. BBB also restricts entry of neuro-therapeutic drugs and hinders treatment modalities. Hence, currently nanotechnology-based approaches are being explored on large scale as alternatives to conventional methodologies. It is necessary to investigate the in-depth characteristic features of BBB to facilitate the discovery of novel drugs that can successfully cross the barrier and target the disease effectively. It is imperative to discover novel strategies to treat life-threatening CNS diseases in humans. Therefore, insights regarding building blocks of BBB, activation of immune response on breach of this barrier, and various autoimmune neurological disorders caused due to BBB dysfunction are discussed. Further, special emphasis is given on delineating BBB disruption leading to CNS disorders. Moreover, various mechanisms of transport pathways across BBB, several novel strategies, and alternative routes by which drugs can be properly delivered into CNS are also discussed.

Drug penetration in pediatric brain tumors: Challenges and opportunities

Larger clinical trial enrollments and a greater understanding of biological heterogeneity have led to improved survival rates for children diagnosed with brain tumors in the last 50 years. However, reducing long-term morbidities and improving survival rates of high-risk tumors remain major challenges. Chemotherapy can reduce tumor burden, but effective drug penetration at the tumor site is limited by barriers in the route of drug administration and within the tumor microenvironment. Bioavailability of drugs is impeded by the blood-brain barrier, plasma protein binding, and structural components by the tumor including the matrix and vasculature contributing to increased interstitial fluid pressure, hypoxia, and acidity. Designing drug delivery systems to circumvent these barriers could lead to improved drug penetration at the tumor site and reduce adverse systemic side effects. In this review, we expand on how systemic and local barriers limit drug penetration and present potential methods to enhance drug penetration in pediatric brain tumors.

Infusion Mechanisms in Brain White Matter and Their Dependence on Microstructure: An Experimental Study of Hydraulic Permeability

OBJECTIVE

Hydraulic permeability is a topic of deep interest in biological materials because of its important role in a range of drug delivery-based therapies. The strong dependence of permeability on the geometry and topology of pore structure and the lack of detailed knowledge of these parameters in the case of brain tissue makes the study more challenging. Although theoretical models have been developed for hydraulic permeability, there is limited consensus on the validity of existing experimental evidence to complement these models. In the present study, we measure the permeability of white matter (WM) of fresh ovine brain tissue considering the localised heterogeneities in the medium using an infusion-based experimental set up, iPerfusion. We measure the flow across different parts of the WM in response to applied pressures for a sample of specific dimensions and calculate the permeability from directly measured parameters. Furthermore, we directly probe the effect of anisotropy of the tissue on permeability by considering the directionality of tissue on the obtained values. Additionally, we investigate whether WM hydraulic permeability changes with post-mortem time. To our knowledge, this is the first report of experimental measurements of the localised WM permeability, also demonstrating the effect of axon directionality on permeability. This work provides a significant contribution to the successful development of intra-tumoural infusion-based technologies, such as convection-enhanced delivery (CED), which are based on the delivery of drugs directly by injection under positive pressure into the brain.

Convection-enhanced drug delivery for glioblastoma: a review

INTRODUCTION

Convection-enhanced delivery (CED) is a method of targeted, local drug delivery to the central nervous system (CNS) that bypasses the blood-brain barrier (BBB) and permits the delivery of high-dose therapeutics to large volumes of interest while limiting associated systemic toxicities. Since its inception, CED has undergone considerable preclinical and clinical study as a safe method for treating glioblastoma (GBM). However, the heterogeneity of both, the surgical procedure and the mechanisms of action of the agents studied-combined with the additional costs of performing a trial evaluating CED-has limited the field's ability to adequately assess the durability of any potential anti-tumor responses. As a result, the long-term efficacy of the agents studied to date remains difficult to assess.

MATERIALS AND METHODS

We searched PubMed using the phrase "convection-enhanced delivery and glioblastoma". The references of significant systematic reviews were also reviewed for additional sources. Articles focusing on physiological and physical mechanisms of CED were included as well as technological CED advances.

RESULTS

We review the history and principles of CED, procedural advancements and characteristics, and outcomes from key clinical trials, as well as discuss the potential future of this promising technique for the treatment of GBM.

CONCLUSION

While the long-term efficacy of the agents studied to date remains difficult to assess, CED remains a promising technique for the treatment of GBM.

Therapeutic Delivery to Central Nervous System

Therapies for glioblastoma face several physiologic hurdles. The blood-brain barrier (BBB) and blood-brain-tumor barrier (BTB) present impediments to therapeutic delivery of drugs to the central nervous system. Strategies to disrupt or bypass the native BBB are necessary to deliver therapeutic agents. Techniques to bypass the BBB/BTB include implantable controlled-release polymer systems, intracavitary drug delivery, direct injection of viral vectors, and infusion via convection-enhanced delivery. Ideal methods and agents to accomplish the goal providing survival benefit are yet to be determined. Further development of methods to break down or bypass the BBB and BTB is necessary for patients with glioblastoma.

Intratumoral injection of hydrogel-embedded nanoparticles enhances retention in glioblastoma

Intratumoral drug delivery is a promising approach for the treatment of glioblastoma multiforme (GBM). However, drug washout remains a major challenge in GBM therapy. Our strategy, aimed at reducing drug clearance and enhancing site-specific residence time, involves the local administration of a multi-component system comprised of nanoparticles (NPs) embedded within a thermosensitive hydrogel (HG). Herein, our objective was to examine the distribution of NPs and their cargo following intratumoral administration of this system in GBM. We hypothesized that the HG matrix, which undergoes rapid gelation upon increases in temperature, would contribute towards heightened site-specific retention and permanence of NPs in tumors. BODIPY-containing, infrared dye-labeled polymeric NPs embedded in a thermosensitive HG (HG-NPs) were fabricated and characterized. Retention and distribution dynamics were subsequently examined over time in orthotopic GBM-bearing mice. Results demonstrate that the HG-NPs system significantly improved site-specific, long-term retention of both NPs and BODIPY, with co-localization analyses showing that HG-NPs covered larger areas of the tumor and the peri-tumor region at later time points. Moreover, NPs released from the HG were shown to undergo uptake by surrounding GBM cells. Findings suggest that intratumoral delivery with HG-NPs has immense potential for GBM treatment, as well as other strategies where site-specific, long-term retention of therapeutic agents is warranted.

Leveraging the interplay of nanotechnology and neuroscience: Designing new avenues for treating central nervous system disorders

Nanotechnology has the potential to open many novel diagnostic and treatment avenues for disorders of the central nervous system (CNS). In this review, we discuss recent developments in the applications of nanotechnology in CNS therapies, diagnosis and biology. Novel approaches for the diagnosis and treatment of neuroinflammation, brain dysfunction, psychiatric conditions, brain cancer, and nerve injury provide insights into the potential of nanomedicine. We also highlight nanotechnology-enabled neuroscience techniques such as electrophysiology and intracellular sampling to improve our understanding of the brain and its components. With nanotechnology integrally involved in the advancement of basic neuroscience and the development of novel treatments, combined diagnostic and therapeutic applications have begun to emerge. Nanotheranostics for the brain, able to achieve single-cell resolution, will hasten the rate in which we can diagnose, monitor, and treat diseases. Taken together, the recent advances highlighted in this review demonstrate the prospect for significant improvements to clinical diagnosis and treatment of a vast array of neurological diseases. However, it is apparent that a strong dialogue between the nanoscience and neuroscience communities will be critical for the development of successful nanotherapeutics that move to the clinic, benefit patients, and address unmet needs in CNS disorders.

Treatment Strategies in Diffuse Midline Gliomas With the H3K27M Mutation: The Role of Convection-Enhanced Delivery in Overcoming Anatomic Challenges

Diffuse midline gliomas harboring the H3 K27M mutation—including the previously named diffuse intrinsic pontine glioma (DIPG)—are lethal high-grade pediatric brain tumors that are inoperable and without cure. Despite numerous clinical trials, the prognosis remains poor, with a median survival of ~1 year from diagnosis. Systemic administration of chemotherapeutic agents is often hindered by the blood brain barrier (BBB), and even drugs that successfully cross the barrier may suffer from unpredictable distributions. The challenge in treating this deadly disease relies on effective delivery of a therapeutic agent to the bulk tumor as well as infiltrating cells. Therefore, methods that can enhance drug delivery to the brain are of great interest. Convection-enhanced delivery (CED) is a strategy that bypasses the BBB entirely and enhances drug distribution by applying hydraulic pressure to deliver agents directly and evenly into a target region. This technique reliably distributes infusate homogenously through the interstitial space of the target region and achieves high local drug concentrations in the brain. Moreover, recent studies have also shown that continuous delivery of drug over an extended period of time is safe, feasible, and more efficacious than standard single session CED. Therefore, CED represents a promising technique for treating midline tumors with the H3K27M mutation.

Brain microglia activation induced by intracranial administration of oligonucleotides and its pharmacological modulation

Oligonucleotide overloading results in type I interferonopathies such as the Aicardi-Goutiéres Syndrome, a progressive encephalopathy determined by an immune response against endogenous DNA/RNA molecules. No therapy targeting pathogenic mechanisms is available for affected patients. Accordingly, we set up an in vitro/in vivo experimental model aimed at reproducing the pathogenic mechanisms of type I interferonopathies, in order to develop an effective pharmacological modulation and toxicological alterations caused by intracranial delivery of encapsulated CpG. The in vitro model used Aicardi-Goutiéres Syndrome immortalized lymphocytes activated by interferon I and co-cultured with human astrocytes; lymphocyte neurotoxicity was attenuated by the calcineurin-inhibitor Tacrolimus and by the anti-interferon monoclonal antibody Sifalimumab. The in vivo model was set up in mice by subcutaneous injection of encapsulated CpG oligonucleotides; the immune-stimulating activity was demonstrated by cytometric analysis in the spleen. To mime pathogenesis of type I interferonopathies in the central nervous system, CpG oligonucleotides were administered intracranially in mice. In the brain, CpG overload induced a rapid activation of macrophage-like microglial cells and focal accumulation mononuclear cells. The subcutaneous administration of Tacrolimus and, more potently, Sifalimumab attenuated CpG-induced brain alterations. These findings shed light on molecular mechanisms triggered by oligonucleotides to induce brain damage. Monoclonal antibodies inhibiting interferon seem a promising therapeutic strategy to protect brain in type I interferonopathies.

Developments in Blood-Brain Barrier Penetrance and Drug Repurposing for Improved Treatment of Glioblastoma

Glioblastoma (GBM) is one of the most common, deadly, and difficult-to-treat adult brain tumors. Surgical removal of the tumor, followed by radiotherapy (RT) and temozolomide (TMZ) administration, is the current treatment modality, but this regimen only modestly improves overall patient survival. Invasion of cells into the surrounding healthy brain tissue prevents complete surgical resection and complicates treatment strategies with the goal of preserving neurological function. Despite significant efforts to increase our understanding of GBM, there have been relatively few therapeutic advances since 2005 and even fewer treatments designed to effectively treat recurrent tumors that are resistant to therapy. Thus, while there is a pressing need to move new treatments into the clinic, emerging evidence suggests that key features unique to GBM location and biology, the blood-brain barrier (BBB) and intratumoral molecular heterogeneity, respectively, stand as critical unresolved hurdles to effective therapy. Notably, genomic analyses of GBM tissues has led to the identification of numerous gene alterations that govern cell growth, invasion and survival signaling pathways; however, the drugs that show pre-clinical potential against signaling pathways mediated by these gene alterations cannot achieve effective concentrations at the tumor site. As a result, identifying BBB-penetrating drugs and utilizing new and safer methods to enhance drug delivery past the BBB has become an area of intensive research. Repurposing and combining FDA-approved drugs with evidence of penetration into the central nervous system (CNS) has also seen new interest for the treatment of both primary and recurrent GBM. In this review, we discuss emerging methods to strategically enhance drug delivery to GBM and repurpose currently-approved and previously-studied drugs using rational combination strategies.

Biodegradable PEG-poly(ω-pentadecalactone-co-p-dioxanone) nanoparticles for enhanced and sustained drug delivery to treat brain tumors

Intracranial delivery of therapeutic agents is limited by penetration beyond the blood-brain barrier (BBB) and rapid metabolism of the drugs that are delivered. Convection-enhanced delivery (CED) of drug-loaded nanoparticles (NPs) provides for local administration, control of distribution, and sustained drug release. While some investigators have shown that repeated CED procedures are possible, longer periods of sustained release could eliminate the need for repeated infusions, which would enhance safety and translatability of the approach. Here, we demonstrate that nanoparticles formed from poly(ethylene glycol)-poly(ω-pentadecalactone-co-p-dioxanone) block copolymers [PEG-poly(PDL-co-DO)] are highly efficient nanocarriers that provide long-term release: small nanoparticles (less than 100 nm in diameter) continuously released a radiosensitizer (VE822) over a period of several weeks in vitro, provided widespread intracranial drug distribution during CED, and yielded significant drug retention within the brain for over 1 week. One advantage of PEG-poly(PDL-co-DO) nanoparticles is that hydrophobicity can be tuned by adjusting the ratio of hydrophobic PDL to hydrophilic DO monomers, thus making it possible to achieve a wide range of drug release rates and drug distribution profiles. When administered by CED to rats with intracranial RG2 tumors, and combined with a 5-day course of fractionated radiation therapy, VE822-loaded PEG-poly(PDL-co-DO) NPs significantly prolonged survival when compared to free VE822. Thus, PEG-poly(PDL-co-DO) NPs represent a new type of versatile nanocarrier system with potential for sustained intracranial delivery of therapeutic agents to treat brain tumors.

Drug delivery challenges and future of chemotherapeutic nanomedicine for glioblastoma treatment

Glioblastoma (GBM) is one of the most aggressive and deadliest central nervous system tumors, and the current standard treatment is surgery followed by radiotherapy with concurrent chemotherapy. Nevertheless, the survival period is notably low. Although ample research has been performed to develop an effective therapeutic strategy for treating GBM, the success of extending patients' survival period and quality of life is limited. This review focuses on the strategies developed to address the challenges associated with drug delivery in GBM, particularly nanomedicine. The first part describes major obstacles to the development of effective GBM treatment strategies. The second part focuses on the conventional chemotherapeutic nanomedicine strategies, their limitations and the novel and advanced strategies of nanomedicine, which could be promising for GBM treatment. We also highlighted the prominence of nanomedicine clinical translation. The near future looks bright following the beginning of clinical translation of nanochemotherapy for GBM.

Nanomaterials for convection-enhanced delivery of agents to treat brain tumors

Nanomaterials represent a promising and versatile platform for the delivery of therapeutics to the brain. Treatment of brain tumors has been a long-standing challenge in the field of neuro-oncology. The current standard of care - a multimodal approach of surgery, radiation and chemotherapy - yields only a modest therapeutic benefit for patients with malignant gliomas. A major obstacle for treatment is the failure to achieve sufficient delivery of therapeutics at the tumor site. Recent advances in local drug delivery techniques, along with the development of highly effective brain-penetrating nanocarriers, have significantly improved treatment and imaging of brain tumors in preclinical studies. The major advantage of this combined strategy is the ability to optimize local therapy, by maintaining an effective and sustained concentration of therapeutics in the brain with minimal systemic toxicity. This review highlights some of the latest developments, significant advancements and current challenges in local delivery of nanomaterials for the treatment of brain tumors.

Convection-Enhanced Delivery

Convection-enhanced delivery (CED) is a promising technique that generates a pressure gradient at the tip of an infusion catheter to deliver therapeutics directly through the interstitial spaces of the central nervous system. It addresses and offers solutions to many limitations of conventional techniques, allowing for delivery past the blood-brain barrier in a targeted and safe manner that can achieve therapeutic drug concentrations. CED is a broadly applicable technique that can be used to deliver a variety of therapeutic compounds for a diversity of diseases, including malignant gliomas, Parkinson's disease, and Alzheimer's disease. While a number of technological advances have been made since its development in the early 1990s, clinical trials with CED have been largely unsuccessful, and have illuminated a number of parameters that still need to be addressed for successful clinical application. This review addresses the physical principles behind CED, limitations in the technique, as well as means to overcome these limitations, clinical trials that have been performed, and future developments.

Convection-enhanced Delivery of Therapeutics for Malignant Gliomas

Convection-enhanced delivery (CED) circumvents the blood–brain barrier by delivering agents directly into the tumor and surrounding parenchyma. CED can achieve large volumes of distribution by continuous positive-pressure infusion. Although promising as an effective drug delivery method in concept, the administration of therapeutic agents via CED is not without challenges. Limitations of distribution remain a problem in large brains, such as those of humans. Accurate and consistent delivery of an agent is another challenge associated with CED. Similar to the difficulties caused by immunosuppressive environments associated with gliomas, there are several mechanisms that make effective local drug distribution difficult in malignant gliomas. In this review, methods for local drug application targeting gliomas are discussed with special emphasis on CED. Although early clinical trials have failed to demonstrate the efficacy of CED against gliomas, CED potentially can be a platform for translating the molecular understanding of glioblastomas achieved in the laboratory into effective clinical treatments. Several clinical studies using CED of chemotherapeutic agents are ongoing. Successful delivery of effective agents should prove the efficacy of CED in the near future.

Characterization of the distribution, retention, and efficacy of internal radiation of 188Re-lipid nanocapsules in an immunocompromised human glioblastoma model

Internal radiation strategies hold great promise for glioblastoma (GB) therapy. We previously developed a nanovectorized radiotherapy that consists of lipid nanocapsules loaded with a lipophilic complex of Rhenium-188 (LNC¹⁸⁸Re-SSS). This approach resulted in an 83 % cure rate in the 9L rat glioma model, showing great promise. The efficacy of LNC¹⁸⁸Re-SSS treatment was optimized through the induction of a T-cell immune response in this model, as it is highly immunogenic. However, this is not representative of the human situation where T-cell suppression is usually encountered in GB patients. Thus, in this study, we investigated the efficacy of LNC¹⁸⁸Re-SSS in a human GB model implanted in T-cell deficient nude mice. We also analyzed the distribution and tissue retention of LNC¹⁸⁸Re-SSS. We observed that intratumoral infusion of LNCs by CED led to their complete distribution throughout the tumor and peritumoral space without leakage into the contralateral hemisphere except when large volumes were used. Seventy percent of the ¹⁸⁸Re-SSS activity was present in the tumor region 24 h after LNC¹⁸⁸Re-SSS injection and no toxicity was observed in the healthy brain. Double fractionated internal radiotherapy with LNC¹⁸⁸Re-SSS triggered survival responses in the immunocompromised human GB model with a cure rate of 50 %, which was not observed with external radiotherapy. In conclusion, LNC¹⁸⁸Re-SSS can induce long-term survival in an immunosuppressive environment, highlighting its potential for GB therapy.

Advances in drug delivery to high grade gliomas

If cancer is hard to be treated, brain cancer is even more, caused by the inability of many effective drugs given systemically to cross the blood brain and blood tumor barriers and reach adequate concentrations at the tumor sites. Effective delivery of drugs to brain cancer tissues is thus a necessary, albeit not sufficient, condition to effectively target the disease. In order to analyze the current status of research on drug delivery to high grade gliomas (HGG-WHO grades III and IV), the most frequent and aggressive brain cancers, a literature search was conducted in PubMed using the terms: "drug delivery and brain tumor" over the publication year 2015. Currently explored drug delivery techniques for HGG include the convection and permeabilization-enhanced deliveries, drug-releasing depots and Ommaya reservoirs. The efficacy/safety ratio widely varies among these techniques and the success of current efforts to increase this ratio widely varies as well.

Distribution of polymer nanoparticles by convection-enhanced delivery to brain tumors

Glioblastoma multiforme (GBM) is a fatal brain tumor characterized by infiltration beyond the margins of the main tumor mass and local recurrence after surgery. The blood-brain barrier (BBB) poses the most significant hurdle to brain tumor treatment. Convection-enhanced delivery (CED) allows for local administration of agents, overcoming the restrictions of the BBB. Recently, polymer nanoparticles have been demonstrated to penetrate readily through the healthy brain when delivered by CED, and size has been shown to be a critical factor for nanoparticle penetration. Because these brain-penetrating nanoparticles (BPNPs) have high potential for treatment of intracranial tumors since they offer the potential for cell targeting and controlled drug release after administration, here we investigated the intratumoral CED infusions of PLGA BPNPs in animals bearing either U87 or RG2 intracranial tumors. We demonstrate that the overall volume of distribution of these BPNPs was similar to that observed in healthy brains; however, the presence of tumors resulted in asymmetric and heterogeneous distribution patterns, with substantial leakage into the peritumoral tissue. Together, our results suggest that CED of BPNPs should be optimized by accounting for tumor geometry, in terms of location, size and presence of necrotic regions, to determine the ideal infusion site and parameters for individual tumors.

Promising approaches to circumvent the blood-brain barrier: progress, pitfalls and clinical prospects in brain cancer

Brain drug delivery is a major challenge for therapy of central nervous system (CNS) diseases. Biochemical modifications of drugs or drug nanocarriers, methods of local delivery, and blood-brain barrier (BBB) disruption with focused ultrasound and microbubbles are promising approaches which enhance transport or bypass the BBB. These approaches are discussed in the context of brain cancer as an example in CNS drug development. Targeting to receptors enabling transport across the BBB offers noninvasive delivery of small molecule and biological cancer therapeutics. Local delivery methods enable high dose delivery while avoiding systemic exposure. BBB disruption with focused ultrasound and microbubbles offers local and noninvasive treatment. Clinical trials show the prospects of these technologies and point to challenges for the future.

The TWEAK receptor Fn14 is a potential cell surface portal for targeted delivery of glioblastoma therapeutics

Fibroblast growth factor-inducible 14 (Fn14; TNFRSF12A) is the cell surface receptor for the tumor necrosis factor (TNF) family member TNF-like weak inducer of apoptosis (TWEAK). The Fn14 gene is normally expressed at low levels in healthy tissues but expression is significantly increased after tissue injury and in many solid tumor types, including glioblastoma (GB; formerly referred to as 'GB multiforme'). GB is the most common and aggressive primary malignant brain tumor and the current standard-of-care therapeutic regimen has a relatively small impact on patient survival, primarily because glioma cells have an inherent propensity to invade into normal brain parenchyma, which invariably leads to tumor recurrence and patient death. Despite major, concerted efforts to find new treatments, a new GB therapeutic that improves survival has not been introduced since 2005. In this review article, we summarize studies indicating that (i) Fn14 gene expression is low in normal brain tissue but is upregulated in advanced brain cancers and, in particular, in GB tumors exhibiting the mesenchymal molecular subtype; (ii) Fn14 expression can be detected in glioma cells residing in both the tumor core and invasive rim regions, with the maximal levels found in the invading glioma cells located within normal brain tissue; and (iii)

TWEAK

Fn14 engagement as well as Fn14 overexpression can stimulate glioma cell migration, invasion and resistance to chemotherapeutic agents in vitro. We also discuss two new therapeutic platforms that are currently in development that leverage Fn14 overexpression in GB tumors as a way to deliver cytotoxic agents to the glioma cells remaining after surgical resection while sparing normal healthy brain cells.