Maximising coverage of brain structures using controlled reflux, convection-enhanced delivery and the recessed step catheter

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.

Dopaminergic Cell Replacement for Parkinson's Disease: Addressing the Intracranial Delivery Hurdle

Parkinson's disease (PD) is an increasingly prevalent neurological disorder, affecting more than 8.5 million individuals worldwide. α-Synucleinopathy in PD is considered to cause dopaminergic neuronal loss in the substantia nigra, resulting in characteristic motor dysfunction that is the target for current medical and surgical therapies. Standard treatment for PD has remained unchanged for several decades and does not alter disease progression. Furthermore, symptomatic therapies for PD are limited by issues surrounding long-term efficacy and side effects. Cell replacement therapy (CRT) presents an alternative approach that has the potential to restore striatal dopaminergic input and ameliorate debilitating motor symptoms in PD. Despite promising pre-clinical data, CRT has demonstrated mixed success clinically. Recent advances in graft biology have renewed interest in the field, resulting in several worldwide ongoing clinical trials. However, factors surrounding the effective neurosurgical delivery of cell grafts have remained under-studied, despite their significant potential to influence therapeutic outcomes. Here, we focus on the key neurosurgical factors to consider for the clinical translation of CRT. We review the instruments that have been used for cell graft delivery, highlighting current features and limitations, while discussing how future devices could address these challenges. Finally, we review other novel developments that may enhance graft accessibility, delivery, and efficacy. Challenges surrounding neurosurgical delivery may critically contribute to the success of CRT, so it is crucial that we address these issues to ensure that CRT does not falter at the final hurdle.

Evaluating drug distribution in children and young adults with diffuse midline glioma of the pons (DIPG) treated with convection-enhanced drug delivery

AIMS

To determine an imaging protocol that can be used to assess the distribution of infusate in children with DIPG treated with CED.

METHODS

13 children diagnosed with DIPG received between 3.8 and 5.7 ml of infusate, through two pairs of catheters to encompass tumor volume on day 1 of cycle one of treatment. Volumetric T2-weighted (T2W) and diffusion-weighted MRI imaging (DWI) were performed before and after day 1 of CED. Apparent diffusion coefficient (ADC) maps were calculated. The tumor volume pre and post CED was automatically segmented on T2W and ADC on the basis of signal intensity. The ADC maps pre and post infusion were aligned and subtracted to visualize the infusate distribution.

RESULTS

There was a significant increase (p < 0.001) in mean ADC and T2W signal intensity (SI) ratio and a significant (p < 0.001) increase in mean tumor volume defined by ADC and T2W SI post infusion (mean ADC volume pre: 19.8 ml, post: 24.4 ml; mean T2W volume pre: 19.4 ml, post: 23.4 ml). A significant correlation (p < 0.001) between infusate volume and difference in ADC/T2W SI defined tumor volume was observed (ADC, r = 0.76; T2W, r = 0.70). Finally, pixel-by-pixel subtraction of the ADC maps pre and post infusion demonstrated a volume of high signal intensity, presumed infusate distribution.

CONCLUSIONS

ADC and T2W MRI are proposed as a combined parameter method for evaluation of CED infusate distribution in brainstem tumors in future clinical trials.

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.

Overcoming translational barriers in H3K27-altered diffuse midline glioma: Increasing the drug-tumor residence time

Background

H3K27-altered diffuse midline glioma (DMG) is the deadliest pediatric brain tumor; despite intensive research efforts, every clinical trial to date has failed. Is this because we are choosing the wrong drugs? Or are drug delivery and other pharmacokinetic variables at play? We hypothesize that the answer is likely a combination, where optimization may result in a much needed novel therapeutic approach.

Methods

We used in vitro drug screening, patient samples, and shRNA knockdown models to identify an upregulated target in DMG. A single small molecule protein kinase inhibitor with translational potential was selected for systemic and direct, loco-regional delivery to patient-derived xenografts (PDX) and genetically engineered mouse models (GEMM). Pharmacokinetic studies were conducted in non-tumor bearing rats.

Results

Aurora kinase (AK) inhibitors demonstrated strong antitumor effects in DMG drug screens. Additional in vitro studies corroborated the importance of AK to DMG survival. Systemic delivery of alisertib showed promise in subcutaneous PDX but not intracranial GEMM and PDX models. Repeated loco-regional drug administration into the tumor through convection-enhanced delivery (CED) was equally inefficacious, and pharmacokinetic studies revealed rapid clearance of alisertib from the brain. In an effort to increase the drug to tumor residence time, continuous CED over 7 days improved drug retention in the rodent brainstem and significantly extended survival in both orthotopic PDXs and GEMMs.

Conclusions

These studies provide evidence for increasing drug-tumor residence time of promising targeted therapies via extended CED as a valuable treatment strategy for DMG.

Solid Fiber Inside of Capillary and Modified Fusion-Spliced Fiber Optic Microneedle Devices for Improved Light Transmission Efficiency

Convection-enhanced delivery (CED) is a drug delivery technique used to deliver therapeutics directly to the brain and is a continually evolving technique to treat glioblastoma. Early versions of CED have proven to result in inadequate drug volume dispersed (Vd), increasing the likelihood of tumor recurrence. Fiber optic microneedle devices (FMDs) with the ability to deliver fluid and thermal energy simultaneously have shown an ability to increase Vd, but FMDs have historically had low light transmission efficiency. In this study, we present a new fabrication method, solid fiber inside capillary (SFIC) FMD, and a modified fusion splicing (FS) method with the goal of increasing light delivery efficiency. The modified FS FMD resulted in an increase in light transmission efficiency between 49% and 173% compared to previous prototypes. However, the FS FMD resulted in significantly lower transmission efficiencies compared to the SFIC FMD (p ≤ 0.04) and FS FMDs perform much worse when light-absorptive materials, like black dye, are placed in the bore. The light absorption of a candidate cytotoxic agent, QUAD-CTX, appear to be similar to water, and light delivery through FS FMDs filled with QUAD-CTX achieves a transmission efficiency of 85.6 ± 5.4%. The fabrication process of the SFIC FMDs results in extremely fragile FMDs. Therefore, the use of a modified FS FMD fabrication process appears to be better suited for balancing the desire to increase light transmission efficiency while retaining a sturdy FMD construction.

In vivo measurement of human brain material properties under quasi-static loading

Computational modelling of the brain requires accurate representation of the tissues concerned. Mechanical testing has numerous challenges, in particular for low strain rates, like neurosurgery, where redistribution of fluid is biomechanically important. A finite-element (FE) model was generated in FEBio, incorporating a spring element/fluid-structure interaction representation of the pia-arachnoid complex (PAC). The model was loaded to represent gravity in prone and supine positions. Material parameter identification and sensitivity analysis were performed using statistical software, comparing the FE results to human in vivo measurements. Results for the brain Ogden parameters µ, α and k yielded values of 670 Pa, -19 and 148 kPa, supporting values reported in the literature. Values of the order of 1.2 MPa and 7.7 kPa were obtained for stiffness of the pia mater and out-of-plane tensile stiffness of the PAC, respectively. Positional brain shift was found to be non-rigid and largely driven by redistribution of fluid within the tissue. To the best of our knowledge, this is the first study using in vivo human data and gravitational loading in order to estimate the material properties of intracranial tissues. This model could now be applied to reduce the impact of positional brain shift in stereotactic neurosurgery.

Constant Pressure Convection-Enhanced Delivery Increases Volume Dispersed With Catheter Movement in Agarose

Convection-enhanced delivery (CED) has been extensively studied for drug delivery to the brain due to its inherent ability to bypass the blood-brain barrier. Unfortunately, CED has also been shown to inadequately distribute therapeutic agents over a large enough targeted tissue volume to be clinically beneficial. In this study, we explore the use of constant pressure infusions in addition to controlled catheter movement as a means to increase volume dispersed (Vd) in an agarose gel brain tissue phantom. Constant flow rate and constant pressure infusions were conducted with a stationary catheter, a catheter retracting at a rate of 0.25 mm/min, and a catheter retracting at a rate of 0.5 mm/min. The 0.25 mm/min and 0.5 mm/min retracting constant pressure catheters resulted in significantly larger Vd compared to any other group, with a 105% increase and a 155% increase compared to the stationary constant flow rate catheter, respectively. These same constant pressure retracting infusions resulted in a 42% and 45% increase in Vd compared to their constant flow rate counterparts. Using constant pressure infusions coupled with controlled catheter movement appears to have a beneficial effect on Vd in agarose gel. Furthermore, constant pressure infusions reveal the fundamental limitation of flow-driven infusions in both controlled catheter movement protocols as well as in stationary protocols where maximum infusion volume can never be reliably obtained.

Convection-enhanced delivery with controlled catheter movement: A parametric finite element analysis

Convection-enhanced delivery (CED) is an investigational method for delivering therapeutics directly to the brain for the treatment of glioblastoma. However, it has not become a common clinical therapy due to an inability of CED treatments to deliver therapeutics in a large enough tissue volume to fully saturate the target region. We have recently shown that the combination of controlled catheter movement and constant pressure infusions can be used to significantly increase volume dispersed (Vd ) in an agarose gel brain tissue phantom. In the present study, we develop a computational model to predict Vd achieved by various retraction rates with both constant pressure and constant flow rate infusions. An increase in Vd is achieved with any movement rate, but increase in Vd between successive movement rates drops off at rates above 0.3-0.35 mm/min. Finally, we found that infusions with retraction result in a more even distribution in concentration level compared to the stationary catheter, suggesting a potential increased ability for moving catheters to have a therapeutic impact regardless of the required therapeutic concentration level.

Drug delivery across the blood-brain barrier for the treatment of pediatric brain tumors - An update

Even though the last decade has seen a surge in the identification of molecular targets and targeted therapies in pediatric brain tumors, the blood brain barrier (BBB) remains a significant challenge in systemic drug delivery. This continues to undermine therapeutic efficacy. Recent efforts have identified several strategies that can facilitate enhanced drug delivery into pediatric brain tumors. These include invasive methods such as intra-arterial, intrathecal, and convection enhanced delivery and non-invasive technologies that allow for transient access across the BBB, including focused ultrasound and nanotechnology. This review discusses current strategies that are being used to enhance delivery of different therapies across the BBB to the tumor site - a major unmet need in pediatric neuro-oncology.

Design and Validation of a Multi-Point Injection Technology for MR-Guided Convection Enhanced Delivery in the Brain

Convection enhanced delivery (CED) allows direct intracranial administration of neuro-therapeutics. Success of CED relies on specific targeting and broad volume distributions (V_D). However, to prevent off-target delivery and tissue damage, CED is typically conducted with small cannulas and at low flow rates, which critically limit the maximum achievable V_D. Furthermore, in applications such as gene therapy requiring injections of large fluid volumes into broad subcortical regions, low flow rates translate into long infusion times and multiple surgical trajectories. The cannula design is a major limiting factor in achieving broad V_D, while minimizing infusion time and backflow. Here we present and validate a novel multi-point cannula specifically designed to optimize distribution and delivery time in MR-guided intracranial CED of gene-based therapeutics. First, we evaluated the compatibility of our cannula with MRI and common viral vectors for gene therapy. Then, we conducted CED tests in agarose brain phantoms and benchmarked the results against single-needle delivery. 3T MRI in brain phantoms revealed minimal susceptibility-induced artifacts, comparable to the device dimensions. Benchtop CED of adeno-associated virus demonstrated no viral loss or inactivation. CED in agarose brain phantoms at 3, 6, and 9 μL/min showed >3x increase in volume distribution and 60% time reduction compared to single-needle delivery. This study confirms the validity of a multi-point delivery approach for improving infusate distribution at clinically-compatible timescales and supports the feasibility of our novel cannula design for advancing safety and efficacy of MR-guided CED to the central nervous system.

Transduction profiles in minipig following MRI guided delivery of AAV-5 into thalamic and corona radiata areas

BACKGROUND

As a step towards clinical use of AAV-mediated gene therapy, brains of large animals are used to settle delivery parameters as most brain connections, and relative sizes in large animals and primates, are reasonably common. Prior to application in the clinic, approaches that have shown to be successful in rodent models are tested in larger animal species, such as dogs, non-human primates, and in this case, minipigs.

NEW METHOD

We evaluated alternate delivery routes to target the basal ganglia by injections into the more superficial corona radiata, and, deeper into the brain, the thalamus. Anatomically known connections can be used to predict the expression of the transgene following infusion of AAV5. For optimal control over delivery of the vector with regards to anatomical location in the brain and spread in the tissue, we have used magnetic resonance image-guided convection-enhanced diffusion delivery.

RESULTS

While the transduction of the cortex was observed, only partial transduction of the basal ganglia was achieved via the corona radiata. Thalamic administration, on the other hand, resulted in widespread transduction from the midbrain to the frontal cortex COMPARISON WITH EXISTING METHODS: Compared to other methods, such as delivery directly to the striatum, thalamic injection may provide an alternative when for instance, injection into the basal ganglia directly is not feasible.

CONCLUSIONS

The study results suggest that thalamic administration of AAV5 has significant potential for indications where the transduction of specific areas of the brain is required.

Convection-Enhanced Delivery in Children: Techniques and Applications

Since its first description in 1994, convection-enhanced delivery (CED) has become a reliable method of administering drugs directly into the brain parenchyma. More predictable and effective than simple diffusion, CED bypasses the challenging boundary of the blood brain barrier, which has frustrated many attempts at delivering large molecules or polymers into the brain parenchyma. Although most of the clinical work with CED has been carried out on adults with incurable neoplasms, principally glioblastoma multiforme, an increasing number of studies have recognized its potential for paediatric applications, which now include treatment of currently incurable brain tumours such as diffuse intrinsic pontine glioma (DIPG), as well as metabolic and neurotransmitter diseases. The roadmap for the development of hardware and use of pharmacological agents in CED has been well-established, and some neurosurgical centres throughout the world have successfully undertaken clinical trials, admittedly mostly early phase, on the basis of in vitro, small animal and large animal pre-clinical foundations. However, the clinical efficacy of CED, although theoretically logical, has yet to be unequivocally demonstrated in a clinical trial; this applies particularly to neuro-oncology.This review aims to provide a broad description of the current knowledge of CED as applied to children. It reviews published studies of paediatric CED in the context of its wider history and developments and underlines the challenges related to the development of hardware, the selection of pharmacological agents, and gene therapy. It also reviews the difficulties related to the development of clinical trials involving CED and looks towards its potential disease-modifying opportunities in the future.

New Developments in the Pathogenesis, Therapeutic Targeting, and Treatment of H3K27M-Mutant Diffuse Midline Glioma

H3K27M-mutant diffuse midline gliomas (DMGs) are rare childhood central nervous system tumors that carry a dismal prognosis. Thus, innovative treatment approaches are greatly needed to improve clinical outcomes for these patients. Here, we discuss current trends in research of H3K27M-mutant diffuse midline glioma. This review highlights new developments of molecular pathophysiology for these tumors, as they relate to epigenetics and therapeutic targeting. We focus our discussion on combinatorial therapies addressing the inherent complexity of treating H3K27M-mutant diffuse midline gliomas and incorporating recent advances in immunotherapy, molecular biology, genetics, radiation, and stereotaxic surgical diagnostics.

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.

The Challenge of Gene Therapy for Neurological Diseases: Strategies and Tools to Achieve Efficient Delivery to the Central Nervous System

For more than 10 years, gene therapy for neurological diseases has experienced intensive research growth and more recently therapeutic interventions for multiple indications. Beneficial results in several phase 1/2 clinical studies, together with improved vector technology have advanced gene therapy for the central nervous system (CNS) in a new era of development. Although most initial strategies have focused on orphan genetic diseases, such as lysosomal storage diseases, more complex and widespread conditions like Alzheimer's disease, Parkinson's disease, epilepsy, or chronic pain are increasingly targeted for gene therapy. Increasing numbers of applications and patients to be treated will require improvement and simplification of gene therapy protocols to make them accessible to the largest number of affected people. Although vectors and manufacturing are a major field of academic research and industrial development, there is a growing need to improve, standardize, and simplify delivery methods. Delivery is the major issue for CNS therapies in general, and particularly for gene therapy. The blood-brain barrier restricts the passage of vectors; strategies to bypass this obstacle are a central focus of research. In this study, we present the different ways that can be used to deliver gene therapy products to the CNS. We focus on results obtained in large animals that have allowed the transfer of protocols to human patients and have resulted in the generation of clinical data. We discuss the different routes of administration, their advantages, and their limitations. We describe techniques, equipment, and protocols and how they should be selected for safe delivery and improved efficiency for the next generation of gene therapy trials for CNS diseases.

Radiation therapy combined with intracerebral convection-enhanced delivery of cisplatin or carboplatin for treatment of the F98 rat glioma

BACKGROUND

The purpose of this review is to summarize our own experimental studies carried out over a 13-year period of time using the F98 rat glioma as model for high grade gliomas. We evaluated a binary chemo-radiotherapeutic modality that combines either cisplatin (CDDP) or carboplatin, administered intracerebrally (i.c.) by means of convection-enhanced delivery (CED) or osmotic pumps, in combination with either synchrotron or conventional X-irradiation.

METHODS

F98 glioma cells were implanted stereotactically into the brains of syngeneic Fischer rats. Approximately 14 days later, either CDDP or carboplatin was administered i.c. by CED, followed 24 h later by radiotherapy using either a synchrotron or, subsequently, megavoltage linear accelerators (LINAC).

RESULTS

CDDP was administered at a dose of 3 µg in 5 µL, followed 24 h later with an irradiation dose of 15 Gy or carboplatin at a dose of 20 µg in 10 µL, followed 24 h later with 3 fractions of 8 Gy each, at the source at the European Synchrotron Radiation Facility (ESRF). This resulted in a median survival time (MeST) > 180 days with 33% long term survivors (LTS) for CDDP and a MeST > 60 days with 8 to 22% LTS, for carboplatin. Subsequently it became apparent that comparable survival data could be obtained with megavoltage X-irradiation using a LINAC source. The best survival data were obtained with a dose of 72 µg of carboplatin administered by means of Alzet® osmotic pumps over 7 days. This resulted in a MeST of > 180 days, with 55% LTS. Histopathologic examination of all the brains of the surviving rats revealed no residual tumor cells or evidence of significant radiation related effects.

CONCLUSIONS

The results obtained using this combination therapy has, to the best of our knowledge, yielded the most promising survival data ever reported using the F98 glioma model.

Controlled Catheter Movement Affects Dye Dispersal Volume in Agarose Gel Brain Phantoms

The standard of care for treatment of glioblastoma results in a mean survival of only 12 to 15 months. Convection-enhanced delivery (CED) is an investigational therapy to treat glioblastoma that utilizes locoregional drug delivery via a small-caliber catheter placed into the brain parenchyma. Clinical trials have failed to reach their endpoints due to an inability of standard catheters to fully saturate the entire brain tumor and its margins. In this study, we examine the effects of controlled catheter movement on dye dispersal volume in agarose gel brain tissue phantoms. Four different catheter movement control protocols (stationary, continuous retraction, continuous insertion, and intermittent insertion) were applied for a single-port stepped catheter capable of intrainfusion movement. Infusions of indigo carmine dye into agarose gel brain tissue phantoms were conducted during the controlled catheter movement. The dispersal volume (Vd), forward dispersal volume (Vdf), infusion radius, backflow distance, and forward flow distance were quantified for each catheter movement protocol using optical images recorded throughout the experiment. Vd and Vdf for the retraction and intermittent insertion groups were significantly higher than the stationary group. The stationary group had a small but significantly larger infusion radius than either the retracting or the intermittent insertion groups. The stationary group had a greater backflow distance and lower forward flow distance than either the retraction or the intermittent insertion groups. Continuous retraction of catheters during CED treatments can result in larger Vd than traditional stationary catheters, which may be useful for improving the outcomes of CED treatment of glioblastoma. However, catheter design will be crucial in preventing backflow of infusate up the needle tract, which could significantly alter both the Vd and shape of the infusion.

Electrokinetic Convection-Enhanced Delivery of Solutes to the Brain

Pressure-induced infusion of solutions into brain tissue is used both in research and in medicine. In medicine, convection enhanced delivery (CED) may be used to deliver agents to localized areas of the brain, such as with gene therapy to functional targets or with deep tumors not readily amenable to resection. However, clinical trials have demonstrated mixed results from CED. CED is limited by a lack of control of the infusion flow path and may cause damage or even neurological deficits due to neuronal distortion. In laboratory research, infusions may be achieved using pressure or using brief bursts of electrical current in iontophoresis. Electrokinetic convection enhanced delivery (ECED) has the potential to deliver drugs and other bioactive substances to local regions in the brain with improved control and lower applied pressures than pressure-based CED. ECED improves control over the infusion profile because the fluid follows the electrical current path and thus can be directed. Both small molecules and macromolecules can be delivered. Here we demonstrate proof-of-principal that electrokinetic (electroosmosis and electrophoresis) convection-enhanced delivery is a viable means for delivering solutes to the brain. We assessed the volume of tissue exposed to the infusates tris(2,2'-bipyridine)ruthenium(II) and fluorescent dextrans. Control of the direction of the transport was also achieved over distances ranging from several hundred micrometers to more than 4 mm. Electrokinetic delivery has the potential to improve control over infusions.

Convection Enhanced Delivery for Diffuse Intrinsic Pontine Glioma: Review of a Single Institution Experience

Diffuse intrinsic pontine gliomas (DIPGs) are a pontine subtype of diffuse midline gliomas (DMGs), primary central nervous system (CNS) tumors of childhood that carry a terrible prognosis. Because of the highly infiltrative growth pattern and the anatomical position, cytoreductive surgery is not an option. An initial response to radiation therapy is invariably followed by recurrence; mortality occurs approximately 11 months after diagnosis. The development of novel therapeutics with great preclinical promise has been hindered by the tightly regulated blood-brain barrier (BBB), which segregates the tumor comportment from the systemic circulation. One possible solution to this obstacle is the use of convection enhanced delivery (CED), a local delivery strategy that bypasses the BBB by direct infusion into the tumor through a small caliber cannula. We have recently shown CED to be safe in children with DIPG (NCT01502917). In this review, we discuss our experience with CED, its advantages, and technical advancements that are occurring in the field. We also highlight hurdles that will likely need to be overcome in demonstrating clinical benefit with this therapeutic strategy.

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.