Prolonged convection-enhanced delivery into the rat brainstem

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.

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.

Status Quo and Trends of Intra-Arterial Therapy for Brain Tumors: A Bibliometric and Clinical Trials Analysis

Intra-arterial drug delivery circumvents the first-pass effect and is believed to increase both efficacy and tolerability of primary and metastatic brain tumor therapy. The aim of this update is to report on pertinent articles and clinical trials to better understand the research landscape to date and future directions. Elsevier's Scopus and ClinicalTrials.gov databases were reviewed in August 2021 for all possible articles and clinical trials of intra-arterial drug injection as a treatment strategy for brain tumors. Entries were screened against predefined selection criteria and various parameters were summarized. Twenty clinical trials and 271 articles satisfied all inclusion criteria. In terms of articles, 201 (74%) were primarily clinical and 70 (26%) were basic science, published in a total of 120 different journals. Median values were: publication year, 1986 (range, 1962-2021); citation count, 15 (range, 0-607); number of authors, 5 (range, 1-18). Pertaining to clinical trials, 9 (45%) were phase 1 trials, with median expected start and completion years in 2011 (range, 1998-2019) and 2022 (range, 2008-2025), respectively. Only one (5%) trial has reported results to date. Glioma was the most common tumor indication reported in both articles (68%) and trials (75%). There were 215 (79%) articles investigating chemotherapy, while 13 (65%) trials evaluated targeted therapy. Transient blood-brain barrier disruption was the commonest strategy for articles (27%) and trials (60%) to optimize intra-arterial therapy. Articles and trials predominately originated in the United States (50% and 90%, respectively). In this bibliometric and clinical trials analysis, we discuss the current state and trends of intra-arterial therapy for brain tumors. Most articles were clinical, and traditional anti-cancer agents and drug delivery strategies were commonly studied. This was reflected in clinical trials, of which only a single study had reported outcomes. We anticipate future efforts to involve novel therapeutic and procedural strategies based on recent advances in the field.

Deformational changes after convection-enhanced delivery in the pediatric brainstem

OBJECTIVE

In the brainstem, there are concerns regarding volumetric alterations following convection-enhanced delivery (CED). The relationship between distribution volume and infusion volume is predictably greater than one. Whether this translates into deformational changes and influences clinical management is unknown. As part of a trial using CED for diffuse intrinsic pontine glioma (DIPG), the authors measured treatment-related volumetric alterations in the brainstem and ventricles.

METHODS

Enrolled patients underwent a single infusion of radioimmunotherapy. Between 2012 and 2019, 23 patients with volumetric pre- and postoperative day 1 (POD1) and day 30 (POD30) MRI scans were analyzed using iPlan® Flow software for semiautomated volumetric measurements of the ventricles and pontine segment of the brainstem.

RESULTS

Children in the study had a mean age of 7.7 years (range 2-18 years). The mean infusion volume was 3.9 ± 1.7 ml (range 0.8-8.8 ml). Paired t-tests demonstrated a significant increase in pontine volume immediately following infusion (p < 0.0001), which trended back toward baseline by POD30 (p = 0.046; preoperative 27.6 ± 8.4 ml, POD1 30.2 ± 9.0 ml, POD30 29.5 ± 9.4 ml). Lateral ventricle volume increased (p = 0.02) and remained elevated on POD30 (p = 0.04; preoperative 23.5 ± 15.4 ml, POD1 26.3 ± 16.0, POD30 28.6 ± 21.2). Infusion volume had a weak, positive correlation with pontine and lateral ventricle volume change (r2 = 0.22 and 0.27, respectively). Four of the 23 patients had an increase in preoperative neurological deficits at POD30. No patients required shunt placement within 90 days.

CONCLUSIONS

CED infusion into the brainstem correlates with immediate but self-limited deformation changes in the pons. The persistence of increased ventricular volume and no need for CSF diversion post-CED are inconsistent with obstructive hydrocephalus. Defining the degree and time course of these deformational changes can assist in the interpretation of neuroimaging along the DIPG disease continuum when CED is incorporated into the treatment algorithm.

Evaluating infusate parameters for direct drug delivery to the brainstem: a comparative study of convection-enhanced delivery versus osmotic pump delivery

OBJECTIVE

Convection-enhanced delivery (CED) and osmotic pump delivery both have been promoted as promising techniques to deliver drugs to pediatric diffuse intrinsic pontine gliomas (DIPGs). Correspondingly, the aim of this study was to understand how infusate molecular weight (MW), duration of delivery, and mechanism of delivery (CED or osmotic pump) affect volume of distribution (Vd) in the brainstem, to better inform drug selection and delivery in future DIPG investigations.

METHODS

A series of in vivo experiments were conducted using rat models. CED and osmotic pump delivery systems were surgically implanted in the brainstem, and different MW fluorescent dextran beads were infused either once (acute) or daily for 5 days (chronic) in a volume infused (Vi). Brainstems were harvested after the last infusion, and Vd was quantified using serial sectioning and fluorescence imaging.

RESULTS

Fluorescence imaging showed infusate uptake within the brainstem for both systems without complication. A significant inverse relationship was observed between infusate MW and Vd in all settings, which was distinctly exponential in nature in the setting of acute delivery across the 570-Da to 150-kDa range. Chronic duration and CED technique resulted in significantly greater Vd compared to acute duration or osmotic pump delivery, respectively. When accounting for Vi, acute infusion yielded significantly greater Vd/Vi than chronic infusion. The distribution in CED versus osmotic pump delivery was significantly affected by infusate MW at higher weights.

CONCLUSIONS

Here the authors demonstrate that infusate MW, duration of infusion, and infusion mechanism all impact the Vd of an infused agent and should be considered when selecting drugs and infusion parameters for novel investigations to treat DIPGs.

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.

Volume of distribution and clearance of peptide-based nanofiber after convection-enhanced delivery

OBJECTIVE Drug clearance may be a limiting factor in the clinical application of convection-enhanced delivery (CED). Peptide-based nanofibers (NFPs) have a high aspect ratio, and NFPs loaded with drugs could potentially maintain effective drug concentrations for an extended period sufficient for cancer therapy. The objective of this study was to assess the volume of distribution (Vd) and clearance of variable lengths of NFPs when administered using CED. METHODS NFPs composed of multiple methoxypolyethylene glycol (mPEG)-conjugated constructs (mPEG₂₀₀₀-KLDLKLDLKLDL-K( FITC)-CONH₂, for which FITC is fluorescein isothiocyanate) were assembled in an aqueous buffer. The NFPs were approximately 5 nm in width and were formulated into different lengths: 100 nm (NFP-100), 400 nm (NFP-400), and 1000 nm (NFP-1000). The NFP surface was covalently conjugated with multiple Cy5.5 fluorophores as the optical reporters to track the post-CED distribution. Forty-two 6- to 8-week-old Ntv-a;p53^fl/fl mice underwent CED to the striatum. Animals were killed immediately, 24 hours or 72 hours after CED. The brains were extracted and sectioned for assessing NFP Vd to volume of infusion (Vi) ratio, and clearance using fluorescence microscopy. RESULTS CED of NFPs was well tolerated by all the animals. The average Vd/Vi ratios for NFP-100, NFP-400, NFP-1000, and unconjugated positive control (free Cy5.5) were 1.87, 2.47, 1.07, and 3.0, respectively, which were statistically different (p = 0.003). The percentages remaining of the original infusion volume at 24 hours for NFP-100, -400, and -1000 were 40%, 90%, and 74%, respectively. The percentages remaining at 72 hours for NFP-100, -400, and -1000 were 15%, 30%, and 46%, respectively. Unconjugated Cy5.5 was not detected at 24 or 72 hours after CED. CONCLUSIONS CED of NFPs is feasible with Vd/Vi ratios and clearance rates comparable to other nanocarriers. Of the 3 NFPs, NFP-400 appears to provide the best distribution and slowest clearance after 24 hours. NFP provides a dynamic theranostic platform, with the potential to deliver clinically efficacious drug payload to brain tumor after CED.

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.

Advances in Molecular Imaging of Locally Delivered Targeted Therapeutics for Central Nervous System Tumors

Thanks to the recent advances in the development of chemotherapeutics, the morbidity and mortality of many cancers has decreased significantly. However, compared to oncology in general, the field of neuro-oncology has lagged behind. While new molecularly targeted chemotherapeutics have emerged, the impermeability of the blood–brain barrier (BBB) renders systemic delivery of these clinical agents suboptimal. To circumvent the BBB, novel routes of administration are being applied in the clinic, ranging from intra-arterial infusion and direct infusion into the target tissue (convection enhanced delivery (CED)) to the use of focused ultrasound to temporarily disrupt the BBB. However, the current system depends on a “wait-and-see” approach, whereby drug delivery is deemed successful only when a specific clinical outcome is observed. The shortcomings of this approach are evident, as a failed delivery that needs immediate refinement cannot be observed and corrected. In response to this problem, new theranostic agents, compounds with both imaging and therapeutic potential, are being developed, paving the way for improved and monitored delivery to central nervous system (CNS) malignancies. In this review, we focus on the advances and the challenges to improve early cancer detection, selection of targeted therapy, and evaluation of therapeutic efficacy, brought forth by the development of these new agents.

Local delivery methods of therapeutic agents in the treatment of diffuse intrinsic brainstem gliomas

Brainstem gliomas comprise 10-20% of all pediatric central nervous system (CNS) tumors and diffuse intrinsic pontine gliomas (DIPGs) account for the majority of these lesions. DIPG is a rapidly progressive disease with almost universally fatal outcomes and a median survival less than 12 months. Current standard-of-care treatment for DIPG includes radiation therapy, but its long-term survival effects are still under debate. Clinical trials investigating the efficacy of systemic administration of various therapeutic agents have been associated with disappointing outcomes. Recent efforts have focused on improvements in chemotherapeutic agents employed and in methods of localized and targeted drug delivery. This review provides an update on current preclinical and clinical studies investigating treatment options for brainstem gliomas.

On-demand pulsatile intracerebral delivery of carisbamate with closed-loop direct neurostimulation therapy in an electrically induced self-sustained focal-onset epilepsy rat model

OBJECT

The authors evaluated the preclinical feasibility of acutely stabilizing an active bihemispheric limbic epileptic circuit using closed-loop direct neurostimulation therapy in tandem with "on-demand'" convection-enhanced intracerebral delivery of the antiepileptic drug (AED) carisbamate. A rat model of electrically induced self-sustained focal-onset epilepsy was employed.

METHODS

A 16-contact depth-recording microelectrode was implanted bilaterally in the dentate gyrus (DG) of the hippocampus of Fischer 344 rats. The right microelectrode array included an integrated microcatheter for drug delivery at the distal tip. Bihemispheric spontaneous self-sustained limbic status epilepticus (SSLSE) was induced in freely moving rats using a 90-minute stimulation paradigm delivered to the right medial perforant white matter pathway. Immediately following SSLSE induction, closed-loop right PP stimulation therapy concurrent with on-demand nanoboluses of the AED [(14)C]-carisbamate (n = 4), or on-demand [(14)C]-carisbamate alone (n = 4), was introduced for a mean of 10 hours. In addition, 2 reference groups received either closed-loop stimulation therapy alone (n = 4) or stimulation therapy with saline vehicle only (n = 4). All animals were sacrificed after completing the specified therapy regimen. In situ [(14)C]-autoradiography was used to determine AED distribution.

RESULTS

Closed-loop direct stimulation therapy delivered unilaterally in the right PP aborted ictal runs detected in either ipsi- or contralateral hippocampi. Freely moving rats receiving closed-loop direct stimulation therapy with ondemand intracerebral carisbamate delivery experienced a significant reduction in seizure frequency (p < 0.001) and minimized seizure frequency variability during the final 50% of the therapy/recording session compared with closed-loop stimulation therapy alone.

CONCLUSIONS

Unilateral closed-loop direct stimulation therapy delivered to afferent hippocampal white matter pathways concurrent with on-demand ipsilateral intracerebral delivery of nano-bolused carisbamate can rapidly decrease the frequency of electrographic seizures in an active bihemispheric epileptic network. Additionally, direct pulsatile delivery of carisbamate can stabilize seizure frequency variability compared with direct stimulation therapy alone.

Convection enhanced delivery of carmustine to the murine brainstem: a feasibility study

BACKGROUND

Systemic delivery of therapeutic agents remains ineffective against diffuse intrinsic pontine glioma (DIPG), possibly due to an intact blood-brain-barrier (BBB) and to dose-limiting toxicity of systemic chemotherapeutic agents. Convection-enhanced delivery (CED) into the brainstem may provide an effective local delivery alternative for DIPG patients.

NEW METHOD

The aim of this study is to develop a method to perform CED into the murine brainstem and to test this method using the chemotherapeutic agent carmustine (BiCNU). To this end, a newly designed murine CED catheter was tested in vitro and in vivo. After determination of safety and distribution, mice bearing VUMC-DIPG-3 and E98FM-DIPG brainstem tumors were treated with carmustine dissolved in DW 5% or carmustine dissolved in 10% ethanol.

RESULTS

Our results show that CED into the murine brainstem is feasible and well tolerated by mice with and without brainstem tumors. CED of carmustine dissolved in 5% DW increased median survival of mice with VUMC-DIPG-3 and E98FM-DIPG tumors with 35% and 25% respectively. Dissolving carmustine in 10% ethanol further improved survival to 45% in mice with E98FM-DIPG tumors.

COMPARISON WITH EXISTING METHODS

Since genetically engineered and primary DIPG models are currently only available in mice, murine CED studies have clear advantages over CED studies in other animals.

CONCLUSION

CED in the murine brainstem can be performed safely, is well tolerated and can be used to study efficacy of chemotherapeutic agents orthotopically. These results set the foundation for more CED studies in murine DIPG models.

The potential of theragnostic ¹²⁴I-8H9 convection-enhanced delivery in diffuse intrinsic pontine glioma

BACKGROUND

Reasons for failure in prior human glioma convection-enhanced delivery (CED) clinical trials remain unclear. Concentration-dependent volume of distribution (Vd) measurement of CED-infused agents in the human brain is challenging and highlights a potential technical shortcoming. Activity of iodine isotope 124 ((124)I ) in tissue can be directly measured in vivo with high resolution via PET. With the potential therapeutic utility of radioimmunotherapy, we postulate (124)I conjugated to the antiglioma monoclonal antibody 8H9 may serve as a "theragnostic" agent delivered via CED to diffuse intrinsic pontine glioma.

METHODS

Fifteen rats underwent CED of 0.1-1.0 mCi of (131)I-8H9 to the pons for toxicity evaluation. Six additional rats underwent CED of 10 µCi of (124)I-8H9 to the pons for dosimetry, with serial microPET performed for 1 week. Two primates underwent CED of gadolinium-albumin and 1.0 mCi of (124)I-8H9 to the pons for safety and dosimetry analysis. Serial postoperative PET, blood, and CSF radioactivity counts were performed.

RESULTS

One rat (1.0 mCi (131)I-8H9 infusion) suffered toxicity necessitating early sacrifice. PET analysis in rats yielded a pontine absorbed dose of 37 Gy/mCi. In primates, no toxicity was observed, and absorbed pontine dose was 3.8 Gy/mCi. Activity decreased 10-fold with 48 h following CED in both animal models. Mean Vd was 0.14 cc(3) (volume of infusion [Vi] to Vd ratio = 14) in the rat and 6.2 cc(3) (Vd/Vi = 9.5) in primate.

CONCLUSION

The safety and feasibility of (124)I dosimetry following CED via PET is demonstrated, establishing a preclinical framework for a trial evaluating CED of (124)I-8H9 for diffuse intrinsic pontine glioma.

Convection-enhanced delivery of topotecan into diffuse intrinsic brainstem tumors in children

Convection-enhanced delivery (CED) for the treatment of malignant gliomas is a technique that can deliver chemotherapeutic agents directly into the tumor and the surrounding interstitium through sustained, low-grade positive-pressure infusion. This allows for high local concentrations of drug within the tumor while minimizing systemic levels that often lead to dose-limiting toxicity. Diffuse intrinsic pontine gliomas (DIPGs) are universally fatal childhood tumors for which there is currently no effective treatment. In this report the authors describe CED of the topoisomerase inhibitor topotecan for the treatment of DIPG in 2 children. As part of a pilot feasibility study, the authors treated 2 pediatric patients with DIPG. Stereotactic biopsy with frozen section confirmation of glial tumor was followed by placement of bilateral catheters for CED of topotecan during the same procedure. The first patient underwent CED 210 days after initial diagnosis, after radiation therapy and at the time of tumor recurrence, with a total dose of 0.403 mg in 6.04 ml over 100 hours. Her Karnofsky Performance Status (KPS) score was 60 before CED and 50 posttreatment. Serial MRI initially demonstrated a modest reduction in tumor size and edema, but the tumor progressed and the patient died 49 days after treatment. The second patient was treated 24 days after the initial diagnosis prior to radiation with a total dose of 0.284 mg in 5.30 ml over 100 hours. Her KPS score was 70 before CED and 50 posttreatment. Serial MRI similarly demonstrated an initial modest reduction in tumor size. The patient subsequently underwent fractionated radiation therapy, but the tumor progressed and she died 120 days after treatment. Topotecan delivered by prolonged CED into the brainstem in children with DIPG is technically feasible. In both patients, high infusion rates (> 0.12 ml/hr) and high infusion volumes (> 2.8 ml) resulted in new neurological deficits and reduction in the KPS score, but lower infusion rates (< 0.04 ml/hr) were well tolerated. While serial MRI showed moderate treatment effect, CED did not prolong survival in these 2 patients. More studies are needed to improve patient selection and determine the optimal flow rates for CED of chemotherapeutic agents into DIPG to maximize safety and efficacy. Clinical trial registration no.: NCT00324844.

Evaluation of the hematoma consequences, neurobehavioral profiles, and histopathology in a rat model of pontine hemorrhage

OBJECT

Primary pontine hemorrhage (PPH) represents approximately 7% of all intracerebral hemorrhages (ICHs) and is a clinical condition of which little is known. The aim of this study was to characterize the early brain injury, neurobehavioral outcome, and long-term histopathology in a novel preclinical rat model of PPH.

METHODS

The authors stereotactically infused collagenase (Type VII) into the ventral pontine tegmentum of the rats, in accordance with the most commonly affected clinical region. Measures of cerebrovascular permeability (brain water content, hemoglobin assay, Evans blue, collagen Type IV, ZO-1, and MMP-2 and MMP-9) and neurological deficit were quantified at 24 hours postinfusion (Experiment 1). Functional outcome was measured over a 30-day period using a vertebrobasilar scale (the modified Voetsch score), open field, wire suspension, beam balance, and inclined-plane tests (Experiment 2). Neurocognitive ability was determined at Week 3 using the rotarod (motor learning), T-maze (working memory), and water maze (spatial learning and memory) (Experiment 3), followed by histopathological analysis 1 week later (Experiment 4).

RESULTS

Stereotactic collagenase infusion caused dose-dependent elevations in hematoma volume, brain edema, neurological deficit, and blood-brain barrier rupture, while physiological variables remained stable. Functional outcomes mostly normalized by Week 3, whereas neurocognitive deficits paralleled the cystic cavitary lesion at 30 days. Obstructive hydrocephalus did not develop despite a clinically relevant 30-day mortality rate (approximately 54%).

CONCLUSIONS

These results suggest that the model can mimic several translational aspects of pontine hemorrhage in humans and can be used in the evaluation of potential preclinical therapeutic interventions.

The effects of temozolomide delivered by prolonged intracerebral microinfusion against the rat brainstem GBM allograft model

OBJECTIVE

Diffuse intrinsic brainstem gliomas are considered to be inoperable. We report our initial experience of temozolomide (TMZ) administration into brainstem by intracerebral (i.c.) microinfusion using a rat brainstem glioblastoma allograft model.

METHODS

Forty-eight Fischer 344 female rats were used. In a feasibility study, various doses of i.c.-TMZ (1-10 mg) were administered into the brainstem using AlzetTM pumps in order to evaluate survival rates and neurotoxicity. For tumor implantation, rats received an injection of 10(5) 9 L gliosarcoma cells. For local therapy, 5 days after inoculation, a total amount of 1 mg of TMZ or saline was administered into the brainstem at 1 μl/h over 7 days (n = 8/group). For systemic therapy, rats were treated with an orally administered maximum daily dose of 50 mg/kg TMZ for 5 consecutive days. Survival time and neurological deficit were recorded as outcome parameters.

RESULTS

In the neurotoxicity study, low dose TMZ (1 mg) was feasible to be administered into brainstem over 7 days without neurological deficit. Using high dose TMZ (5-10 mg), marked neurotoxic effect was observed. In the brainstem tumor study, survival was significantly prolonged in low dose i.c.-TMZ group compared to control rats (median survival 23.5 versus 29.5 days; p < 0.01). Systemic therapy with maximal oral-TMZ dose resulted in longer survival time compared to low dose i.c.-TMZ group (median survival 33.5 versus 29.5 days; p < 0.01).

CONCLUSIONS

i.c.-TMZ is feasible and effective against rat brainstem glioblastoma allograft. However, we could not show superior potential of i.c.-TMZ compared to oral-TMZ administration. Modification of TMZ infusion with systemic therapy warrants future investigations.

Convection-enhanced delivery of therapeutic agents into the brain

CED of therapeutic agents remains a promising strategy for treating malignant gliomas and non-neoplastic neurological diseases. Although initial clinical trials have failed to show survival benefit for new agents delivered via this approach, multiple earlier stage trials have addressed only a fraction of the myriad of technical and technological issues that surround this novel approach. Development of CED has been limited by the fact that both new technologies and novel therapeutic agents are being developed simultaneously.New trials are being planned to investigate agents that can be coinfused with radiographic tracers, as well as novel catheters that avoid problems with backflow and potentially will provide more reliable drug distribution.

Rapid microelectrode measurements and the origin and regulation of extracellular glutamate in rat prefrontal cortex

Glutamate in the prefrontal cortex (PFC) plays a significant role in several mental illnesses, including schizophrenia, addiction and anxiety. Previous studies on PFC glutamate-mediated function have used techniques that raise questions on the neuronal versus astrocytic origin of glutamate. The present studies used enzyme-based microelectrode arrays to monitor second-by-second resting glutamate levels in the PFC of awake rats. Locally applied drugs were employed in an attempt to discriminate between the neuronal or glial components of the resting glutamate signal. Local application of tetrodotoxin (sodium channel blocker), produced a significant (∼ 40%) decline in resting glutamate levels. In addition significant reductions in extracellular glutamate were seen with locally applied ω-conotoxin (MVIIC; ∼ 50%; calcium channel blocker), and the mGluR(2/3) agonist, LY379268 (∼ 20%), and a significant increase with the mGluR(2/3) antagonist LY341495 (∼ 40%), effects all consistent with a large neuronal contribution to the resting glutamate levels. Local administration of D,L-threo-β-benzyloxyaspartate (glutamate transporter inhibitor) produced an ∼ 120% increase in extracellular glutamate levels, supporting that excitatory amino acid transporters, which are largely located on glia, modulate clearance of extracellular glutamate. Interestingly, local application of (S)-4-carboxyphenylglycine (cystine/glutamate antiporter inhibitor), produced small, non-significant bi-phasic changes in extracellular glutamate versus vehicle control. Finally, pre-administration of tetrodotoxin completely blocked the glutamate response to tail pinch stress. Taken together, these results support that PFC resting glutamate levels in rats as measured by the microelectrode array technology are at least 40-50% derived from neurons. Furthermore, these data support that the impulse flow-dependent glutamate release from a physiologically -evoked event is entirely neuronally derived.

Interstitial infusion of glioma-targeted recombinant immunotoxin 8H9scFv-PE38

Monoclonal antibodies have the potential to target therapy for high-grade gliomas. Monoclonal antibody 8H9 is specific for membrane protein B7H3 and is reactive with most human high-grade gliomas. We tested the 8H9scFv-PE38 recombinant Pseudomonas immunotoxin in a preclinical model of high-grade glioma. The half maximal inhibitory concentration (IC(50)) of 8H9scFv-PE38 in vitro was determined using glioblastoma cell lines U87 and U251. Maximum tolerated infusion dose of 8H9scFv-PE38 following interstitial infusion to the striatum and pons was defined using athymic rats. Maximum tolerated infusion dose of 8H9scFv-PE38 or PBS control were interstitially delivered to athymic rats xenografted with U87 in the striatum or brain stem. Radiographic response and survivals were measured and compared between treatment groups. The in vitro IC(50) of 8H9scFv-PE38 for U87 was 1,265 ng/mL and, for U251, 91 ng/mL. The maximum tolerated infusion doses of interstitially infused 8H9scFv-PE38 to the striatum and brain stem were 0.75 and 1.8 mug, respectively. For rats harboring intracranial U87 xenografts, infusion of 8H9scFv-PE38 increased mean survival (striatum, 43.4 versus 24.6 days; brain stem, 80.6 versus 45.5 days; n = 28 total) and produced three long-term survivors past 120 days. None of the 14 placebo-treated animals survived >54 days. Tumors also showed volumetric response to infusion of 8H9scFv-PE38 by magnetic resonance imaging. Interstitial infusion of 8H9scFv-PE38 shows potential for the treatment of hemispherical and brain stem glioma. Mol Cancer Ther; 9(4); 1039-46. (c)2010 AACR.

Treatment of diffuse intrinsic brainstem gliomas: failed approaches and future strategies

Diffuse intrinsic pontine gliomas constitute ~ 60-75% of tumors found within the pediatric brainstem. These malignant lesions present with rapidly progressive symptoms such as cranial nerve, long tract, or cerebellar dysfunctions. Magnetic resonance imaging is usually sufficient to establish the diagnosis and obviates the need for surgical biopsy in most cases. The prognosis of the disease is dismal, and the median survival is < 12 months. Resection is not a viable option. Standard therapy involves radiotherapy, which produces transient neurological improvement with a progression-free survival benefit, but provides no improvement in overall survival. Clinical trials have been conducted to assess the efficacy of chemotherapeutic and biological agents in the treatment of diffuse pontine gliomas. In this review, the authors discuss recent studies in which systemic therapy was administered prior to, concomitantly with, or after radiotherapy. For future perspective, the discussion includes a rationale for stereotactic biopsies as well as possible therapeutic options of local chemotherapy in these lesions.

Local chemotherapy in the rat brainstem with multiple catheters: a feasibility study

OBJECTS

Technical aspects of local chemotherapy in inoperable brainstem gliomas by convection-enhanced delivery (CED) are still under experimental considerations. In this study, we characterize the feasibility of multiple cannula placements in the rat brainstem.

MATERIALS AND METHODS

In 38 male Fisher rats, up to three guided screws were positioned in burr holes paramedian at 2.5 mm anterior and posterior to as well as at the lambdoid suture. Using Alzettrade mark pumps (1 microl/h flow rate over 7 days) either vehicle (5% dextrose) or 0.1 mg carboplatin was delivered via one, two, or three cannulas, respectively. During cannula insertion, electrocardiogram and respiratory rate was monitored. All rats were subsequently evaluated neurologically for 8 days. For drug distribution in coronal sections, the brain tissue concentration of platinum was measured. HE staining was used to evaluate the local site of drug delivery. Heart and respiratory rate remained within normal range during surgical procedure. Neurological scoring showed only mild neurological impairment in the groups receiving two or three cannulas, which resolved after vehicle delivery. However, after carboplatin delivery, this deficit remained unchanged. Drug distribution was more homogeneous in the three cannula group. Histological slices visualized edematous changes at the sight of cannula placement.

CONCLUSION

The unilateral application of up to three cannulas in the brainstem of rats for local drug delivery studies is feasible. The remaining neurological deficit in carboplatin-treated animals underlines the need of low toxicity drugs for CED in the brainstem.

Second-by-second measures of L-glutamate in the prefrontal cortex and striatum of freely moving mice

l-Glutamate (Glu) is the main excitatory neurotransmitter in the mammalian central nervous system, and it is involved in most aspects of normal brain function, including cognition, memory and learning, plasticity, and motor movement. Although microdialysis techniques have been used to study Glu, the slow temporal resolution of the technique may be inadequate to properly examine tonic and phasic Glu. Thus, our laboratory has developed an enzyme-based microelectrode array (MEA) with fast response time and low detection limits for Glu. We have modified the MEA design to allow for reliable measures in the brain of awake, freely moving mice. In this study, we chronically implanted the MEA in prefrontal cortex (PFC) or striatum (Str) of awake, freely moving C57BL/6 mice. We successfully measured Glu levels 7 days postimplantation without loss of MEA sensitivity. In addition, we determined resting (tonic) Glu levels to be 3.3 microM in the PFC and 5.0 microM in the Str. Resting Glu levels were subjected to pharmacological manipulation with tetrodotoxin (TTX) and dl-threo-beta-hydroxyaspartate (THA). TTX significantly (p < 0.05) decreased resting Glu by 20%, whereas THA significantly (p < 0.05) increased resting Glu by 60%. Taken together, our data show that chronic recordings of tonic and phasic clearance of exogenously applied Glu can be carried out in awake mice for at least 7 days in vivo, allowing for longer term studies of Glu regulation.

A rat model of pontine hemorrhage

Approximately 15% of all strokes are due to intracerebral hemorrhage, and of these, 5 to 9% will occur in the pons, with mortality approximately 60% of the time. However, there is not an adequate animal model to fully address this important clinical problem. To this end, pontine hemorrhage was induced in rats using stereotaxic injection of 0.15 units of collagenase. At 24, 48, and 72h (n = 4 per group), the hemorrhagic volume, brain water content, body temperature, and neurological function (corner turn, inclined plane, and neurological deficit score) were assessed. All tested parameters were significantly increased, compared to sham, without any differences between time points. Furthermore, the extent of brainstem edema was highly correlated with neurological score, inclined plane, and body temperature. This new pontine hemorrhage rat model demonstrated brain edema and neurological deficits, and can be used to test treatment strategies for pontine hemorrhage.

Prolonged attenuation of amygdala-kindled seizure measures in rats by convection-enhanced delivery of the N-type calcium channel antagonists omega-conotoxin GVIA and omega-conotoxin MVIIA

Convection-enhanced delivery (CED) permits the homogeneous distribution of therapeutic agents throughout localized regions of the brain parenchyma without causing tissue damage as occurs with bolus injection. Here, we examined whether CED infusion of the N-type calcium channel antagonists omega-conotoxin GVIA (omega-CTX-G) and omega-conotoxin MVIIA (omega-CTX-M) can attenuate kindling measures in fully amygdala-kindled rats. Rats were implanted with a combination infusion cannula-stimulating electrode assembly into the right basolateral amygdala. Fully kindled animals received infusions of vehicle, omega-CTX-G (0.005, 0.05, and 0.5 nmol), omega-CTX-M (0.05, 0.15, and 0.5 nmol), proteolytically inactivated omega-CTX-M (0.5 nmol), or carbamazepine (500 nmol) into the stimulation site. CED of omega-CTX-G and omega-CTX-M over a 20-min period resulted in a dose-dependent increase in the afterdischarge threshold and a decrease in the afterdischarge duration and behavioral seizure score and duration during a period of 20 min to 1 week after the infusion, indicating an inhibitory effect on the triggering and expression of kindled seizures. The protective effects of omega-conotoxins reached a maximum at 48 h postinfusion, and then they gradually resolved over the next 5 days. In contrast, carbamazepine was active at 20 min but not at 24 h after the infusion, whereas CED of vehicle or inactivated omega-CTX-M had no effect. Except for transient tremor in some rats receiving the highest toxin doses, no adverse effects were observed. These results indicate that local CED of high-molecular-weight presynaptic N-type calcium channel blockers can produce long-lasting inhibition of brain excitability and that they may provide prolonged seizure protection in focal seizure disorders.

Brainstem tumors: where are we today?

Brainstem tumors comprise 10-20% of all pediatric central nervous system tumors. The management of these tumors has evolved dramatically in the past century. Once considered uniformly fatal, it is now known that brainstem tumors have distinguishing characteristics and do not behave identically. The focality and location of the lesion is determined from the clinical history, presentation, and associated imaging. Based on these findings, it is possible to predict the behavior of the tumor and choose an appropriate intervention. Focal lesions have a good prognosis and are treated operatively while diffuse lesions have a poor prognosis and are managed medically. This article reviews the current classification of brainstem tumors, current management options and future directions for the treatment of these rare tumors.

A novel brainstem tumor model: functional and histopathological characterization

INTRODUCTION

Diffuse pontine gliomas remain a challenging and frustrating disease to treat. The survival rates for these high-grade brainstem tumors (BSTs) is dismal and optimal therapy has yet to be determined. The development of a satisfactory brainstem tumor model is necessary for testing new therapeutic paradigms that may prolong survival.

MATERIALS AND METHODS

We report the surgical technique, functional testing, and histopathological features of a novel brainstem tumor model in rats. Female Fischer 344 rats (n=45) were randomized to receive an injection of either 3 microl of 9L gliosarcoma cells (100,000 cells, n=), 3 microl of F98 glioma cells (100,000 cells, n=10), or 3 microl of medium (Dulbecco's modified eagle medium) into the pontine tegmentum. Using a cannulated guide screw system, implanted in the skull of the animal, we injected each group at coordinates 1.4 mm right of the sagittal and 1.0 mm anterior of the lambdoid sutures, at a depth of 7.0 mm from the dura. The head was positioned 5 degrees from horizontal before injection. The rats were post-operatively evaluated for neurological deficits using an automated test. Kaplan-Meier curves were generated for survival and disease progression, and brains were processed postmortem for histopathology.

RESULTS AND DISCUSSION

9L and F98 tumor cells grew in 100% of animals injected and resulted in a statistically significant mean onset of hemiparesis of 16.5+/-0.56 days (P=0.001, log-rank test), compared to animals in the control group which lacked neurological deficits by day 60. The animals with tumor cells implanted demonstrated significant deterioration of function on the automated rod testing. Animals in the control group showed no functional or pathological signs of tumor. Progression to hemiparesis was consistent in all tumor-injected animals, with predictable onset of symptoms occurring approximately 17 days post-surgery. The histopathological characteristics of the 9L and F98 BSTs were comparable to those of aggressive human BSTs.

CONCLUSION

The establishment of this animal tumor model will facilitate the testing of new therapeutic paradigms for the treatment of BSTs.

Convection-enhanced delivery of targeted toxins for malignant glioma

Malignant gliomas represent a difficult treatment challenge for the neuro-oncologist and the neurosurgeon. These tumours continue to be refractory to standard therapies, such as surgery, radiotherapy and conventional chemotherapy, and new therapeutic options are clearly needed. Therefore, investigators have recently taken a new direction and started to engineer compounds such as recombinant cytotoxins, antiangiogenesis factors and genetic delivery vectors. However, these promising new agents are all dependent on an effective distribution method in order to bypass the blood-brain barrier. Convection-enhanced delivery (CED) allows for the administration of targeted toxins and other agents directly into the brain at the site of a tumour via catheters placed with the aid of stereotactic or image-guided surgery. The use of this technique is gaining momentum as a newly accepted treatment modality where little else has produced durable results in the fight against gliomas. Direct intratumoural infusion was first performed in nude mouse flank tumour models of human malignant glioma. After significant testing in preclinical animal studies, this method of delivery was followed by the successful demonstration of in vivo efficacy in Phase I and II clinical trials. Currently, this technique is being used in the investigational setting at academic medical centres where investigators are starting to define the best practice for CED. Fundamental issues in this method of delivery such as rate of infusion, cannula size, infusate concentration and tissue-cannula sealing time shape the current discussion in the literature. Targeted toxin therapy represents one of the newest and most promising treatments for this unfortunate patient population, with proven clinical efficacy administered through CED, which is a novel approach to drug delivery.

Fabrication and characterization of microfluidic probes for convection enhanced drug delivery

Convection enhanced drug delivery (CED) is a promising therapeutic method for treating diseases of the brain by enhancing the penetration of drugs. Most controlled release delivery methods rely on diffusion from a source to transport drugs throughout tissue. CED relies on direct infusion of drugs into tissue at a sufficiently high rate so that convective transport of drug is at least as important as diffusive transport. This work describes the fabrication and characterization of microfluidic probes for CED protocols and the role diffusion plays in determining penetration. Microfluidic channels were formed on silicon substrates by employing a sacrificial photoresist layer encased in a parylene structural layer. Flow in the microchannels was characterized by applying constant upstream pressures from 35 to 310 kPa, which resulted in flow rates of 0.5-4.5 microL/min. The devices were used to infuse Evans Blue and albumin in hydrogel brain phantoms. The results of these infusions were compared to a simple convection-diffusion model for infusions into porous media. In vivo infusions of albumin were performed in the gray matter of rats at upstream pressures of 35, 70, and 140 kPa. The microfabricated probes show reduced evidence of backflow along the device-tissue interface when compared with conventional needles used for CED.

Intracranial therapy of glioblastoma with the fusion protein DTIL13 in immunodeficient mice

A fusion protein consisting of human interleukin-13 and the first 389 amino acids of diphtheria toxin was assembled in order to target human glioblastoma cell lines in a murine intracranial model. In vitro studies to determine specificity indicated that the protein called DTIL13 was highly selective for human glioblastoma. In vivo, the maximum tolerated dose of DTIL13 was 1 microg/injection given every other day and repeated for 3 days. Doses that exceeded this amount resulted in weight loss and liver damage as determined by histology and enzyme assay. Experiments in IL-4 receptor knockout mice revealed that liver toxicity was receptor-related. This same dose given to nude mice with established U373 MG brain tumors resulted in significant reductions in tumor volume and significantly prolonged survival (p<0.0001). Magnetic resonance imaging (MRI) proved to be extremely useful in (i) determining the ability of DTIL13 to reduce tumor size and (ii) for studying toxicity since diffusion-weighted and gradient echo-weighted MRI revealed that vascular leak syndrome was not a limiting toxicity at this dose. These results suggest that DTIL13 is as effective in an intracranial rodent model as it was in a flank model in previous studies and that DTIL13 might be an effective treatment for glioblastoma multiforme.

New Delivery Approaches for Pediatric Brain Tumors

For many types of childhood brain tumors, including malignant gliomas, disease progression at the primary site is the predominant mode of treatment failure. Accordingly, interest has been directed during the last decade on exploring strategies to enhance the delivery of therapeutically active agents into the tumor microenvironment. Two approaches that have been the focus of considerable attention in the treatment of adult malignant brain tumors include interstitial administration of chemotherapeutic agents using time-release polymers and convection-enhanced delivery of immunotoxin conjugates targeted to receptors overexpressed in brain tumors relative to normal brain cells. Although it remains to be determined whether these approaches will lead to meaningful improvements in disease control and long-term prognosis in children with brain tumors, the encouraging results from studies in adults support the rationale for further exploring these strategies in the pediatric setting.

Brain Stem Tumors

Brain stem tumors are heterogeneous. They range from the diffuse pontine tumors, which are almost invariably fatal despite all known therapies, to lower-grade focal or exophytic tumors that often have a very good prognosis with surgery or observation only. In this article, we review the epidemiology of brain stem tumors and note that diffuse pontine tumors, although rare, are a significant contributor to mortality among pediatric oncology patients. Diagnosis in typical cases is made using a magnetic resonance imaging scan without biopsy. No highly effective standard treatment exists; therefore, inclusion of eligible patients in well-designed clinical research studies is extremely important. If an appropriate trial is not available, conventionally fractionated external beam radiation therapy can provide good short-term palliation to a significant proportion of patients. An important area of preclinical research that may soon be investigated in clinical trials for patients with diffuse pontine tumors is interstitial infusion of therapeutic agents, and the rationale for that approach is described in detail. Lastly, autopsy should be considered for patients who die of diffuse pontine tumors with the goal of obtaining tumor tissue for biological studies that may in the future lead to novel therapies.

A novel brainstem tumor model: guide screw technology with functional, radiological, and histopathological characterization

Object

Survival rates for high-grade brainstem tumors are approximately 10% and optimal therapy has yet to be determined. Development of a satisfactory brainstem tumor model is necessary for testing new therapeutic paradigms that may prolong survival. The authors report the technique, functional progression, radiological appearance, and histopathological features of a novel brainstem tumor model in rats.

Methods

Thirty female Fischer 344 rats were randomized (10 animals/group) to receive an injection of either 3 μl of 9L gliosarcoma cells (100,000 cells), 3 μl of F98 glioma cells (100,000 cells), or 3 μl of medium (Dulbecco modified Eagle medium) into the pontine tegmentum of the brainstem. Using a cannulated guide screw system implanted in the skull of the animal, rats in each group were injected at coordinates 1.4 mm to the right of the sagittal and 1 mm anterior to the lambdoid sutures, at a depth of 7 mm from the dura mater. The angle of the syringe during injection was anteflexed 5° from the vertical. Postoperatively, the rats were evaluated for neurological deficits by using an automated rotarod test. High-resolution [18F]fluorodeoxyglucose–positron emission tomography (FDG-PET) fused with computerized tomography (CT) scans were acquired pre- and postoperatively through the onset of hemiparesis and correlated accordingly. Kaplan–Meier curves were generated for survival and disease progression, and brains were processed postmortem for histopathological investigation.

The 9L and F98 tumor cells grew in 95% of the animals in which they were injected and resulted in a statistically significant mean onset of hemiparesis of 16.5 ± 0.56 days (p = 0.001, log-rank test), compared with animals in the control group, which had no neurological deficits by Day 45. The FDG-PET studies coregistered with CT scans demonstrated space-occupying brainstem lesions, and this finding was confirmed by histological studies. Animals in the control group showed no functional, radiological, or pathological signs of tumor.

Conclusions

Progression to hemiparesis was consistent in all tumor-injected animals, with predictable onset of symptoms occurring approximately 17 days postsurgery. The histopathological and radiological characteristics of the 9L and F98 brainstem tumors were comparable to those of aggressive primary human brainstem tumors. Establishment of this animal tumor model will facilitate the testing of new therapeutic paradigms for the treatment of these lesions.

Experimental models of brainstem tumors: development of a neonatal rat model

OBJECTIVE

Brainstem tumor models are required to advance the treatment for diffuse pontine gliomas in children. The feasibility of creating an experimental rodent model by inoculating newborn pups with tumor cells was examined. The study was performed to create an animal model for diffuse brainstem tumors.

METHODS

Eighty-two Fischer rat pups aged 12-24 h were anesthetized by hypothermia. The brainstem was injected with saline to identify anatomical coordinates for subsequent tumor cell challenges. The newborn pups were then inoculated with F98 (n=30) or 9L (n=30) glioma cells. Animals were returned to their mother for nursing. Tumor growth was assessed by survival and histopathology.

RESULTS

Twenty-one percent of the saline-treated animals (17 out of 82) and 5% of the tumor cell-challenged pups (3 out of 60) were eliminated by their mothers. Inoculations with 9L and F98 cells produced brainstem tumors in 83% (24 out of 29) and 93% of animals (26 out of 28) respectively that were evaluated.

CONCLUSIONS

Our results demonstrate that neonatal rat models for brainstem tumors can be prepared using known injection coordinates and orthotopic cell lines. Decreasing rates of maternal removal during the course of the work suggests that the method involves a learning curve.

Pediatric surgical neuro-oncology: current best care practices and strategies

Significant advances have been made in the diagnosis and treatment of childhood brain tumors. Gross total surgical resection combined with appropriate adjuvant therapies can achieve a high rate of disease control for low grade gliomas, ependymomas and medulloblastomas. High grade gliomas, tumors involving the optic apparatus or diencepahalic structures, diffuse brainstem lesions, and recurrent or metastatic disease still pose considerable therapeutic challenges. We review the current treatment strategies of the three most common types of pediatric brain tumors: gliomas, medulloblastomas and ependymomas, and discuss current and future diagnostic and therapeutic modalities.

Comparing monoclonal antibodies and small peptidic hormones for local targeting of malignant gliomas

Monoclonal antibodies, F(ab')2 fragments and peptidic vectors have been clinically tested for systemic and locoregional treatment of malignant gliomas. Since these brain-intrinsic neoplasms are characterized by relentless tumor cell infiltration of normal brain parenchyma, targeting agents require diffusive properties in order to reach invading tumor cell clusters that migrate along vascular clefts and axonal pathways. Tumor uptake was significantly improved by using small peptidic hormone receptors, e.g. modified octreotide, following systemic injections as compared to macromolecules which only led to limited stabilization of the disease. More importantly, biodistribution was found to be superior following direct intratumoral injection by using these small drug-like radioconjugates. Rapid and extensive distribution within 30 minutes was observed in large tumors, even crossing the corpus callosum in bihemispheric lesions following injection of 2-3 ml of the radiopharmakon injected into the center of non-resected tumors. Distribution was far more extensive after direct intratumoral injection as compared to intracavitary injection after surgical debulking. Increased interstitial pressure gradients and the much larger and chaotic structure of the interstitial space of a tumor compared to the extremely tight architecture of normal brain tissue might explain this unexpected biodistribution pattern. Peptidic hormone vectors might become useful agents to deliver radiopharmaceuticals into human invasive gliomas.