Convection-enhanced delivery into the rat brainstem

Intranasal delivery of nanoliposomal SN-38 for treatment of diffuse midline glioma

OBJECTIVE

Diffuse midline gliomas, including diffuse intrinsic pontine gliomas (DIPGs), are among the most malignant and devastating childhood brain cancers. Despite aggressive treatment, nearly all children with these tumors succumb to their disease within 2 years of diagnosis. Due to the anatomical location of the tumors within the pons, surgery is not a treatment option, and distribution of most systematically administered drugs is limited by the blood-brain barrier (BBB). New drug delivery systems that bypass the BBB are desperately needed to improve outcomes of DIPG patients. Intranasal delivery (IND) is a practical and noninvasive drug delivery system that bypasses the BBB and delivers the drugs to the brain through the olfactory and trigeminal neural pathways. In this study, the authors evaluated the efficacy of nanoliposomal (LS) irinotecan (CPT-11) and an active metabolite of CPT-11, 7-ethyl-10-hydroxycamptothecin (SN-38), using IND in DIPG patient-derived xenograft models.

METHODS

In vitro responses to LS-CPT-11 and LS-SN-38 in DIPG cells were evaluated with cell viability, colony formation, and apoptosis assays. The cellular uptakes of rhodamine-PE (Rhod)-labeled LS-CPT-11 and LS-SN-38 were analyzed with fluorescence microscopy. Mice bearing DIPG patient-derived xenografts were treated with IND of LS-control (empty liposome), LS-CPT-11, or LS-SN-38 by IND for 4 weeks. In vivo responses were measured for tumor growth by serial bioluminescence imaging and animal subject survival. The concentration of SN-38 in the brainstem tumor administered by IND was determined by liquid chromatography-mass spectrometry (LC-MS). Immunohistochemical analyses of the proliferative and apoptotic responses of in vivo tumor cells were performed with Ki-67 and TUNEL staining.

RESULTS

LS-SN-38 inhibited DIPG cell growth and colony formation and increased apoptosis, outperforming LS-CPT-11. Rhod-labeled LS-SN-38 showed intracellular fluorescence signals beginning at 30 minutes and peaking at 24 hours following treatment. LC-MS analysis revealed an SN-38 concentration in the brainstem tumor of 0.66 ± 0.25 ng/ml (5.43% ± 0.31% of serum concentration). IND of LS-SN-38 delayed tumor growth and significantly prolonged animal survival compared with IND of LS-control (p < 0.0001) and LS-CPT-11 (p = 0.003). IND of LS-SN-38 increased the number of TUNEL-positive cells and decreased the Ki-67-positive cells in the brainstem tumor.

CONCLUSIONS

This study demonstrates that IND of LS-SN-38 bypasses the BBB and enables efficient and noninvasive drug delivery to the brainstem tumor, providing a promising therapeutic approach for treating DIPG.

Functionalized Macrophage Exosomes with Panobinostat and PPM1D-siRNA for Diffuse Intrinsic Pontine Gliomas Therapy

Diffuse intrinsic pontine glioma (DIPG) is a rare and fatal pediatric brain tumor. Mutation of p53-induced protein phosphatase 1 (PPM1D) in DIPG cells promotes tumor cell proliferation, and inhibition of PPM1D expression in DIPG cells with PPM1D mutation effectively reduces the proliferation activity of tumor cells. Panobinostat effectively kills DIPG tumor cells, but its systemic toxicity and low blood-brain barrier (BBB) permeability limits its application. In this paper, a nano drug delivery system based on functionalized macrophage exosomes with panobinostat and PPM1D-siRNA for targeted therapy of DIPG with PPM1D mutation is prepared. The nano drug delivery system has higher drug delivery efficiency and better therapeutic effect than free drugs. In vivo and in vitro experimental results show that the nano drug delivery system can deliver panobinostat and siRNA across the BBB and achieve a targeted killing effect of DIPG tumor cells, resulting in the prolonged survival of orthotopic DIPG mice. This study provides new ideas for the delivery of small molecule drugs and gene drugs for DIPG therapy.

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.

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.

Clinical experience of convection-enhanced delivery (CED) of carboplatin and sodium valproate into the pons for the treatment of diffuse intrinsic pontine glioma (DIPG) in children and young adults after radiotherapy

PURPOSE

Effective treatment of diffuse intrinsic pontine glioma (DIPG) remains a formidable challenge due to inadequate penetration of the blood-brain barrier (BBB) by systemically administered chemotherapies. The BBB can be overcome by directly infusing drugs into pons using method of convection-enhanced delivery (CED). We describe our clinical experience and what we have learned about the safety and feasibility of treating DIPG with intermittent CED of carboplatin and sodium valproate to the pons through the Renishaw Drug Delivery System (RDDS).

METHODS

Retrospective review (2017-2020) of children with DIPG, who following radiotherapy, received compassionate treatment commencing 3.3-10 months post-diagnosis (median 4.9 months). They received up to 7 cycles of 3-6 weekly pontine infusions of carboplatin (0.12-0.18 mg/ml) and sodium valproate (14.4-28.8 mg/ml).

RESULTS

13 children 3-19 years (mean 6.9 years) were treated. There were no surgical complications. With the exception of infusion channels blocking in one device, there were no adverse device effects. Two patients developed persistent 6th nerve palsies, which led to drug concentration reduction in the combination therapy. Subsequently infusion/ drug-related toxicities were transient. Tumour was controlled in pons in 10/13 patients. Median progression-free survival (PFS) was 13.0 months, while median overall survival (OS) was 15.3 months.

CONCLUSIONS

Use of the RDDS was safe and well tolerated in all 13 patients. Treatment improved control of pontine disease resulting in longer PFS and OS and merits further evaluation in a clinical trial.

ABC Transporter Inhibition Plus Dexamethasone Enhances the Efficacy of Convection Enhanced Delivery in H3.3K27M Mutant Diffuse Intrinsic Pontine Glioma

BACKGROUND

An impermeable blood-brain barrier and drug efflux via ATP-binding cassette (ABC) transporters such as p-glycoprotein may contribute to underwhelming efficacy of peripherally delivered agents to treat diffuse intrinsic pontine glioma (DIPG).

OBJECTIVE

To explore the pharmacological augmentation of convection-enhanced delivery (CED) infusate for DIPG.

METHODS

The efficacy of CED dasatinib, a tyrosine kinase inhibitor, in a transgenic H3.3K27M mutant murine model was assessed. mRNA expression of ABCB1 (p-glycoprotein) was analyzed in 14 tumor types in 274 children. In Vitro viability studies of dasatinib, the p-glycoprotein inhibitor, tariquidar, and dexamethasone were performed in 2 H3.3K27M mutant cell lines. Magnetic resonance imaging (MRI) was used to evaluate CED infusate (gadolinium/dasatinib) distribution in animals pretreated with tariquidar and dexamethasone. Histological assessment of apoptosis was performed.

RESULTS

Continuous delivery CED dasatinib improved median overall survival (OS) of animals harboring DIPG in comparison to vehicle (39.5 and 28.5 d, respectively; P = .0139). Mean ABCB1 expression was highest in K27M gliomas. In Vitro, the addition of tariquidar and dexamethasone further enhanced the efficacy of dasatinib (P < .001). In Vivo, MRI demonstrated no difference in infusion dispersion between animals pretreated with dexamethasone plus tariquidar prior to CED dasatinib compared to the CED dasatinib. However, tumor apoptosis was the highest in the pretreatment group (P < .001). Correspondingly, median OS was longer in the pretreatment group (49 d) than the dasatinib alone group (39 d) and no treatment controls (31.5 d, P = .0305).

CONCLUSION

ABC transporter inhibition plus dexamethasone enhances the efficacy of CED dasatinib, resulting in enhanced tumor cellular apoptosis and improved survival in H3.3K27M mutant DIPG.

The intersect of neurosurgery with diffuse intrinsic pontine glioma

An invited article highlighting diffuse intrinsic pontine glioma (DIPG) to celebrate the 75th Anniversary of the Journal of Neurosurgery, a journal known to define surgical nuance and enterprise, is paradoxical since DIPG has long been relegated to surgical abandonment. More recently, however, the neurosurgeon is emerging as a critical stakeholder given our role in tissue sampling, collaborative scientific research, and therapeutic drug delivery. The foundation for this revival lies in an expanding reliance on tissue accession for understanding tumor biology, available funding to fuel research, and strides with interventional drug delivery.

Time-Resolved MRI Assessment of Convection-Enhanced Delivery by Targeted and Nontargeted Nanoparticles in a Human Glioblastoma Mouse Model

Convection-enhanced delivery (CED) provides direct access of infusates to brain tumors; however, clinical translation of this technology has not been realized because of the inability to accurately visualize infusates in real-time and lack of targeting modalities against diffuse cancer cells. In this study, we use time-resolved MRI to reveal the kinetics of CED processes in a glioblastoma (GBM) model using iron oxide nanoparticles (NP) modified with a glioma-targeting ligand, chlorotoxin (CTX). Mice bearing orthotopic human GBM tumors were administered a single dose of targeted CTX-conjugated NP (NPCP-CTX) or nontargeted NP (NPCP) via CED. High-resolution T2-weighted, T2*-weighted, and quantitative T2 MRI were utilized to image NP delivery in real time and determined the volume of distribution (VD) of NPs at multiple time points over the first 48 hours post-CED. GBM-specific targeting was evaluated by flow cytometry and intracellular NP localization by histologic assessment. NPCP-CTX produced a VD of 121 ± 39 mm3 at 24 hours, a significant increase compared with NPCP, while exhibiting GBM specificity and localization to cell nuclei. Notably, CED of NPCP-CTX resulted in a sustained expansion of VD well after infusion, suggesting a possible active transport mechanism, which was further supported by the presence of NPs in endothelial and red blood cells. In summary, we show that time-resolved MRI is a suitable modality to study CED kinetics, and CTX-mediated CED facilitates extensive distribution of infusate and specific targeting of tumor cells. SIGNIFICANCE: MRI is used to monitor convection-enhanced delivery in real time using a nanoparticle-based contrast agent, and glioma-specific targeting significantly improves the volume of distribution in tumors.

Magnetic hyperthermia therapy for the treatment of glioblastoma: a review of the therapy's history, efficacy and application in humans

Hyperthermia therapy (HT) is the exposure of a region of the body to elevated temperatures to achieve a therapeutic effect. HT anticancer properties and its potential as a cancer treatment have been studied for decades. Techniques used to achieve a localised hyperthermic effect include radiofrequency, ultrasound, microwave, laser and magnetic nanoparticles (MNPs). The use of MNPs for therapeutic hyperthermia generation is known as magnetic hyperthermia therapy (MHT) and was first attempted as a cancer therapy in 1957. However, despite more recent advancements, MHT has still not become part of the standard of care for cancer treatment. Certain challenges, such as accurate thermometry within the tumour mass and precise tumour heating, preclude its widespread application as a treatment modality for cancer. MHT is especially attractive for the treatment of glioblastoma (GBM), the most common and aggressive primary brain cancer in adults, which has no cure. In this review, the application of MHT as a therapeutic modality for GBM will be discussed. Its therapeutic efficacy, technical details, and major experimental and clinical findings will be reviewed and analysed. Finally, current limitations, areas of improvement, and future directions will be discussed in depth.

The Integration of Biology Into the Treatment of Diffuse Intrinsic Pontine Glioma: A Review of the North American Clinical Trial Perspective

Dramatic advances in the molecular analysis of diffuse intrinsic pontine glioma have occurred over the last decade and resulted in the identification of potential therapeutic targets. In spite of these advances, no significant improvement in the outcome has been achieved and median survival remains approximately 10 months. An understanding of the approaches that have been taken to date, why they failed, and how that information can lead the field forward is critical if we are to change the status quo. In this review, we will discuss the clinical trial landscape in North America with an overview of historical approaches that failed and what might account for this failure. We will then provide a discussion of how our understanding of the genotype of this disease has led to the development of a number of trials targeting the mutations and epigenome of diffuse intrinsic pontine gliomas and the issues related to these trials. Similarly, the introduction of methodologies to address penetration across the blood–brain barrier will be considered in the context of both targeted approaches, epigenetic modification, and immune surveillance of these tumors. The comprehensive analysis of these data, generated through cooperative groups, collaborative clinical trials, and pilot studies in North America will be the focus of the IVth Memorial Alicia Pueyo international symposium in Barcelona on March 12th, 2018 and will be compared and contrasted with a similar comprehensive analysis of the European data with the goal of bringing all of these data together to develop a uniform platform on which new rational trials can be based.

Developing chemotherapy for diffuse pontine intrinsic gliomas (DIPG)

Prognosis of diffuse intrinsic pontine glioma (DIPG) is poor, with a median survival of 10 months after radiation. At present, chemotherapy has failed to show benefits over radiation. Advances in biotechnology have enabled the use of autopsy specimens for genomic analyses and molecular profiling of DIPG, which are quite different from those of supratentorial high grade glioma. Recently, combined treatments of cytotoxic agents with target inhibitors, based on biopsied tissue, are being examined in on-going trials. Spontaneous DIPG mice models have been recently developed that is useful for preclinical studies. Finally, the convection-enhanced delivery could be used to infuse drugs directly into the brainstem parenchyma, to which conventional systemic administration fails to achieve effective concentration. The WHO glioma classification defines a diffuse midline glioma with a H3-K27M-mutation, and we expect increase of tissue confirmation of DIPG, which will give us the biological information helping the development of a targeted therapy.

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.

Dual Inhibition of PI3K/AKT and MEK/ERK Pathways Induces Synergistic Antitumor Effects in Diffuse Intrinsic Pontine Glioma Cells

Diffuse intrinsic pontine glioma (DIPG) is a devastating disease with an extremely poor prognosis. Recent studies have shown that platelet-derived growth factor receptor (PDGFR) and its downstream effector pathway, PI3K/AKT/mTOR, are frequently amplified in DIPG, and potential therapies targeting this pathway have emerged. However, the addition of targeted single agents has not been found to improve clinical outcomes in DIPG, and targeting this pathway alone has produced insufficient clinical responses in multiple malignancies investigated, including lung, endometrial, and bladder cancers. Acquired resistance also seems inevitable. Activation of the Ras/Raf/MEK/ERK pathway, which shares many nodes of cross talk with the PI3K/AKT pathway, has been implicated in the development of resistance. In the present study, perifosine, a PI3K/AKT pathway inhibitor, and trametinib, a MEK inhibitor, were combined, and their therapeutic efficacy on DIPG cells was assessed. Growth delay assays were performed with each drug individually or in combination. Here, we show that dual inhibition of PI3K/AKT and MEK/ERK pathways synergistically reduced cell viability. We also reveal that trametinib induced AKT phosphorylation in DIPG cells that could not be effectively attenuated by the addition of perifosine, likely due to the activation of other compensatory mechanisms. The synergistic reduction in cell viability was through the pronounced induction of apoptosis, with some effect from cell cycle arrest. We conclude that the concurrent inhibition of the PI3K/AKT and MEK/ERK pathways may be a potential therapeutic strategy for DIPG.

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.

Convection-Enhanced Delivery for Diffuse Intrinsic Pontine Glioma Treatment

Convection-enhanced delivery (CED) is a technique designed to deliver drugs directly into the brain or tumors. Its ability to bypass the blood-brain barrier (BBB), one of the major hurdles in delivering drugs to the brain, has made it a promising drug delivery method for the treatment of primary brain tumors. A number of clinical trials utilizing CED of various therapeutic agents have been conducted to treat patients with supratentorial high-grade gliomas. Significant responses have been observed in certain patients in all of these trials. However, the insufficient ability to monitor drug distribution and pharmacokinetics hampers CED from achieving its potentials on a larger scale. Brainstem CED for diffuse intrinsic pontine glioma (DIPG) treatment is appealing because this tumor is compact and has no definitive treatment. The safety of brainstem CED has been established in small and large animals, and recently in early stage clinical trials. There are a few current clinical trials of brainstem CED in treating DIPG patients using targeted macromolecules such as antibodies and immunotoxins. Future advances for CED in DIPG treatment will come from several directions including: choosing the right agents for infusion; developing better agents and regimen for DIPG infusion; improving instruments and technique for easier and accurate surgical targeting and for allowing multisession or prolonged infusion to implement optimal time sequence; and better understanding and control of drug distribution, clearance and time sequence. CED-based therapies for DIPG will continue to evolve with new understanding of the technique and the disease.

Nanotechnology Applications for Diffuse Intrinsic Pontine Glioma

Diffuse intrinsic pontine gliomas (DIPGs) are invariably fatal tumors found in the pons of elementary school aged children. These tumors are grade II-IV gliomas, with a median survival of less than 1 year from diagnosis when treated with standard of care (SOC) therapy. Nanotechnology may offer therapeutic options for the treatment of DIPGs. Multiple nanoparticle formulations are currently being investigated for the treatment of DIPGs. Nanoparticles based upon stable elements, polymer nanoparticles, and organic nanoparticles are under development for the treatment of brain tumors, including DIPGs. Targeting of nanoparticles is now possible as delivery techniques that address the difficulty in crossing the blood brain barrier (BBB) are developed. Theranostic nanoparticles, a combination of therapeutics and diagnostic nanoparticles, improve imaging of the cancerous tissue while delivering therapy to the local region. However, additional time and attention should be directed to developing a nanoparticle delivery system for treatment of the uniformly fatal pediatric disease of DIPG.

Intracerebral Diffusion of Paramagnetic Cationic Liposomes Containing Gd(DTPA)2- Followed by MRI Spectroscopy: Assessment of Patternc Diffusion and Time Steadiness of a Non-Viral Vector Model

Cationic liposomes are generally considered as the non-viral counterparts of the more common viral vectors used in several gene therapy protocols, but their use as delivery vehicles is limited by their efficiency even if they display a lower toxicity. However, cationic liposomes are promising delivery systems in cell biology due to their ability to incorporate small molecules into their inner aqueous spheres and to deliver them into cells. Additionally, on the external surface they can bind therapeutic molecules such as nucleic acids, oligonucleotides, plasmids, etc. through electrostatic interactions. The aim of this work was to study the diffusion properties of such vehicles in vivo with a non-invasive technique and to monitor their tissue migration in order to collect information to be further used in gene therapy procedures. For this purpose, cationic liposomes containing the paramagnetic contrast agent Gd(DTPA)2- (Gd(III)-diethylenetriamine-N,N,N′,N″,N″-pentaacetic acid) were investigated because of their extended paramagnetic persistency in vivo, compared to the use of the contrast agent alone, and they were used to monitor the diffusion of such vehicles in an animal model (rat model). In particular, these vectors were injected into the rat brain through a stereotactic frame in a preformed cavity mimicking the lesion which had originated after surgical removal of the primary tumor. For the purpose of comparison, the same injection procedure was also applied to a control series of animals without a preformed brain lesion. Pattern diffusion and steadiness of the reported paramagnetic cationic liposomes were studied by means of Magnetic Resonance Imaging (MRI) which allowed us to monitor their diffusion and assess their intracerebral time availability up to 24 hours.

A Novel Methodology for Applying Multivoxel MR Spectroscopy to Evaluate Convection-Enhanced Drug Delivery in Diffuse Intrinsic Pontine Gliomas

BACKGROUND AND PURPOSE

Diffuse intrinsic pontine gliomas are inoperable high-grade gliomas with a median survival of less than 1 year. Convection-enhanced delivery is a promising local drug-delivery technique that can bypass the BBB in diffuse intrinsic pontine glioma treatment. Evaluating tumor response is critical in the assessment of convection-enhanced delivery of treatment. We proposed to determine the potential of 3D multivoxel (1)H-MR spectroscopy to evaluate convection-enhanced delivery treatment effect in these tumors.

MATERIALS AND METHODS

We prospectively analyzed 3D multivoxel (1)H-MR spectroscopy data for 6 patients with nonprogressive diffuse intrinsic pontine gliomas who received convection-enhanced delivery treatment of a therapeutic antibody (Phase I clinical trial NCT01502917). To compare changes in the metabolite ratios with time, we tracked the metabolite ratios Cho/Cr and Cho/NAA at several ROIs: normal white matter, tumor within the convection-enhanced delivery infusion site, tumor outside of the infused area, and the tumor average.

RESULTS

There was a comparative decrease in both Cho/Cr and Cho/NAA metabolite ratios at the tumor convection-enhanced delivery site versus tumor outside the infused area. We used MR spectroscopy voxels with dominant white matter as a reference. The difference between changes in metabolite ratios became more prominent with increasing time after convection-enhanced delivery treatment.

CONCLUSIONS

The comparative change in metabolite ratios between the convection-enhanced delivery site and the tumor site outside the infused area suggests that multivoxel (1)H-MR spectroscopy, in combination with other imaging modalities, may provide a clinical tool to accurately evaluate local tumor response after convection-enhanced delivery treatment.

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.

Functionally defined therapeutic targets in diffuse intrinsic pontine glioma

Diffuse Intrinsic Pontine Glioma (DIPG) is a fatal childhood cancer. We performed a chemical screen in patient-derived DIPG cultures along with RNAseq analyses and integrated computational modeling to identify potentially effective therapeutic strategies. The multi-histone deacetylase inhibitor panobinostat demonstrated efficacy in vitro and in DIPG orthotopic xenograft models. Combination testing of panobinostat with histone demethylase inhibitor GSKJ4 revealed synergy. Together, these data suggest a promising therapeutic strategy for DIPG.

Pediatric diffuse intrinsic pontine glioma: can optimism replace pessimism?

Pediatric diffuse intrinsic pontine glioma (DIPG) has a dismal prognosis that has not seen a change in outcome despite multiple clinical trials. Possible reasons for failure to make progress in this aggressive childhood brain tumor include: poor understanding of the underlying molecular biology due to lack of access to tumor material; absence of accurate and relevant DIPG preclinical models for drug development; ill-defined therapeutic targets for novel agents; and inadequate drug delivery to the brainstem. This review will demonstrate that systematic studies to identify solutions for each of these barriers is starting to deliver progress that can turn pessimism to optimism in DIPG.

Convection-enhanced delivery to the central nervous system

Convection-enhanced delivery (CED) is a bulk flow–driven process. Its properties permit direct, homogeneous, targeted perfusion of CNS regions with putative therapeutics while bypassing the blood-brain barrier. Development of surrogate imaging tracers that are co-infused during drug delivery now permit accurate, noninvasive real-time tracking of convective infusate flow in nervous system tissues. The potential advantages of CED in the CNS over other currently available drug delivery techniques, including systemic delivery, intrathecal and/or intraventricular distribution, and polymer implantation, have led to its application in research studies and clinical trials. The authors review the biophysical principles of convective flow and the technology, properties, and clinical applications of convective delivery in the CNS.

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.

Brain metastases of breast cancer

Brain metastases of breast cancer remain a difficult problem for clinical management. Their incidence appears to be increasing, which is likely due to longer survival times for advanced breast cancer patients as well as additional and improved tools for detection. Molecular features of tumors associated with this syndrome are not yet understood. In general, survival may be improving for brain metastases due to better local control in the CNS, as well as improvements in systemic disease management. Selected patients with brain metastases are able to undergo surgical resection, which has been associated with extended disease control in some patients. However, whole-brain radiation has been the mainstay for treatment for most patients. Stereotactic radiosurgery is playing an increasing role in the primary treatment of brain metastases, as well as for salvage after whole-brain radiation. Recent series have reported median survivals of 13 months or longer with stereotactic radiosurgery. Further improvements in radiation-based approaches may come from ongoing studies of radiosensitizing agents. The ability of systemic treatments to impact brain metastases has been debated, and specific treatment regimens have yet to be defined. New approaches include chemotherapy combinations, biologic therapies and novel drug-delivery strategies.

Establishment of experimental glioma models at the intrinsic brainstem region of the rats

OBJECTIVES

As the treatment of human intrinsic brainstem gliomas remains challenging, experimental glioma models are needed.

METHODS

We developed a rat model of intrinsic brain stem glioma that uses a stereotactic frame to fix the head for the delivery of C6 glioma cells to target sites via a permanently implanted cannula. We inoculated the rat midbrain, pons or cerebral cortex with 5 x 10(4) cells suspended in 1 microl culture medium over the course of 2 minutes.

RESULTS

Three days post-implantation, tumor formation was visible in the periaqueductal gray matter in the midbrain and the tegmentum of the pons. On the tenth day, the tumor diameter exceeded over 2 mm; there was no tumor cell seeding into the cerebrospinal fluid space. The tumor manifested the histological features typical of glioblastoma; Ki-67 labeling index was 32%.

DISCUSSION

Because in our model the cannula is permanently implanted, additional inocula can be delivered. Here we detail our rat brainstem glioma model and discuss its usefulness for the investigation of these tumor in humans.

Convection-enhanced delivery in the treatment of malignant glioma

Despite advancements in glioma therapy, median survival remains low because of rapid post-resection recurrence. A regional method of drug delivery to address local invasion may improve clinical outcomes. Convection-enhanced delivery (CED) is a novel therapy that allows distribution of substances throughout the interstitium via positive-pressure infusion. Studies using various agents have investigated the parameters that affect CED including infusion rate, cannula size, infusion volume, extracellular space, particle characteristics and tumor tissue structure. We review models of small animal glioma that have been successfully treated using different substances administered through CED, particularly our favorable results using topotecan in a C6 rat glioma model. We also review Phase I/II trials utilizing CED which have shown promising response rates and acceptable safety profiles. Future studies should include prospective clinical trials and investigation of novel antitumor agents that are ineffective with systemic delivery. Development of a large animal glioma model would enhance pre-clinical investigation of CED. Clinically, methods to monitor distribution of therapeutic agents and real-time patient response should likewise be explored.

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.

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.

Diffuse intrinsic pontine glioma-current status and future strategies

INTRODUCTION

Diffuse intrinsic pontine gliomas which constitute 15% of all childhood brain tumors are inoperable and response to radiation and chemotherapy has not improved long-term survival. Due to lack of newer effective therapies, mean survival after diagnosis has remained less than 12 months. Trials investigating chemotherapy and/or radiation have proven disappointing. As biopsy of these tumors are rarely performed due to the high eloquence of the brain stem, information about the pathology and biology remains elusive hindering development of novel biologic agents. Poor access of most chemotherapeutic agents to these tumors due to the blood-brain barrier continues to undermine therapeutic efficacy. Thus, to date, we remain at a virtual standstill in our attempts to improve the prognosis of children with these tumors.

METHODS

An extensive review of the literature was performed concerning children with diffuse brain stem gliomas including clinical trials, evolving molecular biology, and newer therapeutic endeavors.

CONCLUSION

A pivotal approach in improving the prognosis of these tumors should include the initiation of biopsy and encouraging families to consider autopsy to study the molecular biology. This will help in redefining this tumor by its molecular signature and profiling targeted therapy. Continued advances should be pursued in neuroimaging technology including identifying surrogate markers of early disease progression. Defining strategies to enhance local delivery of drugs into tumors with the help of newer surgical techniques are important. Exhaustive research in all these aspects as a multidisciplinary approach could provide hope to children with these fatal tumors.

Regression of recurrent glioblastoma infiltrating the brainstem after convection-enhanced delivery of nimustine hydrochloride

This 13-year-old boy with a history of cranial irradiation for the CNS recurrence of acute lymphocytic leukemia developed a glioblastoma in the right cerebellum. Resection and chemo- and radiotherapy induced remission of the disease. However, recurrence was noted in the brainstem region 8 months later. Because no effective treatment was available for this recurrent lesion, the authors decided to use convection-enhanced delivery (CED) to infuse nimustine hydrochloride. On stereotactic insertion of the infusion cannula into the brainstem lesion, CED of nimustine hydrochloride was performed with real-time MR imaging to monitor the co-infused chelated gadolinium. The patient's preinfusion symptom of diplopia disappeared after treatment. Follow-up MR imaging revealed the response of the tumor. The authors report on a case of recurrent glioblastoma infiltrating the brainstem that regressed after CED of nimustine hydrochloride.

Gene therapy for late infantile neuronal ceroid lipofuscinosis: neurosurgical considerations

OBJECT

The authors conducted a phase I study of late infantile neuronal ceroid lipofuscinosis using an adenoassociated virus serotype 2 (AAV2) vector containing the deficient CLN2 gene (AAV2(CU)hCLN2). The operative technique, radiographic changes, and surgical complications are presented.

METHODS

Ten patients with late infantile neuronal ceroid lipofuscinosis disease each underwent infusion of AAV2(CU)hCLN2 (3 x 10(12) particle units) into 12 distinct cerebral locations (2 depths/bur hole, 75 minutes/infusion, and 2 microl/minute). Innovative surgical techniques were developed to overcome several obstacles for which little or no established techniques were available. Successful infusion relied on preoperative stereotactic planning to optimize a parenchymal target and diffuse administration. Six entry sites, each having 2 depths of injections, were used to reduce operative time and enhance distribution. A low-profile rigid fixation system with 6 integrated holding arms was utilized to perform simultaneous infusions within a practical time frame. Dural sealant with generous irrigation was used to avoid CSF egress with possible subdural hemorrhage or altered stereotactic registration.

RESULTS

Radiographically demonstrated changes were seen in 39 (65%) of 60 injection sites, confirming localization and infusion. There were no radiographically or clinically defined complications.

CONCLUSIONS

The neurosurgical considerations and results of this study are presented to offer guidance and a basis for the design of future gene therapy or other clinical trials in children that utilize direct therapeutic delivery.

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.

Precision of navigated stereotactic probe implantation into the brainstem

OBJECT

The indications for stereotactic biopsies or implantation of probes for local chemotherapy in diffuse brainstem tumors have recently come under debate. The quality of performing these procedures significantly depends on the precision of the probes' placement in the brainstem. The authors evaluated the precision of brainstem probe positioning using a navigated frameless stereotactic system in an experimental setting.

METHODS

Using the VarioGuide stereotactic system, 33 probes were placed into a specially designed model filled with agarose. In a second experimental series, 8 anatomical specimens were implanted with a total of 32 catheters into the pontine brainstem using either a suboccipital or a precoronal entry point. Before intervention in both experimental settings, a thin-sliced CT scan for planning was obtained and fused to volumetric T1-weighted MR imaging data. After the probe positioning procedures, another CT scan and an MR image were obtained to compare the course of the catheters versus the planned trajectory. The deviation between the planned and the actual locations was measured to evaluate the precision of the navigated intervention.

RESULTS

Using the VarioGuide system, mean total target deviations of 2.8 +/- 1.2 mm on CT scanning and 3.1 +/- 1.2 mm on MR imaging were detected with a mean catheter length of 151 +/- 6.1 mm in the agarose model. The catheter placement in the anatomical specimens revealed mean total deviations of 1.95 +/- 0.6 mm on CT scanning and 1.8 +/- 0.7 mm on MR imaging for the suboccipital approach and a mean catheter length of 59.5 +/- 4.1 mm. For the precoronal approach, deviations of 2.2 +/- 1.2 mm on CT scanning and 2.1 +/- 1.1 mm on MR imaging were measured (mean catheter length 85.9 +/- 4.7 mm).

CONCLUSIONS

The system-based deviation of frameless stereotaxy using the VarioGuide system reveals good probe placement in deep-seated locations such as the brainstem. Therefore, the authors believe that the system can be accurately used to conduct biopsies and place probes in patients with brainstem lesions.

The evolving role of surgery in the management of pediatric brain tumors

Surgery is an integral component and typically the first line of therapy for children with central nervous system tumors. The outcome with regard to surgical morbidity and disease control can be greatly influenced by the initial care that these children receive. Conventional aims of neurosurgery including tumor removal, management of hydrocephalus, and diagnostic sampling have been radically modified with innovative technologies such as navigational guidance, functional mapping, endoscopic surgery, second-look surgery, and physiologic imaging. The overall role of the pediatric neurosurgeon in caring for children with nervous system tumors is also expanding to include unconventional responsibilities including disease staging, tissue procurement, and drug delivery. It is thus anticipated that the pediatric neurosurgeon will be increasingly relied upon for oncologic therapeutic strategies and should thus remain abreast of forthcoming information and technologies.

Targeted drug delivery for treatment and imaging of glioblastoma multiforme

Glioblastoma multiforme is a grade IV astrocytic tumor with a very high mortality rate. Although current treatment often includes surgical resection, this rarely removes all primary tumor cells, so is usually followed by radiation and/or chemotherapy. Remaining migratory tumor cells invade surrounding healthy tissue and contribute to secondary and tertiary tumor recurrence; therefore, despite significant research into glioma removal and treatment, prognosis remains poor. A variety of treatment modalities have been investigated to deliver drug to these cells, including systemic, diffusive and convection-enhanced delivery (CED). As systemic delivery is limited by molecules larger than approximately 500 Da being unable to cross the blood-brain barrier (BBB), therapeutic concentrations are difficult to attain; thus, localized delivery options relying on diffusion and CED have been used to circumvent the BBB. Although CED enables delivery to a greater volume of tissue than diffusive delivery alone, limitations still exist, requiring that these delivery strategies be improved. This review enumerates the strengths and weaknesses of these currently used strategies and details how predictive mathematical modeling can be used to aid investigators in optimizing these delivery modalities for clinical application.

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.

Neurological grading, survival, MR imaging, and histological evaluation in the rat brainstem glioma model

OBJECTIVE

Convection-enhanced delivery using carboplatin in brainstem glioma models was reported to prolong survival. Functional impairment is of additional importance to evaluate the value of local chemotherapy. We established a neurological scoring system for the rat brainstem glioma model.

MATERIAL AND METHODS

In 46 male Fisher rats stereotactically 10(5) F-98 cells were implanted at 1.4-mm lateral to midline and at the lambdoid suture using guided screws. Following 4 days local delivery was performed using Alzet pumps (1 microl/h over 7 days) with either vehicle (5% dextrose) or carboplatin via one or two cannulas, respectively. All rats were subsequently tested neurologically using a specified neurological score. In 38 animals survival time was recorded. Representative MR imaging were acquired in eight rats, respectively, at day 12 after implantation. HE staining was used to evaluate tumor extension.

RESULTS

Neurological scoring showed significantly higher impairment in the high dose carboplatin group during the treatment period. Survival was significantly prolonged compared to control animals in the high dose carboplatin-one cannula group as well as in both low dose carboplatin groups (18.6 +/- 3 versus 26.3 +/- 9, 22.8 +/- 2, 23.6 +/- 2 days; p < 0.05). Overall neurological grading correlated with survival time. MR imaging showed a focal contrast enhancing mass in the pontine brainstem, which was less exaggerated after local chemotherapy. Histological slices visualized decreased cellular density in treatment animals versus controls.

CONCLUSION

Local chemotherapy in the brainstem glioma model showed significant efficacy for histological changes and survival. Our neurological grading enables quantification of drug and tumor-related morbidity as an important factor for functional performance during therapy.

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.

Effects of drug efflux on convection-enhanced paclitaxel delivery to malignant gliomas: technical note

OBJECTIVE

Convection-enhanced delivery (CED) is an approach in local brain tumor treatment. The spread of infusate in CED can be thought of as involving three phases: backflow, convection, and diffusion. Uncontrolled backflow may lead to efflux of the infusate outside the cranium.

METHODS

Based on an interim analysis of a clinical trial, the effects of drug efflux on convection were assessed. In a Phase I/II trial, eight patients with recurrent glioblastomas were treated with CED of paclitaxel. The first group of patients was treated with paclitaxel at a concentration of 0.5 mg/ml according to previously approved protocols.

RESULTS

These Group 1 patients developed severe skin necrosis due to an efflux of paclitaxel out of the cranium. The average volume of distribution (Vd) in these patients was 12.8 cm. To prevent paclitaxel efflux, the burr hole was sealed with bone wax during and after CED in Groups 2 and 3. Surprisingly, patients in Group 2 showed a larger Vd (22.9 cm per catheter), exceeding the boundaries of the previous tumor, which led to subsequent neurological deficits. To allow a large Vd without severe side effects, the infusion volume was maintained, but the concentration of paclitaxel was reduced (paclitaxel concentration in Group 3, 0.25 mg/ml).

CONCLUSION

Vd remained high and no adverse effects were seen in Group 3. Sealing the burr hole during CED prevented efflux. The simple measure of sealing seems to increase Vd. These data demonstrate that uncontrolled backflow may have an important impact on CED and must be avoided.

Imaging cerebral gene transcripts in live animals

To circumvent the limitations of using postmortem brain in molecular assays, we used avidin-biotin binding to couple superparamagnetic iron oxide nanoparticles (SPIONs) (15-20 nm) to phosphorothioate-modified oligodeoxynucleotides (sODNs) with sequence complementary to c-fos and beta-actin mRNA (SPION-cfos and SPION-beta-actin, respectively) (14-22 nm). The Stern-Volmer constant for the complex of SPION and fluorescein isothiocyanate (FITC)-sODN is 3.1 x 10(6)/m. We studied the feasibility of using the conjugates for in vivo magnetic resonance imaging (MRI) to monitor gene transcription, and demonstrated that these complexes at 40 mug of Fe per kilogram of body weight were retained at least 1 d after intracerebroventricular infusion into the left ventricle of C57Black6 mice. SPION retention measured by MRI as T(2)* or R(2)* maps (R(2)* = 1/T(2)*) was compared with histology of iron oxide (Prussian blue) and FITC-labeled sODN. We observed significant reduction in magnetic resonance (MR) T(2)* signal in the right cortex and striatum; retention of SPION-cfos and SPION-beta-actin positively correlated with c-fos and beta-actin mRNA maps obtained from in situ hybridization. Histological examination showed that intracellular iron oxide and FITC-sODN correlated positively with in vivo MR signal reduction. Furthermore, in animals that were administered SPION-cfos and amphetamine (4 mg/kg, i.p.), retention was significantly elevated in the nucleus accumbens, striatum, and medial prefrontal cortex of the forebrain. Control groups that received SPION-cfos and saline or that received a SPION conjugate with a random-sequence probe and amphetamine showed no retention. These results demonstrated that SPION-sODN conjugates can detect active transcriptions of specific mRNA species in living animals with MRI.

Real-time, image-guided, convection-enhanced delivery of interleukin 13 bound to pseudomonas exotoxin

PURPOSE

To determine if the tumor-targeted cytotoxin interleukin 13 bound to Pseudomonas exotoxin (IL13-PE) could be delivered to the brainstem safely at therapeutic doses while monitoring its distribution in real-time using a surrogate magnetic resonance imaging tracer, we used convection-enhanced delivery to perfuse rat and primate brainstems with IL13-PE and gadolinium-bound albumin (Gd-albumin).

EXPERIMENTAL DESIGN

Thirty rats underwent convective brainstem perfusion of IL13-PE (0.25, 0.5, or 10 microg/mL) or vehicle. Twelve primates underwent convective brainstem perfusion of either IL13-PE (0.25, 0.5, or 10 microg/mL; n = 8), co-infusion of 125I-IL13-PE and Gd-albumin (n = 2), or co-infusion of IL13-PE (0.5 microg/mL) and Gd-albumin (n = 2). The animals were permitted to survive for up to 28 days before sacrifice and histologic assessment.

RESULTS

Rats showed no evidence of toxicity at all doses. Primates showed no toxicity at 0.25 or 0.5 microg/mL but showed clinical and histologic toxicity at 10 microg/mL. Quantitative autoradiography confirmed that Gd-albumin precisely tracked IL13-PE anatomic distribution and accurately showed the volume of distribution.

CONCLUSIONS

IL13-PE can be delivered safely and effectively to the primate brainstem at therapeutic concentrations and over clinically relevant volumes using convection-enhanced delivery. Moreover, the distribution of IL13-PE can be accurately tracked by co-infusion of Gd-albumin using real-time magnetic resonance imaging.

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.