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

AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Gene therapy for aromatic L-amino acid decarboxylase deficiency by MR-guided direct delivery of AAV2-AADC to midbrain dopaminergic neurons

Aromatic L-amino acid decarboxylase (AADC) deficiency is a rare genetic disorder characterized by deficient synthesis of dopamine and serotonin. It presents in early infancy, and causes severe developmental disability and lifelong motor, behavioral, and autonomic symptoms including oculogyric crises (OGC), sleep disorder, and mood disturbance. We investigated the safety and efficacy of delivery of a viral vector expressing AADC (AAV2-hAADC) to the midbrain in children with AADC deficiency (ClinicalTrials.gov Identifier NCT02852213). Seven (7) children, aged 4–9 years underwent convection-enhanced delivery (CED) of AAV2-hAADC to the bilateral substantia nigra (SN) and ventral tegmental area (VTA) (total infusion volume: 80 µL per hemisphere) in 2 dose cohorts: 1.3 × 10¹¹ vg (n = 3), and 4.2 × 10¹¹ vg (n = 4). Primary aims were to demonstrate the safety of the procedure and document biomarker evidence of restoration of brain AADC activity. Secondary aims were to assess clinical improvement in symptoms and motor function. Direct bilateral infusion of AAV2-hAADC was safe, well-tolerated and achieved target coverage of 98% and 70% of the SN and VTA, respectively. Dopamine metabolism was increased in all subjects and FDOPA uptake was enhanced within the midbrain and the striatum. OGC resolved completely in 6 of 7 subjects by Month 3 post-surgery. Twelve (12) months after surgery, 6/7 subjects gained normal head control and 4/7 could sit independently. At 18 months, 2 subjects could walk with 2-hand support. Both the primary and secondary endpoints of the study were met. Midbrain gene delivery in children with AADC deficiency is feasible and safe, and leads to clinical improvements in symptoms and motor function.

Aromatic L-amino acid decarboxylase deficiency (AADC) is a rare neurodevelopmental disorder. Here the authors describe a clinical trial of MR-guided delivery of AAV2-AADC for the treatment of AADC.

Evaluation of a patient-specific algorithm for predicting distribution for convection-enhanced drug delivery into the brainstem of patients with diffuse intrinsic pontine glioma

OBJECTIVE

With increasing use of convection-enhanced delivery (CED) of drugs, the need for software that can predict infusion distribution has grown. In the context of a phase I clinical trial for pediatric diffuse intrinsic pontine glioma (DIPG), CED was used to administer an anti-B7H3 radiolabeled monoclonal antibody, iodine-124-labeled omburtamab. In this study, the authors retrospectively evaluated a software algorithm (iPlan Flow) for the estimation of infusate distribution based on the planned catheter trajectory, infusion parameters, and patient-specific MRI. The actual infusate distribution, as determined on MRI and PET imaging, was compared to the distribution estimated by the software algorithm. Similarity metrics were used to quantify the agreement between predicted and actual distributions.

METHODS

Ten pediatric patients treated at the same dose level in the NCT01502917 trial conducted at Memorial Sloan Kettering Cancer Center were considered for this retrospective analysis. T2-weighted MRI in combination with PET imaging was used to determine the distribution of infusate in this study. The software algorithm was applied for the generation of estimated fluid distribution maps. Similarity measures included object volumes, intersection volume, union volume, Dice coefficient, volume difference, and the center and average surface distances. Acceptable similarity was defined as a simulated distribution volume (Vd Sim) object that had a Dice coefficient higher than or equal to 0.7, a false-negative rate (FNR) lower than 50%, and a positive predictive value (PPV) higher than 50% compared to the actual Vd (Vd PET).

RESULTS

Data for 10 patients with a mean infusion volume of 4.29 ml (range 3.84-4.48 ml) were available for software evaluation. The mean Vd Sim found to be covered by the actual PET distribution (PPV) was 77% ± 8%. The mean percentage of PET volume found to be outside the simulated volume (FNR) was 34% ± 10%. The mean Dice coefficient was 0.7 ± 0.05. In 8 out of 10 patients, the simulation algorithm fulfilled the combined acceptance criteria for similarity.

CONCLUSIONS

iPlan Flow software can be useful to support planning of trajectories that produce intraparenchymal convection. The simulation algorithm is able to model the likely infusate distribution for a CED treatment in DIPG patients. The combination of trajectory planning guidelines and infusion simulation in the software can be used prospectively to optimize personalized CED treatment.

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.

Current Clinical Applications of In Vivo Gene Therapy with AAVs

Hereditary diseases are caused by mutations in genes, and more than 7,000 rare diseases affect over 30 million Americans. For more than 30 years, hundreds of researchers have maintained that genetic modifications would provide effective treatments for many inherited human diseases, offering durable and possibly curative clinical benefit with a single treatment. This review is limited to gene therapy using adeno-associated virus (AAV) because the gene delivered by this vector does not integrate into the patient genome and has a low immunogenicity. There are now five treatments approved for commercialization and currently available, i.e., Luxturna, Zolgensma, the two chimeric antigen receptor T cell (CAR-T) therapies (Yescarta and Kymriah), and Strimvelis (the gammaretrovirus approved for adenosine deaminase-severe combined immunodeficiency [ADA-SCID] in Europe). Dozens of other treatments are under clinical trials. The review article presents a broad overview of the field of therapy by in vivo gene transfer. We review gene therapy for neuromuscular disorders (spinal muscular atrophy [SMA]; Duchenne muscular dystrophy [DMD]; X-linked myotubular myopathy [XLMTM]; and diseases of the central nervous system, including Alzheimer’s disease, Parkinson’s disease, Canavan disease, aromatic l-amino acid decarboxylase [AADC] deficiency, and giant axonal neuropathy), ocular disorders (Leber congenital amaurosis, age-related macular degeneration [AMD], choroideremia, achromatopsia, retinitis pigmentosa, and X-linked retinoschisis), the bleeding disorder hemophilia, and lysosomal storage disorders.

Repeat convection-enhanced delivery for diffuse intrinsic pontine glioma

OBJECTIVE

While the safety and efficacy of convection-enhanced delivery (CED) have been studied in patients receiving single-dose drug infusions, agents for oncological therapy may require repeated or chronic infusions to maintain therapeutic drug concentrations. Repeat and chronic CED infusions have rarely been described for oncological purposes. Currently available CED devices are not approved for extended indwelling use, and the only potential at this time is for sequential treatments through multiple procedures. The authors report on the safety and experience in a group of pediatric patients who received sequential CED into the brainstem for the treatment of diffuse intrinsic pontine glioma.

METHODS

Patients in this study were enrolled in a phase I single-center clinical trial using 124I-8H9 monoclonal antibody (124I-omburtamab) administered by CED (clinicaltrials.gov identifier NCT01502917). A retrospective chart and imaging review were used to assess demographic data, CED infusion data, and postoperative neurological and surgical outcomes. MRI scans were analyzed using iPlan Flow software for volumetric measurements. Target and catheter coordinates as well as radial, depth, and absolute error in MRI space were calculated with the ClearPoint imaging software.

RESULTS

Seven patients underwent 2 or more sequential CED infusions. No patients experienced Clinical Terminology Criteria for Adverse Events grade 3 or greater deficits. One patient had a persistent grade 2 cranial nerve deficit after a second infusion. No patient experienced hemorrhage or stroke postoperatively. There was a statistically significant decrease in radial error (p = 0.005) and absolute tip error (p = 0.008) for the second infusion compared with the initial infusion. Sequential infusions did not result in significantly different distribution capacities between the first and second infusions (volume of distribution determined by the PET signal/volume of infusion ratio [mean ± SD]: 2.66 ± 0.35 vs 2.42 ± 0.75; p = 0.45).

CONCLUSIONS

This series demonstrates the ability to safely perform sequential CED infusions into the pediatric brainstem. Past treatments did not negatively influence the procedural workflow, technical application of the targeting interface, or distribution capacity. This limited experience provides a foundation for using repeat CED for oncological purposes.

Gene therapy for neurodegenerative disorders: advances, insights and prospects

Gene therapy is rapidly emerging as a powerful therapeutic strategy for a wide range of neurodegenerative disorders, including Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD). Some early clinical trials have failed to achieve satisfactory therapeutic effects. Efforts to enhance effectiveness are now concentrating on three major fields: identification of new vectors, novel therapeutic targets, and reliable of delivery routes for transgenes. These approaches are being assessed closely in preclinical and clinical trials, which may ultimately provide powerful treatments for patients. Here, we discuss advances and challenges of gene therapy for neurodegenerative disorders, highlighting promising technologies, targets, and future prospects.

Imaging of Convective Drug Delivery in the Nervous System

Convection-enhanced delivery permits the direct homogeneous delivery of small- and large-molecular-weight putative therapeutics to the nervous system in a manner that bypasses the blood-nervous system barrier. The development of co-infused surrogate imaging tracers (for computed tomography and MRI) allows for the real-time, noninvasive monitoring of infusate distribution during convective delivery. Real-time image monitoring of convective distribution of therapeutic agents insures that targeted structures/nervous system regions are adequately perfused, enhances safety, informs efficacy (or lack thereof) of putative agents, and provides critical information regarding the properties of convection-enhanced delivery in normal and various pathologic tissue states.

Convection-enhanced Delivery of Therapeutics for Malignant Gliomas

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

Widespread AAV1- and AAV2-mediated transgene expression in the nonhuman primate brain: implications for Huntington's disease

Huntington’s disease (HD) is caused by a toxic gain-of-function associated with the expression of the mutant huntingtin (htt) protein. Therefore, the use of RNA interference to inhibit Htt expression could represent a disease-modifying therapy. The potential of two recombinant adeno-associated viral vectors (AAV), AAV1 and AAV2, to transduce the cortico-striatal tissues that are predominantly affected in HD was explored. Green fluorescent protein was used as a reporter in each vector to show that both serotypes were broadly distributed in medium spiny neurons in the striatum and cortico-striatal neurons after infusion into the putamen and caudate nucleus of nonhuman primates (NHP), with AAV1-directed expression being slightly more robust than AAV2-driven expression. This study suggests that both serotypes are capable of targeting neurons that degenerate in HD, and it sets the stage for the advanced preclinical evaluation of an RNAi-based therapy for this disease.

Convection-enhanced delivery in glioblastoma: a review of preclinical and clinical studies

Glioblastoma is the most common malignant brain tumor, and it carries an extremely poor prognosis. Attempts to develop targeted therapies have been hindered because the blood-brain barrier prevents many drugs from reaching tumors cells. Furthermore, systemic toxicity of drugs often limits their therapeutic potential. A number of alternative methods of delivery have been developed, one of which is convection-enhanced delivery (CED), the focus of this review. The authors describe CED as a therapeutic measure and review preclinical studies and the most prominent clinical trials of CED in the treatment of glioblastoma. The utilization of this technique for the delivery of a variety of agents is covered, and its shortcomings and challenges are discussed in detail.

AAV viral vector delivery to the brain by shape-conforming MR-guided infusions

Gene transfer technology offers great promise as a potential therapeutic approach to the brain but has to be viewed as a very complex technology. Success of ongoing clinical gene therapy trials depends on many factors such as selection of the correct genetic and anatomical target in the brain. In addition, selection of the viral vector capable of transfer of therapeutic gene into target cells, along with long-term expression that avoids immunotoxicity has to be established. As with any drug development strategy, delivery of gene therapy has to be consistent and predictable in each study subject. Failed drug and vector delivery will lead to failed clinical trials. In this article, we describe our experience with AAV viral vector delivery system, that allows us to optimize and monitor in real time viral vector administration into affected regions of the brain. In addition to discussing MRI-guided technology for administration of AAV vectors we have developed and now employ in current clinical trials, we also describe ways in which infusion cannula design and stereotactic trajectory may be used to maximize the anatomical coverage by using fluid backflow. This innovative approach enables more precise coverage by fitting the shape of the infusion to the shape of the anatomical target.

MRI-Guided Delivery of Viral Vectors

Gene therapy has emerged as a potential avenue of treatment for many neurological disorders. Technological advances in imaging techniques allow for the monitoring of real-time infusions into the brain of rodents, nonhuman primates, and humans. Here, we discuss the use of magnetic resonance imaging (MRI) as a tool in the delivery of adeno-associated viral (AAV) particles into brain of nonhuman primates.

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.

Gene therapy for Parkinson's disease: state-of-the-art treatments for neurodegenerative disease

Pharmacological and surgical treatments offer symptomatic benefits to patients with Parkinson's disease; however, as the condition progresses, patients experience gradual worsening in symptom control, with the development of a range of disabling complications. In addition, none of the currently available therapies have convincingly shown disease-modifying effects - either in slowing or reversing the disease. These problems have led to extensive research into the possible use of gene therapy as a treatment for Parkinson's disease. Several treatments have reached human clinical trial stages, providing important information on the risks and benefits of this novel therapeutic approach, and the tantalizing promise of improved control of this currently incurable neurodegenerative disorder.

Differential effects of two MRI contrast agents on the integrity and distribution of rAAV2 and rAAV5 in the rat striatum

Intraoperative magnetic resonance imaging (MRI) has been proposed as a method to optimize intracerebral targeting and for tracking infusate distribution in gene therapy trials for nervous system disorders. We thus investigated possible effects of two MRI contrast agents, gadoteridol (Gd) and galbumin (Gab), on the distribution and levels of transgene expression in the rat striatum and their effect on integrity and stability of recombinant adeno-associated virus (rAAV) particles. MRI studies showed that contrast agent distribution did not predict rAAV distribution. However, green fluorescent protein (GFP) immunoreactivity revealed an increase in distribution of rAAV5-GFP, but not rAAV2-GFP, in the presence of Gd when compared with viral vector injected alone. In contrast, Gab increased the distribution of rAAV2-GFP not rAAV5-GFP. These observations pointed to a direct effect of infused contrast agent on the rAAV particles. Negative-stain electron microscopy (EM), DNAase treatment, and differential scanning calorimetry (DSC) were used to monitor rAAV2 and rAAV5 particle integrity and stability following contrast agent incubation. EMs of rAAV2-GFP and rAAV5-GFP particles pretreated with Gd appear morphologically similar to the untreated sample; however, Gab treatment resulted in surface morphology changes and aggregation. A compromise of particle integrity was suggested by sensitivity of the packaged genome to DNAase treatment following Gab incubation but not Gd for both vectors. However, neither agent significantly affected particle stability when analyzed by DSC. An increase in T m was observed for AAV2 in lactated Ringer's buffer. These results thus highlight potential interactions between MRI contrast agents and AAV that might affect vector distribution and stability, as well as the stabilizing effect of lactated Ringer's solution on AAV2.

SAFETY AND TOLERABILITY OF MRI-GUIDED INFUSION OF AAV2-hAADC INTO THE MID-BRAIN OF NON-HUMAN PRIMATE

Aromatic L-amino acid decarboxylase (AADC) deficiency is a rare, autosomal-recessive neurological disorder caused by mutations in the DDC gene that leads to an inability to synthesize catecholamines and serotonin. As a result, patients suffer compromised development, particularly in motor function. A recent gene replacement clinical trial explored putaminal delivery of recombinant adeno-associated virus serotype 2 vector encoding human AADC (AAV2-hAADC) in AADC-deficient children. Unfortunately, patients presented only modest amelioration of motor symptoms, which authors acknowledged could be due to insufficient transduction of putamen. We hypothesize that, with the development of a highly accurate MRI-guided cannula placement technology, a more effective approach might be to target the affected mid-brain neurons directly. Transduction of AADC-deficient dopaminergic neurons in the substantia nigra and ventral tegmental area with locally infused AAV2-hAADC would be expected to lead to restoration of normal dopamine levels in affected children. The objective of this study was to assess the long-term safety and tolerability of bilateral AAV2-hAADC MRI-guided pressurized infusion into the mid-brain of nonhuman primates. Animals received either vehicle, low or high AAV2-hAADC vector dose and were euthanized 1, 3, or 9 months after surgery. Our data indicate that effective mid-brain transduction was achieved without untoward effects.

Clinical trials of viral therapy for malignant gliomas

Despite recent scientific advances in the understanding of the biology of malignant gliomas, there has been little change in the overall survival for this devastating disease. New and innovative treatments are under constant investigation. Starting in the 1990s, there was an interest in using viral therapeutics for the treatment of malignant gliomas. Multiple strategies were pursued, including oncolytic viral therapy, enzyme/pro-drug combinations and gene transfer with viral vectors. Multiple Phase I and II trials demonstrated the safety of these techniques, but clinically showed limited efficacy. However, this led to a better understanding of the pitfalls of viral therapy and encouraged the development of new approaches and improved delivery methods. Here we review the prior and ongoing clinical trials of viral therapy for gliomas, and discuss how novel strategies are currently being utilized in clinical trials.

Convection-enhanced drug delivery to the brain: therapeutic potential and neuropathological considerations

Convection-enhanced delivery (CED) describes a direct method of drug delivery to the brain through intraparenchymal microcatheters. By establishing a pressure gradient at the tip of the infusion catheter in order to exploit bulk flow through the interstitial spaces of the brain, CED offers a number of advantages over conventional drug delivery methods-bypass of the blood-brain barrier, targeted distribution through large brain volumes and minimization of systemic side effects. Despite showing early promise, CED is yet to fulfill its potential as a mainstream strategy for the treatment of neurological disease. Substantial research effort has been dedicated to optimize the technology for CED and identify the parameters, which govern successful drug distribution. It seems likely that successful clinical translation of CED will depend on suitable catheter technology being used in combination with drugs with optimal physicochemical characteristics, and on neuropathological analysis in appropriate preclinical models. In this review, we consider the factors most likely to influence the success or failure of CED, and review its application to the treatment of high-grade glioma, Parkinson's disease (PD) and Alzheimer's disease (AD).

Automated segmentation tool for brain infusions

This study presents a computational tool for auto-segmenting the distribution of brain infusions observed by magnetic resonance imaging. Clinical usage of direct infusion is increasing as physicians recognize the need to attain high drug concentrations in the target structure with minimal off-target exposure. By co-infusing a Gadolinium-based contrast agent and visualizing the distribution using real-time using magnetic resonance imaging, physicians can make informed decisions about when to stop or adjust the infusion. However, manual segmentation of the images is tedious and affected by subjective preferences for window levels, image interpolation and personal biases about where to delineate the edge of the sloped shoulder of the infusion. This study presents a computational technique that uses a Gaussian Mixture Model to efficiently classify pixels as belonging to either the high-intensity infusate or low-intensity background. The algorithm was implemented as a distributable plug-in for the widely used imaging platform OsiriX®. Four independent operators segmented fourteen anonymized datasets to validate the tool’s performance. The datasets were intra-operative magnetic resonance images of infusions into the thalamus or putamen of non-human primates. The tool effectively reproduced the manual segmentation volumes, while significantly reducing intra-operator variability by 67±18%. The tool will be used to increase efficiency and reduce variability in upcoming clinical trials in neuro-oncology and gene therapy.

Convection-enhanced delivery: from mechanisms to clinical drug delivery for diseases of the central nervous system

The evolution of cancer chemotherapy has been a major advance in medical science in the late 20th century. However, patients with malignant gliomas have not benefitted much. The blood-brain barrier (BBB), which always hinders the entry of therapeutic agents into the central nervous system (CNS), may at least partly be responsible. Convection-enhanced delivery (CED), a method for distributing large and small molecular weight compounds bypassing the BBB, enables robust distribution of the infused molecules at the site of infusion. CED is promising as an effective treatment not only for malignant gliomas but also for multiple CNS disorders because this method can effectively distribute multiple molecules that are potentially effective against different diseases. Although the method is quite simple, several problems require solution in developing novel CED-based strategies, including what, where, when, and how to infuse. This review discusses basic considerations when developing CED-based strategies for CNS diseases, focusing mainly on brain tumors.

Evaluation of pressure-driven brain infusions in nonhuman primates by intra-operative 7 Tesla MRI

PURPOSE

To characterize the effects of pressure-driven brain infusions using high field intra-operative MRI. Understanding these effects is critical for upcoming neurodegeneration and oncology trials using convection-enhanced delivery (CED) to achieve large drug distributions with minimal off-target exposure.

MATERIALS AND METHODS

High-resolution T2-weighted and diffusion-tensor images were acquired serially on a 7 Tesla MRI scanner during six CED infusions in nonhuman primates. The images were used to evaluate the size, distribution, diffusivity, and temporal dynamics of the infusions.

RESULTS

The infusion distribution had high contrast in the T2-weighted images. Diffusion tensor images showed the infusion increased diffusivity, reduced tortuosity, and reduced anisotropy. These results suggested CED caused an increase in the extracellular space.

CONCLUSION

High-field intra-operative MRI can be used to monitor the distribution of infusate and changes in the geometry of the brain's porous matrix. These techniques could be used to optimize the effectiveness of pressure-driven drug delivery to the brain.

Gene therapy for the treatment of Parkinson's disease: the nature of the biologics expands the future indications

The pharmaceutical industry's development of therapeutic medications for the treatment of Parkinson's disease (PD) endures, as a result of the continuing need for better agents, and the increased clinical demand due to the aging population. Each new drug offers advantages and disadvantages to patients when compared to other medical offerings or surgical options. Deep brain stimulation (DBS) has become a standard surgical remedy for the effective treatment of select patients with PD, for whom most drug regimens have failed or become refractory. Similar to DBS as a surgical option, gene therapy for the treatment of PD is evolving as a future option. In the four different PD gene therapy approaches that have reached clinical trials investigators have documented an excellent safety profile associated with the stereotactic delivery, viral vectors and doses utilized, and transgenes expressed. In this article, we review the clinically relevant gene therapy strategies for the treatment of PD, concentrating on the published preclinical and clinical results, and the likely mechanisms involved. Based on these presentations, we advance an analysis of how the nature of the gene therapy used may eventually expand the scope and utility for the management of PD.

Guided delivery of adeno-associated viral vectors into the primate brain

In this review, we discuss recent developments in the delivery of adeno-associated virus-based vectors (AAV), particularly with respect to the role of axonal transport in vector distribution in the brain. The use of MRI-guidance and new stereotactic aiming devices have now established a strong foundation for neurological gene therapy to become an accepted procedure in interventional neurology.

Long-term evaluation of a phase 1 study of AADC gene therapy for Parkinson's disease

We report the results of a long-term follow-up of subjects in a phase 1 study of AAV2-hAADC (adeno-associated virus type 2-human aromatic L-amino acid decarboxylase) gene therapy for the treatment of Parkinson's disease (PD). Ten patients with moderately advanced PD received bilateral putaminal infusions of either a low or a high dose of AAV2-hAADC vector. An annual positron emission tomography (PET) imaging with [(18)F]fluoro-L-m-tyrosine tracer was used for evaluation of AADC expression, and a standard clinical rating scale [Unified Parkinson's Disease Rating Scale (UPDRS)] was used to assess effect. Our previous analysis of the 6-month data suggested that this treatment was acutely safe and well tolerated. We found that the elevated PET signal observed in the first 12 months persisted over 4 years in both dose groups. A significantly increased PET value compared with the presurgery baseline was maintained over the 4-year monitoring period. The UPDRS in all patients off medication for 12 hr improved in the first 12 months, but displayed a slow deterioration in subsequent years. This analysis demonstrates that apparent efficacy continues through later years with an acceptable safety profile. These data indicate stable transgene expression over 4 years after vector delivery and continued safety, but emphasize the need for a controlled efficacy trial and the use of a higher vector dose.

A phase I trial of carboplatin administered by convection-enhanced delivery to patients with recurrent/progressive glioblastoma multiforme

Glioblastoma multiforme (GBM) is the commonest primary malignant brain tumour in adults. Standard treatment comprises surgery, radiotherapy and chemotherapy; however this condition remains incurable as these tumours are highly invasive and involve critical areas of the brain making it impossible to remove them surgically or cure them with radiotherapy. In the majority of cases the tumour recurs within 2 to 3 cm of the original site of tumour resection. Furthermore, the blood-brain barrier profoundly limits the access of many systemically administered chemotherapeutics to the tumour. Convection-enhanced delivery (CED) is a promising technique of direct intracranial drug delivery involving the implantation of microcatheters into the brain. Carboplatin represents an ideal chemotherapy to administer using this technique as glioblastoma cells are highly sensitive to carboplatin in vitro at concentrations that are not toxic to normal brain in vivo. This protocol describes a single-centre phase I dose-escalation study of carboplatin administered by CED to patients with recurrent or progressive GBM despite full standard treatment. This trial will incorporate 6 cohorts of 3 patients each. Cohorts will be treated in a sequential manner with increasing doses of carboplatin, subject to dose-limiting toxicity not being observed. This protocol should facilitate the identification of the maximum-tolerated infused concentration of carboplatin by CED into the supratentorial brain. This should facilitate the safe application of this technique in a phase II trial, treating patients with GBM, as well as for the treatment of other forms of malignant brain tumours, including metastases.