Real-time MR imaging with Gadoteridol predicts distribution of transgenes after convection-enhanced delivery of AAV2 vectors

Gene therapy for misfolding protein diseases of the central nervous system

Protein aggregation as a result of misfolding is a common theme underlying neurodegenerative diseases. Accordingly, most recent studies aim to prevent protein misfolding and/or aggregation as a strategy to treat these pathologies. For instance, state-of-the-art approaches, such as silencing protein overexpression by means of RNA interference, are being tested with positive outcomes in preclinical models of animals overexpressing the corresponding protein. Therapies designed to treat central nervous system diseases should provide accurate delivery of the therapeutic agent and long-term or chronic expression by means of a nontoxic delivery vehicle. After several years of technical advances and optimization, gene therapy emerges as a promising approach able to fulfill those requirements. In this review we will summarize the latest improvements achieved in gene therapy for central nervous system diseases associated with protein misfolding (e.g., amyotrophic lateral sclerosis, Alzheimer's, Parkinson's, Huntington's, and prion diseases), as well as the most recent approaches in this field to treat these pathologies.

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-based therapy of Parkinson's Disease: Translation from animal model to human clinical trial employing convection enhanced delivery

The existing treatment of Parkinson's disease (PD) is directed towards substituting dopamine loss with either dopamine replacement therapy or pharmacological therapies aimed at increasing dopamine at the synapse level. Emerging viable alternatives include the use of cell-based and gene-based therapeutics. In this review, we discuss efforts in developing in vitro and in vivo models and their translation to human clinical trials for gene-based therapy of this distressing and prevalent neurodegenerative disorder. Given the mismatch between expectations from preclinical data and results of human pivotal trials, drug delivery has been identified as the key emerging area for translational research due to limitation of limited efficacy. The chief highlights of the current topic include use of improved delivery methods of gene-based therapeutic agents. Convection-enhanced delivery (CED), an advanced infusion technique with demonstrated utility in ex vivo and in vivo animal models has recently been adopted for PD gene-based therapy trials. Several preclinical studies suggest that magnetic resonance imaging (MRI)-guided navigation for accurately targeting and real time monitoring viral vector delivery (rCED) in future clinical trials involving detection of gene expression and restoration of dopaminergic function loss using pro-drug approach will greatly enhance these PD treatments.

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.

A novel adenoviral vector labeled with superparamagnetic iron oxide nanoparticles for real-time tracking of viral delivery

In vivo tracking of gene therapy vectors challenges the investigation and improvement of biodistribution of these agents in the brain, a key feature for their targeting of infiltrative malignant gliomas. The glioma-targeting Ad5/3-cRGD gene therapy vector was covalently bound to super-paramagnetic iron oxide (Fe(3)O(4)) nanoparticles (SPION) to monitor its distribution by MRI. Transduction of labeled and unlabeled vectors was assessed on the U87 glioma cell line and normal human astrocytes (NHA), and was higher in U87 compared to NHA, but was similar between labeled and unlabeled virus. An in vivo study was performed by intracranial subcortical injection of labeled-Ad5/3-cRGD particles into a pig brain. The labeled vector appeared in vivo as a T2-weighted hyperintensity and a T2-gradient echo signal at the injection site, persisting up to 72 hours post-injection. We describe a glioma-targeting vector that is labeled with SPION, thereby allowing for MRI detection with no change in transduction capability.

Evaluation of an AAV2-based rapamycin-regulated glial cell line-derived neurotrophic factor (GDNF) expression vector system

Effective regulation of transgene product in anatomically circumscribed brain tissue is dependent on the pharmacokinetics of the regulating agent, the kinetics of transcriptional activation and degradation of the transgene product. We evaluated rapamycin-regulated AAV2-GDNF expression in the rat brain (striatum). Regulated (a dual-component system: AAV2-FBZhGDNF + AAV2-TF1Nc) and constitutive (CMV-driven) expression vectors were compared. Constitutively active AAV2-GDNF directed stable GDNF expression in a dose-dependent manner and it increased for the first month, thereafter reaching a plateau that was maintained over a further 3 months. For the AAV2-regGDNF, rapamycin was administered in a 3-days on/4-days off cycle. Intraperitoneal, oral, and direct brain delivery (CED) of rapamycin were evaluated. Two cycles of rapamycin at an intraperitoneal dose of 10 mg/kg gave the highest GDNF level (2.75±0.01 ng/mg protein). Six cycles at 3 mg/kg resulted in lower GDNF values (1.36±0.3 ng/mg protein). Interestingly, CED of rapamycin into the brain at a very low dose (50 ng) induced GDNF levels comparable to a 6-week intraperitoneal rapamycin cycle. This study demonstrates the effectiveness of rapamycin regulation in the CNS. However, the kinetics of the transgene in brain tissue, the regulator dosing amount and schedule are critical parameters that influence the kinetics of accumulation and zenith of the encoded transgene product.

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.

Glial-derived neurotrophic factor gene transfer for Parkinson's disease: anterograde distribution of AAV2 vectors in the primate brain

Delivery of neurotrophic factors to treat neurodegenerative diseases has not been efficacious in clinical trials despite their known potency for promoting neuronal growth and survival. Direct gene delivery to the brain offers an approach for establishing sustained expression of neurotrophic factors but is dependent on accurate surgical procedures to target specific anatomical regions of the brain. Serotype-2 adeno-associated viral (AAV2) vectors have been investigated in multiple clinical studies for neurological diseases without adverse effects; however the absence of significant clinical efficacy after neurotrophic factor gene transfer has been largely attributed to insufficient coverage of the target region. Our pre-clinical development of AAV2-glial-derived neurotrophic factor (GDNF) for Parkinson's disease involved real-time image guided delivery and optimization of delivery techniques to maximize gene transfer in the putamen. We have demonstrated that AAV2 vectors are anterogradely transported in the primate brain with GDNF expression observed in the substantia nigra after putaminal delivery in both intact and nigrostriatal lesioned primates. Direct midbrain delivery of AAV2-GDNF resulted in extensive anterograde transport to multiple brain regions and significant weight loss.

Analysis of a simulation algorithm for direct brain drug delivery

Convection enhanced delivery (CED) achieves targeted delivery of drugs with a pressure-driven infusion through a cannula placed stereotactically in the brain. This technique bypasses the blood brain barrier and gives precise distributions of drugs, minimizing off-target effects of compounds such as viral vectors for gene therapy or toxic chemotherapy agents. The exact distribution is affected by the cannula positioning, flow rate and underlying tissue structure. This study presents an analysis of a simulation algorithm for predicting the distribution using baseline MRI images acquired prior to inserting the cannula. The MRI images included diffusion tensor imaging (DTI) to estimate the tissue properties. The algorithm was adapted for the devices and protocols identified for upcoming trials and validated with direct MRI visualization of gadoinium in 20 infusions in non-human primates. We found strong agreement between the size and location of the simulated and gadolinium volumes, demonstrating the clinical utility of this surgical planning algorithm.

Potential therapeutic uses of BDNF in neurological and psychiatric disorders

The growth factor brain-derived neurotrophic factor (BDNF) and its receptor tropomyosin-related kinase receptor type B (TRKB) are actively produced and trafficked in multiple regions in the adult brain, where they influence neuronal activity, function and survival throughout life. The diverse presence and activity of BDNF suggests a potential role for this molecule in the pathogenesis and treatment of both neurological and psychiatric disorders. This article reviews the current understanding and future directions in BDNF-related research in the central nervous system, with an emphasis on the possible therapeutic application of BDNF in modifying fundamental processes underlying neural disease.

Novel platform for MRI-guided convection-enhanced delivery of therapeutics: preclinical validation in nonhuman primate brain

BACKGROUND/AIMS

A skull-mounted aiming device and integrated software platform has been developed for MRI-guided neurological interventions. In anticipation of upcoming gene therapy clinical trials, we adapted this device for real-time convection-enhanced delivery of therapeutics via a custom-designed infusion cannula. The targeting accuracy of this delivery system and the performance of the infusion cannula were validated in nonhuman primates.

METHODS

Infusions of gadoteridol were delivered to multiple brain targets and the targeting error was determined for each cannula placement. Cannula performance was assessed by analyzing gadoteridol distributions and by histological analysis of tissue damage.

RESULTS

The average targeting error for all targets (n = 11) was 0.8 mm (95% CI = 0.14). For clinically relevant volumes, the distribution volume of gadoteridol increased as a linear function (R(2) = 0.97) of the infusion volume (average slope = 3.30, 95% CI = 0.2). No infusions in any target produced occlusion, cannula reflux or leakage from adjacent tracts, and no signs of unexpected tissue damage were observed.

CONCLUSIONS

This integrated delivery platform allows real-time convection-enhanced delivery to be performed with a high level of precision, predictability and safety. This approach may improve the success rate for clinical trials involving intracerebral drug delivery by direct infusion.

Interventional MRI-guided putaminal delivery of AAV2-GDNF for a planned clinical trial in Parkinson's disease

Clinical trials involving direct infusion of neurotrophic therapies for Parkinson's disease (PD) have suffered from poor coverage of the putamen. The planned use of a novel interventional-magnetic resonance imaging (iMRI) targeting system for achieving precise, real-time convection-enhanced delivery in a planned clinical trial of adeno-associated virus serotype 2 (AAV2)-glial-derived neurotrophic factor (GDNF) in PD patients was modeled in nonhuman primates (NHP). NHP received bilateral coinfusions of gadoteridol (Gd)/AAV2-GDNF into two sites in each putamen, and three NHP received larger infusion volumes in the thalamus. The average targeting error for cannula tip placement in the putamen was <1 mm, and adjacent putamenal infusions were distributed in a uniform manner. GDNF expression patterns in the putamen were highly correlated with areas of Gd distribution seen on MRI. The distribution volume to infusion volume ratio in the putamen was similar to that in the thalamus, where larger infusions were achieved. Modeling the placement of adjacent 150 and 300 µl thalamic infusions into the three-dimensional space of the human putamen demonstrated coverage of the postcommissural putamen, containment within the striatum and expected anterograde transport to globus pallidus and substantia nigra pars reticulata. The results elucidate the necessary parameters for achieving widespread GDNF expression in the putamenal motor area and afferent substantia nigra of PD patients.

Regeneration of the MPTP-lesioned dopaminergic system after convection-enhanced delivery of AAV2-GDNF

Clinical studies to date have failed to establish therapeutic benefit of glial cell-derived neurotrophic factor (GDNF) in Parkinson's disease (PD). In contrast to previous nonclinical neuroprotective reports, this study shows clinically relevant and long-lasting regeneration of the dopaminergic system in rhesus macaques lesioned with 1-methy-4-phenyl-1,2,3,6-tetrahydropyridine 3-6 months before GDNF gene delivery (AAV2-GDNF). The observed progressive amelioration of functional deficits, recovery of dopamine, and regrowth of fibers to the striatal neuropil demonstrate that high GDNF expression in the putamen promotes restoration of the dopaminergic system in a primate model of advanced PD. Extensive distribution of GDNF within the putamen and transport to the severely lesioned substantia nigra, after convection-enhanced delivery of AAV2-GDNF into the putamen, indicates anterograde transport via striatonigral connections and is anticipated to occur in PD patients. Overall, these data demonstrate nonclinical neurorestoration after putaminal infusion of AAV2-GDNF and suggest that clinical investigation in PD patients is warranted.