Extensive Transduction and Enhanced Spread of a Modified AAV2 Capsid in the Non-human Primate CNS.

The present study was designed to characterize transduction of non-human primate brain and spinal cord with a modified adeno-associated virus serotype 2, incapable of binding to the heparan sulfate proteoglycan receptor, referred to as AAV2-HBKO. AAV2-HBKO was infused into the thalamus, intracerebroventricularly or via a combination of both intracerebroventricular and thalamic delivery. Thalamic injection of this modified vector encoding GFP resulted in widespread CNS transduction that included neurons in deep cortical layers, deep cerebellar nuclei, several subcortical regions, and motor neuron transduction in the spinal cord indicative of robust bidirectional axonal transport. Intracerebroventricular delivery similarly resulted in widespread cortical transduction, with one striking distinction that oligodendrocytes within superficial layers of the cortex were the primary cell type transduced. Robust motor neuron transduction was also observed in all levels of the spinal cord. The combination of thalamic and intracerebroventricular delivery resulted in transduction of oligodendrocytes in superficial cortical layers and neurons in deeper cortical layers. Several subcortical regions were also transduced. Our data demonstrate that AAV2-HBKO is a powerful vector for the potential treatment of a wide number of neurological disorders, and highlight that delivery route can significantly impact cellular tropism and pattern of CNS transduction.

MR-guided delivery of AAV2-BDNF into the entorhinal cortex of non-human primates.

Brain-derived neurotrophic factor (BDNF) gene delivery to the entorhinal cortex is a candidate for treatment of Alzheimer's disease (AD) to reduce neurodegeneration that is associated with memory loss. Accurate targeting of the entorhinal cortex in AD is complex due to the deep and atrophic state of this brain region. Using MRI-guided methods with convection-enhanced delivery, we were able to accurately and consistently target AAV2-BDNF delivery to the entorhinal cortex of non-human primates; 86 ± 3% of transduced cells in the targeted regions co-localized with the neuronal marker NeuN. The volume of AAV2-BDNF (3 × 108 vg/µl) infusion linearly correlated with the number of BDNF labeled cells and the volume (mm3) of BDNF immunoreactivity in the entorhinal cortex. BDNF is normally trafficked to the hippocampus from the entorhinal cortex; in these experiments, we also found that BDNF immunoreactivity was elevated in the hippocampus following therapeutic BDNF vector delivery to the entorhinal cortex, achieving growth factor distribution through key memory circuits. These findings indicate that MRI-guided infusion of AAV2-BDNF to the entorhinal cortex of the non-human primate results in safe and accurate targeting and distribution of BDNF to both the entorhinal cortex and the hippocampus. These methods are adaptable to human clinical trials.

Intermittent convection-enhanced delivery of GDNF into rhesus monkey putamen: absence of local or cerebellar toxicity.

Glial cell line-derived neurotrophic factor (GDNF) has demonstrated neurorestorative and neuroprotective effects in rodent and nonhuman primate models of Parkinson's disease. However, continuous intraputamenal infusion of GDNF (100 µg/day) resulted in multifocal cerebellar Purkinje cell loss in a 6-month toxicity study in rhesus monkeys. It was hypothesized that continuous leakage of GDNF into the cerebrospinal fluid compartment during the infusions led to down-regulation of GDNF receptors on Purkinje cells, and that subsequent acute withdrawal of GDNF then mediated the observed cerebellar lesions. Here we present the results of a 9-month toxicity study in which rhesus monkeys received intermittent intraputamenal infusions via convection-enhanced delivery. Animals were treated with GDNF (87.1 µg; N = 14) or vehicle (N = 6) once every 4 weeks for a total of 40 weeks (11 treatments). Four of the GDNF-treated animals were utilized in a satellite study assessing the impact of concomitant catheter repositioning prior to treatment. In the main study, eight animals (5 GDNF, 3 control) were euthanized at the end of the treatment period, along with the four satellite study animals, while the remaining eight animals (5 GDNF, 3 control) were euthanized at the end of a 12-week recovery period. There were no GDNF-related adverse effects and in particular, no GDNF-related microscopic findings in the brain, spinal cord, dorsal root ganglia, or trigeminal ganglia. Therefore, 87.1 µg/4 weeks is considered the no observed adverse effect level for GDNF in rhesus monkeys receiving intermittent, convection-enhanced delivery of GDNF for 9 months.

AAV9-mediated expression of a non-self protein in nonhuman primate central nervous system triggers widespread neuroinflammation driven by antigen-presenting cell transduction.

Many studies have demonstrated that adeno-associated virus serotype 9 (AAV9) transduces astrocytes and neurons when infused into rat or nonhuman primate (NHP) brain. We previously showed in rats that transduction of antigen-presenting cells (APC) by AAV9 encoding a foreign protein triggered a full neurotoxic immune response. Accordingly, we asked whether this phenomenon occurred in NHP. We performed parenchymal or intrathecal infusion of AAV9 encoding green fluorescent protein (GFP), a non-self protein derived from jellyfish, or human aromatic L-amino acid decarboxylase (hAADC), a self-protein, in separate NHP. Animals receiving AAV9-GFP into cisterna magna (CM) became ataxic, indicating cerebellar pathology, whereas AAV9-hAADC animals remained healthy. In transduced regions, AAV9-GFP elicited inflammation associated with early activation of astrocytic and microglial cells, along with upregulation of major histocompatibility complex class II (MHC-II) in glia. In addition, we found Purkinje neurons lacking calbindin after AAV9-GFP but not after AAV9-hAADC delivery. Our results demonstrate that AAV9-mediated expression of a foreign-protein, but not self-recognized protein, triggers complete immune responses in NHP regardless of the route of administration. Our results warrant caution when contemplating use of serotypes that can transduce APC if the transgene is not syngeneic with the host. This finding has the potential to complicate preclinical toxicology studies in which such vectors encoding human cDNA's are tested in animals.

Dynamic hyperpolarized carbon-13 MR metabolic imaging of nonhuman primate brain.

PURPOSE: To investigate hyperpolarized (13) C metabolic imaging methods in the primate brain that can be translated into future clinical trials for patients with brain cancer. METHODS: (13) C coils and pulse sequences designed for use in humans were tested in phantoms. Dynamic (13) C data were obtained from a healthy cynomolgus monkey brain using the optimized (13) C coils and pulse sequences. The metabolite kinetics were estimated from two-dimensional localized (13) C dynamic imaging data from the nonhuman primate brain. RESULTS: Pyruvate and lactate signal were observed in both the brain and the surrounding tissues with the maximum signal-to-noise ratio of 218 and 29 for pyruvate and lactate, respectively. Apparent rate constants for the conversion of pyruvate to lactate and the ratio of lactate to pyruvate showed a difference between brain and surrounding tissues. CONCLUSION: The feasibility of using hyperpolarized [1-(13) C]-pyruvate for assessing in vivo metabolism in a healthy nonhuman primate brain was demonstrated using a hyperpolarized (13) C imaging experimental setup designed for studying patients with brain tumors. The kinetics of the metabolite conversion suggests that this approach may be useful in future studies of human neuropathology.

Merits of combination cortical, subcortical, and cerebellar injections for the treatment of Niemann-Pick disease type A.

Niemann-Pick disease Type A (NPA) is a neuronopathic lysosomal storage disease (LSD) caused by the loss of acid sphingomyelinase (ASM). The goals of the current study are to ascertain the levels of human ASM that are efficacious in ASM knockout (ASMKO) mice, and determine whether these levels can be attained in non-human primates (NHPs) using a multiple parenchymal injection strategy. Intracranial injections of different doses of AAV1-hASM in ASMKO mice demonstrated that only a small amount of enzyme (<0.5 mg hASM/g tissue) was sufficient to increase survival, and that increasing the amount of hASM did not enhance this survival benefit until a new threshold level of >10 mg hASM/g tissue was reached. In monkeys, injection of 12 tracts of AAV1-hASM resulted in efficacious levels of enzyme in broad regions of the brain that was aided, in part, by axonal transport of adeno-associated virus (AAV) and movement through the perivascular space. This study demonstrates that a combination cortical, subcortical, and cerebellar injection protocol could provide therapeutic levels of hASM to regions of the NHP brain that are highly affected in NPA patients. The information from this study might help design new AAV-mediated enzyme replacement protocols for NPA and other neuronopathic LSDs in future clinical trials.

GDNF gene therapy for alcohol use disorder in male non-human primates.

Alcohol use disorder (AUD) exacts enormous personal, social and economic costs globally. Return to alcohol use in treatment-seeking patients with AUD is common, engendered by a cycle of repeated abstinence-relapse episodes even with use of currently available pharmacotherapies. Repeated ethanol use induces dopaminergic signaling neuroadaptations in ventral tegmental area (VTA) neurons of the mesolimbic reward pathway, and sustained dysfunction of reward circuitry is associated with return to drinking behavior. We tested this hypothesis by infusing adeno-associated virus serotype 2 vector encoding human glial-derived neurotrophic factor (AAV2-hGDNF), a growth factor that enhances dopaminergic neuron function, into the VTA of four male rhesus monkeys, with another four receiving vehicle, following induction of chronic alcohol drinking. GDNF expression ablated the return to alcohol drinking behavior over a 12-month period of repeated abstinence-alcohol reintroduction challenges. This behavioral change was accompanied by neurophysiological modulations to dopamine signaling in the nucleus accumbens that countered the hypodopaminergic signaling state associated with chronic alcohol use, indicative of a therapeutic modulation of limbic circuits countering the effects of alcohol. These preclinical findings suggest gene therapy targeting relapse prevention may be a potential therapeutic strategy for AUD.

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.

Efficient gene therapy-based method for the delivery of therapeutics to primate cortex.

Transduction of the primate cortex with adeno-associated virus (AAV)-based gene therapy vectors has been challenging, because of the large size of the cortex. We report that a single infusion of AAV2 vector into thalamus results in widespread expression of transgene in the cortex through transduction of widely dispersed thalamocortical projections. This finding has important implications for the treatment of certain genetic and neurodegenerative diseases.

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.

Image-guided convection-enhanced delivery of GDNF protein into monkey putamen.

Recently, we developed an MRI-based method that enables tracking of parenchymal infusions of therapeutic agents by inclusion of a contrast reagent in the infusate. We show that both liposomal Gadoteridol (GDL) and free Gadoteridol (Gd) can be used for MRI-monitored infusions into the non-human primate (NHP) putamen to predict the distribution of GDNF protein after convection-enhanced delivery (CED). GDNF and both MRI tracers showed good co-distribution within the putamen and other brain regions. Although the CED infusion technique can distribute GDNF protein over large brain regions, continuous administration of GDNF could cause undesired effects that could counteract the benefits of CED as demonstrated in this study when large volumes of GDNF were delivered that lead to GDNF leakage into CSF. These limitations can be addressed by employing an intermittent CED schedule that permits consistent target coverage without GDNF leakage into CSF or white matter. We present an approach intracranial GDNF infusions that can be optimized by means of real-time monitoring via MRI. Adoption of this new standard, along with advanced, reflux-resistant cannulae, may permit reconsideration of direct GDNF infusion into parenchyma as a clinical strategy, since previous clinical studies involving chronic infusion of recombinant glial cell line-derived neurotrophic factor (GDNF) to the putamen for the treatment of Parkinson's disease have yielded mixed results, a state of affairs that may in part be attributed to suboptimal infusion parameters.

Optimal region of the putamen for image-guided convection-enhanced delivery of therapeutics in human and non-human primates.

Optimal results in the direct brain delivery of brain therapeutics such as growth factors or viral vector into primate brain depend on reproducible distribution throughout the target region. In the present study, we retrospectively analyzed MRI of 25 convection-enhanced delivery (CED) infusions with MRI contrast into the putamen of non-human primates (NHP). Infused volume (V(i)) was compared to total volume of distribution (V(d)) versus V(d) within the target putamen. Excellent distribution of contrast agent within the putamen was obtained in eight cases that were used to define an optimal target volume or "green" zone. Partial or poor distribution with leakage into adjacent anatomical structures was noted in 17 cases, defining "blue" and "red" zones, respectively. Quantitative containment (99±1%) of infused gadoteridol within the putamen was obtained when the cannula was placed in the green zone, 87±3% in the blue zone and 49±0.05% in the red zone. These results were used to determine a set of 3D stereotactic coordinates that define an optimal site for putaminal infusions in NHP and human putamen. We conclude that cannula placement and definition of optimal (green zone) stereotactic coordinates have important implications in ensuring effective delivery of therapeutics into the putamen utilizing routine stereotactic MRI localization procedures and should be considered when local therapies such as gene transfer or protein administration are being translated into clinical therapy.

Eight years of clinical improvement in MPTP-lesioned primates after gene therapy with AAV2-hAADC.

This study completes the longest known in vivo monitoring of adeno-associated virus (AAV)-mediated gene expression in nonhuman primate (NHP) brain. Although six of the eight parkinsonian NHP originally on study have undergone postmortem analysis, as described previously, we monitored the remaining two animals for a total of 8 years. In this study, NHP received AAV2-human L-amino acid decarboxylase (hAADC) infusions into the MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine)-lesioned putamen. Restoration of AADC activity restored normal response to levodopa and gene expression could be quantitated repeatedly over many years by 6-[(18)F]fluoro-meta-tyrosine (FMT)-positron emission tomography (PET) and confirm that AADC transgene expression remained unchanged at the 8-year point. Behavioral assessments confirmed continued, normalized response to levodopa (improvement by 35% over historical controls). Postmortem analysis showed that, although only 5.6 + or - 1% and 6.6 + or - 1% of neurons within the transduced volumes of the striatum were transduced, this still secured robust clinical improvement. Importantly, there were no signs of neuroinflammation or reactive gliosis at the 8-year point, indicative of the safety of this treatment. The present data suggest that the improvement in the L-3,4-dihydroxyphenylalanine (L-Dopa) therapeutic window brought about by AADC gene therapy is pronounced and persistent for many years.

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

Gene therapies that utilize convention-enhanced delivery (CED) will require close monitoring of vector infusion in real time and accurate prediction of drug distribution. The magnetic resonance imaging (MRI) contrast agent, Gadoteridol (Gd), was used to monitor CED infusion and to predict the expression pattern of glial cell line-derived neurotrophic factor (GDNF) protein after administration of adeno-associated virus type 2 (AAV2) vector encoding human pre-pro-GDNF complementary DNA. The nonhuman primate (NHP) thalamus was utilized for modeling infusion to allow delivery of volumes more relevant to planned human studies. AAV2 encoding human aromatic L-amino acid decarboxylase (AADC) was coinfused with AAV2-GDNF/Gd to confirm regions of AAV2 transduction versus extracellular GDNF diffusion. There was a close correlation between Gd distribution and GDNF or AADC expression, and the ratios of expression areas of GDNF or AADC versus Gd were both close to 1. Our data support the use of Gd and MRI to monitor AAV2 infusion via CED and to predict the distribution of GDNF protein after AAV2-GDNF administration.

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.

Ultrasound-enhanced drug transport and distribution in the brain.

Drug delivery in the brain is limited by slow drug diffusion in the brain tissue. This study tested the hypothesis that ultrasound can safely enhance the permeation of drugs in the brain. In vitro exposure to ultrasound at various frequencies (85 kHz, 174 kHz, and 1 MHz) enhanced the permeation of tritium-labeled molecules with molecular weight up to 70 kDa across porcine brain tissue. A maximum enhancement of 24-fold was observed at 85 kHz and 1,200 J/cm(2). In vivo exposure to 1-MHz ultrasound further demonstrated the ability of ultrasound to facilitate molecule distribution in the brain of a non-human primate. Finally, ultrasound under conditions similar to those used in vivo was shown to cause no damage to plasmid DNA, siRNA, adeno-associated virus, and fetal rat cortical neurons over a range of conditions. Altogether, these studies demonstrate that ultrasound can increase drug permeation in the brain in vitro and in vivo under conditions that did not cause detectable damage.

Real-time MR imaging of adeno-associated viral vector delivery to the primate brain.

We are developing a method for real-time magnetic resonance imaging (MRI) visualization of convection-enhanced delivery (CED) of adeno-associated viral vectors (AAV) to the primate brain. By including gadolinium-loaded liposomes (GDL) with AAV, we can track the convective movement of viral particles by continuous monitoring of distribution of surrogate GDL. In order to validate this approach, we infused two AAV (AAV1-GFP and AAV2-hAADC) into three different regions of non-human primate brain (corona radiata, putamen, and thalamus). The procedure was tolerated well by all three animals in the study. The distribution of GFP determined by immunohistochemistry in both brain regions correlated closely with distribution of GDL determined by MRI. Co-distribution was weaker with AAV2-hAADC, although in vivo PET scanning with FMT for AADC activity correlated well with immunohistochemistry of AADC. Although this is a relatively small study, it appears that AAV1 correlates better with MRI-monitored delivery than does AAV2. It seems likely that the difference in distribution may be due to differences in tissue specificity of the two serotypes.

Non-PEGylated liposomes for convection-enhanced delivery of topotecan and gadodiamide in malignant glioma: initial experience.

Convection-enhanced delivery (CED) of highly stable PEGylated liposomes encapsulating chemotherapeutic drugs has previously been effective against malignant glioma xenografts. We have developed a novel, convectable non-PEGylated liposomal formulation that can be used to encapsulate both the topoisomerase I inhibitor topotecan (topoCED) and paramagnetic gadodiamide (gadoCED), providing an ideal basis for real-time monitoring of drug distribution. Tissue retention of topoCED following single CED administration was significantly improved relative to free topotecan. At a dose of 10 microg (0.5 mg/ml), topoCED had a half-life in brain of approximately 1 day and increased the area under the concentration-time curve (AUC) by 28-fold over free topotecan (153.8 vs. 5.5 microg day/g). The combination of topoCED and gadoCED was found to co-convect well in both naïve rat brain and malignant glioma xenografts (correlation coefficients 0.97-0.99). In a U87MG cell assay, the 50% inhibitory concentration (IC(50)) of topoCED was approximately 0.8 microM at 48 and 72 h; its concentration-time curves were similar to free topotecan and unaffected by gadoCED. In a U87MG intracranial rat xenograft model, a two-dose CED regimen of topoCED co-infused with gadoCED greatly increased median overall survival at dose levels of 0.5 mg/ml (29.5 days) and 1.0 mg/ml (33.0 days) vs. control (20.0 days; P < 0.0001 for both comparisons). TopoCED at higher concentrations (1.6 mg/ml) co-infused with gadoCED showed no evidence of histopathological changes attributable to either agent. The positive results of tissue pharmacokinetics, co-convection, cytotoxicity, efficacy, and lack of toxicity of topoCED in a clinically meaningful dose range, combined with an ideal matched-liposome paramagnetic agent, gadoCED, implicates further clinical applications of this therapy in the treatment of malignant glioma.

Biodistribution of adeno-associated virus type-2 in nonhuman primates after convection-enhanced delivery to brain.

A combination treatment of AAV2-hAADC with oral levodopa is a novel therapeutic approach that is being developed for late-stage Parkinson's disease. Biodistribution of AAV2-hAADC was assessed over a wide range of vector dose in 12 monkeys with parkinsonian syndrome, 6 months after intraputamenal infusion. Quantitative PCR (Q-PCR) from all the major neuroanatomical regions of the brain indicated a dose-dependent increase in vector DNA, with 99% being detected in the target site and other basal ganglia tissues. Within these tissues, the distribution varied widely between the putamen (PT) and the globus pallidus, and this was attributed to differences in vector transport. Q-PCR and immunocytochemistry were consistent with results reported earlier for various measures of transgene expression including aromatic L-amino acid decarboxylase (AADC) activity assays, behavioral response, and in vivo imaging with positron emission tomography (PET). Outside of the brain, trace amounts of vector DNA were detected in the spleens of animals in the two highest dose groups, but not in any other peripheral tissue, blood, or cerebrospinal fluid. Some increase in neutralizing antibody titers to adeno-associated virus type-2 (AAV2) capsid protein was observed in monkeys that received high doses of AAV2-hAADC or control AAV2-GFP. This study further validates convection-enhanced delivery (CED) as the preferred method of viral vector delivery to the brain, and supports a Phase I clinical testing of AAV2-hAADC in humans with Parkinson's disease.

Infuse-as-you-go convective delivery to enhance coverage of elongated brain targets: technical note.

OBJECTIVE: To develop and assess a convective delivery technique that enhances the effectiveness of drug delivery to nonspherical brain nuclei, the authors developed an occipital "infuse-as-you-go" approach to the putamen and compared it to the currently used transfrontal approach. METHODS: Eleven nonhuman primates received a bilateral putamen injection of adeno-associated virus with 2 mM gadolinium-DTPA by real-time MR-guided convective perfusion via either a transfrontal (n = 5) or occipital infuse-as-you-go (n = 6) approach. RESULTS: MRI provided contemporaneous assessment and monitoring of putaminal infusions for transfrontal (2 to 3 infusion deposits) and occipital infuse-as-you-go (stepwise infusions) putaminal approaches. The infuse-as-you-go technique was more efficient than the transfrontal approach (mean 35 ± 1.1 vs 88 ± 8.3 minutes [SEM; p < 0.001]). More effective perfusion of the postcommissural and total putamen was achieved with the infuse-as-you-go versus transfronatal approaches (100-µl infusion volumes; mean posterior commissural coverage 76.2% ± 5.0% vs 32.8% ± 2.9% [p < 0.001]; and mean total coverage 53.5% ± 3.0% vs 38.9% ± 2.3% [p < 0.01]). CONCLUSIONS: The infuse-as-you-go approach, paralleling the longitudinal axis of the target structure, provides a more effective and efficient method for convective infusate coverage of elongated, irregularly shaped subcortical brain nuclei.