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Piotr Hadaczek, Hanna Mirek, Mitchel S. Berger and Krystof Bankiewicz

Object. Low efficacy of gene transfer, transient gene expression, and toxicity of viral vectors are the major hurdles in successful anticancer gene therapy. The authors conducted in vitro (U87MG cell line) and in vivo (xenograft, tumor-bearing rodent model) studies to address the stability of transduction by using the adenoassociated virus serotype-2 (AAV2)—thymidine kinase (TK) vector over time.

Methods. Standard methods for cell growth and a ganciclovir (GCV) cytotoxicity assay were applied. The AAV2-TK was infused into implanted tumors in athymic rats via convection-enhanced delivery (CED). Thymidine kinase expression was evaluated through immunohistochemical analysis, and the distribution volumes of the transduced tumors were calculated. Twenty-four hours following the viral infusions, animals were treated with GCV (50 mg/kg intraperitoneally every day for 10 days; six rats) or phosphate-buffered saline (six rats).

A rapid decrease in TK expression over time was observed both in vitro and in vivo. A large volume of the tumor (up to 39%) was transduced with AAV2-TK following CED. Administration of GCV resulted in limited therapeutic effects (survival of 25.8 compared with 21.3 days).

Conclusions. Rapid elimination of TK expression from dividing tumor cells and focal transduction of the brain tumor were most likely responsible for the limited bystander effect in this approach. Immediate administration of GCV is crucial to assure maximal efficacy in the elimination of cancer cells. In addition, the complete or diffused transduction of a brain tumor with TK may be required for its total eradication.

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Arman Jahangiri, Aaron T. Chin, Patrick M. Flanigan, Rebecca Chen, Krystof Bankiewicz and Manish K. Aghi

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.

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Vivek Sudhakar, Amin Mahmoodi, John R. Bringas, Jerusha Naidoo, Adrian Kells, Lluis Samaranch, Massimo S. Fiandaca and Krystof S. Bankiewicz

OBJECTIVE

Successful convection-enhanced delivery of therapeutic agents to subcortical brain structures requires accurate cannula placement. Stereotactic guiding devices have been developed to accurately target brain nuclei. However, technologies remain limited by a lack of MRI compatibility, or by devices’ size, making them suboptimal for direct gene delivery to brain parenchyma. The goal of this study was to validate the accuracy of a novel frameless skull-mounted ball-joint guide array (BJGA) in targeting the nonhuman primate (NHP) brain.

METHODS

Fifteen MRI-guided cannula insertions were performed on 9 NHPs, each targeting the putamen. Optimal trajectories were planned on a standard MRI console using 3D multiplanar baseline images. After cannula insertion, the intended trajectory was compared to the final trajectory to assess deviation (euclidean error) of the cannula tip.

RESULTS

The average cannula tip deviation was 1.18 ± 0.60 mm (mean ± SD) as measured by 2 independent reviewers. Topological analysis showed a superior, posterior, and rightward directional bias, and the intra- and interclass correlation coefficients were > 0.85, indicating valid and reliable intra- and interobserver evaluation.

CONCLUSIONS

The data demonstrate that the BJGA can be used to reliably target subcortical brain structures by using MRI guidance, with accuracy comparable to current frameless stereotactic systems. The size and versatility of the BJGA, combined with a streamlined workflow, allows for its potential applicability to a variety of intracranial neurosurgical procedures, and for greater flexibility in executing MRI-guided experiments within the NHP brain.

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John H. Sampson, Gamal Akabani, Allan H. Friedman, Darell Bigner, Sandeep Kunwar, Mitchel S. Berger and Krystof S. Bankiewicz

Objectives

Convection-enhanced delivery (CED) is a novel technique used to deliver agents to the brain parenchyma for treatment of neoplastic, infectious, and degenerative conditions. The purpose of this study was to determine if CED would provide a larger volume of distribution (Vd) of a radiolabeled monoclonal antibody (mAb) than a bolus injection.

Methods

Patients harboring a recurrent glioblastoma multiforme that reacted with the antitenascin mAb 81C6 during immunohistochemical analysis were randomized to receive an intratumoral injection of the human–murine chimeric mAb Ch81C6, which had been labeled with the 123I tracer. The mAb was administered by either a bolus injection or CED via a stereotactically placed catheter; between 48 and 72 hours later the mAb was again administered using the other technique. Injections of escalating doses of a 131I-labeled therapeutic mAb were then delivered using the technique shown to produce the largest Vd by single-photon emission computerized tomography.

Conclusions

Convection-enhanced delivery has enormous potential for administering drugs to sites within the central nervous system. For the relatively small volumes injected in this study, however, CED did not provide a significant increase in the Vd when compared with the bolus injection. Nevertheless, a clear cross-over effect was seen, which was probably related to the temporal proximity of the two infusions.

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Dali Yin, R. Mark Richardson, Massimo S. Fiandaca, John Bringas, John Forsayeth, Mitchel S. Berger and Krystof S. Bankiewicz

Object

The purpose of this study was to optimize stereotactic coordinates for delivery of therapeutic agents into the thalamus and brainstem, using convection-enhanced delivery (CED) to avoid leakage into surrounding anatomical structures while maximizing CED of therapeutics within the target volume.

Methods

The authors recently published targeting data for the nonhuman primate putamen in which they defined infusion parameters, referred to as “red,” “blue,” and “green” zones, that describe cannula placements resulting in poor, suboptimal, and optimal volumes of distribution, respectively. In the present study, the authors retrospectively analyzed 22 MR images with gadoteridol as a contrast reagent, which were obtained during CED infusions into the thalamus (14 cases) and brainstem (8 cases) of nonhuman primates.

Results

Excellent distribution of gadoteridol within the thalamus was obtained in 8 cases and these were used to define an optimal target locus (or green zone). Good distribution in the thalamus, with variable leakage into adjacent anatomical structures, was noted in 6 cases, defining a blue zone. Quantitative containment (99.7 ± 0.2%) of gadoteridol within the thalamus was obtained when the cannula was placed in the green zone, and less containment (85.4 ± 3.8%) was achieved with cannula placement in the blue zone. Similarly, a green zone was also defined in the brainstem, and quantitative containment of infused gadoteridol within the brainstem was 99.4 ± 0.6% when the cannula was placed in the green zone. These results were used to determine a set of 3D stereotactic coordinates that define an optimal site for infusions intended to cover the thalamus and brainstem of nonhuman primates.

Conclusions

The present study provides quantitative analysis of cannula placement and infusate distribution using real-time MR imaging and defines an optimal zone for infusion in the nonhuman primate thalamus and brainstem. Cannula placement recommendations developed from such translational nonhuman primate studies have significant implications for the design of anticipated clinical trials featuring CED therapy into the thalamus and brainstem for CNS diseases.

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Michal T. Krauze, Ryuta Saito, Charles Noble, Matyas Tamas, John Bringas, John W. Park, Mitchel S. Berger and Krystof Bankiewicz

Object. Clinical application of the convection-enhanced delivery (CED) technique is currently limited by low infusion speed and reflux of the delivered agent. The authors developed and evaluated a new step-design cannula to overcome present limitations and to introduce a rapid, reflux-free CED method for future clinical trials.

Methods. The CED of 0.4% trypan blue dye was performed in agarose gel to test cannula needles for distribution and reflux. Infusion rates ranging from 0.5 to 50 µl/minute were used. Agarose gel findings were translated into a study in rats and then in cynomolgus monkeys (Macaca fascicularis) by using trypan blue and liposomes to confirm the efficacy of the reflux-free step-design cannula in vivo.

Results of agarose gel studies showed reflux-free infusion with high flow rates using the step-design cannula. Data from the study in rats confirmed the agarose gel findings and also revealed increasing tissue damage at a flow rate above 5-µl/minute. Robust reflux-free delivery and distribution of liposomes was achieved using the step-design cannula in brains in both rats and nonhuman primates.

Conclusions. The authors developed a new step-design cannula for CED that effectively prevents reflux in vivo and maximizes the distribution of agents delivered in the brain. Data in the present study show reflux-free infusion with a constant volume of distribution in the rat brain over a broad range of flow rates. Reflux-free delivery of liposomes into nonhuman primate brain was also established using the cannula. This step-design cannula may allow reflux-free distribution and shorten the duration of infusion in future clinical applications of CED in humans.

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Vivek Sudhakar, Jerusha Naidoo, Lluis Samaranch, John R. Bringas, Russell R. Lonser, Massimo S. Fiandaca and Krystof S. Bankiewicz

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.

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Vanja Varenika, Peter Dickinson, John Bringas, Richard LeCouteur, Robert Higgins, John Park, Massimo Fiandaca, Mitchel Berger, John Sampson and Krystof Bankiewicz

Object

The authors have shown that convection-enhanced delivery (CED) of gadoteridol-loaded liposomes (GDLs) into different regions of normal monkey brain results in predictable, widespread distribution of this tracking agent as detected by real-time MR imaging. They also have found that this tracking technique allows monitoring of the distribution of similar nanosized agents such as therapeutic liposomes and viral vectors. A limitation of this procedure is the unexpected leakage of liposomes out of targeted parenchyma or malignancies into sulci and ventricles. The aim of the present study was to evaluate the efficacy of CED after the onset of these types of leakage.

Methods

The authors documented this phenomenon in a study of 5 nonhuman primates and 7 canines, comprising 54 CED infusion sessions. Approximately 20% of these infusions resulted in leakage into cerebral ventricles or sulci. All of the infusions and leakage events were monitored with real-time MR imaging. The authors created volume-distributed versus volume-infused graphs for each infusion session. These graphs revealed the rate of distribution of GDL over the course of each infusion and allowed the authors to evaluate the progress of CED before and after leakage.

Results

The distribution of therapeutics within the target structure ceased to increase or resulted in significant attenuation after the onset of leakage.

Conclusions

An analysis of the cases in this study revealed that leakage undermines the efficacy of CED. These findings reiterate the importance of real-time MR imaging visualization during CED to ensure an accurate, robust distribution of therapeutic agents.

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Toshio Kikuchi, Ryuta Saito, Shin-ichirou Sugiyama, Yoji Yamashita, Toshihiro Kumabe, Michal Krauze, Krystof Bankiewicz and Teiji Tominaga

Object

The characteristics of polyethylene glycol–coated liposomal doxorubicin (PLD), the only liposomal drug now clinically available for intravenous injection, were investigated after convection-enhanced delivery (CED) into the rat brain parenchyma.

Methods

The distribution, tissue retention, and toxicity profile were evaluated after CED into the rat brain parenchyma. The antitumor efficacy was also determined in rodent intracranial U-251MG and U-87MG glioma models.

Results

Convection-enhanced delivery of PLD achieved wider distributions and delayed onset of toxicity in the brain parenchyma compared with CED of free doxorubicin infusion. Fluorescence generated from doxorubicin infused as PLD was detected until at least 30 days after infusion. Local toxicity was not observed when a 10% dilution of the commercially available PLD solution was used (0.2 mg/ml doxorubicin), but was significant at higher concentrations. Results after 10% PLD was delivered locally with CED demonstrated significant survival prolongation in both intracranial U-251MG and U-87MG xenograft models.

Conclusions

Convection-enhanced delivery of PLD achieved extensive tissue distribution and sustained drug release. Convection-enhanced delivery of PLD is a promising chemotherapy for the treatment of malignant gliomas.

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Peter J. Dickinson, Richard A. Lecouteur, Robert J. Higgins, John R. Bringas, Byron Roberts, Richard F. Larson, Yoji Yamashita, Michal Krauze, Charles O. Noble, Daryl Drummond, Dmitri B. Kirpotin, John W. Park, Mitchel S. Berger and Krystof S. Bankiewicz

Object

Many factors relating to the safety and efficacy of convection-enhanced delivery (CED) into intracranial tumors are poorly understood. To investigate these factors further and establish a more clinically relevant large animal model, with the potential to investigate CED in large, spontaneous tumors, the authors developed a magnetic resonance (MR) imaging–compatible system for CED of liposomal nanoparticles into the canine brain, incorporating real-time MR imaging. Additionally any possible toxicity of liposomes containing Gd and the chemotherapeutic agent irinotecan (CPT-11) was assessed following direct intraparenchymal delivery.

Methods

Four healthy laboratory dogs were infused with liposomes containing Gd, rhodamine, or CPT-11. Convection-enhanced delivery was monitored in real time by sequential MR imaging, and the volumes of distribution were calculated from MR images and histological sections. Assessment of any toxicity was based on clinical and histopathological evaluation. Convection-enhanced delivery resulted in robust volumes of distribution in both gray and white matter, and real-time MR imaging allowed accurate calculation of volumes and pathways of distribution.

Results

Infusion variability was greatest in the gray matter, and was associated with leakage into ventricular or subarachnoid spaces. Complications were minimal and included mild transient proprioceptive deficits, focal hemorrhage in 1 dog, and focal, mild perivascular, nonsuppurative encephalitis in 1 dog.

Conclusions

Convection-enhanced delivery of liposomal Gd/CPT-11 is associated with minimal adverse effects in a large animal model, and further assessment for use in clinical patients is warranted. Future studies investigating real-time monitored CED in spontaneous gliomas in canines are feasible and will provide a unique, clinically relevant large animal translational model for testing this and other therapeutic strategies.