Convective distribution of macromolecules in the primate brain demonstrated using computerized tomography and magnetic resonance imaging

OBJECT: Convection-enhanced delivery (CED), the delivery and distribution of drugs by the slow bulk movement of fluid in the extracellular space, allows delivery of therapeutic agents to large volumes of the brain at relatively uniform concentrations. This mode of drug delivery offers great potential for the treatment of many neurological disorders, including brain tumors, neurodegenerative diseases, and seizure disorders. An analysis of the treatment efficacy and toxicity of this approach requires confirmation that the infusion is distributed to the targeted region and that the drug concentrations are in the therapeutic range. METHODS: To confirm accurate delivery of therapeutic agents during CED and to monitor the extent of infusion in real time, albumin-linked surrogate tracers that are visible on images obtained using noninvasive techniques (iopanoic acid [IPA] for computerized tomography [CT] and Gd-diethylenetriamine pentaacetic acid for magnetic resonance [MR] imaging) were developed and investigated for their usefulness as surrogate tracers during convective distribution of a macromolecule. The authors infused albumin-linked tracers into the cerebral hemispheres of monkeys and measured the volumes of distribution by using CT and MR imaging. The distribution volumes measured by imaging were compared with tissue volumes measured using quantitative autoradiography with [14C]bovine serum albumin coinfused with the surrogate tracer. For in vivo determination of tracer concentration, the authors examined the correlation between the concentration of the tracer in brain homogenate standards and CT Hounsfield units. They also investigated the long-term effects of the surrogate tracer for CT scanning, IPA-albumin, on animal behavior, the histological characteristics of the tissue, and parenchymal toxicity after cerebral infusion. CONCLUSIONS: Distribution of a macromolecule to clinically significant volumes in the brain is possible using convection. The spatial dimensions of the tissue distribution can be accurately defined in vivo during infusion by using surrogate tracers and conventional imaging techniques, and it is expected that it will be possible to determine local concentrations of surrogate tracers in voxels of tissue in vivo by using CT scanning. Use of imaging surrogate tracers is a practical, safe, and essential tool for establishing treatment volumes during high-flow interstitial microinfusion of the central nervous system.     

Real-time imaging of convection-enhanced delivery of viruses and virus-sized particles

OBJECT: Despite recent evidence showing that convection-enhanced delivery (CED) of viruses and virus-sized particles to the central nervous system (CNS) is possible, little is known about the factors influencing distribution of these vectors with convection. To better define the delivery of viruses and virus-sized particles in the CNS, and to determine optimal parameters for infusion, the authors coinfused adeno-associated virus ([AAV], 24-nm diameter) and/or ferumoxtran-10 (24 nm) by using CED during real-time magnetic resonance (MR) imaging. METHODS: Sixteen rats underwent intrastriatal convective coinfusion with 4 microl of 35S-AAV capsids (0.5-1.0 x 10(14) viral particles/ml) and increasing concentrations (0.1, 0.5, 1, and 5 mg/ml) of a similar sized iron oxide MR imaging agent (ferumoxtran-10). Five nonhuman primates underwent either convective coinfusion of 35S-AAV capsids and 1 mg/ml ferumoxtran-10 (striatum, one animal) or infusion of 1 mg/ml ferumoxtran-10 alone (striatum in two animals; frontal white matter in two). Clinical effects, MR imaging studies, quantitative autoradiography, and histological data were analyzed. RESULTS: Real-time, T2-weighted MR imaging of ferumoxtran-10 during infusion revealed a clearly defined hypointense region of perfusion. Quantitative autoradiography confirmed that MR imaging of ferumoxtran-10 at a concentration of 1 mg/ml accurately tracked viral capsid distribution in the rat and primate brain (the mean difference in volume of distribution [Vd] was 7 and 15% in rats and primates, respectively). The Vd increased linearly with increasing volume of infusion (Vi) (R2 = 0.98). The mean Vd/Vi ratio was 4.1 +/- 0.2 (mean +/- standard error of the mean) in gray and 2.3 +/- 0.1 in white matter (p < 0.01). The distribution of infusate was homogeneous. Postinfusion MR imaging revealed leakback along the cannula track at infusion rates greater than 1.5 microl/minute in primate gray and white matter. No animal had clinical or histological evidence of toxicity. CONCLUSIONS: The CED method can be used to deliver AAV capsids and similar sized particles to the CNS safely and effectively over clinically relevant volumes. Moreover, real-time MR imaging of ferumoxtran-10 during infusion reveals that AAV capsids and similar sized particles have different convective delivery properties than smaller proteins and other compounds.     

Effect of ependymal and pial surfaces on convection-enhanced delivery

OBJECT: Convection-enhanced delivery (CED) is increasingly used to investigate new treatments for central nervous system disorders. Although the properties of CED are well established in normal gray and white matter central nervous system structures, the effects on drug distribution imposed by ependymal and pial surfaces are not precisely defined. To determine the effect of these anatomical boundaries on CED, the authors infused low MW and high MW tracers for MR imaging near ependymal (periventricular) and pial (pericisternal) surfaces. METHODS: Five primates underwent CED of Gd-diethylenetriamine pentaacetic acid (Gd-DTPA; MW 590 D) or Gd-bound albumin (Gd-albumin; MW 72,000 D) during serial real-time MR imaging (FLAIR and T1-weighted sequences). Periventricular (caudate) infusions were performed unilaterally in 1 animal (volume of infusion [Vi] 57 microl) and bilaterally in 1 animal with Gd-DTPA (Vi = 40 mul on each side), and bilaterally in 1 animal with Gd-albumin (Vi = 80 microl on each side). Pericisternal infusions were performed in 2 animals with Gd-DTPA (Vi = 190 microl) or with Gd-albumin (Vi = 185 microl) (1 animal each). Clinical effects, MR imaging, and histology were analyzed. RESULTS: Large regions of the brain and brainstem were perfused with both tracers. Intraparenchymal distribution was successfully tracked in real time by using T1-weighted MR imaging. During infusion, the volume of distribution (Vd) increased linearly (R2 = 0.98) with periventricular (mean Vd/Vi ratio +/- standard deviation; 4.5 +/- 0.5) and pericisternal (5.2 +/- 0.3) Vi, but did so only until the leading edge of distribution reached the ependymal or pial surfaces, respectively. After the infusate reached either surface, the Vd/Vi decreased significantly (ependyma 2.9 +/- 0.8, pia mater 3.6 +/- 1.0; p < 0.05) and infusate entry into the ventricular or cisternal cerebrospinal fluid (CSF) was identified on FLAIR but not on T1-weighted MR images. CONCLUSIONS: Ependymal and pial boundaries are permeable to small and large molecules delivered interstitially by convection. Once infusate reaches these surfaces, a portion enters the adjacent ventricular or cisternal CSF and the tissue Vd/Vi ratio decreases. Although T1-weighted MR imaging is best for tracking intraparenchymal infusate distribution, FLAIR MR imaging is the most sensitive and accurate for detecting entry of Gd-labeled imaging compounds into CSF during CED.     

Successful and safe perfusion of the primate brainstem: in vivo magnetic resonance imaging of macromolecular distribution during infusion

OBJECT: Intrinsic disease processes of the brainstem (gliomas, neurodegenerative disease, and others) have remained difficult or impossible to treat effectively because of limited drug penetration across the blood-brainstem barrier with conventional delivery methods. The authors used convection-enhanced delivery (CED) of a macromolecular tracer visible on magnetic resonance (MR) imaging to examine the utility of CED for safe perfusion of the brainstem. METHODS: Three primates (Macaca mulatta) underwent CED of various volumes of infusion ([Vis]; 85, 110, and 120 microl) of Gd-bound albumin (72 kD) in the pontine region of the brainstem during serial MR imaging. Infusate volume of distribution (Vd), homogeneity, and anatomical distribution were visualized and quantified using MR imaging. Neurological function was observed and recorded up to 35 days postinfusion. Histological analysis was performed in all animals. Large regions of the pons and midbrain were successfully and safely perfused with the macromolecular protein. The Vd was linearly proportional to the Vi (R2 = 0.94), with a Vd/Vi ratio of 8.7 +/- 1.2 (mean +/- standard deviation). Furthermore, the concentration across the perfused region was homogeneous. The Vd increased slightly at 24 hours after completion of the infusion, and remained larger until the intensity of infusion faded (by Day 7). No animal exhibited a neurological deficit after infusion. Histological analysis revealed normal tissue architecture and minimal gliosis that was limited to the region immediately surrounding the cannula track. CONCLUSIONS: First, CED can be used to perfuse the brainstem safely and effectively with macromolecules. Second, a large-molecular-weight imaging tracer can be used successfully to deliver, monitor in vivo, and control the distribution of small- and large-molecular-weight putative therapeutic agents for treatment of intrinsic brainstem processes.     

Convection-enhanced delivery into the rat brainstem

OBJECT: Convection-enhanced delivery (CED) can be used safely to achieve high local infusate concentrations within the brain and spinal cord. The use of CED in the brainstem has not been previously reported and may offer an alternative method for treating diffuse pontine gliomas. In the present study the authors tested CED within the rat brainstem to assess its safety and establish distribution parameters. METHODS: Eighteen rats underwent stereotactic cannula placement into the pontine nucleus oralis without subsequent infusions. Twenty rats underwent stereotactic cannula placement followed by infusion of fluorescein isothiocyanate (FITC)-dextran at a constant rate (0.1 microl/minute) until various total volumes of infusion (V(i)s) were reached: 0.5, 1, 2, and 4 microl. Additional rats underwent FITC-dextran infusion (V, 4 microl) and were observed for 48 hours (five animals) or 14 days (five animals). Serial (20-microm thick) brain sections were imaged using confocal microscopy with ultraviolet illumination, and the volume of distribution (Vd) was calculated using computer image analysis. Histological analysis was performed on adjacent sections. No animal exhibited a postoperative neurological deficit, and there was no histological evidence of tissue disruption. The Vd increased linearly (range 15.4-55.8 mm3) along with increasing Vi, with statistically significant correlations for all groups that were compared (p < 0.022). The Va/Vi ratio ranged from 14 to 30.9. The maximum cross-sectional area of fluorescence (range 9.8-20.9 mm2) and the craniocaudal extent of fluorescence (range 2.8-5.1 mm) increased with increasing Vi. CONCLUSIONS: Convection-enhanced delivery can be safely applied to the rat brainstem with substantial and predictable V(d)s. This study provides the basis for investigating delivery of various candidate agents for the treatment of diffuse pontine gliomas.     

Image-guided convection-enhanced delivery of gemcitabine to the brainstem

OBJECT: To determine if the potent antiglioma chemotherapeutic agent gemcitabine could be delivered to the brainstem safely at therapeutic doses while monitoring its distribution using a surrogate magnetic resonance (MR) imaging tracer, the authors used convection-enhanced delivery to perfuse the primate brainstem with gemcitabine and Gd-diethylenetriamine pentaacetic acid (DTPA). METHODS: Six primates underwent convective brainstem perfusion with gemcitabine (0.4 mg/ml; two animals), Gd-DTPA (5 mM; two animals), or a coinfusion of gemcitabine (0.4 mg/ml) and Gd-DTPA (5 mM; two animals), and were killed 28 days afterward. These primates were observed over time clinically (six animals), and with MR imaging (five animals), quantitative autoradiography (one animal), and histological analysis (all animals). In an additional primate, 3H-gemcitabine and Gd-DTPA were coinfused and the animal was killed immediately afterward. In the primates there was no histological evidence of infusate-related tissue toxicity. Magnetic resonance images obtained during infusate delivery demonstrated that the anatomical region infused with Gd-DTPA was clearly distinguishable from surrounding noninfused tissue. Quantitative autoradiography confirmed that Gd-DTPA tracked the distribution of 3H-gemcitabine and closely approximated its volume of distribution (mean volume of distribution difference 13.5%). Conclusions. Gemcitabine can be delivered safely and effectively to the primate brainstem at therapeutic concentrations and at volumes that are higher than those considered clinically relevant. Moreover, MR imaging can be used to track the distribution of gemcitabine by adding Gd-DTPA to the infusate. This delivery paradigm should allow for direct therapeutic application of gemcitabine to brainstem gliomas while monitoring its distribution to ensure effective tumor coverage and to maximize safety.     

Real-time image-guided direct convective perfusion of intrinsic brainstem lesions. Technical note

Recent preclinical studies have demonstrated that convection-enhanced delivery (CED) can be used to perfuse the brain and brainstem with therapeutic agents while simultaneously tracking their distribution using coinfusion of a surrogate magnetic resonance (MR) imaging tracer. The authors describe a technique for the successful clinical application of this drug delivery and monitoring paradigm to the brainstem. Two patients with progressive intrinsic brainstem lesions (one with Type 2 Gaucher disease and one with a diffuse pontine glioma) were treated with CED of putative therapeutic agents mixed with Gd-diethylenetriamene pentaacetic acid (DTPA). Both patients underwent frameless stereotactic placement of MR imaging-compatible outer guide-inner infusion cannulae. Using intraoperative MR imaging, accurate cannula placement was confirmed and real-time imaging during infusion clearly demonstrated progressive filling of the targeted region with the drug and Gd-DTPA infusate. Neither patient had clinical or imaging evidence of short- or long-term infusate-related toxicity. Using this technique, CED can be used to safely perfuse targeted regions of diseased brainstem with therapeutic agents. Coinfused imaging surrogate tracers can be used to monitor and control the distribution of therapeutic agents in vivo. Patients with a variety of intrinsic brainstem and other central nervous system disorders may benefit from a similar treatment paradigm.     

A realistic brain tissue phantom for intraparenchymal infusion studies

OBJECT: The goal of this study was to validate a simple, inexpensive, and robust model system to be used as an in vitro surrogate for in vivo brain tissues in preclinical and exploratory studies of infusion-based intraparenchymal drug and cell delivery. METHODS: Agarose gels of varying concentrations and porcine brain were tested to determine the infusion characteristics of several different catheters at flow rates of 0.5 and 1 microl per minute by using bromophenol blue (BPB) dye (molecular weight [MW] approximately 690) and gadodiamide (MW approximately 573). Magnetic resonance (MR) imaging and videomicroscopy were used to measure the distribution of these infusates, with a simultaneous measurement of infusion pressures. In addition, the forces of catheter penetration and movement through gel and brain were measured. Agarose gel at a 0.6% concentration closely resembles in vivo brain with respect to several critical physical characteristics. The ratio of distribution volume to infusion volume of agarose was 10 compared with 7.1 for brain. The infusion pressure of the gel demonstrated profiles similar in configuration and magnitude to those of the brain (plateau pressures 10-20 mm Hg). Gadodiamide infusion in agarose closely resembled that in the brain, as documented using T1-weighted MR imaging. Gadodiamide distribution in agarose gel was virtually identical to that of BPB dye, as documented by MR imaging and videomicroscopy. The force profile for insertion of a silastic catheter into agarose gel was similar in magnitude and configuration to the force profile for insertion into the brain. Careful insertion of the cannula using a stereotactic guide is critical to minimize irregularity and backflow of infusate distribution. CONCLUSIONS: Agarose gel (0.6%) is a useful surrogate for in vivo brain in exploratory studies of convection-enhanced delivery.     

Reflux-free cannula for convection-enhanced high-speed delivery of therapeutic agents

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 microl/minute were used. Agarose gel findings were translated into a study in rats and then in cynomolgus monkeys (Macacafascicularis) 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-microl/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.     

Distribution of AAV-TK following intracranial convection-enhanced delivery into rats

Adeno-associated virus (AAV)-based vectors are being tested in animal models as viable treatments for glioma and neurodegenerative disease and could potentially be employed to target a variety of central nervous system disorders. The relationship between dose of injected vector and its resulting distribution in brain tissue has not been previously reported nor has the most efficient method of delivery been determined. Here we report that convection-enhanced delivery (CED) of 2.5 x 10(8), 2.5 x 10(9), or 2.5 x 10(10) particles of AAV-thymidine kinase (AAV-TK) into rat brain revealed a clear dose response. In the high-dose group, a volume of 300 mm3 of brain tissue was partially transduced. Results showed that infusion pump and subcutaneous osmotic pumps were both capable of delivering vector via CED and that total particle number was the most important determining factor in obtaining efficient expression. Results further showed differences in histopathology between the delivery groups. While administration of vector using infusion pump had relatively benign effects, the use of osmotic pumps resulted in notable toxicity to the surrounding brain tissue. To determine tissue distribution of vector following intracranial delivery, PCR analysis was performed on tissues from rats that received high doses of AAV-TK. Three weeks following CED, vector could be detected in both hemispheres of the brain, spinal cord, spleen, and kidney.     

Canine model of convection-enhanced delivery of liposomes containing CPT-11 monitored with real-time magnetic resonance imaging: laboratory investigation

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.     

Robot-guided convection-enhanced delivery of carboplatin for advanced brainstem glioma

Background

Patients with diffuse intrinsic pontine glioma (DIPG) have a poor prognosis with median survival reported as 9 months. The failure of systemic chemotherapy to improve prognosis may be due to inadequate penetration of the blood–brain barrier (BBB). Convection-enhanced delivery (CED) has the potential to improve outcomes by facilitating bypass of the BBB. We describe the first use of carboplatin for the treatment of advanced DIPG using a robot-guided catheter implantation technique.

Methods

A 5-year-old boy presented with a pontine mass lesion. The tumor continued to progress despite radiotherapy. Using an in-house modification to neuroinspire stereotactic planning software (Renishaw Plc., Gloucestershire, UK), the tumor volume was calculated as 43.6 ml. A transfrontal trajectory for catheter implantation was planned facilitating the in-house manufacture of a recessed-step catheter. The catheter was implanted using a neuromate robot (Renishaw Plc., Gloucestershire, UK). The initial infusion of carboplatin (0.09 mg/ml) was commenced with real-time T2-weighted MRI, facilitating estimation of the volume of infusate distribution. Infusions were repeated on a total of 5 days.

Results

The catheter implantation and infusions were well tolerated. A total volume of 49.8 ml was delivered over 5 days. T2-weighted MRI on completion of the final infusion demonstrated signal change through a total volume of 35.1 ml, representing 95 % of the targeted tumor volume. Follow-up at 4 weeks revealed clinical signs of improvement and increased T2 signal change throughout the volume of distribution. However, there was tumor progression in the regions outside the volume of distribution.

Conclusions

This case demonstrates the feasibility of accurately and safely delivering small-diameter catheters to the brainstem using a robot-guided implantation procedure, and real-time MRI tracking of infusate distribution.     

Convection-enhanced delivery in intact and lesioned peripheral nerve.

OBJECT: Although the use of multiple agents is efficacious in animal models of peripheral nerve injury, translation to clinical applications remains wanting. Previous agents used in trials in humans either engendered severe side effects or were ineffective. Because the blood-central nervous system barrier exists in nerves as it does in the brain, limited drug delivery poses a problem for translation of basic science advances into clinical applications. Convection-enhanced delivery (CED) is a promising adjunct to current therapies for peripheral nerve injury. In the present study the authors assessed the capacity of convection to ferry macromolecules across sites of nerve injury in rat and primate models, examined the functional effects of convection on the intact nerve, and investigated the possibility of delivering a macromolecule to the spinal cord via retrograde convection from a peripherally introduced catheter. METHODS: The authors developed a rodent model of convective delivery to lesioned sciatic nerves (injury due to crush or laceration in 76 nerves) and compared the results to a smaller series of five primates with similar injuries. In the intact nerve, convective delivery of vehicle generated only a transient neurapraxic deficit. Early after injury (postinjury Days 1, 3, 7, and 10), infusion failed to cross the site of injury in crushed or lacerated nerves. Fourteen days after crush injury, CED of radioactively-labeled albumin resulted in perfusion through the site of injury to distal growing neurites. In primates, successful convection through the site of crush injury occurred by postinjury Day 28. In contrast, in laceration models there was complete occlusion of the extracellular space to convective distribution at the site of laceration and repair, and convective distribution in the extracellular space crossed the site of injury only after there was histological evidence of completion of nerve regeneration. Finally, in two primates, retrograde infusion into the spinal cord through a peripheral nerve was achieved. CONCLUSIONS: Convection provides a safe and effective means to deliver macromolecules to regenerating neurites in crush-injured peripheral nerves. Convection block in lacerated and suture-repaired nerves indicates a significant intraneural obstruction of the extracellular space. a disruption that suggests an anatomical obstruction to extracellular and, possibly, intraaxonal flow, which may impair nerve regeneration. Through peripheral retrograde infusion, convection can be used for delivery to spinal cord gray matter. Convection-enhanced delivery provides a promising approach to distribute therapeutic agents to targeted sites for treatment of disorders of the nerve and spinal cord.     

Prolonged convection-enhanced delivery into the rat brainstem

OBJECTIVE: Prolonged convection-enhanced delivery was used in an attempt to achieve large volumes of distribution (V(d)) in the rat brainstem. Clinical assessment and histological analysis were performed to establish the safety of this approach. METHODS: For evaluation of V(d,), 10 rats underwent stereotactic cannula placement into the brainstem. Five rats underwent a 24-hour infusion (volume of infusion [V(i)], 200 microl), and 5 rats underwent a 7-day infusion (V(i), 2 ml) of fluorescein isothiocyanate-dextran. Serial brainstem sections were imaged with ultraviolet illumination, and V(d) was assessed. For assessment of clinical tolerance, 30 additional rats underwent chronic infusions of an isotonic saline solution into the brainstem. Serial neurological examinations were performed, followed by histological analysis after the animals' death. RESULTS: No animal demonstrated clinically recognized neurological deficits. Foci of organizing necrosis were limited to the site of infusion and cannula tract. V(d) increased linearly with increasing V(i) (range, 24.8-130.6 mm(3)). Maximal cross sectional area of fluorescence and craniocaudal extent of fluorescence increased with increasing V(i). Fluorescence was detected throughout the entire brainstem beyond the compact area of highly concentrated tracer. CONCLUSION: Prolonged convection-enhanced delivery can be applied safely in the rat brainstem with no recognized limitations of V(d) and minimal histological changes beyond the site of infusion. Chronic brainstem infusions may enhance the potential application of convection-enhanced delivery for therapeutic purposes in treating diffuse pontine gliomas.     

Convective delivery of glial cell line-derived neurotrophic factor in the human putamen

OBJECT: The authors conducted an analysis of the distribution of glial cell line-derived neurotrophic factor in the human striatum following convection-enhanced delivery. METHODS: Computational examinations of the effects of differing catheters, infusion rates, infusate concentrations, and target placement on distribution were completed based on the protocols of three recent clinical trials. RESULTS: Similar drug distributions around on-target end-hole catheters were predicted in two of the trials (AmgenUT study and Bristol study), although there was slightly deeper penetration for one of the trials (Bristol) due to a higher infusate concentration. However, when positioning uncertainly located catheter tips close to gray-white matter interfaces, backflow could diminish delivery, shunting infusate across the interfaces. For delivery via a multiport catheter at a constant base infusion rate plus a periodic bolus inflow rate (Kentucky study), base inflow alone generated a somewhat smaller distribution volume relative to those in the other trials, was positioned more anteriorly in the putamen, and was somewhat elongated axially; the bolus component extended this putaminal distribution to a larger relative volume but may have been reduced by backflow loss. CONCLUSIONS: Results of these computations indicated that for catheters placed exactly on the intended target, ideal drug distributions were similar for two of the trials (AmgenUT and Bristol) and different in terms of location and extent in the third study (Kentucky); yet the pattern of trial outcomes did not reflect these same groupings. This finding suggests that other factors are at play, widely varying statistical power and the possible effects of not excluding data from patients who experienced large drug losses across gray tissue boundaries due to variation in catheter placement.     

Distribution kinetics of targeted cytotoxin in glioma by bolus or convection-enhanced delivery in a murine model

OBJECT: Interleukin-13 receptor (IL-13R)-targeted cytotoxin (IL-13-PE38) displays a potent antitumor activity against a variety of human tumors including glioblastoma multiforme (GBM) and, thus, this agent is being tested in the clinical trial for the treatment of recurrent GBM. In this study, the authors determined the safety and distribution kinetics of IL-13 cytotoxin when infused intracranially by a bolus injection and by convection-enhanced delivery (CED) in an athymic nude mouse model of GBM. METHODS: For the safety studies, athymic nude mice were given intracranial infusions of IL-13 cytotoxin into normal parenchyma by either a bolus injection or a 7-day-long CED. Toxicity was assessed by performing a histological examination of the mouse brains. For the drug distribution studies, nude mice with intracranially implanted U251 GBM tumors were given an intratumor bolus or a CED infusion of IL-13 cytotoxin. Brain tumor samples obtained between 0.25 and 72 hours after the infusion were assessed for drug distribution kinetics by performing immunohistochemical and Western blot analyses. Based on the histological changes in the tumor and brain, the maximum tolerated dose of intracranial IL-13 cytotoxin infusion in nude mice was determined to be 4 microg when delivered by a bolus injection and 10 microg when CED was used. Drug distribution reached the maximum level 1 hour after the bolus injection and the volume of distribution was determined to be 19.3 +/- 5.8 mm3. Interleukin-13 cytotoxin was barely detectable 6 hours after the injection. Interestingly, when delivered by bolus injections IL-13 cytotoxin exhibited superior distribution in larger rather than smaller tumors. Convection-enhanced delivery was superior for drug distribution in the U251 tumors because when CED was used the drug remained in the tumors 6 hours after the infusion. CONCLUSIONS: These studies provide confirmation of a previous hypothesis that CED of IL-13 cytotoxin is superior to bolus injections not only for the safety of the normal brain but also for maintaining drug levels for a prolonged period in infused brain tumors. These findings are highly relevant and important for the optimal clinical development of IL-13 cytotoxin or any other targeted antitumor agent for GBM therapy, in which multiple routes of delivery of an agent are being contemplated.     

Protection of the ischemic myocardium. Volume-duration relationships and the efficacy of myocardial infusates.

In studies in the isolated rat heart that were designed to optimize the composition of the infusion conditions for a cardioplegic protective solutuin, we have observed a complex relationship between the duration and volume of infusion and the extent of tissue protection. Our results would indicate that solutions, such as that formulated at St. Thomas' Hospital, which are based on extracellular electrolyte content, afford (after a brief equilibration period) a constant degree of protection, irrespective of infusion volume or duration. In contrast other solutions, such as the Bretschneider solution, which have extremes of electrolyre concentration, are associated with a complex dose-response relationship. In the latter instance, infusion of small volumes for short durations affords an increasing degree of protection against ischemia. Increasing the infusate volume may result in a progressive loss of protection. Excessive infusion may lead to an exacerbation of ischemia-induced damage. Our studies suggest that the relative patterns and rates of re-equilibration of various ions, especially sodium and calcium, during infusion may play a major role in determining the efficacy of the infusate.     

Novel online infusate-assisted dialysis system performs microbiologically safely

Administration of adequate amounts of commercial infusion fluids renders modern convective dialysis modalities, such as hemodiafiltration, labor-intensive and costly. Preparation of infusate by cold sterilization of dialysis fluid, which is abundantly available, and its immediate (online) use, in contrast, enables a large volume fluid exchange in a cost-effective manner. Recent developments aimed at more hygienic and user-friendly online systems with increased operational flexibility. As a result the novel ONLINEplus system does not only provide online prepared infusate for convective dialysis therapy, but also for priming and rinsing of the extracorporeal blood circuit, for intradialytic bolus administration, and for re-infusion of patients' blood as well. Production of infusate from potentially impure dialysis fluid containing endotoxins and other pyrogens raises severe concerns of affecting the patients' well-being. To assess its safety, the online system was challenged with microbially contaminated dialysis fluid. Despite high levels of microbial counts (7.5 x 104 +/- 105 CFU/ml), endotoxin concentration (14.1 +/- 7.7 IU/ml and 9.265 +/- 3.000 IU/ml, as measured turbidimetrically and chromogenically, respectively) and cytokine-inducing activity (20,827 +/- 3,082 pg IL-1Ra/Mio WBC), we failed to detect contaminants in the final infusate during a 5 week laboratory testing period. In addition, infusate samples complied consistently with the European Pharmacopeia test for sterility. The present online system is comprehensive, operates user-friendly, and provides microbiologically safe infusate in large quantities. In this way, both patients and dialysis staff will benefit from improved dialysis therapy and reduced treatment-related labor burden, respectively. Moreover, convective dialysis modalities will become less expensive.     

Improved distribution of small molecules and viral vectors in the murine brain using a hollow fiber catheter

OBJECT: A hollow fiber catheter was developed to improve the distribution of drugs administered via direct infusion into the central nervous system (CNS). It is a porous catheter that significantly increases the surface area of brain tissue into which a drug is infused. METHODS: Dye was infused into the mouse brain through convection-enhanced delivery (CED) using a 28-gauge needle compared with a 3-mm-long hollow fiber catheter. To determine whether a hollow fiber catheter could increase the distribution of gene therapy vectors, a recombinant adenovirus expressing the firefly luciferase reporter was injected into the mouse striatum. Gene expression was monitored using in vivo bioluminescent imaging. To assess the distribution of gene transfer, an adenovirus expressing green fluorescent protein was injected into the striatum using a hollow fiber catheter or a needle. RESULTS: Hollow fiber catheter-mediated infusion increased the volume of brain tissue labeled with dye by 2.7 times relative to needle-mediated infusion. In vivo imaging revealed that catheter-mediated infusion of adenovirus resulted in gene expression that was 10-times greater than that mediated by a needle. The catheter appreciably increased the area of brain transduced with adenovirus relative to a needle, affecting a significant portion of the injected hemisphere. CONCLUSIONS: The miniature hollow fiber catheter used in this study significantly increased the distribution of dye and adenoviral-mediated gene transfer in the mouse brain compared with the levels reached using a 28-gauge needle. Compared with standard single-port clinical catheters, the hollow fiber catheter has the advantage of millions of nanoscale pores to increase surface area and bulk flow in the CNS. Extending the scale of the hollow fiber catheter for the large mammalian brain shows promise in increasing the distribution and efficacy of gene therapy and drug therapy using CED.     

Intravascular streaming during carotid artery infusions. Demonstration in humans and reduction using diastole-phased pulsatile administration.

Intra-arterial carotid artery chemotherapy for malignant gliomas is limited by focal injuries to the eye and brain which may be caused by poor mixing of the drug with blood at the infusion site. This inadequate mixing can be eliminated in animal models with diastole-phased pulsatile infusion (DPPI) which creates 1-ml/sec spurts during the slow blood flow phase of diastole. Before treatment with intracarotid cisplatin, 10 patients with malignant gliomas were studied to determine whether intravascular streaming occurs after intracarotid infusion in humans, and if so, if it is reduced with DPPI. Regional cerebral blood flow (rCBF) studies were performed by intravenous injection of H2(15)O and positron emission tomography. This was followed by supra- or infraophthalmic internal carotid artery (ICA) injections of H2(15)O with either continuous infusion or DPPI. Local H2(15)O concentration in the brain was determined and the images of radiotracer distribution in the continuous infusion and DPPI studies were compared to the rCBF images. Intravascular streaming of the infusate was identified by a heterogeneous distribution of the infused H2(15)O in brain compared to rCBF. Extensive and variable intravascular streaming occurred in three patients who received infusions into the supraophthalmic segment of the ICA. Some brain areas received up to 11 times the expected radiotracer delivery, while other regions received as little as one-tenth. This streaming pattern was markedly reduced or eliminated by DPPI. In the five patients who received infraophthalmic infusions, a minimally heterogeneous distribution of the infusate was detected. The authors conclude that extensive intravascular streaming accompanies supraophthalmic ICA infusions in patients. The magnitude of streaming can be substantially reduced or eliminated with DPPI. Those who perform intra-arterial infusion should consider using DPPI to assure uniform drug delivery to brain.