Targeting brain tumors by intra-arterial delivery of cell-penetrating peptides: a novel approach for primary and metastatic brain malignancy.

Computational modeling shows that intra-arterial delivery is most efficient when the delivered drugs rapidly and avidly bind to the target site. The cell-penetrating peptide trans-activator of transcription (TAT) is a candidate carrier molecule that could mediate such specificity for brain tumor chemotherapeutics. To test this hypothesis we first performed in vitro studies testing the uptake of TAT by one primary and three potentially metastatic brain cancer cell lines (9L, 4T-1, LLC, SKOV-3). Then we performed in vivo studies in a rat model where TAT was delivered either intra-arterially (IA) or intravenously (IV) to 9L brain tumors. We observed robust uptake of TAT by all tumor cell lines in vitro. Flow cytometry and confocal microscopy revealed a rapid uptake of fluorescein-labeled TAT within 5 min of exposure to the cancer cells. IA injections done under transient cerebral hypoperfusion (TCH) generated a four-fold greater tumor TAT concentration compared to conventional IV injections. We conclude that it is feasible to selectively target brain tumors with TAT-linked chemotherapy by the IA-TCH method.

Flow arrest intra-arterial delivery of small TAT-decorated and neutral micelles to gliomas.

The cell-penetrating trans-activator of transcription (TAT) is a cationic peptide derived from human immunodeficiency virus-1. It has been used to facilitate macromolecule delivery to various cell types. This cationic peptide is capable of crossing the blood-brain barrier and therefore might be useful for enhancing the delivery of drugs that target brain tumors. Here we test the efficiency with which relatively small (20 nm) micelles can be delivered by an intra-arterial route specifically to gliomas. Utilizing the well-established method of flow-arrest intra-arterial injection we compared the degree of brain tumor deposition of cationic TAT-decorated micelles versus neutral micelles. Our in vivo and post-mortem analyses confirm glioma-specific deposition of both TAT-decorated and neutral micelles. Increased tumor deposition conferred by the positive charge on the TAT-decorated micelles was modest. Computational modeling suggested a decreased relevance of particle charge at the small sizes tested but not for larger particles. We conclude that continued optimization of micelles may represent a viable strategy for targeting brain tumors after intra-arterial injection. Particle size and charge are important to consider during the directed development of nanoparticles for intra-arterial delivery to brain tumors.

Safety, feasibility, and optimization of intra-arterial mitoxantrone delivery to gliomas.

Mitoxantrone is a highly cytotoxic antineoplastic drug, however, its poor penetration of the blood-brain barrier has limited its role in the treatment of brain cancers. We hypothesize that intra-arterial (IA) delivery of mitoxantrone may enhance its capacity for regional brain deposition thus expanding its potential as a brain tumor therapy agent. In this study we assessed the dose-response characteristics as well as the feasibility and safety of mitoxantrone delivery to the brain and specifically to gliomas in a rodent model. We show that delivery optimization utilizing the technique of intra-arterial transient cerebral hypoperfusion (IA-TCH) facilitates achieving the highest peak- and end- brain drug concentrations as compared to intravenous and IA delivery without hypoperfusion. Additionally, we observed significant tumor-specific uptake of mitoxantrone when delivered by the IA-TCH method. No untoward effects of IA-TCH delivery of mitoxantrone were observed. The IA-TCH method is shown to be a safely tolerated and feasible strategy for delivering mitoxantrone to tumors in the glioma model tested. Additional investigation is warranted to determine if IA-TCH delivery of mitoxantrone produces clinically relevant benefit.

Cationizable lipid micelles as vehicles for intraarterial glioma treatment.

The relative abundance of anionic lipids on the surface of endothelia and on glioma cells suggests a workable strategy for selective drug delivery by utilizing cationic nanoparticles. Furthermore, the extracellular pH of gliomas is relatively acidic suggesting that tumor selectivity could be further enhanced if nanoparticles can be designed to cationize in such an environment. With these motivating hypotheses the objective of this study was to determine whether nanoparticulate (20 nm) micelles could be designed to improve their deposition within gliomas in an animal model. To test this, we performed intra-arterial injection of micelles labeled with an optically quantifiable dye. We observed significantly greater deposition (end-tissue concentration) of cationizable micelles as compared to non-ionizable micelles in the ipsilateral hemisphere of normal brains. More importantly, we noted enhanced deposition of cationizable as compared to non-ionizable micelles in glioma tissue as judged by semiquantitative fluorescence analysis. Micelles were generally able to penetrate to the core of the gliomas tested. Thus we conclude that cationizable micelles may be constructed as vehicles for facilitating glioma-selective delivery of compounds after intraarterial injection.

Intraarterial drug delivery for glioblastoma mutiforme: Will the phoenix rise again?

Intraarterial (IA) drug delivery is a physiologically appealing strategy as drugs are widely distributed throughout the tumor capillary network and high regional tissue concentrations can be achieved with low total doses. IA treatment of glioblastoma multiforme (GBM) has been attempted since the 1950s but success has been elusive. Although IA treatments have been embraced for the treatment of retinoblastoma and advanced liver cancers, this has not been the case for GBM. The development of IA drug delivery for the treatment of brain cancer over the last several decades reveals a number of critical oversights. For example, very few studies took into consideration the underlying hydrodynamic factors. Therapeutic failures were often blamed on an inability to penetrate the blood brain barrier or on the streaming of drugs. Similarly, there were few methods to investigate the ultra-fast pharmacokinetics of IA drugs. Despite past failures, clinical interest in IA drugs for the treatment of GBM persists. The advent of modern imaging methods along with a better understanding of hydrodynamics factors, better appreciation of the complex morphology of GBM, improved drug selection and formulations, and development of methods to minimize treatment-related neurological injury, promise to considerably advance the application of IA drugs for GBM treatment. There are several clinical trials with IA treatments in the National Trial Registry that are actively recruiting patients. This review of IA drug delivery for GBM treatment is therefore timely and is intended to assess how this method of drug delivery could be better applied to future treatments.

Transient cerebral hypoperfusion assisted intraarterial cationic liposome delivery to brain tissue.

Transient cerebral hypoperfusion (TCH) has empirically been used to assist intraarterial (IA) drug delivery to brain tumors. Transient (<3 min) reduction of cerebral blood flow (CBF) occurs during many neuro- and cardiovascular interventions and has recently been used to better target IA drugs to brain tumors. In the present experiments, we assessed whether the effectiveness of IA delivery of cationic liposomes could be improved by TCH. Cationic liposomes composed of 1:1 DOTAP:PC (dioleoyl-trimethylammonium-propane:phosphatidylcholine) were administered to three groups of Sprague-Dawley rats. In the first group, we tested the effect of blood flow reduction on IA delivery of cationic liposomes. In the second group, we compared TCH-assisted IA liposomal delivery versus intravenous (IV) administration of the same dose. In the third group, we assessed retention of cationic liposomes in brain 4 h after TCH assisted delivery. The liposomes contained a near infrared dye, DilC18(7), whose concentration could be measured in vivo by diffuse reflectance spectroscopy. IA injections of cationic liposomes during TCH increased their delivery approximately fourfold compared to injections during normal blood flow. Optical pharmacokinetic measurements revealed that relative to IV injections, IA injection of cationic liposomes during TCH produced tissue concentrations that were 100-fold greater. The cationic liposomes were retained in the brain tissue 4 h after a single IA injection. There was no gross impairment of neurological functions in surviving animals. Transient reduction in CBF significantly increased IA delivery of cationic liposomes in the brain. High concentrations of liposomes could be delivered to brain tissue after IA injections with concurrent TCH while none could be detected after IV injection. IA-TCH injections were well tolerated and cationic liposomes were retained for at least 4 h after IA administration. These results should encourage development of cationic liposomal formulations of chemotherapeutic drugs and their IA delivery during TCH.

Cationic surface charge enhances early regional deposition of liposomes after intracarotid injection.

Rapid first pass uptake of drugs is necessary to increase tissue deposition after intraarterial (IA) injection. Here we tested whether brain tissue deposition of a nanoparticulate liposomal carrier could be enhanced by coordinated manipulation of liposome surface charge and physiological parameters, such as IA injection during transient cerebral hypoperfusion (TCH). Different degrees of blood-brain barrier disruption were induced by focused ultrasound in three sets of Sprague-Dawley rats. Brain tissue retention was then compared for anionic, cationic, and charge-neutral liposomes after IA injection combined with TCH. The liposomes contained a non-exchangeable carbocyanine membrane optical label that could be quantified using diffuse reflectance spectroscopy (DRS) or visualized by multispectral imaging. Real-time concentration-time curves in brain were obtained after each liposomal injection. Having observed greater tissue retention of cationic liposomes compared to other liposomes in all three groups, we tested uptake of cationic liposomes in C6 tumor bearing rats. DRS and multispectral imaging of postmortem sections revealed increased liposomal uptake by the C6 brain tumor as compared to non-tumor contralateral hemisphere. We conclude that regional deposition of liposomes can be enhanced without BBB disruption using IA injection of cationic liposomal formulations in healthy and C6 tumor bearing rats.

The feasibility of real-time in vivo optical detection of blood-brain barrier disruption with indocyanine green.

Osmotic disruption of the blood-brain barrier (BBB) by intraarterial mannitol injection is sometimes required for the delivery of chemotherapeutic drugs to brain tissue. Osmotic disruption is affected by a number of factors, and there is a significant variability in the degree and distribution of BBB disruption in clinical and experimental settings. Brain tissue concentrations of indocyanine green (ICG) can be measured by optical techniques. The aim of this experiment was to determine whether the disruption of the BBB significantly altered the regional pharmacokinetics of ICG. We were able to track in vivo brain tissue concentrations of ICG in 13 New Zealand white rabbits by employing a novel optical approach. Evan's blue was used to assess the distribution of BBB disruption on post mortem examination. BBB disruption by intraarterial mannitol injection was found to be highly variable, and only five of the 13 animals demonstrated the disruption at the site of optical measurements. In these animals, we observed a ninefold increase in ICG concentrations and fourfold increase in the area under the concentration-time curve, compared to those without BBB disruption at the site of measurement. This study shows the feasibility of optical monitoring of BBB disruption with intravenous (IV) ICG injections. Virtual real-time optical monitoring of the BBB disruption could help improve intraarterial delivery of chemotherapeutic drugs.

Inconsistent blood brain barrier disruption by intraarterial mannitol in rabbits: implications for chemotherapy.

The novel ability to quantify drug and tracer concentrations in vivo by optical means leads to the possibility of detecting and quantifying blood brain barrier (BBB) disruption in real-time by monitoring concentrations of chromophores such as Evan's Blue. In this study, experiments were conducted to assess the disruption of the BBB, by intraarterial injection of mannitol, in New Zealand white rabbits. Surgical preparation included: tracheotomy for mechanical ventilation, femoral and selective internal carotid artery (ICA) catheterizations, skull screws for monitoring electrocerebral activity, bilateral placement of laser Doppler probes and a small craniotomy for the placement of a fiber optic probe to determine tissue Evan's Blue dye concentrations. Evans Blue (6.5 mg/kg) was injected intravenously (IV) just before BBB disruption with intracarotid mannitol (25%, 8 ml/40 s). Brain tissue concentrations of the dye in mannitol-treated and control animals were monitored using the method of optical pharmacokinetics (OP) during the subsequent 60 min. Hemodynamic parameters, heart rate, blood pressure, and EKG remained stable throughout the experiments in both the control and the mannitol-treated group. Brain tissue concentrations of Evan's Blue and the brain:plasma Evan's Blue partition coefficient progressively increased during the period of observation. A wide variation in brain tissue Evan's Blue concentrations was observed in the mannitol group. The experiments demonstrate the feasibility of measuring tissue concentrations of Evan's Blue without invading the brain parenchyma, and in real-time. The data suggest that there are significant variations in the degree and duration of BBB disruption induced with intraarterial mannitol. The ability to optically monitor the BBB disruption in real-time could provide a feedback control for hypertonic disruption and/or facilitate dosage control for chemotherapeutic drugs that require such disruption.

Development of hierarchical magnesium composites using hybrid microwave sintering.

In this work, hierarchical magnesium based composites with a micro-architecture comprising reinforcing constituent that is a composite in itself were fabricated using powder metallurgy route including microwave assisted rapid sintering technique and hot extrusion. Different level-I composite particles comprises sub-micron pure aluminum (Al) matrix containing Al2O3 particles of different length scale (from micrometer to nanometer size). Microstructural characterization of the hierarchical composites revealed reasonably uniform distribution of level-I composite particles and significant grain refinement compared to monolithic Mg. Hierarchical composite configurations exhibited different mechanical performance as a function of Al2O3 length scale. Among the different hierarchical formulations synthesized, the hierarchical configuration with level-I composition comprising Al and nano-Al2O3 (0.05 microm) exhibited the highest improvement in tensile yield strength (0.2% YS), ultimate tensile strength (UTS), tensile failure strain (FS), compressive yield strength (0.2% CYS) and ultimate compressive strength (UCS) (+96%, +80%, +42%, +80%, and +83%) as compared to monolithic Mg. An attempt has been made in the present study to correlate the effect of different length scales of Al2O3 particulates on the microstructural and mechanical response of magnesium.

Intracarotid delivery of drugs: the potential and the pitfalls.

The major efforts to selectively deliver drugs to the brain in the past decade have relied on smart molecular techniques to penetrate the blood-brain barrier, whereas intraarterial drug delivery has drawn relatively little attention. Meanwhile, rapid progress has been made in the field of endovascular surgery. Modern endovascular procedures can permit highly targeted drug delivery by the intracarotid route. Intracarotid drug delivery can be the primary route of drug delivery or it could be used to facilitate the delivery of smart neuropharmaceuticals. There have been few attempts to systematically understand the kinetics of intracarotid drugs. Anecdotal data suggest that intracarotid drug delivery is effective in the treatment of cerebral vasospasm, thromboembolic strokes, and neoplasms. Neuroanesthesiologists are frequently involved in the care of such high-risk patients. Therefore, it is necessary to understand the applications of intracarotid drug delivery and the unusual kinetics of intracarotid drugs.

Optical method for real-time monitoring of drug concentrations facilitates the development of novel methods for drug delivery to brain tissue.

The understanding of drug delivery to organs, such as the brain, has been hampered by the inability to measure tissue drug concentrations in real time. We report an application of an optical spectroscopy technique that monitors in vivo the real-time drug concentrations in small volumes of brain tissue. This method will facilitate development of new protocols for delivery of drugs to treat brain cancers. The delivery of many anticancer drugs to the brain is limited by the presence of the blood-brain barrier (BBB). Mitoxantrone (MTX) is a water-soluble anticancer drug that poorly penetrates the BBB. It is preliminarily determined in an animal model that the brain tissue uptake of chemotherapy agents-in this demonstration, MTX-delivered intra-arterially is enhanced when the BBB is disrupted.

Electrocerebral silence after intracarotid propofol injection is a function of transit time.

BACKGROUND: We hypothesized that the duration of electrocerebral (electroencephalogram, EEG) silence after bolus injection of propofol, a highly lipid soluble anesthetic drug, during transient cerebral hypoperfusion, will be directly related to the time taken by the bolus of drug to transit the cerebral circulation. METHODS: We randomly divided 24 New Zealand White rabbits into two propofol volume groups: 0.5 and 0.8 mL groups. In each group, 12 animals received two intracarotid injections of 1% propofol: the first injection was made under normal physiological conditions and the second injection during cerebral hypoperfusion produced by bilateral carotid occlusion and IV bolus injection of adenosine and esmolol. We determined the duration of electrocerebral silence and the transit time of propofol emulsion under both cerebral circulation conditions. The transit time was measured by videomicroscopy through an implanted cranial window. RESULTS: Cerebral hypoperfusion increased transit time with both low (2.3 +/- 0.7 to 55.7 +/- 21.4 s, n = 12, P < 0.0001) and high (2.2 +/- 0.6 to 62.5 +/- 31 s, n = 12, P < 0.0001) bolus volumes. The duration of electrocerebral silence during cerebral hypoperfusion was a function of the transit time with low (electrocerebral silence s = 152 + 2.3 x transit time, n = 12, r = 0.73, P = 0.007) and high (electrocerebral silence s = 186 + 3.2 x transit time, n = 12, r = 0.68, P = 0.02) bolus volumes. CONCLUSION: These results suggest that manipulation of the transit time of highly lipid-soluble drugs profoundly enhances the effect site delivery.

Enhanced disruption of the blood brain barrier by intracarotid mannitol injection during transient cerebral hypoperfusion in rabbits.

Fairly large volumes of intracarotid mannitol (20% to 25%) are required to disrupt the blood brain barrier (BBB), that is, 200 to 300 mL/30 s in humans or 10 mL/40 s in rabbits. During transient cerebral hypoperfusion blood flow to the rabbit brain is decreased to 0.2 to 0.3 mL/30 s. We therefore hypothesized that if the disruption of the BBB by intracarotid mannitol was primarily due to its osmotic effects, injection of 0.2 to 0.3 mL of mannitol during transient cerebral hypoperfusion will be sufficient to disrupt the BBB, thereby dramatically (by 20-folds) decrease the dose requirements compared with injections during normal blood flow. After preliminary studies, 4 doses of intracarotid mannitol were first tested: (1) 2 mL with cerebral hypoperfusion, (2) 4 mL with cerebral hypoperfusion, (3) 4 mL without cerebral hypoperfusion, and (4) 8 mL without cerebral hypoperfusion. Next, we compared the extent to which methods of drug delivery (infusion vs. bolus injection) affected BBB disruption in 12 rabbits. Finally, we assessed the duration of BBB disruption with intracarotid mannitol in another 12 rabbits. We observed that BBB disruption during injection of 4 mL of mannitol with cerebral hypoperfusion was comparable to 8 mL mannitol without cerebral hypoperfusion. Bolus injections of 4 mL mannitol were more effective than steady-state infusions. The BBB disruption with intracarotid mannitol lasted for 60 minutes postinjection. We conclude that cerebral hypoperfusion decreases the dose of intracarotid mannitol by a modest 2-fold. Our results suggest that mechanical factors may play a significant role in the osmotic disruption of the BBB by intracarotid mannitol.

Intra-arterial drug delivery: a concise review.

The therapeutic potential of intra-arterial (IA) drug delivery to the brain has received limited attention in the last decade. In the 1980s, efforts to treat brain tumors with IA chemotherapy, the leading application of this technology, yielded modest results. Poor control of tissue drug concentrations and the potential risk of permanent neurologic injury further prevented the wider use of IA drugs. Yet, IA drugs were anecdotally used for treating a wide spectrum of brain diseases. Recent advances in endovascular technology and the increased safety of angiographic procedures now compel us to reevaluate IA drug delivery. This review describes the pharmacologic principles, applications, and pitfalls of IA drug delivery to the brain.

Bolus configuration affects dose requirements of intracarotid propofol for electroencephalographic silence.

We hypothesized that an intracarotid bolus injection of propofol to produce electroencephalographic (EEG) silence would require a smaller dose of the drug compared with the continuous infusion of the drug. Furthermore, the bolus propofol dose will be a function of the bolus characteristics in each bolus (mass/volume). We compared the dose requirements of intracarotid propofol needed to maintain EEG silence when delivered as bolus injections to continuous infusions in rabbits. Subsequently, we compared whether four different bolus characteristics (concentration and volume) of propofol (0.33% x 0.1 mL, 0.33% x 0.3 mL, 1% x 0.1 mL, and 1% x 0.3 mL) affected the dose required to produce EEG silence. We found that the infusion rate of propofol required to sustain EEG silence was three-fold larger than the dose required by bolus injections, 22.8 +/- 11.9 vs 6.2 +/- 2.9 mL/h for infusion versus bolus, respectively (n = 7, P < 0.004). Furthermore, during bolus injection, the doses of propofol required to produce EEG silence were a direct function of the bolus volume and the mass of drug in each bolus, total dose = 3.6 + 29 x mg/bolus, n = 32, r = 0.85. For maximum regional effects of the bolus intracarotid drug injection, the bolus characteristics (volume and drug concentration) have to be optimized.

Comparison of intracarotid anesthetics for EEG silence.

The goal of this study was to compare systemic and cerebrovascular effects of three anesthetic drugs (etomidate, thiopental, and propofol) when delivered by intracarotid and intravenous routes in doses that produce electrocerebral silence (electroencephalography [EEG]). EEG activity, mean arterial pressure (MAP), and laser Doppler flow as a proxy of cerebral blood flow (CBF) of 24 anesthetized New Zealand white rabbits were continuously recorded. Data were compared at three timepoints: baseline, during EEG silence, and after recovery of EEG activity. Drugs were randomly injected via the carotid artery to produce 10 minutes of EEG silence. After 30 minutes of rest, intravenous boluses of the same drug were injected to achieve 10 minutes of EEG silence. During EEG silence, transient hypotension was seen with intracarotid propofol, but there was no decrease in CBF. MAP and CBF did not decrease with either intracarotid etomidate or thiopental during EEG silence. Intracarotid/intravenous dose ratio of propofol (26%+/-22%; n=8, P<0.02) was much higher than that of etomidate and thiopental (14%+/-2% and 19%+/-11%, respectively; NS). Collectively, these results suggest intracarotid etomidate and thiopental are more useful than propofol in producing EEG silence because they offer better dose advantage and are less likely to impair cerebral or systemic hemodynamics.

Computational pharmacokinetic rationale for intra-arterial delivery to the brain.

Intra-arterial (IA) drug delivery has been proposed for the treatment of a wide range of brain diseases, including malignant brain tumors. However, pharmacokinetic optimization for IA drug delivery to the brain remains a challenge. In this report, we apply and expand the well-established Dedrick model of IA drug delivery to the brain and test the effects of modifying drug and delivery parameters. These simulations show that altering the properties of candidate drugs and physiological variables can have profound effects on regional deposition after IA injections. We show that drug and physiological optimization aimed at rapid drug extraction and sustained retention is necessary to maximize regional deposition after of IA injections.

Liposome size and charge optimization for intraarterial delivery to gliomas.

Nanoparticles such as liposomes may be used as drug delivery vehicles for brain tumor therapy. Particle geometry and electrostatic properties have been hypothesized to be important determinants of effective tumor targeting after intraarterial injection. In this study, we investigate the combined roles of liposome size and surface charge on the effectiveness of delivery to gliomas after intraarterial injection. Intracarotid injection of liposomes was performed in separate cohorts of both healthy and C6 glioma-bearing Sprague Dawley rats after induction of transient cerebral hypoperfusion. Large (200 nm) and small (60-80 nm) fluorescent dye-loaded liposomes that were either cationic or neutral in surface charge were utilized. Delivery effectiveness was quantitatively measured both with real-time, in vivo and postmortem diffuse reflectance spectroscopy. Semi-quantitative multispectral fluorescence imaging was also utilized to assess the pattern and extent of liposome targeting within tumors. Large cationic liposomes demonstrated the most effective hemispheric and glioma targeting of all the liposomes tested. Selective large cationic liposome retention at the site of glioma growth was observed. The liposome deposition pattern within tumors after intraarterial injection was variable with both core penetration and peripheral deposition observed in specific tumors. This study provides evidence that liposome size and charge are important determinants of effective brain and glioma targeting after intraarterial injection. Our results support the future development of 200-nm cationic liposomal formulations of candidate intraarterial anti-glioma agents for further pre-clinical testing.

Suppression of Shear Banding and Transition to Necking and Homogeneous Flow in Nanoglass Nanopillars.

In order to improve the properties of metallic glasses (MG) a new type of MG structure, composed of nanoscale grains, referred to as nanoglass (NG), has been recently proposed. Here, we use large-scale molecular dynamics (MD) simulations of tensile loading to investigate the deformation and failure mechanisms of Cu64Zr36 NG nanopillars with large, experimentally accessible, 50 nm diameter. Our results reveal NG ductility and failure by necking below the average glassy grain size of 20 nm, in contrast to brittle failure by shear band propagation in MG nanopillars. Moreover, the results predict substantially larger ductility in NG nanopillars compared with previous predictions of MD simulations of bulk NG models with columnar grains. The results, in excellent agreement with experimental data, highlight the substantial enhancement of plasticity induced in experimentally relevant MG samples by the use of nanoglass architectures and point out to exciting novel applications of these materials.