The influence of anesthetic choice, PaCO2, and other factors on osmotic blood-brain barrier disruption in rats with brain tumor xenografts

Blood-brain barrier opening by intracarotid artery hyperosmolar mannitol induces sterile inflammatory and innate immune responses

Intracarotid arterial hyperosmolar mannitol (ICAHM) blood-brain barrier disruption (BBBD) is effective and safe for delivery of therapeutics for central nervous system malignancies. ICAHM osmotically alters endothelial cells and tight junction integrity to achieve BBBD. However, occurrence of neuroinflammation following hemispheric BBBD by ICAHM remains unknown. Temporal proteomic changes in rat brains following ICAHM included increased damage-associated molecular patterns, cytokines, chemokines, trophic factors, and cell adhesion molecules, indicative of a sterile inflammatory response (SIR). Proteomic changes occurred within 5 min of ICAHM infusion and returned to baseline by 96 h. Transcriptomic analyses following ICAHM BBBD further supported an SIR. Immunohistochemistry revealed activated astrocytes, microglia, and macrophages. Moreover, proinflammatory proteins were elevated in serum, and proteomic and histological findings from the contralateral hemisphere demonstrated a less pronounced SIR, suggesting neuroinflammation beyond regions of ICAHM infusion. Collectively, these results demonstrate ICAHM induces a transient SIR that could potentially be harnessed for neuroimmunomodulation.

Pseudo-Leptomeningeal Contrast Enhancement at 3T in Pediatric Patients Sedated by Propofol

BACKGROUND AND PURPOSE

Propofol is a cerebral vasoconstrictor that modulates cerebral perfusion by decreasing the metabolic rate of oxygen. Because younger children often undergo intravenous sedation for MR imaging, this study set out to evaluate the degree of leptomeningeal contrast enhancement on 3T postcontrast brain MR imaging and to determine whether this phenomenon relates to sequence, sedation dosage, or patient age or weight.

MATERIALS AND METHODS

During a 2-year period, of 152 children 1-5 years of age who underwent MR imaging, 43 were included for MRI review. Of these, 37 underwent postcontrast imaging with either solely gradient-echo T1WI (n = 20) or spin-echo T1WI (n = 17); notably, 6 patients underwent both sequences. Three neuroradiologists separately graded the degree of leptomeningeal contrast enhancement (grades 0-3) that was correlated with various factors and calculated the interobserver reliability.

RESULTS

For the 43 patients, the mean patient age was 3.1 ± 1.4 years. The leptomeningeal contrast-enhancement grade was significantly greater (P < .0001) on spin-echo T1WI (1.9-2.1) versus gradient-echo TIWI (1.2-1.4). Patient weight (r = -0.366 to -.418, P = .003-.01) and age (r = -0.315 to -0.418, P = .004-.032) moderately and inversely correlated with the leptomeningeal contrast-enhancement grade, while the propofol dosage, sedation duration, and time to T1WI post-contrast administration did not (each, P > .05). The interobserver κ was strong regarding the leptomeningeal contrast-enhancement grade on both spin-echo T1WI (κ = 0.609-0.693, P < .0001) and gradient-echo TIWI (κ = 0.567-0.698, P < .0001).

CONCLUSIONS

Leptomeningeal contrast enhancement (or "pseudo"-leptomeningeal contrast enhancement) occurs with a greater frequency and degree on 3T postcontrast spin-echo T1WI relative to gradient-echo TIWI in younger children sedated with propofol and should not be mistaken for disease. This phenomenon may be more prominent with lower age or size and may arise from propofol-induced vascular smooth-muscle dilation.

Real-time monitoring of human blood-brain barrier disruption

Chemotherapy aided by opening of the blood-brain barrier with intra-arterial infusion of hyperosmolar mannitol improves the outcome in primary central nervous system lymphoma. Proper opening of the blood-brain barrier is crucial for the treatment, yet there are no means available for its real-time monitoring. The intact blood-brain barrier maintains a mV-level electrical potential difference between blood and brain tissue, giving rise to a measurable electrical signal at the scalp. Therefore, we used direct-current electroencephalography (DC-EEG) to characterize the spatiotemporal behavior of scalp-recorded slow electrical signals during blood-brain barrier opening. Nine anesthetized patients receiving chemotherapy were monitored continuously during 47 blood-brain barrier openings induced by carotid or vertebral artery mannitol infusion. Left or right carotid artery mannitol infusion generated a strongly lateralized DC-EEG response that began with a 2 min negative shift of up to 2000 μV followed by a positive shift lasting up to 20 min above the infused carotid artery territory, whereas contralateral responses were of opposite polarity. Vertebral artery mannitol infusion gave rise to a minimally lateralized and more uniformly distributed slow negative response with a posterior-frontal gradient. Simultaneously performed near-infrared spectroscopy detected a multiphasic response beginning with mannitol-bolus induced dilution of blood and ending in a prolonged increase in the oxy/deoxyhemoglobin ratio. The pronounced DC-EEG shifts are readily accounted for by opening and sealing of the blood-brain barrier. These data show that DC-EEG is a promising real-time monitoring tool for blood-brain barrier disruption augmented drug delivery.

Transporters at CNS barrier sites: obstacles or opportunities for drug delivery?

The blood-brain barrier (BBB) and blood-cerebrospinal fluid (BCSF) barriers are critical determinants of CNS homeostasis. Additionally, the BBB and BCSF barriers are formidable obstacles to effective CNS drug delivery. These brain barrier sites express putative influx and efflux transporters that precisely control permeation of circulating solutes including drugs. The study of transporters has enabled a shift away from "brute force" approaches to delivering drugs by physically circumventing brain barriers towards chemical approaches that can target specific compounds of the BBB and/or BCSF barrier. However, our understanding of transporters at the BBB and BCSF barriers has primarily focused on understanding efflux transporters that efficiently prevent drugs from attaining therapeutic concentrations in the CNS. Recently, through the characterization of multiple endogenously expressed uptake transporters, this paradigm has shifted to the study of brain transporter targets that can facilitate drug delivery (i.e., influx transporters). Additionally, signaling pathways and trafficking mechanisms have been identified for several endogenous BBB/BCSF transporters, thereby offering even more opportunities to understand how transporters can be exploited for optimization of CNS drug delivery. This review presents an overview of the BBB and BCSF barrier as well as the many families of transporters functionally expressed at these barrier sites. Furthermore, we present an overview of various strategies that have been designed and utilized to deliver therapeutic agents to the brain with a particular emphasis on those approaches that directly target endogenous BBB/BCSF barrier transporters.

Delivery of chemotherapeutics across the blood-brain barrier: challenges and advances

The blood-brain barrier (BBB) limits drug delivery to brain tumors. We utilize intraarterial infusion of hyperosmotic mannitol to reversibly open the BBB by shrinking endothelial cells and opening tight junctions between the cells. This approach transiently increases the delivery of chemotherapy, antibodies, and nanoparticles to brain. Our preclinical studies have optimized the BBB disruption (BBBD) technique and clinical studies have shown its safety and efficacy. The delivery of methotrexate-based chemotherapy in conjunction with BBBD provides excellent outcomes in primary central nervous system lymphoma (PCNSL) including stable or improved cognitive function in survivors a median of 12 years (range 2-26 years) after diagnosis. The addition of rituximab to chemotherapy with BBBD for PCNSL can be safely accomplished with excellent overall survival. Our translational studies of thiol agents to protect against platinum-induced toxicities led to the development of a two-compartment model in brain tumor patients. We showed that delayed high-dose sodium thiosulfate protects against carboplatin-induced hearing loss, providing the framework for large cooperative group trials of hearing chemoprotection. Neuroimaging studies have identified that ferumoxytol, an iron oxide nanoparticle blood pool agent, appears to be a superior contrast agent to accurately assess therapy-induced changes in brain tumor vasculature, in brain tumor response to therapy, and in differentiating central nervous system lesions with inflammatory components. This chapter reviews the breakthroughs, challenges, and future directions for BBBD.

Elevated cerebral blood volume contributes to increased FLAIR signal in the cerebral sulci of propofol-sedated children

BACKGROUND AND PURPOSE

Hyperintense FLAIR signal in the cerebral sulci of anesthetized children is attributed to supplemental oxygen (fraction of inspired oxygen) but resembles FLAIR hypersignal associated with perfusion abnormalities in Moyamoya disease and carotid stenosis. We investigated whether cerebral perfusion, known to be altered by anesthesia, contributes to diffuse signal intensity in sulci in children and explored the relative contributions of supplemental oxygen, cerebral perfusion, and anesthesia to signal intensity in sulci.

MATERIALS AND METHODS

Supraventricular signal intensity in sulci on pre- and postcontrast T2 FLAIR images of 24 propofol-sedated children (6.20 ± 3.28 years) breathing supplemental oxygen and 18 nonsedated children (14.28 ± 2.08 years) breathing room air was graded from 0 to 3. The Spearman correlation of signal intensity in sulci with the fraction of inspired oxygen and age in 42 subjects, and with dynamic susceptibility contrast measures of cortical CBF, CBV, and MTT available in 25 subjects, were evaluated overall and compared between subgroups. Factors most influential on signal intensity in sulci were identified by stepwise logistic regression.

RESULTS

CBV was more influential on noncontrast FLAIR signal intensity in sulci than the fraction of inspired oxygen or age in propofol-sedated children (CBV: r = 0.612, P = .026; fraction of inspired oxygen: r = -0.418, P = .042; age: r = 0.523, P = .009) and overall (CBV: r = 0.671, P = .0002; fraction of inspired oxygen: r = 0.442, P = .003; age: r = -0.374, P = .015). MTT (CBV/CBF) was influential in the overall cohort (r = 0.461, P = .020). Signal intensity in sulci increased with contrast in 45% of subjects, decreased in none, and was greater (P < .0001) in younger propofol-sedated subjects, in whom the signal intensity in sulci increased with age postcontrast (r = .600, P = .002).

CONCLUSIONS

Elevated cortical CBV appears to contribute to increased signal intensity in sulci on noncontrast FLAIR in propofol-sedated children. The effects of propofol on age-related cerebral perfusion and vascular permeability may play a role.

Real-time hemodynamic response and mitochondrial function changes with intracarotid mannitol injection

Disruption of blood brain barrier (BBB) is used to enhance chemotherapeutic drug delivery. The purpose of this study was to understand the time course of hemodynamic and metabolic response to intraarterial (IA) mannitol infusions in order to optimize the delivery of drugs for treating brain tumors.

PRINCIPAL RESULTS

We compared hemodynamic response, EEG changes, and mitochondrial function as judged by relative changes in tissue NADH concentrations, after intracarotid (IC) infusion of equal volumes of normal saline and mannitol in our rabbit IC drug delivery model. We observed significantly greater, though transient, hyperemic response to IC infusion of mannitol compared to normal saline. Infusion of mannitol also resulted in a greater increase in tissue NADH concentrations relative to the baseline. These hemodynamic, and metabolic changes returned to baseline within 5min of mannitol injection.

CONCLUSION

Significant, though transient, changes in blood flow and brain metabolism occur with IA mannitol infusion. The observed transient hyperemia would suggest that intravenous (IV) chemotherapy should be administered either just before, or concurrent with IA mannitol injections. On the other hand, IA chemotherapy should be delayed until the peak hyperemic response has subsided.

Targeted delivery of antibody-based therapeutic and imaging agents to CNS tumors: crossing the blood-brain barrier divide

INTRODUCTION

Brain tumors are inherently difficult to treat in large part due to the cellular blood-brain barriers (BBBs) that limit the delivery of therapeutics to the tumor tissue from the systemic circulation. Virtually no large molecules, including antibody-based proteins, can penetrate the BBB. With antibodies fast becoming attractive ligands for highly specific molecular targeting to tumor antigens, a variety of methods are being investigated to enhance the access of these agents to intracranial tumors for imaging or therapeutic applications.

AREAS COVERED

This review describes the characteristics of the BBB and the vasculature in brain tumors, described as the blood-brain tumor barrier (BBTB). Antibodies targeted to molecular markers of central nervous system (CNS) tumors will be highlighted, and current strategies for enhancing the delivery of antibodies across these cellular barriers into the brain parenchyma to the tumor will be discussed. Noninvasive imaging approaches to assess BBB/BBTB permeability and/or antibody targeting will be presented as a means of guiding the optimal delivery of targeted agents to brain tumors.

EXPERT OPINION

Preclinical and clinical studies highlight the potential of several approaches in increasing brain tumor delivery across the BBB divide. However, each carries its own risks and challenges. There is tremendous potential in using neuroimaging strategies to assist in understanding and defining the challenges to translating and optimizing molecularly targeted antibody delivery to CNS tumors to improve clinical outcomes.

Rat model of blood-brain barrier disruption to allow targeted neurovascular therapeutics

Endothelial cells with tight junctions along with the basement membrane and astrocyte end feet surround cerebral blood vessels to form the blood-brain barrier(1). The barrier selectively excludes molecules from crossing between the blood and the brain based upon their size and charge. This function can impede the delivery of therapeutics for neurological disorders. A number of chemotherapeutic drugs, for example, will not effectively cross the blood-brain barrier to reach tumor cells(2). Thus, improving the delivery of drugs across the blood-brain barrier is an area of interest. The most prevalent methods for enhancing the delivery of drugs to the brain are direct cerebral infusion and blood-brain barrier disruption(3). Direct intracerebral infusion guarantees that therapies reach the brain; however, this method has a limited ability to disperse the drug(4). Blood-brain barrier disruption (BBBD) allows drugs to flow directly from the circulatory system into the brain and thus more effectively reach dispersed tumor cells. Three methods of barrier disruption include osmotic barrier disruption, pharmacological barrier disruption, and focused ultrasound with microbubbles. Osmotic disruption, pioneered by Neuwelt, uses a hypertonic solution of 25% mannitol that dehydrates the cells of the blood-brain barrier causing them to shrink and disrupt their tight junctions. Barrier disruption can also be accomplished pharmacologically with vasoactive compounds such as histamine(5) and bradykinin(6). This method, however, is selective primarily for the brain-tumor barrier(7). Additionally, RMP-7, an analog of the peptide bradykinin, was found to be inferior when compared head-to-head with osmotic BBBD with 25% mannitol(8). Another method, focused ultrasound (FUS) in conjunction with microbubble ultrasound contrast agents, has also been shown to reversibly open the blood-brain barrier(9). In comparison to FUS, though, 25% mannitol has a longer history of safety in human patients that makes it a proven tool for translational research(10-12). In order to accomplish BBBD, mannitol must be delivered at a high rate directly into the brain's arterial circulation. In humans, an endovascular catheter is guided to the brain where rapid, direct flow can be accomplished. This protocol models human BBBD as closely as possible. Following a cut-down to the bifurcation of the common carotid artery, a catheter is inserted retrograde into the ECA and used to deliver mannitol directly into the internal carotid artery (ICA) circulation. Propofol and N2O anesthesia are used for their ability to maximize the effectiveness of barrier disruption(13). If executed properly, this procedure has the ability to safely, effectively, and reversibly open the blood-brain barrier and improve the delivery of drugs that do not ordinarily reach the brain (8,13,14).

Intra-arterial chemotherapy for malignant gliomas: a critical analysis

Intra-arterial (IA) chemotherapy for malignant gliomas including glioblastoma multiforme was initiated decades ago, with many preclinical and clinical studies having been performed since then. Although novel endovascular devices and techniques such as microcatheter or balloon assistance have been introduced into clinical practice, the question remains whether IA therapy is safe and superior to other drug delivery modalities such as intravenous (IV) or oral treatment regimens. This review focuses on IA delivery and surveys the available literature to assess the advantages and disadvantages of IA chemotherapy for treatment of malignant gliomas. In addition, we introduce our hypothesis of using IA delivery to selectively target cancer stem cells residing in the perivascular stem cell niche.

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.

Imaging and therapy with rituximab anti-CD20 immunotherapy in an animal model of central nervous system lymphoma

PURPOSE

To evaluate the effect of rituximab monoclonal antibody (mAb) on MRI tumor volumetrics and efficacy in a rat model of central nervous system (CNS) lymphoma when delivery to the brain was optimized with osmotic blood-brain barrier disruption (BBBD).

EXPERIMENTAL DESIGN

Female nude rats with intracerebral MC116 human B-cell lymphoma xenografts underwent baseline MRI and were randomized into 5 groups (n = 6 per group): (i) BBBD saline control; (ii) methotrexate with BBBD; (iii) rituximab with BBBD; (iv) rituximab and methotrexate with BBBD; and (v) intravenous rituximab. Tumor volumes were assessed by MRI at 1 week, and rats were followed for survival.

RESULTS

BBBD increased delivery of yttrium-90-radiolabeled mAb in the model of CNS lymphoma. Control rats showed 201 ± 102% increase in tumor volume on MRI 1 week after entering the study and median 14-day survival (range: 6-33). Tumor growth on MRI was slowed in the methotrexate treatment group, but survival time (median: 7 days; range: 5-12) was not different from controls. Among 17 evaluable rats treated with rituximab, 10 showed decreased tumor volume on MRI. All rituximab groups had increased survival compared with control, with a combined median of 43 days (range: 20-60, P < 0.001). There were no differences by route of delivery or combination with methotrexate.

CONCLUSIONS

Rituximab was effective at decreasing tumor volume and improving survival in a model of CNS lymphoma and was not affected by combination with methotrexate or by BBBD. We suggest that rituximab warrants further study in human primary CNS lymphoma.

Blood-brain barrier disruption in the treatment of brain tumors

Standard chemotherapy administered systemically has a limited efficacy in the treatment of brain tumors. One of the major obstacles in the treatment of brain neoplasias is the impediment to delivery across the intact blood-brain barrier (BBB). Many innovative approaches have been developed to circumvent this obstacle. One such strategy is BBB disruption (BBBD), which successfully increases the delivery of antineoplastic agents to the central nervous system (CNS). This chapter describes the application of the BBBD technique in rats. Different methods to evaluate and measure BBB permeability following hyperosmolar mannitol infusion including Evans blue staining, albumin immunohistochemistry, and dynamic magnetic resonance imaging are also described.

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.

Anaesthetic-related neuroprotection: intravenous or inhalational agents?

In designing the anaesthetic plan for patients undergoing surgery, the choice of anaesthetic agent may often appear irrelevant and the best results obtained by the use of a technique or a drug with which the anaesthesia care provider is familiar. Nevertheless, in those surgical procedures (cardiopulmonary bypass, carotid surgery and cerebral aneurysm surgery) and clinical situations (subarachnoid haemorrhage, stroke, brain trauma and post-cardiac arrest resuscitation) where protecting the CNS is a priority, the choice of anaesthetic drug assumes a fundamental role. Treating patients with a neuroprotective agent may be a consideration in improving overall neurological outcome. Therefore, a clear understanding of the relative degree of protection provided by various agents becomes essential in deciding on the most appropriate anaesthetic treatment geared to these objectives. This article surveys the current literature on the effects of the most commonly used anaesthetic drugs (volatile and gaseous inhalation, and intravenous agents) with regard to their role in neuroprotection. A systematic search was performed in the MEDLINE, Cumulative Index to Nursing and Allied Health Literature (CINHAL®) and Cochrane Library databases using the following keywords: 'brain' (with the limits 'newborn' or 'infant' or 'child' or 'neonate' or 'neonatal' or 'animals') AND 'neurodegeneration' or 'apoptosis' or 'toxicity' or 'neuroprotection' in combination with individual drug names ('halothane', 'isoflurane', 'desflurane', 'sevoflurane', 'nitrous oxide', 'xenon', 'barbiturates', 'thiopental', 'propofol', 'ketamine'). Over 600 abstracts for articles published from January 1980 to April 2010, including studies in animals, humans and in vitro, were examined, but just over 100 of them were considered and reviewed for quality. Taken as a whole, the available data appear to indicate that anaesthetic drugs such as barbiturates, propofol, xenon and most volatile anaesthetics (halothane, isoflurane, desflurane, sevoflurane) show neuroprotective effects that protect cerebral tissue from adverse events--such as apoptosis, degeneration, inflammation and energy failure--caused by chronic neurodegenerative diseases, ischaemia, stroke or nervous system trauma. Nevertheless, in several studies, the administration of gaseous, volatile and intravenous anaesthetics (especially isoflurane and ketamine) was also associated with dose-dependent and exposure time-dependent neurodegenerative effects in the developing animal brain. At present, available experimental data do not support the selection of any one anaesthetic agent over the others. Furthermore, the relative benefit of one anaesthetic versus another, with regard to neuroprotective potential, is unlikely to form a rational basis for choice. Each drug has some undesirable adverse effects that, together with the patient's medical and surgical history, appear to be decisive in choosing the most suitable anaesthetic agent for a specific situation. Moreover, it is important to highlight that many of the studies in the literature have been conducted in animals or in vitro; hence, results and conclusions of most of them may not be directly applied to the clinical setting. For these reasons, and given the serious implications for public health, we believe that further investigation--geared mainly to clarifying the complex interactions between anaesthetic drug actions and specific mechanisms involved in brain injury, within a setting as close as possible to the clinical situation--is imperative.

Xenon is an inhibitor of tissue-plasminogen activator: adverse and beneficial effects in a rat model of thromboembolic stroke

Preclinical evidence in rodents has proven that xenon may be a very promising neuroprotective agent for treating acute ischemic stroke. This has led to the general thinking that clinical trials with xenon could be initiated in acute stroke patients in a next future. However, an unappreciated physicochemical property of xenon has been that this gas also binds to the active site of a series of serine proteases. Because the active site of serine proteases is structurally conserved, we have hypothesized and investigated whether xenon may alter the catalytic efficiency of tissue-type plasminogen activator (tPA), a serine protease that is the only approved therapy for acute ischemic stroke today. Here, using molecular modeling and in vitro and in vivo studies, we show (1) xenon is a tPA inhibitor; (2) intraischemic xenon dose dependently inhibits tPA-induced thrombolysis and subsequent reduction of ischemic brain damage; (3) postischemic xenon virtually suppresses ischemic brain damage and tPA-induced brain hemorrhages and disruption of the blood-brain barrier. Taken together, these data indicate (1) xenon should not be administered before or together with tPA therapy; (2) xenon could be a golden standard for treating acute ischemic stroke if given after tPA-induced reperfusion, with both unique neuroprotective and antiproteolytic (anti-hemorrhaging) properties.

Intra-arterial chemotherapy with osmotic blood-brain barrier disruption for aggressive oligodendroglial tumors: results of a phase I study

OBJECTIVE

Refractory anaplastic oligodendroglioma and oligoastrocytoma tumors are challenging to treat. This trial primarily evaluated toxicity and estimated the maximum tolerated dose of intra-arterial (IA) melphalan, IA carboplatin, and intravenous (IV) etoposide phosphate in conjunction with blood-brain barrier disruption in these tumors. The secondary measure was efficacy.

METHODS

Thirteen patients with temozolomide-refractory anaplastic oligodendroglioma (11 patients) or oligoastrocytoma (2 patients) underwent blood-brain barrier disruption with carboplatin (IA, 200 mg/m(2)/d), etoposide phosphate (IV, 200 mg/m(2)/d), and melphalan (IA, dose escalation) every 4 weeks, for up to 1 year. Patients underwent melphalan dose escalation (4, 8, 12, 16, and 20 mg/m(2)/d) until the maximum tolerated dose (1 level below that producing grade 4 toxicity) was determined. Toxicity and efficacy were assessed.

RESULTS

Two of 4 patients receiving IA melphalan at 8 mg/m(2)/d developed grade 4 thrombocytopenia; thus, the melphalan maximum tolerated dose was 4 mg/m/d. Adverse events included asymptomatic subintimal tear (1 patient) and grade 4 thrombocytopenia (3 patients). Two patients demonstrated complete response, 3 had partial responses, 5 demonstrated stable disease, and 3 progressed. Median overall progression-free survival was 11 months. Patients with complete or partial response demonstrated deletion of chromosomes 1p and 19q. In the 5 patients with stable disease, 2 demonstrated 1p and 19q deletion, and 3 demonstrated 19q deletion only.

CONCLUSION

In patients with anaplastic oligodendroglioma or oligoastrocytoma tumors in whom temozolomide treatment has failed, osmotic blood-brain barrier disruption with IA carboplatin, IV etoposide phosphate, and IA melphalan (4 mg/m(2)/d for 2 days) shows acceptable toxicity and encouraging efficacy, especially in patients demonstrating 1p and/or 19q deletion.

Recent advances in blood-brain barrier disruption as a CNS delivery strategy

The blood-brain barrier (BBB) is a complex functional barrier composed of endothelial cells, pericytes, astrocytic endfeets and neuronal cells. This highly organized complex express a selective permeability for molecules that bear, amongst other parameters, adequate molecular weight and sufficient liposolubility. Unfortunately, very few therapeutic agents currently available do cross the BBB and enters the CNS. As the BBB limitation is more and more acknowledged, many innovative surgical and pharmacological strategies have been developed to circumvent it. This review focuses particularly on the osmotic opening of the BBB, a well-documented approach intended to breach the BBB. Since its inception by Rapoport in 1972, pre-clinical studies have provided important information on the extent of BBB permeation. Thanks to Neuwelt and colleagues, the osmotic opening of the BBB made its way to the clinic. However, many questions remain as to the detailed physiology of the procedure, and its best application to the clinic. Using different tools, amongst which MRI as a real-time in vivo characterization of the BBB permeability and CNS delivery, we attempt to better define the osmotic BBB permeabilization physiology. These ongoing studies are described, and data related to spatial and temporal distribution of a molecule after osmotic BBB breaching, as well as the window of BBB permeabilization, are discussed. We also summarize recent clinical series highlighting promising results in the application of this procedure to maximize delivery of chemotherapy in the treatment of brain tumor patients.

Bone marrow chemoprotection without compromise of chemotherapy efficacy in a rat brain tumor model

Thiol chemoprotective agents can reduce chemotherapy side effects, but clinical use is limited due to concerns of impaired chemotherapeutic efficacy. We evaluated whether an optimized bone marrow chemoprotection regimen impaired the efficacy of enhanced chemotherapy against rat brain tumors. Nude rats with intracerebral human lung carcinoma xenografts were treated with carboplatin, melphalan, and etoposide phosphate delivered intra-arterially with osmotic blood-brain barrier disruption (n = 8/group). Thiol chemoprotection was N-acetyl-L-cysteine (1000 mg/kg) 60 min before chemotherapy and/or sodium thiosulfate (8 g/m(2)) 4 and 8 h after chemotherapy, when the blood-brain barrier is reestablished. Blood counts were obtained before treatment on day 3 and at sacrifice on day 9. N-acetylcysteine serum clearance half-life was 9 to 11 min. Pretreatment with N-acetylcysteine combined with delayed administration of sodium thiosulfate protected against toxicity toward total white cells, granulocytes, and platelets (P = 0.0016). Enhanced chemotherapy reduced intracerebral tumor volume to 4.3 +/- 1.0 mm(3) compared with 29.1 +/- 4.1 mm(3) in untreated animals (P < 0.0001). Tumor volume was 3.7 +/- 0.6 mm(3) in rats that received N-acetylcysteine before and sodium thiosulfate after chemotherapy. The data indicate the efficacy of enhanced chemotherapy for rat brain tumors was not affected by thiol chemoprotection that provided excellent protection for hematological toxicity. Negative interactions of thiols with antitumor efficacy were avoided by temporal and spatial separation of chemoprotectants and chemotherapy.