Intravenous Cereport (RMP-7) Enhances Delivery of Hydrophilic Chemotherapeutics and Increases Survival in Rats with Metastatic Tumors in the Brain

Purpose. The following experiments determined whether intravenous infusions of Cereport enhance delivery of chemotherapeutics and prolong survival in rats with metastatic tumors in the brain. Methods. Autoradiography and scintillation were used to examine uptake of the lipophilic (paclitaxel and carmustine) and the hydrophilic (carboplatin) chemotherapeutic agents, as well as the large hydrophilic marker, 70 kDa dextran. Cereport was also tested in combination with the chemotherapeutic drugs carboplatin, vinorelbine, gemcitabine and carmustine to determine if Cereport could enhance the survival benefit beyond that provided by chemotherapy alone. Results. Cereport enhanced the uptake of carboplatin and dextran, but not paclitaxel or carmustine. The pattern of Cereport's uptake effect with carboplatin revealed that Cereport selectively increased the proportion of highly permeable regions. Survival was significantly enhanced when Cereport was combined with either carboplatin, vinorelbine, or gemcitabine, but not carmustine, compared to each chemotherapeutic agent alone. Conclusions. These data provide the first evidence that Cereport, or any receptor-mediated approach intended to enhance the permeability of the blood-brain tumor barrier, can increase the delivery hydrophilic drugs to metastatic tumors in the brain, increasing survival in tumor-bearing rats.     

The development of the bradykinin agonist labradimil as a means to increase the permeability of the blood-brain barrier: from concept to clinical evaluation

Labradimil (Cereport; also formerly referred to as RMP-7) is a 9-amino-acid peptide designed for selectivity for the bradykinin B2 receptor and a longer plasma half-life than bradykinin. It has been developed to increase the permeability of the blood-brain barrier (BBB) and is the first compound with selective bradykinin B2 receptor agonist properties to progress from concept design through to tests of efficacy in patients. In vitro studies demonstrate that labradimil has a longer half-life than bradykinin and selectively binds to bradykinin B2 receptors, initiating typical bradykinin-like second messenger systems, including increases in intracellular calcium and phosphatidylinositol turnover. Initial proof of principle studies using electron microscopy demonstrated that intravenous labradimil increases the permeability of the BBB by disengaging the tight junctions of the endothelial cells that comprise the BBB. Autoradiographic studies in rat models further demonstrated that labradimil increases the permeability of the BBB in gliomas. Intravenous or intra-arterial labradimil increases the uptake of many different radiolabelled tracers and chemotherapeutic agents into the tumour in a dose-related fashion. These effects are selective for the tumour and for the brain surrounding the tumour, and are particularly robust in tumour areas that are normally relatively impermeable. The increased chemotherapeutic concentrations are maintained for at least 90 minutes, well beyond the transient effects on the BBB. The increase in permeability with labradimil occurs rapidly but is transient, in that restoration of the BBB occurs very rapidly (2 to 5 minutes) following cessation of infusion. Even with continuous infusion of labradimil, spontaneous restoration of the barrier begins to occur within 10 to 20 minutes. Collectively, these data demonstrate that the B2 receptor system that modulates permeability of the BBB is highly sensitive and autoregulated and that careful attention to the timing of labradimil and the chemotherapeutic agent is important to achieve maximal effects. Survival studies in rodent models of both gliomas and metastatic tumours in the brain demonstrate that the enhanced uptake observed with the combination of labradimil and water-soluble chemotherapeutics enhances survival to a greater extent than achieved with chemotherapy alone. Finally, preliminary clinical trials in patients with gliomas provide confirmatory evidence that labradimil permeabilises the blood-brain tumour barrier and might, therefore, be used to increase delivery of agents such as carboplatin to tumours without the toxicity typically associated with dose escalation.     

Intracarotid administration of short-chain alkylglycerols for increased delivery of methotrexate to the rat brain

1 The intracarotid administration of alkylglycerols has been reported previously by us to be a novel strategy for increased delivery of various chemotherapeutic drugs to the normal brain and brain tumors in rats. 2 Effectiveness and structure-activity relations of the most promising pentyl- and hexylglycerol derivatives have been elucidated in vivo by analyzing the transfer of methotrexate (MTX) across the blood-brain barrier (BBB) in normal rats. The effects were compared with BBB disruption using hypertonic mannitol or intracarotid infusion of bradykinin. Furthermore, toxicity of the alkylglycerols has been studied in long-term experiments. 3 Apart from 1-O-pentyldiglycerol, all alkylglycerols induced a concentration-dependent increase in MTX delivery to the brain varying from 1.1 to more than 300-fold compared to intra-arterial MTX alone. Enhanced barrier permeability rapidly approached baseline values within 5 and 120 min at the latest. Chemical structure, concentration, time schedule of injections and combination of different alkylglycerols were identified as instruments suited to regulate the MTX accumulation within a wide range. Mannitol 1.4 M resulted in very high MTX levels in the brain as observed using the highest concentrations of alkylglycerols. Intracarotid infusion of bradykinin had only a minor effect on the BBB. Using 1-O-pentylglycerol or 2-O-hexyldiglycerol, both cell culture experiments and long-term in vivo analyses including clinical, laboratory and histopathological evaluations revealed no signs of toxicity. 4 In summary, intracarotid short-chain alkylglycerols constitute a very effective and low toxic strategy for transient opening of the BBB to overcome the limited access of cytotoxic drugs to the brain.     

缓激肽开放血瘤屏障过程中诱发快速耐受性的机制探讨

目的探讨缓激肽(bradykinin,BK)开放血瘤屏障过程中,HSF1和HSP70对BK诱发快速耐受性的影响。方法首先通过立体定向法接种C6细胞制备恶性胶质瘤大鼠模型。模型制备成功后,经颈内动脉缓慢小剂量给予缓激肽(或生理盐水)10μg.kg-1.min-1,动态观察肿瘤组织内热休克因子1(heatshockfactor1,HSF1)蛋白单体和三聚体的活性及热休克蛋白70(heatshockprotein70,HSP70)的表达(Westernblot法)。免疫组织化学技术检测血瘤屏障上紧密连接蛋白occludin的变化。利用伊文思蓝连续监测缓激肽处理后的C6恶性胶质瘤大鼠血瘤屏障的通透性,同时电镜观察血瘤屏障的病理学改变。结果缓激肽作用于C6大鼠后,紧密连接增宽,血瘤屏障通透性增加,伊文思蓝渗出量分别较对照组增加了5.19μg.g-1(0min),5.06μg.g-1(5min),11.35μg.g-1(10min,P<0.05),21.54μg.g-1(15min,P<0.01),12.81μg.g-1(30min,P<0.05),7.28μg.g-1(60min)。肿瘤组织内HSF1蛋白三聚体活性和HSP70蛋白的表达逐渐增加,且分别于处理后的5min和30min时达高峰(P<0.01,与对照组相比),最大值为对照组的2～3倍。免疫组化检测结果发现,处理后的C6动物,其血瘤屏障的紧密连接蛋白occludin表达减少,15min后逐渐增加。结论缓激肽作用于血瘤屏障后,激活了HSF1并促进了hsp70蛋白的表达。增加的hsp70可能通过发挥分子伴侣作用来修复紧密连接蛋白,进而诱发快速耐受性。     

Ligand-modified homologous targeted cancer cell membrane biomimetic nanostructured lipid carriers for glioma therapy

The main treatment measure currently used for glioma treatment is chemotherapy; the biological barrier of solid tumors hinders the deep penetration of nanomedicines and limits anticancer therapy. Furthermore, the poor solubility of many chemotherapeutic drugs limits the efficacy of antitumor drugs. Therefore, improving the solubility of chemotherapeutic agents and drug delivery to tumor tissues through the blood–brain barrier (BBB) and blood–brain tumor barrier (BBTB) are major challenges in glioma treatment. Nanostructured lipid carriers (NLCs) have high drug loading capacity, high stability, and high in vivo safety; moreover, they can effectively improve the solubility of insoluble drugs. Therefore, in this study, we used solvent volatilization and ultrasonic melting methods to prepare dihydroartemisinin nanostructured lipid carrier (DHA-NLC). We further used the glioma C6 cancer cell (CC) membrane to encapsulate DHA-NLC owing to the homologous targeting mechanism of the CC membrane; however, the targeting ability of the CC membrane was weak. We accordingly used targeting ligands for modification, and developed a bionanostructured lipid carrier with BBB and BBTB penetration and tumor targeting abilities. The results showed that DHA-loaded NGR/CCNLC (asparagine–glycine–arginine, NGR) was highly targeted, could penetrate the BBB and BBTB, and showed good anti-tumor effects both in vitro and in vivo, which could effectively prolong the survival time of tumor-bearing mice. Thus, the use of DHA-loaded NGR/CCNLC is an effective strategy for glioma treatment and has the potential to treat glioma.     

Current strategies for targeted delivery of bio-active drug molecules in the treatment of brain tumor

Brain tumor is one of the most challenging diseases to treat. The major obstacle in the specific drug delivery to brain is blood–brain barrier (BBB). Mostly available anti-cancer drugs are large hydrophobic molecules which have limited permeability via BBB. Therefore, it is clear that the protective barriers confining the passage of the foreign particles into the brain are the main impediment for the brain drug delivery. Hence, the major challenge in drug development and delivery for the neurological diseases is to design non-invasive nanocarrier systems that can assist controlled and targeted drug delivery to the specific regions of the brain. In this review article, our major focus to treat brain tumor by study numerous strategies includes intracerebral implants, BBB disruption, intraventricular infusion, convection-enhanced delivery, intra-arterial drug delivery, intrathecal drug delivery, injection, catheters, pumps, microdialysis, RNA interference, antisense therapy, gene therapy, monoclonal/cationic antibodies conjugate, endogenous transporters, lipophilic analogues, prodrugs, efflux transporters, direct conjugation of antitumor drugs, direct targeting of liposomes, nanoparticles, solid–lipid nanoparticles, polymeric micelles, dendrimers and albumin-based drug carriers.     

Peri-tumoral leakage during intra-tumoral convection-enhanced delivery has implications for efficacy of peri-tumoral infusion before removal of tumor

In cases of malignant brain tumors, infiltrating tumor cells that exist at the tumor-surrounding brain tissue always escape from cytoreductive surgery and, protected by blood-brain barrier (BBB), survive the adjuvant chemoradiotherapy, eventually leading to tumor recurrence. Local interstitial delivery of chemotherapeutic agents is a promising strategy to target these cells. During our effort to develop effective drug delivery methods by intra-tumoral infusion of chemotherapeutic agents, we found consistent pattern of leakage from the tumor. Here we describe our findings and propose promising strategy to cover the brain tissue surrounding the tumor with therapeutic agents by means of convection-enhanced delivery. First, the intracranial tumor isograft model was used to define patterns of leakage from tumor mass after intra-tumoral infusion of the chemotherapeutic agents. Liposomal doxorubicin, although first distributed inside the tumor, distributed diffusely into the surrounding normal brain once the leakage happen. Trypan blue dye was used to evaluate the distribution pattern of peri-tumoral infusions. When infused intra- or peri-tumorally, infusates distributed robustly into the tumor border. Subsequently, volume of distributions with different infusion scheduling; including intra-tumoral infusion, peri-tumoral infusion after tumor resection, peri-tumoral infusion without tumor removal with or without systemic infusion of steroids, were compared with Evans-blue dye. Peri-tumoral infusion without tumor removal resulted in maximum volume of distribution. Prior use of steroids further increased the volume of distribution. Local interstitial drug delivery targeting tumor surrounding brain tissue before tumor removal should be more effective when targeting the invading cells.     

Light-induced deterioration test of carboplatin under clinical settings

Chemotherapeutic drug dosages are calculated precisely based on the patient's height, body weight, and renal function, etc. To ensure safe and favorable outcomes of treatment, dosing solutions are prepared by appropriate mixing of the drug solutions based on such calculations. The package inserts for many injectable preparations include a warning for storing the product "shielded from light." However, there are no reports of stability assessment of a mixed product against light exposure or the residual amount of active ingredient in the dosing solution during or at the end of treatment. We evaluated the stability of carboplatin from the time of mixing of the dosing solution until the end of drug infusion in a clinical-like setting. With 4-hour exposure to outdoor scattered light, the dosing solution began to show discoloration by 1 hour, becoming dark yellow by 4 hours, with reduction of the percent residual carboplatin to about 23%. To identify the optimal light-shielding shade, the dosing solution was shielded from outdoor scattered light with 1 of 3 protective covers: aluminum foil, yellow plastic shade, and brown plastic shade. The yellow plastic shade prevented any changes of the appearance of the dosing solution during the 4-hour exposure period. The percent residual carboplatin, determined by HPLC, in the dosing solution shielded with a yellow plastic shade was about 85.2% at 2 hours and 78.6% at 4 hours. Thus carboplatin dosing solution should be completely shielded from light until infusion is completed.     

Stability of cancer chemotherapeutic agents in a totally implanted drug delivery system

The stability and compatibility of serveral chemotherapeutic agents with an implantable infusion device were evaluated. The totally implantable drug delivery system can be placed subcutaneously in an ambulatory patient to permit the regional administration of antineoplastic drugs. The in vitro method of assessing the stability of three chemotherapeutic agents with the pumping device involved placing the pumps, filled with cytarabine, dichloromethotrexate, and vinblastine, in a 37 degree C water bath with mild agitation. Control solutions placed in amber vials were maintained under simulated physiological conditions. Samples (1 ml) were removed periodically, frozen at -20 degrees C and later toward and batch assayed by high pressure liquid chromatography to determine drug concentrations. An in vivo assessment of the stability of floxuridine was also conducted in five patients receiving intra-arterial hepatic infusions by the device. The concentrations placed in the pump were compared with the contractions removed at the time of refill. Cytarabine and dichloromethotrexate showed no appreciable drug decomposition in the control vials or the pump over the 15-day and 28-day study periods, respectively. Vinblastine underwent a 48% and 20% drugs loss in the pump and control, respectively, during a 14-day period. In the vivo assessment of floxuridine, less than 5% drug degradation was found for infusion times ranging from four to 12 days. Cytarabine, dichloromethothrexate, and floxuridine were stable and compatible with the implantable infusion evice, and vinblastine was found to be unstable. The compatibility of all agents with the infusion device should be evaluated before clinical application.     

Hyperthermia and Thermosensitive Liposomes for Improved Delivery of Chemotherapeutic Drugs to Solid Tumors

Lipid-based nanocarriers or liposomes have been proven successful in the delivery of chemotherapeutic agents and are currently applied clinically in the treatment of various types of cancer. Liposomes offer the advantage of a high drug payload, decreased drug toxicity and enhanced drug accumulation at tumor sites. Increased accumulation is due to the relatively leaky tumor vasculature that allows liposome extravasation. Between different types of tumors and even within one tumor, vascular permeability and thus liposome extravasation may differ greatly. Furthermore, upon accumulation of liposomes in the tumor area, drug bioavailability is not guaranteed. At present, these are the major issues for clinically used liposomal drugs.     

Nasal administration of an angiotensin antagonist in the rat model: effect of bioadhesive formulations on the distribution of drugs to the systemic and central nervous systems

The effect of bioadhesive formulations on the direct transport of an angiotensin antagonist drug ((14)C-GR138950) from the nasal cavity to the central nervous system was evaluated in a rat model. Three different bioadhesive polymer formulations (3% pectin LM-5, 1.0% pectin LM-12 and 0.5% chitosan G210) containing the drug were administered nasally to rats by inserting a dosing cannula 7mm into the nasal cavity after which the plasma and brain tissue levels were measured. It was found that the polymer formulations provided significantly higher plasma levels and significantly lower brain tissue levels of drug than a control, in the form of a simple drug solution. Changing the depth of insertion of the cannula from 7 to 15mm, in order to reach the olfactory region in the nasal cavity significantly decreased plasma levels and significantly increased brain tissue levels of drug for the two formulations studied (1.0% pectin LM-12 and a simple drug solution). There was no significant difference between the drug availability for the bioadhesive formulation and the control in the brain when the longer cannula was used for administration. It is suggested that the conventional rat model is not suitable for evaluation of the effects of bioadhesive formulations in nose-to-brain delivery.     

Evaluation of Calvert's formula for dosage adjustment of carboplatin in Japanese patients with hormone refractory prostate cancer

For hormone refractory prostate carcinoma, a combination therapy of paclitaxel and carboplatin is used to expect life extension. We investigated the pharmacokinetics of carboplatin in Japanese prostate cancer patients (n=10, 55-72 years), and evaluated the usefulness of Calvert's formula in the individualized dosing adjustment. They were intravenously administered carboplatin (area under the free plasma concentration versus time curve (AUC)=5 mg.min/ml), following the intravenous administration of paclitaxel (175 mg/m(2)). The dosage of carboplatin for each patient was determined with Calvert's formula using individual creatinine clearance values. Plasma concentration of total platinum was measured sequentially and the pharmacokinetic parameters of carboplatin were determined in each patient. Plasma concentration of total carboplatin after intravenous infusion well fitted the two-compartment model. Carboplatin clearance was 62.0+/-12.7 ml/min (mean+/-S.D.), and linearly related to the individual creatinine clearance (r(2)=0.64, p<0.01). The actual AUC for total carboplatin was 8.20+/-1.11 mg.min/ml, and its inter-individual variability was decreased to 65% of that in carboplatin clearance, indicating the effectiveness of Calvert's formula for dosage adjustment of carboplatin. Leucopenia of grade 4 according to the National Cancer Institute's Common Toxicity Criteria was found in one patient, but no patient demonstrated thrombocytopenia. In conclusion, determining carboplatin dosage based on Calvert's formula decreased the inter-individual variability in the actual AUC compared with that in the carboplatin clearance, and a target AUC of 5 mg.min/ml of carboplatin was comparatively safe for Japanese patients with prostate cancer.     

A novel, quantitative bio-assay for cholecystokinin type-1 receptor activity in the anaesthetised rat

INTRODUCTION: Cholecystokinin type-1 (CCK(1)) receptors mediate many of the physiological functions of CCK including delay of gastric emptying, pancreatic enzyme secretion, intestinal motility and gallbladder contractility. Existing in-vivo assays for the quantitative measurement of CCK(1) receptor mediated function are generally variable, limited in precision and require a relatively large number of animals to obtain statistically meaningful data. We found that they did not provide robust pharmacokinetic-pharmacodynamic data for profiling compounds acting at these receptors. Accordingly, here we describe a novel rat duodenal contractility assay that addresses these problems. METHODS: Rats were anaesthetised and a saline-filled balloon was inserted through the body of the stomach and secured in the duodenum approximately 1 cm from the pyloric sphincter for measurement of intra-lumenal pressure. Studies were performed to determine a dose, rate and frequency of administration of CCK8S that produced a readily quantifiable response. RESULTS: Initial experiments revealed that sustained exposure to CCK8S resulted in the rapid development of tachyphylaxis. After investigating different dosing paradigms, it was found that pulsatile delivery of CCK8S (intravenous infusion for 1 min every 10 min) produced a readily quantifiable contractile response that did not exhibit tachyphylaxis. The assay response output was defined as the number of contractions >5 mm Hg over baseline. The contractions were blocked in a dose-dependent manner by intravenous bolus injections of the CCK(1) receptor antagonists, dexloxiglumide (2 and 20 micromol/kg), and devazepide (3-100 nmol/kg) but not by the CCK(2) receptor antagonist gastrazole (10 micromol/kg). CONCLUSION: A novel, simple, high quality assay for the quantification of the in-vivo activity of CCK(1) receptor ligands is described. CCK8S delivered by pulsatile intravenous infusion to anesthetized rats produced a burst of contractile activity of the duodenum mediated by CCK(1) receptors. This activity was highly reproducible and sustained for more than 3 h providing an assay that circumvents problems associated with agonist-induced tachyphylaxis.     

Cereport™ (RMP-7) Increases the Permeability of Human Brain Microvascular Endothelial Cell Monolayers1

Purpose. To study Cereport (RMP-7, bradykinin B2 agonist) effects on human brain microvascular endothelial cell (HBMEC) monolayer permeability. Methods. HBMEC grown on transwell membranes were exposed to Cereport. The monolayer permeability was determined with [^I4C]-inulin (MW. 5,200) and [³H]-dextran (MW. 70,000). Results. Cereport increased the HBMEC permeability to [^l4C]-inulin, but not to [³H]-dextran. The effect was transient, maximal at 15 min (i.e., 79.3% increase), and polarized to the basolateral membrane. An inverted U, dose-response curve was observed with active concentrations of Cereport from 0.01 to 0.5 nmol/L, the plateau maximal effect between 0.5 and 10 nmol/L, and loss of activity at the highest concentration, i.e., 20 nmol/L. Cyclic AMP-specific phosphodiesterase 3 (PDE3) inhibitor rolipram (10 mol/L) abolished Cereport effects, while cGMP-specific PDE5 inhibitor, zaniprast (50 mol/L) enhanced by 31 % (p < 0.05) the effect of 0.1 nmol/L Cereport. Unlabeled Cereport displaced [^{12 5}I]-bradykinin and/or [¹²⁵I]-Cereport from the basolateral side. There was no specific Cereport binding to the apical side. Conclusions. Cereport exerts specific time, dose and size dependent actions on HMBEC monolayer that are restricted to the basolateral membrane. Its effects can be further modulated through changes in cAMP and cGMP second messenger systems.     

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.     

Glioma targeting peptide modified apoferritin nanocage

Therapeutic outcome for the treatment of glioma was often limited due to the non-targeted nature of drugs and the physiological barriers, including the blood-brain barrier (BBB) and the blood-brain tumor barrier (BBTB). An ideal glioma-targeted delivery system must be sufficiently potent to cross the BBB and BBTB and then target glioma cells with adequate optimized physiochemical properties and biocompatibility. However, it is an enormous challenge to the researchers to engineer the above-mentioned features into a single nanocarrier particle. New frontiers in nanomedicine are advancing the research of new biomaterials. In this study, we demonstrate a strategy for glioma targeting by encapsulating vincristine sulfate (VCR) into a naturally available apoferritin nanocage-based drug delivery system with the modification of GKRK peptide ligand (GKRK-APO). Apoferritin (APO), an endogenous nanosize spherical protein, can specifically bind to brain endothelial cells and glioma cells via interacting with the transferrin receptor 1 (TfR1). GKRK is a peptide ligand of heparan sulfate proteoglycan (HSPG) over-expressed on angiogenesis and glioma, presenting excellent glioma-homing property. By combining the dual-targeting delivery effect of GKRK peptide and parent APO, GKRK-APO displayed higher glioma localization than that of parent APO. After loading with VCR, GKRK-APO showed the most favorable antiglioma effect in vitro and in vivo. These results demonstrated that GKRK-APO is an important potential drug delivery system for glioma-targeted therapy.     

Calcium-dependent potassium channels as a target protein for modulation of the blood-brain tumor barrier

Even though the blood-brain tumor barrier (BTB) is more permeable than the blood-brain barrier (BBB), the BTB still significantly restricts the delivery of anticancer drugs to brain tumors. Brain tumor capillaries that form the BTB, however, express certain unique protein markers that are absent or barely detectable in normal brain capillaries. We were able to biochemically modulate one such protein marker, the calcium-dependent potassium (K(Ca)) channel, by using a specific K(Ca) channel agonist, NS-1619, to obtain sustained enhancement of selective drug delivery, including molecules of varying sizes, to tumors in rat syngeneic and xenograft brain tumor models. Immunolocalization and potentiometric studies showed increased K(Ca) channel distribution on tumor cells compared with normal cells, suggesting that tumor cell-specific signals might induce overexpression of K(Ca) channels in capillary endothelial cells, leading to increased BTB permeability. We also demonstrated that the cellular mechanism for K(Ca) channel-mediated BTB permeability increase is due to accelerated formation of pinocytotic vesicles, which can transport therapeutic molecules across the BTB. This concept was investigated by using NS-1619 to facilitate increased delivery of carboplatin to brain tumor leading to enhanced survival in rats with brain tumors. Additionally, we showed that K(Ca) channel modulation resulted in enhanced permeability to macromolecules, including Her-2 monoclonal antibody and green fluorescent protein-adenoviral vectors, in a human, primary brain-tumor xenograft model. Therefore, K(Ca) channels are a potential, promising target for biochemical modulation of BTB permeability to increase antineoplastic drug delivery selectively to brain tumors.     

Effect of pentobarbital anaesthesia on intestinal absorption and hepatic first-pass metabolism of oxacillin in rats, evaluated by portal-systemic concentration difference.

The effects of anaesthesia on intestinal drug absorption and hepatic first-pass metabolism in rats were investigated by observing the difference in the drug concentration between portal and systemic bloods. Oxacillin and pentobarbital were selected as a model drug and as an anaesthetic, respectively. Rats were divided into a conscious control group and an anaesthetized group. All rats were cannulated simultaneously in the portal vein and in the femoral artery, and oxacillin was orally administered after its intra-arterial injection (double dosing). For the anaesthetized group, pentobarbital was intrasubcutaneously administered twice, first before intra-arterial injection and again before oral administration of oxacillin. The arterial blood alone was sampled from the cannula in the femoral artery before oral administration, whereas the arterial and portal bloods were simultaneously sampled from both cannulated sites after oral administration. Oxacillin concentrations in plasma were assayed by HPLC. The anaesthesia increased the absolute bioavailability (F), the mean absorption time (MAT) and the hepatic recovery ratio (F(H)), but caused little change in the local absorption ratio into the portal system (Fa) and the total clearance (CL). The hepatic clearance (CL(H)) was significantly decreased, resulting in an apparent small change in CL-CL(H) which is considered to be renal clearance. By this method, it was shown directly that an increase in F due to pentobarbital anaesthesia was attributable to the significant increase in F(H). It is expected that the method is useful not only to evaluate the effect of anaesthesia on the first-pass effect, but also to assess the effect of co-administration of drugs on first-pass metabolism.     

Evaluation of drug delivery following the administration of magnetic albumin microspheres containing adriamycin to the rat

The disposition of adriamycin following its intra-arterial administration in rats as a solution (control) or via magnetic albumin microspheres (treatment group) has been investigated. The rat tail was demarcated into three segments: T1, the pre-target site; T2, the target site; and T3, the post-target site. In both groups, 2.0 mg/kg of adriamycin HCl was injected into the ventral caudal artery in T1 through a T-piece cannula. A magnetic field of 8000 G was directed towards T2. The concentration of adriamycin was measured in the heart, kidney, liver, lung, serum, small intestine, spleen, T1, T2, and T3 as a function of time using an ion-pairing HPLC assay. Areas under the mean adriamycin concentration-time curves were used to determine two indices of drug delivery: the relative tissue exposure and targeting efficiency. It was demonstrated that the magnetically responsive albumin microspheres altered the tissue distribution of adriamycin in rats. Administration of drug via magnetic microspheres was shown to increase the relative drug exposure to both T2 and liver.