Assessing the rate of drug delivery to the central nervous system (CNS) in vitro has been used for decades to predict whether CNS drug candidates are likely to attain their pharmacological targets, located within the brain parenchyma, at an effective dose. The predictive value of in vitro blood-brain barrier (BBB) models is therefore frequently assessed by comparing in vitro BBB permeability, usually quoted as the endothelial permeability coefficient (Pe) or apparent permeability (Papp), to their rate of BBB permeation measured in vivo, the latter being commonly assessed in rodents. In collaboration with AstraZeneca (DMPK department, Södertälje, Sweden), the in vitro BBB permeability (Papp and Pe) of 27 marketed CNS drugs has been determined using a bovine in vitro BBB model and compared to their in vivo permeability (Pvivo), obtained by rat in-situ brain perfusion. The latter was taken from published data from Summerfield et al. (2007). This comparison confirmed previous reports, showing a strong in vitro/in vivo correlation for hydrophilic compounds, characterized by low brain tissue binding and a weak correlation for lipophilic compounds, characterized by high brain tissue binding. This observation can be explained by the influence of brain tissue binding on the uptake of drugs into the CNS in vivo and the absence of possible brain tissue binding in vitro. The use of glial cells (GC) in the in vitro BBB model to mimic brain tissue binding and the introduction of a new calculation method for in vitro BBB permeability (Pvitro) resulted in a strong correlation between the in vitro and in vivo rate of BBB permeation for the whole set of compounds. These findings might facilitate further in vitro to in vivo extrapolation for CNS drug candidates.

Background: Positron emission tomography microdosing of radiolabeled drugs allows for noninvasive studies of organ exposure in vivo. The aim of the present study was to examine and compare the brain exposure of 12 commercially available CNS drugs and one non-CNS drug. Methods: The drugs were radiolabeled with 11C (t 1/2 = 20.4 minutes) and examined using a high resolution research tomograph. In cynomolgus monkeys, each drug was examined twice. In rhesus monkeys, a first positron emission tomography microdosing measurement was repeated after preadministration with unlabeled drug to examine potential dose-dependent effects on brain exposure. Partition coefficients between brain and plasma (K P) were calculated by dividing the AUC0-90 min for brain with that for plasma or by a compartmental analysis (V T). Unbound K P (K P u,u) was obtained by correction for the free fraction in brain and plasma. Results: After intravenous injection, the maximum radioactivity concentration (C max, %ID) in brain ranged from 0.01% to 6.2%. For 10 of the 12 CNS drugs, C max, %ID was >2%, indicating a preferential distribution to brain. A lower C max, %ID was observed for morphine, sulpiride, and verapamil. K P ranged from 0.002 (sulpiride) to 68 (sertraline) and 7 of 13 drugs had K P u,u close to unity. For morphine, sulpiride, and verapamil, K P u,u was <0.3, indicating impaired diffusion and/or active efflux. Brain exposure at microdosing agreed with pharmacological dosing conditions for the investigated drugs. Conclusions: This study represents the largest positron emission tomography study on brain exposure of commercially available CNS drugs in nonhuman primates and may guide interpretation of positron emission tomography microdosing data for novel drug candidates.

Historically, the focus has been to use in vitro BBB models to optimize rate of drug delivery to the CNS, whereas total in vivo brain/plasma ratios have been used for optimizing extent. However, these two parameters do not necessarily show good correlations with receptor occupancy data or other pharmacological readouts. In line with the free drug hypothesis, the use of unbound brain concentrations (Cu,br) has been shown to provide the best correlations with pharmacological data. However, typically the determination of this parameter requires microdialysis, a technique not ideally suited for screening in early drug development. Alternative, and less resource-demanding methodologies to determine Cu,br employ either equilibrium dialysis of brain homogenates or incubations of brain slices in buffer to determine fraction unbound brain (fu,br), which is subsequently multiplied by the total brain concentration to yield Cu,br. To determine Cu,br/Cu,pl ratios this way, still requires both in vitro and in vivo experiments that are quite time consuming. The main objective of this study was to explore the possibility to directly generate Cu,br/Cu,pl ratios in a single in vitro model of the BBB, using a co-culture of brain capillary endothelial and glial cells in an attempt to mimick the in vivo situation, thereby greatly simplifying existing experimental procedures. Comparison to microdialysis brain concentration profiles demonstrates the possibility to estimate brain exposure over time in the BBB model. A stronger correlation was found between in vitro Cu,br/Cu,pl ratios and in vivo Cu,br/Cu,pl obtained using fu,br from brain slice than with fu,br from brain homogenate for a set of 30 drugs. Overall, Cu,br/Cu,pl ratios were successfully predicted in vitro for 88% of the 92 studied compounds. This result supports the possibility to use this methodology for identifying compounds with a desirable in vivo response in the CNS early on in the drug discovery process.

Introduction: By culturing Caco-2 cells according to a new and optimized protocol, it has been possible to accelerate the cell culture process in such a way that the cells can be used for experiments after only 6 days. The accelerated Caco-2 model has been compared to the traditional model (requiring 21-25 days of culture) in terms of tightness of the junctions, ability to rank chemical compounds for apparent permeability, active efflux and to discriminate P-gp substrates. Methods and results: In the new protocol, Caco-2 cells were cultured with the classical Caco-2 medium supplemented with puromycin. The initial cell seeding density was increased two times compared to the traditional procedure and the presence of a low concentration of puromycin in the culture medium reduced the Caco-2 permeability of mannitol. Bi-directional studies were performed with known P-gp substrates (rhodamine 123, digoxin and saquinavir) and with a total of 20 marketed drugs covering a wide range of physicochemical characteristics and therapeutic indications. Strong correlations were obtained between the apparent permeability in absorptive (Papp A -> B) or secretory (Papp B -> A) of the drugs in the accelerated model and in the traditional models and comparable efflux ratios were observed in the two studied models. Discussion: The new protocol reduces costs for screening and leads to higher throughput compared to traditional Caco-2 cell models. This accelerated model provides short time-feedback to the drug design during the early stage of drug discovery. (C) 2013 Elsevier Inc. All rights reserved.

Background: Modelling the blood-CNS barriers of the brain and spinal cord in vitro continues to provide a considerable challenge for research studying the passage of large and small molecules in and out of the central nervous system, both within the context of basic biology and for pharmaceutical drug discovery. Although there has been considerable success over the previous two decades in establishing useful in vitro primary endothelial cell cultures from the blood-CNS barriers, no model fully mimics the high electrical resistance, low paracellular permeability and selective influx/efflux characteristics of the in vivo situation. Furthermore, such primary-derived cultures are typically labour-intensive and generate low yields of cells, limiting scope for experimental work. We thus aimed to establish protocols for the high yield isolation and culture of endothelial cells from both rat brain and spinal cord. Our aim was to optimise in vitro conditions for inducing phenotypic characteristics in these cells that were reminiscent of the in vivo situation, such that they developed into tight endothelial barriers suitable for performing investigative biology and permeability studies.Methods: Brain and spinal cord tissue was taken from the same rats and used to specifically isolate endothelial cells to reconstitute as in vitro blood-CNS barrier models. Isolated endothelial cells were cultured to expand the cellular yield and then passaged onto cell culture inserts for further investigation. Cell culture conditions were optimised using commercially available reagents and the resulting barrier-forming endothelial monolayers were characterised by functional permeability experiments and in vitro phenotyping by immunocytochemistry and western blotting.Results: Using a combination of modified handling techniques and cell culture conditions, we have established and optimised a protocol for the in vitro culture of brain and, for the first time in rat, spinal cord endothelial cells. High yields of both CNS endothelial cell types can be obtained, and these can be passaged onto large numbers of cell culture inserts for in vitro permeability studies. The passaged brain and spinal cord endothelial cells are pure and express endothelial markers, tight junction proteins and intracellular transport machinery. Further, both models exhibit tight, functional barrier characteristics that are discriminating against large and small molecules in permeability assays and show functional expression of the pharmaceutically important P-gp efflux transporter.Conclusions: Our techniques allow the provision of high yields of robust sister cultures of endothelial cells that accurately model the blood-CNS barriers in vitro. These models are ideally suited for use in studying the biology of the blood-brain barrier and blood-spinal cord barrier in vitro and for pre-clinical drug discovery.

Myeloperoxidase (MPO) is a prime candidate for promoting oxidative stress during inflammation. This abundant enzyme of neutrophils uses hydrogen peroxide to oxidize chloride to highly reactive and toxic chlorine bleach. We have identified 2-thioxanthines as potent mechanism-based inactivators of MPO. Mass spectrometry and x-ray crystal structures revealed that these inhibitors become covalently attached to the heme prosthetic groups of the enzyme. We propose a mechanism whereby 2-thioxanthines are oxidized, and their incipient free radicals react with the heme groups of the enzyme before they can exit the active site. 2-Thioxanthines inhibited MPO in plasma and decreased protein chlorination in a mouse model of peritonitis. They slowed but did not prevent neutrophils from killing bacteria and were poor inhibitors of thyroid peroxidase. Our study shows that MPO is susceptible to the free radicals it generates, and this Achilles' heel of the enzyme can be exploited to block oxidative stress during inflammation.

NXY-059, a polar compound with limited transport across the blood-brain barrier, has demonstrated neuroprotection in several animal models of acute ischemic stroke but failed to confirm clinical benefit in the second phase III trial (SAINT-II). To improve the understanding of the mechanisms responsible for its neuroprotective action in preclinical models a series of experiments was carried out in an in vitro blood-brain barrier (BBB) model. A clinically attainable concentration of 250 mumol/L of NXY-059 administered at the onset or up to 4 h after oxygen glucose deprivation (OGD) produced a significant reduction in the increased BBB permeability caused by OGD. Furthermore, OGD produced a huge influx of tissue plasminogen activator across the BBB, which was substantially reduced by NXY-059. This study suggests that the neuroprotective effects of NXY-059 preclinically, may at least in part be attributed to its ability to restore functionality of the brain endothelium.

The market for neuropharmaceuticals is potentially one of the largest sectors of the global pharmaceutical market owing to the increase in average life expectancy and the fact that many neurological disorders have been largely refractory to pharmacotherapy. The brain is a delicate organ that can efficiently protect itself from harmful compounds and precisely regulate its microenvironment. Unfortunately, the same mechanisms can also prove to be formidable hurdles in drug development. An improved understanding of the regulatory interfaces that exist between blood and brain may provide novel and more effective strategies to treat neurological disorders.

The penetration of the free radical trapping neuroprotectant NXY-059 into the brain has been examined in rats subjected to permanent middle cerebral artery occlusion (pMCAO). NXY-059 (125 mg/kg bolus followed by 125 mg/kg/h) was infused for 4 h 45 min starting 15 min after right pMCAO or sham operation. At 5 h, there was a similar plasma total NXY-059 concentration (mu mol/L) in both groups [sham: 623 44 (6); pMCAO: 605 43 (5)] and a similar drug concentration (nmol/g) in the right cortex [sham: 6.92 +/- 1.05 (6); pMCAO: 6.14 +/- 2.18 (6)]. A subsequent experiment in normal rats, infusing NXY-059 at both a similar and higher concentration (252 mg/kg bolus and 252 mg/kg/h), demonstrated that the concentration of NXY-059 in cortex increased linearly with respect to the plasma concentration. These data demonstrate that NXY-059 does penetrate brain tissue in control animals and ischemic tissue of animals subjected to pMCAO. (c) 200S Elsevier B.V. All rights reserved.

PURPOSE:The objective of the current study was to investigate whether blood-brain barrier (BBB) permeability studies in vitro could be accelerated by running several compounds together in the same experiment.METHODS:To address this question, we compared the transport of six compounds run separately with the results of the same compounds run together (cocktails).RESULTS:The study clearly demonstrated that the outcome of the experiments were totally different depending on the strategy used. Furthermore, the study highlights the importance of having the resistance to drug transport offered by filters without cells under control, as the filter membrane itself can be the rate-limiting step for some compounds; in addition, there is always a potential risk of interactions between molecules in cocktails as well as drug-drug interaction at the level of BBB transporters. In this study, the presence of several P-glycoprotein substrates in the drug cocktail was found to cause breakdown of the BBB.CONCLUSIONS:The results demonstrate that unless a strategy that involves running several compounds in the same experiment is properly validated, the results are of little predictive value.

Successful drug delivery to the central nervous system (CNS) is highly dependent on DMPK as well as physicochemical properties and it is therefore important to characterise these properties and take them into account when designing chemical lead series that act at CNS targets. Since the drug discovery/development process is becoming increasingly focused on reducing the time required to enter molecules into the market, industrial DMPK scientists have emerged from their traditional supportive role in drug development to provide valuable support in the drug discovery process, using novel methods to meet the demands of combinatorial chemistry and bioscience groups.

The free radical trapping nitrone compounds α-phenyl-N-tert-butylnitrone (PBN), 2-sulfophenyl-N-tert-butylnitrone (S-PBN) and disodium 2,4-disulfophenyl-N-tert-butyl nitrone (NXY-059) are effective neuroprotective agents in experimental models of both transient and permanent focal ischemia. A recent in vivo study suggested that NXY-059 had poor brain uptake in a transient ischemia model. We have now examined its blood–brain barrier permeability and cerebral endothelial uptake during hypoxic and ischemic conditions using an in vitro model of the blood–brain barrier. The in vitro blood–brain barrier permeability and cerebral endothelial uptake of NXY-059 and S-PBN were low during normoxic conditions. In contrast, PBN had very high blood–brain barrier penetration in vitro which confirmed earlier in vivo results. The permeability of [14C]NXY-059 increased 3.5 times after 9 h of hypoxia or 3 h of ischemia. There was, respectively, a 5-fold and more than 10-fold increase, after 6 and 9 h of ischemia. The control molecule [3H]inulin (Mr≈5000) showed a similar increase in permeability under the same experimental conditions indicating a major change in the transport properties of the endothelium. There was a 60% reduction in the ATP levels of astrocytes after 3 h of ischemia and a 90% reduction after 9 h. The reduction in ATP levels in endothelial cells was somewhat lower. The uptake of NXY-059 in cerebral endothelial cells under normoxic, hypoxic or 9 h of ischemic conditions was negligible. NXY-059, S-PBN and PBN showed no effects on vesicular transport or the integrity of the blood–brain barrier in normoxic or ischemic conditions, nor did the compounds induce any change in the ATP levels of the cells. In conclusion, it is possible that the increase in blood–brain barrier permeability of [14C]NXY-059 which occurs during prolonged ischemia in vitro reflects a change which may be of importance to the neuroprotective effects of this nitrone free radical trapping agent.

Purpose. Studies were conducted to evaluate whether the use of an in vitro model of the blood-brain barrier (BBB) resulted in more accurate predictions of the in vivo transport of compounds compared to the use of a human intestinal cell line (Caco-2).Methods. The in vitro BBB model employs bovine brain capillary endothelial cells co-cultured with primary rat astrocytes. The Caco-2 cells originate from a human colorectal carcinoma. The rat was used as experimental animal for the in vivo studies.Results. Strong correlations (r = 0.93-0.95) were found between the results generated by the in vitro model of the BBB and two different methodologies to measure the permeability across the BBB in vivo. In contrast, a poor correlation (r = 0.68) was obtained between Caco-2 cell data and in vivo BBB transport. A relatively poor correlation (r = 0.74) was also found between the two in vitro models.Conclusion. The present study illustrates the limitations of the Caco-2 model to predict BBB permeability of compounds in vivo. The results emphasize the fact that the BBB and the intestinal mucosa are two fundamentally different biologic barriers, and to be able to make accurate predictions about the in vivo CNS penetration of potential drug candidates, it is important that the in vitro model possesses the main characteristics of the in vivo BBB.

Clomethiazole (CMZ) was used as a model drug to be incorporated into an emulsion vehicle. The effects of drug concentration and number of homogenisation steps were evaluated using multiple linear regression. The droplet size, measured as a z-average diameter by photon correlation spectroscopy (PCS), was found to be between 60 and 260 nm in the investigated range of CMZ concentrations, highly dependent on the concentration, but more weakly so on the number of homogenisation steps. Slow-scanning high-sensitivity differential scanning calorimetry (DSC) measurements showed that CMZ depresses the phospholipid chain melting temperature in the emulsion system, whereas (13)C nuclear magnetic resonance (NMR) experiments suggested that the CMZ molecules are to a large extent located in the surface region of the emulsion droplets. This interpretation is compatible with results from NMR self-diffusion measurements, which showed that most of the CMZ molecules are rapidly exchanged between emulsion droplets and the aqueous surrounding. It can be concluded that the surface-active drug CMZ has a significant influence on the characteristics of phospholipid-stabilised emulsions through its ability to interact with the phospholipid interface. Thus, the results underline the importance of characterising drug-lipid interactions for the development of lipid-based formulations.

The passage of substances across the blood-brain barrier (BBB) is regulated in the cerebral capillaries, which possess certain distinct different morphological and enzymatic properties compared with the capillaries of other organs. Investigations of the functional characteristics of brain capillaries have been facilitated by the use of cultured brain endothelial cells, but in most studies some characteristics of the in vivo BBB are lost. To provide an in vitro system for studying brain capillary functions, we have developed a process of coculture that closely mimics the in vivo situation by culturing brain capillary endothelial cells on one side of a filter and astrocytes on the other. In order to assess the drug transport across the blood-brain barrier, we compared the extraction ratios in vivo to the permeability of the in vitro model. The in vivo and the in vitro values showed a strong correlation. The relative ease with which such cocultures can be produced in large quantities facilitates the screening of new centrally active drugs. This model provides an easier, reproducible and mass-production method to study the blood-brain barrier in vitro.

The superconducting Bi2Sr2CaCu2O8+x phase is deposited on polycrystalline silver substrates by halide CVD in the temperature interval 760-820 degrees C. Metal iodides and oxygen are used as precursor materials. The films grow with a pronounced [001] orientation, and a superconducting critical temperature of about 80 K was observed without any post-annealing. As far as the authors know, this is the first report of in situ CVD of the Bi-2212 phase on silver substrates. Some of the films were postannealed in a two-step process. The [001] orientation was now considerably improved, but the superconducting critical temperature was reduced to about 75 K.