Pharmacokinetics of a once-daily tacrolimus formulation in first nations and caucasian liver transplant recipients.

Patient ethnicity may influence the pharmacokinetics (PK) of tacrolimus. Because the Canadian First Nations (FN) constitute a large and increasing segment of the liver transplant population, we undertook to determine whether PK differences exist for a once-daily, extended release formulation of tacrolimus (Advagraf) in FN compared to Caucasian (CAUC) liver transplant recipients. Following achievement of a steady state with Advagraf, blood samples were drawn at 0, 1, 2, 4, 6, 8 and 24 hours for whole blood tacrolimus levels by commercial immunoassay and CYP3A4 and CYP3A5 allele analyses were performed by polymerase chain reactions. Nineteen subjects participated in the study (7 FN and 12 CAUC). The FN cohort had significantly higher AUC (214 ± 48 versus 168 ± 25, P < 0.05), Cmax (16.7 ± 4.4 ng/ml versus 11.3 ± 1.7 ng/ml, P < 0.05), Cmin (6.1 ± 1.0 ng/ml versus 4.7 ± 0.5 ng/ml, P < 0.05) and shorter Tmax (1.6 ± 0.2 hours versus 2.8 ± 0.3 hours, P < 0.05) values than CAUCs. CYP3A4 genotypes were C/C in both cohorts, while the CYP3A5 *1/*3 allele was present in 2/5 FN and 0/9 CAUC. The results of this study indicate that once-daily, extended release Advagraf results in higher blood tacrolimus levels and shorter times to Cmax in FN compared to CAUC liver transplant recipients.

Validation of Cadherin HAV6 Peptide in the Transient Modulation of the Blood-Brain Barrier for the Treatment of Brain Tumors.

The blood-brain barrier (BBB) poses a major obstacle by preventing potential therapeutic agents from reaching their intended brain targets at sufficient concentrations. While transient disruption of the BBB has been used to enhance chemotherapeutic efficacy in treating brain tumors, limitations in terms of magnitude and duration of BBB disruption exist. In the present study, the preliminary safety and efficacy profile of HAV6, a peptide that binds to the external domains of cadherin, to transiently open the BBB and improve the delivery of a therapeutic agent, was evaluated in a murine brain tumor model. Transient opening of the BBB in response to HAV6 peptide administration was quantitatively characterized using both a gadolinium magnetic resonance imaging (MRI) contrast agent and adenanthin (Ade), the intended therapeutic agent. The effects of HAV6 peptide on BBB integrity and the efficacy of concurrent administration of HAV6 peptide and the small molecule inhibitor, Ade, in the growth and progression of an orthotopic medulloblastoma mouse model using human D425 tumor cells was examined. Systemic administration of HAV6 peptide caused transient, reversible disruption of BBB in mice. Increases in BBB permeability produced by HAV6 were rapid in onset and observed in all regions of the brain examined. Concurrent administration of HAV6 peptide with Ade, a BBB impermeable inhibitor of Peroxiredoxin-1, caused reduced tumor growth and increased survival in mice bearing medulloblastoma. The rapid onset and transient nature of the BBB modulation produced with the HAV6 peptide along with its uniform disruption and biocompatibility is well-suited for CNS drug delivery applications, especially in the treatment of brain tumors.

Modulation of intercellular junctions by cyclic-ADT peptides as a method to reversibly increase blood-brain barrier permeability.

It is challenging to deliver molecules to the brain for diagnosis and treatment of brain diseases. This is primarily because of the presence of the blood-brain barrier (BBB), which restricts the entry of many molecules into the brain. In this study, cyclic-ADT peptides (ADTC1, ADTC5, and ADTC6) have been shown to modify the BBB to enhance the delivery of marker molecules [e.g., (14) C-mannitol, gadolinium-diethylenetriaminepentacetate (Gd-DTPA)] to the brain via the paracellular pathways of the BBB. The hypothesis is that these peptides modulate cadherin interactions in the adherens junctions of the vascular endothelial cells forming the BBB to increase paracellular drug permeation. In vitro studies indicated that ADTC5 had the best profile to inhibit adherens junction resealing in Madin-Darby canine kidney cell monolayers in a concentration-dependent manner (IC50 = 0.3 mM) with a maximal response at 0.4 mM. Under the current experimental conditions, ADTC5 improved the delivery of (14) C-mannitol to the brain about twofold compared with the negative control in the in situ rat brain perfusion model. Furthermore, ADTC5 peptide increased in vivo delivery of Gd-DTPA to the brain of Balb/c mice when administered intravenously. In conclusion, ADTC5 has the potential to improve delivery of diagnostic and therapeutic agents to the brain.

Modulation of blood-brain barrier permeability in mice using synthetic E-cadherin peptide.

The present work characterizes the effects of synthetic E-cadherin peptide (HAV) on blood-brain barrier (BBB) integrity using various techniques including magnetic resonance imaging (MRI) and near-infrared fluorescent imaging (NIRF). The permeability of small molecular weight permeability marker gadolinium diethylenetriaminepentaacetate (Gd-DTPA) contrast agent, the large molecular weight permeability marker, IRDye 800CW PEG, and the P-glycoprotein (P-gp) efflux transporter contrast agent, rhodamine 800 (R800), were examined in the presence and absence of HAV peptide. The results consistently demonstrated that systemic iv administration of HAV peptide resulted in a reversible disruption of BBB integrity and enhanced the accumulation of all the dyes examined. The magnitude of increase ranged from 2-fold to 5-fold depending on the size and the properties of the permeability markers. The time frame for BBB disruption with HAV peptide was rapid, occurring within 3-6 min following injection of the peptide. Furthermore, modulation of BBB permeability was reversible with the barrier integrity being restored within 60 min of the injection. The increased BBB permeability observed following HAV peptide administration was not attributable to changes in cerebral blood flow. These studies support the potential use of cadherin peptides to rapidly and reversibly modulate BBB permeability of a variety of therapeutic agents.

Transporter-based delivery of anticancer drugs to the brain: improving brain penetration by minimizing drug efflux at the blood-brain barrier.

The delivery of many drugs to the central nervous system (CNS) is limited due to the restrictive nature of the blood-brain barrier (BBB). The reduced paracellular diffusion and the presence of various drug efflux transporters in the brain microvessel endothelial cells forming the BBB make effective treatment of brain tumors with chemotherapeutic agents particularly problematic. While Pglycoprotein (P-gp) plays an important role in limiting BBB permeability of chemotherapeutic agents, other drug efflux transporters such as breast cancer resistance protein (BCRP) and multidrug resistance-associated proteins (MRPs) are likely to impact on chemotherapeutic levels within the brain and brain tumor. The current review examines the restrictive role that drug efflux transporters have in the delivery of chemotherapeutic agents to the brain. Consideration of different approaches taken to minimize the impact of drug efflux transporters in the BBB and improve chemotherapeutic response in treating brain tumors is also discussed.

Rapid and reversible enhancement of blood-brain barrier permeability using lysophosphatidic acid.

The present study characterizes the effects of lysophosphatidic acid (LPA) on blood-brain barrier (BBB) permeability focusing specifically on the time of onset, duration, and magnitude of LPA-induced changes in cerebrovascular permeability in the mouse using both magnetic resonance imaging (MRI) and near infrared fluorescence imaging (NIFR). Furthermore, potential application of LPA for enhanced drug delivery to the brain was also examined by measuring the brain accumulation of radiolabeled methotrexate. Exposure of primary cultured brain microvessel endothelial cells (BMECs) to LPA produced concentration-dependent increases in permeability that were completely abolished by clostridium toxin B. Administration of LPA disrupted BBB integrity and enhanced the permeability of small molecular weight marker gadolinium diethylenetriaminepentaacetate (Gd-DTPA) contrast agent, the large molecular weight permeability marker, IRdye800cwPEG, and the P-glycoprotein efflux transporter probe, Rhodamine 800 (R800). The increase in BBB permeability occurred within 3 minutes after LPA injection and barrier integrity was restored within 20 minutes. A decreased response to LPA on large macromolecule BBB permeability was observed after repeated administration. The administration of LPA also resulted in 20-fold enhancement of radiolabeled methotrexate in the brain. These studies indicate that administration of LPA in combination with therapeutic agents may increase drug delivery to the brain.

Examination of blood-brain barrier (BBB) integrity in a mouse brain tumor model.

The present study evaluates, both functionally and biochemically, brain tumor-induced alterations in brain capillary endothelial cells. Brain tumors were induced in Balb/c mice via intracranial injection of Lewis Lung carcinoma cells into the right hemisphere of the mouse brain using stereotaxic apparatus. Blood-brain barrier (BBB) permeability was assessed at various stages of tumor development, using both radiolabeled tracer permeability and magnetic resonance imaging with gadolinium diethylene-triamine-pentaacetate contrast enhancement (Gad-DTPA). The expression of the drug efflux transporter, P-glycoprotein (P-gp), in the BBB at various stages of tumor development was also evaluated by Western blot and immunohistochemistry. Median mouse survival following tumor cell injection was 17 days. The permeability of the BBB to (3)H-mannitol was similar in both brain hemispheres at 7 and 10 days post-injection. By day 15, there was a twofold increase in (3)H-mannitol permeability in the tumor bearing hemispheres compared to the non-tumor hemispheres. Examination of BBB permeability with Gad-DTPA contrast enhanced MRI indicated cerebral vascular permeability changes were confined to the tumor area. The permeability increase observed at the later stages of tumor development correlated with an increase in cerebral vascular volume suggesting angiogenesis within the tumor bearing hemisphere. Furthermore, the Gad-DPTA enhancement observed within the tumor area was significantly less than Gad-DPTA enhancement within the circumventricular organs not protected by the BBB. Expression of P-gp in both the tumor bearing and non-tumor bearing portions of the brain appeared similar at all time points examined. These studies suggest that although BBB integrity is altered within the tumor site at later stages of development, the BBB is still functional and limiting in terms of solute and drug permeability in and around the tumor.

Assessment of P-glycoprotein activity in the Blood-Brain Barrier (BBB) using Near Infrared Fluorescence (NIRF) imaging techniques.

PURPOSE: To examine functional activity of P-glycoprotein (P-gp) in the blood-brain barrier (BBB) using near infrared fluorescence (NIRF) imaging techniques. METHODS: Cellular accumulation and bi-directional permeability of the NIRF probe, rhodamine 800 (R800) was determined in MDCKMDR1 and MDCKwt monolayers under normal conditions and following P-gp inhibition with GF120918. Functional P-gp activity was also assessed in mice following administration of R800 alone and with GF230918. Quantitative analysis of R800 fluorescence in brain tissue and blood was measured ex-vivo using Odyssey Near Infrared imaging. RESULTS: R800 accumulation was reduced in MDCKMDR1 compared to MDCKwt monolayers. Addition of GF120918, resulted in increased R800 accumulation in MDCKMDR1 monolayers. Permeability of R800 in MDCKMDR1 monolayers was significantly enhanced (4-fold) in the basolateral to apical direction under control conditions and was abolished following treatment with GF120918. With the exception of the choriod plexus, there was very little penetration of R800 into the brain under control conditions. Treatment of mice with GF120918 resulted in a nearly 4-fold increase in R800 fluorescence in the brain. In contrast, GF120918 had no effect on brain penetration of a vascular permeability marker. CONCLUSIONS: In vitro studies demonstrate the P-gp transporter properties of the NIRF probe R800. Preliminary in vivo studies confirm the P-gp transporter liabilities of R800 and suggest this probe may be useful as a molecular imaging agent for examining P-gp activity in the BBB.

Fatty acid transport protein expression in human brain and potential role in fatty acid transport across human brain microvessel endothelial cells.

The blood-brain barrier (BBB), formed by the brain capillary endothelial cells, provides a protective barrier between the systemic blood and the extracellular environment of the CNS. Passage of fatty acids from the blood to the brain may occur either by diffusion or by proteins that facilitate their transport. Currently several protein families have been implicated in fatty acid transport. The focus of the present study was to identify the fatty acid transport proteins (FATPs) expressed in the brain microvessel endothelial cells and characterize their involvement in fatty acid transport across an in vitro BBB model. The major fatty acid transport proteins expressed in human brain microvessel endothelial cells (HBMEC), mouse capillaries and human grey matter were FATP-1, -4 and fatty acid binding protein 5 and fatty acid translocase/CD36. The passage of various radiolabeled fatty acids across confluent HBMEC monolayers was examined over a 30-min period in the presence of fatty acid free albumin in a 1 : 1 molar ratio. The apical to basolateral permeability of radiolabeled fatty acids was dependent upon both saturation and chain length of the fatty acid. Knockdown of various fatty acid transport proteins using siRNA significantly decreased radiolabeled fatty acid transport across the HBMEC monolayer. Our findings indicate that FATP-1 and FATP-4 are the predominant fatty acid transport proteins expressed in the BBB based on human and mouse expression studies. While transport studies in HBMEC monolayers support their involvement in fatty acid permeability, fatty acid translocase/CD36 also appears to play a prominent role in transport of fatty acids across HBMEC.