Transit Compartment Research Articles

Single point mutations result in the miss-sorting of Glut4 to a novel membrane compartment associated with stress granule proteins.

Insulin increases cellular glucose uptake and metabolism in the postprandial state by acutely stimulating the translocation of the Glut4 glucose transporter from intracellular membrane compartments to the cell surface in muscle and fat cells. The intracellular targeting of Glut4 is dictated by specific structural motifs within cytoplasmic domains of the transporter. We demonstrate that two leucine residues at the extreme C-terminus of Glut4 are critical components of a motif (IRM, insulin responsive motif) involved in the sorting of the transporter to insulin responsive vesicles in 3T3L1 adipocytes. Light microscopy, immunogold electron microscopy, subcellular fractionation, and sedimentation analysis indicate that mutations in the IRM cause the aberrant targeting of Glut4 to large dispersed membrane vesicles that are not insulin responsive. Proteomic characterization of rapidly and slowly sedimenting membrane vesicles (RSVs and SSVs) that were highly enriched by immunoadsorption for either wild-type Glut4 or an IRM mutant revealed that the major vesicle fraction containing the mutant transporter (IRM-RSVs) possessed a relatively small and highly distinct protein population that was enriched for proteins associated with stress granules. We suggest that the IRM is critical for an early step in the sorting of Glut4 to insulin-responsive subcellular membrane compartments and that IRM mutants are miss-targeted to relatively large, amorphous membrane vesicles that may be involved in a degradation pathway for miss-targeted or miss-folded proteins or represent a transitional membrane compartment that Glut4 traverses en route to insulin responsive storage compartments.

Challenges of a mechanistic feedback model describing nicotinic acid-induced changes in non-esterified fatty acids in rats

Previously, we developed a feedback model to describe the tolerance and oscillatory rebound of non-esterified fatty acid (NEFA) plasma concentrations in male Sprague Dawley rats after intravenous infusions of nicotinic acid (NiAc). This study challenges that model, using the following regimens of intravenous and oral NiAc dosing in male Sprague Dawley rats (n = 95) to create different patterns of exposure: (A) 30 min infusion at 0, 1, 5 or 20 μmol kg(-1) body weight; (B) 300 min infusion at 0, 5, 10 or 51 μmol kg(-1); (C) 30 min infusion at 5 μmol kg(-1), followed by a stepwise decrease in rate every 10 min for 180 min; (D) 30 min infusion at 5 μmol kg(-1), followed by a stepwise decrease in rate every 10 min for 180 min and another 30 min infusion at 5 μmol kg(-1) from 210 to 240 min; (E) an oral dose of 0, 24.4, 81.2 or 812 μmol kg(-1). Serial arterial blood samples were taken for measurement of plasma NiAc and NEFA concentrations. The gradual decrease in infusion rate in (C) and (D) were also designed to test the hypothesis that a gradual reduction in NiAc plasma concentration may be expected to reduce or prevent rebound. The absorption of NiAc was described by parallel linear and non-linear processes and the disposition of NiAc by a two-compartment model with endogenous turnover rate and two parallel capacity-limited elimination processes. NEFA (R) turnover, which was driven by the plasma concentration of NiAc via an inhibitory drug-mechanism function acting on NEFA formation, was described by a feedback model with a moderator distributed over a series of transit compartments, where the first compartment (M 1) inhibited the formation of R and the last compartment (M N ) stimulated the loss of R. All processes regulating the plasma NEFA concentration were assumed to be captured by the moderator function. Data were analyzed using non-linear mixed effects modeling (NONMEM). The potency IC 50 of NiAc was 68 nmol L(-1), the fractional turnover rate k out 0.27 L mmol(-1) min(-1), and the turnover rate of moderator k tol 0.023 min(-1). The lower physiological limit of NEFA, which was modeled as a NiAc-independent release (k cap ) of NEFA into plasma, was estimated to 0.023 mmol L(-1) min(-1). The parameter estimates derived in this study were consistent with our previous estimates, suggesting that the model may be used for prediction of the NEFA response time-course following different modes and routes administration of NiAc or NiAc analogues. In order to avoid NiAc-induced NEFA rebound, a slow decline in the NiAc exposure pattern is needed at or below IC (50).

Population Pharmacokinetics of JNJ-37822681, a Selective Fast-Dissociating Dopamine D2-Receptor Antagonist, in Healthy Subjects and Subjects with Schizophrenia and Dose Selection Based on Simulated D2-Receptor Occupancy

JNJ-37822681 is a selective, fast-dissociating dopamine D2-receptor antagonist currently in development as a candidate antipsychotic. The aim of the analyses was to develop a population pharmacokinetic model to describe the pharmacokinetics of JNJ-37822681 in healthy subjects and patients with schizophrenia and to identify covariates of interest. The model was then used to simulate D2-receptor occupancy in support of dose selection for subsequent studies. Data were obtained from 378 subjects enrolled in three phase I and two phase II studies. Nonlinear mixed effects modeling of pooled data was conducted using NONMEM(®) to estimate population pharmacokinetic parameters and the effect of covariates on these parameters. The model was evaluated on a subset of data that was not used for model building and was subsequently used to simulate steady-state exposure for each subject in the phase IIb study. Striatal D2-receptor occupancy was predicted using simulated exposure combined with pharmacodynamic parameters from a sigmoid maximum effect model established from previous [(11)C]raclopride positron emission tomography studies. A two-compartment disposition model with zero-order input in a depot compartment followed by first-order absorption into and first-order elimination from the central compartment combined with a transit compartment provided the best fit to the data. Significant covariates were sex and bioavailability on apparent clearance and food intake on the absorption rate constant. Clearance was 11 % higher in females compared with males. The model passed external evaluation. The estimated pharmacokinetic parameters for the phase IIb study were similar to those observed in the phase IIa study. D2-receptor occupancy was predicted to be in the 65-80 % range at 10 mg twice daily and partially or fully reaching the 80 % threshold at doses of 20 and 30 mg twice daily. The population pharmacokinetic model of JNJ-37822681 successfully described the pharmacokinetics of JNJ-37822681 and allowed the reliable determination of individual exposure parameters in a phase IIb study. It was concluded that 5 or 7.5 mg twice daily would likely be minimal- or no-effect doses, whereas 10 mg twice daily was expected to provide an optimal balance of efficacy and tolerability.

PWE-009 Caecal PH Measurement is an Objective Biomarker of Excessive Fermentation in Patients with Bloating and Distension

IntroductionFermentation of undigested carbohydrates by the colonic microbiota is an important part of maintaining a healthy colonic environment. However, excessive fermentation is thought to play a role in exacerbating symptoms...

Population Pharmacokinetic Analysis for Hydrocodone Following the Administration of Hydrocodone Bitartrate Extended-Release Capsules

Hydrocodone is a semi-synthetic narcotic analgesic and antitussive. Although hydrocodone products have been on the market for over 50 years, relatively little is known about its pharmacokinetics. Additionally, there are no published reports of population pharmacokinetic analyses for hydrocodone. Furthermore, current labeling of hydrocodone-containing products provides little guidance in terms of the impact of patient descriptors on the pharmacokinetics of hydrocodone. The objectives of this analysis were to develop a population pharmacokinetic model that characterizes the pharmacokinetics of hydrocodone following single and multiple oral doses of hydrocodone extended-release capsules (hydrocodone bitartrate ER capsules) in healthy subjects and patients, to examine the impact of patient descriptors on pharmacokinetic parameters and to assess the dose-proportionality of hydrocodone pharmacokinetic. A total of 4,714 plasma hydrocodone concentrations from 220 subjects were available for this analysis. The data were extracted from seven studies (five phase 1 and two phase 2 studies). A two-compartment open mamillary model with linear elimination and a complex absorption model was used to fit the data, using NONMEM(®) version 7.1.2 software. The absorption model involved two sequential first-order absorption processes with the delay in the first process accomplished by means of multiple transit compartments. Covariate analysis was performed using standard forward selection followed by backward elimination processes. Model evaluation was performed using a prediction-corrected visual predictive check (pcVPC). The population estimates of apparent oral central volume of distribution and apparent oral linear clearance were 714 L and 64.4 L/h, respectively. The first absorption process was rapid. Creatinine clearance and body surface area (BSA) were statistically significant predictors of the apparent oral clearance and apparent oral volume of distribution. The pcVPC indicated that the model provided a robust and unbiased fit to the data. A linear model for hydrocodone elimination provided an adequate fit to the observed data over the entire dose range, which supports that hydrocodone bitartrate ER capsules exhibit dose-proportional pharmacokinetics. The formulation of hydrocodone bitartrate ER capsules results in absorption profiles that are variable across and within subjects. Despite the variability in absorption profiles, a relatively simple model provided an adequate fit to the data. Creatinine clearance and BSA were statistically significant predictors of the apparent oral clearance and apparent oral volume of distribution. Absorption characteristics of hydrocodone bitartrate ER capsules should still allow effective plasma concentrations of hydrocodone to be reached quickly and for effective concentrations to be maintained for a long period.

A Semi‐Physiological Model of Amyloid‐β Biosynthesis and Clearance in Human Cerebrospinal Fluid: A Tool for Alzheimer's Disease Research and Drug Development

Stable isotope labeling kinetics (SILK) was successfully applied to quantify endogenous amyloid-β (Aβ) metabolism in human cerebrospinal fluid (CSF). A semi-physiological model describing Aβ biosynthesis and degradation in human CSF and the impact of the γ-secretase inhibitor semagacestat should be developed and validated based on digitized data from three published SILK studies. Aβ biosynthesis was adequately characterized by six transit compartments. At each transition step, a first-order degradation process was implemented. A two-compartment model best described semagacestat CSF concentration-time profiles. Semagacestat concentrations were linked to the Aβ production by an inhibitory Emax model. For model validation, three individual Aβ profiles from literature were successfully predicted. Model application demonstrated a 35% decreased Aβ elimination rate constant in Alzheimer's disease (AD) patients. Study design optimization revealed that SILK studies could be conducted with significant less sampling points compared to the standard protocol without losing information about the Aβ metabolism, if analyzed by the presented model. In conclusion, the analysis outlined the advantages and opportunities of integrating all available data and knowledge into a semi-physiological model. The model can serve as valuable tool for researchers and clinicians interested in the pathology of AD as well as in the development of new therapeutics for AD.

Application of mechanism-based PKPD model to identify optimal dosing regimens for future development of oraxol.

e13505 Background: Paclitaxel (PTX) is a widely used potent anticancer drug that blocks mitosis by stabilization of microtubules. Previous attempts for oral administration of PTX have been unsuccessful at least partly due to its affinity for the efflux pump, P-gp. Oraxol is an oral formulation of PTX combined with a novel potent P-gp inhibitor, HM30181A, to maximize absorption of paclitaxel without itself being systemically absorbed. A population PK/PD model was developed to characterize the temporal relationship between PTX exposure and neutropenia, and subsequently model-based simulations were utilized to determine the optimal dosing strategy for oraxol. Methods: Oraxol was administered to 68 (51M/17F) patients with various malignancies. Oraxol dose levels ranged from 60 to 420 mg/m2 QW, and 90-150 QWx2 for 3/4 weeks. Population PKPD modeling was performed with the following patient factors: [BSA (1.29-2.15 m2), ECOG PS scores (97% pts ≤ 1), age (36-81.4 yrs), CrCL (39.6-132.8 ml/min), ALB (2.3-4.8 mg/dL), ALT (6-61 IU/L), TBIL (0.2-1.6 mg/dL), and smoking status (NS:57%)]; followed by model validation. Simulations assessed the influence of dose and schedule on the time course and the extent of neutropenia. Results: A precursor-dependent indirect PKPD response model, including three transit compartments was employed to describe the time course of ANC after oraxol administration. Mean predicted (%SEM) baseline ANC and MTT of neutrophils in plasma were 3.6 (3.9) x109 cells/L and 6.3 (4.2) days. The magnitude of the inhibition on marrow cells was 3.3% per 100 ng/mL of PTX. Model validation results showed excellent concordance with the observed and simulated ANC profiles at the 150 mg/m2 dose level. Simulations showed that severity of neutropenia was dose- and schedule-dependent. The optimal dosing scenarios for oraxol 150 mg/m2QDx3 and QDx5 showed the incidence of grade ³3 neutropenia to be 53.8% and 58%, respectively. Simulated grade 4 neutropenia was 25 and 34.6% for the same regimens; similar to IV PTX. Conclusions: A PKPD model quantifying the neutropenic effect of oraxol has been developed. The model predicts that the QDx3 or QDx5 oraxol dosing 3/4 weeks may optimize efficacy with manageable toxicity.

Romiplostim dose–response in patients with myelodysplastic syndromes

To characterize the romiplostim dose-response in subjects with low or intermediate-1 risk myelodysplastic syndromes (MDS) receiving subcutaneous romiplostim. Data from 44 MDS subjects receiving subcutaneous romiplostim (dose range 300-1500 μg week(-1) ) were used to develop a pharmacodynamic model consisting of a romiplostim-sensitive progenitor cell compartment linked to the peripheral blood compartment through four transit compartments representing the maturation in the bone marrow from megakaryocytes to platelets. A kinetics of drug effect model was used to quantify the stimulatory effect of romiplostim on the proliferation of sensitive progenitor cells and pharmacodynamics-mediated disposition was modelled by assuming the kinetics of drug effect constant (kDE ) to be proportional to the change in platelet count relative to baseline. The estimated values (between subject variability) for baseline platelet count, mean transit time, and kDE were 24 × 10(9) l(-1) (47%), 9.6 days (44%) and 0.28 days(-1) , respectively. MDS subjects had a shorter platelet lifespan (42 h) than healthy subjects (257 h). Romiplostim effect was described for responders (78%) and non-responders (22%). The average weekly stimulatory effect of romiplostim on the production rate of sensitive progenitor cells at baseline was 269% per 100 μg week(-1) for responders. Body weight, age, gender and race were not statistically related to romiplostim pharmacodynamic parameters. Visual predictive checks confirmed the model adequacy. The time course of platelet counts in MDS subjects receiving subcutaneous administration of escalating doses of romiplostim was characterized and showed a linear dose-response for romiplostim responders to increase the platelet counts.

Pharmacokinetic/pharmacodynamic modeling of antipyretic and reducing plasma concentration of NO effects of Rheum palmatum in rat

Pharmacokinetic-pharmacodynamic (PK-PD) modeling was used to characterize the antipyretic and anti-inflammatory effects in rats of Rhein, a major component in rhubarb. Twenty-four healthy male Sprague-Dawley (SD) rats were randomly into four groups, of 6 each. The rats in first group were injected intravenously with lipopolysaccharide (LPS, 100 microg x kg(-1)). The second group rats were given rhubarb decoction (RD, 1.54 g x kg(-1)) by oral administration alone. The rats belonging to third group were administered orally RD 30 min after LPS injection. The rest rats were given normal saline only as control group. Orbital sinus blood sampling was collected at different time points. The Rhein and NO concentration in plasma and body temperature (BT) were measured. Relevant data of PK-PD modeling were performed with Kinetica 5. 0. 11. RD could suppress the rise in BT and plasma NO concentration. The antipyretic and anti-inflammatory responses were best described by a Sigmod-E(max) model. Delay between exposure and response was accounted for by a transit compartment model with two parallel transit compartment chains. The results showed that some parameters such as t1/2, C(max) and AUC were significantly increased in rats treated with LPS, compared to those in rats treated with normal saline. The EC50 for antipyretic effect and decrease of plasma NO concentration was respectively equal to 114.1, 90.80 microg x L(-1). The E(max) for antipyretic effect was about 111% of that for increase in BT after LPS injection. The E(max) for anti-inflammatory action was close to 8.399% of that for elevated NO level after modeling. Meanwhile, there was a difference in pharmacokinetic process of Rhein between the impact of normal saline and LPS. So, it can be concluded that the targets of regulating NO production and BT after RD administration may be at the same location. Not only do that, the antipyretic effect induced by RD maybe completely manifest through reducing the plasma concentration of NO.

Mathematical Model Approach to Describe Tumour Response in Mice After Vaccine Administration and its Applicability to Immune-Stimulatory Cytokine-Based Strategies

Immunotherapy is a growing therapeutic strategy in oncology based on the stimulation of innate and adaptive immune systems to induce the death of tumour cells. In this paper, we have developed a population semi-mechanistic model able to characterize the mechanisms implied in tumour growth dynamic after the administration of CyaA-E7, a vaccine able to target antigen to dendritic cells, thus triggering a potent immune response. The mathematical model developed presented the following main components: (1) tumour progression in the animals without treatment was described with a linear model, (2) vaccine effects were modelled assuming that vaccine triggers a non-instantaneous immune response inducing cell death. Delayed response was described with a series of two transit compartments, (3) a resistance effect decreasing vaccine efficiency was also incorporated through a regulator compartment dependent upon tumour size, and (4) a mixture model at the level of the elimination of the induced signal vaccine (k 2) to model tumour relapse after treatment, observed in a small percentage of animals (15.6%). The proposed model structure was successfully applied to describe antitumor effect of IL-12, suggesting its applicability to different immune-stimulatory therapies. In addition, a simulation exercise to evaluate in silico the impact on tumour size of possible combination therapies has been shown. This type of mathematical approaches may be helpful to maximize the information obtained from experiments in mice, reducing the number of animals and the cost of developing new antitumor immunotherapies.

Model-Based Estimates of the Effects of Efavirenz on Bedaquiline Pharmacokinetics and Suggested Dose Adjustments for Patients Coinfected with HIV and Tuberculosis

Safe, effective concomitant treatment regimens for tuberculosis (TB) and HIV infection are urgently needed. Bedaquiline (BDQ) is a promising new anti-TB drug, and efavirenz (EFV) is a commonly used antiretroviral. Due to EFV's induction of cytochrome P450 3A4, the metabolic enzyme responsible for BDQ biotransformation, the drugs are expected to interact. Based on data from a phase I, single-dose pharmacokinetic study, a nonlinear mixed-effects model characterizing BDQ pharmacokinetics and interaction with multiple-dose EFV was developed. BDQ pharmacokinetics were best described by a 3-compartment disposition model with absorption through a dynamic transit compartment model. Metabolites M2 and M3 were described by 2-compartment models with clearance of BDQ and M2, respectively, as input. Impact of induction was described as an instantaneous change in clearance 1 week after initialization of EFV treatment and estimated for all compounds. The model predicts average steady-state concentrations of BDQ and M2 to be reduced by 52% (relative standard error [RSE], 3.7%) with chronic coadministration. A range of models with alternative structural assumptions regarding onset of induction effect and fraction metabolized resulted in similar estimates of the typical reduction and did not offer a markedly better fit to data. Simulations to investigate alternative regimens mitigating the estimated interaction effect were performed. The results suggest that simple adjustments of the standard regimen during EFV coadministration can prevent reduced exposure to BDQ without increasing exposures to M2. However, exposure to M3 would increase. Evaluation in clinical trials of adjusted regimens is necessary to ensure appropriate dosing for HIV-infected TB patients on an EFV-based regimen.

Characterizing Systemic Exposure of Inhaled Drugs: Application to the Long-Acting β2-Agonist PF-00610355

PF-00610355 is an orally inhaled long-acting β2-adrenoreceptor agonist that is being developed for the once-daily treatment of chronic obstructive pulmonary disease (COPD). The pharmacological effect is exerted in the lungs. However, systemic exposure of PF-00610355 is expected to be responsible for certain drug-related adverse effects. This analysis characterizes PF-00610355 using an integrated analysis of systemic exposure, across trials and patient populations. A total of 6,107 samples of PF-00610355 plasma concentration, collected in 264 subjects from eight studies in healthy volunteers, asthma, and COPD patients, were analyzed using non-linear mixed-effects models. Model-based mean (95 % CI) exposure profiles for a range of PF-00610355 doses in COPD patients were simulated. PF-00610355 exposure profiles were described by a three-compartment disposition model with first-order absorption through a transit compartment. Patient status, inhalation device, and demographic factors were found to influence systemic drug exposure. Relative fine particle dose had a minor effect, whereas no effect of baseline lung function on the systemic exposure was found. An implicit method to address pharmacokinetic variability between occasions of drug intake yielded similar results as the established explicit method, yet in a much more efficient way. The estimated systemic pre-dose and maximum PF-00610355 plasma concentration was 23 and 38 % in COPD patients compared to healthy volunteers, respectively. The analysis illustrated the value of an integrated pharmacokinetic analysis to address specific challenges in the clinical development of long-/ultra-long-acting β2-agonists and inhaled compounds in general, both in relation to selecting a safe starting dose in patients, but also in understanding exposure and systemic safety information across different patient populations and different inhalation devices/formulations.

A new method of segmentation of compact-appearing, transitional and trabecular compartments and quantification of cortical porosity from high resolution peripheral quantitative computed tomographic images

A transitional or cortico-trabecular junctional zone exists at any location composed of both cortical and trabecular bones such as the metaphyses of tubular bones and short bones like the femoral neck. The transitional zone comprises the inner cortex adjacent to the medullary canal and trabeculae abutting against the cortex contiguous with the endocortical surface. This is a site of vigorous remodeling. Intracortical remodeling cavitates the inner cortex expanding this transitional zone at the price of compact-appearing cortex so that it contains porosity, cortical fragments that resemble trabeculae, and trabeculae abutting the eroding cortex. The porosity of the transitional zone is an important source of bone loss. It reduces bone strength exponentially and is a quantifiable `fingerprint' of structural deterioration.A new automated method of segmentation of bone from background and bone into its compact-appearing cortex, transitional zone, and trabecular compartment is described, with a new approach to quantification of cortical porosity. Segmentation is achieved by automatically selecting attenuation profile curves perpendicular to the periosteal surface. Local bone edges are identified as the beginning and the end of the rising and falling S-shaped portions of the curve enabling the delineation of the compartments. Analyzing ~3600 consecutive overlapping profiles around the perimeter of each cross-sectional slice segments the compartments.Porosity is quantified as the average void volume fraction of all voxels within each compartment. To assess accuracy at the distal radius and tibia, μCT images of cadaveric specimens imaged at 19μm voxel size served as the gold standard. To assess accuracy at the proximal femur, scanning electron microscopy (SEM) images of specimens collected at 2.5μm resolution served as the gold standard.Agreement between HRpQCT and the gold standards for segmentation and quantification of porosity at the distal radius and tibia ranged from R2=0.87 to 0.99, and for the proximal femur ranged from 0.93 to 0.99. The precision error in vivo for segmentation and quantification of porosity in HRpQCT images at the distal radius, given by the root mean square error of the coefficient of variation, ranged from 0.54% for porosity of the transitional zone to 3.98% for area of the compact-appearing cortex.Segmentation of the transitional zone minimizes errors in apportioning cortical fragments and cortical porosity to the medullary compartment and so is likely to allow accurate assessment of fracture risk and the morphological effects of growth, aging, diseases and therapies.

Cellular Mechanism for the Pharmacological Correction of hERG Mutations Linked to the Long QT Syndrome

The human Ether-a-go-go Related Gene (hERG) encodes Kv11.1 and underlies the rapidly activating delayed rectifier K+ current in the heart, and loss-of-function hERG mutations cause the type 2 long QT syndrome (LQT2). The majority of LQT2-linked missense mutations decrease the trafficking of Kv11.1. An important finding is drugs that bind to Kv11.1 and block current (IKv11.1) can correct the trafficking for most of these mutations (pharmacological correction). We tested the hypothesis that pharmacological correction increases the trafficking of mutant LQT2 channels from the Endoplasmic Reticulum (ER). Voltage-clamping and Western blotting experiments of HEK293 cells expressing the trafficking-deficient LQT2 mutation G601S showed that pharmacological correction still occurred in cells treated with the protein synthesis inhibitor cycloheximide. Confocal analyses of HEK293 cells stably expressing wild type Kv11.1 or G601S showed that G601S is selectively stored in an intermediate ER compartment with BAP31. The intermediate BAP31 compartment does not overlap with the perinuclear ER compartment, transitional ER compartment, or the ER Golgi Intermediate Compartment. Treating cells in E-4031, a drug that corrects G601S trafficking, decreased G601S co-localization with intermediate BAP31 compartment and increased G601S immunostaining at the cell surface membrane. Additional experiments showed that treating cell in E-4031 for as little as 30 min was sufficient to caused the pharmacological correction of IKv11.1 for many hours. Together these data demonstrate that a steady-state subpopulation of LQT2 channels is stored separately in the BAP31 transitional ER compartment and their functional expression is readily corrected by E-4031 treatment.

Dose selection using a semi-mechanistic integrated glucose-insulin-glucagon model: designing phase 2 trials for a novel oral glucokinase activator

Selecting dosing regimens for phase 2 studies for a novel glucokinase activator LY2599506 is challenging due to the difficulty in modeling and assessing hypoglycemia risk. A semi-mechanistic integrated glucose-insulin-glucagon (GIG) model was developed in NONMEM based on pharmacokinetic, glucose, insulin, glucagon, and meal data obtained from a multiple ascending dose study in patients with Type 2 diabetes mellitus treated with LY2599506 for up to 26 days. The series of differential equations from the NONMEM model was translated into an R script to prospectively predict 24-h glucose profiles following LY2599506 treatment for 3 months for a variety of doses and dosing regimens. The reduction in hemoglobin A1c (HbA1c) at the end of the 3-month treatment was estimated using a transit compartment model based on the simulated fasting glucose values. Two randomized phase 2 studies, one with fixed dosing and the other employing conditional dose titration were conducted. The simulation suggested that (1) Comparable HbA1c lowering with lower hypoglycemia risk occurs with titration compared to fixed-dosing; and (2) A dose range of 50-400 mg BID provides either greater efficacy or lower hypoglycemia incidence or both than glyburide. The predictions were in reasonable agreement with the observed clinical data. The model predicted HbA1c reduction and hypoglycemia risk provided the basis for the decision to focus on the dose-titration trial and for the selection of doses for the demonstration of superiority of LY2599506 to glyburide. The integrated GIG model represented a valuable tool for the evaluation of hypoglycemia incidence.

Joint Population Pharmacokinetic/Pharmacodynamic Model for the Heart Rate Effects at Rest and at the End of Exercise for Cilobradine

To develop a semi-mechanistic population pharmacokinetic/pharmacodynamic (PKPD) model for the selective bradycardic agent cilobradine describing simultaneously the heart rate (HR) measured at rest and just after the end of exercise sharing the same set of PKPD parameters. Healthy subjects received cilobradine orally once daily over 2weeks at 0.25-5mg doses or placebo. Plasma drug concentrations and HR were measured at rest and following 3min of exercise over the entire study period. PK and HR data were analyzed using the population approach with NONMEM VII. Plasma disposition of cilobradine was described with a three compartment model. Cilobradine showed dose proportional and time independent pharmacokinetics. HR response was drug concentration dependent and appeared with a significant delay with respect to PK profiles, a phenomenon modeled using two transit compartments. Perturbation in HR at rest as a consequence of exercise was described assuming that physiological processes controlling cardiac frequency were constantly increased over the period of exercise only. The selected model provides a useful modeling tool for cases where the PD response measured is the result of a temporal experimental induced perturbation.

A Population Pharmacokinetic and Pharmacodynamic Study of a Peripheral κ-Opioid Receptor Agonist CR665 and Oxycodone

Peripherally acting opioids, particularly peripheral κ-opioid agonists, may be effective for treating visceral pain by activating receptors expressed on afferent nerves within the gut. The objective of this study was to investigate the pharmacokinetic/pharmacodynamic profile of a novel peripherally selective κ-opioid agonist, CR665 (JNJ-38488502), and compare it to that of oxycodone, a non-selective brain-penetrant opioid. In a randomized, placebo-controlled, double-blind, three-way crossover study, healthy male volunteers were administered CR665 (0.36 mg/kg, intravenous), oxycodone (15 mg, oral) or placebo (intravenous and oral), followed by assessment of visceral pain tolerance thresholds (VPTT) measured as volume of water (mL) in the bag placed on an oesophageal probe. Plasma drug concentration data were used to generate pharmacokinetic models, which were then used to fit the VPTT data using NONMEM(®) VI to generate population pharmacokinetic/pharmacodynamic models. CR665 kinetics were optimally fitted with a two-compartment model, while oxycodone kinetics were best described by a one-compartment model with transit compartment absorption feeding directly into the central compartment. For both drugs, the plasma concentration effects on VPTT were best fit by a direct linear model, i.e. without the concentration-analgesia delay characteristic of brain-penetrant opioids. The slope of oxycodone (0.089 mL per ng/mL) was steeper than that of CR665 (0.0035 mL per ng/mL) for the plasma drug concentration acting on the VPTT. The results are consistent with the peripheral selectivity of CR665, as well as the possibility that peripheral actions of oxycodone contribute to its visceral analgesic efficacy.

A Simultaneous D‐Optimal Designed Study for Population Pharmacokinetic Analyses of Mycophenolic Acid and Tacrolimus Early After Renal Transplantation

Mycophenolic acid (MPA) and tacrolimus (TAC) are immunosuppressive agents used in combination with corticosteroids for the prevention of acute rejection after solid organ transplantation. Their pharmacokinetics (PK) show considerable unexplained intraindividual and interindividual variability, particularly in the early period after transplantation. The main objective of the present work was to design a study based on D-optimality to describe the PK of the 2 drugs with good precision and accuracy and to explain their variability by means of patients' demographics, biochemical test results, and physiological characteristics. Pharmacokinetic profiles of MPA and TAC were obtained from 65 stable adult renal allograft recipients on a single occasion (ie, day 15 after transplantation). A sampling schedule was estimated based on the D-optimality criterion with the POPED software, using parameter values from previously published studies on MPA and TAC modeling early after transplantation. Subsequently, a population PK model describing MPA and TAC concentrations was developed using nonlinear mixed-effects modeling. Optimal blood-sampling times for determination of MPA and TAC concentrations were estimated to be at 0 (predose) and at 0.24, 0.64, 0.98, 1.37, 2.38, and 11 hours after oral intake of mycophenolate and TAC. The PK of MPA and TAC were best described by a 2-compartment model with first-order elimination. For MPA, the absorption was best described by a transit compartment model, whereas first-order absorption with a lag time best described TAC transfer from the gastrointestinal tract. Parameters were estimated with good precision and accuracy. While hematocrit levels and CYP3A5 genetic polymorphism significantly influenced TAC clearance, the pharmaceutical formulation and MRP2 genetic polymorphism were retained as significant covariates on MPA absorption and elimination, respectively. The prospective use of the simultaneous D-optimal design approach for MPA and TAC has allowed good estimation of MPA and TAC PK parameters in the early period after transplantation characterized by a very high unexplained variability. The influence of some relevant covariates could be shown.

Understanding pharmacokinetic food effects using molecular dynamics simulation coupled with physiologically based pharmacokinetic modeling

In this study, a molecular dynamics (MD) method is assessed as a new front-end tool for deriving relevant drug-micelle partitioning rates for use in conjunction with a compartmental-style gastrointestinal absorption model. A refined mechanistic approach for handling micelle-associated vs unbound drug is presented and examined in terms of its utility for projecting human oral pharmacokinetic food/formulation effects. Similar to predecessor oral absorption models, the intestinal drug absorption rate is formulated as a function of the combined permeability through the unstirred water layer and the epithelial membrane, however, an additional diffusion coefficient adjustment is applied to account for the viscosity changes of the postprandial small intestine. Bulk passage of drug particles through the GI tract is simulated by compartmental transit through a network of nine compartments comprising the stomach, small intestine and colon. The tandem MD simulation/compartmental absorption algorithm is applied to identify factors influencing the fed vs fasted absorption ratios of a structurally diverse set of orally administered drugs. The data illustrate the interplay and apparent compromise between micelle solubilization and permeability.

Systems Pharmacological Analysis of Paclitaxel-Mediated Tumor Priming That Enhances Nanocarrier Deposition and Efficacy

Paclitaxel (PAC)-mediated apoptosis decompresses and primes tumors for enhanced deposition of nanoparticulate agents such as pegylated liposomal doxorubicin (DXR). A quantitative pharmacokinetic/pharmacodynamic (PK/PD) approach was developed to analyze efficacy and identify optima for PAC combined with sterically stabilized liposome (SSL)-DXR. Using data extracted from diverse literature sources, Cremophor-paclitaxel (Taxol(®)) PK was described by a carrier-mediated dispositional model and SSL-DXR PK was described by a two-compartment model with first-order drug release. A hybrid-physiologic, well-stirred model with partition coefficients (Kp) captured intratumor concentrations. Apoptotic responses driving tumor priming were modeled using nonlinear, time-dependent transduction functions. The tumor growth model used net first-order growth and death rate constants, and two transit compartments that captured the temporal displacement of tumor exposure versus effect, and apoptotic signals from each agent were used to drive cytotoxic effects of the combination. The final model captured plasma and intratumor PK data, apoptosis induction profiles, and tumor growth for all treatments/sequences. A feedback loop representing PAC-induced apoptosis effects on Kp(_DXR) enabled the model to capture tumor-priming effects. Simulations to explore time- and sequence-dependent effects of priming indicated that PAC priming increased K(p_DXR) 3-fold. The intratumor concentrations producing maximal and half-maximal effects were 18 and 7.2 μg/ml for PAC, and 17.6 and 14.3 μg/ml for SSL-DXR. The duration of drug-induced apoptosis was 27.4 h for PAC and 15.8 h for SSL-DXR. Simulations suggested that PAC administered 24 h before peak priming could increase efficacy 2.5-fold over experimentally reported results. The quantitative approach developed in this article is applicable for evaluating tumor-priming strategies using diverse agents.