Optimized conditions for MDCK permeability and turbidimetric solubility studies using compounds representative of BCS classes I-IV

Bridging the Gap between in vitro and in vivo Solubility-Permeability Interplay

Use of solubilization carriers for poorly soluble drugs may disturb transmembrane absorption by lowering the activity of drug molecules, which is known as the solubility-permeability interplay. However, although many in vitro studies have indicated the negative impacts of use of solubilization carriers for oral absorption, in vivo studies that showed the interplay effect are limited. This study provides systematic in vitro, in situ, and in vivo investigation of the interplay effect of cyclodextrin using dexamethasone as a model drug. The evaluation methods included permeation through polymeric, artificial lipid, cell, and intestinal closed-loop membranes. Then, the results were compared with oral administration studies in mice and dogs. Although the interplay effect was clearly observed in the in vitro studies, no obvious interplay was found in the in vivo studies, suggesting that the interplay effect is more prominent in the in vitro permeation studies. Absence of in vivo interplay was attributed to the dilution effect in the gastrointestinal tract, interaction of the drug with living components, and clearance of the drug after membrane permeation. Overall, this investigation clearly demonstrated the applicability and limitations of in vitro permeation studies for predicting the interplay effects of solubilizers after the oral administration.

Openable artificial intestinal tract device integrated with a permeable filter for evaluating drug permeation through cells

Organs-on-chips using cultured cells have been developed and applied for evaluating in vitro biological phenomena. We previously reported an openable artificial intestinal tract system, as an in vitro model of the small intestine, for in vitro drug screening. The intestinal tract device could be transformed using an integrated artificial muscle actuator. An initial flat state was suitable for cell culture, and the transformed tubular structure was used as a fluidic channel for perfusion tests. The previously developed intestinal tract system could be used to evaluate drug absorption by cells through perfusion testing. This study presents an improved artificial intestinal tract system for analysis of drug permeation, in addition to absorption. Permeable filters were integrated into the intestinal tract device. Integration of additional filters into the design of the existing artificial muscle actuator was accomplished by considering device performance and available filter locations. Filter permeability was evaluated by perfusion testing. MDCK-II cells were cultured on the device and visually and electrically evaluated. The openable device, equipped with new functions for further pharmacokinetic analysis, could perform and evaluate drug disposition using cultured cells. We anticipate that the improved, openable organ-on-a-chip device system will contribute to advances in in vitro drug screening technology.

Effects of medicagenic acid metabolites, originating from biotransformation of an Herniaria hirsuta extract, on calcium oxalate crystallization in vitro

ETHNOPHARMACOLOGICAL RELEVANCE

Herniaria hirsuta is traditionally used in Moroccan folk medicine for treatment of urinary stones and as a diuretic. It is rich in saponins, which are known to be deglycosylated in the colon, whereafter aglycones such as medicagenic acid are absorbed and further metabolized in the liver.

AIM OF THE STUDY

A sample of hepatic metabolites of medicagenic acid, with medicagenic acid glucuronide as the most abundant one, was evaluated for in vitro activity against urinary stones. A crystallization assay and a crystal-cell interaction assay were used to evaluate in vitro activity of hepatic metabolites of medicagenic acid on CaC₂O₄ (calciumoxalate) crystals, present in the majority of urinary stones.

MATERIALS AND METHODS

In the crystallization assay the effects on nucleation of Ca²⁺ and C₂O₄^2- and aggregation of the CaC₂O₄ crystals are studied. In the crystal-cell interaction assay crystal retention is investigated by determining the amount of Ca²⁺ bound to injured monolayers of MDCK I cells.

RESULTS

Results of the crystallization assay showed a tentative effect on crystal aggregation. The crystal-cell interaction assay showed a significant inhibition of crystal binding, which may reduce crystal retention in the urinary tract.

CONCLUSIONS

As both formation of crystals by inhibiting aggregation and retention of crystals is affected, the beneficial effect of H. hirsuta against urinary stones may at least in part be attributed to medicagenic acid metabolites, indicating that saponins containing medicagenic acid may act as prodrugs.

Considerations for application of biopharmaceutics classification system in chicken: Exemplified by seven drugs classification

Biopharmaceutics Classification System (BCS) has gained broad acceptance in promoting the development of human drugs. To date, the applicability of existing human BCS criteria has not been evaluated in chickens. The objective of this study was to discuss the feasibility of BCS extrapolation between species and establish a preliminary chicken BCS by classifying seven veterinary commonly used drugs including metronidazole, amoxicillin, sulfamethoxazole, sulfadiazine, ciprofloxacin hydrochloride, doxycycline hydrochloride, and trimethoprim. Firstly, we finished the determination of physiological parameters affecting solubility in chickens, including body temperature, gastrointestinal pH, and the fluid volume in the gastrointestinal tract (GI), and the drug is considered highly soluble in chicken BCS when the highest dose strength is soluble in 20.40 ml (fed) or 6.73 ml (fasted) over the pH range of 1-8 at 41°C. Drug solubility classification was based on dose number calculation. Metronidazol and amoxicillin were classed differently under fed and fasted conditions. Secondly, we discussed the effect of ABC transporters (MDCK vs. MDCK-chAbcb1/Abcg2) and pH (5.5 vs. 7.4) on drug permeability and classification. The drug is classified as highly permeable when its permeability is equal to or greater than metoprolol tartrate. Though ABC transporters and pH significantly affected the permeability values of drugs (p < .05), the permeability classification of the drugs has not been changed except for sulfamethoxazole. This work highlights some of the significant challenges that would be encountered in order to develop a chicken BCS, this valuable information could serve as a helpful tool during chicken drugs development and to minimize the potential risks when developing formulations.

Comparison of Various Cell Lines and Three-Dimensional Mucociliary Tissue Model Systems to Estimate Drug Permeability Using an In Vitro Transport Study to Predict Nasal Drug Absorption in Rats

Recently, various types of cultured cells have been used to research the mechanisms of transport and metabolism of drugs. Although many studies using cultured cell systems have been published, a comparison of different cultured cell systems has never been reported. In this study, Caco-2, Calu-3, Madin–Darby canine kidney (MDCK), EpiAirway and MucilAir were used as popular in vitro cell culture systems, and the permeability of model compounds across these cell systems was evaluated to compare barrier characteristics and to clarify their usefulness as an estimation system for nasal drug absorption in rats. MDCK unexpectedly showed the best correlation (r = 0.949) with the fractional absorption (F_n) in rats. Secondly, a high correlation was observed in Calu-3 (r = 0.898). Also, Caco-2 (r = 0.787) and MucilAir (r = 0.750) showed a relatively good correlation with F_n. The correlation between F_n and permeability to EpiAirway was the poorest (r = 0.550). Because EpiAirway forms leakier tight junctions than other cell culture systems, the paracellular permeability was likely overestimated with this system. On the other hand, because MDCK formed such tight cellular junctions that compounds of paracellular model were less likely permeated, the paracellular permeability could be underestimated. Calu-3, Caco-2 and MucilAir form suitable cellular junctions and barriers, indicating that those cell systems enable the precise estimation of nasal drug absorption.

Comparisons of in vitro Fick's first law, lipolysis, and in vivo rat models for oral absorption on BCS II drugs in SNEDDS

Purpose

The objective of this study was to compare the in vitro Fick’s first law, in vitro lipolysis, and in vivo rat assays for oral absorption of Biopharmaceutical Classification Systems Class II (BCS II) drugs in self-nanoemulsifying drug delivery system (SNEDDS), and studied drugs and oils properties effects on the absorption.

Methods

The transport abilities of griseofulvin (GRI), phenytoin (PHE), indomethacin (IND), and ketoprofen (KET) in saturated water solutions and SNEDDS were investigated using the in vitro Madin-Darby canine kidney cell model. GRI and cinnarizine (CIN) in medium-chain triglycerides (MCT)-SNEDDS and long-chain triglycerides (LCT)-SNEDDS were administered in the in vivo SD rat and in vitro lipolysis models to compare the oral absorption and the distribution behaviors in GIT and build an in vitro-in vivo correlation (IVIVC).

Results

In the cell model, the solubility of GRI, PHE, IND, and KET increased 6–8 fold by SNEDDS, but their permeability were only 18%, 4%, 8%, and 33% of those of their saturated water solutions, respectively. However, in vivo absorption of GRI-SNEDDS was twice that of the GRI suspension and those of CIN-SNEDDS were 15–21 fold those of the CIN suspension. In the lipolysis model, the GRI% in aqueous and pellet phases of MCT were similar to that in LCT. In contrast, the CIN% in the aqueous and pellet phases were decreased but that of the lipid phase increased. In addition, an IVIVC was found between the CIN% in the lipid phase and in vivo relative oral bioavailability (F_r).

Conclusion

The in vitro cell model was still a suitable tool to study drug properties effects on biofilm transport and SNEDDS absorption mechanisms. The in vitro lipolysis model provided superior oral absorption simulation of SNEDDS and helped to build correlation with in vivo rats. The oral drug absorption was affected by drug and oil properties in SNEDDS.

Automated assays for thermodynamic (equilibrium) solubility determination

Solubility is a crucial physicochemical property for drug candidates and is important in both drug discovery and development. Poor solubility is detrimental to absorption after oral administration and can mask compound activity in bioassays in various ways. Hence, solubility liabilities should ideally be identified as early as possible in the drug development process. With the increasing number of compounds as potential drug candidates, automated thermodynamic solubility assays for high throughput screening enabling rapid evaluation of a large number of compounds are becoming increasingly important. This review discusses the current status of the most widely used automated assays for thermodynamic solubility, followed by recent high throughput measurements of properties related to solubility (e.g. dissolution rate and supersaturation) and a brief overview of predictive computational methods for thermodynamic solubility reported in the literature.

The conditional stimulation of rat organic cation transporter 2, but not its human ortholog, by mesoridazine: the possibility of the involvement of the high-affinity binding site of the transporter in the stimulation

Objectives

To study the functional consequences of the human and rat forms of OCT2 in the presence of phenothiazines.

Methods

MDCK cells expressing human or rat OCT2 were established, and MPP+ transport was determined by uptake assays. Concentration dependency was studied for the stimulatory/inhibitory effects of phenothiazines on MPP+ transport.

Key findings

Among the 11 phenothiazines examined, the majority were found to have comparable effects on transporter function between the orthologous forms, while three phenothiazines, particularly mesoridazine, had complex impacts on transporter function. For rOCT2, mesoridazine stimulated transport at 0.1 and 1 μmMPP+ with the mesoridazine concentration–uptake curve becoming bell-shaped. This conditional effect became less pronounced at 30 μmMPP+, resulting in an inhibition curve with a typical profile. For hOCT2, mesoridazine behaved as a typical inhibitor of transporter function at all MPP+ concentrations, although the kinetics of inhibition were still affected by the substrate concentration.

Conclusions

The conditional stimulation by mesoridazine in rOCT2, and the lack thereof in hOCT2, may be a manifestation of the interaction of phenothiazine with substrate binding at the high-affinity site of the OCT2. As OCT2 was previously indicated in some drug–drug interactions, the conditional stimulation of OCT2 and its potential species-differences may be of practical relevance.

Development of a Novel Maternal-Fetal Physiologically Based Pharmacokinetic Model I: Insights into Factors that Determine Fetal Drug Exposure through Simulations and Sensitivity Analyses

Determining fetal drug exposure (except at the time of birth) is not possible for both logistical and ethical reasons. Therefore, we developed a novel maternal-fetal physiologically based pharmacokinetic (m-f-PBPK) model to predict fetal exposure to drugs and populated this model with gestational age-dependent changes in maternal-fetal physiology. Then, we used this m-f-PBPK to: 1) perform a series of sensitivity analyses to quantitatively demonstrate the impact of fetoplacental metabolism and placental transport on fetal drug exposure for various drug-dosing regimens administered to the mother; 2) predict the impact of gestational age on fetal drug exposure; and 3) demonstrate that a single umbilical venous (UV)/maternal plasma (MP) ratio (even after multiple-dose oral administration to steady state) does not necessarily reflect fetal drug exposure. In addition, we verified the implementation of this m-f-PBPK model by comparing the predicted UV/MP and fetal/MP AUC ratios with those predicted at steady state after an intravenous infusion. Our simulations yielded novel insights into the quantitative contribution of fetoplacental metabolism and/or placental transport on gestational age-dependent fetal drug exposure. Through sensitivity analyses, we demonstrated that the UV/MP ratio does not measure the extent of fetal drug exposure unless obtained at steady state after an intravenous infusion or when there is little or no fluctuation in MP drug concentrations after multiple-dose oral administration. The proposed m-f-PBPK model can be used to predict fetal exposure to drugs across gestational ages and therefore provide the necessary information to assess the risk of drug toxicity to the fetus.

BCS class IV drugs: Highly notorious candidates for formulation development

BCS class IV drugs (e.g., amphotericin B, furosemide, acetazolamide, ritonavir, paclitaxel) exhibit many characteristics that are problematic for effective oral and per oral delivery. Some of the problems associated include low aqueous solubility, poor permeability, erratic and poor absorption, inter and intra subject variability and significant positive food effect which leads to low and variable bioavailability. Also, most of the class IV drugs are substrate for P-glycoprotein (low permeability) and substrate for CYP3A4 (extensive pre systemic metabolism) which further potentiates the problem of poor therapeutic potential of these drugs. A decade back, extreme examples of class IV compounds were an exception rather than the rule, yet today many drug candidates under development pipeline fall into this category. Formulation and development of an efficacious delivery system for BCS class IV drugs are herculean tasks for any formulator. The inherent hurdles posed by these drugs hamper their translation to actual market. The importance of the formulation composition and design to successful drug development is especially illustrated by the BCS class IV case. To be clinically effective these drugs require the development of a proper delivery system for both oral and per oral delivery. Ideal oral dosage forms should produce both a reasonably high bioavailability and low inter and intra subject variability in absorption. Also, ideal systems for BCS class IV should produce a therapeutic concentration of the drug at reasonable dose volumes for intravenous administration. This article highlights the various techniques and upcoming strategies which can be employed for the development of highly notorious BCS class IV drugs. Some of the techniques employed are lipid based delivery systems, polymer based nanocarriers, crystal engineering (nanocrystals and co-crystals), liquisolid technology, self-emulsifying solid dispersions and miscellaneous techniques addressing the P-gp efflux problem. The review also focuses on the roadblocks in the clinical development of the aforementioned strategies such as problems in scale up, manufacturing under cGMP guidelines, appropriate quality control tests, validation of various processes and variable therein etc. It also brings to forefront the current lack of regulatory guidelines which poses difficulties during preclinical and clinical testing for submission of NDA and subsequent marketing. Today, the pharmaceutical industry has as its disposal a series of reliable and scalable formulation strategies for BCS Class IV drugs. However, due to lack of understanding of the basic physical chemistry behind these strategies formulation development is still driven by trial and error.

An Automated Screening Assay for Determination of Aqueous Equilibrium Solubility Enabling SPR Study During Drug Lead Optimization

Aqueous solubility is one of the most critical physicochemical properties to be determined in the process of drug lead optimization. Particularly, an equilibrium solubility method is highly valuable to the study of structure property relationship (SPR), while meeting the needs of analytical sensitivity, reproducibility, and throughput. In this report, an automated solubility assay in a 96-well library format was designed and developed by means of robotic liquid handling, centrifugal separation, and HPLC-UV quantification. Requiring 1 mg of solid compound, this assay was used to determine the equilibrium solubility in three user-selected media, that is, 0.01 N HCl, phosphate buffer saline (PBS), and fasted state simulated intestinal fluid (SIF), with a throughput of up to 192 compounds a week. The assay parameters, including the equilibration time and the separation technique, were optimized to ensure that the thermodynamic solubility was measured at the presence of excess solid compound. A fast gradient HPLC method was developed with single-point on-plate calibration for each compound, followed by a customized 96-well chromatographic data analysis. The reporting solubility range was 1–200 μg/mL, appropriate for oral drug candidate selection at the stage of discovery lead optimization. Based on the test results obtained on the commercially available drugs and Amgen research compounds, this assay was considered to be equivalent to the conventional shake-flask methods. Examples were given to demonstrate that the thermodynamic solubility determined by this assay enabled the SPR study to support drug lead optimization.

Specific Inhibition of the Distribution of Lobeglitazone to the Liver by Atorvastatin in Rats: Evidence for a Rat Organic Anion Transporting Polypeptide 1B2-Mediated Interaction in Hepatic Transport

Cytochrome P450 enzymes and human organic anion transporting polypeptide (OATP) 1B1 are reported to be involved in the pharmacokinetics of lobeglitazone (LB), a new peroxisome proliferator-activated receptor γ agonist. Atorvastatin (ATV), a substrate for CYP3A and human OATP1B1, is likely to be coadministered with LB in patients with the metabolic syndrome. We report herein on a study of potential interactions between LB and ATV in rats. When LB was administered intravenously with ATV, the systemic clearance and volume of distribution at steady state for LB remained unchanged (2.67 ± 0.63 ml/min per kg and 289 ± 20 ml/kg, respectively), compared with that of LB without ATV (2.34 ± 0.37 ml/min per kg and 271 ± 20 ml/kg, respectively). Although the tissue-to-plasma partition coefficient (K_p) of LB was not affected by ATV in most major tissues, the liver K_p for LB was decreased by ATV coadministration. Steady-state liver K_p values for three levels of LB were significantly decreased as a result of ATV coadministration. LB uptake was inhibited by ATV in rat OATP1B2-overexpressing Madin-Darby canine kidney cells and in isolated rat hepatocytes in vitro. After incorporating the kinetic parameters for the in vitro studies into a physiologically based pharmacokinetics model, the characteristics of LB distribution to the liver were consistent with the findings of the in vivo study. It thus appears that the distribution of LB to the liver is mediated by the hepatic uptake of transporters such as rat OATP1B2, and carrier-mediated transport is involved in the liver-specific drug-drug interaction between LB and ATV in vivo.

Development of a Novel Maternal-Fetal Physiologically Based Pharmacokinetic Model II: Verification of the model for passive placental permeability drugs

Fetal exposure to drugs cannot be readily estimated from single time point cord blood sampling at the time of delivery. Therefore, we developed a physiologically based pharmacokinetic (PBPK) model to estimate fetal drug exposure throughout pregnancy. In this study, we report verification of this novel maternal-fetal PBPK (m-f-PBPK) model for drugs that passively diffuse across the placenta and are not metabolized/transported there. Our recently built m-f-PBPK model was populated with gestational age-dependent changes in maternal drug disposition and maternal-fetal physiology. Using midazolam as an in vivo calibrator, the transplacental passive diffusion clearance of theophylline and zidovudine was first estimated. Then, for verification, the predicted maternal plasma (MP) and umbilical venous (UV) plasma drug concentrations by our m-f-PBPK were compared against those observed at term. Overall, our m-f-PBPK model well predicted the maternal and fetal exposure to the two verification drugs, theophylline and zidovudine, at term, across a range of dosing regimens, with nearly all observed MP and UV plasma drug concentrations falling within the 90% prediction interval [i.e., 5th-95th percentile range of a virtual pregnant population (n = 100)]. Prediction precision and bias of theophylline MP and UV were 14.5% and 12.4%, and 9.4% and 7.5%, respectively. Furthermore, for zidovudine, after the exclusion of one unexpectedly low MP concentration, prediction precision and bias for MP and UV were 50.3% and 30.2, and 28.3% and 15.0%, respectively. This m-f-PBPK should be useful to predict fetal exposure to drugs, throughout pregnancy, for drugs that passively diffuse across the placenta.

Human Airway Primary Epithelial Cells Show Distinct Architectures on Membrane Supports Under Different Culture Conditions

To facilitate drug development for lung delivery, it is highly demanding to establish appropriate airway epithelial cell models as transport barriers to evaluate pharmacokinetic profiles of drug molecules. Besides the cancer-derived cell lines, as the primary cell model, normal human bronchial epithelial (NHBE) cells have been used for drug screenings because of physiological relevance to in vivo. Therefore, to accurately interpret drug transport data in NHBE measured by different laboratories, it is important to know biophysical characteristics of NHBE grown on membranes in different culture conditions. In this study, NHBE was grown on the polyester membrane in a different medium and its transport barrier properties as well as cell architectures were fully characterized by functional assays and confocal imaging throughout the days of cultures. Moreover, NHBE cells on inserts in a different medium were subject to either of air-interfaced culture (AIC) or liquid-covered culture (LCC) condition. Cells in the AIC condition were cultivated on the membrane with medium in the basolateral side only, whereas cells with medium in apical and basolateral sides under the LCC condition. Quantitative microscopic imaging with biophysical examination revealed distinct multilayered architectures of differentiated NHBE cells, suggesting NHBE as functional cell barriers for the lung-targeting drug transport.

Functional and cytometric examination of different human lung epithelial cell types as drug transport barriers

To develop inhaled medications, various cell culture models have been used to examine the transcellular transport or cellular uptake properties of small molecules. For the reproducible high throughput screening of the inhaled drug candidates, a further verification of cell architectures as drug transport barriers can contribute to establishing appropriate in vitro cell models. In the present study, side-by-side experiments were performed to compare the structure and transport function of three lung epithelial cells (Calu-3, normal human bronchial primary cells (NHBE), and NL-20). The cells were cultured on the nucleopore membranes in the air-liquid interface (ALI) culture conditions, with cell culture medium in the basolateral side only, starting from day 1. In transport assays, paracellular transport across all three types of cells appeared to be markedly different with the NHBE or Calu-3 cells, showing low paracellular permeability and high TEER values, while the NL-20 cells showed high paracellular permeability and low TEER. Quantitative image analysis of the confocal microscope sections further confirmed that the Calu-3 cells formed intact cell monolayers in contrast to the NHBE and NL-20 cells with multilayers. Among three lung epithelial cell types, the Calu-3 cell cultures under the ALI condition showed optimal cytometric features for mimicking the biophysical characteristics of in vivo airway epithelium. Therefore, the Calu-3 cell monolayers could be used as functional cell barriers for the lung-targeted drug transport studies.

Curcumin, bisdemethoxycurcumin and dimethoxycurcumin complexed with cyclodextrins have structure specific effect on the paracellular integrity of lung epithelia in vitro

The phytochemical curcumin may improve translocation of the cystic fibrosis transmembrane regulatory (CFTR) protein in lung epithelium and therefore be helpful in the treatment of cystic fibrosis (CF) symptoms. However, previous studies often use commercial curcumin that is a combination of curcumin, demethoxycurcumin and bisdemethoxycurcumin which could affect the investigated cells differently. In the present study, we investigated the potential difference between curcumin, bisdemethoxycurcumin and dimethoxycurcumin on the epithelial tight junction complex, in the bronchial epithelial cell line VA10, by measuring transepithelial electrical resistance (TER), immunofluorescence and western blotting of tight junction proteins. The curcuminoids were complexed with hydroxypropyl-γ–cyclodextrin for increased solubility and stability. Curcumin (10 µg/ml) increased the TER significantly after 24 h of treatment while four times higher concentration of bisdemethoxycurcumin was required to obtain similar increase in TER as curcumin. Interestingly, dimethoxycurcumin did not increase TER. Curcumin clearly affected the F-actin structures both apically and basolaterally. These results begin to define possible effects of curcuminoids on healthy bronchial epithelia and shows that difference in the phenyl moiety structure of the curcuminoids influences the paracellular epithelial integrity.

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Curcuminoids formulized with cyclodextrin for increased solubility and stability.

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Curcumin increases TER in a concentration dependent manner and causes decrease in apical F-actin staining.

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Higher concentration required for bisdemethoxycurcumin to increase TER compared to curcumin.

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Dimethoxycurcumin did not increase TER.

Intestinal uptake and toxicity evaluation of acetazolamide and its multicomponent complexes with hidroxypropyl-β-cyclodextrin in rats

Large oral doses of ACZ lower the intraocular pressure (IOP), but usually lead to a multitude of systemic side effects, including gastrointestinal upset. The present study was undertaken to evaluate the effect of ACZ on the histological structure of rat duodenal mucosa and to assess a possible protective role of the complex formation of ACZ with HP-β-CD, either separately or in combination with a third compound, on the gut epithelial layer by histological and ultrastructural examinations of sections of rat duodenum exposed to ACZ or its formulations. In addition, the transport process of ACZ and its binary or ternary complexes across the duodenal mucosa by means of the single-pass intestinal perfusion (SPIP) method in rats was evaluated. Evidence was found that ACZ alters intestinal permeability and induces damage to the rat small intestine. In contrast, ACZ-induced intestinal injury may be abrogated by ACZ complexation. In addition, the complexation of ACZ with HP-β-CD, alone or in combination with a third compound, facilitated significant levels of ACZ uptake across the rat duodenal segment. Ternary complexes of ACZ with HP-β-CD in combination with TEA (triethanolamine) or calcium ions were found to provide an excellent approach that enabled an increased apparent permeability of ACZ across the duodenal epithelium, with a concomitant ability to preserve the integrity of the gut epithelium from ACZ-induced injury. These results could be useful for the design and development of novel ACZ formulations that can reduce GI toxicity, while still maintaining their essential therapeutic efficacies.

A novel in vitro approach for simultaneous evaluation of CYP3A4 inhibition and kinetic aqueous solubility

In the early stages of the drug discovery process, evaluation of the drug metabolism and physicochemical properties of new chemical entities is crucial to prioritize those candidates displaying a better profile for further development. In terms of metabolism, drug-drug interactions mediated through CYP450 inhibition are a significant safety concern, and therefore the effect of new candidate drugs on CYP450 activity should be screened early. In the initial stages of drug discovery, when physicochemical properties such as aqueous solubility have not been optimized yet, there might be a large number of candidate compounds showing artificially low CYP450 inhibition, and consequently potential drug-drug interaction toxicity might be overlooked. In this work, we present a novel in vitro approach for simultaneous evaluation of CYP3A4 inhibition potential and kinetic aqueous solubility (NIVA-CYPI-KS). This new methodology is based on fluorogenic CYP450 activities and turbidimetric measurements for compound solubility, and it provides a significant improvement in the use of resources and a better understanding of CYP450 inhibition data.

The extracellular microenvironment explains variations in passive drug transport across different airway epithelial cell types

PURPOSE

We sought to identify key variables in cellular architecture and physiology that might explain observed differences in the passive transport properties of small molecule drugs across different airway epithelial cell types.

METHODS

Propranolol (PR) was selected as a weakly basic, model compound to compare the transport properties of primary (NHBE) vs. tumor-derived (Calu-3) cells. Differentiated on Transwell™ inserts, the architecture of pure vs. mixed cell co-cultures was studied with confocal microscopy followed by quantitative morphometric analysis. Cellular pharmacokinetic modeling was used to identify parameters that differentially affect PR uptake and transport across these two cell types.

RESULTS

Pure Calu-3 and NHBE cells possessed different structural and functional properties. Nevertheless, mixed Calu-3 and NHBE cell co-cultures differentiated as stable cell monolayers. After measuring the total mass of PR, the fractional areas covered by Calu-3 and NHBE cells allowed deconvoluting the transport properties of each cell type. Based on the apparent thickness of the unstirred, cell surface aqueous layer, local differences in the extracellular microenvironment explained the measured variations in passive PR uptake and permeation between Calu-3 and NHBE cells.

CONCLUSION

Mixed cell co-cultures can be used to compare the local effects of the extracellular microenvironment on drug uptake and transport across two epithelial cell types.

Biowaiver extension potential and IVIVC for BCS Class II drugs by formulation design: Case study for cyclosporine self-microemulsifying formulation

The objective of this work was to suggest the biowaiver potential of biopharmaceutical classification system (BCS) Class II drugs in self-microemulsifying drug delivery systems (SMEDDS) which are known to increase the solubility, dissolution and oral absorption of water-insoluble drugs. Cyclosporine was selected as a representative BCS Class II drug. New generic candidate of cyclosporine SMEDDS (test) was applied for the study with brand SMEDDS (reference I) and cyclosporine self-emulsifying drug delivery systems (SEDDS, reference II). Solubility and dissolution of cyclosporine from SMEDDS were critically enhanced, which were the similar behaviors with BCS class I drug. The test showed the identical dissolution rate and the equivalent bioavailability (0.34, 0.42 and 0.68 of p values for AUC₀(→)₂₄(h), C(max) and T(max), respectively) with the reference I. Based on the results, level A in vitro-in vivo correlation (IVIVC) was established from these two SMEDDS formulations. This study serves as a good example for speculating the biowaiver extension potential of BCS Class II drugs specifically in solubilizing formulation such as SMEDDS.

In vitro release, rheological, and stability studies of mefenamic acid coprecipitates in topical formulations

A suitable topical formulation of mefenamic acid was developed in order to eliminate the gastrointestinal disorders associated with its oral administration. Drug coprecipitates prepared with different polymers at various drug-to-polymer ratios improved drug solubility and dissolution compared to pure drug and physical mixtures. PVP polymers (ratio 1:4) produced the best results. Aqueous ionic cream, ointments of absorption and water soluble bases and gels of methylcellulose, carboxymethylcellulose sodium, HPMC, Carbopol® 934 and 940, and Pluronic® F127 bases containing 1-10% drug as coprecipitates of PVP polymers (1:4) were prepared. The highest drug release was achieved at 1% drug concentration from water soluble base and methylcellulose among cream/ointment and gel bases, respectively. Gels, in general yielded better release than creams/ointments. All tested medicated creams/ointments exhibited plastic flow while all gels conformed to pseudoplasticity. Most of them showed thixotropy, a desired property of topical preparations. Stability studies revealed that HPMC and methylcellulose had the smallest changes in drug content, viscosity, and pH among the formulations. Considering drug release, rheological properties, and stability, methylcellulose gel containing 1% drug as coprecipitates of PVP K90 was the best among the studied formulations, was promising for improving bioavailability of mefenamic acid and can be used in future studies.

The effect of brimonidine on transepithelial resistance in a human retinal pigment epithelial cell line

PURPOSE

To investigate the effects of brimonidine, an alpha-2-adrenergic agonist, on barrier function in ARPE-19 cells by measuring transepithelial resistance (TER).

METHODS

ARPE-19 cells were cultured into a confluent monolayer on a microporous filter. Brimonidine was added to the apical medium, and the barrier function of the cells was evaluated by measuring TER. A subset of cells was treated under hypoxic conditions, and the TER changes observed upon administration of brimonidine were compared to those observed in cells in normoxic conditions.

RESULTS

The ARPE cell membrane reached a peak resistance of 29.1+/-7.97 Omegacm(2) after four weeks of culture. The TER of the cells treated under normoxic conditions increased with brimonidine treatment; however, the TER of the cells treated under hypoxic conditions did not change following the administration of brimonidine.

CONCLUSIONS

Barrier function in ARPE-19 cells increased with brimonidine treatment. Understanding the exact mechanism of this barrier function change requires further investigation.

An evaluation of the relative roles of the unstirred water layer and receptor sink in limiting the in-vitro intestinal permeability of drug compounds of varying lipophilicity

The roles of the unstirred water layer (UWL) and receptor sink on the in-vitro transmembrane permeability of an increasingly lipophilic series of compounds (mannitol (MAN), diazepam (DIA) and cinnarizine (CIN)) have been assessed. Altered carbogen bubbling rates were used as a means to change the UWL thickness and polysorbate-80 (PS-80), bovine serum albumin (BSA) and α-1-acid glycoprotein (AAG) were employed to alter sink conditions. After correction for solubilisation, Papp data for MAN, DIA and CIN were consistent across varying donor PS-80 concentrations suggesting that for the drugs examined here, the donor UWL did not limit in-vitro permeability. Similarly, altered bubbling rates and receptor sink conditions had no impact on the permeability of MAN. In contrast, decreasing the size of the receptor UWL or adding solubilising agents to the receptor sink resulted in modest enhancements to the permeability of the more lipophilic probe DIA. For the most lipophilic compound, CIN, very significant changes to measured permeability (&gt;30 fold) were possible, but were most evident only after concomitant changes to both the UWL and sink conditions, suggesting that the effectiveness of enhanced sink conditions were dependent on a decrease in the width of the UWL.

Disruption of the epithelial barrier by botulinum haemagglutinin (HA) proteins – differences in cell tropism and the mechanism of action between HA proteins of types A or B, and HA proteins of type C

Orally ingested botulinum neurotoxin (BoNT) causes food-borne botulism, but BoNT must pass through the gut lining and enter the bloodstream. We have previously found that type B haemagglutinin (HA) proteins in the toxin complex play an important role in the intestinal absorption of BoNT by disrupting the paracellular barrier of the intestinal epithelium, and therefore facilitating the transepithelial delivery of BoNT. Here, we show that type A HA proteins in the toxin complex have a similar disruptive activity and a greater potency than type B HA proteins in the human intestinal epithelial cell lines Caco-2 and T84 and in the canine kidney epithelial cell line MDCK I. In contrast, type C HA proteins in the toxin complex (up to 300 nM) have no detectable effect on the paracellular barrier in these human cell lines, but do show a barrier-disrupting activity and potent cytotoxicity in MDCK I. These findings may indicate that type A and B HA proteins contribute to the development of food-borne botulism, at least in humans, by facilitating the intestinal transepithelial delivery of BoNTs, and that the relative inability of type C HA proteins to disrupt the paracellular barrier of the human intestinal epithelium is one of the reasons for the relative absence of food-borne human botulism caused by type C BoNT.

Several major antiepileptic drugs are substrates for human P-glycoprotein

One of the current hypotheses of pharmacoresistant epilepsy proposes that transport of antiepileptic drugs (AEDs) by drug efflux transporters such as P-glycoprotein (Pgp) at the blood-brain barrier may play a significant role in pharmacoresistance in epilepsy by extruding AEDs from their intended site of action. However, several recent in vitro studies using cell lines that overexpress efflux transporters indicate that human Pgp may not transport AEDs to any relevant extent. In this respect it has to be considered that most AEDs are highly permeable, so that conventional bi-directional transport assays as used in these previous studies may fail to identify AEDs as Pgp substrates, particularly if these drugs are not high-affinity substrates for Pgp. In the present study, we used a modified transport assay that allows evaluating active transport independently of the passive permeability component. In this concentration equilibrium transport assay (CETA), the drug is initially added at identical concentration to both sides of a polarized, Pgp-overexpressing cell monolayer instead of applying the drug to either the apical or basolateral side for studying bi-directional transport. Direct comparison of the conventional bi-directional (concentration gradient) assay with the CETA, using MDR1-transfected LLC cells, demonstrated that CETA, but not the conventional assay, identified phenytoin and phenobarbital as substrates of human Pgp. Furthermore, directional transport was determined for lamotrigine and levetiracetam, but not carbamazepine. Transport of AEDs could be completely or partially (>50%) inhibited by the selective Pgp inhibitor, tariquidar. However, transport of phenobarbital and levetiracetam was also inhibited by MK571, which preferentially blocks transport by multidrug resistance transporters (MRPs), indicating that, in addition to Pgp, these AEDs are substrates of MRPs. The present study provides the first direct evidence that several AEDS are substrates of human Pgp, thus further substantiating the transporter hypothesis of pharmacoresistant epilepsy.

Effect of albumin on the biliary clearance of compounds in sandwich-cultured rat hepatocytes

The purpose of the present study was to evaluate the effects of bovine serum albumin (BSA) and essentially fatty acid-free BSA (BSA-FAF) on the biliary clearance of compounds in sandwich-cultured rat hepatocytes. Unbound fraction, biliary excretion index (BEI), and unbound intrinsic biliary clearance (intrinsic Clbiliary') were determined for digoxin, pravastatin, and taurocholate in the absence or presence of BSA or BSA-FAF. BSA had little effect on the BEI or intrinsic Clbiliary' of these compounds. Surprisingly, BSA-FAF decreased both BEI and intrinsic Clbiliary' for digoxin and pravastatin, which represent low and moderately bound compounds, respectively. The BEI and intrinsic Clbiliary' of taurocholate, a highly bound compound, were not altered significantly by BSA-FAF. Neither BSA nor BSA-FAF had a discernable effect on the bile canalicular networks based on carboxydichlorofluorescein retention. Neither the addition of physiological concentrations of calcium nor the addition of fatty acids to BSA-FAF was able to restore the BEI or intrinsic Clbiliary' of the model compounds to similar values in the absence or presence of BSA. Careful consideration is warranted when selecting the type of BSA for addition to in vitro systems such as sandwich-cultured rat hepatocytes.

Predicting drug disposition, absorption/elimination/transporter interplay and the role of food on drug absorption

The ability to predict drug disposition involves concurrent consideration of many chemical and physiological variables and the effect of food on the rate and extent of availability adds further complexity due to postprandial changes in the gastrointestinal (GI) tract. A system that allows for the assessment of the multivariate interplay occurring following administration of an oral dose, in the presence or absence of meal, would greatly benefit the early stages of drug development. This is particularly true in an era when the majority of new molecular entities are highly permeable, poorly soluble, extensively metabolized compounds (BDDCS Class 2), which present the most complicated relationship in defining the impact of transporters due to the marked effects of transporter-enzyme interplay. This review evaluates the GI luminal environment by taking into account the absorption/transport/elimination interplay and evaluates the physiochemical property issues by taking into account the importance of solubility, permeability and metabolism. We concentrate on the BDDCS and its utility in predicting drug disposition. Furthermore, we focus on the effect of food on the extent of drug availability (F), which appears to follow closely what might be expected if a significant effect of high fat meals is inhibition of transporters. That is, high fat meals and lipidic excipients would be expected to have little effect on F for Class 1 drugs; they would increase F of Class 2 drugs, while decreasing F for Class 3 drugs.

High throughput solubility measurement in drug discovery and development

Measurement of drug solubility in various solvents is one of the key elements of compound characterization during the whole discovery and development process. This review summarizes current experimental approaches and addresses recent advances in the experimental methods used to determine drug solubility in drug discovery and early development. This paper focuses on high throughput methods designed to determine kinetic and thermodynamic (equilibrium) solubility but traditional methods are also presented. The focus, positioning, experimental setup, pros and cons, and limitations of individual assays are discussed and differences in solubility studies in discovery and development environments are highlighted. Finally, future needs and trends in solubility assay development designed to overcome current bottlenecks and trade-offs between speed and quality/quantity of measurements are addressed.

Development of a partially automated solubility screening (PASS) assay for early drug development

A medium-throughput, compound-saving, thermodynamic solubility assay for early drug development was developed. Solid compound suspended in heptane was used for simple, time-saving, and flexible compound distribution into 96-well plates, with minor risk to generate new physical forms during dispensing. Low volume, well-stirred incubation vessels were generated by using a combination of V-shaped wells, well caps, and vertically inserted stir bars. This allowed solubility determination up to 100 mg/mL in 40-80 microL volumes in aqueous and nonaqueous, low- and high-viscosity solvents. After removal of residual solid through syringe filters mounted on microtiter plates, the filtrate was quantified by ultra performance liquid chromatography (UPLC) using a 1.2 min gradient. Combined with a robotic liquid handling system, throughput was 45 samples per hour and >600 solubility measurements per week. Results from the partially automated solubility screening (PASS) assay correlated well with reported solubility values (r2 = 0.882). The PASS assay is useful for compound-saving, thermodynamic solubility measurement at the discovery-development interface where maximal solubility in many commonly used solvents needs to be determined. PASS results provide a basis for the identification of formulation strategies, the selection of appropriate excipients, and for the prediction of the potential in vivo behavior of compounds.

Evaluation of bioadhesive polymers as delivery systems for nose to brain delivery: in vitro characterisation studies

There is an increasing need for nasal drug delivery systems that could improve the efficiency of the direct nose to brain pathway especially for drugs for treatment of central nervous system disorders. Novel approaches that are able to combine active targeting of a formulation to the olfactory region with controlled release bioadhesive characteristics, for maintaining the drug on the absorption site are suggested. If necessary an absorption enhancer could be incorporated. Low methylated pectins have been shown to gel and be retained in the nasal cavity after deposition. Chitosan is known to be bioadhesive and also to work as an absorption enhancer. Consequently, two types of pectins, LM-5 and LM-12, together with chitosan G210, were selected for characterisation in terms of molecular weight, gelling ability and viscosity. Furthermore, studies on the in vitro release of model drugs from candidate formulations and the transport of drugs across MDCK1 cell monolayers in the presence of pectin and chitosan were also performed. Bioadhesive formulations providing controlled release with increased or decreased epithelial transport were developed. Due to their promising characteristics 3% LM-5, 1% LM-12 pectin and 1% chitosan G210 formulations were selected for further biological evaluation in animal models.

Computational models to predict aqueous drug solubility, permeability and intestinal absorption

In the last decade, poor intestinal absorption of candidate drugs intended for oral administration has been identified as a major bottleneck in drug development. Poor intestinal absorption can often be related to poor aqueous solubility and/or poor permeability across the intestinal wall. Other factors, such as poor stability and the metabolism of the compounds, can also decrease the amount of compound absorbed. In an effort to design compounds with enhanced absorption profile, theoretical predictions of solubility and permeability, among other factors, have gained increased interest, and a large number of papers have been published. In this review, the databases and techniques used for the development of in silico absorption models will be discussed. The focus is on aqueous drug solubility, which has become a major problem in drug development.

Impact of Extracellular Protein Binding on Passive and Active Drug Transport Across Caco-2 Cells

AIM

The objective of the study is to evaluate the mechanism behind alterations in passive and active transport of drugs in the presence of basolaterally applied extracellular protein using the Caco-2 cell model.

METHODS

The permeation across Caco-2 monolayers of two groups of compounds, transported either solely by passive diffusion or partly also by active transport in the secretory direction, was studied at two donor concentrations in the absence or presence of bovine serum albumin (BSA, 0-4%). Each group contained compounds with high or low protein binding (PB) capabilities and high or low absorption in humans (fraction absorbed, f(a)). The unbound fraction (f(u)) of each compound was determined by ultrafiltration.

RESULTS

The transport rate of the passively permeating compounds was the same in both apical-to-basolateral (absorptive) and basolateral-to-apical (secretory) directions in the absence of BSA. Basolaterally applied BSA increased the transport rate in the absorptive direction and decreased it in the secretory direction for all compounds, in direct proportion to the extent of PB. The efflux ratios for the actively transported compounds were reduced in the presence of BSA.

CONCLUSIONS

Basolaterally applied BSA, which mimics in vivo PB, alters both passive and active drug transport in the Caco-2 cell model. Using C(u) in the calculations of transport rate allowed elucidation of the different mechanisms behind these alterations. Our data also suggest that active secretory transport for highly protein-bound compounds might have less effect in vivo than predicted from traditional Caco-2 cell models (without BSA).

Predicting Drug Disposition via Application of BCS: Transport/Absorption/ Elimination Interplay and Development of a Biopharmaceutics Drug Disposition Classification System

The Biopharmaceutics Classification System (BCS) was developed to allow prediction of in vivo pharmacokinetic performance of drug products from measurements of permeability (determined as the extent of oral absorption) and solubility. Here, we suggest that a modified version of such a classification system may be useful in predicting overall drug disposition, including routes of drug elimination and the effects of efflux and absorptive transporters on oral drug absorption; when transporter-enzyme interplay will yield clinically significant effects (e.g., low bioavailability and drug-drug interactions); the direction, mechanism, and importance of food effects; and transporter effects on postabsorption systemic drug concentrations following oral and intravenous dosing. These predictions are supported by a series of studies from our laboratory during the past few years investigating the effect of transporter inhibition and induction on drug metabolism. We conclude by suggesting that a Biopharmaceutics Drug Disposition Classification System (BDDCS) using elimination criteria may expand the number of Class 1 drugs eligible for a waiver of in vivo bioequivalence studies and provide predictability of drug disposition profiles for Classes 2, 3, and 4 compounds.

Caco-2 replace or refine?

Multiple screening techniques have been developed to gain simplicity and rapidness in prediction of human intestinal permeability. The most extensively used method for years has been the Caco-2 cell monolayers. Are the less time- and resource-consuming artificial membranes and computational-based predictions on their way to replace the Caco-2 cells? The importance of mechanistic approaches and correct interpretation of the data using the techniques available is compared and discussed in this article.:

Automated robotic liquid handling/laser-based nephelometry system for high throughput measurement of kinetic aqueous solubility

The ability to rapidly and consistently measure aqueous solubility in a preclinical environment is critical to the successful identification of promising discovery compounds. The advantage of an early solubility screen is timely attrition of compounds likely to fail due to poor absorption or low bioavailability before more costly screens are performed. However, due to the large number of compounds and limited sample amounts, thermodynamic solubility measurements are not feasible at this stage. A kinetic solubility measurement is an alternative to thermodynamic measurements at the discovery stage that provides a rank listing of solubility values with minimal sample requirements. A kinetic solubility measurement is attractive from an automation vantage because it features rapid data acquisition and is amenable to multi-well formats. We describe the use of a robotic liquid/plate handler coupled to nephelometry detection for the measurement of kinetic solubility. We highlight the liquid handling validation, serial dilution parameters, and a comparison to the previous method. Experiments to further enhance throughput, or increase confidence in the automation steps, are described and the effects of these experiments are presented. In our integrated nephelometry method, we observe rapid liquid handling with an error of less than 10%, after a series of validation studies, and a sample throughput up to 1800 compounds per week. We compare the nephelometry method with our semi-thermodynamic flow-injection analysis (FIA) method, and find a 75% bin agreement between the methods.

Biological, pharmaceutical, and analytical considerations with respect to the transport media used in the absorption screening system, Caco-2

During the evaluation and selection of drug candidates, the Caco-2 cell culture system is commonly used for the determination of intestinal transport characteristics and to anticipate permeability limited drug absorption. Although classic HBSS-like buffered salt solutions are commonly used to perform Caco-2 transport experiments, different shortcomings (e.g., adsorption and low solubility) have been associated with the use of plain aqueous buffers. As transport experiments performed with unoptimized conditions may compromize the value of the Caco-2 model as a permeation screening tool, many efforts have been made to optimize the experimental conditions of Caco-2 transport assays. In this minireview, the hurdles associated with the use of saline aqueous buffers in Caco-2 transport experiments are summarized and the different options, which have been proposed to overcome these issues, are reviewed and discussed. Biologically, pharmaceutically, as well as analytically relevant media affecting the outcome of the transport experiments are described. Unfortunately, up to now, no systematic studies comparing the different experimental conditions have been performed, jeopardizing the possibility to define a (single) optimal solution to overcome the different issues associated with the use of saline aqueous buffers. Based on the reported options it can be proposed to use DMSO (<or=1%) in standard screening procedures for the ranking of compounds based on their apical to basolateral transport. If compounds are not soluble in DMSO 1%, dimethylacetamide (3%) or N-1-methyl-pyrrolidone (2.5%) are good alternatives. However, these options do not imitate the in vivo situation. If one wants to take into account the physiological relevance of the media, the use of a biologically relevant apical medium (e.g., FASSIF) in combination with an analytically friendly, sink condition creating basolateral solvent (e.g., containing a micelle forming agent) can be suggested.