In vitro models to evaluate the permeability of poorly soluble drug entities: Challenges and perspectives

Using microfluidic platforms to develop CNS-targeted polymeric nanoparticles for HIV therapy

The human immunodeficiency virus (HIV) uses the brain as reservoir, which turns it as a promising target to fight this pathology. Nanoparticles (NPs) of poly(lactic-co-glycolic) acid (PLGA) are potential carriers of anti-HIV drugs to the brain, since most of these antiretrovirals, as efavirenz (EFV), cannot surpass the blood-brain barrier (BBB). Forasmuch as the conventional production methods lack precise control over the final properties of particles, microfluidics emerged as a prospective alternative. This study aimed at developing EFV-loaded PLGA NPs through a conventional and microfluidic method, targeted to the BBB, in order to treat HIV neuropathology. Compared to the conventional method, NPs produced through microfluidics presented reduced size (73 nm versus 133 nm), comparable polydispersity (around 0.090), less negative zeta-potential (-14.1 mV versus -28.0 mV), higher EFV association efficiency (80.7% versus 32.7%) and higher drug loading (10.8% versus 3.2%). The microfluidics-produced NPs also demonstrated a sustained in vitro EFV release (50% released within the first 24 h). NPs functionalization with a transferrin receptor-binding peptide, envisaging BBB targeting, proved to be effective concerning nuclear magnetic resonance analysis (δ = -0.008 ppm; δ = -0.017 ppm). NPs demonstrated to be safe to BBB endothelial and neuron cells (metabolic activity above 70%), as well as non-hemolytic (1-2% of hemolysis, no morphological alterations on erythrocytes). Finally, functionalized nanosystems were able to interact more efficiently with BBB cells, and permeability of EFV associated with NPs through a BBB in vitro model was around 1.3-fold higher than the free drug.

Application of the rainbow trout derived intestinal cell line (RTgutGC) for ecotoxicological studies: molecular and cellular responses following exposure to copper

There is an acknowledged need for in vitro fish intestinal model to help understand dietary exposure to chemicals in the aquatic environment. The presence and use of such models is however largely restrictive due to technical difficulties in the culturing of enterocytes in general and the availability of appropriate established cell lines in particular. In this study, the rainbow trout (Oncorhynchus mykiss) intestinal derived cell line (RTgutGC) was used as a surrogate for the "gut sac" method. To facilitate comparison, RTgutGC cells were grown as monolayers (double-seeded) on permeable Transwell supports leading to a two-compartment intestinal model consisting of polarised epithelium. This two-compartment model divides the system into an upper apical (lumen) and a lower basolateral (portal blood) compartment. In our studies, these cells stained weakly for mucosubstances, expressed the tight junction protein ZO-1 in addition to E-cadherin and revealed the presence of polarised epithelium in addition to microvilli protrusions. The cells also revealed a comparable transepithelial electrical resistance (TEER) to the in vivo situation. Importantly, the cell line tolerated apical saline (1:1 ratio) thus mimicking the intact organ to allow assessment of uptake of compounds across the intestine. Following an exposure over 72 h, our study demonstrated that the RTgutGC cell line under sub-lethal concentrations of copper sulphate (Cu) and modified saline solutions demonstrated uptake of the metal with saturation levels comparable to short term ex situ gut sac preparations. Gene expression analysis revealed no significant influence of pH or time on mRNA expression levels of key stress related genes (i.e. CYP3A, GST, mtA, Pgp and SOD) in the Transwell model. However, significant positive correlations were found between all genes investigated suggesting a co-operative relationship amongst the genes studied. When the outlined characteristics of the cell line are combined with the division of compartments, the RTgutGC double seeded model represents a potential animal replacement model for ecotoxicological studies. Overall, this model could be used to study the effects and predict aquatic gastrointestinal permeability of metals and other environmentally relevant contaminants in a cost effective and high throughput manner.

Assessment of Passive Intestinal Permeability Using an Artificial Membrane Insert System

Despite reasonable predictive power of current cell-based and cell-free absorption models for the assessment of intestinal drug permeability, high costs and lengthy preparation steps hamper their use. The use of a simple artificial membrane (without any lipids present) as intestinal barrier substitute would overcome these hurdles. In the present study, a set of 14 poorly water-soluble drugs, dissolved in 2 different media (fasted state simulated/human intestinal fluids [FaSSIF/FaHIF]), were applied to the donor compartment of an artificial membrane insert system (AMI-system) containing a regenerated cellulose membrane. Furthermore, to investigate the predictive capacity of the AMI-system as substitute for the well-established Caco-2 system to assess intestinal permeability, the same set of 14 drugs dissolved in FaHIF were applied to the donor compartment of a Caco-2 system. For 14 drugs, covering a broad range of physicochemical parameters, a reasonable correlation between both absorption systems was observed, characterized by a Pearson correlation coefficient r of 0.95 (FaHIF). Using the AMI-system, an excellent predictive capacity of FaSSIF as surrogate medium for FaHIF was demonstrated (r = 0.96). Based on the acquired data, the AMI-system appears to be a time- and cost-effective tool for the early-stage estimation of passive intestinal permeability for poorly water-soluble drugs.

Gastrointestinal behavior of itraconazole in humans - Part 2: The effect of intraluminal dilution on the performance of a cyclodextrin-based solution

Hydroxypropyl-β-cyclodextrin (HP-β-CD) is known to enable absorption of the lipophilic drug itraconazole. Since the interaction between HP-β-CD and itraconazole is characterized by a non-lineair, A_P-type phase-solubility diagram, the present study aimed to investigate the influence of intraluminal dilution (water intake) on the behavior and performance of an orally administered cyclodextrin-based solution of itraconazole. Subsequently, the in vivo behavior was simulated by combining in vitro dilution with permeation assessment. After the administration of a Sporanox^® solution to healthy volunteers with or without a glass of water, gastrointestinal and systemic concentrations of itraconazole were simultaneously monitored. Independently of the intake of water, no gastric precipitation of itraconazole was observed. After transfer to the duodenum, precipitation occurred and was more pronounced in the condition with water, resulting in a 7.6-fold reduction in duodenal AUC_0-3h compared to the condition without water. Nevertheless, plasma concentration-time profiles did not demonstrate any significant differences in AUC_0-8h, C_max and t_max. Application of freshly aspirated intestinal fluids on Caco-2 cells clearly confirmed that higher intestinal itraconazole concentrations after intake of Sporanox^® without water do not generate a substantially increased itraconazole uptake. A two-stage in vitro dilution test was combined with a permeation compartment to capture this solubility-permeability interplay. In conclusion, this work demonstrates that variations in intraluminal dilution may have a drastic impact on the gastrointestinal behavior of lipophilic drugs in the presence of cyclodextrins. In the case of an AP-type interaction with cyclodextrins, the trade-off between solubility and permeability may be affected.

Development of Cassette PAMPA for Permeability Screening

The parallel artificial membrane permeability assay (PAMPA) is widely used in early-stage drug discovery to discriminate compounds by intestinal permeability. The purpose of the current study was to establish a cassette (n-in-1) PAMPA to enable permeability screening of lipophilic compounds. A double-sink PAMPA consisting of a pH gradient (i.e., pH 6.5 and 7.4 for the donor and receiver compartments, respectively) and a lipophilic sink (i.e., a surfactant in the receiver solution) was utilized with cassette incubation of 10 reference compounds. Sample analysis was conducted using selected reaction monitoring (SRM) with a triple quadrupole LC-MS/MS system. Correlation between PAMPA permeability and human intestinal absorption (HIA) of the reference compounds yielded two false negatives, namely propranolol (PPN) and verapamil (VER); these two compounds showed a substantially lower recovery (ca. 10%) than other reference compounds (>69%). This cassette PAMPA was repeated subsequently with polysorbate 80 added to the donor compartments, which resulted in a significant increase in both the recovery and the permeability of the false negatives. Accordingly, the permeability class of all reference compounds could be unambiguously differentiated using this cassette PAMPA. Also, a strong linear correlation (r=0.9845) was observed between the cassette and discrete permeability of all reference compounds.

Pentacyclic Triterpene Bioavailability: An Overview of In Vitro and In Vivo Studies

Pentacyclic triterpenes are naturally found in a great variety of fruits, vegetables and medicinal plants and are therefore part of the human diet. The beneficial health effects of edible and medicinal plants have partly been associated with their triterpene content, but the in vivo efficacy in humans depends on many factors, including absorption and metabolism. This review presents an overview of in vitro and in vivo studies that were carried out to determine the bioavailability of pentacyclic triterpenes and highlights the efforts that have been performed to improve the dissolution properties and absorption of these compounds. As plant matrices play a critical role in triterpene bioaccessibility, this review covers literature data on the bioavailability of pentacyclic triterpenes ingested either from foods and medicinal plants or in their free form.

Evaluation of a dynamic dissolution/permeation model: Mutual influence of dissolution and barrier-flux under non-steady state conditions

Combined dissolution/permeation testing is gaining increasing attention as an in vitro tool for predictive performance ranking of enabling oral formulations. The current aim was to study how in vitro drug permeation evolves under conditions, where the donor concentration is changing (non-steady state). To this end, a model case was construed: compacts of pure crystalline hydrocortisone methanolate (HC·MeOH) of slow release rates were prepared, and their dissolution and permeation determined simultaneously in a side-by-side setup, separated by a biomimetic barrier (Permeapad^®). This was compared to a corresponding setup for a suspension of micronized hydrocortisone (HC). The HC suspension showed constant dissolved HC concentration and constant flux across the barrier, representing the permeation-limited situation. For the HC·MeOH compacts, various dynamic scenarios were observed, where dissolution rate and flux influenced each other. Interestingly, for all the dynamic scenarios, the incremental flux values obtained correlated nicely with the corresponding actual donor concentrations. Furthermore, donor depletion was tested using a HC solution. The dynamic interplay between decrease in donor concentration (down to less than 10% of the initial concentration) and flux was studied. The experiences gained are discussed in terms of further developing combined dissolution/permeation setups.

Nonionic Microemulsions as Solubilizers of Hydrophobic Drugs: Solubilization of Paclitaxel

The strategy using nonionic microemulsion as a solubilizer for hydrophobic drugs was studied and is demonstrated in this work. The aqueous phase behaviors of mixed nonionic surfactants with various oils at 37 °C are firstly constructed to give the optimal formulations of nonionic microemulsions with applications in the enhanced solubilization of the model hydrophobic drug, paclitaxel, at 37 °C. Briefly, the suitable oil phase with paclitaxel significantly dissolved is microemulsified with appropriate surfactants. Surfactants utilized include Tween 80, Cremophor EL, and polyethylene glycol (4.3) cocoyl ether, while various kinds of edible oils and fatty esters are used as the oil phase. On average, the apparent solubility of paclitaxel is increased to ca. 70-100 ppm in the prepared microemulsions at 37 °C using tributyrin or ethyl caproate as the oil phases. The sizes of the microemulsions attained are mostly from ca. 60 nm to ca. 200 nm. The cytotoxicity of the microemulsion formulations is assessed with the cellular viability of 3T3 cells. In general, the cell viability is above 55% after 24 h of cultivation in media containing these microemulsion formulations diluted to a concentration of total surfactants equal to 50 ppm and 200 ppm.

The solubility-permeability interplay and oral drug formulation design: Two heads are better than one

Poor aqueous solubility is a major challenge in today's biopharmaceutics. While solubility-enabling formulations can significantly increase the apparent solubility of the drug, the concomitant effect on the drug's apparent permeability has been largely overlooked. The mathematical equation to describe the membrane permeability of a drug comprises the membrane/aqueous partition coefficient, which in turn is dependent on the drug's apparent solubility in the GI milieu, suggesting that the solubility and the permeability are closely related, exhibit a certain interplay between them, and treating the one irrespectively of the other may be insufficient. In this article, an overview of this solubility-permeability interplay is provided, and the available data is analyzed in the context of the effort to maximize the overall drug exposure. Overall, depending on the type of solubility-permeability interplay, the permeability may decrease, remain unchanged, and even increase, in a way that may critically affect the formulation capability to improve the overall absorption. Therefore, an intelligent design of solubility-enabling formulation needs to consider both the solubility afforded by the formulation and the permeability in the new luminal environment resulting from the formulation.

Permeapad™ for investigation of passive drug permeability: The effect of surfactants, co-solvents and simulated intestinal fluids (FaSSIF and FeSSIF)

The aim of the present work was to investigate the potential of the new and innovative artificial barrier, Permeapad™, when exposed to surfactants and co-solvents, often employed for poorly water soluble compounds. The barrier was in addition also exposed to fasted and fed state simulated intestinal fluids versions 1 and 2 (FaSSIF and FeSSIF), all of which the Permeapad™ barrier was compatible with based upon relative comparison of the permeability of the hydrophilic marker calcein in phosphate buffer. The new barrier therefore holds a huge potential due to its functional stability and robustness. It can be used as a standard tool to investigate permeability of drugs in the presence of different surfactants and co-solvents, from DMSO stock solutions at even high concentrations and for the evaluation of permeability in the presence of biomimetic media (BMM).

Applying Biopharmaceutical Classification System (BCS) Criteria to Predict Oral Absorption of Drugs in Dogs: Challenges and Pitfalls

The Biopharmaceutical Classification System (BCS) has been a prognostic tool for assessing the potential effects of formulation on the human drug oral bioavailability. When used in conjunction with in vitro dissolution tests, the BCS can support the prediction of in vivo product performance and the development of mechanistic models that support formulation assessments through the generation of "what if" scenarios. To date, the applicability of existing human BCS criteria has not been evaluated in dogs, thereby limiting its use in canine drug development. Therefore, we examined 50 drugs for which absolute bioavailability (F) was available both in dogs and humans. The drugs were also evaluated for any potential association between solubility (calculated from the dose number, Do) or lipophilicity (LogP) and F in dogs. In humans, solubility is determined in 250 mL of fluid. However, the appropriate volume for classifying drug solubility in dogs has not been established. In this analysis, the estimated volume of a water flush administered to fasted dogs (6 mL) and a volume of 250 mL scaled to a Beagle dog (35 mL) were examined. In addition, in humans, a Do value greater than 1.0 is used to define a compound as highly soluble and a LogP value greater than 1.72 as high permeability. These same criteria were applied for defining highly soluble and highly permeable in dogs. Whether using 35 or 6 mL to determine Do, the canine solubility classification remained unchanged for all but seven compounds. There were no clear associations between a drug's F in dogs and humans or between the canine value of F and either its human BCS classification, its LogP value, or the canine Do estimate. There was a tendency for those drugs with canine values of F equal to or greater than 80% to have LogP values equal to or greater than 1.0. Exceptions to this observation tended to be those compounds known to be absorbed via mechanisms other than passive diffusion (e.g., via transporters or paracellular transporters). Although there are limitations to the approach used in this study, the results of our assessment strongly suggest that the human BCS classification system requires substantial modification before it can be reliably applied to dogs.

Formulation and evaluation of biodegradable nanoparticles for the oral delivery of fenretinide

Fenretinide is an anticancer drug with low water solubility and poor bioavailability. The goal of this study was to develop biodegradable polymeric nanoparticles of fenretinide with the intent of increasing its apparent aqueous solubility and intestinal permeability. Three biodegradable polymers were investigated for this purpose: two different poly lactide-co-glycolide (PLGA) polymers, one acid terminated and one ester terminated, and one poly lactide-co-glycolide/polyethylene glycol (PLGA/PEG) diblock copolymer. Nanoparticles were obtained by using an emulsification solvent evaporation technique. The formulations were characterized by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and particle size analysis. Dissolution studies and Caco-2 cell permeation studies were also carried out for all formulations. Ultra high performance liquid chromatography coupled with mass spectrometry (UPLC/MS) and ultraviolet detection was used for the quantitative determination of fenretinide. Drug loading and the type of polymer affected the nanoparticles' physical properties, drug release rate, and cell permeability. While the acid terminated PLGA nanoparticles performed the best in drug release, the ester terminated PLGA nanoparticles performed the best in the Caco-2 cell permeability assays. The PLGA/PEG copolymer nanoparticles performed better than the formulations with ester terminated PLGA in terms of drug release but had the poorest performance in terms of cell permeation. All three categories of formulations performed better than the drug alone in both drug release and cell permeation studies.

Preparation and in vitro evaluation of hydrophilic fenretinide nanoparticles

Fenretinide is an effective anti-cancer drug with high in vitro cytotoxicity and low in vivo systemic toxicity. In clinical trials, fenretinide has shown poor therapeutic efficacy following oral administration - attributed to its low bioavailability and solubility. The long term goal of this project is to develop a formulation for the oral delivery of fenretinide. The purpose of this part of the study was to prepare and characterize hydrophilic nanoparticle formulations of fenretinide. Three different ratios of polyvinyl pyrrolidone (PVP) to fenretinide were used, namely, 3:1, 4:1, and 5:1. Both drug and polymer were dissolved in a mixture of methanol and dichloromethane (2:23 v/v). Rotary evaporation was used to remove the solvents, and, following reconstitution with water, a high pressure homogenizer was used to form nanoparticles. The particle size and polydispersity index were measured before and after lyophilization. The formulations were studied by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and X-ray powder diffraction (XRPD). The effectiveness of the formulations was assessed by release studies and Caco-2 cell permeability assays. As the PVP content increased, the recovered particle size following lyophilization became more consistent with the pre-lyophilization particle size, especially for those formulations with less lactose. The DSC scans of the formulations did not show any fenretinide melting endotherms, indicating that the drug was either present in an amorphous form in the formulation or that a solid solution of the drug in PVP had formed. For the release studies, the highest drug release among the formulations was 249.2±35.5ng/mL for the formulation with 4:1 polymer-to-drug. When the permeability of the formulations was evaluated in a Caco-2 cell model, the mean normalized flux for each treatment group was significantly higher (p<0.05) from the fenretinide control. The formulation containing 4:1 polymer-to-drug ratio and 6:5 lactose-to-formulation ratio emerged as the optimal choice for further evaluation as a potential oral delivery formulation for fenretinide.

Decision trees to characterise the roles of permeability and solubility on the prediction of oral absorption

Oral absorption of compounds depends on many physiological, physiochemical and formulation factors. Two important properties that govern oral absorption are in vitro permeability and solubility, which are commonly used as indicators of human intestinal absorption. Despite this, the nature and exact characteristics of the relationship between these parameters are not well understood. In this study a large dataset of human intestinal absorption was collated along with in vitro permeability, aqueous solubility, melting point, and maximum dose for the same compounds. The dataset allowed a permeability threshold to be established objectively to predict high or low intestinal absorption. Using this permeability threshold, classification decision trees incorporating a solubility-related parameter such as experimental or predicted solubility, or the melting point based absorption potential (MPbAP), along with structural molecular descriptors were developed and validated to predict oral absorption class. The decision trees were able to determine the individual roles of permeability and solubility in oral absorption process. Poorly permeable compounds with high solubility show low intestinal absorption, whereas poorly water soluble compounds with high or low permeability may have high intestinal absorption provided that they have certain molecular characteristics such as a small polar surface or specific topology.

Recent approaches of lipid-based delivery system for lymphatic targeting via oral route

Lymphatic system is a key target in research field due to its distinctive makeup and huge contributing functions within the body. Intestinal lymphatic drug transport (chylomicron pathway) is intensely described in research field till date because it is considered to be the best for improving oral drug delivery by avoiding first pass metabolism. The lymphatic imaging techniques and potential therapeutic candidates are engaged for evaluating disease states and overcoming these conditions. The novel drug delivery systems such as self-microemulsifying drug delivery system, nanoparticles, liposomes, nano-lipid carriers, solid lipid carriers are employed for delivering drugs through lymphatic system via various routes such as subcutaneous route, intraperitoneal route, pulmonary route, gastric sub-mucosal injection, intrapleural and intradermal. Among these colloidal particles, lipid-based delivery system is considered to be the best for lymphatic delivery. From the last few decades, mesenteric lymph duct cannulation and thoracic lymph duct cannulation are followed to assess lymphatic uptake of drugs. Due to their limitations, chylomicrons inhibitors and in-vitro models are employed, i.e. lipolysis model and permeability model. Currently, research on this topic still continues and drainage system used to deliver the drugs against lymphatic disease as well as targeting other organs by modulating the chylomicron pathway.

Utility of models of the gastrointestinal tract for assessment of the digestion and absorption of engineered nanomaterials released from food matrices

Engineered metal/mineral, lipid and biochemical macromolecule nanomaterials (NMs) have potential applications in food. Methodologies for the assessment of NM digestion and bioavailability in the gastrointestinal tract are nascent and require refinement. A working group was tasked by the International Life Sciences Institute NanoRelease Food Additive project to review existing models of the gastrointestinal tract in health and disease, and the utility of these models for the assessment of the uptake of NMs intended for food. Gastrointestinal digestion and absorption could be addressed in a tiered approach using in silico computational models, in vitro non-cellular fluid systems and in vitro cell culture models, after which the necessity of ex vivo organ culture and in vivo animal studies can be considered. Examples of NM quantification in gastrointestinal tract fluids and tissues are emerging; however, few standardized analytical techniques are available. Coupling of these techniques to gastrointestinal models, along with further standardization, will further strengthen methodologies for risk assessment.

Overview of the role of nanotechnological innovations in the detection and treatment of solid tumors

Nanotechnology, although still in its infantile stages, has the potential to revolutionize the diagnosis, treatment, and monitoring of disease progression and success of therapy for numerous diseases and conditions, not least of which is cancer. As it is a leading cause of mortality worldwide, early cancer detection, as well as safe and efficacious therapeutic intervention, will be indispensable in improving the prognosis related to cancers and overall survival rate, as well as health-related quality of life of patients diagnosed with cancer. The development of a relatively new field of nanomedicine, which combines various domains and technologies including nanotechnology, medicine, biology, pharmacology, mathematics, physics, and chemistry, has yielded different approaches to addressing these challenges. Of particular relevance in cancer, nanosystems have shown appreciable success in the realm of diagnosis and treatment. Characteristics attributable to these systems on account of the nanoscale size range allow for individualization of therapy, passive targeting, the attachment of targeting moieties for more specific targeting, minimally invasive procedures, and real-time imaging and monitoring of in vivo processes. Furthermore, incorporation into nanosystems may have the potential to reintroduce into clinical practice drugs that are no longer used because of various shortfalls, as well as aid in the registration of new, potent drugs with suboptimal pharmacokinetic profiles. Research into the development of nanosystems for cancer diagnosis and therapy is thus a rapidly emerging and viable field of study.

PBTK modelling platforms and parameter estimation tools to enable animal-free risk assessment: recommendations from a joint EPAA--EURL ECVAM ADME workshop

Information on toxicokinetics is critical for animal-free human risk assessment. Human external exposure must be translated into human tissue doses and compared with in vitro actual cell exposure associated to effects (in vitro-in vivo comparison). Data on absorption, distribution, metabolism and excretion in humans (ADME) could be generated using in vitro and QSAR tools. Physiologically-based toxicokinetic (PBTK) computer modelling could serve to integrate disparate in vitro and in silico findings. However, there are only few freely-available PBTK platforms currently available. And although some ADME parameters can be reasonably estimated in vitro or in silico, important gaps exist. Examples include unknown or limited applicability domains and lack of (high-throughput) tools to measure penetration of barriers, partitioning between blood and tissues and metabolic clearance. This paper is based on a joint EPAA--EURL ECVAM expert meeting. It provides a state-of-the-art overview of the availability of PBTK platforms as well as the in vitro and in silico methods to parameterise basic (Tier 1) PBTK models. Five high-priority issues are presented that provide the prerequisites for wider use of non-animal based PBTK modelling for animal-free chemical risk assessment.

Human in vivo regional intestinal permeability: importance for pharmaceutical drug development

Both the development and regulation of pharmaceutical dosage forms have undergone significant improvements and development over the past 25 years, due primarily to the extensive application of the biopharmaceutical classification system (BCS). The Biopharmaceutics Drug Disposition Classification System, which was published in 2005, has also been a useful resource for predicting the influence of transporters in several pharmacokinetic processes. However, there remains a need for the pharmaceutical industry to develop reliable in vitro/in vivo correlations and in silico methods for predicting the rate and extent of complex gastrointestinal (GI) absorption, the bioavailability, and the plasma concentration-time curves for orally administered drug products. Accordingly, a more rational approach is required, one in which high quality in vitro or in silico characterizations of active pharmaceutical ingredients and formulations are integrated into physiologically based in silico biopharmaceutics models to capture the full complexity of GI drug absorption. The need for better understanding of the in vivo GI process has recently become evident after an unsuccessful attempt to predict the GI absorption of BCS class II and IV drugs. Reliable data on the in vivo permeability of the human intestine (Peff) from various intestinal regions is recognized as one of the key biopharmaceutical requirements when developing in silico GI biopharmaceutics models with improved predictive accuracy. The Peff values for human jejunum and ileum, based on historical open, single-pass, perfusion studies are presented in this review. The main objective of this review is to summarize and discuss the relevance and current status of these human in vivo regional intestinal permeability values.

Oral biopharmaceutics tools - time for a new initiative - an introduction to the IMI project OrBiTo

OrBiTo is a new European project within the IMI programme in the area of oral biopharmaceutics tools that includes world leading scientists from nine European universities, one regulatory agency, one non-profit research organization, four SMEs together with scientists from twelve pharmaceutical companies. The OrBiTo project will address key gaps in our knowledge of gastrointestinal (GI) drug absorption and deliver a framework for rational application of predictive biopharmaceutics tools for oral drug delivery. This will be achieved through novel prospective investigations to define new methodologies as well as refinement of existing tools. Extensive validation of novel and existing biopharmaceutics tools will be performed using active pharmaceutical ingredient (API), formulations and supporting datasets from industry partners. A combination of high quality in vitro or in silico characterizations of API and formulations will be integrated into physiologically based in silico biopharmaceutics models capturing the full complexity of GI drug absorption. This approach gives an unparalleled opportunity to initiate a transformational change in industrial research and development to achieve model-based pharmaceutical product development in accordance with the Quality by Design concept. Benefits include an accelerated and more efficient drug candidate selection, formulation development process, particularly for challenging projects such as low solubility molecules (BCS II and IV), enhanced and modified-release formulations, as well as allowing optimization of clinical product performance for patient benefit. In addition, the tools emerging from OrBiTo are expected to significantly reduce demand for animal experiments in the future as well as reducing the number of human bioequivalence studies required to bridge formulations after manufacturing or composition changes.

Fast profiling ecotoxicity and skin permeability of benzophenone ultraviolet filters using biopartitioning micellar chromatography based on penetrable silica spheres

Penetrable silica possesses hierarchical pores, mesopores and penetrable macropores, offering fast mass transfer, satisfactory mechanical strength as well as low column pressure. In the present study, penetrable octadecyl-bonded silica (ODS) was for the first time used as biopartitioning micellar chromatography (BMC) stationary phase to profile ecotoxicity and skin permeability of benzophenone UV-filters. Mobile phase (MP) pH and concentration of polyoxyethylene(23)lauryl ether in the MP were systematically studied. Quantitative retention-activity relationships (QRARs) model was established to correlate retention factors (k) on BMC with bioconcentration factor (BCF) and transdermal rate (TR) of UV-filters. Coefficient of determination (r(2)) of the QRARs model between log BCF and log k were 0.9398-0.9753, while r(2) between TR and log k were 0.7569-0.8434, which demonstrated satisfactory predictive ability of the methodology. It was a powerful tool for fast screening by combining penetrable ODS with BMC, and avoiding column blockage often occurring in BMC.

Toward the practical implementation of eye-related bioavailability prediction models

The development and registration of reformulated ophthalmic products (OPs) requires eye-related bioavailability (BA) assessments. Common BA algorithms associated with other routes of application, such as the oral route, cannot be easily applied to eye-related BA testing. Here, we provide an analysis of the current literature and suggestions for further directions in the development of high-capacity, cost-effective, and highly predictive nonclinical models of eye-related drug BA. One, or a combination of these models, has the potential for routine use in research laboratories and/or the pharmaceutical industry to overcome various obstacles in reformulated OP development and registration.

The applications of Vitamin E TPGS in drug delivery

D-α-Tocopheryl polyethylene glycol 1000 succinate (simply TPGS or Vitamin E TPGS) is formed by the esterification of Vitamin E succinate with polyethylene glycol 1000. As novel nonionic surfactant, it exhibits amphipathic properties and can form stable micelles in aqueous vehicles at concentration as low as 0.02 wt%. It has been widely investigated for its emulsifying, dispersing, gelling, and solubilizing effects on poorly water-soluble drugs. It can also act as a P-glycoprotein (P-gp) inhibitor and has been served as an excipient for overcoming multidrug resistance (MDR) and for increasing the oral bioavailability of many anticancer drugs. Since TPGS has been approved by FDA as a safe pharmaceutic adjuvant, many TPGS-based drug delivery systems (DDS) have been developed. In this review, we discuss TPGS properties as a P-gp inhibitor, solubilizer/absorption and permeation enhancer in drug delivery and TPGS-related formulations such as nanocrystals, nanosuspensions, tablets/solid dispersions, adjuvant in vaccine systems, nutrition supplement, plasticizer of film, anticancer reagent and so on. This review will greatly impact and bring out new insights in the use of TPGS in DDS.

Highly stabilized curcumin nanoparticles tested in an in vitro blood-brain barrier model and in Alzheimer's disease Tg2576 mice

The therapeutic effects of curcumin in treating Alzheimer's disease (AD) depend on the ability to penetrate the blood-brain barrier. The latest nanoparticle technology can help to improve the bioavailability of curcumin, which is affected by the final particle size and stability. We developed a stable curcumin nanoparticle formulation to test in vitro and in AD model Tg2576 mice. Flash nanoprecipitation of curcumin, polyethylene glycol-polylactic acid co-block polymer, and polyvinylpyrrolidone in a multi-inlet vortex mixer, followed by freeze drying with β-cyclodextrin, produced dry nanocurcumin with mean particle size <80 nm. Nanocurcumin powder, unformulated curcumin, or placebo was orally administered to Tg2576 mice for 3 months. Before and after treatment, memory was measured by radial arm maze and contextual fear conditioning tests. Nanocurcumin produced significantly (p=0.04) better cue memory in the contextual fear conditioning test than placebo and tendencies toward better working memory in the radial arm maze test than ordinary curcumin (p=0.14) or placebo (p=0.12). Amyloid plaque density, pharmacokinetics, and Madin-Darby canine kidney cell monolayer penetration were measured to further understand in vivo and in vitro mechanisms. Nanocurcumin produced significantly higher curcumin concentration in plasma and six times higher area under the curve and mean residence time in brain than ordinary curcumin. The P(app) of curcumin and tetrahydrocurcumin were 1.8×10(-6) and 1.6×10(-5)cm/s, respectively, for nanocurcumin. Our novel nanocurcumin formulation produced highly stabilized nanoparticles with positive treatment effects in Tg2576 mice.

Amorphous solid dispersion enhances permeation of poorly soluble ABT-102: true supersaturation vs. apparent solubility enhancement

Amorphous solid dispersions (ASDs) represent a promising formulation approach for poorly soluble drugs. We explored the formulation-related impact of ASDs on permeation rate, apparent solubility and molecular solubility of the poorly soluble drug ABT-102. The influence of fasted state simulated intestinal fluid (FaSSIF) as dispersion medium was also studied. ASDs were prepared by hot-melt extrusion. Permeation rate was assessed by the Caco-2 transwell assay. Cell viability and barrier integrity were assured by AlamarBlue©, TEER and permeability of the hydrophilic marker carboxyfluorescein. Apparent solubility and molecular solubility were evaluated by using centrifugation and inverse dialysis, respectively. The in vitro permeation rate of ABT-102 from aqueous dispersions of the ASD was found 4 times faster than that from the dispersions of the crystals, while apparent solubility and molecular solubility of ABT-102 were increased. Yet, a further increase in apparent solubility due to micellar solubilization as observed when dispersing the ASD in FaSSIF, did not affect molecular solubility or permeation rate. Overall, a good correlation between permeation rate and molecular solubility but not apparent solubility was seen.