Comparison of the permeability of metoprolol and labetalol in rat, mouse, and Caco-2 cells: use as a reference standard for BCS classification

Challenges in Permeability Assessment for Oral Drug Product Development

Drug permeation across the intestinal epithelium is a prerequisite for successful oral drug delivery. The increased interest in oral administration of peptides, as well as poorly soluble and poorly permeable compounds such as drugs for targeted protein degradation, have made permeability a key parameter in oral drug product development. This review describes the various in vitro, in silico and in vivo methodologies that are applied to determine drug permeability in the human gastrointestinal tract and identifies how they are applied in the different stages of drug development. The various methods used to predict, estimate or measure permeability values, ranging from in silico and in vitro methods all the way to studies in animals and humans, are discussed with regard to their advantages, limitations and applications. A special focus is put on novel techniques such as computational approaches, gut-on-chip models and human tissue-based models, where significant progress has been made in the last few years. In addition, the impact of permeability estimations on PK predictions in PBPK modeling, the degree to which excipients can affect drug permeability in clinical studies and the requirements for colonic drug absorption are addressed.

Canine Intestinal Organoids as a Novel In Vitro Model of Intestinal Drug Permeability: A Proof-of-Concept Study

A key component of efforts to identify the biological and drug-specific aspects contributing to therapeutic failure or unexpected exposure-associated toxicity is the study of drug-intestinal barrier interactions. While methods supporting such assessments are widely described for human therapeutics, relatively little information is available for similar evaluations in support of veterinary pharmaceuticals. There is, therefore, a critical need to develop novel approaches for evaluating drug-gut interactions in veterinary medicine. Three-dimensional (3D) organoids can address these difficulties in a reasonably affordable system that circumvents the need for more invasive in vivo assays in live animals. However, a first step in developing such systems is understanding organoid interactions in a 2D monolayer. Given the importance of orally administered medications for meeting the therapeutic need of companion animals, we demonstrate growth conditions under which canine-colonoid-derived intestinal epithelial cells survive, mature, and differentiate into confluent cell systems with high monolayer integrity. We further examine the applicability of this canine-colonoid-derived 2D model to assess the permeability of three structurally diverse, passively absorbed β-blockers (e.g., propranolol, metoprolol, and atenolol). Both the absorptive and secretive apparent permeability (P_app) of these drugs at two different pH conditions were evaluated in canine-colonoid-derived monolayers and compared with that of Caco-2 cells. This proof-of-concept study provides promising preliminary results with regard to the utility of canine-derived organoid monolayers for species-specific assessments of therapeutic drug passive permeability.

Separate Evaluation of Fraction Absorbed and Intestinal Availability after Oral Administration of Drugs Based on the Measurement of Portal and Systemic Plasma Concentrations and Luminal Concentration

There are several experimental methods to estimate the product of the fraction absorbed (Fa) and intestinal availability (Fg) in vivo after oral administration of drugs. Metabolic enzyme inhibitors are typically used to separate Fg from Fa·Fg. Since Fa·Fg can be regarded as Fa under metabolism-inhibited conditions, Fg can be isolated by dividing Fa·Fg by Fa. However, if the inhibition of intestinal metabolism is insufficient, Fa is overestimated, which results in an underestimation of Fg compared to the actual value. In this study, to avoid this problem, an experimental method for the separate estimation of Fa and Fg in rats without utilizing metabolic enzyme inhibitors was established. Buspirone, a CYP3A substrate, and ribavirin, a substrate of purine nucleoside phosphorylase and adenosine kinase, were selected as models. Following oral administration of the drugs with fluorescein isothiocyanate dextran 4000 (FD-4, an unabsorbable marker), Fa·Fg was pharmacokinetically calculated from portal and systemic plasma concentration-time profiles of model drugs and Fa was calculated from the difference in the ileal concentration profiles of the drugs and FD-4. Fg was evaluated by dividing Fa·Fg by Fa. Following oral administration, buspirone was not detected in any segment of the small intestine, indicating that the administered buspirone was completely absorbed. In addition, buspirone was extensively metabolized in enterocytes (Fg = 20.1). Ribavirin was primarily absorbed in the upper segment of the small intestine, and 64.4% of the ribavirin was absorbed before it reached the ileum. In addition, it was revealed that ribavirin was metabolized more extensively in the intestine than in the liver. Our method may be effective in quantitatively assessing Fa and Fg in vivo, which can help in the formulation design and prediction of drug-drug interactions.

Exploring a Bioequivalence Failure for Silodosin Products Due to Disintegrant Excipients

Some years ago, excipients were considered inert substances irrelevant in the absorption process. However, years of study have demonstrated that this belief is not always true. In this study, the reasons for a bioequivalence failure between two formulations of silodosin are investigated. Silodosin is a class III drug according to the Biopharmaceutics Classification System, which has been experimentally proven by means of solubility and permeability experiments. Dissolution tests have been performed to identify conditions concordant with the non-bioequivalent result obtained from the human bioequivalence study and it has been observed that paddles at 50 rpm are able to detect inconsistent differences between formulations at pH 4.5 and pH 6.8 (which baskets at 100 rpm are not able to do), whereas the GIS detects differences at the acidic pH of the stomach. It has also been observed that the differences in excipients between products did not affect the disintegration process, but disintegrants did alter the permeability of silodosin through the gastrointestinal barrier. Crospovidone and povidone, both derivatives of PVP, are used as disintegrants in the test product, instead of the pregelatinized corn starch used in the reference product. Permeability experiments show that PVP increases the absorption of silodosin-an increase that would explain the greater C_max observed for the test product in the bioequivalence study.

Preclinical Characterization and Development on NAQ as a Mu Opioid Receptor Partial Agonist for Opioid Use Disorder Treatment

Mu opioid receptor (MOR) selective antagonists and partial agonists have clinical utility for the treatment of opioid use disorders (OUDs). However, the development of many has suffered due to their poor pharmacokinetic properties and/or rapid metabolism. Our recent efforts to identify MOR modulators have provided 17-cyclopropylmethyl-3,14β-dihydroxy-4,5α-epoxy-6α-(isoquinoline-3-carboxamido)morphinan (NAQ), a low-efficacy partial agonist, that showed sub-nanomolar binding affinity to the MOR (K i 0.6 nM) with selectivity over the delta opioid receptor (δ/μ 241) and the kappa opioid receptor (κ/μ 48). Its potent inhibition of the analgesic effect of morphine (AD50 0.46 mg/kg) and precipitation of significantly less withdrawal symptoms even at 100-fold greater dose than naloxone represents a promising molecule for further development as a novel OUD therapeutic agent. Therefore, further in vitro and in vivo characterization of its pharmacokinetics and pharmacodynamics properties was conducted to fully understand its pharmaceutical profile. NAQ showed favorable in vitro ADMET properties and no off-target binding to several classes of GPCRs, enzymes, and ion channels. Following intravenous administration, 1 mg/kg dose of NAQ showed a similar in vivo pharmacokinetic profile to naloxone; however, orally administered 10 mg/kg NAQ demonstrated significantly improved oral bioavailability over both naloxone and naltrexone. Abuse liability assessment of NAQ in rats demonstrated that NAQ functioned as a less potent reinforcer than heroin. Chronic 5 day NAQ pretreatment decreased heroin self-administration in a heroin-vs-food choice procedure similar to the clinically used MOR partial agonist buprenorphine. Taken together, these studies provide evidence supporting NAQ as a promising lead to develop novel OUD therapeutics.

Development and Evaluation of a Physiologically Based Pharmacokinetic Model of Labetalol in Healthy and Diseased Populations

Labetalol is a drug that exhibits both alpha and beta-adrenergic receptor-blocking properties. The American Heart Association/American Stroke Association (AHA/ASA) has recommended labetalol as an initial treatment option for the management of severe hypertension. The physiologically based pharmacokinetic (PBPK) model is an in silico approach to determining the pharmacokinetics (PK) of a drug by incorporating blood flow and tissue composition of the organs. This study was conducted to evaluate the primary reasons for the difference in PK after intravenous (IV) and oral administration in healthy and diseased (renal and hepatic) populations. A comprehensive literature search was done using two databases, PubMed and Google Scholar. Various PK parameters were screened for the development of the PBPK model utilizing a population-based PK-Sim simulator. Simulations were performed after creating building blocks firstly in healthy individuals and then in diseased patients after IV and oral administration. The disposition of labetalol after IV and oral administration occurring in patients with the hepatic and renal disease was predicted. The model was evaluated by calculating the Robs/pred ratio and average fold error (AFE), which was in the two-fold error range. Moreover, Box-whisker plots were made to compare the overall concentration of the drug in the body at various stages of disease severity. The presented model provides useful quantitative estimates of drug dosing in patients fighting against severe chronic diseases.

Fighting Plasmodium chloroquine resistance with acetylenic chloroquine analogues

Malaria is among the tropical diseases that cause the most deaths in Africa. Around 500,000 malaria deaths are reported yearly among African children under the age of five. Chloroquine (CQ) is a low-cost antimalarial used worldwide for the treatment of Plasmodium vivax malaria. Due to resistance mechanisms, CQ is no longer effective against most malaria cases caused by P. falciparum. The World Health Organization recommends artemisinin combination therapies for P. falciparum malaria, but resistance is emerging in Southeast Asia and some parts of Africa. Therefore, new medicines for treating malaria are urgently needed. Previously, our group identified the 4-aminoquinoline DAQ, a CQ analog containing an acetylenic bond in its side chain, which overcomes CQ resistance in K1 P. falciparum strains. In this work, the antiplasmodial profile, drug-like properties, and pharmacokinetics of DAQ were further investigated. DAQ showed no cross-resistance against standard CQ-resistant strains (e.g., Dd2, IPC 4912, RF12) nor against P. falciparum and P. vivax isolates from patients in the Brazilian Amazon. Using drug pressure assays, DAQ showed a low propensity to generate resistance. DAQ showed considerable solubility but low metabolic stability. The main metabolite was identified as a mono N-deethylated derivative (DAQ_M), which also showed significant inhibitory activity against CQ-resistant P. falciparum strains. Our findings indicated that the presence of a triple bond in CQ-analogues may represent a low-cost opportunity to overcome known mechanisms of resistance in the malaria parasite.

A Stability Indicating RP-HPLC Method for Determination of the COVID-19 Drug Molnupiravir Applied Using Nanoformulations in Permeability Studies

Antiviral drugs have gained much more attention in recent years due to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection and many drug candidates are currently under investigation in order to end pandemic. Molnupiravir, a prodrug of the synthetic nucleoside derivative N4-hydroxycytidine, is one of the promising candidates for SARS-CoV-2 treatment. In this study, a RP-HPLC method was developed for the determination of Molnupiravir and applied for in vitro permeability studies of self-emulsifying drug delivery system (SEDDS) formulations using Caco-2 cell line. Discovery® HS C18 Column (75 ×4.6 mm, 3 µm) was used at 30 °C. Isocratic elution was performed with ACN:water (20:80 v/v) mixture. The flow rate was 0.5 mL/min and UV detection was at 240 nm. Molnupiravir eluted within 5 min. Molnupiravir was exposed to thermal, photolytic, hydrolytic, and oxidative stress conditions. Peak homogeneity data of Molnupiravir in the stressed samples peak obtained using photodiode array detector, in the stressed sample chromatograms, demonstrated the specificity of the method for their estimation in presence of degradants. The developed method was validated according to the International Council for Harmonisation (ICH) guidelines and found to be linear within the range 0.1–60.0 μg/mL. The method was simple, rapid, selective, sensitive, accurate, precise, robust and rugged. Thus, it was applied successfully for permeability quantitation of Molnupiravir in nanoformulations. The apparent permeability of Molnupiravir in SEDDS formulations, which have droplet size under 350 nm, was calculated as 3.20 ± 0.44 × 10⁻⁶ cm/s.

The impact of quantity of lipid based formulations with different compositions on the oral absorption of ritonavir: A trade-off between apparent solubility and permeability

In this study, the effect of the quantity of lipid-based formulations (LBFs) on the oral absorption of ritonavir (RTV), a model for poorly water-soluble drugs, was investigated. Two types of LBFs, comprising short- and medium-chain lipids (LBF-SMC) and long-chain lipids (LBF-LC) loaded with different masses of RTV, were prepared. Then, the respective LBFs were dispersed in distilled water at concentrations of 1.0, 2.0, and 3.0% w/w, which provided the same drug concentration for all formulations. When 1.0% LBF-SMC and LBF-LC were orally administered to rats, the oral absorption was significantly improved compared with that of the suspension (a reference formulation) because of enhanced solubilization of RTV in the gastrointestinal tract; however, this improvement was lower for LBF-LC than for LBF-SMC. The oral absorption decreased with increasing LBF concentration for both LBF-SMC and LBF-LC. The in vitro permeation in sequence with in vitro digestion revealed that this phenomenon was caused by a reduction in the free drug concentration in the gastrointestinal tract. Moreover, the effect of decreasing the free concentration was more remarkable for LBF-LC than for LBF-SMC because of the greater solubilization capacity of LC digestion products. These findings may be useful for designing improved drug delivery systems.

Comparative pharmacokinetics, intestinal absorption and urinary excretion of six alkaloids from herb pair Phellodendri Chinensis cortex-Atractylodis Rhizoma

Phellodendri Chinensis Cortex (PCC) and Atractylodis Rhizoma (AR) are frequently used as herb pair to treat eczema and gout owing to their synergistic effects. Alkaloids are the major ingredients from PCC and the effect of their combination on the in vivo processing of alkaloids remains unclear. In this study, a simple and reliable UPLC-MS/MS method for simultaneous determination of six alkaloids in rat plasma was developed. This method was applied to a comparative pharmacokinetic study between PCC and PCC-AR in rats. Effect of AR on absorption of alkaloids was investigated by a single-pass intestinal perfusion study. The effect of AR on urinary excretion of alkaloids was studied. Pharmacokinetic studies showed that the values of rea under the concentration-time curve of phellodendrine, magnoflorine and palmatine were greater in the PCC-AR group than in the PCC group. The intestinal absorptive parameters absorption rate constant and effective permeability of phellodendrine and jatrorrhizine in PCC-AR groups were higher than those in the PCC group. Urinary excretion studies revealed that the excreted amount of alkaloids in the PCC-AR group was lower than that in the PCC group. The results revealed that the combination of PCC and AR improves intestinal absorption of alkaloids and reduces their urinary excretion, which enhances their systemic exposure. This study may explain the synergetic effects of PCC and AR in clinical applications.

A versatile, compartmentalised gut-on-a-chip system for pharmacological and toxicological analyses

A novel, integrated, in vitro gastrointestinal (GI) system is presented to study oral bioavailability parameters of small molecules. Three compartments were combined into one hyphenated, flow-through set-up. In the first compartment, a compound was exposed dynamically to enzymatic digestion in three consecutive microreactors, mimicking the processes of the mouth, stomach, and intestine. The resulting solution (chyme) continued to the second compartment, a flow-through barrier model of the intestinal epithelium allowing absorption of the compound and metabolites thereof. The composition of the effluents from the barrier model were analysed either offline by electrospray-ionisation-mass spectrometry (ESI-MS), or online in the final compartment using chip-based ESI-MS. Two model drugs, omeprazole and verapamil, were used to test the integrated model. Omeprazole was shown to be broken down upon treatment with gastric acid, but reached the cell barrier unharmed when introduced to the system in a manner emulating an enteric-coated formulation. In contrast, verapamil was unaffected by digestion. Finally, a reduced uptake of verapamil was observed when verapamil was introduced to the system dissolved in apple juice, a simple food matrix. It is envisaged that this integrated, compartmentalised GI system has potential for enabling future research in the fields of pharmacology, toxicology, and nutrition.

Reply to "Comment on López-Yerena et al. 'Absorption and Intestinal Metabolic Profile of Oleocanthal in Rats' Pharmaceutics 2020, 12, 134"

Recently, in February 2020, we published a study exploring the intestinal absorption and metabolism of oleocanthal (OLC) in rats. A single-pass intestinal perfusion technique (SPIP) was used, involving simultaneous sampling from the luminal perfusate and mesenteric blood. Later, comments on our published paper were released, requesting clarification of specific data. In this detailed reply, we hope to have addressed and clarified all the concerns of A. Kaddoumi and K. El Sayed and that the scientific community will benefit from both the study and the comments it has generated.

Biopharmaceutical characterization of rebamipide: The role of mucus binding in regional-dependent intestinal permeability

In this study, we aimed to elucidate biopharmaceutical characteristics of the anti-ulcer drug rebamipide, with special emphasis on the influence of gastrointestinal (GI) mucus on rebamipide segmental-dependent permeability and absorption. Experimental studies and physiologically-based pharmacokinetic (GastroPlus^TM) simulations were used to elucidate segmental-dependent absorption and pharmacokinetic (PK) profile, accounting for various drug properties, including solubility/dissolution limitations, regional-dependent drug affinity to mucus and membrane permeability, as well as physiological factors such as regional-pH differences along the intestine, thickness and types of mucus, transit time and surface areas. Low permeability and extensive binding to GI mucus were the key modeling features, and accounting for these resulted in good fitting between the predicted and in-vivo PK profiles, validating the ability of the model to pinpoint the underlying mechanisms of rebamipide limited oral bioavailability. Furthermore, the simulations indicated regional-dependent intestinal permeability of rebamipide, with absorption rank order of jejunum>ileum>duodenum>colon, mainly attributable to segmental mucus differences. Food effect simulations indicated somewhat decreased rebamipide absorption in the fed state, in corroboration with previous reports. Since this anti-ulcer drug is currently examined for additional indications, this work provides important input for future development of rebamipide.

In Silico Prediction of Intestinal Permeability by Hierarchical Support Vector Regression

The vast majority of marketed drugs are orally administrated. As such, drug absorption is one of the important drug metabolism and pharmacokinetics parameters that should be assessed in the process of drug discovery and development. A nonlinear quantitative structure-activity relationship (QSAR) model was constructed in this investigation using the novel machine learning-based hierarchical support vector regression (HSVR) scheme to render the extremely complicated relationships between descriptors and intestinal permeability that can take place through various passive diffusion and carrier-mediated active transport routes. The predictions by HSVR were found to be in good agreement with the observed values for the molecules in the training set (n = 53, r² = 0.93, q CV 2 = 0.84, RMSE = 0.17, s = 0.08), test set (n = 13, q² = 0.75-0.89, RMSE = 0.26, s = 0.14), and even outlier set (n = 8, q² = 0.78-0.92, RMSE = 0.19, s = 0.09). The built HSVR model consistently met the most stringent criteria when subjected to various statistical assessments. A mock test also assured the predictivity of HSVR. Consequently, this HSVR model can be adopted to facilitate drug discovery and development.

Segmental-Dependent Solubility and Permeability as Key Factors Guiding Controlled Release Drug Product Development

The main factors influencing the absorption of orally administered drugs are solubility and permeability, which are location-dependent and may vary along the gastrointestinal tract (GIT). The purpose of this work was to investigate segmental-dependent intestinal absorption and its role in controlled-release (CR) drug product development. The solubility/dissolution and permeability of carvedilol (vs. metoprolol) were thoroughly studied, in vitro/in vivo (Octanol-buffer distribution coefficients (Log D), parallel artificial membrane permeability assay (PAMPA), rat intestinal perfusion), focusing on location-dependent effects. Carvedilol exhibits changing solubility in different conditions throughout the GIT, attributable to its zwitterionic nature. A biorelevant pH-dilution dissolution study for carvedilol immediate release (IR) vs. CR scenario elucidates that while the IR dose (25 mg) may dissolve in the GIT luminal conditions, higher doses used in CR products would precipitate if administered at once, highlighting the advantage of CR from the solubility/dissolution point of view. Likewise, segmental-dependent permeability was evident, with higher permeability of carvedilol vs. the low/high Peff marker metoprolol throughout the GIT, confirming it as a biopharmaceutical classification system (BCS) class II drug. Theoretical analysis of relevant physicochemical properties confirmed these results as well. A CR product may shift the carvedilol's solubility behavior from class II to I since only a small dose portion needs to be solubilized at a given time point. The permeability of carvedilol surpasses the threshold of metoprolol jejunal permeability throughout the entire GIT, including the colon, establishing it as a suitable candidate for CR product development. Altogether, this work may serve as an analysis model in the decision process of CR formulation development and may increase our biopharmaceutical understanding of a successful CR drug product.

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.

Enhanced dissolution/caco-2 permeability, pharmacokinetic and pharmacodynamic performance of re-dispersible eprosartan mesylate nanopowder

Eprosartan mesylate is an angiotensin receptor blocker which suffers from extremely poor bioavailability owing to its poor solubility and poor permeability. The rationale of the present work was to design the drug delivery system capable of overcoming these constraints. Nanoformulation of eprosartan mesylate was developed using ultrasonic wave-assisted liquid-antisolvent technique. Nanoformulation was further freeze dried with the addition of 1% of mannitol resulting in formation of re-dispersible EPM nanopowder. To prove our proof of principle, the re-dispersed nanopowder with z-average particle size 165.2 ± 1.8 nm was evaluated enormously for in-vitro dissolution behaviour and permeability assay through Caco-2 cell model. In-vitro dissolution study was performed at pH 1.2, pH 4.5 and pH 6.8. Result demonstrates enhanced dissolution from EPM nanopowder with negligible pH dependence. Transport studies accomplished using validated Caco-2 based cell model showed 11-fold enhanced apparent permeability of redispersed nanopowder when compared to pure EPM and corresponding physical mixture (p < 0.0001). In-vivo study reveals, exceptionally strong variations in plasma concentration of EPM through nanopowder (62 mg/kg) formulation when compared with physical mixture and pure EPM (62 mg/kg) group. Moreover, study manifests that 5-fold lower dose (12.4 mg/kg) of developed formulation yields higher exposure (4600 ± 36 ng·mL^-1·h) than pure EPM (2349 ± 34 ng·mL^-1·h) and corresponding physical mixture (2456 ± 49 ng·mL^-1·h) at therapeutic dose (62 mg/kg). Further, L-NAME induced hypertensive model was undertaken to investigate effect of reduced dose of EPM nanopowder on systolic blood pressure, biochemical analysis and histopathology of heart. Results revealed pronounced antihypertensive potential of re-dispersed EPM nanopowder at 5-fold lower dose (12.4 mg/kg). In conclusion, our study indicates that nanopowder delivery might be the promising approach for providing enhanced oral bioavailability at lower dose.

Comparative pharmacokinetics of major bioactive components from Puerariae Radix-Gastrodiae Rhizome extracts and their intestinal absorption in rats

Puerariae Radix (PR) and Gastrodiae Rhizome (GR) is frequently used in traditional herbal formulas to treat cardio-cerebral vascular diseases due to their synergistic effects. In this study, to elucidate the action mechanism of PR-GR in vivo, a simple and reliable ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method for simultaneous determination of nine bioactive ingredients from PR-GR in plasma was developed and applied to a comparative pharmacokinetic study following oral administration of PR, GR, and PR-GR aqueous extracts in rats. The effect of GR on the absorption of components of PR was also investigated by single-pass intestinal perfusion study. Results showed that comparing to the single herbs, PR-GR extract significantly increased the systemic exposure of puerarin, 3'-hydroxypuerarin, 3'-methoxypuerarin, 6″-O-xylosylpuerarin, daidzin, genistein, and gastrodin. Moreover, the intestinal absorption of puerarin and daidzin could be improved by GR extract and inhibitors of P-glycoprotein and multidrug resistanceassociated protein 2, respectively. These results indicate that the combination of PR and GR increases the levels of their bioactive ingredients exposed in the blood, and GR increases the absorption of ingredients of PR may by inhibition of the efflux mediated by P-glycoprotein and multidrug resistanceassociated protein 2. This is the first report for the pharmacokinetics and intestinal absorption of PR-GR, which may explain their synergetic effects in the treatment of circulatory systematic diseases and provide a meaningful insight for their clinical applications.

Drug Transport at the Brain and Endothelial Dysfunction in Preeclampsia: Implications and Perspectives

Transport of drugs across biological barriers has been a subject of study for decades. The discovery and characterization of proteins that confer the barrier properties of endothelia and epithelia, including tight junction proteins and membrane transporters belonging to the ATP-binding cassette (ABC) and Solute Carrier (SLC) families, represented a significant step forward into understanding the mechanisms that govern drug disposition. Subsequently, numerous studies, including both pre-clinical approaches and clinical investigations, have been carried out to determine the influence of physiological and pathological states on drug disposition. Importantly, there has been increasing interest in gaining a better understanding of drug disposition during pregnancy, since epidemiological and clinical studies have demonstrated that the use of medications by pregnant women is significant and this condition embodies a series of significant anatomical and physiological modifications, particularly at excretory organs and barrier sites (e.g., placenta, breast) expressing transporter proteins which influence pharmacokinetics. Currently, most of the research in this field has focused on the expression profiling of transporter proteins in trophoblasts and endothelial cells of the placenta, regulation of drug-resistance mechanisms in disease states and pharmacokinetic studies. However, little attention has been placed on the influence that the cerebrovascular dysfunction present in pregnancy-related disorders, such as preeclampsia, might exert on drug disposition in the mother’s brain. This issue is particularly important since recent findings have demonstrated that preeclamptic women suffer from long-term alterations in the integrity of the blood-brain barrier (BBB). In this review we aim to analyze the available evidence regarding the influence of pregnancy on the expression of transporters and TJ proteins in brain endothelial cells, as well the mechanisms that govern the pathophysiological alterations in the BBB of women who experience preeclampsia. Future research efforts should be focused not only on achieving a better understanding of the influence of preeclampsia-associated endothelial dysfunction on drug disposition, but also in optimizing the pharmacological treatments of women suffering pregnancy-related disorders, its comorbidities and to develop new therapies aiming to restore the integrity of the BBB.

Effect of Complexes and Microemulsions on the Permeability of Drugs: Determination Using a New Biomimetic Artificial Membrane

The aim of this work was to predict the permeability of two model drugs, sulfamerazine (SMR) and indomethacin (INM), and to determine the effect on their apparent permeabilities by complexation with cyclodextrins and/or meglumine or incorporation in microemulsions. Permeation experiments were performed using two-chamber diffusion cells with a new composition of bio-mimetic membrane composed of 80% of Lipoid® S100 and 20% of cholesterol in n-octanol 10% w/w solution, at 37 ± 0.5°C and 14,000 rpm. The predictive capacity of the permeability of passive diffusion absorbed compounds was evaluated using 20 drug standards and showed an exponential correlation between the apparent permeability coefficients (P_app) and the fraction absorbed percentages in humans (Fa%), with an R² value of 0.67942 and a constant value of - 4.1 ± 0.8. SMR and INM were classified as Class II and I, respectively, according to the Biopharmaceutical Classification System. These drugs were complexed and incorporated in microemulsions. The Fa% from all the drug products was higher than 90%. SMR in the complexes and both drugs in microemulsions were classified as highly soluble. Thus, SMR and INM incorporated in these pharmaceutical products could be classified as Class I.

Preclinical models for colonic absorption, application to controlled release formulation development

Oral controlled release (CR) formulations have many benefits and have become a valuable resource for the local and systemic administration of drugs. The most important characteristic of these pharmaceutical products is that drug absorption occurs mainly in the colon. Therefore, this review analyses the physiological and physicochemical features that may affect an orally administered CR product, as well as the different strategies to develop a CR dosage form and the methods used to evaluate the formulation efficacy. The models available to study the intestinal permeability and their applicability to colonic permeability determinations are also discussed.

Artificial Lipid Membrane Permeability Method for Predicting Intestinal Drug Transport: Probing the Determining Step in the Oral Absorption of Sulfadiazine; Influence of the Formation of Binary and Ternary Complexes with Cyclodextrins

We propose an in vitro permeability assay by using a modified lipid membrane to predict the in vivo intestinal passive permeability of drugs. Two conditions were tested, one with a gradient pH (pH 5.5 donor/pH 7.4 receptor) and the other with an iso-pH 7.4. The predictability of the method was established by correlating the obtained apparent intestinal permeability coefficients (P_app) and the oral dose fraction absorbed in humans (f_a) of 16 drugs with different absorption properties. The P_app values correlated well with the absorption rates under the two conditions, and the method showed high predictability and good reproducibility. On the other hand, with this method, we successfully predicted the transport characteristics of oral sulfadiazine (SDZ). Also, the tradeoff between the increase in the solubility of SDZ by its complex formation with cyclodextrins and/or aminoacids and its oral permeability was assessed. Results suggest that SDZ is transported through the gastrointestinal epithelium by passive diffusion in a pH-dependent manner. These results support the classification of SDZ as a high/low borderline permeability compound and are in agreement with the Biopharmaceutics Classification Systems (BCS). This conclusion is consistent with the in vivo pharmacokinetic properties of SDZ.

Clinical Implications of P-Glycoprotein Modulation in Drug-Drug Interactions

Drug-drug interactions (DDIs) occur commonly and may lead to severe adverse drug reactions if not handled appropriately. Considerable information to support clinical decision making regarding potential DDIs is available in the literature and through various systems providing electronic decision support for healthcare providers. The challenge for the prescribing physician lies in sorting out the evidence and identifying those drugs for which potential interactions are likely to become clinically manifest. P-glycoprotein (P-gp) is a drug transporting protein that is found in the plasma membranes in cells of barrier and elimination organs, and plays a role in drug absorption and excretion. Increasingly, P-gp has been acknowledged as an important player in potential DDIs and a growing body of information on the role of this transporter in DDIs has become available from research and from the drug approval process. This has led to a clear need for a comprehensive review of P-gp-mediated DDIs with a focus on highlighting the drugs that are likely to lead to clinically relevant DDIs. The objective of this review is to provide information for identifying and interpreting evidence of P-gp-mediated DDIs and to suggest a classification for individual drugs based on both in vitro and in vivo evidence (substrates, inhibitors and inducers). Further, various ways of handling potential DDIs in clinical practice are described and exemplified in relation to drugs interfering with P-gp.

Carrier-Mediated Prodrug Uptake to Improve the Oral Bioavailability of Polar Drugs: An Application to an Oseltamivir Analogue

The goal of this study was to improve the intestinal mucosal cell membrane permeability of the poorly absorbed guanidino analogue of a neuraminidase inhibitor, oseltamivir carboxylate (GOC) using a carrier-mediated strategy. Valyl amino acid prodrug of GOC with isopropyl-methylene-dioxy linker (GOC-ISP-Val) was evaluated as the potential substrate for intestinal oligopeptide transporter, hPEPT1 in Xenopus laevis oocytes heterologously expressing hPEPT1, and an intestinal mouse perfusion system. The diastereomers of GOC-ISP-Val were assessed for chemical and metabolic stability. Permeability of GOC-ISP-Val was determined in Caco-2 cells and mice. Diastereomer 2 was about 2 times more stable than diastereomer 1 in simulated intestinal fluid and rapidly hydrolyzed to the parent drug in cell homogenates. The prodrug had a 9 times-enhanced apparent permeability (P(app)) in Caco-2 cells compared with the parent drug. Both diastereomer exhibited high effective permeability (P(eff)) in mice, 6.32 ± 3.12 and 5.20 ± 2.81 × 10(-5) cm/s for diastereomer 1 and 2, respectively. GOC-ISP-Val was found to be a substrate of hPEPT1. Overall, this study indicates that the prodrug, GOC-ISP-Val, seems to be a promising oral anti-influenza agent that has sufficient stability at physiologically relevant pHs before absorption, significantly improved permeability via hPEPT1 and potentially rapid activation in the intestinal cells.

In vivo evaluation of supersaturation/precipitation/re-dissolution behavior of cinnarizine, a lipophilic weak base, in the gastrointestinal tract: the key process of oral absorption

The aim of this study is to evaluate how supersaturation, precipitation, and re-dissolution processes influence the intestinal absorption of cinnarizine (CNZ), a lipophilic weak base, by monitoring its plasma and luminal concentration-time profile, after oral administration as a HCl solution containing fluorescein isothiocyanate dextran (FD-4), a non-absorbable marker. In the in vitro pH shift experiment, the supersaturation stability was significantly lower when the higher-concentration solution of CNZ (pH1.5) was added to the simulated intestinal fluid. However, although the in vivo bioavailability after oral administration of high and low dose as HCl solutions was greatly improved compared to those as neutral suspensions, the difference in the supersaturation stability was not reflected in the improvement of the in vivo bioavailability. Analysis of CNZ and FD-4 concentrations in each segment of the gastrointestinal tract revealed that most of the CNZ precipitated in the duodenum after gastric emptying, and supersaturation was observed only in the duodenum. Thereafter, the precipitate was rapidly re-dissolved and absorbed in the upper and middle small intestine. The rapid re-dissolution may be caused by smaller particles of the precipitate. In this case, it is considered that the key process for the absorption of CNZ was re-dissolution, not supersaturation. Therefore, different supersaturation stabilities in different doses observed in in vitro precipitation experiment was not reflected to in vivo absorption. These findings may be useful to design efficient supersaturable formulations and to validate and improve current prediction methods.

Absorption and disposition of naringenin and quercetin after simultaneous administration via intestinal perfusion in mice

As common constituents of vegetables, naringenin and quercetin are ingested together; for a clearer understanding of their bioavailability it is insightful to study them together.

Transepithelial Transport of PAMAM Dendrimers Across Isolated Human Intestinal Tissue

Poly(amido amine) (PAMAM) dendrimers have shown transepithelial transport across intestinal epithelial barrier in rats and across Caco-2 cell monolayers. Caco-2 models innately lack mucous barriers, and rat isolated intestinal tissue has been shown to overestimate human permeability. This study is the first report of transport of PAMAM dendrimers across isolated human intestinal epithelium. It was observed that FITC labeled G4-NH2 and G3.5-COOH PAMAM dendrimers at 1 mM concentration do not have a statistically higher permeability compared to free FITC controls in isolated human jejunum and colonic tissues. Mannitol permeability was increased at 10 mM concentrations of G3.5-COOH and G4-NH2 dendrimers. Significant histological changes in human colonic and jejunal tissues were observed at G3.5-COOH and G4-NH2 concentrations of 10 mM implying that dose limiting toxicity may occur at similar concentrations in vivo. The permeability through human isolated intestinal tissue in this study was compared to previous rat and Caco-2 permeability data. This study implicates that PAMAM dendrimer oral drug delivery may be feasible, but it may be limited to highly potent drugs.

Drug gastrointestinal absorption in rat: Strain and gender differences

Predictive animal models of intestinal drug absorption are essential tools in drug development to identify compounds with promising biopharmaceutical properties. In situ perfusion absorption studies are routinely used in the preclinical setting to screen drug candidates. The objective of this work is to explore the differences in magnitude and variability on intestinal absorption associated with rat strain and gender. Metoprolol and Verapamil absorption rate coefficients were determined using the in situ closed loop perfusion model in four strains of rats and in both genders. Strains used were Sprague-Dawley, Wistar-Han, Wistar-Unilever, Long-Evans and CD∗IGS. In the case of Metoprolol only CD∗IGS and Wistar Unilever showed differences between males and females. For Verapamil, Wistar Han and Sprague-Dawley strains do not show differences between male and female rats. That means that in these strains permeability data from male and female could be combined. In male rats, which are commonly used for permeability estimation, there were differences for Metoprolol permeability between Sprague-Dawley (with lower permeability values) and the other strains, while for Verapamil Sprague-Dawley and Wistar-Han showed the lower permeability values. In conclusion, the selection of rat's strain and gender for intestinal absorption experiments is a relevant element during study design and data from different strains may not be always comparable.

High gastrointestinal permeability and local metabolism of naringenin: influence of antibiotic treatment on absorption and metabolism

The present study aims to determine the permeability of naringenin in the stomach, small intestine and colon, to evaluate intestinal and hepatic first-pass metabolism, and to study the influence of the microbiota on the absorption and disposition of naringenin (3.5 μg/ml). A single-pass intestinal perfusion model in mice (n 4-6) was used. Perfusate (every 10 min), blood (at 60 min) and bile samples were taken and analysed to evaluate the presence of naringenin and its metabolites by an HPLC-MS/MS method. To study the influence of the microbiota on the bioavailability of naringenin, a group of animals received the antibiotic rifaximin (50 mg/kg per d) for 5 d, and naringenin permeability was determined in the colon. Naringenin was absorbed well throughout the gastrointestinal tract but mainly in the small intestine and colon (mean permeability coefficient 7.80 (SD 1.54) × 10(-4) cm/s and 5.49 (SD 1.86) × 10(-4) cm/s, respectively), at a level similar to the highly permeable compound, naproxen (6.39 (SD 1.23) × 10(-4) cm/s). According to the high amounts of metabolites found in the perfusate compared to the bile and plasma, naringenin underwent extensive intestinal first-pass metabolism, and the main metabolites excreted were sulfates (84.00 (SD 12.14)%), followed by glucuronides (8.40 (SD 5.67)%). Phase II metabolites were found in all perfusates from 5 min of sampling. Mice treated with rifaximin showed a decrease in naringenin permeability and in the amounts of 4-hydroxyhippuric acid and hippuric acid in the lumen. Naringenin was well absorbed throughout the gastrointestinal tract and its poor bioavailability was due mainly to high intestinal metabolism.

Comprehensive cytotoxic evaluation of morin, a bioflavonoid against verapamil on rat gastrointestinal epithelium for novel pharmaceutical application involving P-glycoprotein inhibition

OBJECTIVE

In this study, a comprehensive and comparative cytotoxic evaluation of morin against verapamil on rat intestinal epithelium as P-gp inhibitors through in-vitro gastrointestinal short-term toxicity assays involving permeability studies for safety evaluation was investigated.

METHODS

In this study, the effect of morin (1 mM or 10 mM) or verapamil (1 mM or 10 mM) or sodium deoxycholate (10 mM) was investigated on intestinal epithelium and isolated brush border membrane using biomarker assays. Cytotoxicity was determined using 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT) assay. The nutrients transport was assessed using everted sacs studies. Paracellular permeability was measured using Lucifer yellow, followed by morphometric analysis of intestinal sacs.

KEY FINDINGS

Our results indicated that morin was effective in maintaining cell viability with no significant changes (P > 0.05) in the activity of intestinal brush border markers, membrane integrity and morphometric analysis as compared with control. On the contrary, dramatic (P < 0.01) changes were noticed in the release of membrane markers, cell viability and surface characteristics of intestinal segments when treated with verapamil or sodium deoxycholate as compared with control or morin.

CONCLUSIONS

Our findings confirm that morin is non-toxic to rat intestinal epithelium against verapamil demonstrating the potential use of bioflavonoid as safe and novel pharmaceutical adjuvant as P-gp inhibitor.

Intestinal permeability study of minoxidil: assessment of minoxidil as a high permeability reference drug for biopharmaceutics classification

The purpose of this study was to evaluate minoxidil as a high permeability reference drug for Biopharmaceutics Classification System (BCS). The permeability of minoxidil was determined in in situ intestinal perfusion studies in rodents and permeability studies across Caco-2 cell monolayers. The permeability of minoxidil was compared with that of metoprolol, an FDA reference drug for BCS classification. In rat perfusion studies, the permeability of minoxidil was somewhat higher than that of metoprolol in the jejunum, while minoxidil showed lower permeability than metoprolol in the ileum. The permeability of minoxidil was independent of intestinal segment, while the permeability of metoprolol was region-dependent. Similarly, in mouse perfusion study, the jejunal permeability of minoxidil was 2.5-fold higher than that of metoprolol. Minoxidil and metoprolol showed similar permeability in Caco-2 study at apical pH of 6.5 and basolateral pH of 7.4. The permeability of minoxidil was independent of pH, while metoprolol showed pH-dependent transport in Caco-2 study. Minoxidil exhibited similar permeability in the absorptive direction (AP-BL) in comparison with secretory direction (BL-AP), while metoprolol had higher efflux ratio (ER > 2) at apical pH of 6.5 and basolateral pH of 7.4. No concentration-dependent transport was observed for either minoxidil or metoprolol transport in Caco-2 study. Verapamil did not alter the transport of either compounds across Caco-2 cell monolayers. The permeability of minoxidil was independent of both pH and intestinal segment in intestinal perfusion studies and Caco-2 studies. Caco-2 studies also showed no involvement of carrier mediated transport in the absorption process of minoxidil. These results suggest that minoxidil may be an acceptable reference drug for BCS high permeability classification. However, minoxidil exhibited higher jejunal permeability than metoprolol and thus to use minoxidil as a reference drug would raise the permeability criteria for BCS high permeability classification.

How drugs get into cells: tested and testable predictions to help discriminate between transporter-mediated uptake and lipoidal bilayer diffusion

One approach to experimental science involves creating hypotheses, then testing them by varying one or more independent variables, and assessing the effects of this variation on the processes of interest. We use this strategy to compare the intellectual status and available evidence for two models or views of mechanisms of transmembrane drug transport into intact biological cells. One (BDII) asserts that lipoidal phospholipid Bilayer Diffusion Is Important, while a second (PBIN) proposes that in normal intact cells Phospholipid Bilayer diffusion Is Negligible (i.e., may be neglected quantitatively), because evolution selected against it, and with transmembrane drug transport being effected by genetically encoded proteinaceous carriers or pores, whose “natural” biological roles, and substrates are based in intermediary metabolism. Despite a recent review elsewhere, we can find no evidence able to support BDII as we can find no experiments in intact cells in which phospholipid bilayer diffusion was either varied independently or measured directly (although there are many papers where it was inferred by seeing a covariation of other dependent variables). By contrast, we find an abundance of evidence showing cases in which changes in the activities of named and genetically identified transporters led to measurable changes in the rate or extent of drug uptake. PBIN also has considerable predictive power, and accounts readily for the large differences in drug uptake between tissues, cells and species, in accounting for the metabolite-likeness of marketed drugs, in pharmacogenomics, and in providing a straightforward explanation for the late-stage appearance of toxicity and of lack of efficacy during drug discovery programmes despite macroscopically adequate pharmacokinetics. Consequently, the view that Phospholipid Bilayer diffusion Is Negligible (PBIN) provides a starting hypothesis for assessing cellular drug uptake that is much better supported by the available evidence, and is both more productive and more predictive.

Provisional in-silico biopharmaceutics classification (BCS) to guide oral drug product development

The main objective of this work was to investigate in-silico predictions of physicochemical properties, in order to guide oral drug development by provisional biopharmaceutics classification system (BCS). Four in-silico methods were used to estimate LogP: group contribution (CLogP) using two different software programs, atom contribution (ALogP), and element contribution (KLogP). The correlations (r(2)) of CLogP, ALogP and KLogP versus measured LogP data were 0.97, 0.82, and 0.71, respectively. The classification of drugs with reported intestinal permeability in humans was correct for 64.3%-72.4% of the 29 drugs on the dataset, and for 81.82%-90.91% of the 22 drugs that are passively absorbed using the different in-silico algorithms. Similar permeability classification was obtained with the various in-silico methods. The in-silico calculations, along with experimental melting points, were then incorporated into a thermodynamic equation for solubility estimations that largely matched the reference solubility values. It was revealed that the effect of melting point on the solubility is minor compared to the partition coefficient, and an average melting point (162.7 °C) could replace the experimental values, with similar results. The in-silico methods classified 20.76% (± 3.07%) as Class 1, 41.51% (± 3.32%) as Class 2, 30.49% (± 4.47%) as Class 3, and 6.27% (± 4.39%) as Class 4. In conclusion, in-silico methods can be used for BCS classification of drugs in early development, from merely their molecular formula and without foreknowledge of their chemical structure, which will allow for the improved selection, engineering, and developability of candidates. These in-silico methods could enhance success rates, reduce costs, and accelerate oral drug products development.

Study on biopharmaceutics classification and oral bioavailability of a novel multikinase inhibitor NCE for cancer therapy

Specific biopharmaceutics classification investigation and study on phamacokinetic profile of a novel drug candidate (2-methylcarbamoyl-4-{4-[3- (trifluoromethyl) benzamido] phenoxy} pyridinium 4-methylbenzenesulfonate monohydrate, NCE) were carried out. Equilibrium solubility and intrinsic dissolution rate (IDR) of NCE were estimated in different phosphate buffers. Effective intestinal permeability (P(eff)) of NCE was determined using single-pass intestinal perfusion technique in rat duodenum, jejunum and ileum at three concentrations. Theophylline (high permeability) and ranitidine (low permeability) were also applied to access the permeability of NCE as reference compounds. The bioavailability after intragastrical and intravenous administration was measured in beagle dogs. The solubility of NCE in tested phosphate buffers was quite low with the maximum solubility of 81.73 μg/mL at pH 1.0. The intrinsic dissolution ratio of NCE was 1 × 10⁻⁴ mg·min⁻¹·cm⁻². The P(eff) value of NCE in all intestinal segments was more proximate to the high-permeability reference theophylline. Therefore, NCE was classified as class II drug according to Biopharmaceutics Classification System due to its low solubility and high intestinal permeability. In addition, concentration-dependent permeability was not observed in all the segments, indicating that there might be passive transportation for NCE. The absolute oral bioavailability of NCE in beagle dogs was 26.75%. Therefore, dissolution promotion will be crucial for oral formulation development and intravenous administration route will also be suggested for further NCE formulation development. All the data would provide a reference for biopharmaceutics classification research of other novel drug candidates.

The low/high BCS permeability class boundary: physicochemical comparison of metoprolol and labetalol

Although recognized as overly conservative, metoprolol is currently the common low/high BCS permeability class boundary reference compound, while labetalol was suggested as a potential alternative. The purpose of this study was to identify the various characteristics that the optimal marker should exhibit, and to investigate the suitability of labetalol as the permeability class reference drug. Labetalol's BCS solubility class was determined, and its physicochemical properties and intestinal permeability were thoroughly investigated, both in vitro and in vivo in rats, considering the complexity of the whole of the small intestine. Labetalol was found to be unequivocally a high-solubility compound. In the pH range throughout the small intestine (6.5-7.5), labetalol exhibited pH-dependent permeability, with higher permeability at higher pH values. While in vitro octanol-buffer partitioning (Log D) values of labetalol were significantly higher than those of metoprolol, the opposite was evident in the in vitro PAMPA permeability assay. The results of the in vivo perfusion studies in rats lay between the two contradictory in vitro studies; metoprolol was shown to have moderately higher rat intestinal permeability than labetalol. Theoretical distribution of the ionic species of the drugs was in corroboration with the experimental in vitro and the in vivo data. We propose three characteristics that the optimal permeability class reference drug should exhibit: (1) fraction dose absorbed in the range of 90%; (2) the optimal marker drug should be absorbed largely via passive transcellular permeability, with no/negligible carrier-mediated active intestinal transport (influx or efflux); and (3) the optimal marker drug should preferably be nonionizable. The data presented in this paper demonstrate that neither metoprolol nor labetalol can be regarded as optimal low/high-permeability class boundary standard. While metoprolol is too conservative due to its complete absorption, labetalol has been shown to be a substrate for P-gp-mediated efflux transport, and both drugs exhibit significant segmental-dependent permeability along the gastrointestinal tract. Nevertheless, the use of metoprolol as the marker compound does not carry a risk of bioinequivalence: Peff value similar to or higher than metoprolol safely indicates high-permeability classification. On the other hand, a more careful data analysis is needed if labetalol is used as the reference compound.

Distinguishing between the permeability relationships with absorption and metabolism to improve BCS and BDDCS predictions in early drug discovery

The biopharmaceutics classification system (BCS) and biopharmaceutics drug distribution classification system (BDDCS) are complementary classification systems that can improve, simplify, and accelerate drug discovery, development, and regulatory processes. Drug permeability has been widely accepted as a screening tool for determining intestinal absorption via the BCS during the drug development and regulatory approval processes. Currently, predicting clinically significant drug interactions during drug development is a known challenge for industry and regulatory agencies. The BDDCS, a modification of BCS that utilizes drug metabolism instead of intestinal permeability, predicts drug disposition and potential drug–drug interactions in the intestine, the liver, and most recently the brain. Although correlations between BCS and BDDCS have been observed with drug permeability rates, discrepancies have been noted in drug classifications between the two systems utilizing different permeability models, which are accepted as surrogate models for demonstrating human intestinal permeability by the FDA. Here, we recommend the most applicable permeability models for improving the prediction of BCS and BDDCS classifications. We demonstrate that the passive transcellular permeability rate, characterized by means of permeability models that are deficient in transporter expression and paracellular junctions (e.g., PAMPA and Caco-2), will most accurately predict BDDCS metabolism. These systems will inaccurately predict BCS classifications for drugs that particularly are substrates of highly expressed intestinal transporters. Moreover, in this latter case, a system more representative of complete human intestinal permeability is needed to accurately predict BCS absorption.

The dipeptide monoester prodrugs of floxuridine and gemcitabine-feasibility of orally administrable nucleoside analogs

Dipeptide monoester prodrugs of floxuridine and gemcitabine were synthesized. Their chemical stability in buffers, enzymatic stability in cell homogenates, permeability in mouse intestinal membrane along with drug concentration in mouse plasma, and anti-proliferative activity in cancer cells were determined and compared to their parent drugs. Floxuridine prodrug was more enzymatically stable than floxuridine and the degradation from prodrug to parent drug works as the rate-limiting step. On the other hand, gemcitabine prodrug was less enzymatically stable than gemcitabine. Those dipeptide monoester prodrugs exhibited 2.4- to 48.7-fold higher uptake than their parent drugs in Caco-2, Panc-1, and AsPC-1 cells. Floxuridine and gemcitabine prodrugs showed superior permeability in mouse jejunum to their parent drugs and exhibited the higher drug concentration in plasma after in situ mouse perfusion. Cell proliferation assays in ductal pancreatic cancer cells, AsPC-1 and Panc-1, indicated that dipeptide prodrugs of floxuridine and gemcitabine were more potent than their parent drugs. The enhanced potency of nucleoside analogs was attributed to their improved membrane permeability. The prodrug forms of 5′-l-phenylalanyl-l-tyrosyl-floxuridine and 5′-l-phenylalanyl-l-tyrosyl-gemcitabine appeared in mouse plasma after the permeation of intestinal membrane and the first-pass effect, suggesting their potential for the development of oral dosage form for anti-cancer agents.

Evaluating the potential of cubosomal nanoparticles for oral delivery of amphotericin B in treating fungal infection

The oral administration of amphotericin B (AmB) has a major drawback of poor bioavailability. The aim of this study was to investigate the potential of glyceryl monoolein (GMO) cubosomes as lipid nanocarriers to improve the oral efficacy of AmB. Antifungal efficacy was determined in vivo in rats after oral administration, to investigate its therapeutic use. The human colon adenocarcinoma cell line (Caco-2) was used in vitro to evaluate transport across a model of the intestinal barrier. In vivo antifungal results showed that AmB, loaded in GMO cubosomes, could significantly enhance oral efficacy, compared against Fungizone®, and that during a 2 day course of dosage 10 mg/kg the drug reached effective therapeutic concentrations in renal tissue for treating fungal infections. In the Caco-2 transport studies, GMO cubosomes resulted in a significantly larger amount of AmB being transported into Caco-2 cells, via both clathrin- and caveolae-mediated endocytosis, but not macropinocytosis. These results suggest that GMO cubosomes, as lipid nanovectors, could facilitate the oral delivery of AmB.