Epithelial transport of drugs in cell culture. I: A model for studying the passive diffusion of drugs over intestinal absorptive (Caco-2) cells

Infant and adult human intestinal enteroids are morphologically and functionally distinct

Human intestinal enteroids (HIEs) are gaining recognition as physiologically relevant models of the intestinal epithelium. While HIEs from adults are used extensively in biomedical research, few studies have used HIEs from infants. Considering the dramatic developmental changes that occur during infancy, it is important to establish models that represent infant intestinal characteristics and physiological responses. We established jejunal HIEs from infant surgical samples and performed comparisons to jejunal HIEs from adults using RNA sequencing (RNA-Seq) and morphologic analyses. We then validated differences in key pathways through functional studies and determined whether these cultures recapitulate known features of the infant intestinal epithelium. RNA-Seq analysis showed significant differences in the transcriptome of infant and adult HIEs, including differences in genes and pathways associated with cell differentiation and proliferation, tissue development, lipid metabolism, innate immunity, and biological adhesion. Validating these results, we observed a higher abundance of cells expressing specific enterocyte, goblet cell, and enteroendocrine cell markers in differentiated infant HIE monolayers, and greater numbers of proliferative cells in undifferentiated 3D cultures. Compared to adult HIEs, infant HIEs portray characteristics of an immature gastrointestinal epithelium including significantly shorter cell height, lower epithelial barrier integrity, and lower innate immune responses to infection with an oral poliovirus vaccine. HIEs established from infant intestinal tissues reflect characteristics of the infant gut and are distinct from adult cultures. Our data support the use of infant HIEs as an ex vivo model to advance studies of infant-specific diseases and drug discovery for this population.

IMPORTANCE

Tissue or biopsy stem cell-derived human intestinal enteroids are increasingly recognized as physiologically relevant models of the human gastrointestinal epithelium. While enteroids from adults and fetal tissues have been extensively used for studying many infectious and non-infectious diseases, there are few reports on enteroids from infants. We show that infant enteroids exhibit both transcriptomic and morphological differences compared to adult cultures. They also differ in functional responses to barrier disruption and innate immune responses to infection, suggesting that infant and adult enteroids are distinct model systems. Considering the dramatic changes in body composition and physiology that begin during infancy, tools that appropriately reflect intestinal development and diseases are critical. Infant enteroids exhibit key features of the infant gastrointestinal epithelium. This study is significant in establishing infant enteroids as age-appropriate models for infant intestinal physiology, infant-specific diseases, and responses to pathogens.

Improving the Accuracy of Permeability Data to Gain Predictive Power: Assessing Sources of Variability in Assays Using Cell Monolayers

The ability to predict the rate of permeation of new compounds across biological membranes is of high importance for their success as drugs, as it determines their efficacy, pharmacokinetics, and safety profile. In vitro permeability assays using Caco-2 monolayers are commonly employed to assess permeability across the intestinal epithelium, with an extensive number of apparent permeability coefficient (Papp) values available in the literature and a significant fraction collected in databases. The compilation of these Papp values for large datasets allows for the application of artificial intelligence tools for establishing quantitative structure-permeability relationships (QSPRs) to predict the permeability of new compounds from their structural properties. One of the main challenges that hinders the development of accurate predictions is the existence of multiple Papp values for the same compound, mostly caused by differences in the experimental protocols employed. This review addresses the magnitude of the variability within and between laboratories to interpret its impact on QSPR modelling, systematically and quantitatively assessing the most common sources of variability. This review emphasizes the importance of compiling consistent Papp data and suggests strategies that may be used to obtain such data, contributing to the establishment of robust QSPRs with enhanced predictive power.

Gastroretentive fibrous dosage forms for prolonged delivery of sparingly-soluble tyrosine kinase inhibitors. Part 4: Experimental validation of the models of drug concentration in blood

In this final part, the models of drug concentration in blood developed in Part 3 are validated on dogs. Both slow-release gastroretentive fibrous and immediate-release particulate dosage forms containing 200 mg nilotinib were tested. After administering, the fibrous dosage form expanded linearly with time in the stomach, to about 1.5 times the initial radius by 4 h. The expanded dosage form fractured after 10 h, and then passed into the intestines. The drug concentration in blood exhibited a broad peak with a maximum of 0.51 μg/ml and a width at half-height of 10.2 h. By contrast, after administering the immediate-release capsule the drug concentration in blood exhibited a sharp peak with a maximum of 0.68 μg/ml and a width at half-height of just 3.6 h. The experimental data validate the theoretical models reasonably. The gastroretentive fibrous dosage forms designed in this study enable a steady drug concentration in blood for increasing the efficacy and mitigating side effects of drug therapies.

Gastroretentive fibrous dosage forms for prolonged delivery of sparingly-soluble tyrosine kinase inhibitors. Part 3: Theoretical models of drug concentration in blood

In this part, drug concentration in blood after ingesting slow-release gastroretentive fibrous dosage forms and immediate-release particulate forms is modeled. The tyrosine kinase inhibitor nilotinib, which is slightly soluble in low-pH gastric fluid but practically insoluble in pH-neutral intestinal fluid is used as drug. The models suggest that upon ingestion, the fibrous dosage form expands, is retained in the stomach for prolonged time, and releases drug into the gastric fluid at a constant rate. The released drug molecules flow into the duodenum with the gastric fluid, and are absorbed by the blood. The drug is eliminated from the blood by the liver at a rate proportional to its concentration. Eventually, the elimination and absorption rates will be equal, and the drug concentration in blood plateaus out. After the gastric residence time drug absorption stops, and the drug concentration in blood drops to zero. By contrast, after administering an immediate-release particulate dosage form the drug particles are swept out of the stomach rapidly, and drug absorption stops much earlier. The drug concentration in blood rises and falls without attaining steady state. The gastroretentive fibrous dosage forms enable a constant drug concentration in blood for drugs that are insoluble in intestinal fluids.

Transcriptomic and western blot characterisation of the human CLEFF4 clone, a new rapid cell line replacement for the Caco2 model

The CLEFF4 sub clone from stock late passage Caco2 cells has a unique property of being able to develop polarised cell monolayers with high P-gp expression and tight junctions much quicker than the original cell line. Instead of being useful for transport studies 21-24 days after initiating culture, the CLEFF4 cell line matures in 5-6 days with tight junctions surpassing that of 3 week old Caco2 cells in that time frame [1]. This has enabled the CLEFF4 cell line to provide measures of apparent permeability for potential drug candidates, so important for pre-clinical drug development, 4 times faster than the original cell line. RNA samples were collected and analysed at days 4 and 7 of culture over a 3 year period and had full RNA transcriptome analysed by the ranaseq.eu open bioinformatics platform. Protein was also collected from day 4 to day 22 of culture. Differential expression data from the FASTQ files have shown significant differences in expression in multiple genes involved with drug efflux, tight junctions, phase 2 metabolism and growth factors, which have been confirmed from protein determination that may hold the key to understanding accelerated human cell maturation. These gene expression results may be significant for other tissues beyond the gastrointestinal tract, and potentially for accelerated cell growth for the new field of laboratory grown tissues for organ replacement. The data also confirms the different genetic expression in CLEFF4 cells compared to Caco2 and the stable nature of the different expression over many years.

Individualized Pharmacotherapy Utilizing Genetic Biomarkers and Novel In Vitro Systems As Predictive Tools for Optimal Drug Development and Treatment

In the area of drug development and clinical pharmacotherapy, a profound understanding of the pharmacokinetics and potential adverse reactions associated with the drug under investigation is paramount. Essential to this endeavor is a comprehensive understanding about interindividual variations in absorption, distribution, metabolism, and excretion (ADME) genetics and the predictive capabilities of in vitro systems, shedding light on metabolite formation and the risk of adverse drug reactions (ADRs). Both the domains of pharmacogenomics and the advancement of in vitro systems are experiencing rapid expansion. Here we present an update on these burgeoning fields, providing an overview of their current status and illuminating potential future directions. SIGNIFICANCE STATEMENT: There is very rapid development in the area of pharmacogenomics and in vitro systems for predicting drug pharmacokinetics and risk for adverse drug reactions. We provide an update of the current status of pharmacogenomics and developed in vitro systems on these aspects aimed to achieve a better personalized pharmacotherapy.

Sirt2 inhibition improves gut epithelial barrier integrity and protects mice from colitis

Sirt2 is a nicotinamide adenine dinucleotide (NAD+)-dependent protein lysine deacylase that can remove both acetyl group and long-chain fatty acyl groups from lysine residues of many proteins. It was reported to affect inflammatory bowel disease (IBD) symptoms in a mouse model. However, conflicting roles were reported, with genetic knockout aggravating while pharmacological inhibition alleviating IBD symptoms. These seemingly conflicting reports cause confusion and deter further efforts in developing Sirt2 inhibitors as a potential treatment strategy for IBD. We investigated these conflicting reports and elucidated the role of Sirt2 in the mouse model of IBD. We essentially replicated these conflicting results and confirmed that Sirt2 inhibitors' protective effect is not through off-targets as two very different Sirt2 inhibitors (TM and AGK2) showed similar protection in the IBD mouse model. We believe that the differential effects of inhibitors and knockout are due to the fact that the Sirt2 inhibitors only inhibit some but not all the activities of Sirt2. This hypothesis is confirmed by the observation that a PROTAC degrader of Sirt2 did not protect mice in the IBD model, similar to Sirt2 knockout. Our study provides an interesting example where genetic knockout and pharmacological inhibition do not align and emphasizes the importance of developing substrate-dependent inhibitors. Importantly, we showed that the effect of Sirt2 inhibition in IBD is through regulating the gut epithelium barrier by inhibiting Arf6-mediated endocytosis of E-cadherin, a protein important for the intestinal epithelial integrity. This mechanistic understanding further supports Sirt2 as a promising therapeutic target for treating IBD.

Detailed survey of an in vitro intestinal epithelium model by single-cell transcriptomics

The co-culture of two adult human colorectal cancer cell lines, Caco-2 and HT29, on Transwell is commonly used as an in vitro gut mimic, yet the translatability of insights from such a system to adult human physiological contexts is not fully characterized. Here, we used single-cell RNA sequencing on the co-culture to obtain a detailed survey of cell type heterogeneity in the system and conducted a holistic comparison with human physiology. We identified the intestinal stem cell-, transit amplifying-, enterocyte-, goblet cell-, and enteroendocrine-like cells in the system. In general, the co-culture was fetal intestine-like, with less variety of gene expression compared to the adult human gut. Transporters for major types of nutrients were found in the majority of the enterocytes-like cells in the system. TLR 4 was not expressed in the sample, indicating that the co-culture model is incapable of mimicking the innate immune aspect of the human epithelium.

Balanced Permeability Index: A Multiparameter Index for Improved In Vitro Permeability

The optimization of passive permeability is a key objective for orally available small molecule drug candidates. For drugs targeting the central nervous system (CNS), minimizing P-gp-mediated efflux is an additional important target for optimization. The physicochemical properties most strongly associated with high passive permeability and lower P-gp efflux are size, polarity, and lipophilicity. In this study, a new metric called the Balanced Permeability Index (BPI) was developed that combines these three properties. The BPI was found to be more effective than any single property in classifying molecules based on their permeability and efflux across a diverse range of chemicals and assays. BPI is easy to understand, allowing researchers to make decisions about which properties to prioritize during the drug development process.

Synthesis of salcaprozate sodium and its significance in enhancing pancreatic kininogenase absorption performance

We conducted pharmacokinetic research wherein salcaprozate sodium (SNAC) was utilized as a penetration enhancer by incorporating it into pancreatic kininogenase (PK) to improve the bioavailability of pancreatic kininogenase enteric-coated tablets. We conducted in vitro studies on PK using the Caco-2 cell model and quantified PK levels using the enzyme-linked immunosorbent assay (ELISA) method. We conducted methodological verification by blending SNAC and PK powders into enteric-coated capsules, and studied the pharmacokinetic characteristics. Based on the PK transport assay, the cumulative permeation rates of the test group that employed a SNAC to PK ratio of 32:1, 16:1, 8:1, 4:1, and 2:1 were 13.574%, 7.597%, 10.653%, 3.755%, and 2.523%, respectively. We conducted a uniformity test on the powder that contained a blend of SNAC and PK. The relative standard deviations (RSDs) for both the power containing SNAC and the power not containing SNAC were less than 10%. Based on the methodological verification, in vivo pharmacokinetic study of PK met the experimental requirements. As indicated by the results of in vivo pharmacokinetic research on rats, the test group (This group used SNAC) had a PK AUC0-12 h of 5679.747 ng/L*h and t1/2 of 4.569 h, while the control group (This group did not use SNAC) had a PK AUC0-12 h of 4639.665 ng/L*h and t1/2 of 3.13 h. This study has established a low-cost, environmentally friendly, and safe SNAC synthesis route with high process yield suitable for industrial production. SNAC demonstrates an absorption-enhancing effect on PK, and the optimal ratio of SNAC to PK is determined to be 32:1.

Repetitive head trauma and apoE4 induce chronic cerebrovascular alterations that impair tau elimination from the brain

Repetitive mild traumatic brain injuries (r-mTBI) sustained in the military or contact sports have been associated with the accumulation of extracellular tau in the brain, which may contribute to the pathogenesis of neurodegenerative tauopathies. The expression of the apolipoprotein E4 (apoE4) isoform has been associated with higher levels of tau in the brain, and worse clinical outcomes after r-mTBI, though the influence of apoE genotype on extracellular tau dynamics in the brain is poorly understood. We recently demonstrated that extracellular tau can be eliminated across blood-brain barrier (BBB), which is progressively impaired following r-mTBI. The current studies investigated the influence of repetitive mild TBI (r-mTBI) and apoE genotype on the elimination of extracellular solutes from the brain. Following intracortical injection of biotin-labeled tau into humanized apoE-Tr mice, the levels of exogenous tau residing in the brain of apoE4 mice were elevated compared to other isoforms, indicating reduced tau elimination. Additionally, we found exposure to r-mTBI increased tau residence in apoE2 mice, similar to our observations in E2FAD animals. Each of these findings may be the result of diminished tau efflux via LRP1 at the BBB, as LRP1 inhibition significantly reduced tau uptake in endothelial cells and decreased tau transit across an in vitro model of the BBB (basolateral-to-apical). Notably, we showed that injury and apoE status, (particularly apoE4) resulted in chronic alterations in BBB integrity, pericyte coverage, and AQP4 polarization. These aberrations coincided with an atypical reactive astrocytic gene signature indicative of diminished CSF-ISF exchange. Our work found that CSF movement was reduced in the chronic phase following r-mTBI (>18 months post injury) across all apoE genotypes. In summary, we show that apoE genotype strongly influences cerebrovascular homeostasis, which can lead to age-dependent deficiencies in the elimination of toxic proteins from the brain, like tau, particularly in the aftermath of head trauma.

In vitro and in vivo pharmacokinetics, disposition, and drug-drug interaction potential of tinengotinib (TT-00420), a promising investigational drug for treatment of cholangiocarcinoma and other solid tumors

Early-stage clinical evaluation of tinengotinib (TT-00420) demonstrated encouraging preliminary efficacies in multiple types of refractory cancers, including fibroblast growth factor receptors (FGFR) inhibitors relapsed cholangiocarcinoma (CCA), castrate-resistant prostate cancer (CRPC), and HR+/HER2- breast cancer and triple negative breast cancer (TNBC). To further evaluate drug-like properties of the drug candidate, it is imperative to understand its metabolism and pharmacokinetic properties. This manuscript presented the investigation results of in vitro permeability, plasma protein binding, metabolic stability, metabolite identification, and drug-drug interaction of tinengotinib. Preclinical ADME (absorption, distribution, excretion, and metabolism) studies in rats and dogs was also conducted using a radioactive labeled tinengotinib, [14C]tinengotinib. Tinengotinib was found to have high permeability and high plasma protein binding and equally distributed between blood and plasma. There were no unique metabolites in human liver microsomes and tinengotinib showed moderate hepatic clearance. Tinengotinib is neither a potential inhibitor nor an inducer of P450 enzymes at clinically relevant concentrations, and unlikely to cause drug-drug interactions when used in combination with other drugs mediated by a key transporter, either as victim or perpetrator. Taken together, tinengotinib demonstrated a minimal risk of clinically relevant drug-drug interactions. Tinengotinib showed good oral bioavailability and dose-dependent exposures in both rat and dog after oral administration. The total radioactivity was largely distributed in the gastrointestinal system and liver, and tinengotinib could not easily pass through the blood-brain barrier. The major drug-related component in rat and dog plasma was unchanged drug (>89 %) with primary route of elimination via feces (>93 % of the dose) and minor via renal excretion (<4 % of the dose). Tinengotinib metabolism is mediated largely by CYP3A4, with minor contributions from CYP2D6 and CYP2C8. Major metabolic pathways include oxidation, oxidative cleavage of the morpholine ring, glucuronide and glutathione conjugations. The overall preclinical pharmacokinetics profile supported the selection and development of tinengotinib as a clinical candidate.

Wheat germ agglutinin conjugated chitosan nanoparticles for gemcitabine delivery in MCF-7 cells; synthesis, characterisation and in vitro cytotoxicity studies

OBJECTIVE AND AIM

Numerous clinical trials indicated combination regimens containing gemcitabine could extend progression-free survival of breast cancer patients without increasing the incidence of serious adverse effects. Orally administered gemcitabine is being metabolized by enzymes present in intestinal cells rapidly; thereupon, the current study was aimed to preparing, optimizing, and evaluating cytotoxicity of wheat germ agglutinin conjugated gemcitabine-chitosan nanoparticles (WGA-Gem-CNPs) in MCF-7 and HEK293 cells and to determining their cellular uptake by Caco-2 cells.

METHODS

Gem-CNPs were prepared by Ionic Gelation method and optimum formulation was implied for WGA conjugation optimisation. Nanoparticles formation was approved by FTIR and DSC analyses; then particles were characterized by DLS and release profile was prepared. MTT assay was performed in MCF-7 and HEK293.

RESULTS

Optimized Gem-CNPs and WGA-Gem-CNPs particle size were estimated as 126.6 ± 21.8 and 144.8 ± 36.1 nm, respectively. WGA conjugation efficacy was calculated as 50.98 ± 2.32 percent and encapsulation efficiency in WGA-Gem-CNPs was 69.44 ± 3.41 percent. Three-hour Caco-2 cellular uptake from Gem-CNPs and WGA-Gem-CNPs were estimated as averagely 3.5 and 4.5 folds higher than free drug, respectively. Gem-CNPs and WGA-Gem-CNPs reduced IC50 in MCF-7 cells by 2 and 2.5 folds, respectively; such decrease for HEK293 cells was as much as 2.4 and 6.3 folds, in same order.

CONCLUSION

Demonstrated significant in vitro uptake of WGA-Gem-CNPs and cytotoxicity might be considered for more studies as a potential carrier for oral delivery of gemcitabine.

Enhancing Oral Bioavailability of Domperidone Maleate: Formulation, In vitro Permeability Evaluation In-caco-2 Cell Monolayers and In situ Rat Intestinal Permeability Studies

BACKGROUND

The domperidone maleate, a lipophilic agent classified as a Biopharmaceutical Classification System Class II substance with weak water solubility. Self- Emulsifying Drug Delivery System is a novel approach to improve water solubility and, ultimately bioavailability of drugs.

OBJECTIVE

This study aimed to develop and characterize new domperidone-loaded self-emulsifying drug delivery systems as an alternative formulation and to evaluate the permeability of domperidone-loaded self-emulsifying drug delivery systems by using Caco-2 cells and via single-pass intestinal perfusion method.

METHODS

Three self-emulsifying drug delivery systems were prepared and characterized in terms of pH, viscosity, droplet size, zeta potential, polydispersity index, conductivity, etc. Each formulation underwent 10, 100, 200, and 500 times dilution in intestinal buffer pH 6.8 and stomach buffer pH 1.2, respectively. Female Sprague Dawley rats were employed for in situ single-pass intestinal perfusion investigations.

RESULTS

Results of the study revealed that the ideal self-emulsifying drug delivery systems formulation showed narrow droplet size, ideal zeta potential, and no conductivity. Additionally, as compared to the control groups, the optimum formulation had better apparent permeability (12.74 ± 0.02×10-4) from Caco-2 cell monolayer permeability experiments. The study also revealed greater Peff values (2.122 ± 0.892×10-4 cm/s) for the optimal formulation from in situ intestinal perfusion analyses in comparison to control groups (Domperidone; 0.802 ± 0.418×10-4 cm/s).

CONCLUSION

To conclude, prepared formulations can be a promising way of oral administration of Biopharmaceutical Classification System Class II drugs.

Endothelial tissue remodeling induced by intraluminal pressure enhances paracellular solute transport

The endothelial layers of the microvasculature regulate the transport of solutes to the surrounding tissues. It remains unclear how this barrier function is affected by blood flow-induced intraluminal pressure. Using a 3D microvessel model, we compare the transport of macromolecules through endothelial tissues at mechanical rest or with intraluminal pressure, and correlate these data with electron microscopy of endothelial junctions. On application of an intraluminal pressure of 100 Pa, we demonstrate that the flow through the tissue increases by 2.35 times. This increase is associated with a 25% expansion of microvessel diameter, which leads to tissue remodeling and thinning of the paracellular junctions. We recapitulate these data with the deformable monopore model, in which the increase in paracellular transport is explained by the augmentation of the diffusion rate across thinned junctions under mechanical stress. We therefore suggest that the deformation of microvasculatures contributes to regulate their barrier function.

N-Trimethylated chitosan coating white adipose tissue vascular-targeting oral nano-system for the enhanced anti-obesity effects of celastrol

Oral nanoparticles (NPs) are more suitable for obesity control compared to NPs administered intravenously, as their convenience increases patient compliance. Herein, we developed an oral nano-system to improve the anti-obesity efficacy of celastrol (Cel). The observed enhanced efficacy was mediated by zein core NPs decorated with adipose-homing peptides that were coated with N-trimethylated chitosan. The optimized Cel/AHP-NPs@TMC exhibited spherical morphology by TEM, as well as narrow size distribution (221.76 ± 6.73 nm) and adequate stability in a gastrointestinal environment. Based on the combined delivery advantages of AHP-NPs@TMC - i.e., improved cellular internalization within Caco-2 cells and enhanced white adipose tissue (WAT) vascular targeting - Cel/AHP-NPs@TMC significantly reduced the body weight, blood lipid levels, adipose inflammation, and WAT distribution in diet-induced obese mice without side-effects. In short, this study provides clear evidence that TMC-based oral NPs can effectively improve celastrol for obesity treatment.

Fat fighting liraglutide based nano-formulation to reverse obesity: Design, development and animal trials

Obesity is a metabolic disease, which is one of the major causes of morbidity and mortality, where therapeutic options are limited. Treatment of obesity is necessary as it is associated with fatal complications like diabetes mellitus, cardiovascular disease, non-alcoholic fatty liver disease, osteoarthritis, and many more. Liraglutide (Lir), a synthetic analogue of Glucagon-like Peptide-1 (GLP-1), is the FDA approved anti-obesity drug, however, its major limitation is its clinical application which needs frequent parenteral injections. To address the issue of regular injection, we have synthesized a fat fighting oral nano-formulation of liraglutide with a sustained release feature, which was evaluated against high fat diet (HFD) induced obesity in mice. Experimental obesity was induced in mice by feeding HFD for 26 weeks. Lir nanoparticles (NP) were fabricated with chitosan via ion-gelation technique and were coated with Eudragit@S100 to protect the drug in harsh gastric conditions. Physiochemical characterization of Eu-Lir-Cs-NP demonstrated a small particle size of 253.1 ± 1.21 nm with ∼ 9.74 % loading and ∼ 72.11 % encapsulation efficiency of the drug. In-vitro studies showed successful cellular uptake of NP in Caco-2 cells and were stable in various enteric fluid pH conditions. Eudragit@S100 coated chitosan NP were able to protect the drug from harsh gastric pH conditions with more than ∼ 74% of recovery. Treatment of two weeks of liraglutide Eu-Lir-Cs-NP (0.1, 0.2 and 0.4 mg/kg, orally; twice daily) moderately reduces obesity in mice as evidenced by a reduction in the body weight, blood glucose, serum total cholesterol, serum triglyceride, serum resistin and serum insulin level of mice. In addition, significant reduction of liver weight, abdominal white adipose tissue, and hepatic oxidative stress were noted. Our results suggest that chitosan-based NP of liraglutide can be an effective and convenient formulation for the management of obesity.

How Does the Study MD of pH-Dependent Exposure of Nanoparticles Affect Cellular Uptake of Anticancer Drugs?

The lack of knowledge about the uptake of NPs by biological cells poses a significant problem for drug delivery. For this reason, designing an appropriate model is the main challenge for modelers. To address this problem, molecular modeling studies that can describe the mechanism of cellular uptake of drug-loaded nanoparticles have been conducted in recent decades. In this context, we developed three different models for the amphipathic nature of drug-loaded nanoparticles (MTX-SS-γ-PGA), whose cellular uptake mechanism was predicted by molecular dynamics studies. Many factors affect nanoparticle uptake, including nanoparticle physicochemical properties, protein-particle interactions, and subsequent agglomeration, diffusion, and sedimentation. Therefore, the scientific community needs to understand how these factors can be controlled and the NP uptake of nanoparticles. Based on these considerations, in this study, we investigated for the first time the effects of the selected physicochemical properties of the anticancer drug methotrexate (MTX) grafted with hydrophilic-γ-polyglutamic acid (MTX-SS-γ-PGA) on its cellular uptake at different pH values. To answer this question, we developed three theoretical models describing drug-loaded nanoparticles (MTX-SS-γ-PGA) at three different pH values, such as (1) pH 7.0 (the so-called neutral pH model), (2) pH 6.4 (the so-called tumor pH model), and (3) pH 2.0 (the so-called stomach pH model). Exceptionally, the electron density profile shows that the tumor model interacts more strongly with the head groups of the lipid bilayer than the other models due to charge fluctuations. Hydrogen bonding and RDF analyses provide information about the solution of the NPs with water and their interaction with the lipid bilayer. Finally, dipole moment and HOMO-LUMO analysis showed the free energy of the solution in the water phase and chemical reactivity, which are particularly useful for determining the cellular uptake of the NPs. The proposed study provides fundamental insights into molecular dynamics (MD) that will allow researchers to determine the influence of pH, structure, charge, and energetics of NPs on the cellular uptake of anticancer drugs. We believe that our current study will be useful in developing a new model for drug delivery to cancer cells with a much more efficient and less time-consuming model.

Stereochemistry and Intermolecular Interactions Influence Carrier Peptide-Mediated Insulin Delivery

The inherent low oral bioavailability of therapeutic peptides can be enhanced by the cell-penetrating peptide penetratin and its analogues shuffle and penetramax applied as carriers for delivery of insulin. In this study, the objective was to gain mechanistic insights on the effect of the carrier peptide stereochemistry on their interactions with insulin and on insulin delivery. Insulin-carrier peptide interactions were investigated using small-angle X-ray scattering and cryogenic transmission electron microscopy, while the insulin and peptide stability and transepithelial insulin permeation were evaluated in the Caco-2 cell culture model along with the carrier peptide-induced effects on epithelial integrity and cellular metabolic activity. Interestingly, the insulin transepithelial permeation was influenced by the degree of insulin-carrier peptide complexation and depended on the stereochemistry of penetramax but not of penetratin and shuffle. The l-form of the peptides initially decreased the epithelial integrity comparable to that induced by the d-peptides, suggesting a comparable mechanism of action. The immediate decrease was reversible during exposure of the Caco-2 epithelium to the l-peptides but not during exposure to the d-peptides, likely a result of their higher stability. Overall, exploration of the stereochemistry showed to be an interesting strategy for carrier peptide-mediated insulin delivery.

Chemical- and Drug-Induced Allergic, Inflammatory, and Autoimmune Diseases Via Haptenation

Haptens are small molecules that only elicit an immune response when bound to proteins. Haptens initially bind to self-proteins and activate innate immune responses by complex mechanisms via inflammatory cytokines and damage-associated molecular patterns and the subsequent upregulation of costimulatory signals such as cluster of differentiation 86 (CD86) on dendritic cells. Subsequent interactions between CD86 and CD28 on T cells are critically important for properly activating naive T cells and inducing interleukin 2 production, leading to the establishment of adaptive immunity via effector and memory T cells. Accumulating evidence revealed the involvement of haptens in the development of various autoimmune-like diseases such as allergic, inflammatory, and autoimmune diseases including allergic contact dermatitis, atopy, asthma, food allergy, inflammatory bowel diseases, hemolytic anemia, liver injury, leukoderma, and even antitumor immunity. Therefore, the development of in vitro testing alternatives to evaluate in advance whether a substance might lead to the development of these diseases is highly desirable. This review summarizes and discusses recent advances in chemical- and drug-induced allergic, inflammatory, and autoimmune diseases via haptenation and the possible molecular underlying mechanisms, as well as in vitro testing alternatives to evaluate in advance whether a substance might cause the development of these diseases.

Inflammatory bowel disease addressed by Caco-2 and monocyte-derived macrophages: an opportunity for an in vitro drug screening assay

Inflammatory bowel disease (IBD) is a widespread disease, affecting a growing demographic. The treatment of chronic inflammation located in the GI-tract is dependent on the severity; therefore, the IBD treatment pyramid is commonly applied. Animal experimentation plays a key role for novel IBD drug development; nevertheless, it is ethically questionable and limited in its throughput. Reliable and valid in vitro assays offer the opportunity to overcome these limitations. We combined Caco-2 with monocyte-derived macrophages and exposed them to known drugs, targeting an in vitro-in vivo correlation (IVIVC) with a focus on the severity level and its related drug candidate. This co-culture assay addresses namely the intestinal barrier and the immune response in IBD. The drug efficacy was analyzed by an LPS-inflammation of the co-culture and drug exposure according to the IBD treatment pyramid. Efficacy was defined as the range between LPS control (0%) and untreated co-culture (100%) independent of the investigated read-out (TEER, Papp, cytokine release: IL-6, IL-8, IL-10, TNF-α). The release of IL-6, IL-8, and TNF-α was identified as an appropriate readout for a fast drug screening ("yes-no response"). TEER showed a remarkable IVIVC correlation to the human treatment pyramid (5-ASA, Prednisolone, 6-mercaptopurine, and infliximab) with an R2 of 0.68. Similar to the description of an adverse outcome pathway (AOP) framework, we advocate establishing an "Efficacy Outcome Pathways (EOPs)" framework for drug efficacy assays. The in vitro assay offers an easy and scalable method for IBD drug screening with a focus on human data, which requires further validation.

Supplementary Information

The online version contains supplementary material available at 10.1007/s44164-022-00035-8.

Inhibition of Viral RNA-Dependent RNA Polymerases by Nucleoside Inhibitors: An Illustration of the Unity and Diversity of Mechanisms

RNA-dependent RNA polymerase (RdRP) is essential for the replication and expression of RNA viral genomes. This class of viruses comprise a large number of highly pathogenic agents that infect essentially all species of plants and animals including humans. Infections often lead to epidemics and pandemics that have remained largely out of control due to the lack of specific and reliable preventive and therapeutic regimens. This unmet medical need has led to the exploration of new antiviral targets, of which RdRP is a major one, due to the fact of its obligatory need in virus growth. Recent studies have demonstrated the ability of several synthetic nucleoside analogs to serve as mimics of the corresponding natural nucleosides. These mimics cause stalling/termination of RdRP, or misincorporation, preventing virus replication or promoting large-scale lethal mutations. Several such analogs have received clinical approval and are being routinely used in therapy. In parallel, the molecular structural basis of their inhibitory interactions with RdRP is being elucidated, revealing both traditional and novel mechanisms including a delayed chain termination effect. This review offers a molecular commentary on these mechanisms along with their clinical implications based on analyses of recent results, which should facilitate the rational design of structure-based antiviral drugs.

Bile Duct Ligation Impairs Function and Expression of Mrp1 at Rat Blood-Retinal Barrier via Bilirubin-Induced P38 MAPK Pathway Activations

Liver injury is often associated with hepatic retinopathy, resulting from accumulation of retinal toxins due to blood-retinal barrier (BRB) dysfunction. Retinal pigment epithelium highly expresses MRP1/Mrp1. We aimed to investigate whether liver injury affects the function and expression of retinal Mrp1 using bile duct ligation (BDL) rats. Retinal distributions of fluorescein and 2,4-dinitrophenyl-S-glutathione were used for assessing Mrp1 function. BDL significantly increased distributions of the two substrates and bilirubin, downregulated Mrp1 protein, and upregulated phosphorylation of p38 and MK2 in the retina. BDL neither affected the retinal distribution of FITC-dextran nor expressions of ZO-1 and claudin-5, demonstrating intact BRB integrity. In ARPE-19 cells, BDL rat serum or bilirubin decreased MRP1 expression and enhanced p38 and MK2 phosphorylation. Both inhibiting and silencing p38 significantly reversed the bilirubin- and anisomycin-induced decreases in MRP1 protein. Apparent permeability coefficients of fluorescein in the A-to-B direction (Papp, A-to-B) across the ARPE-19 monolayer were greater than Papp, B-to-A. MK571 or bilirubin significantly decreased Papp, A-to-B of fluorescein. Bilirubin treatment significantly downregulated Mrp1 function and expression without affecting integrity of BRB and increased bilirubin levels and phosphorylation of p38 and MK2 in rat retina. In conclusion, BDL downregulates the expression and function of retina Mrp1 by activating the p38 MAPK pathway due to increased bilirubin levels.

Lack of NHE6 and Inhibition of NKCC1 Associated With Increased Permeability in Blood Labyrinth Barrier-Derived Endothelial Cell Layer

Acoustic trauma, autoimmune inner ear disease, and presbycusis feature loss of the integrity of the blood-labyrinth barrier (BLB). Normal BLB function depends on endothelial structural integrity, which is supported and maintained by tight junctions and adherens junctions within the microvascular endothelial layer. When these junctions are disrupted, vascular leakage occurs. Tight junctions and adherens junctions are functionally and structurally linked, but the exact signaling pathways underlying their interaction remain unknown. In addition, solute carriers (SC) are essential for optimal exchange through BLB. Previously, we found that SC family member, the sodium–hydrogen exchanger NHE6, was expressed in all wildtype cochlear tissues, and that Nhe6-knockout mice displayed moderate hearing loss. Moreover, NHE6 depletion affected Trk protein turnover and endosomal signaling. Here, we investigated whether NHE6 might impact BLB integrity. We found that Nhe6-knockout, BLB-derived endothelial cells showed reduced expression of major junctional genes: Tjp1, F11r, Ocln, Cdh5, and Cldn5. Co-culturing BLB-derived endothelial cells with pericytes and/or perivascular resident macrophage-like melanocytes in a transwell system showed that monolayers of Nhe6-knockout BLB-derived cells had lower electrical resistance and higher permeability, compared to wildtype endothelial monolayers. Additionally, another SC, NKCC1, which was previously linked to congenital deafness, was downregulated in our Nhe6-knockout mouse model. Blocking NKCC1 with a NKCC1-specific inhibitor, bumetanide, in wildtype BLB-derived endothelial cells also caused the downregulation of major junctional proteins, particularly Tjp1 and F11r, which encode the zonula occludens and junctional adhesion molecule-1 proteins, respectively. Moreover, bumetanide treatment increased cell permeability. In conclusion, we showed that the lack or inhibition of NHE6 or NKCC1 affected the permeability of endothelial BLB-derived cells. These findings suggested that NHE6 and NKCC1 could serve as potential targets for modifying BLB permeability to facilitate drug delivery across the BLB to the cochlea or to protect the cochlea from ototoxic insults.

Application of Fucoidan in Caco-2 Model Establishment

The Caco-2 model is a common cell model for material intestinal absorption in vitro, which usually takes 21 days to establish. Although some studies have shown that adding puromycin (PM) can shorten the model establishment period to 7 days, this still requires a long modeling time. Therefore, exploring a shorter modeling method can reduce the experimental costs and promote the development and application of the model. Fucoidan is an acidic polysaccharide with various biological activities. Our study showed that the transepithelial electrical resistance (TEER) value could reach 600 Ω·cm2 on the fourth day after the addition of fucoidan and puromycin, which met the applicable standards of the model (>500 Ω). Moreover, the alkaline phosphatase (AKP) activity, fluorescein sodium transmittance, and cell morphology of this model all met the requirements of model establishment. Fucoidan did not affect the absorption of macromolecular proteins and drugs. The results indicate that fucoidan can be applied to establish the Caco-2 model and can shorten the model establishment period to 5 days.

Exploring the permeability of covid-19 drugs within the cellular membrane: a molecular dynamics simulation study

The diffusion of drugs into the cellular membrane is an important step in the drug delivery systems. Furthermore, predicting the interaction and permeability of drugs across the cellular membrane could help scientists to design bioavailable and high-efficient drugs. Discovering the COVID-19 drugs has recently drawn remarkable attention to tackle its outbreak. Due to the rapid replication of the coronavirus in the human body, searching for highly permeable drugs into the cellular membrane is vital. Herein, we performed the molecular dynamics (MD) simulation and density functional (DFT) calculations to investigate the permeability of keto and enol tautomers of the favipiravir (FAV) as well as hydroxychloroquine (HCQ) COVID-19 drugs into the cellular membrane. Our results reveal that though both keto and enol tautomers of the FAV are feasible to transfer through the cellular membrane, the keto form moves faster and diffuses deeper; however, the HCQ molecules aggregate in the water phase and remain near the cellular membrane. It is worth pointing out that the obtained results are consistent with the reactivity trends projected by the calculated reactivity descriptors of the considered drugs. Despite the pair correlation function and H-bond analyses revealing the interactions between the membrane and HCQ, the aggregation of the HCQ molecules resists their passage through the cellular membrane. Besides, the lower free energy barrier of FAV confirms its higher permeability than HCQ. These findings suggest that due to the deeper permeability of the FAV drug, its effectiveness can be more than that of HCQ. These molecular insights might help with a better understanding of the interactions between COVID-19 drugs and cellular membranes. Moreover, these theoretical findings could help experimental researchers find high-efficient strategies for COVID-19 therapy.

Decabromodiphenyl ether induces ROS-mediated intestinal toxicity through the Keap1-Nrf2 pathway

Polybrominated diphenyl ethers (PBDEs) are widely used brominated flame retardants as commercial products. PBDEs have been demonstrated to induce hepatic, reproductive, neural, and thyroid toxicity effects. This study aimed to clarify the potential intestinal toxicity effects of decabrominated diphenyl ether (PBDE-209) in vivo and in vitro. First, we investigated the change of PBDE-209 on oxidative stress in the intestine of mice. Subsequently, the potential toxicity mechanism of PBDE-209 in vitro was investigated. Caco-2 cells were treated with different concentrations of PBDE-209 (1, 5, and 25 μmol/L) for 24  and 48 h. We determined the cell viability, reactive oxygen species (ROS) level, multiple cellular parameters, and relative mRNA expressions. The results showed that PBDE-209 significantly injured the colon of mice, increased the intestinal levels of malondialdehyde (MDA), and changed the antioxidant enzyme activities. PBDE-209 inhibited the proliferation and induced cytotoxicity of Caco-2 cells. The change in ROS production and mitochondrial membrane potential (MMP) revealed that PBDE-209 caused oxidative stress in Caco-2 cells. The real-time PCR assays revealed that PBDE-209 inhibited the mRNA expression level of antioxidative defense factor, nuclear factor erythroid 2-related factor 2 (Nrf2). Furthermore, the FAS and Cytochrome P450 1A1 (CYP1A1) mRNA expression levels were increased in Caco-2 cells. These results suggested that PBDE-209 exerts intestinal toxicity effects in vivo and in vitro and inhibits the antioxidative defense gene expression in Caco-2 cells. This study provides an opportunity to advance the understanding of toxicity by the persistent environmental pollutant PBDE-209 to the intestine.

Milk protein-shelled gold nanoparticles with gastrointestinally active absorption for aurotherapy to brain tumor

Orally absorbable gold nanoparticles (AuNP) having cancer ablation therapy is strongly demanded to treat glioblastoma multiforme (GBM) for patients with its highest incidence rate. Here, we develop a milk protein lactoferrin-conjugated AuNP for its oral absorption and targeting to the GBM through the interaction between lactoferrin (Lf) and lactoferrin receptor (LfR) that is highly expressed in the intestine, blood-brain barrier and GBM. For stability and long circulation of AuNP, glutathione and polyethylene glycol (PEG) is introduced, which is called to Lf-PEG-AuNP. When Lf-PEG-AuNP are orally administered to orthotopic GBM-bearing mice, 11-fold and 8-fold higher concentrations of AuNP are measured in bloodstreams and GBM in the brain, respectively, compared with unconjugated-AuNP. Therefore, orally administered Lf-PEG-AuNP exhibit an outstanding temperature rise in GBM by irradiating laser and significantly reduce tumor volume. Collectively, we suggest that the Lf-PEG-AuNP can fundamentally target GBM in the brain through oral absorption, and that its efficient photothermal therapy is possible.

Integration of In Silico, In Vitro and In Situ Tools for the Preformulation and Characterization of a Novel Cardio-Neuroprotective Compound during the Early Stages of Drug Development

The main aim of this work is the biopharmaceutical characterization of a new hybrid benzodiazepine-dihydropyridine derivative, JM-20, derived with potent anti-ischemic and neuroprotective effects. In this study, the pKa and the pH-solubility profile were experimentally determined. Additionally, effective intestinal permeability was measured using three in vitro epithelial cell lines (MDCK, MDCK-MDR1 and Caco-2) and an in situ closed-loop intestinal perfusion technique. The results indicate that JM-20 is more soluble at acidic pH (9.18 ± 0.16); however, the Dose number (Do) was greater than 1, suggesting that it is a low-solubility compound. The permeability values obtained with in vitro cell lines as well as with the in situ perfusion method show that JM-20 is a highly permeable compound (Caco-2 value 3.8 × 10-5). The presence of an absorption carrier-mediated transport mechanism was also demonstrated, as well as the efflux effect of P-glycoprotein on the permeability values. Finally, JM-20 was provisionally classified as class 2 according to the biopharmaceutical classification system (BCS) due to its high intestinal permeability and low solubility. The potential good oral absorption of this compound could be limited by its solubility.

In Silico-Based Experiments on Mechanistic Interactions between Several Intestinal Permeation Enhancers with a Lipid Bilayer Model

Oral administration of drugs is generally considered convenient and patient-friendly. However, oral administration of biological drugs exhibits low oral bioavailability (BA) due to enzymatic degradation and low intestinal absorption. A possible approach to circumvent the low BA of oral peptide drugs is to coformulate the drugs with permeation enhancers (PEs). PEs have been studied since the 1960s and are molecules that enhance the absorption of hydrophilic molecules with low permeability over the gastrointestinal epithelium. In this study, we investigated the impact of six PEs on the structural properties of a model membrane using molecular dynamics (MD) simulations. The PEs included were the sodium salts of the medium chain fatty acids laurate, caprate, and caprylate and the caprylate derivative SNAC─all with a negative charge─and neutral caprate and neutral sucrose monolaurate. Our results indicated that the PEs, once incorporated into the membrane, could induce membrane leakiness in a concentration-dependent manner. Our simulations suggest that a PE concentration of at least 70-100 mM is needed to strongly affect transcellular permeability. The increased aggregation propensity seen for neutral PEs might provide a molecular-level mechanism for the membrane disruptions seen at higher concentrations in vivo. The ability for neutral PEs to flip-flop across the lipid bilayer is also suggestive of possible intracellular modes of action other than increasing membrane fluidity. Taken together, our results indicate that MD simulations are useful for gaining insights relevant to the design of oral dosage forms based around permeability enhancer molecules.

Generation of Human Pluripotent Stem Cell-Derived Polarized Hepatocytes

Human pluripotent stem cell (hPSC)-derived hepatocyte-like cells (HLCs) are valuable tools to study liver biology. HLCs, however, lack certain key in vivo characteristics relevant to their physiological function. One such characteristic is cellular polarity, which is critical to hepatocyte counter-current flow systems involving canalicular bile secretion and sinusoidal secretion of large quantities of serum proteins into blood. Model systems using non-polarized hepatocytes, therefore, cannot recapitulate this physiological function of hepatocytes. Here, we describe a stepwise protocol to generate hPSC-derived polarized HLCs (pol-HLCs), which feature clearly defined basolateral and apical membranes separated by tight junctions. Pol-HLCs not only display many hepatic functions but are also capable of directional cargo secretion, mimicking the counter-current flow systems. We describe protocols for stem cell culture maintenance and for differentiating hPSCs into pol-HLCs. In addition, we describe protocols to assay the pol-HLCs for basic hepatic functions and polarized hepatic characteristics. Once successfully differentiated, these pol-HLCs can be used as an in vitro model system to study hepatocyte biology, disease mechanisms, genetic variation, and drug metabolism. The establishment of hepatic polarity from non-polarized hPSCs also provides a useful tool to study the development and maintenance of hepatic polarity. © 2022 Wiley Periodicals LLC. Basic Protocol 1: Maintenance of hPSCs Basic Protocol 2: Differentiation of hPSCs to pol-HLCs Basic Protocol 3: Assaying pol-HLCs for basic hepatic functions Support Protocol 1: Assessment of pol-HLC monolayer tightness Support Protocol 2: Assessment of pol-HLC polarity.

Best practices in current models mimicking drug permeability in the gastrointestinal tract - an UNGAP review

The absorption of orally administered drug products is a complex, dynamic process, dependent on a range of biopharmaceutical properties; notably the aqueous solubility of a molecule, stability within the gastrointestinal tract (GIT) and permeability. From a regulatory perspective, the concept of high intestinal permeability is intrinsically linked to the fraction of the oral dose absorbed. The relationship between permeability and the extent of absorption means that experimental models of permeability have regularly been used as a surrogate measure to estimate the fraction absorbed. Accurate assessment of a molecule's intestinal permeability is of critical importance during the pharmaceutical development process of oral drug products, and the current review provides a critique of in vivo, in vitro and ex vivo approaches. The usefulness of in silico models to predict drug permeability is also discussed and an overview of solvent systems used in permeability assessments is provided. Studies of drug absorption in humans are an indirect indicator of intestinal permeability, but in vitro and ex vivo tools provide initial screening approaches are important tools for direct assessment of permeability in drug development. Continued refinement of the accuracy of in silico approaches and their validation with human in vivo data will facilitate more efficient characterisation of permeability earlier in the drug development process and will provide useful inputs for integrated, end-to-end absorption modelling.

Intestinal permeation enhancers enable oral delivery of macromolecules up to 70 kDa in size

The decades-long effort to deliver peptide drugs orally has resulted in several clinically successful formulations. These formulations are enabled by the inclusion of permeation enhancers that facilitate the intestinal absorption of peptides. Thus far, these oral peptide drugs have been limited to peptides less than 5 kDa, and it is unclear whether there is an upper bound of protein size that can be delivered with permeation enhancers. In this work, we examined two permeation enhancers, 1-phenylpiperazine (PPZ) and sodium deoxycholate (SDC), for their ability to increase intestinal transport of a model macromolecule (FITC-Dextran) as a function of its size. Specifically, the permeability of dextrans with molecular weights of 4, 10, 40, and 70 kDa was assessed in an in vitro and in vivo model of the intestine. In Caco-2 monolayers, both PPZ and SDC significantly increased the permeability of only FD4 and FD10. However, in mice, PPZ and SDC behaved differently. While SDC improved the absorption of all tested sizes of dextrans, PPZ was effective only for FD4 and FD10. This work is the first report of PPZ as a permeation enhancer in vivo, and it highlights the ability of permeation enhancers to improve the absorption of macromolecules across a broad range of sizes relevant for protein drugs.

Combined Methodologies for Determining In Vitro Bioavailability of Drugs and Prediction of In Vivo Bioequivalence From Pharmaceutical Oral Formulations

With the aim of developing an in vitro model for the bioavailability (BA) prediction of drugs, we focused on the study of levonorgestrel (LVN) released by 1.5 mg generic and brand-name tablets. The developed method consisted in combining a standard dissolution test with an optimized parallel artificial membrane permeability assay (PAMPA) to gain insights into both drug release and gastrointestinal absorption. Interestingly, the obtained results revealed that the tablet standard dissolution test, combined with an optimized PAMPA, highlighted a significant decrease in the release (15 ± 0.01 μg min⁻¹ vs 30 ± 0.01 μg min⁻¹) and absorption (19 ± 7 × 10^–6 ± 7 cm/s Pe vs 41 ± 15 × 10^–6 cm/s Pe) profiles of a generic LVN tablet when compared to the brand-name formulation, explaining unbalanced in vivo bioequivalence (BE). By using this new approach, we could determine the actual LVN drug concentration dissolved in the medium, which theoretically can permeate the gastrointestinal (GI) barrier. In fact, insoluble LVN/excipient aggregates were found in the dissolution media giving rise to non-superimposable dissolution profiles between generic and brand-name LVN tablets. Hence, the results obtained by combining the dissolution test and PAMPA method provided important insights confirming that the combined methods can be useful in revealing crucial issues in the prediction of in vivo BE of drugs.

Navigating Through Cell-Based In vitro Models Available for Prediction of Intestinal Permeability and Metabolism: Are We Ready for 3D?

Traditionally, in vitro studies to quantify the intestinal permeability of drugs have relied on two-dimensional cell culture models using human colorectal carcinoma cell lines, namely Caco-2, HT 29 and T84 cells. Although these models have been commonly used for high-throughput screening of xenobiotics in preclinical studies, they do not fully recapitulate the morphology and functionality of enterocytes found in the human intestine in vivo. Efforts to improve the physiological and functional relevance of in vitro intestinal models have led to the development of enteroids/intestinal organoids and microphysiological systems. These models leverage advances in three-dimensional cell culture techniques and stem cell technology (in addition to microfluidics for microphysiological systems), to mimic the architecture and microenvironment of the in vivo intestine more accurately. In this commentary, we will discuss the advantages and limitations of these established and emerging intestinal models, as well as their current and potential future applications for the pre-clinical assessment of oral therapies.

Effect of Coformer Selection on In Vitro and In Vivo Performance of Adefovir Dipivoxil Cocrystals

PURPOSE

This study aimed to improve the in vitro dissolution, permeability and oral bioavailability of adefovir dipivoxil (ADD) by cocrystal technology and clarify the important role of coformer selection on the cocrystal's properties.

METHODS

ADD was cocrystallized with three small molecules (i.e., paracetamol (PA), saccharin (SAC) and nicotinamide (NIC)), respectively. The obtained ADD-PA cocrystal was characterized by DSC, TGA, PXRD and FTIR. Comparative study on dissolution rates among the three ADD cocrystals were conducted in water and pH 6.8 phosphate buffer. Besides, effects of coformers on intestinal permeability of ADD were evaluated via in vitro Caco-2 cell model and in situ single-pass intestinal perfusion model in rats. Furthermore, in vivo pharmacokinetic study of ADD cocrystals was also compared.

RESULTS

Dissolution rates of ADD cocrystals were improved with the order of ADD-SAC cocrystal > ADD-PA cocrystal > ADD-NIC cocrystal. The permeability studies on Caco-2 cell model and single-pass intestinal perfusion model indicated that PA could enhance intestinal absorption of ADD by P-gp inhibition, while SAC and NIC did not. Further in vivo pharmacokinetic study showed that ADD-SAC cocrystal exhibited higher C_max (1.4-fold) and AUC_0-t (1.3-fold) of ADD than administration of ADD alone, and C_max and AUC_0-t of ADD-PA cocrystal were significantly enhanced by 2.1-fold and 2.2-fold, respectively, which was attributed to its higher dissolution and improved intestinal permeability.

CONCLUSION

Coformer selection had an important role on cocrystal's properties, and cocrystallization of ADD with a suitable coformer was an effective approach to enhance both dissolution and bioavailability of ADD.

Influence of traumatic brain injury on extracellular tau elimination at the blood-brain barrier

Repetitive head trauma has been associated with the accumulation of tau species in the brain. Our prior work showed brain vascular mural cells contribute to tau processing in the brain, and that these cells progressively degenerate following repetitive mild traumatic brain injury (r-mTBI). The current studies investigated the role of the cerebrovasculature in the elimination of extracellular tau from the brain, and the influence of r-mTBI on these processes. Following intracranial injection of biotin-labeled tau, the levels of exogenous labeled tau residing in the brain were elevated in a mouse model of r-mTBI at 12 months post-injury compared to r-sham mice, indicating reduced tau elimination from the brain following head trauma. This may be the result of decreased caveolin-1 mediated tau efflux at the blood–brain barrier (BBB), as the caveolin inhibitor, methyl-β-cyclodextrin, significantly reduced tau uptake in isolated cerebrovessels and significantly decreased the basolateral-to-apical transit of tau across an in vitro model of the BBB. Moreover, we found that the upstream regulator of endothelial caveolin-1, Mfsd2a, was elevated in r-mTBI cerebrovessels compared to r-sham, which coincided with a decreased expression of cerebrovascular caveolin-1 in the chronic phase following r-mTBI (> 3 months post-injury). Lastly, angiopoietin-1, a mural cell-derived protein governing endothelial Mfsd2a expression, was secreted from r-mTBI cerebrovessels to a greater extent than r-sham animals. Altogether, in the chronic phase post-injury, release of angiopoietin-1 from degenerating mural cells downregulates caveolin-1 expression in brain endothelia, resulting in decreased tau elimination across the BBB, which may describe the accumulation of tau species in the brain following head trauma.

Increasing the Transport of Celecoxib over a Simulated Intestine Cell Membrane Model Using Mesoporous Magnesium Carbonate

In the current work, mesoporous magnesium carbonate (MMC) was used to suppress crystallization of the poorly soluble drug celecoxib (CXB). This resulted in both a higher dissolution rate and supersaturation of the substance in vitro as well as an increased transfer of CXB over a Caco-2 cell membrane mimicking the membrane in the small intestine. The CXB flux over the cell membrane showed a linear behavior over the explored time period. These results indicate that MMC may be helpful in increasing the bioavailability and obtaining a continuous release of CXB, and similar substances, in vivo. Neusilin US2 was used as a reference material and showed a more rapid initial release with subsequent crystallization of the incorporated CXB in the release media. The presented results form the foundation of future development of MMC as a potential carrier for poorly soluble drugs.

Caco-2/HT29-MTX co-cultured cells as a model for studying physiological properties and toxin-induced effects on intestinal cells

Infectious gastrointestinal diseases are frequently caused by toxins secreted by pathogens which may impair physiological functions of the intestines, for instance by cholera toxin or by heat-labile enterotoxin. To obtain a functional model of the human intestinal epithelium for studying toxin-induced disease mechanisms, differentiated enterocyte-like Caco-2 cells were co-cultured with goblet cell-like HT29-MTX cells. These co-cultures formed a functional epithelial barrier, as characterized by a high electrical resistance and the presence of physiological intestinal properties such as glucose transport and chloride secretion which could be demonstrated electrophysiologically and by measuring protein expression. When the tissues were exposed to cholera toxin or heat-labile enterotoxin in the Ussing chamber, cholera toxin incubation resulted in an increase in short-circuit currents, indicating an increase in apical chloride secretion. This is in line with typical cholera toxin-induced secretory diarrhea in humans, while heat-labile enterotoxin only showed an increase in short-circuit-current in Caco-2 cells. This study characterizes for the first time the simultaneous measurement of physiological properties on a functional and structural level combined with the epithelial responses to bacterial toxins. In conclusion, using this model, physiological responses of the intestine to bacterial toxins can be investigated and characterized. Therefore, this model can serve as an alternative to the use of laboratory animals for characterizing pathophysiological mechanisms of enterotoxins at the intestinal level.

Towards prevention of ischemia-reperfusion kidney injury: Pre-clinical evaluation of 6-chromanol derivatives and the lead compound SUL-138✰

Acute kidney injury (AKI) is a global healthcare burden attributable to high mortality and staggering costs of dialysis. The underlying causes of AKI include hypothermia and rewarming (H/R), ischemia/reperfusion (I/R), mitochondrial dysfunction and reactive oxygen species production. Inspired by the mechanisms conferring organ protection in hibernating hamster, 6-chromanol derived compounds were developed to address the need of effective prevention and treatment of AKI. Here we report on the pre-clinical screening of 6-chromanol leads that confer protection during I/R to select compounds with favorable profiles for clinical testing in AKI. A library of 6-chromanols (n = 63) was screened in silico for pharmacochemical properties and druggability. Selected compounds (n = 15) were screened for the potency to protect HEK293 cells from H/R cell death and subjected to a panel of in vitro safety assays. Based on these parameters, SUL-138 was selected as the lead compound and was found to safeguard kidney function and decrease renal injury after I/R in rats. The compound was without cardiovascular or respiratory effects in vivo. SUL-138 pharmacokinetics of control animals (mouse, rat) and those undergoing I/R (rat) was identical, showing a two-phase elimination profile with terminal half-life of about 8 h. Collectively, our phenotype-based screening approach led to the identification of 3 candidates for pre-clinical studies (5%, 3/64). SUL-138 emerged from this small-scale library of 6-chromanols as a novel prophylactic for AKI. The presented efficacy and safety data provide a basis for future development and clinical testing. SECTION ASSIGNMENTS: : Drug discovery and translational medicine, renal, metabolism SIGNIFICANCE STATEMENT: : Based on in silico druggability parameters, a 63 compound 6-chromanol library was narrowed down to 15 compounds. These compounds were subjected to phenotypical screening of cell survival following hypothermia damage and hit compounds were identified. After subsequent assessment of in vivo efficacy, toxicity, pharmacokinetics, and cardiovascular and respiratory safety, SUL-138 emerged as a lead compound that prevented kidney injury after ischemia/reperfusion and demonstrated a favorable pharmacokinetic profile unaffected by renal ischemia.

Re-Use of Caco-2 Monolayers in Permeability Assays-Validation Regarding Cell Monolayer Integrity

Caco-2 monolayers are a common in vitro model used to evaluate human intestinal absorption. The reference protocol requires 21 days post-seeding to establish a stable and confluent cell monolayer, which is used in a single permeability assay during the period of monolayer stability (up to day 30). In this work, we characterize variations in the tightness of the cell monolayer over the stable time interval and evaluate the conditions required for their re-use in permeability assays. The monolayer integrity was assessed through TEER measurements and permeability of the paracellular marker Lucifer Yellow (LY), complemented with nuclei and ZO-1 staining for morphological studies and the presence of tight junctions. Over 150 permeability assays were performed, which showed that manipulation of the cell monolayer in the permeability assay may contribute significantly to the flux of LY, leading to P_app values that are dependent on the sampling duration. The assay also leads to a small decrease in the cell monolayer TEER, which is fully recovered when cell monolayers are incubated with culture media for two full days. When this procedure is followed, the cell monolayers may be used for permeability assays on days 22, 25, and 28, triplicating the throughput of this important assay.

Drug Penetration into the Central Nervous System: Pharmacokinetic Concepts and In Vitro Model Systems

Delivery of most drugs into the central nervous system (CNS) is restricted by the blood-brain barrier (BBB), which remains a significant bottleneck for development of novel CNS-targeted therapeutics or molecular tracers for neuroimaging. Consistent failure to reliably predict drug efficiency based on single measures for the rate or extent of brain penetration has led to the emergence of a more holistic framework that integrates data from various in vivo, in situ and in vitro assays to obtain a comprehensive description of drug delivery to and distribution within the brain. Coupled with ongoing development of suitable in vitro BBB models, this integrated approach promises to reduce the incidence of costly late-stage failures in CNS drug development, and could help to overcome some of the technical, economic and ethical issues associated with in vivo studies in animal models. Here, we provide an overview of BBB structure and function in vivo, and a summary of the pharmacokinetic parameters that can be used to determine and predict the rate and extent of drug penetration into the brain. We also review different in vitro models with regard to their inherent shortcomings and potential usefulness for development of fast-acting drugs or neurotracers labeled with short-lived radionuclides. In this regard, a special focus has been set on those systems that are sufficiently well established to be used in laboratories without significant bioengineering expertise.

Engineering mesoporous silica nanoparticles towards oral delivery of vancomycin

Vancomycin (Van) is a key antibiotic of choice for the treatment of systemic methicillin resistant Staphylococcus aureus (MRSA) infections. However, due to its poor membrane permeability, it is administered parenterally, adding to the cost and effort of treatment. The poor oral bioavailability of Van is mainly due to its physico-chemical properties that limit its paracellular and transcellular transport across gastrointestinal (GI) epithelium. Herein we report the development of silica nanoparticles (SNPs)-based formulations that are able to enhance the epithelial permeability of Van. We synthesized SNPs of different pore sizes (2 nm and 9 nm) and modified their surface charge and polarity by attaching different functional groups (-NH₂, -PO₃, and -CH₃). Van was loaded within these SNPs at a loading capacity in the range of ca. 18-29 wt%. The Van-loaded SNPs exhibited a controlled release behaviour when compared to un-encapsulated Van which showed rapid release due to its hydrophilic nature. Among Van-loaded SNPs, SNPs with large pores showed a prolonged release compared to SNPs with small pores while SNPs functionalised with -CH₃ groups exhibited a slowest release among the functionalised SNPs. Importantly, Van-loaded SNPs, especially the large pore SNPs with negative charge, enhanced the permeability of Van across an epithelial cell monolayer (Caco-2 cell model) by up to 6-fold, with P_app values up to 1.716 × 10^-5 cm s^-1 (vs. 0.304 × 10^-5 cm s^-1 for un-encapsulated Van) after 3 h. The enhancement was dependent on both the type of SNPs and their surface functionalisation. The permeation enhancing effect of SNPs was due to its ability to transiently open the tight junctions measured by decrease in transepithelial resistance (TEER) which was reversible after 3 h. All in all, our data highlights the potential of SNPs (especially SNPs with large pores) for oral delivery of Van or other antimicrobial peptides.

Similarities and differences in the localization, trafficking, and function of P-glycoprotein in MDR1-EGFP-transduced rat versus human brain capillary endothelial cell lines

Background

In vitro models based on brain capillary endothelial cells (BCECs) are among the most versatile tools in blood–brain barrier research for testing drug penetration into the brain and how this is affected by efflux transporters such as P-glycoprotein (Pgp). However, compared to freshly isolated brain capillaries or primary BCECs, the expression of Pgp in immortalized BCEC lines is markedly lower, which prompted us previously to transduce the widely used human BCEC line hCMEC/D3 with a doxycycline-inducible MDR1-EGFP fusion plasmid. The EGFP-labeled Pgp in these cells allows studying the localization and trafficking of the transporter and how these processes are affected by drug exposure. Here we used this strategy for the rat BCEC line RBE4 and performed a face-to-face comparison of RBE4 and hCMEC/D3 wild-type (WT) and MDR1-EGFP transduced cells.

Methods

MDR1-EGFP-transduced variants were derived from WT cells by lentiviral transduction, using an MDR1-linker-EGFP vector. Localization, trafficking, and function of Pgp were compared in WT and MDR1-EGFP transduced cell lines. Primary cultures of rat BCECs and freshly isolated rat brain capillaries were used for comparison.

Results

All cells exhibited typical BCEC morphology. However, significant differences were observed in the localization of Pgp in that RBE4-MDR1-EGFP cells expressed Pgp primarily at the plasma membrane, whereas in hCMEC/D3 cells, the Pgp-EGFP fusion protein was visible both at the plasma membrane and in endolysosomal vesicles. Exposure to doxorubicin increased the number of Pgp-EGFP-positive endolysosomes, indicating a lysosomotropic effect. Furthermore, lysosomal trapping of doxorubicin was observed, likely contributing to the protection of the cell nucleus from damage. In cocultures of WT and MDR1-EGFP transduced cells, intercellular Pgp-EGFP trafficking was observed in RBE4 cells as previously reported for hCMEC/D3 cells. Compared to WT cells, the MDR1-EGFP transduced cells exhibited a significantly higher expression and function of Pgp. However, the junctional tightness of WT and MDR1-EGFP transduced RBE4 and hCMEC/D3 cells was markedly lower than that of primary BCECs, excluding the use of the cell lines for studying vectorial drug transport.

Conclusions

The present data indicate that MDR1-EGFP transduced RBE4 cells are an interesting tool to study the biogenesis of lysosomes and Pgp-mediated lysosomal drug trapping in response to chemotherapeutic agents and other compounds at the level of the blood–brain barrier.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12987-021-00266-z.

An overview of in vitro, ex vivo and in vivo models for studying the transport of drugs across intestinal barriers

Oral administration is the most commonly used route for drug delivery owing to its cost-effectiveness, ease of administration, and high patient compliance. However, the absorption of orally delivered compounds is a complex process that greatly depends on the interplay between the characteristics of the drug/formulation and the gastrointestinal tract. In this contribution, we review the different preclinical models (in vitro, ex vivo and in vivo) from their development to application for studying the transport of drugs across intestinal barriers. This review also discusses the advantages and disadvantages of each model. Furthermore, the authors have reviewed the selection and validation of these models and how the limitations of the models can be addressed in future investigations. The correlation and predictability of the intestinal transport data from the preclinical models and human data are also explored. With the increasing popularity and prevalence of orally delivered drugs/formulations, sophisticated preclinical models with higher predictive capacity for absorption of oral formulations used in clinical studies will be needed.

High-throughput PBTK models for in vitro to in vivo extrapolation

INTRODUCTION

Toxicity data are unavailable for many thousands of chemicals in commerce and the environment. Therefore, risk assessors need to rapidly screen these chemicals for potential risk to public health. High-throughput screening (HTS) for in vitro bioactivity, when used with high-throughput toxicokinetic (HTTK) data and models, allows characterization of these thousands of chemicals.

AREAS COVERED

This review covers generic physiologically based toxicokinetic (PBTK) models and high-throughput PBTK modeling for in vitro-in vivo extrapolation (IVIVE) of HTS data. We focus on 'httk', a public, open-source set of computational modeling tools and in vitro toxicokinetic (TK) data.

EXPERT OPINION

HTTK benefits chemical risk assessors with its ability to support rapid chemical screening/prioritization, perform IVIVE, and provide provisional TK modeling for large numbers of chemicals using only limited chemical-specific data. Although generic TK model design can increase prediction uncertainty, these models provide offsetting benefits by increasing model implementation accuracy. Also, public distribution of the models and data enhances reproducibility. For the httk package, the modular and open-source design can enable the tool to be used and continuously improved by a broad user community in support of the critical need for high-throughput chemical prioritization and rapid dose estimation to facilitate rapid hazard assessments.

Avoiding hindsight in non-obviousness determination: case law review of pharmaceutical patents and guidance from the KSR v Teleflex decision

Introduction: Hindsight bias is the tendency to estimate an outcome once it is known. Legal systems are often prone to hindsight bias. In patent law, the non-obviousness or inventive step is the most critical determinant of patentability and often subjected to hindsight bias.Areas covered: Scholarly literature confirms the existence of hindsight bias in different patent systems. This communication hence addresses factors, which lead to hindsight bias specifically in chemical and pharmaceutical arts, guidance from the case law that can be helpful in avoiding hindsight bias in non-obviousness determination.Expert opinion: The Supreme Court in 2007, advocated a more expansive and flexible approach to where the Teaching Suggestion or Motivation test could come from. In the case of chemical and pharmaceutical active compounds, the considerations such as i) was there sufficient motivation to modify the lead compound and arrive at the claimed compound and its properties, ii) was there a reasonable expectation of success to achieve the claimed property and other such considerations highlighted in this review may contribute to avoid hindsight bias in non-obviousness determination.