Mouse embryonic stem cell-derived blood-brain barrier model: applicability to studying antibody triggered receptor mediated transcytosis

Blood brain barrier (BBB) models in vitro are an important tool to aid in the pre-clinical evaluation and selection of BBB-crossing therapeutics. Stem cell derived BBB models have recently demonstrated a substantial advantage over primary and immortalized brain endothelial cells (BECs) for BBB modeling. Coupled with recent discoveries highlighting significant species differences in the expression and function of key BBB transporters, the field is in need of robust, species-specific BBB models for improved translational predictability. We have developed a mouse BBB model, composed of mouse embryonic stem cell (mESC-D3)-derived brain endothelial-like cells (mBECs), employing a directed monolayer differentiation strategy. Although the mBECs showed a mixed endothelial-epithelial phenotype, they exhibited high transendothelial electrical resistance, inducible by retinoic acid treatment up to 400 Ω cm². This tight cell barrier resulted in restricted sodium fluorescein permeability (1.7 × 10^-5 cm/min), significantly lower than that of bEnd.3 cells (1.02 × 10^-3 cm/min) and comparable to human induced pluripotent stem cell (iPSC)-derived BECs (2.0 × 10^-5 cm/min). The mBECs expressed tight junction proteins, polarized and functional P-gp efflux transporter and receptor mediated transcytosis (RMT) receptors; collectively important criteria for studying barrier regulation and drug delivery applications in the CNS. In this study, we compared transport of a panel of antibodies binding species selective or cross-reactive epitopes on BBB RMT receptors in both the mBEC and human iPSC-derived BEC model, to demonstrate discrimination of species-specific BBB transport mechanisms.

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

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

Quality-by-design based development of a self-microemulsifying drug delivery system to reduce the effect of food on Nelfinavir mesylate

Poor aqueous solubility and moderate permeability of Nelfinavir mesylate (NFM) leads to high variability in absorption after oral administration. To improve the solubility and bioavailability of NFM, the self microemulsifying drug delivery system (SMEDDS) was developed. For this purpose, Quality by design (QbD) approach employing D-optimal mixture design was used to prepare SMEDDS of NFM. Further, the software generated numerically optimized SMEDDS were developed by utilizing desirability function. Maisine 35-1, Tween 80, and Transcutol HP were identified as oil, surfactant, and co-surfactant that had best solubility for NFM. Ternary phase diagrams were plotted to identify the self-emulsification region. Dissolution of putative NFM in simulated fasted or fed small intestinal conditions, respectively, predicted that there is a positive food effect. However, NFM loaded SMEDDS showed absence of food effect with no significant difference in dissolution performance either in Fasted or fed state simulated intestinal fluid (FaSSIF or FeSSIF) biorelevent dissolution media. The prepared SMEDDS were thermodynamically stable with droplet size (121 nm), poly dispersity index (PDI) (0.198) and emulsification time (<1 min). Transmission electron microscopy (TEM) analysis confirmed the spherical shape of the reconstituted SMEDDS droplets. The ex vivo performance revealed 4.57 fold enhancement in the apparent permeability of NFM as compared to NFM suspension. The animal pharmacokinetic analysis in New Zealand strain rabbits indicated food effect on pure NFM suspension. However, absence of food effect and 3.5-3.6 fold enhancement in the oral bioavailability was observed when NFM was formulated into SMEDDS. Thus, it could be envisaged that development of SMEDDS formulation of NFM could be one of the best alternative to enhance oral bioavailability of NFM.

A new PAMPA model using an in-house brain lipid extract for screening the blood-brain barrier permeability of drug candidates

The determination of the permeability of drug candidates across the blood-brain barrier (BBB) is a fundamental step during drug discovery programs. The parallel artificial membrane permeability assay (PAMPA) is a high throughput screening tool applied to evaluate the passive permeability and adapted to predict BBB penetration. Herein, a new PAMPA model was developed using an in-house brain lipid extract capable of discriminating BBB permeable from non-permeable compounds. The apparent permeability (Papp) of 18 reference molecules and 10 test compounds was assessed and compared with phosphatidylcholine and commercial porcine polar brain lipid (PBL). The physicochemical selectivity of the in-house brain lipid extract was demonstrated by correlating Papp values with physicochemical properties and its predictive capacity estimated by establishing in vitro-in vivo correlations. The strong correlations achieved between 2% (w/v) in-house lipid extract and PBL for reference (r(2)=0.77) and test compounds (r(2)=0.94) support an equivalent discriminatory capacity and validate the presented model. Moreover, PAMPA studies performed with PBL and in-house lipid extract exhibited a higher correlation with the in vivo parameter logBB (r(2)=0.76 and r(2)=0.72, respectively) than phosphatidylcholine (r(2)=0.51). Overall, the applied lipid extraction process was reproducible, economical and provided lipid extracts that can be used to reliably assess BBB permeation.

Formulation optimization of aprepitant microemulsion-loaded silicated corn fiber gum particles for enhanced bioavailability

The present investigation was aimed at development of silicate corn fiber gum (SCFG) particles as superior solid carrier for the preparation of Aprepitant (APT)-loaded self-emulsifying powder (SEP) system. 2(4) D-optimal mixture design with three level process variables was employed to develop SCFG particles, utilizing flow descriptors and hydrophobicity descriptors as response variables. The results indicated that blending of CFG (51.4% w/w) and magnesium silicate (MS) (48.6% w/w) using freeze-drying technique was found to have highest desirability (0.904). The developed SEP showed highest oil desorbing capacity, low self-emulsification time and highest drug content. It was observed that SCFG-SEP (F2 formulation) showed lowest PDI (0.2445 ± 0.03) as well as smallest particle size (127 ± 5.8 nm). The droplets were uniform and maintain their integrity after reconstitution (TEM analysis). Furthermore, APT-loaded SEP showed enhanced in vitro dissolution (4 folds) and ex vivo performance (7-fold enhanced Papp) as compared to pure APT. Furthermore, in vivo pharmacokinetic study showed that significant enhancement (p > 0.05) in Cmax was evident with APT-loaded F2 (SCFG-SEP) (1.93-fold) and F4 (Aerosil 200-SEP) (1.58-fold). The data also suggested increase in absorption rate when APT incorporated into SCFG-SEP. Thus, findings pointed toward enhanced bioavailability of APT when loaded into SCFG particles. Overall, the developed SCFG particles could be considered as a better alternative to already available solid carrier(s).

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

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

Aprepitant loaded solid preconcentrated microemulsion for enhanced bioavailability: A comparison with micronized Aprepitant

Aprepitant (APT) is a lipophilic, poorly water soluble drug with moderate permeability characteristic. Therefore, we aimed to improve solubility as well as permeability that could possibly improve oral bioavailability of APT. For this purpose, Quality by design (QbD) approach employing simplex lattice mixture design was used to prepare solid preconcentrated microemulsion (S-PCM). Further, the software generated numerically optimized S-PCM formulations were developed by utilizing desirability function. The spectral attributes (powder X-ray diffraction, ATR-FTIR, and differential scanning calorimetry) of S-PCM formulations suggested that APT was present in amorphous form. The results of droplet size (150-180 nm), zeta potential (-13 to -15 mV), poly dispersity index (PDI) (0.211-0.238) and emulsification time (<1 min), of these S-PCM formulations (SP1, SP2 and SP3) suggested spherical shape morphology (Transmission electron microscopy) with thermodynamic stability. The comparison of in vitro/ex vivo behavior of S-PCM (SP1) with micronized and non-micronized formulations of APT suggested 2-fold and 5-fold enhancement in solubility and permeability, respectively. This was further evident from pharmacokinetic studies in rabbits that showed 1.5-fold enhancement in bioavailability of S-PCM with respect to micronized APT. Thus, it could be envisaged that development of S-PCM formulation of APT is the best alternative to micronization technology based APT formulations reported earlier.

Low in vitro permeability of the cyanotoxin microcystin-LR across a Caco-2 monolayer: with identification of the limiting factors using modelling

Microcystins (MCs) are toxins produced by several cyanobacteria species found worldwide. MC-LR is the most frequent. Here, we used the human Caco-2 cell line grown on semi-permeable filter supports as an in vitro model for determining MC-LR intestinal bidirectional transport. In this study, there was very low and time-dependent apparent permeability of MC-LR. To identify the limiting factors involved in the low permeability of MC-LR, a mathematical model was constructed to get physiologically relevant and informative parameters. The apical-to-basolateral transport was characterised by a rapid and substantial decrease in apical MC-LR concentrations (24-40% of the initial amount). In the basolateral compartment, the concentrations increased slowly after a lag time, but represented only a small fraction of the loaded concentrations (0.3-1.3%) after 24 h. This weak permeability was mainly due to a low clearance of efflux (from the cellular to the basolateral compartment) and effective secretion (from the cellular to the apical compartment). During the basolateral-to-apical transport, we observed a slow decrease in basolateral concentrations and a rapid increase in apical concentrations. In conclusion, modelling has the potential to highlight the key mechanisms involved in the complex kinetics of toxin transport.