Impact of P-Glycoprotein on Intestinal Absorption of an Inhibitor of Apoptosis Protein Antagonist in Rats: Mechanisms of Nonlinear Pharmacokinetics and Food Effects

Ensemble Machine Learning Approaches Based on Molecular Descriptors and Graph Convolutional Networks for Predicting the Efflux Activities of MDR1 and BCRP Transporters

Multidrug resistance (MDR1) and breast cancer resistance protein (BCRP) play important roles in drug absorption and distribution. Computational prediction of substrates for both transporters can help reduce time in drug discovery. This study aimed to predict the efflux activity of MDR1 and BCRP using multiple machine learning approaches with molecular descriptors and graph convolutional networks (GCNs). In vitro efflux activity was determined using MDR1- and BCRP-expressing cells. Predictive performance was assessed using an in-house dataset with a chronological split and an external dataset. CatBoost and support vector regression showed the best predictive performance for MDR1 and BCRP efflux activities, respectively, of the 25 descriptor-based machine learning methods based on the coefficient of determination (R2). The single-task GCN showed a slightly lower performance than descriptor-based prediction in the in-house dataset. In both approaches, the percentage of compounds predicted within twofold of the observed values in the external dataset was lower than that in the in-house dataset. Multi-task GCN did not show any improvements, whereas multimodal GCN increased the predictive performance of BCRP efflux activity compared with single-task GCN. Furthermore, the ensemble approach of descriptor-based machine learning and GCN achieved the highest predictive performance with R2 values of 0.706 and 0.587 in MDR1 and BCRP, respectively, in time-split test sets. This result suggests that two different approaches to represent molecular structures complement each other in terms of molecular characteristics. Our study demonstrated that predictive models using advanced machine learning approaches are beneficial for identifying potential substrate liability of both MDR1 and BCRP.

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

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

Meta-Analysis of Food Effect on Oral Absorption of Efflux Transporter Substrate Drugs: Does Delayed Gastric Emptying Influence Drug Transport Kinetics?

The oral route of drug administration is the most convenient method of drug delivery, but it is associated with variable bioavailability. Food is one of the major factors that affect oral drug absorption by influencing drug properties (e.g., solubility and dissolution rate) and physiological factors (e.g., metabolism and transport across the gastrointestinal tract). The aim of this work was to investigate the effect of food on the high-affinity intestinal efflux transporter substrate drugs. We hypothesized that transport efficiency is higher in the fed state as compared to the fasted state because of the lower intestinal lumen drug concentration due to prolonged gastric emptying time. A systematic analysis of reported clinical food-effect (FE) studies on 311 drugs was performed and the association of the efflux transport efficiency was investigated on the FE magnitude, i.e., changes in maximal plasma concentration and area under the plasma concentration-time profile curve for both solubility and permeability-limited drugs. In total, 124 and 88 drugs showed positive and negative FE, respectively, whereas 99 showed no FE. As expected, the solubility-limited drugs showed positive FE, but interestingly, drugs with a high potential for efflux transport, were associated with negative FE. Moreover, a high-fat diet was associated with a higher magnitude of negative FE for high-affinity efflux transporter substrates as compared to a low-fat diet. To account for changes in drug absorption after food intake, the prolonged gastric emptying time should be considered in the physiologically based pharmacokinetic (PBPK) modeling of orally absorbed efflux transporter substrate drugs.

Quantitation of Cell Membrane Permeability of Cyclic Peptides by Single-Cell Cytoplasm Mass Spectrometry

Cyclic peptides (CPs) have attracted attention as next-generation drugs because they possess both cell-permeable potential as small molecules and specific affinity similar to antibodies. As intracellular molecules are important targets of CPs, quantitation of the intracellular retention and transmembrane permeability of CPs is necessary for drug development. However, permeated CPs within cells cannot be directly assessed by conventional permeability assays using methods such as artificial membranes and cell monolayers. Here, we propose a new approach using single-cell cytoplasm mass spectrometry (SCC-MS). After cells were incubated with CPs, the cytoplasm was directly collected from a single cell using a microneedle followed by nanoelectrospray ionization mass spectrometry detection of the CPs. The height of the CP peak was plotted against time and fitted with a simple function, y = a(1 - e^-bx), to calculate the apparent permeability coefficient (P_app) for both the influx and efflux directions. MCF-7 cells were selected as model cancer cells and cultured with cyclosporin A (CsA) and its demethylated analogs (dmCsA-1, -2, and -3) as model CPs. P_app values (10^-6 cm/s) obtained from cells incubated with 50 μM CPs ranged from 0.017 to 0.121 for influx and 0.20 to 1.48 for efflux. The higher efflux ratio was possibly caused by efflux transporters such as P-glycoprotein, a well-known receptor of CsA. The equilibrated intracellular concentration of CPs was estimated to be as low as 4.1-6.8 μM, which showed good consistency with the high efflux ratio. SCC-MS is promising as a reliable permeability assay for next-generation CP-based pharmaceuticals.

Evaluation of the Role of P-glycoprotein (P-gp)-Mediated Efflux in the Intestinal Absorption of Common Substrates with Elacridar, a P-gp Inhibitor, in Rats

BACKGROUND AND OBJECTIVES

P-glycoprotein (P-gp) has been shown previously to contribute to the intestinal absorption of verapamil, diltiazem, tacrolimus, colchicine and indinavir in situ; however, its contribution in vivo is unknown. The present study aimed to evaluate the in vivo involvement of P-gp using elacridar as its inhibitor to distinguish the contribution of P-gp from cytochrome P450 (CYP) 3A.

METHODS

Fexofenadine (5 mg/kg) and buspirone (1 mg/kg) were used as probe substrates of P-gp and CYP3A, respectively. Each dual substrate (1 or 2 mg/kg) was orally administered to rats after elacridar pre-treatment (3 mg/kg). Additionally, verapamil, diltiazem or tacrolimus was orally co-administered with fexofenadine.

RESULTS

Elacridar drastically increased the area under the plasma concentration-time curve (AUC_0-t) of oral fexofenadine by 8.6-fold; however, it did not affect the AUC_0-t of oral buspirone. Therefore, elacridar inhibited P-gp without affecting CYP3A. The absorption of oral verapamil, diltiazem and tacrolimus was not influenced by elacridar pre-treatment, and the increase in the AUC_0-t of fexofenadine was approximately 3-fold when co-administered with each substrate; the minimal effect of elacridar was attributable to the limited contribution of P-gp but not to their self-inhibition against the transporter. Conversely, elacridar significantly increased the AUC_0-t of colchicine (5.3-fold) and indinavir (2.0-fold), indicating that P-gp contributes to their absorption.

CONCLUSIONS

Elacridar is useful for distinguishing the contribution of P-gp from CYP3A to the absorption of drugs in rats. The in vivo contribution of P-gp is minimal for high permeable compounds owing to their fraction absorbed of nearly 1.0.