Gastrointestinal absorption of pimozide is enhanced by inhibition of P-glycoprotein

Optimisation of pharmacotherapy in psychiatry through therapeutic drug monitoring, molecular brain imaging and pharmacogenetic tests: focus on antipsychotics

BACKGROUND

For psychotic disorders (i.e. schizophrenia), pharmacotherapy plays a key role in controlling acute and long-term symptoms. To find the optimal individual dose and dosage strategy, specialized tools are used. Three tools have been proven useful to personalize drug treatments: therapeutic drug monitoring (TDM) of drug levels, pharmacogenetic testing (PG), and molecular neuroimaging.

METHODS

In these Guidelines, we provide an in-depth review of pharmacokinetics, pharmacodynamics, and pharmacogenetics for 50 antipsychotics. Over 30 international experts in psychiatry selected studies that have measured drug concentrations in the blood (TDM), gene polymorphisms of enzymes involved in drug metabolism, or receptor/transporter occupancies in the brain (positron emission tomography (PET)).

RESULTS

Study results strongly support the use of TDM and the cytochrome P450 (CYP) genotyping and/or phenotyping to guide drug therapies. Evidence-based target ranges are available for titrating drug doses that are often supported by PET findings.

CONCLUSION

All three tools discussed in these Guidelines are essential for drug treatment. TDM goes well beyond typical indications such as unclear compliance and polypharmacy. Despite its enormous potential to optimize treatment effects, minimize side effects and ultimately reduce the global burden of diseases, personalized drug treatment has not yet become the standard of care in psychiatry.

Impact of P-Glycoprotein-Mediated Drug-Endogenous Substrate Interactions on Androgen and Blood-Brain Barrier Permeability

This report focuses on pharmacokinetic drug-endogenous substrate interactions (DEIs). We hypothesized that P-glycoprotein (P-gp)-mediated DEI might affect androgen kinetics, especially its blood-brain barrier (BBB) permeability. The intracellular accumulation of the endogenous substrates of P-gp, testosterone (TES) and androstenedione (ADO) was increased by several tested drugs in uptake studies using P-gp overexpressing cells, indicating that these drugs inhibit P-gp-mediated efflux of TES of ADO from the cells. In a transport study using rat BBB kit, we found that the BBB limited the penetration of TES and ADO into the central nervous system. In addition, tested drugs that cause DEI were found to increase BBB permeability of TES and ADO via P-gp inhibition. In short, this study provides new findings regarding the possibility that DEI may affect the kinetics of endogenous substrates of P-gp.

Novel Screening System for Biliary Excretion of Drugs Using Human Cholangiocyte Organoid Monolayers with Directional Drug Transport

It has recently been reported that cholangiocyte organoids can be established from primary human hepatocytes. The purpose of this study was to culture the organoids in monolayers on inserts to investigate the biliary excretory capacity of drugs. Cholangiocyte organoids prepared from hepatocytes had significantly higher mRNA expression of CK19, a bile duct epithelial marker, compared to hepatocytes. The organoids also expressed mRNA for efflux transporters involved in biliary excretion of drugs, P-glycoprotein (P-gp), multidrug resistance-associated protein 2 (MRP2), and breast cancer resistance protein (BCRP). The subcellular localization of each protein was observed. These results suggest that the membrane-cultured cholangiocyte organoids are oriented with the upper side being the apical membrane side (A side, bile duct lumen side) and the lower side being the basolateral membrane side (B side, hepatocyte side), and that each efflux transporter is localized to the apical membrane side. Transport studies showed that the permeation rate from the B side to the A side was faster than from the A side to the B side for the substrates of each efflux transporter, but this directionality disappeared in the presence of inhibitor of each transporter. In conclusion, the cholangiocyte organoid monolayer system has the potential to quantitatively evaluate the biliary excretion of drugs. The results of the present study represent an unprecedented system using human cholangiocyte organoids, which may be useful as a screening model to directly quantify the contribution of biliary excretion to the clearance of drugs.

P-Glycoprotein-Mediated Interaction Is a Risk Factor for QT Prolongation in Concomitant Use of Antipsychotics and SSRIs as P-Glycoprotein-Mediated Inhibitors: Analysis of the Japanese Adverse Drug Event Report Database

The inhibition of human ether-a-go-go-related gene (hERG) channels is a known cause of QT prolongation triggered by antipsychotic drugs. Our previous studies suggest that P-glycoprotein (P-gp)-mediated drug interactions may lead to increased gastrointestinal absorption of pimozide and its accumulation in cardiomyocytes, thereby enhancing the inhibitory effect of hERG channels. There is a paucity of epidemiological studies examining the risk of QT prolongation by antipsychotic drugs in terms of P-gp-mediated interactions with concomitant drugs. Therefore, using the Japanese Adverse Event Reporting Database, we investigated whether the risk of QT prolongation triggered by antipsychotic drugs associated with hERG inhibition is affected by the concomitant use of selective serotonin reuptake inhibitors (SSRIs) associated with P-gp inhibition. The results showed that the frequency of QT prolongation increased when the antipsychotic drugs quetiapine and sulpiride, which are P-gp substrates, were combined with SSRIs with P-gp inhibition. In contrast, no association with QT prolongation was observed in patients on non-P-gp-substrate antipsychotics, irrespective of the P-gp inhibitory effect of the concomitant SSRI. These results suggest that P-gp-mediated interactions are a risk factor for antipsychotic-induced QT prolongation. There is a need for further investigation into the risks of specific drug combinations.

P-Glycoprotein-Mediated Pharmacokinetic Interactions Increase Pimozide hERG Channel Inhibition

Pimozide, an antipsychotic drug, is a potent inhibitor of the hERG channel. A case of death due to cardiac arrest has been reported in a boy who received pimozide together with sertraline and aripiprazole. In this study, we focused on drug-drug interactions and investigated the relationships between transporter-mediated intracellular accumulation and the hERG inhibitory effect of pimozide. The accumulation of pimozide in cardiomyocyte-derived AC16 cells was significantly increased by sertraline and aripiprazole, which are thought to have a P-glycoprotein (P-gp) inhibitory effect, and under P-gp siRNA conditions. These results suggest P-gp inhibition increases pimozide accumulation in AC16 cells. We introduced the hERG plasmid into AC16 cells and investigated the concentration-dependent hERG inhibitory effect of pimozide from within AC16 cells. Addition of 10 nM or more pimozide significantly inhibited the hERG current with concentration dependence. These results indicate P-gp-mediated pharmacokinetic interaction increases pimozide accumulation in AC16 cells, and the subsequent elevated pimozide levels within the cells may result in an increased risk of hERG channel inhibition. Our present study calls attention to the risks associated with the combined use of cardiotoxic P-gp substrate(s) and P-gp inhibitory medicines.

Directional Drug Transport through Membrane-Supported Monolayers of Human Liver-Derived Cell Lines

The aim of this work is to develop a new assay system for screening biliary excretion drugs. When monolayers of human liver-derived cell lines HepG2 and Huh-7 were grown on an insert membrane, the efflux ratio (ER: ratio of the apparent permeability coefficient in the basal-to-apical direction (P_app,B-to-A) to that in the apical to basal direction (P_app,A-to-B)) of sulfobromophthalein (BSP), a model substrate of multidrug resistance-associated protein 2 (MRP2), was greater than 1.0, indicating transport of BSP in the efflux direction. The efflux transport was significantly suppressed by MK-571, an inhibitor of MRPs, in both cell lines. Expression of MRP2 mRNA in HepG2 and Huh-7 was 3.5- and 1.4-fold higher, respectively, than in primary human hepatocytes, while expression of P-glycoprotein and breast cancer resistance protein mRNAs was markedly lower, supporting the idea that MRP2 is the main mediator of directional BSP transport in this assay system. The advantage of our system is the potential to quantitatively evaluate biliary excretion of MRP2 substrates in vitro.

An evaluation of ledipasvir + sofosbuvir for the treatment of chronic hepatitis C infection

Introduction: Hepatitis C (HCV) is viral disease with a global impact. Over the last 10 years, the treatment of this disease has evolved. Treatment guidelines have evolved to adopt new medications for HCV. These drugs have shown efficacy over 90% throughout the class as well as a better safety profile than the previous recommended pharmacotherapy. Dual-therapy DAAs emerged with FDA approval of Ledipasvir/Sofosbuvir (LDV/SOF) in 2014.Areas Covered: LDV/SOF is a dual-therapy option for chronic HCV patients (>6 months of infection) in select genotypes. This article reviews the studies relevant to the pharmacokinetic/pharmacodynamic properties of these drugs as well as its trials leading to approval.Expert opinion: LDV/SOF is included in the AASLD/IDSA guidelines for the treatment of HCV genotypes 1a and 1b with or without cirrhosis and genotype 4 without cirrhosis with an evidence and recommendation rating of IA. Genotype 4 with cirrhosis and genotypes 5 and 6 carry a Class IIa level B recommendation. The combination is not FDA approved for genotypes 2 and 3. Single-pill regimens, like LDV/SOF, are important to maintain the quality of life of children and other special populations infected with HCV by shortening treatment regimens, avoiding complex pill regimens, and eliminating injection therapies.

Rapid Increase of Gastrointestinal P-Glycoprotein Functional Activity in Response to Etoposide Stimulation

We previously reported that exposure of human colon adenocarcinoma (Caco-2) cells to the bitter substance phenylthiocarbamide (PTC) rapidly enhanced the transport function of P-glycoprotein (P-gp). In this study, we investigated the short-term effect of etoposide, another bitter-tasting P-gp substrate, on P-gp transport function in the same cell line. We found that etoposide exposure significantly increased both the P-gp protein level in the plasma membrane fraction and the efflux rate of rhodamine123 (Rho123) in Caco-2 cells within 10 min. The efflux ratio (ratio of the apparent permeability coefficient in the basal-to-apical direction to that in the apical-to-basal direction) of Rho123 in etoposide-treated cells was also significantly increased compared with the control. These results indicated that etoposide rapidly enhances P-gp function in Caco-2 cells. In contrast, P-gp expression in whole cells at both the mRNA and protein level was unchanged by etoposide exposure, compared with the levels in non-treated cells. Furthermore, etoposide increased the level of phosphorylated ezrin, radixin and moesin (P-ERM) proteins in the plasma membrane fraction of Caco-2 cells within 10 min. P-gp functional changes were blocked by YM022, an inhibitor of cholecystokinin (CCK) receptor. These results suggest that etoposide induces release of CCK, causing activation of the CCK receptor followed by phosphorylation of ERM proteins, which recruit intracellular P-gp for trafficking to the gastrointestinal membrane, thereby increasing the functional activity of P-gp.