Transcription factor-mediated regulation of the BCRP/ABCG2 efflux transporter: a review across tissues and species

The role of ABCG2 in health and disease: Linking cancer therapy resistance and other disorders

All biological systems have adenosine triphosphate (ATP) binding cassette (ABC) transporters, one of the significant protein superfamilies involved in transport across membranes. ABC transporters have been implicated in the etiology of diseases like metabolic disorders, cancer, and Alzheimer's disease. ATP-binding cassette superfamily G member 2 (ABCG2), one of the ABC transporters, is necessary for the ATP-dependent efflux of several endogenous and exogenous substances. Consequently, it maintained cellular homeostasis and shielded tissue from xenobiotic substances. ABCG2 was initially identified in an Adriamycin-selected breast cancer cell line (MCF-7/AdrVp) and was linked to the emergence of multidrug resistance (MDR) in cancerous cells. Under many pathophysiological conditions, including inflammation, disease pathology, tissue injury, infection, and in response to xenobiotics and endogenous substances, the expression of ABCG2 undergoes alterations that result in modifications in its function and activity. Genetic variants in the ABCG2 transporter can potentially impact its expression and function, contributing to the development of many disorders. This review aimed to illustrate the impact of ABCG2 expression and its variants on oral drug bioavailability, MDR in specific cancer cells, explore the relationship between ABCG2 expression and other disorders such as gout, Alzheimer's disease, epilepsy, and erythropoietic protoporphyria, and demonstrate the influence of various synthetic and natural compounds in regulating ABCG2 expression.

A close examination of BCRP's role in lactation and methods for predicting drug distribution into milk

Breastfeeding is the most complete nutritional method of feeding infants, but several impediments affect the decision to breastfeed, including questions of drug safety for medications needed during lactation. Despite recent FDA guidance, few labels provide clear dosing advice during lactation. Physiologically based pharmacokinetic modeling (PBPK) is well suited to mechanistically explore pharmacokinetics and dosing paradigms to fill gaps in the absence of extensive clinical studies and complement existing real-world data. For lactation-focused PBPK (Lact-PBPK) models, information on system parameters (e.g., expression of drug transporters in mammary epithelial cells) is sparse. The breast cancer resistance protein (BCRP) is expressed on the apical side of mammary epithelial cells where it actively transports drugs/substrates into milk (reported milk: plasma ratios range from 2 to 20). A critical review of BCRP and its role in lactation was conducted. Longitudinal changes in BCRP mRNA expression have been identified in women with a maximum reached around 5 months postpartum. Limited data are available on the ontogeny of BCRP in infant intestine; however, data indicate lower BCRP abundance in infants compared to adults. Current status of incorporation of drug transporter information in Lact-PBPK models to predict active secretion of drugs into breast milk and consequential exposure of breast-fed infants is discussed. In addition, this review highlights novel clinical tools for evaluation of BCRP activity, namely a potential non-invasive BCRP biomarker (riboflavin) and liquid biopsy that could be used to quantitatively elucidate the role of this transporter without the need for administration of drugs and to inform Lact-PBPK models.

Roles of the ABCG2 Transporter in Protoporphyrin IX Distribution and Toxicity

ATP-binding cassette transporter subfamily G member 2 (ABCG2) is a membrane-bound transporter responsible for the efflux of various xenobiotics and endobiotics, including protoporphyrin IX (PPIX), an intermediate in the heme biosynthesis pathway. Certain genetic mutations and chemicals impair the conversion of PPIX to heme and/or increase PPIX production, leading to PPIX accumulation and toxicity. In mice, deficiency of ABCG2 protects against PPIX-mediated phototoxicity and hepatotoxicity by modulating PPIX distribution. In addition, in vitro studies revealed that ABCG2 inhibition increases the efficacy of PPIX-based photodynamic therapy by retaining PPIX inside target cells. In this review, we discuss the roles of ABCG2 in modulating the tissue distribution of PPIX, PPIX-mediated toxicity, and PPIX-based photodynamic therapy. SIGNIFICANCE STATEMENT: This review summarized the roles of ABCG2 in modulating PPIX distribution and highlighted the therapeutic potential of ABCG2 inhibitors for the management of PPIX-mediated toxicity.

The PPP2R1A cancer hotspot mutant p.R183W increases clofarabine resistance in uterine serous carcinoma cells by a gain-of-function mechanism

PURPOSE

Uterine serous carcinoma (USC) is generally associated with poor prognosis due to a high recurrence rate and frequent treatment resistance; hence, there is a need for improved therapeutic strategies. Molecular analysis of USC identified several molecular markers, useful to improve current treatments or identify new druggable targets. PPP2R1A, encoding the Aα subunit of the tumor suppressive Ser/Thr phosphatase PP2A, is mutated in up to 40% of USCs. Here, we investigated the effect of the p.R183W PPP2R1A hotspot variant on treatment response to the nucleoside analogue clofarabine.

METHODS AND RESULTS

USC cells stably expressing p.R183W Aα showed increased resistance to clofarabine treatment in vitro and, corroborated by decreased clofarabine-induced apoptosis, G1 phase arrest, DNA-damage (γH2AX) and activation of ATM and Chk1/2 kinases. Phenotypic rescue by pharmacologic PP2A inhibition or dicer-substrate siRNA (dsiRNA)-mediated B56δ subunit knockdown supported a gain-of-function mechanism of Aα p.R183W, promoting dephosphorylation and inactivation of deoxycytidine kinase (dCK), the cellular enzyme responsible for the conversion of clofarabine into its bioactive form. Therapeutic assessment of related nucleoside analogues (gemcitabine, cladribine) revealed similar effects, but in a cell line-dependent manner. Expression of two other PPP2R1A USC mutants (p.P179R or p.S256F) did not affect clofarabine response in our cell models, arguing for mutant-specific effects on treatment outcome as well.

CONCLUSIONS

While our results call for PPP2R1A mutant and context-dependent effects upon clofarabine/nucleoside analogue monotherapy, combining clofarabine with a pharmacologic PP2A inhibitor proved synergistically in all tested conditions, highlighting a new generally applicable strategy to improve treatment outcome in USC.

Risk factors associated with high-dose methotrexate induced toxicities

INTRODUCTION

High-dose methotrexate (HDMTX) therapy poses challenges in various neoplasms due to individualized pharmacokinetics and associated adverse effects. Our purpose is to identify early risk factors associated with HDMTX-induced toxicities, paving the way for personalized treatment.

AREAS COVERED

A systematic review of PubMed and Cochrane databases was conducted for articles from inception to July 2023. Eligible studies included reviews, clinical trials, and real-world analyses. Irrelevant studies were excluded, and manual searches and citation reviews were performed. Factors such as MTX exposure, drug interactions, demographics, serum albumin, urine pH, serum calcium, and genetic polymorphisms affecting MTX transport (e.g. SLCO1B1), intracellular folate metabolism (MTHFR), cell development (ARID5B), metabolic pathways (UGT1A1, PNPLA3), as well as epigenetics were identified.

EXPERT OPINION

This comprehensive review aids researchers and clinicians in early identification of HDMTX toxicity risk factors. By understanding the multifaceted risk factors associated with hematologic malignancies, personalized treatment approaches can be tailored to optimize therapeutic outcomes.

Natural medicinal compounds target signal transduction pathways to overcome ABC drug efflux transporter-mediated multidrug resistance in cancer

ATP-binding cassette (ABC) transporters such as ABCB1, ABCG2, and ABCC1 are the major players in drug efflux-mediated multidrug resistance (MDR), which severely affects the efficacy of chemotherapy. Several synthetic compounds block the drug transport by ABC transporters; however, they exhibit a narrow therapeutic window, and produce side effects in non-target normal tissues. Conversely, the downregulation of the expression of ABC drug transporters seems to be a promising strategy to reverse MDR in cancer cells. Several signaling pathways, such as NF-κB, STAT3, Gli, NICD, YAP/TAZ, and Nrf2 upregulate the expression of ABC drug transporters in drug-resistant cancers. Recently, natural medicinal compounds have gained importance to overcome the ABC drug-efflux pump-mediated MDR in cancer. These compounds target transcription factors and the associated signal transduction pathways, thereby downregulating the expression of ABC transporters in drug-resistant cancer cells. Several potent natural compounds have been identified as lead candidates to synergistically enhance chemotherapeutic efficacy, and a few of them are already in clinical trials. Therefore, modulation of signal transduction pathways using natural medicinal compounds for the reversal of ABC drug transporter-mediated MDR in cancer is a novel approach for improving the efficiency of the existing chemotherapeutics. In this review, we discuss the modulatory role of natural medicinal compounds on cellular signaling pathways that regulate the expression of ABC transporters in drug-resistant cancer cells.

Clinical relevance of stem cells in lung cancer

Lung cancer is the major cause of cancer-related deaths worldwide, it has one of the lowest 5-year survival rate, mainly because it is diagnosed in the late stage of the disease. Lung cancer is classified into two groups, small cell lung cancer (SCLC) and non-SCLC (NSCLC). In turn, NSCLC is categorized into three distinct cell subtypes: Adenocarcinoma, squamous cell carcinoma, and large cell carcinoma. NSCLC is the most common lung cancer, accounting for 85% of all lung cancers. Treatment for lung cancer is linked to the cell type and stage of the disease, involving chemotherapy, radiation therapy, and surgery. Despite improvements in therapeutic treatments, lung cancer patients show high rates of recurrence, metastasis, and resistance to chemotherapy. Lung stem cells (SCs) are undifferentiated cells capable of self-renewal and proliferation, are resistant to chemotherapy and radiotherapy and, due to their properties, could be involved in the development and progression of lung cancer. The presence of SCs in the lung tissue could be the reason why lung cancer is difficult to treat. The identification of lung cancer stem cells biomarkers is of interest for precision medicine using new therapeutic agents directed against these cell populations. In this review, we present the current knowledge on lung SCs and discuss their functional role in the initiation and progression of lung cancer, as well as their role in tumor resistance to chemotherapy.

A pharmacokinetic drug-drug interaction study between rosuvastatin and emvododstat, a potent anti-SARS-CoV-2 (COVID-19) DHODH (dihydroorotate dehydrogenase) inhibitor

A therapeutic agent that targets both viral replication and the hyper-reactive immune response would offer a highly desirable treatment for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2; COVID-19) management. Emvododstat (PTC299) was found to be a potent inhibitor of immunomodulatory and inflammation-related processes by the inhibition of dihydroorotate dehydrogenase (DHODH) to reduce SARS-CoV-2 replication. DHODH is the rate-limiting enzyme of the de novo pyrimidine nucleotide biosynthesis pathway. This drug interaction study was performed to determine whether emvododstat was an inhibitor of breast cancer resistance protein (BCRP) transporters in humans. Potential drug-drug interactions (DDIs) between emvododstat and a BCRP transporter substrate (rosuvastatin) were investigated by measuring plasma rosuvastatin concentrations before and after emvododstat administration. There was no apparent difference in rosuvastatin plasma exposure. The geometric means of maximum plasma rosuvastatin concentrations (Cmax ) were 4369 (rosuvastatin) and 5141 pg/mL (rosuvastatin + emvododstat) at 4 h postdose. Geometric mean rosuvastatin area under the concentration-time curve (AUC) from time 0 to the last measurable plasma concentration was 45 616 and 48 975 h·pg/mL when administered alone and after 7 days of b.i.d. emvododstat dosing, respectively. Geometric least squares mean ratios for Cmax and AUC were approximately equal to 1. Overall, administration of multiple doses of 100 mg emvododstat b.i.d. for 7 days in combination with a single dose of rosuvastatin was safe and well tolerated. Emvododstat can be safely administered with other BCRP substrate drugs. Hence, pharmacokinetic DDI mediated via BCRP inhibition is not expected when emvododstat and BCRP substrates are coadministered.

Dual-drug codelivery nanosystems: An emerging approach for overcoming cancer multidrug resistance

Multidrug resistance (MDR) promotes tumor recurrence and metastasis and heavily reduces anticancer efficiency, which has become a primary reason for the failure of clinical chemotherapy. The mechanisms of MDR are so complex that conventional chemotherapy usually fails to achieve an ideal therapeutic effect and even accelerates the occurrence of MDR. In contrast, the combination of chemotherapy with dual-drug has significant advantages in tumor therapy. A novel dual-drug codelivery nanosystem, which combines dual-drug administration with nanotechnology, can overcome the application limitation of free drugs. Both the characteristics of nanoparticles and the synergistic effect of dual drugs contribute to circumventing various drug-resistant mechanisms in tumor cells. Therefore, developing dual-drug codelivery nanosystems with different multidrug-resistant mechanisms has an important reference value for reversing MDR and enhancing the clinical antitumor effect. In this review, the advantages, principles, and common codelivery nanocarriers in the application of dual-drug codelivery systems are summarized. The molecular mechanisms of MDR and the dual-drug codelivery nanosystems designed based on different mechanisms are mainly introduced. Meanwhile, the development prospects and challenges of codelivery nanosystems are also discussed, which provide guidelines to exploit optimized combined chemotherapy strategies in the future.

[Quantitative assessment of breast cancer resistance protein during pregnancy in rabbits]

Breast cancer resistance protein (BCRP,ABCG2) is an efflux transporter protein that transports various substrates from the cell to the extracellular space or organ cavities. The aim of this study was a complex assessment of the amount of BCRP during pregnancy in rabbits. The amount of BCRP in samples of the rabbit jejunum, liver, kidney, cerebral cortex, and placenta was determined by enzyme immunoassay, and in human hepatocellular carcinoma (HepG2) cells by the Western blot. To study the mechanisms involved in control of the dynamic BCRP levels during pregnancy, serum concentrations of sex hormones were investigated by radioimmunoassay and relative amounts of constitutive androstane receptor (CAR) and pregnane X receptor (PXR) in these organs were evaluated using the Western blot method. The putative role of CAR and PXR in regulation of the BCRP level by progesterone was evaluated in vitro experiments on HepG2 cells. It was found that amount of BCRP in the jejunum of pregnant rabbits was higher than in the placenta, liver, kidneys, and cerebral cortex. An increase in the amount of BCRP in the liver of rabbits was noted on the 21st day of pregnancy and a tendency to the increase was also detected on the 28th day; in the kidney and cerebral cortex increased BCRP levels were detected on the 28th day and 14th day of pregnancy, respectively, as compared with non-pregnant females. In vitro experiments with HepG2 cells have shown that the increase in the BCRP level is determined by the activating effect of progesterone on PXR.

Chicken xenobiotic receptor upregulates the BCRP/ABCG2 transporter

The transporter breast cancer resistance protein (BCRP, encoded by ABCG2) influences the bioavailability and elimination of numerous substrate drugs during clinical therapy. The xenobiotic-sensing nuclear receptors pregnane X receptor (PXR) and constitutive androstane receptor (CAR) reportedly regulate functional expression of BCRP in mammalian species. However, it is unknown whether chicken xenobiotic receptor (CXR) regulates the expression and activity of BCRP. This study aimed to investigate the role of CXR in regulation of BCRP in chicken using in vitro and in vivo models. CXR was expressed in the main drug-metabolizing tissues of chickens, and its expression correlated well with that of the prototypical target genes CYP2H1 and ABCG2. BCRP expression was upregulated, and transporter activity was increased, in chicken primary hepatocytes exposed to the CXR agonist metyrapone. Using RNA interference and ectopic expression techniques to manipulate the cellular CXR status, we confirmed that ABCG2 gene regulation depended on CXR. In vivo experiments showed that metyrapone induced BCRP in the liver, kidney, duodenum, and jejunum of chickens. Coadministration of metyrapone significantly changed the pharmacokinetic behavior of orally administered florfenicol (substrate of chicken BCRP), with a lower C_max (4.62 vs. 7.35 µg/mL, P < 0.01) and AUC_0-t (15.83 vs. 24.18 h·mg/L, P < 0.01) as well as a higher T_max (0.96 vs. 0.79 h, P < 0.05) and Cl/F (0.13 vs. 0.08 L/h/kg, P < 0.05). Together, our data suggest that CXR is involved in regulation of BCRP, and consequently, coadministration of a CXR agonist can affect the pharmacokinetic behavior of an orally administered BCRP substrate.

Causative Role of Anoxic Environment in Bacterial Regulation of Human Intestinal Function

Introduction

Life on Earth depends on oxygen; human tissues require oxygen signaling, whereas many microorganisms, including bacteria, thrive in anoxic environments. Despite these differences, human tissues and bacteria coexist in close proximity to each other such as in the intestine. How oxygen governs intestinal-bacterial interactions remains poorly understood.

Methods

To address to this gap, we created a dual-oxygen environment in a microfluidic device to study the role of oxygen in regulating the regulation of intestinal enzymes and proteins by gut bacteria. Two-layer microfluidic devices were designed using a fluid transport model and fabricated using soft lithography. An oxygen-sensitive material was integrated to determine the oxygen levels. The intestinal cells were cultured in the upper chamber of the device. The cells were differentiated, upon which bacterial strains, a facultative anaerobe, Escherichia coli Nissle 1917, and an obligate anaerobe, Bifidobacterium Adolescentis, were cultured with the intestinal cells.

Results

The microfluidic device successfully established a dual-oxygen environment. Of particular importance in our findings was that both strains significantly upregulated mucin proteins and modulated several intestinal transporters and transcription factors but only under the anoxic-oxic oxygen gradient, thus providing evidence of the role of oxygen on bacterial-epithelial signaling.

Conclusions

Our work that integrates cell and molecular biology with bioengineering presents a novel strategy to engineer an accessible experimental system to provide tailored oxygenated environments. The work could provide new avenues to study intestine-microbiome signaling and intestinal tissue engineering, as well as a novel perspective on the indirect effects of gut bacteria on tissues including tumors.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-022-00735-x.

O-Sulfation disposition of curcumin and quercetin in SULT1A3 overexpressing HEK293 cells: the role of arylsulfatase B in cellular O-sulfation regulated by transporters

Extensive phase II metabolic reactions (i.e., glucuronidation and sulfation) have resulted in low bioavailability and decreased biological effects of curcumin and quercetin. Compared to glucuronidation, information on the sulfation disposition of curcumin and quercetin is limited. In this study, we identified that BCRP and MRP4 played a critical role in the cellular excretion of curcumin-O-sulfate (C-O-S) and quercetin-O-sulfate (Q-O-S) by integrating chemical inhibition with transporter knock-down experiments. Inhibited excretion of sulfate (C-O-S and Q-O-S) caused significant reductions in cellular O-sulfation of curcumin (a maximal 74.4% reduction) and quercetin (a maximal 76.9% reduction), revealing a strong interplay of sulfation with efflux transport. It was further identified that arylsulfatase B (ARSB) played a crucial role in the regulation of cellular O-sulfation by transporters. ARSB overexpression significantly enhanced the reduction effect of MK-571 on the cellular O-sulfation (f_met) of the model compound (38.8% reduction for curcumin and 44.2% reduction for quercetin). On the contrary, ARSB knockdown could reverse the effect of MK-571 on the O-sulfation disposition of the model compound (29.7% increase for curcumin and 47.3% increase for quercetin). Taken together, ARSB has been proven to be involved in cellular O-sulfation, accounting for transporter-dependent O-sulfation of curcumin and quercetin. A better understanding of the interplay beneath metabolism and transport will contribute to the exact prediction of in vivo drug disposition and drug-drug interactions.

Pros and cons of NRF2 activation as adjunctive therapy in rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disease with an important inflammatory component accompanied by deregulated redox-dependent signaling pathways that are feeding back into inflammation. In this context, we bring into focus the transcription factor NRF2, a master redox regulator that exerts exquisite antioxidant and anti-inflammatory effects. The review does not intend to be exhaustive, but to point out arguments sustaining the rationale for applying an NRF2-directed co-treatment in RA as well as its potential limitations. The involvement of NRF2 in RA is emphasized through an analysis of publicly available transcriptomic data on NRF2 target genes and the findings from NRF2-knockout mice. The impact of NRF2 on concurrent pathologic mechanisms in RA is explained by its crosstalk with major redox-sensitive inflammatory and cell death-related pathways, in the context of the increased survival of pathologic cells in RA. The proposed adjunctive therapy targeted to NRF2 is further sustained by the existence of promising NRF2 activators that are in various stages of drug development. The interference of NRF2 with conventional anti-rheumatic therapies is discussed, including the cytoprotective effects of NRF2 for alleviating drug toxicity. From another perspective, the review presents how NRF2 activation would be decreasing the efficacy of synthetic anti-rheumatic drugs by increasing drug efflux. Future perspectives regarding pharmacologic NRF2 activation in RA are finally proposed.

Ivermectin induces chicken BCRP/ABCG2 expression and function: Involvement of CXR signaling pathway and mRNA stabilization

Ivermectin is a macrocyclic lactone antiparasitic drug widely used in human and veterinary medicine. Previous studies indicated that ivermectin could interact with P-glycoprotein, being a good inducer and substrate; however, it is unknown whether ivermectin affects BCRP of chicken. In this study, we found that ivermectin distinctly affected the expression of BCRP in a time- and concentration-dependent up-regulatory way in chicken primary hepatocytes. Subsequent series of experiments showed that the BCRP induction is related with the increase of CXR expression and, promoting CXR translocations to the nucleus and enhancing the stability of Abcg2 mRNA at the post-transcriptional level by ivermectin. Furthermore, we observed that ivermectin also enhanced the stability of Abcg2 mRNA at the post-transcriptional level by Act-D chase assay. We got the similar results by in vivo test that ivermectin-induced BCRP and CXR expression in pharmacologically important tissues, and decreased the apparent permeability coefficient of florfenicol (substrate of chicken BCRP). In conclusion, the results indicated that ivermectin could induce chicken BCRP expression and function through the transcriptional CXR signaling pathway and post-transcriptional mRNA stabilization.

Significance of the Vitamin D Receptor on Crosstalk with Nuclear Receptors and Regulation of Enzymes and Transporters

The vitamin D receptor (VDR), in addition to other nuclear receptors, the pregnane X receptor (PXR) and constitutive androstane receptor (CAR), is involved in the regulation of enzymes, transporters and receptors, and therefore intimately affects drug disposition, tissue health, and the handling of endogenous and exogenous compounds. This review examines the role of 1α,25-dihydroxyvitamin D₃ or calcitriol, the natural VDR ligand, on activation of the VDR and its crosstalk with other nuclear receptors towards the regulation of enzymes and transporters, notably many of the cytochrome P450s including CYP3A4 and sulfotransferase 2A1 (SULT2A1) as well as cholesterol 7α-hydroxylase (CYP7A1). Moreover, the VDR upregulates the intestinal channel, TRPV6, for calcium absorption, LDL receptor-related protein 1 (LRP1) and receptor for advanced glycation end products (RAGE) in brain for β-amyloid peptide efflux and influx, the sodium phosphate transporters (NaP_i), the apical sodium-dependent bile acid transporter (ASBT) and organic solute transporters (OSTα-OSTβ) for bile acid absorption and efflux, respectively, the renal organic anion transporter 3 (OAT3) and several of the ATP-binding cassette protein transporters-the multidrug resistance protein 1 (MDR1) and the multidrug resistance-associated proteins (MRPs). Hence, the role of the VDR is increasingly being recognized for its therapeutic potential and pharmacologic activity, giving rise to drug-drug interactions (DDI). Therapeutically, ligand-activated VDR shows anti-inflammatory effects towards the suppression of inflammatory mediators, improves cognition by upregulating amyloid-beta (Aβ) peptide clearance in brain, and maintains phosphate, calcium, and parathyroid hormone (PTH) balance and kidney function and bone health, demonstrating the crucial roles of the VDR in disease progression and treatment of diseases.

A Systematic Review of Population Pharmacokinetic Models of Methotrexate

BACKGROUND AND OBJECTIVES

Methotrexate (MTX) is widely used for the treatment of a variety of neoplastic and autoimmune diseases. However, its toxicity and efficacy varied greatly among individuals, and they could be predicted by its pharmacokinetics. Many population pharmacokinetic models have been published to describe MTX pharmacokinetics. The objective of this systematic review was to summarize and discuss covariates with significant influence on MTX pharmacokinetics.

METHODS

We searched PubMed and EMBASE databases from their inception to April 2021 for population pharmacokinetic of MTX. The articles were screened by inclusion and exclusion criteria. The characteristics of studies and information for model construction and validation were extracted, summarized and discussed.

RESULTS

Thirty-five articles were included. The two-compartment model well described the pharmacokinetic behavior of MTX. For inter-individual variability, an exponential distribution error model was usually used for high-dose MTX population pharmacokinetic models, while a proportional distribution error model was used for low-dose MTX population pharmacokinetic models. Proportional and combined proportional and additive error models were used to describe residual error. Renal function was an independent indicator of MTX clearance. Body weight, age, gene polymorphisms (SLCO1B1, ABCC2, ABCB1, ABCG2 and MTHFR) and co-medications (proton pump inhibitors, non-steroidal anti-inflammatory drug, dexamethasone, vancomycin, penicillin and salicylic acid) could influence MTX clearance. Body weight, body surface area, age and dosage regimen have significant influence on MTX central compartment volume. Internal bootstrap test, external validation and visual predictive check were used to evaluate model predictive ability.

CONCLUSIONS

Various covariates could affect MTX pharmacokinetics, and their relationships have been summarized and discussed. This review will be helpful for researchers to develop their own population pharmacokinetic models and select appropriate models for individualized therapy of MTX.

Investigation of the role and quantitative impact of breast cancer resistance protein on drug distribution into brain and CSF in rats

Breast cancer resistance protein (BCRP) expressed in the blood-brain barrier plays a major role in limiting drug distribution into the central nervous system (CNS). However, functional involvement of BCRP in drug distribution into the brain and cerebrospinal fluid (CSF) remains unclear. The aim of present study was to reveal the role and quantitative impact of BCRP on CNS distribution. The brain-to-plasma unbound concentration ratio (K_p,uu,brain) and CSF-to-plasma unbound concentration ratio (K_p,uu,CSF) values of BCRP-specific substrates were determined in rats. The K_p,uu,brain values decreased, as the in vitro BCRP corrected flux ratio (CFR) increased. The K_p,uu,CSF values of BCRP-specific substrates were greater than the K_p,uu,brain values. Increase in the K_p,uu,brain values induced by co-administration of BCRP inhibitor correlated with the in vitro BCRP CFR and were greater than the increase in K_p,uu,CSF values induced by BCRP inhibitor except nebicapone. The contribution of BCRP to the brain and CSF distribution of the dual P-glycoprotein/BCRP substrates, imatinib and prazosin, was similar to that of BCRP-specific substrates. Thus, we revealed that the impact of in vivo BCRP on CNS distribution is correlated with in vitro BCRP CFR, and that BCRP limits drug distribution into the brain more strongly than into the CSF.

Impact of kidney dysfunction on hepatic and intestinal drug transporters

Emerging information suggests that pathology of the kidney may not only affect expression and function of membrane transporters in the organ, but also in the gastrointestinal tract and the liver. Transporter dysfunction may cause effects on handling of drug as well as endogenous compounds with subsequent clinical consequences. A literature search was conducted on Ovid and PubMed databases to select relevant in vitro, animal and human studies that have reported expression, protein abundance and function of the gastrointestinal and liver localized ABC transporters and SLC carriers in kidney dysfunction or uremia states. The altered function of drug transporters in the liver and intestines in kidney failure subjects may provide compensatory activity in handling endogenous compounds (e.g. uremic toxins), which is expected to affect drug pharmacokinetics and local drug actions.

Drug-herb interactions between Scutellaria baicalensis and pharmaceutical drugs: Insights from experimental studies, mechanistic actions to clinical applications

Whilst the popular use of herbal medicine globally, it poses challenges in managing potential drug-herb interaction. There are two folds of the drug-herb interaction, a beneficial interaction that may improve therapeutic outcome and minimise the toxicity of drug desirably; by contrast, negative interaction may evoke unwanted clinical consequences, especially with drugs of narrow therapeutic index. Scutellaria baicalensis Georgi is one of the most popular medicinal plants used in Asian countries. It has been widely used for treating various diseases and conditions such as cancer, diabetes, inflammation, and oxidative stress. Studies on its extract and bioactive compounds have shown pharmacodynamic and pharmacokinetic interactions with a wide range of pharmaceutical drugs as evidenced by plenty of in vitro, in vivo and clinical studies. Notably, S. baicalensis and its bioactives including baicalein, baicalin and wogonin exhibited synergistic interactions with many pharmaceutical drugs to enhance their efficacy, reduce toxicity or overcome drug resistance to combat complex diseases such as cancer, diabetes and infectious diseases. On the other hand, S. baicalensis and its bioactives also affected the pharmacokinetic profile of many drugs in absorption, distribution, metabolism and elimination via the regulatory actions of the efflux pumps and cytochrome P450 enzymes. This review provides comprehensive references of the observed pharmacodynamic and pharmacokinetic drug interactions of Scutellaria baicalensis and its bioactives. We have elucidated the interaction with detailed mechanistic actions, identified the knowledge gaps for future research and potential clinical implications. Such knowledge is important for the practice of both conventional and complementary medicines, and it is essential to ensure the safe use of related herbal medicines. The review may be of great interest to practitioners, consumers, clinicians who require comprehensive information on the possible drug interactions with S. baicalensis and its bioactives.

ABCB1, ABCG2, ABCC1, ABCC2, and ABCC3 drug transporter polymorphisms and their impact on drug bioavailability: what is our current understanding?

INTRODUCTION

Interindividual differences in drug response are a frequent clinical challenge partly due to variation in pharmacokinetics. ATP-binding cassette (ABC) transporters are crucial determinants of drug disposition. They are subject of gene regulation and drug-interaction; however, it is still under debate to which extend genetic variants in these transporters contribute to interindividual variability of a wide range of drugs.

AREAS COVERED

This review discusses the current literature on the impact of genetic variants in ABCB1, ABCG2 as well as ABCC1, ABCC2, and ABCC3 on pharmacokinetics and drug response. The aim was to evaluate if results from recent studies would increase the evidence for potential clinically relevant pharmacogenetic effects.

EXPERT OPINION

Although enormous efforts have been made to investigate effects of ABC transporter genotypes on drug pharmacokinetics and response, the majority of studies showed only weak if any associations. Despite few unique results, studies mostly failed to confirm earlier findings or still remained inconsistent. The impact of genetic variants on drug bioavailability is only minor and other factors regulating the transporter expression and function seem to be more critical. In our opinion, the findings on the so far investigated genetic variants in ABC efflux transporters are not suitable as predictive biomarkers.

Intestinal Efflux Transporters P-gp and BCRP Are Not Clinically Relevant in Apixaban Disposition

PURPOSE

The involvement of the intestinally expressed xenobiotic transporters P-glycoprotein (P-gp) and Breast Cancer Resistance Protein (BCRP) have been implicated in apixaban disposition based on in vitro studies. Recommendations against co-administration of apixaban with inhibitors of these efflux transporters can be found throughout the literature as well as in the apixaban FDA label. However, the clinical relevance of such findings is questionable due to the high permeability and high solubility characteristics of apixaban.

METHODS

Using recently published methodologies to discern metabolic- from transporter- mediated drug-drug interactions, a critical evaluation of all published apixaban drug-drug interaction studies was conducted to investigate the purported clinical significance of efflux transporters in apixaban disposition.

RESULTS

Rational examination of these clinical studies using basic pharmacokinetic theory does not support the clinical significance of intestinal efflux transporters in apixaban disposition. Further, there is little evidence that efflux transporters are clinically significant determinants of systemic clearance.

CONCLUSIONS

Inhibition or induction of intestinal CYP3A4 can account for exposure changes of apixaban in all clinically significant drug-drug interactions, and lack of intestinal CYP3A4 inhibition can explain all studies with no exposure changes, regardless of the potential for these perpetrators to inhibit intestinal or systemic efflux transporters.

Genomic resources for dissecting the role of non-protein coding variation in gene-environment interactions

The majority of single nucleotide variants (SNVs) identified in Genome Wide Association Studies (GWAS) fall within non-protein coding DNA and have the potential to alter gene expression. Non-protein coding DNA can control gene expression by acting as transcription factor (TF) binding sites or by regulating the organization of DNA into chromatin. SNVs in non-coding DNA sequences can disrupt TF binding and chromatin structure and this can result in pathology. Further, environmental health studies have shown that exposure to xenobiotics can disrupt the ability of TFs to regulate entire gene networks and result in pathology. However, there is a large amount of interindividual variability in exposure-linked health outcomes. One explanation for this heterogeneity is that genetic variation and exposure combine to disrupt gene regulation, and this eventually manifests in disease. Many resources exist that annotate common variants from GWAS and combine them with conservation, functional genomics, and TF binding data. These annotation tools provide clues regarding the biological implications of an SNV, as well as lead to the generation of hypotheses regarding potentially disrupted target genes, epigenetic markers, pathways, and cell types. Collectively this information can be used to predict how SNVs can alter an individual's response to exposure and disease risk. A basic understanding of the regulatory information contained within non-protein coding DNA is needed to predict the biological consequences of SNVs, and to determine how these SNVs impact exposure-related disease. We hope that this review will aid in the characterization of disease-associated genetic variation in the non-protein coding genome.