Role of the liver-specific transporters OATP1B1 and OATP1B3 in governing drug elimination

Targeting a xenobiotic transporter to ameliorate vincristine-induced sensory neuropathy

Vincristine is a widely used chemotherapeutic drug for the treatment of multiple malignant diseases that causes a dose-limiting peripheral neurotoxicity. There is no clinically effective preventative treatment for vincristine-induced sensory peripheral neurotoxicity (VIPN), and mechanistic details of this side effect remain poorly understood. We hypothesized that VIPN is dependent on transporter-mediated vincristine accumulation in dorsal root ganglion neurons. Using a xenobiotic transporter screen, we identified OATP1B3 as a neuronal transporter regulating the uptake of vincristine. In addition, genetic or pharmacological inhibition of the murine orthologue transporter OATP1B2 protected mice from various hallmarks of VIPN - including mechanical allodynia, thermal hyperalgesia, and changes in digital maximal action potential amplitudes and neuronal morphology - without negatively affecting plasma levels or antitumor effects of vincristine. Finally, we identified α-tocopherol from an untargeted metabolomics analysis as a circulating endogenous biomarker of neuronal OATP1B2 function, and it could serve as a companion diagnostic to guide dose selection of OATP1B-type transport modulators given in combination with vincristine to prevent VIPN. Collectively, our findings shed light on the fundamental basis of VIPN and provide a rationale for the clinical development of transporter inhibitors to prevent this debilitating side effect.

Transporter-Mediated Drug Delivery

Transmembrane transport of small organic and inorganic molecules is one of the cornerstones of cellular metabolism. Among transmembrane transporters, solute carrier (SLC) proteins form the largest, albeit very diverse, superfamily with over 400 members. It was recognized early on that xenobiotics can directly interact with SLCs and that this interaction can fundamentally determine their efficacy, including bioavailability and intertissue distribution. Apart from the well-established prodrug strategy, the chemical ligation of transporter substrates to nanoparticles of various chemical compositions has recently been used as a means to enhance their targeting and absorption. In this review, we summarize efforts in drug design exploiting interactions with specific SLC transporters to optimize their therapeutic effects. Furthermore, we describe current and future challenges as well as new directions for the advanced development of therapeutics that target SLC transporters.

Machine Learning Models Identify New Inhibitors for Human OATP1B1

The uptake transporter OATP1B1 (SLC01B1) is largely localized to the sinusoidal membrane of hepatocytes and is a known victim of unwanted drug-drug interactions. Computational models are useful for identifying potential substrates and/or inhibitors of clinically relevant transporters. Our goal was to generate OATP1B1 in vitro inhibition data for [3H] estrone-3-sulfate (E3S) transport in CHO cells and use it to build machine learning models to facilitate a comparison of seven different classification models (Deep learning, Adaboosted decision trees, Bernoulli naïve bayes, k-nearest neighbors (knn), random forest, support vector classifier (SVC), logistic regression (lreg), and XGBoost (xgb)] using ECFP6 fingerprints to perform 5-fold, nested cross validation. In addition, we compared models using 3D pharmacophores, simple chemical descriptors alone or plus ECFP6, as well as ECFP4 and ECFP8 fingerprints. Several machine learning algorithms (SVC, lreg, xgb, and knn) had excellent nested cross validation statistics, particularly for accuracy, AUC, and specificity. An external test set containing 207 unique compounds not in the training set demonstrated that at every threshold SVC outperformed the other algorithms based on a rank normalized score. A prospective validation test set was chosen using prediction scores from the SVC models with ECFP fingerprints and were tested in vitro with 15 of 19 compounds (84% accuracy) predicted as active (≥20% inhibition) showed inhibition. Of these compounds, six (abamectin, asiaticoside, berbamine, doramectin, mobocertinib, and umbralisib) appear to be novel inhibitors of OATP1B1 not previously reported. These validated machine learning models can now be used to make predictions for drug-drug interactions for human OATP1B1 alongside other machine learning models for important drug transporters in our MegaTrans software.

Relationship Between the In Vitro Efficacy, Pharmacokinetics and In Vivo Efficacy of Curcumin

Considerable interest continues to be focused on the development of curcumin either as an effective stand-alone therapeutic or as an adjunct therapy to established therapies. Curcumin (1, 7-bis (4-hydroxy-3-methoxyphenyl)-1, 6-heptadiene-3, 5- dione; also called diferuloylmethane) is a polyphenolic phytochemical extracted from the root of curcuma longa, commonly called turmeric. Despite evidence from in vitro (cell culture) and preclinical studies in animals, clinical studies have not provided strong evidence for a therapeutic effect of curcumin. The relevance of curcumin as a drug has been questioned based on its classification as a compound with pan assay interference and invalid metabolic panaceas properties bringing into question the relevance of the therapeutic targets identified for curcumin. To some extent this is due to the lack of a complete understanding of the link between the in vitro (cell culture activity), pharmacokinetics and in vivo activity of curcumin. In this review and using NF-κB as a cellular target for curcumin, we have investigated the relationship between the potency of curcumin as an inhibitor of NF-κB in cell culture, the pharmacokinetics of curcumin and curcumin's anticancer and anti-inflammatory effects in preclinical models of cancer and inflammation. Plausible explanations and rationale are provided to link these activities together and suggest that both curcumin and its more soluble Phase II metabolite curcumin glucuronide may play a key role in the treatment effects of curcumin in vivo mediated at NF-κB.

Identification of Potential Insect Growth Inhibitor against Aedes aegypti: A Bioinformatics Approach

Aedes aegypti is the main vector that transmits viral diseases such as dengue, hemorrhagic dengue, urban yellow fever, zika, and chikungunya. Worldwide, many cases of dengue have been reported in recent years, showing significant growth. The best way to manage diseases transmitted by Aedes aegypti is to control the vector with insecticides, which have already been shown to be toxic to humans; moreover, insects have developed resistance. Thus, the development of new insecticides is considered an emergency. One way to achieve this goal is to apply computational methods based on ligands and target information. In this study, sixteen compounds with acceptable insecticidal activities, with 100% larvicidal activity at low concentrations (2.0 to 0.001 mg·L−1), were selected from the literature. These compounds were used to build up and validate pharmacophore models. Pharmacophore model 6 (AUC = 0.78; BEDROC = 0.6) was used to filter 4793 compounds from the subset of lead-like compounds from the ZINC database; 4142 compounds (dG < 0 kcal/mol) were then aligned to the active site of the juvenile hormone receptor Aedes aegypti (PDB: 5V13), 2240 compounds (LE < −0.40 kcal/mol) were prioritized for molecular docking from the construction of a chitin deacetylase model of Aedes aegypti by the homology modeling of the Bombyx mori species (PDB: 5ZNT), which aligned 1959 compounds (dG < 0 kcal/mol), and 20 compounds (LE < −0.4 kcal/mol) were predicted for pharmacokinetic and toxicological prediction in silico (Preadmet, SwissADMET, and eMolTox programs). Finally, the theoretical routes of compounds M01, M02, M03, M04, and M05 were proposed. Compounds M01−M05 were selected, showing significant differences in pharmacokinetic and toxicological parameters in relation to positive controls and interaction with catalytic residues among key protein sites reported in the literature. For this reason, the molecules investigated here are dual inhibitors of the enzymes chitin synthase and juvenile hormonal protein from insects and humans, characterizing them as potential insecticides against the Aedes aegypti mosquito.

Benign inheritable disorders of bilirubin metabolism manifested by conjugated hyperbilirubinemia-A narrative review

Bilirubin, a breakdown product of heme, is normally glucuronidated and excreted by the liver into bile. Failure of this system can lead to a buildup of conjugated bilirubin in the blood, resulting in jaundice. Hyperbilirubinemia is an important clinical sign that needs to be investigated under a stepwise evaluation. Inherited non-hemolytic conjugated hyperbilirubinemic conditions include Dubin-Johnson syndrome (caused by mutations affecting ABCC2 gene) and Rotor syndrome (caused by the simultaneous presence of mutations in SLCO1B1 and SLCO1B3 genes). Although classically viewed as benign conditions requiring no treatment, they lately gained an increased interest since recent studies suggested that mutations in the responsible genes leading to hyperbilirubinemia, as well as minor genetic variants, may result in an increased susceptibility to drug toxicity. This article provides a comprehensive review on the pathophysiology of Dubin-Johnson and Rotor syndromes, presenting the current knowledge concerning the molecular details and basis of these conditions.

Gadolinium-free Magnetic Resonance Imaging of the Liver via an Oatp1-Targeted Manganese(III) Porphyrin

Controversy surrounding gadolinium-based contrast agents (GBCAs) has rendered their continued utility highly contentious, but the liver-specific GBCA Gd(III) ethoxybenzyl-diethylene triamine pentaacetic acid (Gd(III)-EOB-DTPA) remains in use because it provides unique diagnostic information that could not be obtained by any other means. To address the need for an alternate liver-specific MRI probe, we synthesized Mn(III) 20-(4-ethoxyphenyl) porphyrin-5,10,15-tricarboxylate (Mn(III)TriCP-PhOEt), which exhibited significantly higher r1 relaxivity than Gd(III)-EOB-DTPA in vitro, while also targeting hepatocyte-specific organic anion-transporting polypeptide 1 (Oatp1) channels as a marker of viability. In mice, Mn(III)TriCP-PhOEt resulted in significant and specific increases in liver signal intensity on T1-weighted images and significant decreases in liver T1 time relative to pre-contrast measurements. Our findings suggest that Mn(III)TriCP-PhOEt operates as a specific and sensitive MR probe for Oatp1-targeted imaging in vivo.

The individual and global impact of copy-number variants on complex human traits

The impact of copy-number variations (CNVs) on complex human traits remains understudied. We called CNVs in 331,522 UK Biobank participants and performed genome-wide association studies (GWASs) between the copy number of CNV-proxy probes and 57 continuous traits, revealing 131 signals spanning 47 phenotypes. Our analysis recapitulated well-known associations (e.g., 1q21 and height), revealed the pleiotropy of recurrent CNVs (e.g., 26 and 16 traits for 16p11.2-BP4-BP5 and 22q11.21, respectively), and suggested gene functionalities (e.g., MARF1 in female reproduction). Forty-eight CNV signals (38%) overlapped with single-nucleotide polymorphism (SNP)-GWASs signals for the same trait. For instance, deletion of PDZK1, which encodes a urate transporter scaffold protein, decreased serum urate levels, while deletion of RHD, which encodes the Rhesus blood group D antigen, associated with hematological traits. Other signals overlapped Mendelian disorder regions, suggesting variable expressivity and broad impact of these loci, as illustrated by signals mapping to Rotor syndrome (SLCO1B1/3), renal cysts and diabetes syndrome (HNF1B), or Charcot-Marie-Tooth (PMP22) loci. Total CNV burden negatively impacted 35 traits, leading to increased adiposity, liver/kidney damage, and decreased intelligence and physical capacity. Thirty traits remained burden associated after correcting for CNV-GWAS signals, pointing to a polygenic CNV architecture. The burden negatively correlated with socio-economic indicators, parental lifespan, and age (survivorship proxy), suggesting a contribution to decreased longevity. Together, our results showcase how studying CNVs can expand biological insights, emphasizing the critical role of this mutational class in shaping human traits and arguing in favor of a continuum between Mendelian and complex diseases.

Role and Regulation of Wnt/β-Catenin in Hepatic Perivenous Zonation and Physiological Homeostasis

Metabolic heterogeneity or functional zonation is a key characteristic of the liver that allows different metabolic pathways to be spatially regulated within the hepatic system and together contribute to whole body homeostasis. These metabolic pathways are segregated along the portocentral axis of the liver lobule into three hepatic zones: periportal, intermediate or midzonal, and perivenous. The liver performs complementary or opposing metabolic functions within different hepatic zones while synergistic functions are regulated by overlapping zones, thereby maintaining the overall physiological stability. The Wnt/β-catenin signaling pathway is well known for its role in liver growth, development, and regeneration. In addition, the Wnt/β-catenin pathway plays a fundamental and dominant role in hepatic zonation and signals to orchestrate various functions of liver metabolism and pathophysiology. The β-catenin protein is the central player in the Wnt/β-catenin signaling cascade, and its activation is crucial for metabolic patterning of the liver. However, dysregulation of Wnt/β-catenin signaling is also implicated in different liver pathologies, including those associated with metabolic syndrome. β-Catenin is preferentially localized in the central region of the hepatic lobule surrounding the central vein and regulates multiple functions of this region. This review outlines the role of Wnt/β-catenin signaling pathway in controlling the different metabolic processes surrounding the central vein and its relation to liver homeostasis and dysfunction.

Effect of type 2 diabetes on Gd-EOB-DTPA uptake into liver parenchyma: replication study in human subjects

PURPOSE

Gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) is a contrast agent for magnetic resonance imaging (MRI), which specifically taken up by hepatocytes through organic anion-transporting polypeptides (OATPs). Previous research in mice has shown that type 2 diabetes is associated with reduced uptake of Gd-EOB-DTPA into the liver parenchyma, reflecting reduced expression of OATP. Since considerable differences in OATP expression exist between mice and humans, human studies are necessary to clarify the effect of diabetes to Gd-EOB-DTPA uptake. The purpose of this study was to validate the effect of diabetes to Gd-EOB-DTPA liver uptake by a confirmatory study in humans.

METHODS

Patients who underwent Gd-EOB-DTPA-enhanced MRI were retrospectively reviewed and divided into two groups: severe or uncontrolled diabetic group (patients with insulin therapy and/or HbA1c ≥ 8.4%) and the control group. Liver-to-spleen ratio (LSR) and relative enhancement of the liver (REL) were calculated to represent Gd-EOB-DTPA liver uptake.

RESULTS

A total of 94 patients fulfilled the criteria. The severe or uncontrolled diabetic group (n = 15) showed significantly lower LSR (1.74 ± 0.26 vs. 1.98 ± 0.31, p = 0.007) and REL (0.69 ± 0.23 vs. 0.87 ± 0.31, p = 0.005), compared to the control group (n = 79).

CONCLUSION

Our study revealed decreased uptake of Gd-EOB-DTPA into liver parenchyma in the severe or uncontrolled diabetic patients. Further studies to determine the impact of the reduced liver enhancement on clinical diagnostic practice will be needed.

ABCB1 Single Nucleotide Polymorphism Genotypes as Predictors of Paclitaxel-Induced Peripheral Neuropathy in Breast Cancer

Background: Paclitaxel is a key antineoplastic agent in the treatment of breast cancer and many other malignancies. However, paclitaxel-induced peripheral neuropathy (PIPN) is a common adverse event that occurs with paclitaxel therapy and frequently causes considerable pain and a decline in patients' quality of life. Single nucleotide polymorphisms (SNPs) in the ABCB1 gene have been frequently associated with increased severity of PIPN. However, the validity of ABCB1 SNP markers to predict the incidence of PIPN has not been confirmed. Methods: We extracted genomic DNA from samples collected from 92 Egyptian female breast cancer patients receiving weekly paclitaxel and used them to genotype ABCB1 G1236A (rs1128503) and ABCB1 G3435A (rs1045642). Markers that correlated with PIPN, together with baseline clinical factors, were used to fit additive, dominant, overdominant, and recessive genetic models. We applied a repeated k-fold cross-validation algorithm to select the model with the highest predictive accuracy. We finally performed model diagnostics and receiver operating characteristics (ROCs) analysis for the model with the highest classification accuracy. Results: The additive model achieved the highest classification accuracy. The G1236A homozygous AA variant correlated with grade ≥2 PIPN (p = 0.018). PIPN also correlated with body surface area (BSA) (p = 0.003) and history of diabetes before treatment (p = 0.015). ROCs analysis showed a sensitivity of 76.9%, a specificity of 86.8%, a positive predictive value of 83.64%, and a negative predictive value of 81.08% for the additive model. Conclusion: The ABCB1 G1236A, BSA, and history of diabetes are valid predictors of PIPN, which can enable the personalization of paclitaxel dosing to prevent PIPN.

Correlation between single-nucleotide polymorphisms and statin-induced myopathy: a mixed-effects model meta-analysis

PURPOSE

A meta-analysis was performed to evaluate the correlation between single-nucleotide polymorphisms (SNPs) and risk of statin-induced myopathy (SIM).

METHODS

We retrieved the studies published on SIM until April 2019 from the PubMed, Embase, and Cochrane Library databases. We collected data from 32 studies that analyzed 10 SNPs in five genes and included 21,692 individuals and nine statins.

RESULTS

The analysis of the heterozygous (p = 0.017), homozygous (p = 0.002), dominant (p = 0.005), and recessive models (p = 0.009) of SLCO1B1 rs4149056 showed that this SNP increases the risk of SIM. Conversely, heterozygous (p = 0.048) and dominant models (p = 0.030) of SLCO1B1 rs4363657 demonstrated that this SNP is associated with a reduced risk of SIM. Moreover, an increased risk of SIM was predicted for carriers of the rs4149056 C allele among simvastatin-treated patients, whereas carriers of the GATM rs9806699 A allele among rosuvastatin-treated patients had a lower risk of SIM.

CONCLUSION

The meta-analysis revealed that the rs4149056 and rs4363657 SNPs in SLCO1B1 and the rs9806699 SNP in GATM are correlated with the risk of SIM.

Solubility and ADMET profiles of short oligomers of lactic acid

Polylactic acid (PLA) is a polymer with an increased potential to be used in different medical applications, including tissue engineering and drug-carries. The use of PLA in medical applications implies the evaluation of the human organism's response to the polymer inserting and to its degradation products. Consequently, within this study, we have investigated the solubility and ADMET profiles of the short oligomers (having the molecular weight lower than 3000 Da) resulting in degradation products of PLA. There is a linear decrease of the molar solubility of investigated oligomers with molecular weight. The results that are obtained also reveal that short oligomers of PLA have promising pharmacological profiles and limited toxicological effects on humans. These oligomers are predicted as potential inhibitors of the organic anion transporting peptides OATP1B1 and OATP1B3, they present minor probability to affect the androgen and glucocorticoid receptors, have a weak potential of hepatotoxicity, and may produce eye injuries. These outcomes may be used to guide or to supplement in vitro and/or in vivo toxicity tests such as to enhance the biodegradation properties of the biopolymer.

Drug interaction study of flavonoids toward OATP1B1 and their 3D structure activity relationship analysis for predicting hepatoprotective effects

Organic anion transporting polypeptide 1B1 (OATP1B1), a liver-specific uptake transporter, was associated with drug induced liver injury (DILI). Screening and identifying potent OATP1B1 inhibitors with little toxicity is of great value in reducing OATP1B1-mediated DILI. Flavonoids are a group of polyphenols ubiquitously present in vegetables, fruits and herbal products, some of them were reported to produce transporter-mediated DDI. Our objective was to investigate potential inhibitors of OATP1B1 from 99 flavonoids, and to assess the hepatoprotective effects on bosentan induced liver injury. Eight flavonoids, including biochanin A, hispidulin, isoliquiritigenin, isosinensetin, kaempferol, licochalcone A, luteolin and sinensetin exhibited significant inhibition (>50 %) on OATP1B1 in OATP1B1-HEK293 cells, which reduced the OATP1B1-mediated influx of methotrexate, accordingly decreased its cytotoxicity in OATP1B1-HEK293 cells and increased its AUC_0-t in different extents in rats, from 28.27%-82.71 %. In bosentan-induced rat liver injury models, 8 flavonoids reduced the levels of serum total bile acid (TBA) and the liver concentration of bosentan in different degrees. Among them, kaempferol decreased the concentration most significantly, by 54.17 %, which indicated that flavonoids may alleviate bosentan-induced liver injury by inhibiting OATP1B1-mediated bosentan uptake. Furthermore, the pharmacophore model indicated the hydrogen bond acceptors and hydrogen bond donors may play critical role in the potency of flavonoids inhibition on OATP1B1. Taken together, our findings would provide helpful information for predicting the potential risks of flavonoid-containing food/herb-drug interactions in humans and alleviating bosentan -induced liver injury by OATP1B1 regulation.

Thyroid Hormone Transporters

Thyroid hormone transporters at the plasma membrane govern intracellular bioavailability of thyroid hormone. Monocarboxylate transporter (MCT) 8 and MCT10, organic anion transporting polypeptide (OATP) 1C1, and SLC17A4 are currently known as transporters displaying the highest specificity toward thyroid hormones. Structure-function studies using homology modeling and mutational screens have led to better understanding of the molecular basis of thyroid hormone transport. Mutations in MCT8 and in OATP1C1 have been associated with clinical disorders. Different animal models have provided insight into the functional role of thyroid hormone transporters, in particular MCT8. Different treatment strategies for MCT8 deficiency have been explored, of which thyroid hormone analogue therapy is currently applied in patients. Future studies may reveal the identity of as-yet-undiscovered thyroid hormone transporters. Complementary studies employing animal and human models will provide further insight into the role of transporters in health and disease. (Endocrine Reviews 41: 1 - 55, 2020).

The Emerging Role of the SLCO1B3 Protein in Cancer Resistance

Currently, chemotherapy is one of the mainstays of oncologic therapies. But the efficacy of chemotherapy is often limited by drug resistance and severe side effects. Consequently, it is becoming increasingly important to investigate the underlying mechanism and overcome the problem of anticancer chemotherapy resistance. The solute carrier organic anion transporter family member 1B3 (SLCO1B3), a functional transporter normally expressed in the liver, transports a variety of endogenous and exogenous compounds, including hormones and their conjugates as well as some anticancer drugs. The extrahepatic expression of SLCO1B3 has been detected in different cancer cell lines and cancer tissues. Recently, accumulating data indicates that the abnormal expression and function of SLCO1B3 are involved in resistance to anticancer drugs, such as taxanes, camptothecin and its analogs, SN-38, and Androgen Deprivation Therapy (ADT) in breast, prostate, lung, hepatic, and colorectal cancer, respectively. Thus, more investigations have been implemented to identify the potential SLCO1B3-related mechanisms of cancer drug resistance. In this review, we focus on the emerging roles of SLCO1B3 protein in the development of cancer chemotherapy resistance and briefly discuss the mechanisms of resistance. Elucidating the function of SLCO1B3 in chemoresistance may bring out novel therapeutic strategies for cancer treatment.

Prediction of Atorvastatin Pharmacokinetics in High-Fat Diet and Low-Dose Streptozotocin-Induced Diabetic Rats Using a Semiphysiologically Based Pharmacokinetic Model Involving Both Enzymes and Transporters

Atorvastatin is a substrate of cytochrome P450 3a (CYP3a), organic anion-transporting polypeptides (OATPs), breast cancer-resistance protein (BCRP), and P-glycoprotein (P-gp). We aimed to develop a semiphysiologically based pharmacokinetic (semi-PBPK) model involving both enzyme and transporters for predicting the contributions of altered function and expression of CYP3a and transporters to atorvastatin transport in diabetic rats by combining high-fat diet feeding and low-dose streptozotocin injection. Atorvastatin metabolism and transport parameters comes from in situ intestinal perfusion, primary hepatocytes, and intestinal or hepatic microsomes. We estimated the expressions and functions of these proteins and their contributions. Diabetes increased the expression of hepatic CYP3a, OATP1b2, and P-gp but decreased the expression of intestinal CYP3a, OATP1a5, and P-gp. The expression and function of intestinal BCRP were significantly decreased in 10-day diabetic rats but increased in 22-day diabetic rats. Based on alterations in CYP3a and transporters by diabetes, the developed semi-PBPK model was successfully used to predict atorvastatin pharmacokinetics after oral and intravenous doses to rats. Contributions to oral atorvastatin PK were intestinal OATP1a5 < intestinal P-gp < intestinal CYP3a < hepatic CYP3a < hepatic OATP1b2 < intestinal BRCP. Contributions of decreased expression and function of intestinal CYP3a and P-gp by diabetes to oral atorvastatin plasma exposure were almost attenuated by increased expression and function of hepatic CYP3a and OATP1b2. Opposite alterations in oral plasma atorvastatin exposure in 10- and 22-day diabetic rats may be explained by altered intestinal BCRP. In conclusion, the altered atorvastatin pharmacokinetics by diabetes was the synergistic effects of altered intestinal or hepatic CYP3a and transporters and could be predicted using the developed semi-PBPK.

Asking the Right Questions With Animal Models: Methionine- and Choline-Deficient Model in Predicting Adverse Drug Reactions in Human NASH

In the past few decades, great conceptual and technological advances have been made in the field of toxicology, but animal model-based research still remains one of the most widely used and readily available tools for furthering our current knowledge. However, animal models are not perfect in predicting all systemic toxicity in humans. Extrapolating animal data to accurately predict human toxicities remains a challenge, and researchers are obligated to question the appropriateness of their chosen animal model. This paper provides an assessment of the utility of the methionine- and choline-deficient (MCD) diet fed animal model in reflecting human nonalcoholic steatohepatitis (NASH) and the potential risks of adverse drug reactions and toxicities that are associated with the disease. As a commonly used NASH model, the MCD model fails to exhibit most metabolic abnormalities in a similar manner to the human disease. The MCD model, on the other hand, closely resembles human NASH histology and reflects signatures of drug transporter alterations in humans. Due to the nature of the MCD model, it should be avoided in studies of NASH pathogenesis, metabolic parameter evaluation, and biomarker identification. But it can be used to accurately predict altered drug disposition due to NASH-associated transporter alterations.

Discovery of Orally Bioavailable and Liver-Targeted Hypoxia-Inducible Factor Prolyl Hydroxylase (HIF-PHD) Inhibitors for the Treatment of Anemia

We report herein the design and synthesis of a series of orally active, liver-targeted hypoxia-inducible factor prolyl hydroxylase (HIF-PHD) inhibitors for the treatment of anemia. In order to mitigate the concerns for potential systemic side effects, we pursued liver-targeted HIF-PHD inhibitors relying on uptake via organic anion transporting polypeptides (OATPs). Starting from a systemic HIF-PHD inhibitor (1), medicinal chemistry efforts directed toward reducing permeability and, at the same time, maintaining oral absorption led to the synthesis of an array of structurally diverse hydroxypyridone analogues. Compound 28a was chosen for further profiling, because of its excellent in vitro profile and liver selectivity. This compound significantly increased hemoglobin levels in rats, following chronic QD oral administration, and displayed selectivity over systemic effects.

Effect of SLCO1B1 gene polymorphisms and vitamin D on statin-induced myopathy

Background Statin therapy used to lower cholesterol levels results in a substantial reduction in cardiovascular complications. Previous observations in different ethnic populations showed that rs2306283A>G, p.Asn130Asp and rs4149056T>C, p.Val174Ala in solute carrier organic anion transporter 1B1 (SLCO1B1) gene encoding the organic transporter protein may be responsible for statin uptake, thus explaining the majority of statin-associated symptoms. In addition to the genetic component, vitamin D (vit D) deficiency is common in Saudi Arabia and worldwide and may cause muscle dysfunction and ache. The aim of the present study was first to reveal an effect of vit D, rs2306283A>G, and rs4149056T>C and related haplotypes on statin-associated myopathy (SAM) and then to investigate a possible interaction between low vit D levels and the above-mentioned variants. Methods The genomic DNA obtained from 50 individuals diagnosed with hypercholesterolemia was genotyped using light SNiP hybridization probes. Results Low vit D levels were associated with SAM (OR=3.6, p=0.03); however, CK levels, rs2306283A>G, and rs4149056T>C did not show any association. Interestingly, rs4149056T>C was interacting with vit D to influence SAM (p=0.02). Haplotype analysis showed that SLCO1B1 *1B and *15 were more prevalent in individuals with SAM (p=0.05). When stratified according to vit D levels, rs2306283A allele showed an increase in individuals having SAM along with low vit D (p=0.03). Conclusions Although preliminary, our results show an involvement of vit D and rs4149056T>C of SLCO1B1 in SAM.

Simultaneous determination of rosuvastatin, naringin and naringenin in rat plasma by RRLC-MS/MS and its application to a pharmacokinetic drug interaction study

A rapid resolution liquid chromatography tandem mass spectrometry method was developed and validated for simultaneous determination of rosuvastatin, naringin and naringenin in rat plasma. Chromatographic separation of analytes and internal standard (fluvastatin for rosuvastatin, while isoquercitrin for naringin and naringenin) was performed on Agilent Poroshell 120 EC-C18 column (3.0 × 50 mm, 2.7 μm) using gradient elution with a mobile phase of methanol and water, both with 0.1% formic acid (v/v). The detection was operated in multiple reaction monitoring mode to monitor the precursor-to-product ion transitions of m/z 579.1→270.8 for naringin, m/z 270.9→150.7 for naringenin, m/z 463.1→299.8 for isoquercitrin in negative ionization mode, and m/z 482.2→258.1 for rosuvastatin, m/z 412.1→224.1 for fluvastatin in positive ionization mode. Polarity switch (negative-positive-negative ionization mode) was performed in a total runtime of 5.0 min. The method was validated over a concentration range of 10-2,000 ng/mL for the above three analytes. The intra-day and inter-day precisions and accuracies of the quality control samples at low, medium and high concentration levels exhibited relative standard deviations <10% and the accuracy values ranged from -7.2% to 8.4%. The proposed method was successfully applied to the pharmacokinetic drug interaction study of rosuvastatin combined with naringin in rats.

Intrauterine growth restriction may reduce hepatic drug metabolism in the early neonatal period

The effects of intrauterine growth restriction (IUGR) extend well into postnatal life. IUGR is associated with an increased risk of adverse health outcomes, which often leads to greater medication usage. Many medications require hepatic metabolism for activation or clearance, but hepatic function may be altered in IUGR fetuses. Using a sheep model of IUGR, we determined the impact of IUGR on hepatic drug metabolism and drug transporter expression, both important mediators of fetal drug exposure, in late gestation and in neonatal life. In the late gestation fetus, IUGR decreased the gene expression of uptake drug transporter OATPC and increased P-glycoprotein protein expression in the liver, but there was no change in the activity of the drug metabolising enzymes CYP3A4 or CYP2D6. In contrast, at 3 weeks of age, CYP3A4 activity was reduced in the livers of lambs born with low birth weight (LBW), indicating that LBW results in changes to drug metabolising capacity in neonatal life. Together, these results suggest that IUGR may reduce hepatic drug metabolism in fetal and neonatal life through different mechanisms.

Drug Interactions Between Peficitinib, an Orally Administered, Once-Daily Janus Kinase Inhibitor, and Rosuvastatin in Healthy Subjects

BACKGROUND AND OBJECTIVE

Peficitinib is an orally administered, once-daily Janus kinase inhibitor in development for the treatment of rheumatoid arthritis. Peficitinib and its major metabolite H2 inhibit the hepatic uptake transporter organic anion transporting polypeptide 1B1 (OATP1B1) in vitro. This article reports a clinical study evaluating the effects of peficitinib on the pharmacokinetics of rosuvastatin, a substrate for the OATP1B1 transporter, and vice versa.

METHODS

In an open-label, single-sequence clinical study, 24 healthy adults of East Asian and non-East Asian origin received a single dose of rosuvastatin 10 mg on days 1 and 10. On days 5-13, subjects received a daily dose of 150 mg peficitinib. Serial blood samples for pharmacokinetic assessment of rosuvastatin were collected up to 96 h post-dose on days 1 and 10, and for peficitinib were collected up to 24 h post-dose on days 9 and 10.

RESULTS

Co-administration of peficitinib with rosuvastatin increased rosuvastatin area under the concentration-time curve (AUC) and maximum plasma concentration (C _max) by 18 and 15%, respectively and increased peficitinib AUC and C _max by 16 and 28%, respectively. In East Asian (n = 6) vs. non-East Asian subjects (n = 18), peficitinib mean AUC for a dosing interval was 45 and 21% higher, and mean C _max was 67 and 34% higher, when administered alone or with rosuvastatin. Peficitinib was well tolerated with few adverse events overall.

CONCLUSION

In this study, once-daily oral administration of peficitinib had no clinically significant effect on the pharmacokinetics of rosuvastatin, a probe substrate for OATP1B1. Therefore, it is unlikely that peficitinib will have a clinically significant effect on the exposure of other substrates for OATP1B1. CLINICALTRIALS.

GOV NUMBER

NCT01959399.

Endogenous Metabolites-Mediated Communication Between OAT1/OAT3 and OATP1B1 May Explain the Association Between SLCO1B1 SNPs and Methotrexate Toxicity

Although OATP1B1 is not expressed in the kidney, polymorphisms in SLCO1B1 have been associated with methotrexate clearance or toxicity. This unexpected pharmacogenetic association may reflect remote communication between liver and kidney transporters. This study confirms the pharmacogenetic association with methotrexate toxicity in adult patients with hematological malignancies. Using a targeted urinary metabolomics approach, we identified 38 and 34 metabolites which were differentially excreted between wildtype and carriers of the c.388A>G or c.521T>C variant alleles, respectively, half of them being associated with methotrexate toxicity. These metabolites mainly consisted of fatty acid derivatives and microbiota catabolites, including glycine conjugates and other uremic toxins, all known OATs substrates. These results suggest that dysfunction of a transporter affects the excretion profile of endogenous or exogenous substrates, possibly through metabolite-mediated interactions involving other transport systems, even in distant organs. This opens the way for better comprehension of complex pharmacokinetics and transporter-mediated drug-drug or nutrient-drug interactions.

Low Testosterone Alters the Activity of Mouse Prostate Stem Cells

BACKGROUND

Low serum testosterone (low T) has been repeatedly linked to worse outcomes in men with newly diagnosed prostate cancer (PC). How low T contributes to these outcomes is unknown. Here we demonstrate that exposure to low T causes significant changes in the mouse prostate and prostate stem cells.

METHODS

Mice were castrated and implanted with capsules to achieve castrate, normal, or sub-physiological levels of T. After 6 weeks of treatment, LC-MS/MS was used to quantify the levels of T and dihydrotestosterone (DHT) in serum and prostate tissue. FACS was used to quantify the percentages of purported prostate stem and transit amplifying (TA) cells in mouse prostates. Prostate tissues were also stained for the presence of CD68+ cells and RNA was extracted from prostate tissue or specific cell populations to measure changes in transcript levels with low T treatment.

RESULTS

Despite having significantly different levels of T and DHT in the serum, T and DHT concentrations in prostate tissue from different T treatment groups were similar. Low T treatment resulted in significant alterations in the expression of androgen biosynthesis genes, which may be related to maintaining prostate androgen levels. Furthermore, the expression of androgen-regulated genes in the prostate was similar among all T treatment groups, demonstrating that the mouse prostate can maintain functional levels of androgens despite low serum T levels. Low T increased the frequency of prostate stem and TA cells in adult prostate tissue and caused major transcriptional changes in those cells. Gene ontology analysis suggested that low T caused inflammatory responses and immunofluorescent staining indicated that low T treatment led to the increased presence of CD68+ macrophages in prostate tissue.

CONCLUSIONS

Low T alters the AR signaling axis which likely leads to maintenance of functional levels of prostate androgens. Low T also induces quantitative and qualitative changes in prostate stem cells which appear to lead to inflammatory macrophage infiltration. These changes are proposed to lead to an aggressive phenotype once cancers develop and may contribute to the poor outcomes in men with low T. Prostate 77:530-541, 2017. © 2016 Wiley Periodicals, Inc.

Identification of drug transporters involved in the uptake and efflux of rhein in hepatocytes

Rhein is an herbal medicine with various bioactivities and is derived from an anthraquinone compound. In this study, we aimed to identify drug transporters involved in the uptake and efflux of rhein in hepatocytes.

Liver uptake of cefditoren is mediated by OATP1B1 and OATP2B1 in humans and Oatp1a1, Oatp1a4, and Oatp1b2 in rats

OATPs and Oatps mediated liver uptake of cefditoren in humans and in rats.

Is the unbound concentration of atazanavir of interest in therapeutic drug monitoring?

To date, therapeutic drug monitoring (TDM) is carried out with antiretrovirals and is usually based on total concentrations (C_t ). However, for some patients, TDM does not reflect efficacy or the avoidance of toxicity as is the case for atazanavir (ATV), a HIV protease inhibitor. As the unbound concentration (C_u ) is the pharmacological active form, the aim of the study was to evaluate the value of C_u and the unbound fraction (f_u , f_u = C_u /C_t ) for the TDM of ATV. The variability of C_u and the corresponding f_u of ATV was explored in 43 patients treated with ATV for an average of 13.5 months. C_u was determined by coupling ultrafiltration and liquid chromatography. As ATV is highly bound to alpha-1 acid glycoprotein (AAG), the correlation between f_u and AAG was also evaluated. The viral load was monitored to evaluate the patients' virologic response, while total plasma bilirubin and unconjugated plasma bilirubin were used as biomarkers of ATV toxicity. Median trough C_u and C_t were 37.9 μg/L (Interquartile range (IQR) 20.6-94.9 μg/L) and 628.6 μg/L (IQR 362.7-1078.1 μg/L), respectively. f_u , C_u and C_t showed high variability, but the f_u variability was not correlated with the AAG level. The unbound concentration and fraction were unrelated to the virologic response (P = 0.21 and P = 0.65 for C_u and f_u , respectively) nor to the unconjugated bilirubin (Pearson correlation coefficient (ρ), ρ = 0.22; P = 0.17 for C_u ). Neither total nor unbound concentrations of ATV fully explained hyperbilirubinaemia or virologic failure. From this study, we conclude that unbound ATV did not appear to be more relevant than C_t .

Combined Angiotensin Receptor Antagonism and Neprilysin Inhibition

Heart failure affects ≈5.7 million people in the United States alone. Angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, β-blockers, and aldosterone antagonists have improved mortality in patients with heart failure and reduced ejection fraction, but mortality remains high. In July 2015, the US Food and Drug Administration approved the first of a new class of drugs for the treatment of heart failure: Valsartan/sacubitril (formerly known as LCZ696 and currently marketed by Novartis as Entresto) combines the angiotensin receptor blocker valsartan and the neprilysin inhibitor prodrug sacubitril in a 1:1 ratio in a sodium supramolecular complex. Sacubitril is converted by esterases to LBQ657, which inhibits neprilysin, the enzyme responsible for the degradation of the natriuretic peptides and many other vasoactive peptides. Thus, this combined angiotensin receptor antagonist and neprilysin inhibitor addresses 2 of the pathophysiological mechanisms of heart failure: activation of the renin-angiotensin-aldosterone system and decreased sensitivity to natriuretic peptides. In the Prospective Comparison of ARNI With ACEI to Determine Impact on Global Mortality and Morbidity in Heart Failure (PARADIGM-HF) trial, valsartan/sacubitril significantly reduced mortality and hospitalization for heart failure, as well as blood pressure, compared with enalapril in patients with heart failure, reduced ejection fraction, and an elevated circulating level of brain natriuretic peptide or N-terminal pro-brain natriuretic peptide. Ongoing clinical trials are evaluating the role of valsartan/sacubitril in the treatment of heart failure with preserved ejection fraction and hypertension. We review here the mechanisms of action of valsartan/sacubitril, the pharmacological properties of the drug, and its efficacy and safety in the treatment of heart failure and hypertension.

Effect of OATP-binding on the prediction of biliary excretion

1. Biliary excretion of compounds is dependant on several transporter proteins for the active uptake of compounds from the blood into the hepatocytes. Organic anion-transporting polypeptides (OATPs) are some of the most abundant transporter proteins in the sinusoidal membrane and have been shown to have substrate specificity similar to the structural characteristics of cholephilic compounds. 2. In this study, we sought to use measures of OATP binding as predictors of biliary excretion in conjunction with molecular descriptors in a quantitative structure-activity relationship (QSAR) study. Percentage inhibitions of three subtypes of OATPs were used as surrogate indicators of OATP substrates. Several statistical modelling techniques were incorporated including classification and regression trees, boosted trees, random forest and multivariate adaptive regression splines (MARS) in order to first develop QSARs for the prediction of OATP inhibition of compounds. The predicted OATP percentage inhibition using selected models were then used as features of the QSAR models for the prediction of biliary excretion of compounds in rat. 3. The results indicated that incorporation of predicted OATP inhibition improves accuracy of biliary excretion models. The best result was obtained from a simple regression tree that used predicted OATP1B1 percentage inhibition at the root node of the tree.

A multicenter assessment of single-cell models aligned to standard measures of cell health for prediction of acute hepatotoxicity

Assessing the potential of a new drug to cause drug-induced liver injury (DILI) is a challenge for the pharmaceutical industry. We therefore determined whether cell models currently used in safety assessment (HepG2, HepaRG, Upcyte and primary human hepatocytes in conjunction with basic but commonly used endpoints) are actually able to distinguish between novel chemical entities (NCEs) with respect to their potential to cause DILI. A panel of thirteen compounds (nine DILI implicated and four non-DILI implicated in man) were selected for our study, which was conducted, for the first time, across multiple laboratories. None of the cell models could distinguish faithfully between DILI and non-DILI compounds. Only when nominal in vitro concentrations were adjusted for in vivo exposure levels were primary human hepatocytes (PHH) found to be the most accurate cell model, closely followed by HepG2. From a practical perspective, this study revealed significant inter-laboratory variation in the response of PHH, HepG2 and Upcyte cells, but not HepaRG cells. This variation was also observed to be compound dependent. Interestingly, differences between donors (hepatocytes), clones (HepG2) and the effect of cryopreservation (HepaRG and hepatocytes) were less important than differences between the cell models per se. In summary, these results demonstrate that basic cell health endpoints will not predict hepatotoxic risk in simple hepatic cells in the absence of pharmacokinetic data and that a multicenter assessment of more sophisticated signals of molecular initiating events is required to determine whether these cells can be incorporated in early safety assessment.

In vitro and clinical evaluation of OATP-mediated drug interaction potential of sacubitril/valsartan (LCZ696)

WHAT IS KNOWN AND OBJECTIVE

Sacubitril/valsartan (LCZ696) has been recently approved for the treatment of heart failure (HF) patients with reduced ejection fraction. Several HF patients receive statins as co-medication.

METHODS

Because clearance of statins is meditated via OATP1B1/1B3, the inhibition potential of these transporters by LCZ696 analytes was evaluated in vitro. Furthermore, an open-label, fixed-sequence clinical study was conducted to determine the effect of LCZ696 on the exposure of simvastatin and its active metabolite simvastatin acid. In this clinical study, 26 healthy subjects received simvastatin 40 mg alone or in combination with LCZ696 or after 1 or 2 h of LCZ696 dosing.

RESULTS AND DISCUSSION

Although no significant inhibition by LBQ657 (an active metabolite of sacubitril) and valsartan was observed, sacubitril inhibited OATP1B1 and OATP1B3 in vitro, with IC50 of 1·91 and 3·81 μm, respectively. Upon co-administration of simvastatin with LCZ696, the Cmax of simvastatin and simvastatin acid decreased by 7% and 13%, respectively. When administered 1 h after LCZ696 dosing, the corresponding Cmax of simvastatin and simvastatin acid decreased by 16% and 4%, respectively. When administered 2 h after LCZ696 dosing, the Cmax of simvastatin decreased by 33% and that of simvastatin acid increased by 16%. However, no notable changes were observed in the AUCs of simvastatin or simvastatin acid upon co-administration or time-separated administration with LCZ696. No notable impact of simvastatin co-administration was observed on the pharmacokinetics of LCZ696 analytes. LCZ696 and simvastatin were generally well tolerated when administered alone or in combination.

WHAT IS NEW AND CONCLUSIONS

Overall, the results of this study suggest that although sacubitril inhibited OATP1B1 and OATP1B3 in vitro, it does not translate into any clinically relevant in vivo effect.

A pharmacist’s role in the individualization of treatment of HIV patients

The pharmacological treatment of HIV is complex and varies considerably among patients, as does the response of patients to therapy, requiring treatment plans that are closely tailored to individual needs. Pharmacists can take an active role in individualizing care by employing their knowledge of pharmacokinetics and pharmacogenetics and by interacting directly with patients in counseling sessions. These strategies promote the following: maintenance of plasma concentrations of antiretroviral agents within therapeutic ranges, prediction of pharmacological response of patients with certain genetic characteristics, and clinical control of HIV through the correct use of antiretroviral treatments. Together, these strategies can be used to tailor antiretroviral therapy to individual patients, thus improving treatment efficacy and safety.

The Chinese Herb Jianpijiedu Contributes to the Regulation of OATP1B2 and ABCC2 in a Rat Model of Orthotopic Transplantation Liver Cancer Pretreated with Food Restriction and Diarrhea

Traditional Chinese Medicine Jianpijiedu decoction (JPJD) could improve the general status of liver cancer patients in clinics, especially the symptoms of decreased food intake and diarrhea. In this study, our results showed that the survival rate of the liver cancer with food restriction and diarrhea (FRD-LC) rats was lower than the liver cancer (LC) rats, and the tumor volume of the FRD-LC rats was higher than the LC rats. It was also shown that the high dose of JPJD significantly improved the survival rate, weight, and organ weight when compared with FRD-LC-induced rats. Moreover, JPJD administration upregulated the mRNA and protein levels of ABCC2 and downregulated the mRNA and protein levels of OATP1B2 in liver tissues. However, opposite results were observed in the cancer tissues. In conclusion, the study indicated that the Chinese Medicine JPJD could contribute to the rats with liver cancer which were pretreated with food restriction and diarrhea by regulating the expression of ABCC2 and OATP1B2 in liver tissues and cancer tissues.

Investigation of mutual pharmacokinetic interactions between macitentan, a novel endothelin receptor antagonist, and sildenafil in healthy subjects

AIM

To study the mutual pharmacokinetic interactions between macitentan, an endothelin receptor antagonist, and sildenafil in healthy male subjects.

METHODS

In this open-label, randomized, three way crossover study, 12 healthy male subjects received the following oral treatments: A) a loading dose of 30 mg macitentan on day 1 followed by 10 mg once daily for 3 days, B) sildenafil 20 mg three times a day for 3 days and a single 20 mg dose on day 4 and C) both treatments A and B concomitantly. Plasma concentration-time profiles of macitentan and its active metabolite ACT-132577 (treatments A and C) and sildenafil and its N-desmethyl metabolite (treatments B and C) were determined on day 4 and analyzed non-compartmentally.

RESULTS

The pharmacokinetics of macitentan were not affected by sildenafil. In the presence of sildenafil Cmax and AUCτ of the metabolite ACT-132577 decreased with geometric mean ratios (90% confidence interval (CI)) of 0.82 (0.76, 0.89) and 0.85 (90% CI 0.80, 0.91), respectively. In the presence of macitentan, plasma concentrations of sildenafil were higher than during treatment with sildenafil alone, resulting in increased Cmax and AUCτ values. The respective geometric mean ratios were 1.26 (90% CI 1.07, 1.48) and 1.15 (90% CI 0.94, 1.41). The pharmacokinetics of N-desmethylsildenafil were not affected by macitentan. All treatments were well tolerated.

CONCLUSION

A minor, not clinically relevant, pharmacokinetic interaction was observed between macitentan and sildenafil. Based on these results, no dose adjustment of either compound appears necessary during concomitant treatment with macitentan and sildenafil.

Inhibition of OATP-1B1 and OATP-1B3 by tyrosine kinase inhibitors

BACKGROUND

The potential of tyrosine kinase inhibitors (TKIs) interacting with other therapeutics through hepatic uptake transporter inhibition has not been fully delineated in drug-drug interactions (DDIs). This study was designed to estimate the half-maximal inhibitory concentration (IC50) values of five small-molecule TKIs (pazopanib, nilotinib, vandetanib, canertinib and erlotinib) interacting with organic anion-transporting polypeptides (OATPs): OATP-1B1 and -1B3.

METHODS

The IC50 values of TKIs and rifampicin (positive control) were determined by concentration-dependent inhibition of TKIs on cellular accumulation of radiolabeled probe substrates [3H]estrone sulfate and [3H]cholecystokinin octapeptide. Chinese hamster ovary cells transfected with humanized OATP-1B1 and OATP-1B3 transporter proteins, respectively, were utilized to carry out these studies.

RESULTS

Pazopanib and nilotinib show inhibitory activity on OATP-1B1 transporter protein. IC50 values for rifampicin, pazopanib and nilotinib were 10.46±1.15, 3.89±1.21 and 2.78±1.13 μM, respectively, for OATP-1B1 transporter. Vandetanib, canertinib and erlotinib did not exhibit any inhibitory potency toward OATP-1B1 transporter protein. Only vandetanib expressed inhibitory potential toward OATP-1B3 transporter protein out of the five selected TKIs. IC50 values for rifampicin and vandetanib for OATP-1B3 transporter inhibition were 3.67±1.20 and 18.13±1.21 μM, respectively. No significant inhibition in the presence of increasing concentrations of pazopanib, nilotinib, canertinib and erlotinib were observed for OATP-1B3 transporter.

CONCLUSIONS

Because selected TKIs are inhibitors of OATP-1B1 and -1B3 expressed in hepatic tissue, these compounds can be regarded as molecular targets for transporter-mediated DDIs. These findings provide the basis for further preclinical and clinical studies investigating the transporter-based DDI potential of TKIs.

Genetic determination of the hypothalamic-pituitary-thyroid axis: where do we stand?

For a long time it has been known that both hypo- and hyperthyroidism are associated with an increased risk of morbidity and mortality. In recent years, it has also become clear that minor variations in thyroid function, including subclinical dysfunction and variation in thyroid function within the reference range, can have important effects on clinical endpoints, such as bone mineral density, depression, metabolic syndrome, and cardiovascular mortality. Serum thyroid parameters show substantial interindividual variability, whereas the intraindividual variability lies within a narrow range. This suggests that every individual has a unique hypothalamus-pituitary-thyroid axis setpoint that is mainly determined by genetic factors, and this heritability has been estimated to be 40-60%. Various mutations in thyroid hormone pathway genes have been identified in persons with thyroid dysfunction or altered thyroid function tests. Because these causes are rare, many candidate gene and linkage studies have been performed over the years to identify more common variants (polymorphisms) associated with thyroid (dys)function, but only a limited number of consistent associations have been found. However, in the past 5 years, advances in genetic research have led to the identification of a large number of new candidate genes. In this review, we provide an overview of the current knowledge about the polygenic basis of thyroid (dys)function. This includes new candidate genes identified by genome-wide approaches, what insights these genes provide into the genetic basis of thyroid (dys)function, and which new techniques will help to further decipher the genetic basis of thyroid (dys)function in the near future.

Relationship between SLCO1B3 and ABCA3 polymorphisms and imatinib response in chronic myeloid leukemia patients

BACKGROUND

Genetic variations in membrane transporters may contribute to imatinib mesylate (IM) resistance in chronic myeloid leukemia (CML). Objective To investigate the relationship between SLCO1B3, SLCO1A2, and ABCA3 polymorphisms and IM response in CML patients.

METHODS

Patients in chronic phase CML (N = 118) were studied. All patients were treated with a standard dose of IM (400 mg/day) and classified into one of the two groups according to their responses. Major molecular response (MMR) and complete molecular response (CMR) were evaluated. Criteria for response failure were established according to European LeukemiaNet (2009). Analysis of the SLCO1B3 c.334T > G (rs4149117) and c.699G > A (rs7311358), SLCO1A2 c.516A > C (rs11568563) and c.-62-361G > A (rs3764043), and ABCA3 c.1755C > G (rs323043) and c.4548-191C > A (rs150929) polymorphisms was carried out by real-time polymerase chain reaction.

RESULTS

SLCO1A2 and ABCA3 polymorphisms have similar frequencies between responders and non-responders. SLCO1B3 699GG and 344TT genotypes were more frequent in the responder group (63.8%) than in the non-responder group (44.7%, P = 0.042). Furthermore, carriers of 699GA/AA and 334TG/GG genotypes presented a higher probability of not responding to the standard dose of IM (odds ratio: 2.17; 95% confidence interval: 1.02-4.64, P = 0.04). Poor CMR for ABCA3 4548-91C > A was observed in patients with the CC/CA genotype when compared to AA carriers in the responder group (P = 0.014).

CONCLUSIONS

SLCO1B3 699GG and 344TT genotypes are associated with non-response to IM, while ABCA3 4548-91 CC/CA genotypes are related to poor CMR in CML patients treated with standard-dose imatinib.

OATP and MRP2-mediated hepatic uptake and biliary excretion of eprosartan in rat and human

BACKGROUND

Eprosartan is an angiotensin II receptor antagonist, used in the treatment of hypertension and heart failure in clinical patients. The objective of this study was to clarify the mechanism underlying hepatic uptake and biliary excretion of eprosartan in rats and humans.

METHODS

Perfused rat liver in situ, rat liver slices, isolated rat hepatocytes and human organic anion-transporting polypeptide (OATP)-transfected cells in vitro were used in this study.

RESULTS

Extraction ratio of eprosartan was decreased by rifampicin in perfused rat livers. Uptake of eprosartan in rat liver slices and isolated rat hepatocytes was significantly inhibited by Oatp modulators such as ibuprofen, digoxin, rifampicin and cyclosporine A, but not by tetraethyl ammonium or p-aminohippurate. Uptake of eprosartan in rat hepatocytes indicated a saturable process. Although uptake of eprosartan in OATP1B3-human embryonic kidney cells (HEK) 293 cells was not observed, significant differences in cellular accumulations of eprosartan between vector- and OATP1B1-Madin-Darby canine kidney strain (MDCK) II cells were found in transcellular transport study. Moreover, cumulative biliary excretion rate of eprosartan in the presence of probenecid (Multidrug resistance-associated protein 2 (Mrp2) inhibitor) was significantly decreased in perfused rat livers. Vectorial basal-to-apical transport of eprosartan was also observed in OATP1B1/MRP2 double transfectants.

CONCLUSIONS

Eprosartan was transported by multiple Oatps (at least Oatp1a1 and Oatp1a4)/Mrp2 in rat and OATP1B1/MRP2, at least, in human.

Type VII collagen regulates expression of OATP1B3, promotes front-to-rear polarity and increases structural organisation in 3D spheroid cultures of RDEB tumour keratinocytes

Type VII collagen is the main component of anchoring fibrils, structures that are integral to basement membrane homeostasis in skin. Mutations in the gene encoding type VII collagen COL7A1 cause recessive dystrophic epidermolysis bullosa (RDEB) an inherited skin blistering condition complicated by frequent aggressive cutaneous squamous cell carcinoma (cSCC). OATP1B3, which is encoded by the gene SLCO1B3, is a member of the OATP (organic anion transporting polypeptide) superfamily responsible for transporting a wide range of endogenous and xenobiotic compounds. OATP1B3 expression is limited to the liver in healthy tissues, but is frequently detected in multiple cancer types and is reported to be associated with differing clinical outcome. The mechanism and functional significance of tumour-specific expression of OATP1B3 has yet to be determined. Here, we identify SLCO1B3 expression in tumour keratinocytes isolated from RDEB and UV-induced cSCC and demonstrate that SLCO1B3 expression and promoter activity are modulated by type VII collagen. We show that reduction of SLCO1B3 expression upon expression of full-length type VII collagen in RDEB cSCC coincides with acquisition of front-to-rear polarity and increased organisation of 3D spheroid cultures. In addition, we show that type VII collagen positively regulates the abundance of markers implicated in cellular polarity, namely ELMO2, PAR3, E-cadherin, B-catenin, ITGA6 and Ln332.

Pharmacogenetics of membrane transporters: a review of current approaches

This chapter provides a review of the pharmacogenetics of membrane transporters, including ABC transporters and OATPs. Membrane transporters are heavily involved in drug disposition, by actively transporting substrate drugs between organs and tissues. As such, polymorphisms in the genes encoding these proteins may have a significant effect on the absorption, distribution, metabolism, excretion, and activity of compounds. Although few drug transporter polymorphisms have transitioned from the bench to the bedside, this chapter discusses clinical development of transporter pharmacogenetic markers. Finally, development of SLCO1B1 genotyping to avoid statin induced adverse drug reactions is discussed as a model case for transporter pharmacogenetics clinical development.

Assessment of gadoxetate DCE-MRI as a biomarker of hepatobiliary transporter inhibition

Drug-induced liver injury (DILI) is a clinically important adverse drug reaction, which prevents the development of many otherwise safe and effective new drugs. Currently, there is a lack of sensitive and specific biomarkers that can be used to predict, assess and manage this toxicity. The aim of this work was to evaluate gadoxetate-enhanced MRI as a potential novel biomarker of hepatobiliary transporter inhibition in the rat. Initially, the volume fraction of extracellular space in the liver was determined using gadopentetate to enable an estimation of the gadoxetate concentration in hepatocytes. Using this information, a compartmental model was developed to characterise the pharmacokinetics of hepatic uptake and biliary excretion of gadoxetate. Subsequently, we explored the impact of an investigational hepatobiliary transporter inhibitor on the parameters of the model in vivo in rats. The investigational hepatobiliary transporter inhibitor reduced both the rate of uptake of gadoxetate into the hepatocyte, k1 , and the Michaelis-Menten constant, Vmax , characterising its excretion into bile, whereas KM values for biliary efflux were increased. These effects were dose dependent and correlated with effects on plasma chemistry markers of liver dysfunction, in particular bilirubin and bile acids. These results indicate that gadoxetate-enhanced MRI provides a novel functional biomarker of inhibition of transporter-mediated hepatic uptake and clearance in the rat. Since gadoxetate is used clinically, the technology has the potential to provide a translatable biomarker of drug-induced perturbation of hepatic transporters that may also be useful in humans to explore deleterious functional alterations caused by transporter inhibition.