Identification of novel functional organic anion-transporting polypeptide 1B3 polymorphisms and assessment of substrate specificity

Elucidating nonlinear pharmacokinetics of telmisartan: Integration of target-mediated drug disposition and OATP1B3-mediated hepatic uptake in a physiologically based model

Telmisartan, a selective inhibitor of angiotensin II receptor type 1 (AT1), demonstrates nonlinear pharmacokinetics (PK) when orally administered in ascending doses to healthy volunteers, but the underlying mechanisms remain unclear. This study presents a physiologically based pharmacokinetic model integrated with target-mediated drug disposition (TMDD-PBPK model) to explore the mechanism of its nonlinear PK. We employed the Cluster-Gauss Newton method for top-down analysis, estimating the in vivo Km,OATP1B3 (Michaelis-Menten constant for telmisartan hepatic uptake via Organic Anion Transporting Polypeptide 1B3) to be 2.0-5.7 nM. This range is significantly lower than the reported in vitro value of 810 nM, obtained in 0.3% human serum albumin (HSA) conditions. Further validation was achieved through in vitro assessment in plated human hepatocytes with 4.5% HSA, showing a Km of 4.5 nM. These results underscore the importance of albumin-mediated uptake effect for the hepatic uptake of telmisartan. Our TMDD-PBPK model, developed through a "middle-out" approach, underwent sensitivity analysis to identify key factors in the nonlinear PK of telmisartan. We found that the nonlinearity in the area under the concentration-time curve (AUC) and/or maximum concentration (Cmax) of telmisartan is sensitive to Km,OATP1B3 across all dosages. Additionally, the dissociation constant (Kd) for telmisartan binding to the AT1 receptor, along with its receptor abundance, notably influences PK at lower doses (below 20 mg). In conclusion, the nonlinear PK of telmisartan appears primarily driven by hepatic uptake saturation across all dose ranges and by AT1-receptor binding saturation, notably at lower doses.

Genome-Wide Association Study of Atorvastatin Pharmacokinetics: Associations With SLCO1B1, UGT1A3, and LPP

In a genome-wide association study of atorvastatin pharmacokinetics in 158 healthy volunteers, the SLCO1B1 c.521T>C (rs4149056) variant associated with increased area under the plasma concentration-time curve from time zero to infinity (AUC0-∞) of atorvastatin (P = 1.2 × 10-10), 2-hydroxy atorvastatin (P = 4.0 × 10-8), and 4-hydroxy atorvastatin (P = 2.9 × 10-8). An intronic LPP variant, rs1975991, associated with reduced atorvastatin lactone AUC0-∞ (P = 3.8 × 10-8). Three UGT1A variants linked with UGT1A3*2 associated with increased 2-hydroxy atorvastatin lactone AUC0-∞ (P = 3.9 × 10-8). Furthermore, a candidate gene analysis including 243 participants suggested that increased function SLCO1B1 variants and decreased activity CYP3A4 variants affect atorvastatin pharmacokinetics. Compared with individuals with normal function SLCO1B1 genotype, atorvastatin AUC0-∞ was 145% (90% confidence interval: 98-203%; P = 5.6 × 10-11) larger in individuals with poor function, 24% (9-41%; P = 0.0053) larger in those with decreased function, and 41% (16-59%; P = 0.016) smaller in those with highly increased function SLCO1B1 genotype. Individuals with intermediate metabolizer CYP3A4 genotype (CYP3A4*2 or CYP3A4*22 heterozygotes) had 33% (14-55%; P = 0.022) larger atorvastatin AUC0-∞ than those with normal metabolizer genotype. UGT1A3*2 heterozygotes had 16% (5-25%; P = 0.017) smaller and LPP rs1975991 homozygotes had 34% (22-44%; P = 4.8 × 10-5) smaller atorvastatin AUC0-∞ than noncarriers. These data demonstrate that genetic variation in SLCO1B1, UGT1A3, LPP, and CYP3A4 affects atorvastatin pharmacokinetics. This is the first study to suggest that LPP rs1975991 may reduce atorvastatin exposure. [Correction added on 6 April, after first online publication: An incomplete sentence ("= 0.017) smaller in heterozygotes for UGT1A3*2 and 34% (22%, 44%; P × 10-5) smaller in homozygotes for LPP noncarriers.") has been corrected in this version.].

Atorvastatin-associated myotoxicity: A toxicokinetic review of pharmacogenetic associations to evaluate the feasibility of precision pharmacotherapy

Atorvastatin (ATV) and other statins are highly effective in reducing cholesterol levels. However, in some patients, the development of drug-associated muscle side effects remains an issue as it compromises the adherence to treatment. Since the toxicity is dose-dependent, exploring factors modulating pharmacokinetics (PK) appears fundamental. The purpose of this review aims at reporting the current state of knowledge about the singular genetic susceptibilities influencing the risk of developing ATV muscle adverse events through PK modulations. Multiple single nucleotide polymorphisms (SNP) in efflux (ABCB1, ABCC1, ABCC2, ABCC4 and ABCG2) and influx (SLCO1B1, SLCO1B3 and SLCO2B1) transporters have been explored for their association with ATV PK modulation or with statin-related myotoxicities (SRM) development. The most convincing pharmacogenetic association with ATV remains the influence of the rs4149056 (c.521 T > C) in SLCO1B1 on ATV PK and pharmacodynamics. This SNP has been robustly associated with increased ATV systemic exposure and consequently, an increased risk of SRM. Additionally, the SNP rs2231142 (c.421C > A) in ABCG2 has also been associated with increased drug exposure and higher risk of SRM occurrence. SLCO1B1 and ABCG2 pharmacogenetic associations highlight that modulation of ATV systemic exposure is important to explain the risk of developing SRM. However, some novel observations credit the hypothesis that additional genes (e.g. SLCO2B1 or ABCC1) might be important for explaining local PK modulations within the muscle tissue, indicating that studying the local PK directly at the skeletal muscle level might pave the way for additional understanding.

SLCO1B1 Genetic Variation Influence on Atorvastatin Systemic Exposure in Pediatric Hypercholesterolemia

This clinical study examined the influence of SLCO1B1 c.521T>C (rs4149056) on plasma atorvastatin concentrations in pediatric hypercholesterolemia. The participants (8-21 years), including heterozygous (c.521T/C, n = 13), homozygous (c.521C/C, n = 2) and controls (c.521T/T, n = 13), completed a single-oral-dose pharmacokinetic study. Similar to in adults, the atorvastatin (AVA) area-under-concentration-time curve from 0 to 24 h (AUC0-24) was 1.7-fold and 2.8-fold higher in participants with c.521T/C and c.521C/C compared to the c.521T/T participants, respectively. The inter-individual variability in AVA exposure within these genotype groups ranged from 2.3 to 4.8-fold, indicating that additional factors contribute to the inter-individual variability in the AVA dose-exposure relationship. A multivariate model reinforced the SLCO1B1 c.521T>C variant as the central factor contributing to AVA systemic exposure in this pediatric cohort, accounting for ~65% of the variability in AVA AUC0-24. Furthermore, lower AVA lactone concentrations in participants with increased body mass index contributed to higher exposure within the c.521T/T and c.521T/C genotype groups. Collectively, these factors contributing to higher systemic exposure could increase the risk of toxicity and should be accounted for when individualizing the dosing of atorvastatin in eligible pediatric patients.

When the same treatment has different response: The role of pharmacogenomics in statin therapy

Statins, also known as HMG-CoA reductase inhibitors, are one of the most potently prescribed and thoroughly researched medications, predominantly utilized for managing cardiovascular diseases by modulating serum cholesterol levels. Despite the well-documented efficacy of statins in reducing overall mortality via attenuating the risk of cardiovascular diseases, notable interindividual variability in therapeutic responses persists as such variability could compromise the lipid-lowering efficacy of the drug, potentially increasing susceptibility to adverse effects or attenuating therapeutic outcomes.This phenomenon has catalysed a growing interest in the scientific community to explore common genetic polymorphisms within genes that encode for pivotal enzymes within the pharmacokinetic pathways of statins. In our review, we focus to provide insight into potentially clinically relevant polymorphisms associated with statins' pharmacokinetic participants and assess their consequent implications on modulating the therapeutic outcomes of statins among distinct genetic carrier.

Structure of human drug transporters OATP1B1 and OATP1B3

The organic anion transporting polypeptides OATP1B1 and OATP1B3 are membrane proteins that mediate uptake of drugs into the liver for subsequent conjugation and biliary excretion, a key step in drug elimination from the human body. Polymorphic variants of these transporters can cause reduced drug clearance and adverse drug effects such as statin-induced rhabdomyolysis, and co-administration of OATP substrates can lead to damaging drug-drug interaction. Despite their clinical relevance in drug disposition and pharmacokinetics, the structure and mechanism of OATPs are unknown. Here we present cryo-EM structures of human OATP1B1 and OATP1B3 bound to synthetic Fab fragments and in functionally distinct states. A single estrone-3-sulfate molecule is bound in a pocket located in the C-terminal half of OATP1B1. The shape and chemical nature of the pocket rationalize the preference for diverse organic anions and allow in silico docking of statins. The structure of OATP1B3 is determined in a drug-free state but reveals a bicarbonate molecule bound to the conserved signature motif and a histidine residue that is prevalent in OATPs exhibiting pH-dependent activity.

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.

Characterization of Bile Acid Sulfate Conjugates as Substrates of Human Organic Anion Transporting Polypeptides

Drug interactions involving the inhibition of hepatic organic anion transporting polypeptides (OATPs) 1B1 and OATP1B3 are considered important. Therefore, we sought to study various sulfated bile acids (BA-S) as potential clinical OATP1B1/3 biomarkers. It was determined that BA-S [e.g., glycochenodeoxycholic acid 3-O-sulfate (GCDCA-S) and glycodeoxycholic acid 3-O-sulfate (GDCA-S)] are substrates of OATP1B1, OATP1B3, and sodium-dependent taurocholic acid cotransporting polypeptide (NTCP) transfected into human embryonic kidney 293 cells, with minimal uptake evident for other solute carriers (SLCs) like OATP2B1, organic anion transporter 2, and organic cation transporter 1. It was also shown that BA-S uptake by plated human hepatocytes (PHH) was inhibited (≥96%) by a pan-SLC inhibitor (rifamycin SV), and there was greater inhibition (≥77% versus ≤12%) with rifampicin (OATP1B1/3-selective inhibitor) than a hepatitis B virus myristoylated-preS1 peptide (NTCP-selective inhibitor). Estrone 3-sulfate was also used as an OATP1B1-selective inhibitor. In this instance, greater inhibition was observed with GDCA-S (76%) than GCDCA-S (52%). The study was expanded to encompass the measurement of GCDCA-S and GDCA-S in plasma of SLCO1B1 genotyped subjects. The geometric mean GDCA-S concentration was 2.6-fold (90% confidence interval 1.6, 4.3; P = 2.1 × 10^-4) and 1.3-fold (1.1, 1.7; P = 0.001) higher in individuals homozygous and heterozygous for the SLCO1B1 c.521T > C loss-of-function allele, respectively. For GCDCA-S, no significant difference was noted [1.2-fold (0.8, 1.7; P = 0.384) and 0.9-fold (0.8, 1.1; P = 0.190), respectively]. This supported the in vitro data indicating that GDCA-S is a more OATP1B1-selective substrate (versus GCDCA-S). It is concluded that GCDCA-S and GDCA-S are viable plasma-based OATP1B1/3 biomarkers, but they are both less OATP1B1-selective when compared to their corresponding 3-O-glucuronides (GCDCA-3G and GDCA-3G). Additional studies are needed to determine their utility versus more established biomarkers, such as coproporphyrin I, for assessing inhibitors with different OATP1B1 (versus OATP1B3) inhibition signatures.

SLCO1B3 T334G polymorphisms and mycophenolate mofetil-related adverse reactions in kidney transplant recipients

Background: The correlation between SLCO1B3 T334G polymorphisms and mycophenolate mofetil (MMF) adverse reactions in kidney recipients is unknown. Methods: A single-center, retrospective study was performed in which 111 patients were divided into four groups according to the type of adverse effect experienced. The clinical data and concentrations of MMF at different months after transplantation were statistically analyzed. Results: The G allele in the gastrointestinal reaction group was significantly higher than that in the no adverse effects group (p < 0.05). Logistic regression model showed that the SLCO1B3 T334G genotype was an independent risk factor for gastrointestinal reactions caused by MMF. Conclusion: Patients with the SLCO1B3 T334G GG genotype were more likely to experience gastrointestinal reactions.

SLCO1B1 c.521T>C gene polymorphism decreases hypoglycemia risk in sulfonylurea-treated type 2 diabetic patients

OBJECTIVES

Pharmacogenomics can explain some of the heterogeneity of sulfonylurea (SU)-related hypoglycemia risk. Recently, a role of OATP1B1, encoded by SLCO1B1 gene, on SU liver transport prior of metabolism has been uncovered. The aim of the present study was to explore the potential association of SLCO1B1 c.521T>C polymorphism, leading to reduced OATP1B1 function, with SU-related hypoglycemia risk.

METHODS

Study cohort consists of 176 type 2 diabetes patients treated with the SUs glimepiride or gliclazide. 92 patients reported SU-related hypoglycemia, while 84 patients had never experienced a hypoglycemic event. Patients were previously genotyped for CYP2C9 *2 and *3 variant alleles that lead to decreased enzyme activity of the SU metabolizing enzyme CYP2C9 and have been associated with increased SU-related hypoglycemia risk. SLCO1B1 c.521T>C polymorphism was genotyped by use of PCR-RFLP analysis.

RESULTS

SLCO1B1 c.521TC genotype frequency was significantly lower in hypoglycemic cases than non-hypoglycemic controls (15.2% vs. 32.1%, p=0.008). In an adjusted model, c.521TC genotype significantly reduced the risk of hypoglycemia (OR 0.371; 95% C.I. 0.167-0.822; p=0.015). In CYP2C9 intermediate metabolizers (n=54) c.521TC genotype frequency was significantly decreased in cases compared to controls (3 out of 36 cases, 8.3% vs. 7 out of 18 controls, 38.9%, p=0.012). A similar albeit not significant difference of SLCO1B1 c.521TC genotype was present in CYP2C9 extensive metabolizers (n=120) (18.2% in cases vs. 30.8% in controls, p=0.113).

CONCLUSIONS

We have found a protective effect of SLCO1B1 c.521C variant on SU-related hypoglycemia risk both independently and in interaction with CYP2C9 phenotypes. Our results suggest a possible linkage of SLCO1B1 c.521T>C polymorphism with variants in other genes impairing OATPs expressed in pancreatic islets that could interfere with SU tissue distribution.

The role of OATP1B1 and OATP1B3 transporter polymorphisms in drug disposition and response to anticancer drugs: a review of the recent literature

INTRODUCTION

Members of the solute carrier family of organic anion transporting polypeptides are responsible for the cellular uptake of a broad range of endogenous compounds and xenobiotics in multiple tissues. In particular, the polymorphic transporters OATP1B1 and OATP1B3 are highly expressed in the liver and have been identified as critical regulators of hepatic eliminaton. As these transporters are also expressed in cancer cells, the function alteration of these proteins have important consequences for an individual's susceptibility to certain drug-induced side effects, drug-drug interactions, and treatment efficacy.

AREAS COVERED

In this mini-review, we provide an update of this rapidly emerging field, with specific emphasis on the direct contribution of genetic variants in OATP1B1 and OATP1B3 to the transport of anticancer drugs, the role of these carriers in regulation of their disposition and toxicity profiles, and recent advances in attempts to integrate information on transport function in patients to derive individualized treatment strategies.

EXPERT OPINION

Based on currently available data, it appears imperative that different aspects of disease, physiology, and drugs of relevance should be evaluated along with an individual's genetic signature, and that tools such as biomarker levels can be implemented to achieve the most reliable prediction of clinically relevant pharmacodynamic endpoints.

Association of Drug-Metabolizing Enzyme and Transporter Gene Polymorphisms and Lipid-Lowering Response to Statins in Thai Patients with Dyslipidemia

Purpose

Statins are increasingly widely used in the primary and secondary prevention of cardiovascular disease. However, there is an inter-individual variation in statin response among patients. The study aims to determine the association between genetic variations in drug-metabolizing enzyme and transporter (DMET) genes and lipid-lowering response to a statin in Thai patients with hyperlipidemia.

Patients and Methods

Seventy-nine patients who received statin at steady-state concentrations were recruited. Serum lipid profile was measured at baseline and repeated after 4-month on a statin regimen. The genotype profile of 1936 DMET markers was obtained using Affymetrix DMET Plus genotyping microarrays.

Results

In this DMET microarray platform, five variants; SLCO1B3 (rs4149117, rs7311358, and rs2053098), QPRT (rs13331798), and SLC10A2 (rs188096) showed a suggestive association with LDL-cholesterol-lowering response. HDL-cholesterol-lowering responses were found to be related to CYP7A1 gene variant (rs12542233). Seven variants, SLCO1B3 (rs4149117, rs7311358, and rs2053098); SULT1E1 (rs3736599 and rs3822172); and ABCB11 (rs4148768 and rs3770603), were associated with the total cholesterol-lowering response. One variant of the ABCB4 gene (rs2109505) was significantly associated with triglyceride-lowering response.

Conclusion

This pharmacogenomic study identifies new genetic variants of DMET genes that are associated with the lipid-lowering response to statins. Genetic polymorphisms in DMET genes may impact the pharmacokinetics and lipid-lowering response to statin. The validation studies confirmations are needed in future pharmacogenomic studies.

SLCO1B3 polymorphisms and clinical outcomes in kidney transplant recipients receiving mycophenolate

Aim: Determine the influence of SLCO1B3 polymorphisms on outcomes in kidney transplant recipients. Materials & methods: We retrospectively evaluated 181 adult kidney transplant recipients receiving mycophenolate. Outcomes included treated biopsy-proven acute rejection (tBPAR), de novo donor-specific antibody (dnDSA) formation, graft survival, patient survival and mycophenolate-related adverse effects among SLCO1B3 genotypes. Results: The presence of SLCO1B3 variants was not associated with increased risk of tBPAR (HR: 1.45, 95% CI: 0.76-2.74), dnDSA (HR: 0.46, 95% CI: 0.16-1.36) or composite of tBPAR or dnDSA (HR: 1.14, 95% CI: 0.64-2.03). Graft and patient survival were reduced among variant carriers; however, inconsistent findings with the primary analysis suggest these associations were not due to genotype. Adverse effects were similar between groups. Conclusion: Presence of SLCO1B3 polymorphisms were not predictive of rejection or dnDSA in kidney transplant recipients.

Measuring Pharmacogene Variant Function at Scale Using Multiplexed Assays

As costs of next-generation sequencing decrease, identification of genetic variants has far outpaced our ability to understand their functional consequences. This lack of understanding is a central challenge to a key promise of pharmacogenomics: using genetic information to guide drug selection and dosing. Recently developed multiplexed assays of variant effect enable experimental measurement of the function of thousands of variants simultaneously. Here, we describe multiplexed assays that have been performed on nearly 25,000 variants in eight key pharmacogenes (ADRB2, CYP2C9, CYP2C19, NUDT15, SLCO1B1, TMPT, VKORC1, and the LDLR promoter), discuss advances in experimental design, and explore key challenges that must be overcome to maximize the utility of multiplexed functional data. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Expression and Function of Organic Anion Transporting Polypeptides in the Human Brain: Physiological and Pharmacological Implications

The central nervous system (CNS) is an important pharmacological target, but it is very effectively protected by the blood–brain barrier (BBB), thereby impairing the efficacy of many potential active compounds as they are unable to cross this barrier. Among others, membranous efflux transporters like P-Glycoprotein are involved in the integrity of this barrier. In addition to these, however, uptake transporters have also been found to selectively uptake certain compounds into the CNS. These transporters are localized in the BBB as well as in neurons or in the choroid plexus. Among them, from a pharmacological point of view, representatives of the organic anion transporting polypeptides (OATPs) are of particular interest, as they mediate the cellular entry of a variety of different pharmaceutical compounds. Thus, OATPs in the BBB potentially offer the possibility of CNS targeting approaches. For these purposes, a profound understanding of the expression and localization of these transporters is crucial. This review therefore summarizes the current state of knowledge of the expression and localization of OATPs in the CNS, gives an overview of their possible physiological role, and outlines their possible pharmacological relevance using selected examples.

Pharmacogenomics in the era of next generation sequencing - from byte to bedside

Pharmacogenetic research has resulted in the identification of a multitude of genetic variants that impact drug response or toxicity. These polymorphisms are mostly common and have been included as actionable information in the labels of numerous drugs. In addition to common variants, recent advances in Next Generation Sequencing (NGS) technologies have resulted in the identification of a plethora of rare and population-specific pharmacogenetic variations with unclear functional consequences that are not accessible by conventional forward genetics strategies. In this review, we discuss how comprehensive sequencing information can be translated into personalized pharmacogenomic advice in the age of NGS. Specifically, we provide an update of the functional impacts of rare pharmacogenetic variability and how this information can be leveraged to improve pharmacogenetic guidance. Furthermore, we critically discuss the current status of implementation of pharmacogenetic testing across drug development and layers of care. We identify major gaps and provide perspectives on how these can be minimized to optimize the utilization of NGS data for personalized clinical decision-support.

Hypoglycemia and Glycemic Control With Glyburide in Women With Gestational Diabetes and Genetic Variants of Cytochrome P450 2C9 and/or OATP1B3

Glyburide is mainly metabolized by the cytochrome P450 2C9 (CYP2C9) enzyme and enters the liver via the transporter OATP1B3. The variants OATP1B3*4 (699 G>A; rs7311358) and CYP2C9*2 and *3 are known to have a significant influence on the hepatic uptake and metabolism of glyburide, with lower clearance than in the wild type. In an ancillary study of the INDAO trial, we selected 117 pregnant women with gestational diabetes treated by glyburide and assessed the role of the combined CYP2C9 and OATP1B3 genetic polymorphisms in hypoglycemia and glycemic control. Three groups were constituted: (1) the wild-type genotype group (wild-type allele genotype for both CYP2C9*1 and OATP1B3*1 (699G)), (2) the intermediate group (carriers of CYP2C9*2 allele or OATP1B3*4 (699G>A) heterozygous), and (3) the variant group (carriers of CYP2C9*3 allele and/or OATP1B3*4 (699G>A) homozygous variant). We found that the risk of hypoglycemia was significantly higher in the variant genotype at the second week of treatment: 20.0% (4/20) vs. 8.1% (3/37) in the intermediate group and 4.1% (2/49) in the wild-type genotype group (P = 0.03). The last daily dose of glyburide during pregnancy was lower for patients in the variant genotype group: 4.7 mg (SD 3.5) vs. 8.7 mg (SD 5.7) in the wild-type group and 5.7 mg (SD 3.7) in the intermediate group (P < 0.01). In conclusion, the no-function variants CYP2C9*3 and OATP1B3*4 are associated with a higher risk of hypoglycemia and a lower dose of glyburide in women with gestational diabetes treated with glyburide, which is consistent with the pharmacokinetic roles of both CYP2C9 and OATP1B3.

Late response to rosuvastatin and statin-related myalgia due to SLCO1B1, SLCO1B3, ABCB11, and CYP3A5 variants in a patient with Familial Hypercholesterolemia: a case report

Statins are the most widely used cholesterol-lowering drugs for cardiovascular diseases prevention. However, some patients are refractory to treatment, whereas others experience statin-related adverse events (SRAE). It has been increasingly important to identify pharmacogenetic biomarkers for predicting statin response and adverse events. This case report describes a female patient with familial hypercholesterolemia (FH) who showed late response to rosuvastatin and experienced myalgia on statin treatment. In the first visit (V1), the patient reported myalgia to rosuvastatin 40 mg, which was interrupted for a 6-week wash-out period. In V2, rosuvastatin 20 mg was reintroduced, but her lipid profile did not show any changes after 6 weeks (V3) (LDL-c: 402 vs. 407 mg/dL). Her lipid profile markedly improved after 12 weeks of treatment (V4) (LDL-c: 208 mg/dL), suggesting a late rosuvastatin response. Her adherence to treatment was similar in V1 and V3 and no drug interactions were detected. Pharmacogenetic analysis revealed that the patient carries low-activity variants in SLCO1B1*1B and*5, SLCO1B3 (rs4149117 and rs7311358), and ABCB11 rs2287622, and the non-functional variant in CYP3A5*3. The combined effect of variants in pharmacokinetics-related genes may have contributed to the late response to rosuvastatin and statin-related myalgia. Therefore, they should be considered when assessing a patient’s response to statin treatment. To the best of our knowledge, this is the first report of a pharmacogenetic analysis on a case of late rosuvastatin response.

Post-translational regulation of the major drug transporters in the families of organic anion transporters and organic anion-transporting polypeptides

The organic anion transporters (OATs) and organic anion-transporting polypeptides (OATPs) belong to the solute carrier (SLC) transporter superfamily and play important roles in handling various endogenous and exogenous compounds of anionic charge. The OATs and OATPs are often implicated in drug therapy by impacting the pharmacokinetics of clinically important drugs and, thereby, drug exposure in the target organs or cells. Various mechanisms (e.g. genetic, environmental, and disease-related factors, drug-drug interactions, and food-drug interactions) can lead to variations in the expression and activity of the anion drug-transporting proteins of OATs and OATPs, possibly impacting the therapeutic outcomes. Previous investigations mainly focused on the regulation at the transcriptional level and drug-drug interactions as competing substrates or inhibitors. Recently, evidence has accumulated that cellular trafficking, post-translational modification, and degradation mechanisms serve as another important layer for the mechanisms underlying the variations in the OATs and OATPs. This review will provide a brief overview of the major OATs and OATPs implicated in drug therapy and summarize recent progress in our understanding of the post-translational modifications, in particular ubiquitination and degradation pathways of the individual OATs and OATPs implicated in drug therapy.

Genetic variants of SLCO1B7 are of relevance for the transport function of OATP1B3-1B7

The family of Organic Anion Transporting Polypeptides are known to facilitate the transmembrane transport. OATP1B3-1B7 is a novel member of the OATP1B-subfamily, and is encoded by SLCO1B3-SLCO1B7 readthrough deriving from the genes SLCO1B3 and SLCO1B7 on chromosome 12. The resulting protein is expressed in the smooth endoplasmatic reticulum of hepatocytes, is functional, and transports dehydroepiandrosterone-sulfate (DHEAS). In the gene area encoding for the 1B7-part of the protein, there are coding polymorphisms. It was the aim of this study to test the frequency and the impact of these genetic variants on transport activity. The minor allele frequency (MAF) of the coding polymorphisms was determined in a cohort of 192 individuals. DHEAS transport function was determined by applying the vTF-7 based heterologous expression system using plasmids encoding for OATP1B3-1B7 or the respective variants. The genetic variants 641 T (MAF 0.021), 1073 G (MAF 0.169) and 1775 A (MAF 0.013) significantly reduced DHEAS accumulation in cells transfected with OATP1B3-1B7, albeit without significantly influencing expression of the transporter as determined by Western blot analysis and immunofluorescence after heterologous expression. Genotyping revealed complete linkage of the variants 884A, 1073 G and 1501C. Presence of the haplotype abolished the DHEAS-transport function of OATP1B3-1B7. Naturally and frequently occurring genetic variants located within the gene region of SLCO1B7 encoding for the 1B7-part of OATP1B3-1B7 influence the in vitro function of this member of the OATP1B-family. With their functional characterisation, we provide the basis for pharmacogenetic studies, which may help to understand the in vivo relevance of this transporter.

Uptake Transporters of the SLC21, SLC22A, and SLC15A Families in Anticancer Therapy-Modulators of Cellular Entry or Pharmacokinetics?

Solute carrier transporters comprise a large family of uptake transporters involved in the transmembrane transport of a wide array of endogenous substrates such as hormones, nutrients, and metabolites as well as of clinically important drugs. Several cancer therapeutics, ranging from chemotherapeutics such as topoisomerase inhibitors, DNA-intercalating drugs, and microtubule binders to targeted therapeutics such as tyrosine kinase inhibitors are substrates of solute carrier (SLC) transporters. Given that SLC transporters are expressed both in organs pivotal to drug absorption, distribution, metabolism, and elimination and in tumors, these transporters constitute determinants of cellular drug accumulation influencing intracellular drug concentration required for efficacy of the cancer treatment in tumor cells. In this review, we explore the current understanding of members of three SLC families, namely SLC21 (organic anion transporting polypeptides, OATPs), SLC22A (organic cation transporters, OCTs; organic cation/carnitine transporters, OCTNs; and organic anion transporters OATs), and SLC15A (peptide transporters, PEPTs) in the etiology of cancer, in transport of chemotherapeutic drugs, and their influence on efficacy or toxicity of pharmacotherapy. We further explore the idea to exploit the function of SLC transporters to enhance cancer cell accumulation of chemotherapeutics, which would be expected to reduce toxic side effects in healthy tissue and to improve efficacy.

Variant discovery using next-generation sequencing and its future role in pharmacogenetics

Next-generation sequencing (NGS) has enabled the discovery of a multitude of novel and mostly rare variants in pharmacogenes that may alter a patient’s therapeutic response to drugs. In addition to single nucleotide variants, structural variation affecting the number of copies of whole genes or parts of genes can be detected. While current guidelines concerning clinical implementation mostly act upon well-documented, common single nucleotide variants to guide dosing or drug selection, in silico and large-scale functional assessment of rare variant effects on protein function are at the forefront of pharmacogenetic research to facilitate their clinical integration. Here, we discuss the role of NGS in variant discovery, paving the way for more comprehensive genotype-guided pharmacotherapy that can translate to improved clinical care.

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.

Impact of SLCO1B1 Genetic Variation on Rosuvastatin Systemic Exposure in Pediatric Hypercholesterolemia

This study investigated the impact of SLCO1B1 genotype on rosuvastatin systemic exposure in hypercholesterolemic children and adolescents. Participants (8–21 years) with at least one allelic variant of SLCO1B1 c.521T>C (521TC, n = 13; 521CC, n = 2) and wild type controls (521TT, n = 13) completed a single oral dose pharmacokinetic study. The variability contributed by SLCO1B1 c.521 sequence variation to rosuvastatin (RVA) systemic exposure among our pediatric cohort was comparable to previous studies in adults. RVA concentration‐time curve from 0–24 hours (AUC_0–24) was 1.4‐fold and 2.2‐fold higher in participants with c.521TC and c.521CC genotype compared 521TT participants, respectively. Interindividual variability of RVA exposure within SLCO1B1 genotype groups exceeded the ~ 1.5‐fold to 2‐fold difference in mean RVA exposure observed among SLCO1B1 genotype groups, suggesting that other factors also contribute to interindividual variability in the rosuvastatin dose‐exposure relationship. A multivariate model performed confirmed SLCO1B1 c.521T>C genotype as the primary factor contributing to RVA systemic exposure in this pediatric cohort, accounting for ~ 30% of the variability RVA AUC_0–24. However, of the statins investigated to date in the pediatric population, RVA has the lowest magnitude of variability in systemic exposure.

OATP1B3-1B7, a novel organic anion transporting polypeptide, is modulated by FXR ligands and transports bile acids

Organic anion transporting polypeptide (OATP) 1B3-1B7 (LST-3TM12) is a member of the OATP1B [solute carrier organic anion transporter (SLCO) 1B] family. This transporter is not only functional but also expressed in the membrane of the smooth endoplasmic reticulum of hepatocytes and enterocytes. OATP1B3-1B7 is a splice variant of SLCO1B3 in which the initial part is encoded by SLCO1B3, whereas the rest of the mRNA originates from the gene locus of SLCO1B7. In this study, we not only showed that SLCO1B3 and the mRNA encoding for OATP1B3-1B7 share the 5' untranslated region but also that silencing of an initial SLCO1B3 exon lowered the amount of SLCO1B3 and of SLCO1B7 mRNA in Huh-7 cells. To validate the assumption that both transcripts are regulated by the same promoter we tested the influence of the bile acid sensor farnesoid X receptor (FXR) on their transcription. Treatment of Huh-7 and HepaRG cells with activators of this known regulator of OATP1B3 not only increased SLCO1B3 but also OATP1B3-1B7 mRNA transcription. Applying a heterologous expression system, we showed that several bile acids interact with OATP1B3-1B7 and that taurocholic acid and lithocholic acid are OATP1B3-1B7 substrates. As OATP1B3-1B7 is located in the smooth endoplasmic reticulum, it may grant access to metabolizing enzymes. In accordance are our findings showing that the OATP1B3-1B7 inhibitor bromsulphthalein significantly reduced uptake of bile acids into human liver microsomes. Taken together, we report that OATP1B3-1B7 transcription can be modulated with FXR agonists and antagonists and that OATP1B3-1B7 transports bile acids.NEW & NOTEWORTHY Our study on the transcriptional regulation of the novel organic anion transporting polypeptide (OATP) 1B3-1B7 concludes that the promoter of solute carrier organic anion transporter (SLCO) 1B3 governs SLCO1B3-1B7 transcription. Moreover, the transcription of OATP1B3-1B7 can be modulated by farnesoid X receptor (FXR) agonists and antagonists. FXR is a major regulator in bile acid homeostasis that links OATP1B3-1B7 to this physiological function. Findings in transport studies with OATP1B3-1B7 suggest that this transporter interacts with the herein tested bile acids.

Organic Anion Transporting Polypeptides: Emerging Roles in Cancer Pharmacology

The organic anion transporting polypeptides (OATPs) are a superfamily of drug transporters involved in the uptake and disposition of a wide array of structurally divergent endogenous and exogenous substrates, including steroid hormones, bile acids, and commonly used drugs, such as anti-infectives, antihypertensives, and cholesterol lowering agents. In the past decade, OATPs, primarily OATP1A2, OATP1B1, and OATP1B3, have emerged as potential mediators of chemotherapy disposition, including drugs such as methotrexate, doxorubicin, paclitaxel, docetaxel, irinotecan and its important metabolite 7-ethyl-10-hydroxycamptothecin, and certain tyrosine kinase inhibitors. Furthermore, OATP family members are polymorphic and numerous studies have shown OATP variants to have differential uptake, disposition, and/or pharmacokinetics of numerous drug substrates with important implications for interindividual differences in efficacy and toxicity. Additionally, certain OATPs have been found to be overexpressed in a variety of human solid tumors, including breast, liver, colon, pancreatic, and ovarian cancers, suggesting potential roles for OATPs in tumor development and progression and as novel targets for cancer therapy. This review focuses on the emerging roles for selected OATPs in cancer pharmacology, including preclinical and clinical studies suggesting roles in chemotherapy disposition, the pharmacogenetics of OATPs in cancer therapy, and OATP overexpression in various tumor tissues with implications for OATPs as therapeutic targets.

The Role of Next-Generation Sequencing in Pharmacogenetics and Pharmacogenomics

Inherited genetic variations in pharmacogenetic loci are widely acknowledged as important determinants of phenotypic differences in drug response, and may be actionable in the clinic. However, recent studies suggest that a considerable number of novel rare variants in pharmacogenes likely contribute to a still unexplained fraction of the observed interindividual variability. Next-generation sequencing (NGS) represents a rapid, relatively inexpensive, large-scale DNA sequencing technology with potential relevance as a comprehensive pharmacogenetic genotyping platform to identify genetic variation related to drug therapy. However, many obstacles remain before the clinical use of NGS-based test results, including technical challenges, functional interpretation, and strict requirements for diagnostic tests. Advanced computational analyses, high-throughput screening methodologies, and generation of shared resources with cell-based and clinical information will facilitate the integration of NGS data into candidate genotyping approaches, likely enhancing future drug phenotype predictions in patients.

OATP1B3 (699G>A) and CYP2C9*2, *3 significantly influenced the transport and metabolism of glibenclamide and glipizide

Glibenclamide and glipizide show large substantial inter-individual variation in clinical efficacy, which may be resulted from the genetic differences of metabolic enzymes and transporters in individuals. This study purposed to investigate the effect of OATP1B3 and CYP2C9 genetic polymorphisms on the transport and metabolism of glibenclamide and glipizide in human. An LC-MS method was used to determine the uptake of glibenclamide and glipizide in OATP1B3, OATP1B3 (344T > G) and OATP1B3 (699G > A)-HEK293T cells and their metabolism in CYP2C9*1, *2 and *3 recombinase system. Glibenclamide can be taken in OATP1B3 (wild-type), OATP1B3 (344T > G) and OATP1B3 (699G > A)-HEK293T cells with the V_max values of 44.91 ± 7.97, 46.08 ± 8.69, and 37.31 ± 5.04 pmol/min/mg, while glipizide was taken in with V_max of 16.50 ± 3.64, 16.87 ± 4.23, and 13.42 ± 2.79 pmol/min/mg, respectively. The internal clearance of glibenclamide and glipizide in OATP1B3 (699G > A) was less than that in wild-type. Glibenclamide can be metabolized in CYP2C9*1, *2 and *3 recombinase system with the V_max values of 1.58 ± 0.71, 0.69 ± 0.25, and 0.41 ± 0.13 nmol/min/mg protein, while glipizide was metabolized with V_max of 8.82 ± 2.78, 5.99 ± 1.95, and 2.87 ± 1.03 nmol/min/mg protein, respectively. The internal clearance of glibenclamide and glipizide in CYP2C9*2 and *3 was markedly reduced compared to that in CYP2C9*1. These results collectively demonstrate that OATP1B3 (699G > A) and CYP2C9*2 and *3 have a significant influence on the transport and metabolism of glibenclamide and glipizide.

Genetic variability and population diversity of the human SLCO (OATP) transporter family

Organic anion transporting polypeptides (OATP) encoded by the SLCO gene family constitute clinically important transporters involved in the disposition of endogenous compounds and many commonly prescribed drugs, including statins, methotrexate and antihypertensive medications. Common genetic polymorphisms in SLCO genes are known to affect OATP function and modulate efficacy and safety of OATP substrates. However, current frequency data of these variants and haplotypes is generally based on few rather heterogenous populations of relatively small sample size. Furthermore, the genetic variability beyond these selected pharmacogenetic biomarkers has not been systematically analyzed. Here, we provide a global consolidated map of SLCO variability by leveraging fully compatible Next Generation Sequencing data from 138,632 unrelated individuals across seven major human populations. Overall, we find 9811 exonic single nucleotide variants and 155 copy number variations of which 99.3% were rare with frequencies <1%. Using orthogonal computational functionality predictors optimized for pharmacogenetic assessments, we find that four out of five individuals carry at least one deleterious variant in an SLCO transporter gene and rare variants contribute 23% to the genetically encoded functional variability. Moreover, 74.9% of all variants were found to be population-specific with important consequences for population-specific genotyping strategies and precision public health approaches. Combined, our analyses provide the most comprehensive data set of SLCO variability published to date and incentivize the integration of comprehensive NGS-based genotyping into personalized predictions of OATP substrate disposition.

Effects of Uremic Serum Residue on OATP1B1- and OATP1B3-Mediated Pravastatin Uptake in OATP-Expressing HEK293 Cells and Human Hepatocytes

Patients with end-stage renal disease have increased plasma concentrations of statins, which is a risk factor for rhabdomyolysis, as well as elevated levels of uremic toxins (UTs). We investigated the effects of uremic serum residue and UTs on organic anion-transporting peptide (OATP1B1)- and OATP1B3-mediated pravastatin uptake. We evaluated the effects of normal serum residue with four UTs (hippuric acid, 3-carboxy-4-methyl-5-propyl-2-furan propionate, indole-3-acetic acid, and 3-indoxyl sulfate) and uremic serum residue on pravastatin uptake by OATP1B1- or OATP1B3-expressing HEK293 cells. Furthermore, we assessed the contribution of each transporter using cryopreserved human hepatocytes. Uremic serum residue and UTs significantly inhibited OATP1B1-mediated pravastatin uptake. Uremic serum residue accelerated OATP1B3-mediated pravastatin uptake, while UTs had no effect. There was no difference in pravastatin uptake between uremic- and normal serum residue-treated hepatocytes. The results suggest that the effects of uremic serum on pravastatin hepatic uptake may be considered negligible in end-stage renal disease patients.

Cellular Uptake of the Atypical Antipsychotic Clozapine Is a Carrier-Mediated Process

The weak base antipsychotic clozapine is the most effective medication for treating refractory schizophrenia. The brain-to-plasma concentration of unbound clozapine is greater than unity, indicating transporter-mediated uptake, which has been insufficiently studied. This is important, because it could have a significant impact on clozapine's efficacy, drug-drug interaction, and safety profile. A major limitation of clozapine's use is the risk of clozapine-induced agranulocytosis/granulocytopenia (CIAG), which is a rare but severe hematological adverse drug reaction. We first studied the uptake of clozapine into human brain endothelial cells (hCMEC/D3). Clozapine uptake into cells was consistent with a carrier-mediated process, which was time-dependent and saturable ( V_max = 3299 pmol/million cells/min, K_m = 35.9 μM). The chemical inhibitors lamotrigine, quetiapine, olanzapine, prazosin, verapamil, indatraline, and chlorpromazine reduced the uptake of clozapine by up to 95%. This could in part explain the in vivo interactions observed in rodents or humans for these compounds. An extensive set of studies utilizing transporter-overexpressing cell lines and siRNA-mediated transporter knockdown in hCMEC/D3 cells showed that clozapine was not a substrate of OCT1 (SLC22A1), OCT3 (SLC22A3), OCTN1 (SLC22A4), OCTN2 (SLC22A5), ENT1 (SLC29A1), ENT2 (SLC29A2), and ENT4/PMAT (SLC29A4). In a recent genome-wide analysis, the hepatic uptake transporters SLCO1B1 (OATP1B1) and SLCO1B3 (OATP1B3) were identified as additional candidate transporters. We therefore also investigated clozapine transport into OATP1B-transfected cells and found that clozapine was neither a substrate nor an inhibitor of OATP1B1 and OATP1B3. In summary, we have identified a carrier-mediated process for clozapine uptake into brain, which may be partly responsible for clozapine's high unbound accumulation in the brain and its drug-drug interaction profile. Cellular clozapine uptake is independent from currently known drug transporters, and thus, molecular identification of the clozapine transporter will help to understand clozapine's efficacy and safety profile.

Association of Allelic Interaction of Single Nucleotide Polymorphisms of Influx and Efflux Transporters Genes With Nonhematologic Adverse Events of Docetaxel in Breast Cancer Patients

PURPOSE

Nonhematologic adverse events (AEs) of docetaxel constitute an extra burden in the treatment of cancer patients and necessitate either a dose reduction or an outright switch of docetaxel for other regimens. These AEs are frequently associated with genetic polymorphisms of genes encoding for proteins involved docetaxel disposition. Therefore, we investigated that association in Malaysian breast cancer patients.

MATERIALS AND METHODS

A total of 110 Malaysian breast cancer patients were enrolled in the present study, and their blood samples were investigated for different single nucleotide polymorphisms using polymerase chain reaction restriction fragment length polymorphism. AEs were evaluated using the Common Terminology Criteria for Adverse Events, version 4.0.

RESULTS

Fatigue, nausea, oral mucositis, and vomiting were the most common nonhematologic AEs. Rash was associated with heterozygous and mutant genotypes of ABCB1 3435C>T (P < .05). Moreover, patients carrying the GG genotype of ABCB1 2677G>A/T reported more fatigue than those carrying the heterozygous genotype GA (P < .05). The presence of ABCB1 3435-T, ABCC2 3972-C, ABCC2 1249-G, and ABCB1 2677-G alleles was significantly associated with nausea and oral mucositis. The coexistence of ABCB1 3435-C, ABCC2 3972-C, ABCC2 1249-G, and ABCB1 2677-A was significantly associated with vomiting (P < .05).

CONCLUSION

The prevalence of nonhematologic AEs in breast cancer patients treated with docetaxel has been relatively high. The variant allele of ABCB1 3435C>T polymorphism could be a potential predictive biomarker of docetaxel-induced rash, and homozygous wild-type ABCB1 2677G>A/T might predict for a greater risk of fatigue. In addition, the concurrent presence of specific alleles could be predictive of vomiting, nausea, and oral mucositis.

Prediction and Quantification of Hepatic Transporter-Mediated Uptake of Pitavastatin Utilizing a Combination of the Relative Activity Factor Approach and Mechanistic Modeling

Quantification of the fraction transported (f_t) by a particular transporter will facilitate more robust estimations of transporter interactions. Using pitavastatin as a model uptake transporter substrate, we investigated the utility of the relative activity factor (RAF) approach and mechanistic modeling to estimate f_t in hepatocytes. The transporters evaluated were organic anion-transporting polypeptides OATP1B1 and OATP1B3 and sodium-taurocholate cotransporting polypeptide. Transporter-expressing human embryonic kidney 293 cells and human hepatocytes were used for determining RAF values, which were then incorporated into the mechanistic model to simulate hepatocyte uptake of pitavastatin over time. There was excellent agreement between simulated and observed hepatocyte uptake of pitavastatin, indicating the suitability of this approach for translation of uptake from individual transporter-expressing cells to more holistic in vitro models. Subsequently, f_t values were determined. The largest contributor to hepatocyte uptake of pitavastatin was OATP1B1, which correlates with what is known about the in vivo disposition of pitavastatin. The f_t values were then used for evaluating in vitro-in vivo correlations of hepatic uptake inhibition with OATP inhibitors rifampicin and cyclosporine. Predictions were compared with previously reported plasma exposure changes of pitavastatin with these inhibitors. Although hepatic uptake inhibition of pitavastatin was 2-3-fold underpredicted, incorporation of scaling factors (SFs) into RAF values significantly improved the predictive ability. We propose that calibration of hepatocytes with standard transporter substrates and inhibitors would allow for determination of system-specific SFs, which could subsequently be used for refining predictions of clinical DDI potential for new chemical entities that undergo active hepatic uptake.

Regulation of Organic Anion Transporting Polypeptides (OATP) 1B1- and OATP1B3-Mediated Transport: An Updated Review in the Context of OATP-Mediated Drug-Drug Interactions

Organic anion transporting polypeptides (OATP) 1B1 and OATP1B3 are important hepatic transporters that mediate the uptake of many clinically important drugs, including statins from the blood into the liver. Reduced transport function of OATP1B1 and OATP1B3 can lead to clinically relevant drug-drug interactions (DDIs). Considering the importance of OATP1B1 and OATP1B3 in hepatic drug disposition, substantial efforts have been given on evaluating OATP1B1/1B3-mediated DDIs in order to avoid unwanted adverse effects of drugs that are OATP substrates due to their altered pharmacokinetics. Growing evidences suggest that the transport function of OATP1B1 and OATP1B3 can be regulated at various levels such as genetic variation, transcriptional and post-translational regulation. The present review summarizes the up to date information on the regulation of OATP1B1 and OATP1B3 transport function at different levels with a focus on potential impact on OATP-mediated DDIs.

Challenges and Opportunities for Increasing the Knowledge Base Related to Drug Biotransformation and Pharmacokinetics during Growth and Development

It is generally acknowledged that there is a need and role for informative pharmacokinetic models to improve predictions and simulation as well as individualization of drug therapy in pediatric populations of different ages and developmental stages. This special issue contains more than 20 papers responding to the challenge of providing new information on scaling factors, ontogeny functions for drug metabolizing enzymes and transporters, the mechanisms underlying the observed developmental trajectories for these gene products, age-dependent changes in physiologic processes affecting drug disposition in children, as well as in vitro and in vivo studies describing the relative contribution of ontogeny and genetic factors as sources of variability in drug disposition in children. Considered together, these contributions serve to illustrate some of the current limitations regarding sample availability, number, and quality, but also provide a framework that allows for the potential value of the results of a given study to be interpreted within the context of these limitations. Among the challenges for the future are improving our understanding of the mechanisms regulating age-dependent changes in factors influencing drug disposition and response, thereby facilitating generalization to systems lacking detailed data, better integrating age-dependent changes in pharmacokinetics with age-dependent changes in pharmacodynamics, and allowing better predictability and individualization of drug disposition and response across the pediatric age spectrum.

LST-3TM12 is a member of the OATP1B family and a functional transporter

Organic anion transporting polypeptides (OATPs) and particularly the two members of the OATP1B family are known for their role in pharmacokinetics. Both SLCO1B3 and SLCO1B1 are located on chromosome 12 encompassing the gene locus SLCO1B7. Hitherto, this particular gene has been assumed to be a pseudogene, even though there are published mRNA sequences linked to this chromosomal area. It was aim of this study to further investigate SLCO1B7 and the associated mRNA LST-3TM12. In a first step, we aligned all mRNAs linked to the chromosomal region of SLCO1B-transporters. This in silico analysis revealed that LST-3TM12 is a product of splicing of SLCO1B3 and SLCO1B7, and encodes for a protein with twelve transmembrane domains. The existence of LST-3TM12 mRNA was verified by polymerase chain reaction showing liver enriched expression. In addition, immunohistological staining showed that LST-3TM12 protein was expressed in the endoplasmic reticulum (ER) of hepatocytes. Localization in the ER was further verified by immunoblot analysis showing high amounts of LST-3TM12 in liver microsomes. Function of LST-3TM12 was assessed by transport studies after heterologous expression in HeLa cells, where the transporter was shown to be expressed not only in the ER but also in the plasma membrane. Overexpression of LST-3TM12 was associated with enhanced cellular accumulation of dehydroepiandrosterone sulfate (V_max 300.2 pmol mg^-1 min^-1; K_m 34.2 µm) and estradiol 17β-glucuronide (V_max 29.9 mol mg^-1 min^-1 and K_m 32.8 µM). In conclusion, LST-3TM12 is a functional splice variant of SLCO1B3 and SLCO1B7 expressed in the ER of human liver.

Identification of two novel genes SLC15A2 and SLCO1B3 associated with maintenance dose variability of warfarin in a Chinese population

Warfarin is a commonly prescribed and effective oral anticoagulant. Genetic polymorphisms associated with warfarin metabolism and sensitivity have been implicated in the wide inter-individual dose variation that is observed. Several algorithms integrating patients’ clinical characteristics and genetic polymorphism information have been explored to predict warfarin dose. However, most of these algorithms could explain only over half of the variation in a warfarin maintenance dose, suggesting that additional genetic factors may exist and need to be identified. Here, a drug absorption, distribution, metabolism and excretion (ADME) Core Panel Kit-based pharmacogenetic study was performed to screen for warfarin dose-associated SNP sites in Han-Chinese population patients taking warfarin therapy, and the screen was followed by pyrosequencing-based validation. Finally, we confirmed that the common variant rs9923231 in VKORC1 and two novel genes, SLC15A2 (rs1143671 and rs1143672) and SLCO1B3 (rs4149117 and rs7311358), are associated with the warfarin maintenance dose. As has been shown for those carriers with the variant rs9923231 in VKORC1, it was suggested that those subjects with homozygous minor alleles in those four SNPs should take a lower warfarin dose than those carrying the wild type alleles. Together with the established predictor rs9923231 in VKORC1, those four novel variants on SLC15A2 and SLCO1B3 should be considered as useful biomarkers for warfarin dose adjustment in clinical practice in Han-Chinese populations.

Recent advance in the pharmacogenomics of human Solute Carrier Transporters (SLCs) in drug disposition

Drug pharmacokinetics is influenced by the function of metabolising enzymes and influx/efflux transporters. Genetic variability of these genes is known to impact on clinical therapies. Solute Carrier Transporters (SLCs) are the primary influx transporters responsible for the cellular uptake of drug molecules, which consequently, impact on drug efficacy and toxicity. The Organic Anion Transporting Polypeptides (OATPs), Organic Anion Transporters (OATs) and Organic Cation Transporters (OCTs/OCTNs) are the most important SLCs involved in drug disposition. The information regarding the influence of SLC polymorphisms on drug pharmacokinetics is limited and remains a hot topic of pharmaceutical research. This review summarises the recent advance in the pharmacogenomics of SLCs with an emphasis on human OATPs, OATs and OCTs/OCTNs. Our current appreciation of the degree of variability in these transporters may contribute to better understanding the inter-patient variation of therapies and thus, guide the optimisation of clinical treatments.

Impaired N-linked glycosylation of uptake and efflux transporters in human non-alcoholic fatty liver disease

BACKGROUND & AIMS

N-linked glycosylation of proteins is critical for proper protein folding and trafficking to the plasma membrane. Drug transporters are one class of proteins that have reduced function when glycosylation is impaired. N-linked glycosylation of plasma proteins has also been investigated as a biomarker for several liver diseases, including non-alcoholic fatty liver disease (NAFLD). The purpose of this study was to assess the transcriptomic expression of genes involved in protein processing and glycosylation, and to determine the glycosylation status of key drug transporters during human NAFLD progression.

METHODS

Human liver samples diagnosed as healthy, steatosis, and non-alcoholic steatohepatitis (NASH) were analysed for gene expression of glycosylation-related genes and for protein glycosylation using immunoblot.

RESULTS

Genes involved in protein processing in the ER and biosynthesis of N-glycans were significantly enriched for down-regulation in NAFLD progression. Included in the down regulated N-glycan biosynthesis category were genes involved in the oligosaccharyltransferase complex, N-glycan quality control, N-glycan precursor biosynthesis, N-glycan trimming to the core, and N-glycan extension from the core. N-glycan degradation genes were unaltered in the progression to NASH. Immunoblot analysis of the uptake transporters organic anion transporting polypeptide-1B1 (OATP1B1), OATP1B3, OATP2B1, and Sodium/Taurocholate Co-transporting Polypeptide (NTCP) and the efflux transporter multidrug resistance-associated protein 2 (MRP2) demonstrated a significant loss of glycosylation following the progression to NASH.

CONCLUSIONS

These data suggest that the loss of glycosylation of key uptake and efflux transporters in humans NASH may influence transporter function and contribute to altered drug disposition observed in NASH.

SLCO1B3 screening in colorectal cancer patients using High-Resolution Melting Analysis method and immunohistochemistry

Personalized medicine has made some major advances in colorectal cancer, but new biomarkers still remain a hot issue as an emerging tool with potential prognostic and therapeutic potential. We investigated for SLCO1B3 gene alterations and protein expression in colorectal cancer, using the novel high-resolution melting analysis technique and immunohistochemistry. Formalin-fixed paraffin-embedded tumor samples from 30 colorectal cancer patients were used. The screening for gene alterations was done by high-resolution melting analysis for all exons of SLCO1B3 gene. Organic anion-transporting polypeptide 1B3 protein expression was assessed by immunohistochemistry using the monoclonal mouse MDQ antibody. High level of polymorphism was observed in the SLCO1B3 gene. We identified three previously reported polymorphisms in exons 7, 12, and 14, 699G>A, 1557A>G, and 1833G>A, respectively. In the exon 5, one variant seems to correspond to an as yet unknown SLCO family member. The immunohistochemical study revealed that organic anion-transporting polypeptide 1B3 was expressed in 27/30 samples. Of great interest, the three samples, which were immunohistochemically negative, all appeared to accommodate mutations which lead to either early stop codons or other conformations of the tertiary protein structures affecting the antibody-epitope binding. The results of this study are of much interest as high-resolution melting analysis proved to be a reliable and rapid genotyping/scanning method for mutation detection of SLCO1B3 gene.

Association of genetic variations with pharmacokinetics and lipid-lowering response to atorvastatin in healthy Korean subjects

Background

Statins are effective agents in the primary and secondary prevention of cardiovascular disease, but treatment response to statins varies among individuals. We analyzed multiple genetic polymorphisms and assessed pharmacokinetic and lipid-lowering responses after atorvastatin 80 mg treatment in healthy Korean individuals.

Methods

Atorvastatin 80 mg was given to 50 healthy Korean male volunteers. Blood samples were collected to measure plasma atorvastatin and lipid concentrations up to 48 hours after atorvastatin administration. Subjects were genotyped for 1,936 drug metabolism and transporter genetic polymorphisms using the Affymetrix DMET plus array.

Results

The pharmacokinetics and lipid-lowering effect of atorvastatin showed remarkable interindividual variation. Three polymorphisms in the SLCO1B1, SLCO1B3, and ABCC2 genes were associated with either the maximum concentration (C_max) of atorvastatin or changes in total cholesterol or low-density lipoprotein cholesterol (LDL-C). Minor homozygotes (76.5 ng/mL) of SLCO1B1 c.-910G>A showed higher C_max than heterozygotes (34.0 ng/mL) and major homozygotes (33.5 ng/mL, false discovery rate P=0.040). C_max and the area under the plasma concentration curve from hour 0 to infinity (AUC_∞) were higher in carriers of the SLCO1B1*17 haplotype that included c.-910G>A than in noncarriers (46.1 vs 32.8 ng/mL for C_max; 221.5 vs 154.2 ng/mL for AUC_∞). SLCO1B3 c.334G>T homozygotes (63.0 ng/mL) also showed higher C_max than heterozygotes (34.7 ng/mL) and major homozygotes (31.4 ng/mL, FDR P=0.037). A nonsynonymous ABCC2 c.1249G>A was associated with small total cholesterol and LDL-C responses (0.23% and −0.70% for G/A vs −11.9% and −17.4% for G/G). The C_max tended to increase according to the increase in the number of minor allele of SLCO1B1 c. −910G>A and SLCO1B3 c.334G>T.

Conclusion

Genetic polymorphisms in transporter genes, including SLCO1B1, SLCO1B3, and ABCC2, may influence the pharmacokinetics and lipid-lowering response to atorvastatin administration.

Expression Patterns of Organic Anion Transporting Polypeptides 1B1 and 1B3 Protein in Human Pediatric Liver

Determining appropriate pharmacotherapy in young children can be challenging due to uncertainties in the development of drug disposition pathways. With knowledge of the ontogeny of drug-metabolizing enzymes and an emerging focus on drug transporters, the developmental pattern of the uptake transporters organic anion transporting polypeptide (OATP) 1B1 and 1B3 was assessed by relative protein quantification using Western blotting in 80 human pediatric liver specimens covering an age range from 9 days to 12 years. OATP1B3 exhibited high expression at birth, which declined over the first months of life, and then increased again in the preadolescent period. In comparison with children 6-12 years of age, the relative protein expression of highly glycosylated (total) OATP1B3 was 235% (357%) in children <3 months of age, 33% (64%) in the age group from 3 months to 2 years, and 50% (59%) in children 2-6 years of age. The fraction of highly glycosylated to total OATP1B3 increased with age, indicating ontogenic processes not only at the transcriptional level but also at the post-translational level. Similar to OATP1B3, OATP1B1 showed high interindividual variability in relative protein expression but no statistically significant difference among the studied age groups.

A pharmacogenetic pilot study reveals MTHFR, DRD3, and MDR1 polymorphisms as biomarker candidates for slow atorvastatin metabolizers

Background

The genetic variation underlying atorvastatin (ATV) pharmacokinetics was evaluated in a Mexican population. Aims of this study were: 1) to reveal the frequency of 87 polymorphisms in 36 genes related to drug metabolism in healthy Mexican volunteers, 2) to evaluate the impact of these polymorphisms on ATV pharmacokinetics, 3) to classify the ATV metabolic phenotypes of healthy volunteers, and 4) to investigate a possible association between genotypes and metabolizer phenotypes.

Methods

A pharmacokinetic study of ATV (single 80-mg dose) was conducted in 60 healthy male volunteers. ATV plasma concentrations were measured by high-performance liquid chromatography mass spectrometry. Pharmacokinetic parameters were calculated by the non-compartmental method. The polymorphisms were determined with the PHARMAchip® microarray and the TaqMan® probes genotyping assay.

Results

Three metabolic phenotypes were found in our population: slow, normal, and rapid. Six gene polymorphisms were found to have a significant effect on ATV pharmacokinetics: MTHFR (rs1801133), DRD3 (rs6280), GSTM3 (rs1799735), TNFα (rs1800629), MDR1 (rs1045642), and SLCO1B1 (rs4149056). The combination of MTHFR, DRD3 and MDR1 polymorphisms associated with a slow ATV metabolizer phenotype.

Conclusion

Further studies using a genetic preselection method and a larger population are needed to confirm these polymorphisms as predictive biomarkers for ATV slow metabolizers.

Trial registration

Australian New Zealand Clinical Trials Registry: ACTRN12614000851662, date registered: August 8, 2014.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2062-2) contains supplementary material, which is available to authorized users.

Recessive inheritance of population-specific intronic LINE-1 insertion causes a rotor syndrome phenotype

Sequences of long-interspersed elements (LINE-1, L1) make up ∼17% of the human genome. De novo insertions of retrotransposition-active L1s can result in genetic diseases. It has been recently shown that the homozygous inactivation of two adjacent genes SLCO1B1 and SLCO1B3 encoding organic anion transporting polypeptides OATP1B1 and OATP1B3 causes a benign recessive disease presenting with conjugated hyperbilirubinemia, Rotor syndrome. Here, we examined SLCO1B1 and SLCO1B3 genes in six Japanese diagnosed with Rotor syndrome on the basis of laboratory data and laparoscopy. All six Japanese patients were homozygous for the c.1738C>T nonsense mutation in SLCO1B1 and homozygous for the insertion of a ∼6.1-kbp L1 retrotransposon in intron 5 of SLCO1B3, which altogether make up a Japanese-specific haplotype. RNA analysis revealed that the L1 insertion induced deleterious splicing resulting in SLCO1B3 transcripts lacking exon 5 or exons 5-7 and containing premature stop codons. The expression of OATP1B1 and OATP1B3 proteins was not detected in liver tissues. This is the first documented case of a population-specific polymorphic intronic L1 transposon insertion contributing to molecular etiology of recessive genetic disease. Since L1 activity in human genomes is currently seen as a major source of individual genetic variation, further investigations are warranted to determine whether this phenomenon results in other autosomal-recessive diseases.

Comparison of genetic variations of the SLCO1B1, SLCO1B3, and SLCO2B1 genes among five ethnic groups

Organic anion-transporting polypeptide (OATP; gene symbol, SLCO) transporters are generally involved in the uptake of multiple drugs and their metabolites at most epithelial barriers. The pattern of single-nucleotide polymorphisms (SNPs) in these transporters may be determinants of interindividual variability in drug disposition and response. The objective of this study was to define the distribution of SNPs of three SLCO genes, SLCO1B1, SLCO1B3, and SLCO2B1, in a Korean population and other ethnic groups. The study was screened using the Illumina GoldenGate assay for genomic DNA from 450 interethnic subjects, including 11 pharmacogenetic core variants and 76 HapMap tagging SNPs. The genotype distribution of the Korean population was similar to East Asian populations, but significantly different from African American and European American cohorts. These interethnic differences will be useful information for prospective studies, including genetic association and pharmacogenetic studies of drug metabolism by SLCO families.