Single nucleotide polymorphisms in multidrug resistance associated protein 2 (MRP2/ABCC2): its impact on drug disposition

Drug transporters in drug disposition - the year 2022 in review

On behalf of all the authors, I am pleased to share our third annual review on drug transporter science with an emphasis on articles published and deemed influential in signifying drug transporters' role in drug disposition in the year 2022. As the drug transporter field is rapidly evolving several key findings were noted including promising endogenous biomarkers, rhythmic activity, IVIVE approaches in transporter-mediated clearance, new modality interaction, and transporter effect on gut microbiome. As identified previously (Chothe et Cal. 2021, 2022) the goal of this review is to highlight key findings without a comprehensive overview of each article and to this end, each coauthor independently selected 1-3 peer-reviewed articles published or available online in the year 2022 (Table 1). Each article is summarized in synopsis and commentary with unbiased viewpoints by each coauthor. We strongly encourage readers to consult original articles for specifics of the study. Finally, I would like to thank all coauthors for their continued support in writing this annual review on drug transporters and invite anyone interested in contributing to future versions of this review.

Mechanistic Study for Drug Induced Cholestasis Using Batch-Fabricated 3D Spheroids Developed by Agarose-Stamping Method

Cell spheroid culture can recapitulate the tissue microstructure and cellular responses in vivo. While there is a strong need to understand the modes of toxic action using the spheroid culture method, existing preparation techniques suffer from low efficiency and high cost. Herein, we developed a metal stamp containing hundreds of protrusions for batch bulk preparation of cell spheroids in each well of the culture plates. The agarose matrix imprinted by the stamp can form an array of hemispherical pits, which facilitated the fabrication of hundreds of uniformly sized rat hepatocyte spheroids in each well. Chlorpromazine (CPZ) was used as a model drug to investigate the mechanism for drug induced cholestasis (DIC) by agarose-stamping method. Hepatocyte spheroids showed a more sensitive detection of hepatotoxicity compared to 2D and Matrigel-based culture systems. Cell spheroids were also collected for staining of cholestatic protein and showed a CPZ-concentration-dependent decrease of bile acid efflux related proteins (BSEP and MRP2) and tight junction (ZO-1). In addition, the stamping system successfully delineated the DIC mechanism by CPZ that may be associated with the phosphorylation of MYPT1 and MLC2, two central proteins in the Rho-associated protein kinase pathway (ROCK), which were significantly attenuated by ROCK inhibitors. Our results demonstrated a large-scale fabrication of cell spheroids by the agarose-stamping method, with promising benefits for exploring the mechanisms for drug hepatotoxic responses.

Effects of antimony exposure on DNA damage and genome-wide variation in zebrafish (Danio rerio) liver

Antimony (Sb) is a potentially toxic and carcinogenic cumulative contaminant that poses a serious threat to aquatic ecosystems. To better clarify the genotoxicity of Sb and its mechanism of action. In this study, we investigated DNA damage and genome-wide variation in the liver of a model organism, zebrafish (Danio rerio), under subacute Sb exposure and explored its potential toxicological mechanisms. The results showed that medium and high concentrations of Sb significantly reduced the total antioxidant capacity and increased the content of reactive oxygen species in zebrafish liver, and further studies revealed that it increased oxidative DNA damage and DNA-DNA cross-link (DDC), but had little effect on DNA-protein cross-link (DPC). The result of resequencing showed that the mutation sites of the genes with high concentrations of Sb were higher than those with medium concentrations, and the mutation was mainly a single nucleotide. The pathways significantly enriched for nonsynonymous single nucleotide polymorphisms (SNPs) and insertion/deletion mutations (InDels) variant genes in the coding regions of both the medium and high Sb-treated groups were ECM-receptor interactions, and the high Sb-treated group also included lysine degradation, hematopoietic cell lineage, and cytokine-cytokine receptor interactions. This suggests that ECM-receptor interactions play an important role in the mechanism of antimony toxicity to the liver of zebrafish.

An approach for mixture testing and prioritization based on common kinetic groups

In light of an ever-increasing exposure to chemicals, the topic of potential mixture toxicity has gained increased attention, particularly as the toxicological toolbox to address such questions has vastly improved. Routinely toxicological risk assessments will rely on the analysis of individual compounds with mixture effects being considered only in those specific cases where co-exposure is foreseeable, for example for pesticides or food contact materials. In the field of pesticides, active substances are summarized in so-called cumulative assessment groups (CAG) which are primarily based on their toxicodynamic properties, that is, respective target organs and mode of action (MoA). In this context, compounds causing toxicity by a similar MoA are assumed to follow a model of dose/concentration addition (DACA). However, the respective approach inherently falls short of addressing cases where there are dissimilar or independent MoAs resulting in wider toxicokinetic effects. Yet, the latter are often the underlying cause when effects deviate from the DACA model. In the present manuscript, we therefore suggest additionally to consider toxicokinetic effects (especially related to xenobiotic metabolism and transporter interaction) for the grouping of substances to predict mixture toxicity. In line with the concept of MoA-based CAGs, we propose common kinetics groups (CKGs) as an additional tool for grouping of chemicals and mixture prioritization. Fundamentals of the CKG concept are discussed, along with challenges for its implementation, and methodological approaches and examples are explored.

In silico screening and analysis of single-nucleotide polymorphic variants of the ABCC2 gene affecting Dubin-Johnson syndrome

BACKGROUND AND STUDY AIMS

Dubin-Johnson syndrome (DJS) is a benevolent genetic disorder of the liver with autosomal inheritance. It is a rare disorder characterized by an increase in conjugated bilirubin and anomaly in coproporphyrin clearance. DJS is caused by deleterious mutations in the ABCC2 gene. A polymorphism in the ABCC2 gene causes malfunctions in its ability to regulate the efflux of different organic anions, such as bilirubin, from hepatocytes to the canaliculi. Multidrug resistance protein 2 (MRP2) encoded by the ABCC2 gene is one of the main regulators of the export of bilirubin to respective sites. ABCC2 gene mutations have widely drawn attention in the pathology of DJS in various populations.

PATIENTS AND METHODS

The ABCC2 gene was subjected to the National Center for Biotechnology Information (NCBI) database in 2020, and non-synonymous single-nucleotide polymorphisms (nsSNPs) and variants in untranslated regions were studied using different computational servers. SIFT, Protein variation effect analyzer, and PolyPhen-2 were used to retrieve the damaging Single-nucleotide polymorphisms (SNPs); PhD-SNP, SNPs&GO, and Protein Analysis Through Evolutionary Relationships were used to predict the association of nsSNPs with DJS; Mutation3D illustrated the location of variants in the protein; SNAP2, MutPred2, ELASPIC, and HOPE were used to predict the structural and functional effects of these mutations on MRP2; and I-mutant 3.0 and MuPro were used to determine the effects of polymorphism on the function of MRP2.

RESULTS

In this study, 18,947 SNPs were screened from the NCBI database, followed by a series of refinement of variants using online available servers. We concluded that 41 ABCC2 gene variants are vital etiological candidates for DJS in humans. These 41 variants had highly damaging effects on the MRP2 protein, which may lead to deficient transportation capacity, thereby affecting the efflux of bilirubin across the canalicular membrane.

CONCLUSION

In silico tools are an alternative approach for predicting the target SNPs. Hence, previously unreported variants can be considered strong etiological candidates for diseases related to MRP2.

Adenosine triphosphate-binding cassette subfamily C members in liver hepatocellular carcinoma: Bioinformatics-driven prognostic value

Aberrant expression of adenosine triphosphate-binding cassette subfamily C (ABCC), one of the largest superfamilies and transporter gene families of membrane proteins, is associated with various tumors. However, its relationship with liver hepatocellular carcinoma (LIHC) remains unclear.We used the Oncomine, UALCAN, Human Protein Atlas, GeneMANIA, GO, Kyoto Encyclopedia of Genes and Genomes (KEGG), TIMER, and Kaplan-Meier Plotter databases. On May 20, 2021, we searched these databases for the terms ABCC1, ABCC2, ABCC3, ABCC4, ABCC5, ABCC6, ABCC7, ABCC8, ABCC9, ABCC10, ABCC11, ABCC12, ABCC13, and "liver cancer." The exposure group comprised LIHC patients, and the control group comprised normal patients (those with noncancerous liver tissue). All patients shown in the retrieval language search were included. We compared the mRNA expression of these proteins in LIHC and control patients to examine the potential role of ABCC1-13 in LIHC.Relative to the normal liver tissue, mRNA expression of ABCC1/2/3/4/5/6/10 was significantly upregulated (P < .001), and that of ABCC9/11 significantly downregulated (both P < .001), in LIHC. ABCC mRNA expression varied with gender (P < .05), except for ABCC11-13; with tumor grade (P < 0.05), except for ABCC7/12/13; with tumor stage (P < .05), except for ABCC11-13; and with lymph node metastasis status (P < .05), except for ABCC7/8/11/12/13. Based on KEGG enrichment analysis, these genes were associated with the following pathways: ABC transporters, Bile secretion, Antifolate resistance, and Peroxisome (P < .05). Except for ABCC12/13, the ABCCs were significantly associated with B cell, CD8+ T cell, CD4+ T cell, macrophage, neutrophil, and dendritic cell infiltration (P < .05). High mRNA expression of ABCC1/4/5/8 (P < .05) and low expression of ABCC6/7/9/12/13 (P < .05) indicated poor prognosis. Prognostic significance was indicated for ABCC2/13 for both men and women (P < .05); for ABCC1/6/12/13 for tumor grades 1-3 (P < .05); for ABCC5/11/12/13 for all tumor stages (P < .05); for ABCC1/11/12/13 for American Joint Committee on Cancer T stages 1-3 (P < .05); and for ABCC1/5/6/13 for vascular invasion. None showed prognostic significance for microvascular invasion (P < .05).We identified ABCC1/2/3/4/5/6/9/10/11 as potential diagnostic markers, and ABCC1/4/5/6/7/8/9/12/13 as prognostic markers, of LIHC. Our future work will promote the use of ABCCs in the diagnosis and treatment of LIHC.

In Vitro Assessment of the Drug-Drug Interaction Potential of Verinurad and Its Metabolites as Substrates and Inhibitors of Metabolizing Enzymes and Drug Transporters

Verinurad is a selective uric acid transporter 1 (URAT1) inhibitor in development for the treatment of chronic kidney disease and heart failure. In humans, two major acyl glucuronide metabolites have been identified: direct glucuronide M1 and N-oxide glucuronide M8. Using in vitro systems recommended by regulatory agencies, we evaluated the interactions of verinurad, M1, and M8 with major drug-metabolizing enzymes and transporters and the potential for clinically relevant drug-drug interactions (DDIs). The IC50 for inhibition of CYP2C8, CYP2C9, and CYP3A4/5 for verinurad was ≥14.5 µM, and maximum free plasma concentration (Iu,max)/IC50 was <0.02 at the anticipated therapeutic Cmax and therefore not considered a DDI risk. Verinurad was not an inducer of CYP1A2, CYP2B6, or CYP3A4/5. Verinurad was identified as a substrate of the hepatic uptake transporter organic anion-transporting polypeptide (OATP) 1B3. Since verinurad hepatic uptake involved both active and passive transport, there is a low risk of clinically relevant DDIs with OATP, and further study is warranted. Verinurad was a substrate of the efflux transporters P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP), and renal transporter organic anion transporter 1 (OAT1), although it is not considered a DDI risk in vivo because of dose-proportional pharmacokinetics (P-gp and BCRP) and limited renal excretion of verinurad (OAT1). M1 and M8 were substrates of multidrug resistance-associated protein (MRP) 2 and MRP4 and inhibitors of MRP2. Apart from verinurad being a substrate of OATP1B3 in vitro, the potential for clinically relevant DDIs involving verinurad and its metabolites as victims or perpetrators of metabolizing enzymes or drug transporters is considered low. SIGNIFICANCE STATEMENT: Drug transporters and metabolizing enzymes have an important role in the absorption and disposition of a drug and its metabolites. Using in vitro systems recommended by regulatory agencies, we determined that, apart from verinurad being a substrate of organic anion-transporting polypeptide 1B3, the potential for clinically relevant drug-drug interactions involving verinurad and its metabolites M1 and M8 as victims or perpetrators of metabolizing enzymes or drug transporters is considered low.

A systematic review and meta-analysis of the association of ABCC2/ABCG2 polymorphisms with antiepileptic drug responses in epileptic patients

PURPOSE

Accumulating evidence indicates that genetic polymorphisms in ATP-binding cassette superfamily members, such asABCC2 and ABCG2, alter responses to antiepileptic drugs (AEDs); however, this evidence is controversial and inconclusive. To provide strong evidence of the association between common polymorphisms in ABCC2 and ABCG2 and AED responses in patients with epilepsy, we performed a systematic review and meta-analysis.

METHODS

A literature search of electronic databases (PubMed, EBSCO, Ovid and the China National Knowledge Infrastructure) was performed. To evaluate the association of genetic polymorphisms inABCC2 and ABCG2 and risk of AED treatment, we calculated pooled odds ratios (ORs) and 95 % confidence intervals (CIs) using a fixed- or random-effect model.

RESULTS

A significant association of theABCC2 rs717620 polymorphism with resistance to AEDs was found in the overall pooled populations (homozygous comparison: OR = 1.77, 95 % CI, 1.27-2.48; dominant model: OR = 1.23, 95 % CI, 1.06-1.43; recessive model: OR = 1.75, 95 % CI, 1.28-2.40) and Asians (dominant model: OR = 1.21, 95 % CI, 1.03-1.42; recessive model: OR = 1.80, 95 % CI, 1.30-2.50). Using a recessive model, a similarly significant association of ABCC2 rs3740066 with AED resistance was observed in the overall pooled populations (OR = 2.29, 95 % CI, 1.44-3.64) and Asians (OR = 2.53, 95 % CI, 1.56-4.08). However, ABCC2 rs2273697, ABCG2 rs2231137 and rs2231142 were not found to be associated with AED responsiveness.

CONCLUSION

This meta-analysis suggests thatABCC2 rs717620 and rs3740066 are risk factors that predict responses to AEDs in epileptic patients.

Effect of drug metabolizing enzymes and transporters in Thai colorectal cancer patients treated with irinotecan-based chemotherapy

Genetic polymorphisms in drug metabolizing enzymes and drug transporters may affect irinotecan toxicity. Although genetic polymorphisms have been shown to influence the irinotecan toxicity, data are limited in Thai population. Thus, the aim of this study was to assess the allele and genotype frequencies and the relationship between CYP3A4/5, DPYD, UGT1A1, ABCB1, and ABCC2 genetic variations and irinotecan-induced toxicity in Thai colorectal cancer patients. One hundred and thirty-two patients were genotyped, and the effect of genetic variations on irinotecan-induced toxicity was assessed in 66 patients who received irinotecan-based chemotherapy. Allele frequencies of ABCB1 c.1236C > T, ABCB1 c.3435C > T, ABCC2 c.3972C > T, ABCG2 c.421C > A, CYP3A4*1B, CYP3A4*18, CYP3A5*3, DPYD*5, UGT1A1*28, and UGT1A1*6 were 0.67, 0.43, 0.23, 0.27, 0.01, 0.02, 0.64, 0.19, 0.16, and 0.09, respectively. DPYD*2A and DPYD c.1774C > T variants were not detected in our study population. The ABCC2 c.3972C > T was significantly associated with grade 1–4 neutropenia (P < 0.012) at the first cycle. Patients carrying both UGT1A1*28 and *6 were significantly associated with severe neutropenia at the first (P < 0.001) and second (P = 0.017) cycles. In addition, patients carrying UG1A1*28 and *6 had significantly lower absolute neutrophil count (ANC) nadir at first (P < 0.001) and second (P = 0.001) cycles. This finding suggests that UGT1A1*28, *6, and ABCC2 c.3972C > T might be an important predictor for irinotecan-induced severe neutropenia.

Effects of UGT1A1 Polymorphism, Gender and Triglyceride on the Pharmacokinetics of Telmisartan in Chinese Patients with Hypertension: A Population Pharmacokinetic Analysis

BACKGROUND AND OBJECTIVE

Telmisartan is an angiotensin receptor blocker used for the treatment of hypertension. The effects of gender and uridine diphosphate-glycosytransferase 1A1 (UGT1A1) genetic polymorphisms (rs4124874, rs4148323, and rs6742078) on telmisartan plasma concentration and blood pressure in Chinese patients with hypertension have been reported previously. In this study, we aimed to develop a population pharmacokinetic (PopPK) model to quantify the effects of gender and UGT1A1 polymorphisms on the pharmacokinetics of telmisartan.

METHODS

Population pharmacokinetic analyses were performed using data collected prospectively from 58 Chinese patients with mild to moderate essential hypertension (aged 45-72 years; 36 men, 22 women) receiving 80 mg/day telmisartan orally for 4 weeks. Blood samples were collected in heparinized tubes at 0, 0.5, 1, and 6 h on day 28 after telmisartan administration. The plasma concentrations and UGT1A1 genetic variants were determined by high-performance liquid chromatography-mass spectrometry and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, respectively.

RESULTS

A two-compartment pharmacokinetic structural model with first-order elimination and absorption best described the pharmacokinetic characteristics of telmisartan. Gender and triglyceride influenced the apparent oral clearance (CL) of telmisartan. UGT1A1 (rs4124874) affected the bioavailability (F1) of telmisartan. Lower CL and bioavailability resulted in higher plasma concentrations being observed in female subjects with UGT1A1 CC or CA genotype and high triglyceride.

CONCLUSION

A PopPK model of telmisartan was established to confirm that UGT1A1 genotype, gender and triglyceride can affect the pharmacokinetics of telmisartan in Chinese patients with hypertension. Our findings can provide relevant pharmacokinetic parameters for further study of telmisartan.

Structure affinity relationship and docking studies of flavonoids as substrates of multidrug-resistant associated protein 2 (MRP2) in MDCK/MRP2 cells

This study was aimed to determine the relationship of flavonoid structures to their affinity for an important efflux transporter, multidrug-resistant associated protein 2 (MRP2). The cellular uptake (CU) of 35 flavonoids was investigated in MRP2 overexpression MDCK/MRP2 cells. Resulting data identified 8 flavonoids as MRP2 substrates based on their high CU_MK with MK-571 in MDCK/MRP2 cells. Also, three substrates showed better CU_MD in MDCK cells than did CU_MRP in MDCK/MRP2 cells. Docking analyses showed a good correlation (R = 0.926, p = 0.003) between efflux-fold of flavonoid substrates and their docking S_scoring with the MRP2 model, indicating consistency between in silico and in vitro approaches. A structure affinity relationship (SAR) study indicated that 3-OH, 5-OH, 6-OH, 3'-OH, and 4'-OCH₃ substituents were favourable while, 8-OCH₃, 2'-OH, 3'-OCH₃, 4'-OH and 5'-OH were unfavourable for flavonoid affinity to MRP2. Our study provides valuable information for dietary application of flavonoids with specific structures for high absorption.

Pharmacogenetic variants and response to neoadjuvant single-agent doxorubicin or docetaxel: a study in locally advanced breast cancer patients participating in the NCT00123929 phase 2 randomized trial

OBJECTIVES

Taxanes and anthracyclines are widely used in the treatment of breast cancer, although the benefit is limited to a proportion of patients and predictive biomarkers for clinical outcome remain elusive.

PATIENTS AND METHODS

We carried out a pharmacogenetic study in 181 patients with locally advanced breast cancer enrolled in a phase 2 randomized clinical trial (NCT00123929), where patients were randomly assigned to receive neoadjuvant single-agent docetaxel 100 mg/m(2) (n=84) or doxorubicin 75 mg/m(2) (n=97). We studied the association of 226 single nucleotide polymorphisms (SNPs) in 15 key drug biotransformation genes with neoadjuvant pathological tumor response residual cancer burden index to docetaxel and to doxorubicin.

RESULTS

We identified a significant association for rs162561, an intronic SNP located in the cytochrome P450 family 1 subfamily B member 1 (CYP1B1) gene, with tumor response in patients treated with single-agent docetaxel (dominant model: β=1.02, 95% confidence interval=0.49-1.55; P=1.77×10(-4)), and for rs717620, an SNP located in the promoter of the ATP-binding cassette subfamily C member 2 (ABCC2) gene, in patients treated with neoadjuvant doxorubicin (recessive model: β=1.67; 95% confidence interval=0.26-3.11; P=0.02).

CONCLUSION

We identified two polymorphisms in CYP1B1 and ABCC2 associated with tumor pathological response following docetaxel or doxorubicin neoadjuvant monotherapy, respectively. Although further validation is required, these variants could be potential predictive genetic markers for treatment outcome in breast cancer patients.

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.

Genetic Association of Drug Response to Erlotinib in Chinese Advanced Non-small Cell Lung Cancer Patients

The efficacy of erlotinib treatment for advanced non-small cell lung cancer (NSCLC) is due to its action as an epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI). Patients treated with erlotinib experience different drug responses. The effect of germline mutations on therapeutic responses and adverse drug responses (ADRs) to erlotinib in Chinese patients requires elucidation. Sixty Han Chinese advanced non-small cell lung cancer patients received erlotinib monotherapy and, for each participant, 76 candidate genes (related to EGFR signaling, drug metabolism and drug transport pathways) were sequenced and analyzed. The single-nucleotide polymorphisms (SNPs) rs1042640 in UGT1A10, rs1060463, and rs1064796 in CYP4F11, and rs2074900 in CYP4F2 were significantly associated with therapeutic responses to erlotinib. Rs1064796 in CYP4F11 and rs10045685 in UGT3A1 were significantly associated with adverse drug reaction. Moreover, analysis of a validation cohort confirmed the significant association between rs10045685 in UGT3A1 and erlotinib adverse drug response(unadjusted p = 0.015). This study provides comprehensive, systematic analyses of genetic variants associated with responses to erlotinib in Chinese advanced non-small cell lung cancer patients. Newly-identified SNPs may serve as promising markers to predict responses and safety in erlotinib-treated advanced non-small cell lung cancer patients after chemotherapy doublet.

Genetic polymorphisms and response to 5-fluorouracil, doxorubicin and cyclophosphamide chemotherapy in breast cancer patients

Clinical resistance to chemotherapy is one of the major problems in breast cancer treatment. In this study we analyzed possible impact of 22 polymorphic variants on the treatment response in 324 breast cancer patients. Selected genes were involved in FAC chemotherapy drugs transport (ABCB1, ABCC2, ABCG2, SLC22A16), metabolism (CYP1B1, CYP2C19, GSTT1, GSTM1, GSTP1, TYMS, MTHFR, DPYD), drug-induced damage repair (ERCC1, ERCC2, XRCC1) and involved in regulation of DNA damage response and cell cycle control (ATM, TP53).

Apart from preexisting metastases three polymorphic variants were independent prognostic high risk factors of lack of response to FAC chemotherapy. Our results showed that the response to treatment depended of the variability in genes engaged in drugs’ transport (ABCC2 c.-24C>T, ABCB1 p.Ser893Ala/Thr) and in DNA repair machinery (ERCC2 p.Lys751Gln). Furthermore, the growing number of high-risk genotypes was reflected in gradual increase in risk of the non-responsiveness to treatment- from OR 2.68 for presence of two genotypes to OR 9.93 for carriers of all three negative genotypes in the group of all patients. Similar gene-dosage effect was observed in the subgroup of TNBCs. Also, TFFS significantly shortened with the increasing number of high-risk genotypes, with median of 54.4 months for carriers of one variant, to 51.5 and 34.9 months for the carriers of two and three genotypes, respectively.

Our results demonstrate that results of cancer treatment are the effect of many clinical and genetic factors. It seems that multifactorial polymorphic models could be a potentially useful tool in personalization of cancer therapies. The novelty in our model is the over representation of triple negative breast cancer (TNBC) patients among the carriers of all unfavorable polymorphic variants. This finding contributes to the elucidation of the mechanisms of drug resistance in this subgroup of breast cancer patients.

ABCC2-24C > T polymorphism is associated with the response to platinum/5-Fu-based neoadjuvant chemotherapy and better clinical outcomes in advanced gastric cancer patients

Several studies have evaluated the efficacy of neoadjuvant treatment using oxaliplatin and fluoropyrimidines in advanced gastric cancer (GC). However, preoperative biomarkers predictive of clinical outcome remain lacking. We examined polymorphisms in the MTHFR, DPYD, UMPS, ABCB1, ABCC2, GSTP1, ERCC1, and XRCC1 genes to evaluate their usefulness as pharmacogenetic markers in a cohort of 103 GC patients treated with preoperative chemotherapy. DNA was extracted from peripheral blood cells, and the genotypes were analyzed using a SNaPShot^TM assay, polymerase chain reaction amplification, and sequencing. The ABCC2-24C > T (rs717620) genotype was associated with pathologic response to neoadjuvant chemotherapy. Patients with the TT and TC genotypes responded to neoadjuvant chemotherapy 3.80 times more often than those with the CC genotype (95% CI: 1.27–11.32). Patients with the CC genotype also had poorer outcomes than those with other genotypes. Thus, ABCC2-24C > T polymorphism may help to predict the response to preoperative chemotherapy in GC patients.

Hepatic Tmem30a Deficiency Causes Intrahepatic Cholestasis by Impairing Expression and Localization of Bile Salt Transporters

Mutations in ATP8B1 or ATP11C (members of P4-type ATPases) cause progressive familial intrahepatic cholestasis type 1 in human or intrahepatic cholestasis in mice. Transmembrane protein 30A (TMEM30A), a β-subunit, is essential for the function of ATP8B1 and ATP11C. However, its role in the etiology of cholestasis remains poorly understood. To investigate the function of TMEM30A in bile salt (BS) homeostasis, we developed Tmem30a liver-specific knockout (LKO) mice. Tmem30a LKO mice experienced hyperbilirubinemia, hypercholanemia, inflammatory infiltration, ductular proliferation, and liver fibrosis. The expression and membrane localization of ATP8B1 and ATP11C were significantly reduced in Tmem30a LKO mice, which correlated with the impaired expression and localization of BS transporters, such as OATP1A4, OATP1B2, NTCP, BSEP, and MRP2. The proteasome inhibitor bortezomib partially restored total protein levels of BS transporters but not the localization of BS transporters in the membrane. Furthermore, the expression of nuclear receptors, including FXRα, RXRα, HNF4α, LRH-1, and SHP, was also down-regulated. A cholic acid-supplemented diet exacerbated the liver damage in Tmem30a LKO mice. TMEM30A deficiency led to intrahepatic cholestasis in mice by impairing the expression and localization of BS transporters and the expression of related nuclear receptors. Therefore, TMEM30A may be a novel genetic determinant of intrahepatic cholestasis.

In Vitro Transport Activity and Trafficking of MRP2/ABCC2 Polymorphic Variants

PURPOSE

Multidrug resistance-associated protein 2 (MRP2/ABCC2) is an efflux pump that removes drugs and chemicals from cells. We sought to characterize the expression, trafficking and in vitro activity of seven single nucleotide polymorphisms (SNPs) in the ABCC2 gene.

METHODS

ABCC2 SNPs were generated using site-directed mutagenesis and stably expressed in Flp-In HEK293 cells, which allows targeted insertion of transgenes within the genome. Total and cell surface expression of MRP2 as well as accumulation of substrates (calcein AM and 5(6)-carboxy-2',7'-dichlorofluorescein diacetate, CDCF) were quantified in cells or inverted membrane vesicles expressing wild-type (WT) or variant forms.

RESULTS

The cell surface expression of the C-24T-, G1249A-, G3542T-, T3563A-, C3972T- and G4544A-MRP2 variants was similar to WT-MRP2. While expression was similar, transport of calcein AM was enhanced in cells expressing the G3542T-, T3563A-, C3972T-, and G4544A-MRP2 variants. By comparison, cells expressing the C2366T-MRP2 variant had 40-50% lower surface expression, which increased the accumulation of calcein AM up to 3-fold. Accumulation of CDCF in inverted membrane vesicles expressing the C2366T-MRP2 variant was also reduced by 50%. In addition, the G1249A-MRP2 variant had decreased transport of CDCF.

CONCLUSIONS

Taken together, these data demonstrate that genetic variability in the ABCC2 gene influences the in vitro expression, trafficking, and transport activity of MRP2.

Effects of Catechins and Their Related Compounds on Cellular Accumulation and Efflux Transport of Mitoxantrone in Caco-2 Cell Monolayers

The ability of catechins and their related compounds to inhibit breast cancer resistance protein (BCRP) function in Caco-2 cell monolayers was investigated with mitoxantrone as a BCRP substrate. The gallate or pyrogallol moiety on the catechin structure seemed to promote increased cellular accumulation and inhibit efflux transport of mitoxantrone. The ability of gallate catechins such as (-)-epigallocatechin gallate (EGCG) and (-)-epicatechin gallate (ECG) to increase cellular accumulation and inhibit efflux transport of mitoxantrone was greater than that of nongallate catechins. Gallic acid octyl ester (GAO) also increased intracellular mitoxantrone accumulation. Experiments using GAO derivatives indicated that the gallate moiety required the presence of a long carbon chain for BCRP inhibition. Cellular accumulation and reduced efflux transport of mitoxantrone were greater with epigallocatechin 3-(3″-O-butyl) gallate than with EGCG. EGCG inhibition of BCRP seemed to be restricted by hydrophobicity. The co-administration of catechins, particularly EGCG and related compounds, with greater hydrophobicity may increase the therapeutic activities of BCRP substrates such as mitoxantrone.

ABCC2 (1249G > A) polymorphism implicates altered transport activity for sorafenib

1. Multidrug resistance-associated protein 2 (MRP2), encoded by the ABCC2 gene, is an efflux transporter of several endogenous substrates and xenobiotics. Here, we investigated whether the 1249G > A (rs2273697) polymorphism in ABCC2 affects the ability of MRP2 to pump the multi-tumor drug sorafenib out of cells. 2. Human embryonic kidney 293 (HEK 293) cell lines transfected with ABCC2-1249G and ABCC2-1249A were used to assess the sensitivity and accumulation to sorafenib. The isolated MRP2 were applied to estimate the ATPase activity. 3. The HEK293 cell line overexpressing the ABCC2 1249A allele showed a significantly higher 50% inhibitory concentration (IC₅₀) than a cell line overexpressing ABCC2-1249G or a non-overexpressing control cell line. Intracellular accumulation of sorafenib was much lower in ABCC2-1249A cells than in ABCC2-1249G cells expressing comparable levels of MRP2. Isolated ABCC2-1249A protein showed higher ATPase activity than ABCC2-1249G protein. 4. Our results suggest that the ABCC2 polymorphism 1249G > A increases the ATPase activity of MRP2, leading to greater efflux of sorafenib.

Associations of genetic polymorphisms of the transporters organic cation transporter 2 (OCT2), multidrug and toxin extrusion 1 (MATE1), and ATP-binding cassette subfamily C member 2 (ABCC2) with platinum-based chemotherapy response and toxicity in non-small cell lung cancer patients

Background

Platinum-based chemotherapy is the first-line treatment of non-small cell lung cancer (NSCLC); it is therefore important to discover biomarkers that can be used to predict the efficacy and toxicity of this treatment. Four important transporter genes are expressed in the kidney, including organic cation transporter 2 (OCT2), multidrug and toxin extrusion 1 (MATE1), ATP-binding cassette subfamily B member 1 (ABCB1), and ATP-binding cassette subfamily C member 2 (ABCC2), and genetic polymorphisms in these genes may alter the efficacy and adverse effects of platinum drugs. This study aimed to evaluate the association of genetic polymorphisms of these transporters with platinum-based chemotherapy response and toxicity in NSCLC patients.

Methods

A total of 403 Chinese NSCLC patients were recruited for this study. All patients were newly diagnosed with NSCLC and received at least two cycles of platinum-based chemotherapy. The tumor response and toxicity were evaluated after two cycles of treatment, and the patients’ genomic DNA was extracted. Seven single-nucleotide polymorphisms in four transporter genes were selected to investigate their associations with platinum-based chemotherapy toxicity and response.

Results

OCT2 rs316019 was associated with hepatotoxicity (P = 0.026) and hematological toxicity (P = 0.039), and MATE1 rs2289669 was associated with hematological toxicity induced by platinum (P = 0.016). In addition, ABCC2 rs717620 was significantly associated with the platinum-based chemotherapy response (P = 0.031). ABCB1 polymorphisms were associated with neither response nor toxicity.

Conclusion

OCT2 rs316019, MATE1 rs2289669, and ABCC2 rs717620 might be potential clinical markers for predicting chemotherapy toxicity and response induced by platinum-based treatment in NSCLC patients.

Trial registration Chinese Clinical Trial Registry ChiCTR-RNC-12002892

Halogenated hydrocarbon solvent-related cholangiocarcinoma risk: biliary excretion of glutathione conjugates of 1,2-dichloropropane evidenced by untargeted metabolomics analysis

Recently, the International Agency for Research on Cancer issued a warning about the carcinogenicity of 1,2-dichloropropane (1,2-DCP) to humans based on an epidemiological study suggesting a relationship between the incidence of cholangiocarcinoma and occupational exposure to halogenated hydrocarbon solvent comprised mostly of 1,2-DCP. Although this dihaloalkane has been used in various industrial fields, there has been no biological evidence explaining the cholangiocarcinoma latency, as well as little understanding of general cholangiocarcinoma risk. In the present study, we explored the biliary excretion of 1,2-DCP metabolites by an untargeted metabolomics approach and the related molecular mechanism with in vitro and in vivo experiments. We hypothesized that the biliary excretion of carcinogens derived from 1,2-DCP contribute to the increased cholangiocarcinoma risk. We found that 1,2-DCP was conjugated with glutathione in the liver, and that the glutathione-conjugated forms of 1,2-DCP, including a potential carcinogen that contains a chloride atom, were excreted into bile by the bile canalicular membrane transporter, ABCC2. These results may reflect a risk in the backfiring of biliary excretion as a connatural detoxification systems for xenobiotics. Our findings would contribute to uncover the latent mechanism by which the chronic exposure to 1,2-DCP increases cholangiocarcinoma risk and future understanding of cholangiocarcinoma biology.

Consequences of Mrp2 deficiency for diclofenac toxicity in the rat intestine ex vivo

The non-steroidal anti-inflammatory drug diclofenac (DCF) has a high prevalence of intestinal side effects in humans and rats. It has been reported that Mrp2 transporter deficient rats (Mrp2) are more resistant to DCF induced intestinal toxicity. This was explained in vivo by impaired Mrp2-dependent biliary transport of DCF-acylglucuronide (DAG), leading to decreased intestinal exposure to DAG and DCF. However, it is not known to what extent adaptive changes in the Mrp2 intestine itself influence its sensitivity to DCF toxicity without the influence of liver metabolites. To investigate this, DCF toxicity and disposition were studied ex vivo by precision-cut intestinal slices and Ussing chamber using intestines from wild type(WT) and Mrp2 rats. The results show that adaptive changes due to Mrp2 deficiency concerning Mrp2, Mrp3 and BCRP gene expression, GSH content and DAG formation were different between liver and intestine. Furthermore, Mrp2 intestine was intrinsically more resistant to DCF toxicity than its WT counterpart ex vivo. This can at least partly be explained by a reduced DCF uptake by the Mrp2 intestine, but isnot related to the other adaptive changes in the intestine. The extrapolation of this data to humans with MRP2 deficiency is uncertain due to species differences in activity and regulation of transporters.

Pharmacological correction of misfolding of ABC proteins

The endoplasmic reticulum (ER) quality control system distinguishes between correctly and incorrectly folded proteins to prevent processing of aberrantly folded conformations along the secretory pathway. Non-synonymous mutations can lead to misfolding of ABC proteins and associated disease phenotypes. Specific phenotypes may at least partially be corrected by small molecules, so-called pharmacological chaperones. Screening for folding correctors is expected to open an avenue for treatment of diseases such as cystic fibrosis and intrahepatic cholestasis.

Pharmacogenomics toward personalized tamoxifen therapy for breast cancer

Tamoxifen has been used not only for the treatment or prevention of recurrence in patients with estrogen receptor positive breast cancers but also for recurrent breast cancer. Because CYP2D6 is known to be an important enzyme responsible for the generation of the potent tamoxifen metabolite, ‘endoxifen’, lots of studies reported that genetic variation which reduced its enzyme activity were associated with poor clinical outcome of breast cancer patients treated with tamoxifen. However, there are some discrepant reports questioning the association between CYP2D6 genotype and clinical outcome after tamoxifen therapy. Dose-adjustment study of tamoxifen based on CYP2D6 genotypes provides the evidence that dose adjustment is useful for the patients carrying reduced or null allele of CYP2D6 to maintain the effective endoxifen level. This review describes critical issues in pharmacogenomic studies as well as summarizes the results of the association of CYP2D6 genotype with tamoxifen efficacy.

New insights in the biology of ABC transporters ABCC2 and ABCC3: impact on drug disposition

INTRODUCTION

For the elimination of environmental chemicals and metabolic waste products, the body is equipped with a range of broad specificity transporters that are present in excretory organs as well as in several epithelial blood-tissue barriers.

AREAS COVERED

ABCC2 and ABCC3 (also known as MRP2 and MRP3) mediate the transport of various conjugated organic anions, including many drugs, toxicants and endogenous compounds. This review focuses on the physiology of these transporters, their roles in drug disposition and how they affect drug sensitivity and toxicity. It also examines how ABCC2 and ABCC3 are coordinately regulated at the transcriptional level by members of the nuclear receptor (NR) family of ligand-modulated transcription factors and how this can be therapeutically exploited.

EXPERT OPINION

Mutations in both ABCC2 and ABCC3 have been associated with changes in drug disposition, sensitivity and toxicity. A defect in ABCC2 is associated with Dubin-Johnson syndrome, a recessively inherited disorder characterized by conjugated hyperbilirubinemia. Pharmacological manipulation of the activity of these transporters can potentially improve the pharmacokinetics and thus therapeutic activity of substrate drugs but also affect the physiological function of these transporters and consequently ameliorate associated disease states.

Phase 0 and phase III transport in various organs: combined concept of phases in xenobiotic transport and metabolism

The historical phasing concept of drug metabolism and elimination was introduced to comprise the two phases of metabolism: phase I metabolism for oxidations, reductions and hydrolyses, and phase II metabolism for synthesis. With this concept, biological membrane barriers obstructing the accessibility of metabolism sites in the cells for drugs were not considered. The concept of two phases was extended to a concept of four phases when drug transporters were detected that guided drugs and drug metabolites in and out of the cells. In particular, water soluble or charged drugs are virtually not able to overcome the phospholipid membrane barrier. Drug transporters belong to two main clusters of transporter families: the solute carrier (SLC) families and the ATP binding cassette (ABC) carriers. The ABC transporters comprise seven families with about 20 carriers involved in drug transport. All of them operate as pumps at the expense of ATP splitting. Embedded in the former phase concept, the term "phase III" was introduced by Ishikawa in 1992 for drug export by ABC efflux pumps. SLC comprise 52 families, from which many carriers are drug uptake transporters. Later on, this uptake process was referred to as the "phase 0 transport" of drugs. Transporters for xenobiotics in man and animal are most expressed in liver, but they are also present in extra-hepatic tissues such as in the kidney, the adrenal gland and lung. This review deals with the function of drug carriers in various organs and their impact on drug metabolism and elimination.

Oral anticancer drugs: mechanisms of low bioavailability and strategies for improvement

The use of oral anticancer drugs has increased during the last decade, because of patient preference, lower costs, proven efficacy, lack of infusion-related inconveniences, and the opportunity to develop chronic treatment regimens. Oral administration of anticancer drugs is, however, often hampered by limited bioavailability of the drug, which is associated with a wide variability. Since most anticancer drugs have a narrow therapeutic window and are dosed at or close to the maximum tolerated dose, a wide variability in the bioavailability can have a negative impact on treatment outcome. This review discusses mechanisms of low bioavailability of oral anticancer drugs and strategies for improvement. The extent of oral bioavailability depends on many factors, including release of the drug from the pharmaceutical dosage form, a drug's stability in the gastrointestinal tract, factors affecting dissolution, the rate of passage through the gut wall, and the pre-systemic metabolism in the gut wall and liver. These factors are divided into pharmaceutical limitations, physiological endogenous limitations, and patient-specific limitations. There are several strategies to reduce or overcome these limitations. First, pharmaceutical adjustment of the formulation or the physicochemical characteristics of the drug can improve the dissolution rate and absorption. Second, pharmacological interventions by combining the drug with inhibitors of transporter proteins and/or pre-systemic metabolizing enzymes can overcome the physiological endogenous limitations. Third, chemical modification of a drug by synthesis of a derivative, salt form, or prodrug could enhance the bioavailability by improving the absorption and bypassing physiological endogenous limitations. Although the bioavailability can be enhanced by various strategies, the development of novel oral products with low solubility or cell membrane permeability remains cumbersome and is often unsuccessful. The main reasons are unacceptable variation in the bioavailability and high investment costs. Furthermore, novel oral anticancer drugs are frequently associated with toxic effects including unacceptable gastrointestinal adverse effects. Therefore, compliance is often suboptimal, which may negatively influence treatment outcome.

ABCB1 haplotype influences the sirolimus dose requirements in Chinese renal transplant recipients

Sirolimus, an immunosuppressive drug used to prevent organ rejection after renal transplantation, has a narrow therapeutic index and a large inter-individual variability of pharmacokinetics. The aim of this study was to analyse the dose-normalized trough blood concentrations (C0 /D ratio) of sirolimus in patients with different genotypes and attempt to investigate the possible associations between ABCB1/CYP3A5 genotypes and sirolimus dose requirements in Chinese renal transplant recipients. Blood samples were collected from 85 Chinese renal transplant recipients who were treated with sirolimus for at least 3 months and polymorphisms of the ABCB1 and CYP3A5 were determined by the SNaPShot multiplex assay. The blood concentrations of sirolimus were determined with HPLC. A significant allele-dependent effect was observed between the CYP3A5*3 polymorphism and the C0 /D ratio of sirolimus. The patients bearing at least one CYP3A5*1 allele had a lower sirolimus C0/D ratio compared with those with a homozygous CYP3A5*3 genotype (p < 0.05). No significant differences of sirolimus C0/D ratios were observed among various ABCB1 1236C>T, 2677G>T/A and 3435C>T genotype groups. However, haplotype analysis including ABCB1 1236C>T, 2677G>T/A and 3435C>T SNPs showed that the mean sirolimus C0/D of subjects carrying the CGC/CGC diplotype was about 30% lower compared with those carrying the CGC/TTT or TTT/TTT diplotype, whether or not they expressed the CYP3A5 (p < 0.05). These results demonstrated that the haplotype of ABCB1 might be a better index for the prediction of sirolimus blood concentration than single SNPs. Genotyping of ABCB1 and CYP3A5 might help to optimize individualized sirolimus treatments for Chinese renal transplant recipients.

The effects of ABCC2 G1249A polymorphism on the risk of resistance to antiepileptic drugs: a meta-analysis of the literature

AIMS

The G1249A variant of the multidrug resistance-associated protein 2 (ABCC2) gene may be associated with the development of antiepileptic drug (AED) resistance. Although numerous studies have investigated the association between the G1249A variant and the risk of drug resistance in epilepsy, the results of these studies have been inconclusive. To assess the role of G1249A polymorphism in drug resistance in epilepsy, a meta-analysis was performed.

MATERIALS AND METHODS

We systematically reviewed relevant studies retrieved by the PubMed and Embase. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated based on the date extracted from the studies to evaluate the strength of association. We also analyzed the heterogeneity and sensitivity of each report and the publication bias of the studies.

RESULTS

A total of 6 published studies, involving 2213 patients (1100 patients with drug-resistant epilepsy and 1113 controls with drug-responsive epilepsy) were reviewed in the present meta-analysis. The overall results indicated that the variant genotypes were associated with a significantly decreased risk of AED resistance (AA vs. GG: OR=0.372, 95% CI=0.182-0.762; recessive model: OR=0.399, 95% CI=0.200-0.795) (fixed-effects model). A stratified analysis by ethnicity showed similar findings for Caucasians in an additive model (A vs. G: OR=0.700, 95% CI=0.494-0.992).

CONCLUSIONS

The meta-analysis suggests that the ABCC2 G1249A polymorphism is significantly associated with a decreased risk of AED resistance. However, further functional investigations are warranted to validate the association.

Role of hepatic efflux transporters in regulating systemic and hepatocyte exposure to xenobiotics

Hepatic efflux transporters include numerous well-known and emerging proteins localized to the canalicular or basolateral membrane of the hepatocyte that are responsible for the excretion of drugs into the bile or blood, respectively. Altered function of hepatic efflux transporters due to drug-drug interactions, genetic variation, and/or disease states may lead to changes in xenobiotic exposure in the hepatocyte and/or systemic circulation. This review focuses on transport proteins involved in the hepatocellular efflux of drugs and metabolites, discusses mechanisms of altered transporter function as well as the interplay between multiple transport pathways, and highlights the importance of considering intracellular unbound concentrations of transporter substrates and/or inhibitors. Methods to evaluate hepatic efflux transport and predict the effects of impaired transporter function on systemic and hepatocyte exposure are discussed, and the sandwich-cultured hepatocyte model to evaluate comprehensively the role of hepatic efflux in the hepatobiliary disposition of xenobiotics is characterized.

Polymorphism of ORM1 is associated with the pharmacokinetics of telmisartan

BACKGROUND

The pharmacokinetics (PKs) and pharmacodynamics (PDs) of telmisartan varies among the individuals, and the main causes remain unknown. The aim of this study was to evaluate the impact of ORM1, as well as ABCC2, ABCB1, ABCG2 and SLCO1B3 polymorphisms, on the disposition of the drug and BP change after taking 40 mg telmisartan in 48 healthy Chinese males.

METHOD

A total of 48 healthy males were included in this trial. Every volunteer ingested a single dose of 40 mg telmisartan, and the plasma drug concentration and blood pressure (BP) were measured up to 48 h.

RESULT

In this study, the area under the plasma concentration-time curve (AUC) in the heterozygotes of ORM1 113AG was higher than that in the wild-type homozygotes, AUC(0-48) (113AA vs. 113AG, 1,549.18±859.84 ng·h/ml vs. 2,313.54±1,257.71 ng·h/ml, P = 0.033), AUC(0-∞) (113AA vs. 113AG, 1,753.13±1,060.60 ng·h/ml vs. 2,686.90±1,401.87 ng·h/ml, P = 0.016), and the change(%) of the diastolic blood pressure (DBP) from the baseline BP value also showed a significant difference between the ORM1 113AG and 113AA genotypes at 5 h after taking telmisartan (P = 0.026). This study also showed that the allele of ABCC2 C3972T would affected the disposition of telmsiartan and the DBP change significantly after taking the drug. However, the common SNPs of ABCG2 C421, ABCB1 C3435T, and SLCO1B3 T334G showed no impacts on the PKs of telmisartan or BP change(%) in our trial.

CONCLUSION

The ORM1 A113G polymorphism was associated with the PKs variability after taking telmsiartan, as well as ABCC2 C3972T. The heterozygotes of ORM1 113AG showed a larger AUC and a notable BP change(%) from the baseline compared with the wild-type.

TRIAL REGISTRATION

Chinese Clinical Trial Registry ChiCTR-TNC-10000898.

UGT1A9, UGT2B7, and MRP2 genotypes can predict mycophenolic acid pharmacokinetic variability in pediatric kidney transplant recipients

BACKGROUND

Mycophenolic acid (MPA) exposure in pediatric patients with kidney transplant receiving body surface area (BSA)-based dosing exhibits large variability. Several genetic variants in glucuronosyltransferases (UGTs) and of multidrug resistance-associated protein 2 (MRP2) have independently been suggested to predict MPA exposure in adult patients with varying results. Here, the combined contribution of these genetic variants to MPA pharmacokinetic variability was investigated in pediatric renal transplant recipients who were on mycophenolic mofetil maintenance therapy.

METHODS

MPA and MPA-glucuronide concentrations from 32 patients were quantified by high-performance liquid chromatography. MPA exposure (AUC) was estimated using a 4-point abbreviated sampling strategy (predose/trough and 20 minutes, 1 hour, and 3 hours after dose) using a validated pediatric Bayesian estimator. Genotyping was performed for all of the following single nucleotide polymorphisms (SNPs): UGT1A8 830G>A(*3), UGT1A9 98T>C(*3), UGT1A9-440C>T, UGT1A9-2152C>T, UGT1A9-275T>A, UGT2B7-900A>G, and MRP2-24T>C.

RESULTS

Recipients heterozygous for MRP2-24T>C who also had UGT1A9-440C>T or UGT2B7-900A>G (n = 4), and MRP2-24T>C-negative recipients having both UGT1A9-440C>T and UGT2B7-900A>G (n = 5) showed a 2.2 and 1.7 times higher dose-dependent and BSA-normalized MPA-AUC compared with carriers of no or only 1 UGT-SNP (P < 0.001 and P = 0.01, respectively) (n = 7). Dose-dependent and BSA-normalized predose MPA concentrations were 3.0 and 2.4 times higher, respectively (P < 0.001). Interindividual variability in peak concentrations could be explained by the presence of the UGT1A9-440C>T genotype (P < 0.05).

CONCLUSION

Our preliminary study demonstrates that combined UGT1A9-440C>T, UGT2B7-900A>G, and MRP2-24T>C polymorphisms can be important predictors of interindividual variability in MPA exposure in the pediatric population.

Dietary fat increases quercetin bioavailability in overweight adults

SCOPE

Epidemiologic evidence supports that dietary quercetin reduces cardiovascular disease (CVD) risk, but its oral bioavailability is paradoxically low. The aim of this study was to determine whether dietary fat would improve quercetin bioavailability in adults at high risk for CVD and to assess lipid-mediated micellarization of quercetin in vitro.

METHODS AND RESULTS

In a randomized, cross-over study, overweight/obese men and postmenopausal women (n = 4 M/5 F; 55.9 ± 2.1 years; 30.8 ± 1.4 kg/m(2) ) ingested 1095 mg of quercetin aglycone with a standardized breakfast that was fat-free (<0.5 g), low-fat (4.0 g), or high-fat (15.4 g). Plasma was obtained at timed intervals for 24 h to measure quercetin and its methylated metabolites isorhamnetin and tamarixetin. Compared to the fat-free trial, plasma quercetin maximum concentration (Cmax ), and area under curve (AUC0-24 h ) increased (p < 0.05) by 45 and 32%, respectively, during the high-fat trial. During the high-fat trial, isorhamnetin Cmax and AUC0-24 h also increased by 40 and 19%, respectively, whereas Cmax and AUC0-24 h of tamarixetin increased by 46 and 43%, respectively. Dietary fat dose-dependently increased micellarization efficiency of quercetin aglycone in vitro.

CONCLUSION

Dietary fat improves quercetin bioavailability by increasing its absorption, likely by enhancing its micellarization at the small intestine.

Evaluation of hepatic disposition of paroxetine using sandwich-cultured rat and human hepatocytes

Paroxetine, a selective serotonin reuptake inhibitor, is metabolized in the liver and excreted into bile and urine as metabolites, but species differences have been observed in hepatic disposition between rats and humans. A major metabolite in rats is M1-glucuronide, whereas M1-glucuronide and M1-sulfate are found in humans. The primary excretion route of paroxetine-derived radioactivity in rats and humans is bile and urine, respectively. The aim of this study was to examine the usefulness of sandwich-cultured hepatocytes (SCH) to evaluate in vivo species differences of the hepatic disposition of paroxetine between rats and humans. The metabolite profile of [(3)H]paroxetine in SCH was similar to that in hepatocytes in suspension, and the in vitro metabolite profiles were similar to the published in vivo metabolic pathways for both species. Furthermore, the biliary excretion index (BEI) of formed M1-glucuronide in rat SCH (25.8-50.9%) was higher than that in human SCH (15.1-16.7%). The BEI of formed M1-sulfate (16.4-29.1%) was comparable to that of M1-glucuronide in human SCH, whereas the BEIs of paroxetine were negligible in SCH of both species. Moreover, M1-glucuronide was demonstrated to be a multidrug resistance-associated protein 2 substrate in both species, as determined by its uptake into ATP-binding cassette transporter-expressing membrane vesicles. SCH should prove to be useful to evaluate the processes of hepatic uptake and metabolism of parent drugs and the simultaneous examination of the biliary excretion of both parent drug and liver-derived metabolites.

Single nucleotide polymorphisms in ABCC2 associate with tenofovir-induced kidney tubular dysfunction in Japanese patients with HIV-1 infection: a pharmacogenetic study

BACKGROUND

Tenofovir is a widely used antiretroviral drug although it can cause kidney tubular dysfunction (KTD). The aim of this study was to determine the association between polymorphisms in genes encoding drug transporters and KTD in Japanese patients treated with tenofovir.

METHODS

The association between tenofovir-induced KTD and 14 single nucleotide polymorphisms (SNPs) in the ABCC2, ABCC4, ABCC10, SCL22A6, and ABCB1 genes was investigated in 190 Japanese patients. KTD was diagnosed by the presence of at least 3 abnormalities in the following parameters: fractional tubular resorption of phosphate, fractional excretion of uric acid, urinary β2-microglobulin, urinary α1-microglobulin, and urinary N-acetyl-β-D-glucosaminidase. Genotyping was performed by allelic discrimination using TaqMan 5'-nuclease assays with standard protocols. Associations between genotypes and KTD were tested by univariate and multivariate logistic regression analyses.

RESULTS

KTD was diagnosed in 19 of the 190 (10%) patients. Univariate and multivariate analyses showed a significant association between KTD and genotype CC at position -24 CC (adjusted odds ratio [OR], 20.08; 95% confidence interval [CI], 1.711-235.7; P= .017) and genotype AA at position 1249 (adjusted OR, 16.21; 95% CI, 1.630-161.1; P= .017) of ABCC2. Multivariate analysis showed higher adjusted OR for patients with both homozygotes (adjusted OR, 38.44; 95% CI, 2.051-720.4; P= .015). ABCC2 haplotype -24T and 1249G was a protective haplotype for KTD (OR, 0.098; 95% CI, .002-.603; P= .003

CONCLUSIONS

This is the first study of our knowledge to identify the association between SNPs in ABCC2 and tenofovir-induced KTD in an Asian population. Close monitoring of renal function is warranted in tenofovir-treated patients with these SNPs.

Generation and characterization of a novel multidrug resistance protein 2 humanized mouse line

The multidrug resistance protein (MRP) 2 is predominantly expressed in liver, intestine, and kidney, where it plays an important role in the excretion of a range of drugs and their metabolites or endogenous compounds into bile, feces, and urine. Mrp knockout [Mrp2(-/-)] mice have been used recently to study the role of MRP2 in drug disposition. Here, we describe the first generation and initial characterization of a mouse line humanized for MRP2 (huMRP2), which is nulled for the mouse Mrp2 gene and expresses the human transporter in the organs and cell types where MRP2 is normally expressed. Analysis of the mRNA expression for selected cytochrome P450 and transporter genes revealed no major changes in huMRP2 mice compared with wild-type controls. We show that human MRP2 is able to compensate functionally for the loss of the mouse transporter as demonstrated by comparable bilirubin levels in the humanized mice and wild-type controls, in contrast to the hyperbilirubinemia phenotype that is observed in MRP2(-/-) mice. The huMRP2 mouse provides a model to study the role of the human transporter in drug disposition and in assessing the in vivo consequences of inhibiting this transporter by compounds interacting with human MRP2.

Induction of antioxidative Nrf2 gene transcription by coffee in humans: depending on genotype?

The Nrf2/ARE pathway is a major cellular defense mechanism that prevents damage by reactive oxygen species through induction of antioxidative phase II enzymes. However, the activity of the Nrf2/ARE system is not uniform with variability in response presumed to be dependent on the Nrf2 genotype. We recently completed a pilot human coffee intervention trial with healthy humans, where large interindividual differences in the antioxidative response to the study coffee were examined. Here, we address the question whether differences in the modulation of Nrf2 gene transcription, assessed as an induction of Nrf2 gene transcription by Q-PCR, might be correlated with specific Nrf2 genotypes. To date, nine single nucleotide polymorphisms (SNPs) have been identified in the Nrf2 (NFE2L2) gene. Two of these, the -617C/A and -651G/A SNPs are located within the promoter region and have previously been reported to influence the activity of the Nrf2/ARE pathway by reducing Nrf2 transcriptional activity. Sequencing of the critical Nrf2 gene promoter region not only confirmed the existence of these SNPs within the participants of the trial at the expected frequency (33% carrying the -617C/A, 17% the -651G/A and 56% the -653A/G SNP) but also indicated reduced Nrf2 gene transcription associated with a normal diet if the SNPs at position -617, -651 or -653 were present. Of note, the data also indicated the study coffee increased Nrf2 gene transcription even in SNP carriers. This further highlights the relevance of genotype-dependent induction of Nrf2 gene transcription that appears to be largely influenced by dietary factors.

ABCC2 Haplotype is Associated With Antituberculosis Drug-Induced Maculopapular Eruption

Genetic variants in ATP-binding cassette (ABC) transporter genes are associated with increased susceptibility to adverse drug reactions. We hypothesized that genetic variant ABC transporters (ABCB1 and ABCC2) may be candidate markers for predicting maculopapular eruption (MPE) induced by antituberculosis therapy. We compared the genotype distributions of single nucleotide polymorphisms and haplotypes in the ABCB1 and ABCC2 genes between 62 antituberculosis drug (ATD)-induced MPE cases and 159 ATD-tolerant controls using multivariate logistic regression analysis. There was no significant association between genetic polymorphisms in ABCB1 and ATD-induced MPE (P>0.05). Among seven selected SNPs of ABCC2, IVS3-49C>T in intron and I1324I were associated with ATD-induced MPE (P=0.029 and 0.036, respectively). In an analysis of the ABCC2 haplotypes (ht; -1549G>A_-24C>T_IVS3-49C>T_V417I), ht1[G-C-C-G] was significantly associated with ATD-induced MPE (P=0.032, OR=0.35, 95% CI: 0.16-0.95). No significant association between the other haplotypes and ATD-induced MPE was observed. An ABCC2 haplotype is associated with the presence of ATD-induced MPE in patients with tuberculosis and may be a genetic risk factor for the development of MPE induced by ATD.

Interindividual variability in hepatic expression of the multidrug resistance-associated protein 2 (MRP2/ABCC2): quantification by liquid chromatography/tandem mass spectrometry

Multidrug-associated protein 2 (MRP2) is an efflux transporter that is expressed at the bile canalicular membrane. To allow in vitro to in vivo extrapolation of the contribution of MRP2 toward hepatic disposition of its substrates, data on the interindividual variability of hepatic MRP2 protein expression are required. Therefore, we quantified the expression of MRP2 in the University of Washington (UW) human liver bank (n = 51) using a modified version of a previously validated liquid chromatography/tandem mass spectrometry assay. An unlabeled (LTIIPQDPILFSGSLR) and stable isotope-labeled (LTIIPQDPILFSGSL[(13)C(6)(15)N(1)]R) surrogate peptide for MRP2 were used as the calibrator and internal standard, respectively. After isolation of the membrane fraction from the liver tissue, in-solution tryptic digestion was conducted. Quality control samples created by spiking human serum albumin or pooled human liver (n = 51) matrix with three different MRP2 synthetic peptide concentrations generated error and precision values of less than 15%. As determined by the surrogate peptide, the average MRP2 expression in the UW liver bank samples was 1.54 ± 0.64 fmol/μg liver membrane protein and was found to be independent of age (7-63 years) or sex. A single nucleotide polymorphism in the promoter region (rs717620), previously thought to affect MRP2 expression, did not influence hepatic expression of MRP2. In contrast, the single nucleotide polymorphism 21214G>A (V417I; rs2273697) was associated with significantly higher hepatic MRP2 expression.

Mammalian multidrug-resistance proteins (MRPs)

Subfamily C of the human ABC (ATP-binding cassette) superfamily contains nine proteins that are often referred to as the MRPs (multidrug-resistance proteins). The 'short' MRP/ABCC transporters (MRP4, MRP5, MRP8 and ABCC12) have a typical ABC structure with four domains comprising two membrane-spanning domains (MSD1 and MSD2) each followed by a nucleotide-binding domain (NBD1 and NBD2). The 'long' MRP/ABCCs (MRP1, MRP2, MRP3, ABCC6 and MRP7) have five domains with the extra domain, MSD0, at the N-terminus. The proteins encoded by the ABCC6 and ABCC12 genes are not known to transport drugs and are therefore referred to as ABCC6 and ABCC12 (rather than MRP6 and MRP9) respectively. A large number of molecules are transported across the plasma membrane by the MRPs. Many are organic anions derived from exogenous sources such as conjugated drug metabolites. Others are endogenous metabolites such as the cysteinyl leukotrienes and prostaglandins which have important signalling functions in the cell. Some MRPs share a degree of overlap in substrate specificity (at least in vitro), but differences in transport kinetics are often substantial. In some cases, the in vivo substrates for some MRPs have been discovered aided by studies in gene-knockout mice. However, the molecules that are transported in vivo by others, including MRP5, MRP7, ABCC6 and ABCC12, still remain unknown. Important differences in the tissue distribution of the MRPs and their membrane localization (apical in contrast with basolateral) in polarized cells also exist. Together, these differences are responsible for the unique pharmacological and physiological functions of each of the nine ABCC transporters known as the MRPs.