Functional defect caused by the 4544G>A SNP in ABCC2: potential impact for drug cellular disposition

ABCC2 p.R393W variant contributes to Dubin-Johnson syndrome by targeting MRP2 to proteasome degradation

BACKGROUND

Dubin-Johnson syndrome (DJS), a rare autosomal recessive liver condition, is caused by biallelic loss-of-function mutations of the ABCC2 gene. This study aimed to investigate genetic variations in the drug efflux transporter ABCC2 (MRP2) gene in patients with DJS and to characterise the expression and mechanism of the ABCC2 gene variant.

METHODS

Trio whole exome sequencing was performed in the family to identify the genetic causes. Bioinformatics analysis was performed to assess pathogenicity. In in vitro experiments, site-directed mutagenesis was used to introduce ABCC2 variants in constructs then expressed in HEK293T, HuH-7 and HepG2 cell lines. The expression of total and cell membrane MRP2 was quantified in cells expressing the wild-type or variant forms. Chloroquine and MG132 were used to evaluate the effects of p.R393W on lysosomal and/or proteasomal degradation.

RESULTS

The twin probands carry DJS-associated variants c.1177C>T (rs777902199) in the ABCC2 gene inherited from the father and the c.3632T>C mutation in the other allele inherited from the mother. The ABCC2 variant, c.1177C>T, results in a p.R393W substitution in MRP2 that is highly conserved among vertebrates, drastically decreasing the expression of mutant protein by promoting proteasomal degradation. Another variant c.3632T>C results in a p.L1211P substitution in MRP2, decreasing the expression of membrane MRP2 but not changing the expression of total protein.

CONCLUSION

These results strongly suggest that the p.R393W variant affects the stability of the MRP2 protein and decreases its expression by ubiquitin-mediated proteasomal degradation, and the p.L1211P decreases the expression of membrane MRP2, indicating that these two variants, respectively, cause a loss-of-function of the MRP2 protein and membrane MRP2 ultimately leading to DJS development.

Genetic variations in ABC transporter genes as a predictive biomarker for toxicity in North Indian lung cancer patients undergoing platinum-based doublet chemotherapy

ATP-binding cassette (ABC) transporters are expressed in various human tissues and play a vital role in the efflux of various chemotherapeutic drugs. The current study has assessed genetic variants of ABCB1, ABCC1, ABCC2, and ABCG2 genes in 407 lung cancer patients undergoing platinum-based doublet chemotherapy. The association of ABCB1 (C1236 T, C3435 T, and G2677 T/A), ABCC1 (G3173 A and G2168 A),ABCC2 (G4544 A), and ABCG2 (C421 A) polymorphisms with chemotherapy-induced adverse events were assessed, and statistical analysis was conducted. Our data showed that patients harboring heterozygous (GA) genotype for ABCC1 G3173 A had an increased risk of developing leukopenia (odds ratio [OR] = 1.88, p = 0.04) and anemia (adjusted odds ratio [AOR] = 2.70, p = 0.03). For ABCC2 G4544 A polymorphism, patients harboring one copy of the mutant (GA) allele showed an increased risk of developing anemia (OR = 4.24, p = 0.03). After adjusting with various confounding factors, the heterozygous (GA) genotype showed a 5.63-fold increased risk of developing anemia (AOR = 5.63, p = 0.03). The ABCB1 G2677 A (OR = 0.37, p = 0.008) and ABCC1 G3173 A (OR = 0.54, p = 0.04) polymorphism showed a lower incidence of developing nephrotoxicity. In ABCG2 C421 A polymorphism, patients harboring heterozygous (CA) genotype had a lower incidence of having diarrhea (OR = 0.25, p = 0.04). An increased risk of having diarrhea was observed in the heterozygous genotype (GA) for ABCC1 G3173 A polymorphism (AOR = 2.78, p = 0.04). An increased risk of liver injury was found in the patients carrying heterozygous genotype of the ABCC1 G3173 A (OR = 2.06, p = 0.02) and ABCB1 C1236 T (OR = 1.85, p = 0.01). This study demonstrates the role of polymorphic variations in ABCB1, ABCC1, ABCC2, and ABCG2 in predicting hematological, nephrotoxicity, gastrointestinal, and hepatotoxicity.

An update on pharmacogenetic factors influencing the metabolism and toxicity of artemisinin-based combination therapy in the treatment of malaria

INTRODUCTION

Artemisinin-based combination therapies (ACTs) are recommended first-line antimalarials for uncomplicated Plasmodium falciparum malaria. Pharmacokinetic/pharmacodynamic variation associated with ACT drugs and their effect is documented. It is accepted to an extent that inter-individual variation is genetically driven, and should be explored for optimized antimalarial use.

AREAS COVERED

We provide an update on the pharmacogenetics of ACT antimalarial disposition. Beyond presently used antimalarials, we also refer to information available for the most notable next-generation drugs under development. The bibliographic approach was based on multiple Boolean searches on PubMed covering all recent publications since our previous review.

EXPERT OPINION

The last 10 years have witnessed an increase in our knowledge of ACT pharmacogenetics, including the first clear examples of its contribution as an exacerbating factor for drug-drug interactions. This knowledge gap is still large and is likely to widen as a new wave of antimalarial drug is looming, with few studies addressing their pharmacogenetics. Clinically useful pharmacogenetic markers are still not available, in particular, from an individual precision medicine perspective. A better understanding of the genetic makeup of target populations can be valuable for aiding decisions on mass drug administration implementation concerning region-specific antimalarial drug and dosage options.

The role of pharmacogenetics in Efficacy and safety of protease inhibitor based therapy in human immunodeficiency virus type (HIV) infection

Antiretroviral therapy has markedly reduced morbidity and mortality for persons living with human immunodeficiency virus (HIV). HIV can now be classified as a chronic disease; until a cure is found, patients are likely to require life-long therapy. However, despite these undoubted advances, there are many issues that need to be resolved, including the problems associated with long-term efficacy and toxicity. Moreover, pharmacotherapy of patients infected with HIV is challenging because a great number of comorbidities increase polypharmacy and the risk for drug-drug interactions. There is considerable interindividual variability in patient outcomes in terms of drug disposition, drug efficacy and adverse events. The basis of these differences is multifactorial, but host genetics are believed to play a significant part. HIV-infected population consists of ethnically diverse individuals on complex and potentially toxic antiretroviral regimens on a long-term basis. These individuals would benefit greatly from predictive tests that identify the most durable regimens. Pharmacogenetics holds that promise. Thus, detailed understanding of the metabolism and transport of antiretrovirals and the influence of genetics on these pathways is important. To this end, this review provides an up-to-date overview of the metabolism of antiHIV therapeutics of the protease inhibitors Lopinavir and Ritonavir and the impact of genetic variation in drug metabolism and transport on the treatment of HIV.

Potential Gene Association Studies of Chemotherapy-Induced Cardiotoxicity: A Systematic Review and Meta-Analysis

Chemotherapy is widely used in the treatment of cancer patients, but the cardiotoxicity induced by chemotherapy is still a major concern to most clinicians. Currently, genetic methods have been used to detect patients with high risk of chemotherapy-induced cardiotoxicity (CIC), and our study evaluated the correlation between genomic variants and CIC. The systematic literature search was performed in the PubMed, Cochrane Central Register of Controlled Trials (CENTRAL), China Biology Medicine disc (CBMdisc), the Embase database, China National Knowledge Internet (CNKI) and Wanfang database from inception until June 2020. Forty-one studies were identified that examined the relationship between genetic variations and CIC. And these studies examined 88 different genes and 154 single nucleotide polymorphisms (SNPs). Our study indicated 6 variants obviously associated with the increased risk for CIC, including CYBA rs4673 (pooled odds ratio, 1.93; 95% CI, 1.13–3.30), RAC2 rs13058338 (2.05; 1.11–3.78), CYP3A5 rs776746 (2.15; 1.00–4.62) ABCC1 rs45511401 (1.46; 1.05–2.01), ABCC2 rs8187710 (2.19; 1.38–3.48), and HER2-Ile655Val rs1136201 (2.48; 1.53–4.02). Although further studies are required to validate the diagnostic and prognostic roles of these 6 variants in predicting CIC, our study emphasizes the promising benefits of pharmacogenomic screening before chemotherapy to minimize the CIC.

Impact of variants in ATP-binding cassette transporters on breast cancer treatment

There has been substantial interest in the impact of ATP-binding cassette (ABC) transporter variability on breast cancer drug resistance. Here, we provide a systematic review of ABC variants in breast cancer therapy. Notably, most studies used small heterogeneous cohorts and their identified associations lack statistical stringency, replication and mechanistic support. We conclude that commonly studied ABC polymorphisms are not suitable to accurately predict therapy response or toxicity in breast cancer patients and cannot guide treatment decisions. However, recent research shows that ABC transporters harbor a plethora of rare variants with individually small effect sizes, and we argue that a shift in strategy from target variant interrogation to comprehensive profiling might hold promise to drastically improve the predictive power of outcome models.

Pharmacogenomics and Pharmacogenetics: In Silico Prediction of Drug Effects in Treatments for Novel Coronavirus SARS-CoV2 Disease

The latest developments in precision medicine allow the modulation of therapeutic approaches in different pathologies on the basis of the specific molecular characterization of the patient. This review of the literature coupled with in silico analysis was to provide a selected screening of interactions between single-nucleotide polymorphisms (SNPs) and drugs (repurposed, investigational, and biological agents) showing efficacy and toxicityin counteracting Covid-19 infection. In silico analysis of genetic variants related to each drug was performed on such databases as PharmGKB, Ensembl Genome Browser, www.drugs.com, and SNPedia, with an extensive literature review of papers (to May 10, 2020) on Covid-19 treatments using Medline, Embase, International Pharmaceutical Abstracts, PharmGKB, and Google Scholar. The clinical relevance of SNPs, known as both drug targets and markers, considering genetic variations with known drug responses, and the therapeutic consequences are discussed. In the context of clinical treatment of Covid-19, including infection prevention, control measures, and supportive care, this review highlights the importance of a personalized approach in the final selection of therapy, which is probably essential in the management of the Covid-19 pandemic.

A recurrent ABCC2 p.G693R mutation resulting in loss of function of MRP2 and hyperbilirubinemia in Dubin-Johnson syndrome in China

BACKGROUND

Dubin-Johnson syndrome (DJS) is a rare autosomal recessive disorder characterized by predominantly conjugated hyperbilirubinemia that is caused by pathogenic mutations in the adenosine triphosphate-binding cassette subfamily C member 2 (ABCC2) gene, which encodes multidrug resistance-associated protein 2 (MRP2). However, little is known about the causative mutation of DJS in China. Recently, we have reported ABCC2 p.G693R mutation in two unrelated cases. In the present study, we investigated the pathogenicity of the ABCC2 p.G693R mutation in DJS in China.

METHODS

Clinical and genetic analysis was conducted for the two patients with the ABCC2 p.G693R mutation. Whole exome sequencing for mutations in other known hyperbilirubinemia-related genes was conducted for the cases with ABCC2 p.G693R. Expression and cellular localization of the mutant MRP2 p.G693R were analyzed by Western blotting and immunofluorescence assay, respectively. Organic anion transport activity was evaluated by the analysis of glutathione-conjugated-monochlorobimane.

RESULTS

The two DJS patients with ABCC2 p.G693R mutation, which was conserved among different species, showed typical hyperbilirubinemia phenotype. No pathogenic mutation was identified in the other known hyperbilirubinemia related genes. Functional studies in three cell lines showed that the expression, localization and the organic anion transport activity were significantly compromised by MRP2 p.G693R mutation compared with wild-type MRP2.

CONCLUSIONS

The recurrent ABCC2 p.G693R mutation is associated with loss of function of the MRP2 protein and may result in hyperbilirubinemia in DJS in China.

Novel genetic and epigenetic factors of importance for inter-individual differences in drug disposition, response and toxicity

Individuals differ substantially in their response to pharmacological treatment. Personalized medicine aspires to embrace these inter-individual differences and customize therapy by taking a wealth of patient-specific data into account. Pharmacogenomic constitutes a cornerstone of personalized medicine that provides therapeutic guidance based on the genomic profile of a given patient. Pharmacogenomics already has applications in the clinics, particularly in oncology, whereas future development in this area is needed in order to establish pharmacogenomic biomarkers as useful clinical tools. In this review we present an updated overview of current and emerging pharmacogenomic biomarkers in different therapeutic areas and critically discuss their potential to transform clinical care. Furthermore, we discuss opportunities of technological, methodological and institutional advances to improve biomarker discovery. We also summarize recent progress in our understanding of epigenetic effects on drug disposition and response, including a discussion of the only few pharmacogenomic biomarkers implemented into routine care. We anticipate, in part due to exciting rapid developments in Next Generation Sequencing technologies, machine learning methods and national biobanks, that the field will make great advances in the upcoming years towards unlocking the full potential of genomic data.

Is a pharmacogenomic panel useful to estimate the risk of oxaliplatin-related neurotoxicity in colorectal cancer patients?

Oxaliplatin-induced peripheral neurotoxicity (OXPN) is a dose-limiting toxicity in colorectal cancer (CRC) patients. Single nucleotide polymorphisms (SNPs) in genes involved in drug transport may lead to higher intracellular oxaliplatin accumulation in the dorsal root ganglia and thus increased risk of OXPN. In this study, a panel of 5 SNPs, namely ABCC2 (-24C > T/rs717620 and c.4544 G > A/rs8187710), ABCG2 (c.421 C > A/rs2231142), ABCB1 (c.3435 C > T/rs1045642) and SLC31A1 (c.-36 + 2451 T > G/rs10981694), was evaluated to assess their association with grade 2-3 OXPN in metastatic CRC patients. SNPs were considered according to a dominant model (heterozygous + homozygous). Germline DNA was available from 120 patients who received oxaliplatin between 2010 and 2016. An external cohort of 80 patients was used to validate our results. At the univariable logistic analyses, there were no significant associations between SNPs and incidence of OXPN. Taking into account the strength of observed association between OXPN and the SNPs, a clinical risk score was developed as linear predictor from a multivariable logistic model including all the SNPs together. This score was significantly associated with grade 2-3 OXPN (p = 0.036), but the external calibration was not satisfactory due to relevant discrepancies between the two series. Our data suggest that the concomitant evaluation of multiple SNPs in oxaliplatin transporters is an exploratory strategy that may deserve further investigation for treatment customization in CRC patients.

Unexplained cholestasis in adults and adolescents: diagnostic benefit of genetic examination

OBJECTIVES

A few adult and adolescent patients with even severe cholestatic liver disease remain unexplained after standard diagnostic work-up. We studied the value of genetic examination in such patients and developed a panel of eight genes with known cholestatic associations.

MATERIALS AND METHODS

Thirty-three patients with unexplained cholestasis despite a thorough clinical work-up were examined for sequence variations in the coding regions of the ABCB4, ABCB11, ABCC2, ABCG5, ATP8B1, JAG1, NOTCH2, and UGT1A1 genes and the promoter region of UGT1A1 by massive parallel sequencing of DNA extracted from whole blood. Hepatologists and clinical geneticists evaluated the causal potential of genetic variants.

RESULTS

In 9/33 patients (27%), we identified genetic variants as a certain causal factor and in further 9/33 (27%) variants as a possible contributing factor. In most cases, a detailed family history was necessary to establish the importance of genetic variants. Genetic causes were identified in 6/13 women (46%) with intrahepatic cholestasis during pregnancy and persisting abnormal biochemistry after delivery.

CONCLUSIONS

Our study suggests that a small number of well-known genetic variants are involved in at least 27-54% of patients with unexplained cholestasis. An expanded panel will likely explain more cases. This motivates genetic testing of these patients. Genetic testing, however, cannot stand alone but should be combined with a clinical genetic work-up in collaboration between hepatologists and clinical geneticists.

Genome-wide association study of paclitaxel and carboplatin disposition in women with epithelial ovarian cancer

Identifying single nucleotide polymorphisms (SNPs) that influence chemotherapy disposition may help to personalize cancer treatment and limit toxicity. Genome-wide approaches are unbiased, compared with candidate gene studies, but usually require large cohorts. As most chemotherapy is given cyclically multiple blood sampling is required to adequately define drug disposition, limiting patient recruitment. We found that carboplatin and paclitaxel disposition are stable phenotypes in ovarian cancer patients and tested a genome-wide association study (GWAS) design to identify SNPs associated with chemotherapy disposition. We found highly significant SNPs in ABCC2, a known carboplatin transporter, associated with carboplatin clearance (asymptotic P = 5.2 × 10⁶, empirical P = 1.4 × 10⁻⁵), indicating biological plausibility. We also identified novel SNPs associated with paclitaxel disposition, including rs17130142 with genome-wide significance (asymptotic P = 2.0 × 10⁻⁹, empirical P = 1.3 × 10⁻⁷). Although requiring further validation, our work demonstrated that GWAS of chemotherapeutic drug disposition can be effective, even in relatively small cohorts, and can be adopted in drug development and treatment programs.

Pharmacogenetic Analysis of the Model-Based Pharmacokinetics of Five Anti-HIV Drugs: How Does This Influence the Effect of Aging?

Analysis of aging and pharmacogenetics (PGx) on antiretroviral pharmacokinetics (PKs) could inform precision dosing for older human HIV‐infected patients. Seventy‐four participants receiving either atazanavir/ritonavir (ATV/RTV) or efavirenz (EFV) with tenofovir/emtricitabine (TFV/FTC) provided PK and PGx information. Aging‐PGx‐PK association and interaction analyses were conducted using one‐way analysis of variance (ANOVA), multiple linear regression, and Random Forest ensemble methods. Our analyses associated unbound ATV disposition with multidrug resistance protein (MRP)4, RTV with P‐glycoprotein (P‐gp), and EFV with cytochrome P450 (CYP)2B6 and MRP4 genetic variants. The clearance and cellular distribution of TFV were associated with P‐gp, MRP2, and concentrative nucleoside transporters (CNTs), and FTC parameters were associated with organic cation transporters (OCTs) and MRP2 genetic variants. Notably, p16^INK4a expression, a cellular aging marker, predicted EFV and FTC PK when genetic factors were adjusted. Both age and p16^INK4a expression interacted with PGx on ATV and TFV disposition, implying potential dose adjustment based on aging may depend on genetic background.

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.

MRP2/ABCC2 C1515Y polymorphism modulates exposure to lumefantrine during artemether-lumefantrine antimalarial therapy

AIM

To investigate the potential involvement of the hepatic ATP-binding cassette transporters MRP2 and MDR1 in the disposition of lumefantrine (LUM) among patients with uncomplicated Plasmodium falciparum malaria.

MATERIALS & METHODS

The tag SNPs MDR1/ABCB1 C3435T and MRP2/ABCC2 C1515Y were determined in two artemether-LUM clinical trials, including a pharmacokinetic/pharmacodynamic study focused on the treatment phase (72 h), and an efficacy trial where day 7 (D7) LUM levels were measured.

RESULTS

The 1515YY genotype was significantly associated with higher (p < 0.01) LUM D7 concentrations (median 1.42 μM), compared with 0.77 μM for 1515CY and 0.59 μM for 1515CC. No significant influence of the MDR1/ABCB1 C3435T was found.

CONCLUSION

LUM body disposition may be influenced by MRP2/ABCC2 genotype.

Evaluating the association of single-nucleotide polymorphisms with tenofovir exposure in a diverse prospective cohort of women living with HIV

Higher exposure to tenofovir (TFV) increases the risk for kidney function decline, but the impact of genetic factors on TFV exposure is largely unknown. We investigated whether single-nucleotide polymorphisms (SNPs, n=211) in 12 genes are potentially involved in TFV exposure. Participants (n=91) from the Women's Interagency HIV Study, underwent a 24 h intensive pharmacokinetic sampling of TFV after witnessed dose and TFV area under the time-concentration curves (AUCs) were calculated for each participant. SNPs were assayed using a combination of array genotyping and Sanger sequencing. Linear regression models were applied to logarithmically transformed AUC. Those SNPs that met an a priori threshold of P<0.001 were considered statistically associated with TFV AUC. ABCG2 SNP rs2231142 was associated with TFV AUC with rare allele carriers displaying 1.51-fold increase in TFV AUC (95% confidence interval: 1.26, 1.81; P=1.7 × 10^-5). We present evidence of a moderately strong effect of the rs2231142 SNP in ABCG2 on a 24 h TFV AUC.

Candidate Gene Association Studies of Anthracycline-induced Cardiotoxicity: A Systematic Review and Meta-analysis

Anthracyclines play an important role in the management of patients with cancer but the development of anthracycline-induced cardiotoxicity (ACT) remains a significant concern for most clinicians. Recently, genetic approach has been used to identify patients at increased risk of ACT. This systematic review assessed the association between genomic markers and ACT. A systematic literature search was performed in Medline, PubMed, Cochrane Central Register of Controlled Studies, CINAHL Plus, AMED, EMBASE and HuGE Navigator from inception until May 2016. Twenty-eight studies examining the association of genetic variants and ACT were identified. These studies examined 84 different genes and 147 single nucleotide polymorphisms. Meta-analyses showed 3 risk variants significantly increased the risk for ACT; namely ABCC2 rs8187710 (pooled odds ratio: 2.20; 95% CI: 1.36-3.54), CYBA rs4673 (1.55; 1.05-2.30) and RAC2 rs13058338 (1.79; 1.27-2.52). The current evidence remains unclear on the potential role of pharmacogenomic screening prior to anthracycline therapy. Further research is needed to improve the diagnostic and prognostic role in predicting ACT.

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.

Impact of ABCB1 1236C > T-2677G > T-3435C > T polymorphisms on the anti-proliferative activity of imatinib, nilotinib, dasatinib and ponatinib

Overexpression of ABCB1 (also called P-glycoprotein) confers resistance to multiple anticancer drugs, including tyrosine kinase inhibitors (TKIs). Several ABCB1 single nucleotide polymorphisms affect the transporter activity. The most common ABCB1 variants are 1236C > T, 2677G > T, 3435C > T and have been associated with clinical response to imatinib in chronic myelogenous leukaemia (CML) in some studies. We evaluated the impact of these polymorphisms on the anti-proliferative effect and the intracellular accumulation of TKIs (imatinib, nilotinib, dasatinib and ponatinib) in transfected HEK293 and K562 cells. ABCB1 overexpression increased the resistance of cells to doxorubicin, vinblastine and TKIs. Imatinib anti-proliferative effect and accumulation were decreased to a larger extent in cells expressing the ABCB1 wild-type protein compared with the 1236T-2677T-3435T variant relatively to control cells. By contrast, ABCB1 polymorphisms influenced the activity of nilotinib, dasatinib and ponatinib to a much lesser extent. In conclusion, our data suggest that wild-type ABCB1 exports imatinib more efficiently than the 1236T-2677T-3435T variant protein, providing a molecular basis for the reported association between ABCB1 polymorphisms and the response to imatinib in CML. Our results also point to a weaker impact of ABCB1 polymorphisms on the activity of nilotinib, dasatinib and ponatinib.

ABCC2 polymorphisms and survival in the Princess Margaret cohort study and the NCIC clinical trials group BR.24 trial of platinum-treated advanced stage non-small cell lung cancer patients

BACKGROUND

The drug transporter ABCC2 is upregulated in non-small cell lung cancer (NSCLC) and implicated in platinum resistance. We evaluated the association between germline polymorphisms in the ABCC2 gene and survival outcomes of platinum-treated advanced NSCLC patients.

MATERIAL AND METHODS

Ten candidate and tagging germline polymorphisms in the ABCC2 gene were genotyped in a discovery cohort of 170 platinum-treated stage IV NSCLC patients from the Princess Margaret Cancer Centre. Associations with overall survival were assessed using multivariate Cox proportional hazard models adjusted for prognostic variables. To validate our results, we analyzed the association of the two top polymorphisms in the ABCC2 gene on survival outcomes of 219 stage IIIB-IV NSCLC patients enrolled on the NCIC Clinical Trials Group BR.24 clinical trial.

RESULTS

Only one polymorphism was validated across both cohorts for an association with overall survival: the A allele of the ABCC2 polymorphism, rs8187710 (4544G>A), was associated with adverse overall survival (adjusted hazard ratio [aHR] 2.22; 95% CI: 1.2-4.0; p=0.009) among our stage IV NSCLC patients. A significant association with overall survival (aHR 1.73; 95% CI: 1.0-2.9; p=0.036) was observed for the same ABCC2 polymorphism in the BR.24 validation cohort. No other ABCC2 polymorphisms were associated with outcome.

CONCLUSION

The ABCC2 polymorphism, rs8187710 (4544G>A), is associated with overall survival in platinum-treated advanced NSCLC patients. Additional studies are needed to evaluate the predictive versus prognostic nature of this relationship, and to explore the functional effect of this polymorphism on the pharmacokinetics of platinum drugs.

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.

A pharmacogenetic candidate gene study of tenofovir-associated Fanconi syndrome

BACKGROUND

Tenofovir disoproxil fumarate (TDF) is a widely used antiretroviral agent with favorable efficacy, safety, and tolerability profiles. However, renal adverse events, including the rare Fanconi syndrome (FS), may occur in a small subset of patients treated for HIV infections.

OBJECTIVES

The aim of this study was to identify genetic variants that may be associated with TDF-associated FS (TDF-FS).

METHODS

DNA samples collected from 19 cases with TDF-FS and 36 matched controls were sequenced, and genetic association studies were conducted on eight candidate genes: ATP-binding cassette (ABC) transporters ABCC2 (MRP2) and ABCC4 (MRP4), solute carrier family members SLC22A6 (OAT1) and SLC22A8 (OAT3), adenylate kinases 2 (AK2) and 4 (AK4), chloride transporter CIC-5 CLCN5, and Lowe syndrome protein OCRL. The functional effects of a single nucleotide polymorphism (SNP) predicted to alter the transport of tenofovir were then investigated in cells expressing an identified variant of ABCC4.

RESULTS

The case group showed a trend toward a higher proportion of rare alleles. Six SNPs in ABCC2 (three SNPs), ABCC4 (one SNP), and OCRL (two SNPs) were associated with TDF-FS case status; however, this association did not remain significant after correction for multiple testing. Six SNPs, present in OCRL (four SNPs) and ABCC2 (two SNPs), were significantly associated with increased serum creatinine levels in the cases, and this association remained significant after multiple test correction (P < 2 × 10). One synonymous SNP in ABCC2 (rs8187707, P = 2.10 × 10, β = -73.3 ml/min/1.73 m(2)) was also significantly associated with the decreased estimated glomerular filtration rate of creatinine among cases. However, these results were driven by rare SNPs present in a small number of severely affected cases. Finally, a previously uncharacterized, nonsynonymous SNP, rs11568694, that was predicted to alter MRP4 function had no significant effect on tenofovir cellular accumulation in vitro.

CONCLUSION

Although no single predictive genetic marker for the development of TDF-FS was identified, the findings from our study suggest that rare variants in multiple genes involved in the renal handling of tenofovir, and/or renal cell homeostasis, may be associated with increased susceptibility to TDF-FS.

Population pharmacokinetic/pharmacogenetic model of lopinavir/ritonavir in HIV-infected patients

AIM

This study aims to develop a population pharmacokinetic/pharmacogenetic model for lopinavir/ritonavir (LPV/r) in European HIV-infected patients.

MATERIALS & METHODS

A total of 693 LPV/r plasma concentrations were assessed and 15 single-nucleotide polymorphisms were genotyped. The population pharmacokinetic/pharmacogenetic model was created using a nonlinear mixed-effect approach (NONMEM^® v.7.2.0., ICON Development Solutions, Dublin, Ireland).

RESULTS

Covariates significantly related to LPV/r apparent clearance (CL/F) were ritonavir trough concentration (RTC), BMI, high-density lipoprotein cholesterol (HDL-C) and certain single-nucleotide polymorphisms in genes encoding for metabolizing enzymes, which are representable as follows: CL/F = (0.216BMI + 0.0125HDL-C) × 0.713^RTC × 1.26^{rs28371764[C/T]} × 0.528^{rs6945984[C/C]} × 0.302 ^{CYP3A4[1461insA/del]} Conclusion: The LPV/r standard dose appears to be appropriate for the rs28371764[C/T] genotype. However, lower doses should be recommended for the rs6945984[C/C] and CYP3A4[1461insA/del] genotypes and even for those patients without any of these variants, as the standard dose seems to be higher than that which is required in order to achieve therapeutic levels.

Antiretrovirals and the kidney in current clinical practice: renal pharmacokinetics, alterations of renal function and renal toxicity

Assessment of renal function in HIV-positive patients is of increasing importance in the context of ageing and associated comorbidities. Exposure to nephrotoxic medications is widespread, and several commonly used antiretroviral drugs have nephrotoxic potential. Moreover, specific antiretrovirals inhibit renal tubular transporters resulting in the potential for drug-drug interactions as well as increases in serum creatinine concentrations, which affect estimates of glomerular filtration rate in the absence of changes in actual glomerular filtration rate. This review explores the effects of antiretroviral therapy on the kidney and offers an understanding of mechanisms that lead to apparent and real changes in renal function.

ABCB1 1199G>A genetic polymorphism (Rs2229109) influences the intracellular accumulation of tacrolimus in HEK293 and K562 recombinant cell lines

OBJECTIVE

ATP-binding cassette, subfamily B, member 1 (ABCB1) transporter, or P-glycoprotein, is an efflux protein implicated in the absorption and the distribution of various compounds, including tacrolimus and cyclosporine A. In vivo studies suggest an association between the ABCB1 1199G>A single nucleotide polymorphism (SNP) and tacrolimus intracellular accumulation. The aim of the present experimental study was to clarify in vitro the impact of the coding ABCB1 1199G>A SNP on ABCB1 transport activity towards both immunosuppressive drugs.

METHOD

Two recombinant cell lines, i.e. Human Embryonic Kidney (HEK293) and Human Myelogenous Leukemia (K562) cells, overexpressing ABCB1 carrying either the wild-type allele (1199G) or its mutated counterpart (1199A), were generated. The impact of the 1199G>A SNP on ABCB1 activity towards rhodamine (Rh123), doxorubicin, vinblastine, tacrolimus and cyclosporine A was assessed by accumulation, cytotoxicity and/or kinetic experiments.

RESULTS

Tacrolimus accumulation was strongly decreased in cells overexpressing the wild-type protein (1199G) compared to control cells, confirming the ability of ABCB1 to transport tacrolimus. By contrast, overexpression of the variant protein (1199A) had nearly no effect on tacrolimus intracellular accumulation whatever the model used and the concentration tested. Unlike tacrolimus, our results also indicate that cyclosporine A, Rh123 and doxorubicin are transported in a similar extent by the wild-type and variant ABCB1 proteins while the variant protein seems to be more efficient for the transport of vinblastine.

CONCLUSION

ABCB1 encoded by the 1199G wild-type allele transports more efficiently tacrolimus in comparison to the 1199A variant protein. This observation indicates that the amino-acid substitution (Ser400Asn) encoded by the 1199A allele drastically decreases the ability of ABCB1 to drive the efflux of tacrolimus in a substrate-specific manner, in agreement with our previously published clinical data. Our study emphasizes the importance of the ABCB1 1199G>A polymorphism for ABCB1 activity and its potential to explain differences in drug response.

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.

Irreversible hepatotoxicity after administration of trabectedin to a pleiomorphic sarcoma patient with a rare ABCC2 polymorphism: a case report

We describe here the case of a 60-year old male patient treated for an extensive local progression of a pleiomorphic sarcoma on the right tibial crest with second-line trabectedin. Two cycles were administrated before a major liver toxicity was retrieved, with both cytolytic and cholestatic hepatitis quickly associated with irreversible jaundice. The radiological, histological, chemistry and pharmacogenetic investigations led us to diagnose chronic hepatobiliary toxicity with portal fibrosis, cholangiolitis damages and chronic hepatopathy. The patient had a deficient variant genotype of ABCC2 (c.-24TT, c.4488CT and c.4544GA), which has been suggested to play a role in excretion of toxic metabolites of trabectedin. This case report is, to our knowledge, the first description of trabectedin‘s irreversible liver toxicity in a human patient. Supported by a thorough review of the literature, this hepatitis is thought to have resulted from a multihit process involving genetic variants of ABC proteins and comedication.