Imatinib disposition and ABCB1 (MDR1, P-glycoprotein) genotype

The aim of this study was to explore the impact of individual variation in drug elimination on imatinib disposition. Twenty-two patients with gastrointestinal stromal tumor or chronic myeloid leukemia initially received imatinib 600 mg daily with dosage subsequently toxicity adjusted. Pharmacokinetic parameters on day 1 and at steady-state were compared with elimination phenotype and single-nucleotide polymorphisms of CYP3A5 and ABCB1. A fivefold variation in estimated imatinib clearance (CL/F) was present on day 1 and mean CL/F had fallen by 26% at steady state. This reduction in imatinib CL/F was associated with ABCB1 genotype, being least apparent in thymidine homozygotes at the 1236T>C, 2677G>T/A and 3435C>T loci. Toxicity-related dose reduction also tended to be less common in these individuals. ABCB1 genotype was associated with steady-state CL/F due to an apparent genotype-specific influence of imatinib on elimination. Further evaluation of ABCB1 genotype and imatinib dosage is warranted.     

Hepatic technetium Tc 99m-labeled sestamibi elimination rate and ABCB1 (MDR1) genotype as indicators of ABCB1 (P-glycoprotein) activity in patients with cancer

BACKGROUND AND OBJECTIVE: The adenosine triphosphate-binding cassette transporter ABCB1 (P-glycoprotein) mediates terminal excretion of many chemotherapeutic agents, and variable ABCB1 activity may be an important contributor to interpatient variability in the clearance of chemotherapeutic agents. Our objective was to determine the elimination constant (kH) for hepatic elimination of technetium Tc 99m-labeled sestamibi (99mTc-MIBI) in patients with cancer and to compare this putative indicator of ABCB1 phenotype with clinical features and common ABCB1 genetic variants. METHODS: 99mTc-MIBI kH was determined from the time-dependent elimination profile of 99mTc-MIBI over a 90-minute hepatic scanning period in 66 patients with cancer. Single nucleotide polymorphisms (SNPs) in ABCB1 exons 12 (C1236T), 21 (G2677T/A), and 26 (C3435T) were documented by polymerase chain reaction-restriction fragment length polymorphism analysis. RESULTS: There was a 12-fold variation in 99mTc-MIBI kH across the cohort, which was not correlated with sex, age, conventional liver function test results, previous chemotherapy treatment, or history of liver metastasis. Mean 99mTc-MIBI kH was significantly reduced in patients with SNPs in exons 21 and 26 such that mean 99mTc-MIBI kH was 1.90 times (95% confidence interval, 1.14-2.66; P = .02) and 2.21 times (95% confidence interval, 1.47-2.97; P < .01) higher in subjects homozygous for the wild-type alleles than in those homozygous for these SNPs, respectively. CONCLUSION: Hepatic elimination of 99mTc-MIBI is a potential in vivo probe of hepatic ABCB1 activity that is significantly associated with the presence of common SNPs in ABCB1. 99mTc-MIBI hepatic scanning may provide a useful pretreatment indicator of ABCB1-mediated drug clearance in cancer patients.     

Impact of P-glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2) on the brain distribution of a novel BRAF inhibitor: vemurafenib (PLX4032)

Vemurafenib [N-(3-{[5-(4-chlorophenyl)-1H-pyrrolo[2,3-b]pyridin-3-yl]carbonyl}-2,4-difluorophenyl)propane-1-sulfonamide(PLX4032)] is a novel small-molecule BRAF inhibitor, recently approved by the Food and Drug Administration for the treatment of patients with metastatic melanoma with a BRAF(V600E) mutation. The objective of this study was to investigate the role of P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) in the distribution of vemurafenib to the central nervous system. In vitro studies conducted in transfected Madin-Darby canine kidney II cells show that the intracellular accumulation of vemurafenib is significantly restricted because of active efflux by P-gp and BCRP. Bidirectional flux studies indicated greater transport in the basolateral-to-apical direction than the apical-to-basolateral direction because of active efflux by P-gp and BCRP. The selective P-gp and BCRP inhibitors zosuquidar and (3S,6S,12aS)-1,2,3,4,6,7,12,12a-octahydro-9-methoxy-6-(2-methylpropyl)-1,4-dioxopyrazino(1',2':1,6)pyrido(3,4-b)indole-3-propanoic acid-1,1-dimethylethyl ester (Ko143) were able to restore the intracellular accumulation and bidirectional net flux of vemurafenib. The in vivo studies revealed that the brain distribution coefficient (area under the concentration time profile of brain/area under the concentration time profile of plasma) of vemurafenib was 0.004 in wild-type mice. The steady-state brain-to-plasma ratio of vemurafenib was 0.035 ± 0.009 in Mdr1a/b(-/-) mice, 0.009 ± 0.006 in Bcrp1(-/-) mice, and 1.00 ± 0.19 in Mdr1a/b(-/-)Bcrp1(-/-) mice compared with 0.012 ± 0.004 in wild-type mice. These data indicate that the brain distribution of vemurafenib is severely restricted at the blood-brain barrier because of active efflux by both P-gp and BCRP. This finding has important clinical significance given the ongoing trials examining the efficacy of vemurafenib in brain metastases of melanoma.     

P-glycoprotein (ABCB1) transports the primary active tamoxifen metabolites endoxifen and 4-hydroxytamoxifen and restricts their brain penetration

P-glycoprotein (P-gp, ABCB1) is a highly efficient drug efflux pump expressed in brain, liver, and small intestine, but also in tumor cells, that affects pharmacokinetics and confers therapy resistance for many anticancer drugs. The aim of this study was to investigate the impact of P-gp on tamoxifen and its primary active metabolites, 4-hydroxytamoxifen, N-desmethyltamoxifen, and endoxifen. We used in vitro transport assays and Abcb1a/1b(-/-) mice to investigate the impact of P-gp on the oral availability and brain penetration of tamoxifen and its metabolites. Systemic exposure of tamoxifen and its metabolites after oral administration of tamoxifen (50 mg/kg) was not changed in the absence of P-gp. However, brain accumulation of tamoxifen, 4-hydroxytamoxifen, and N-desmethyltamoxifen were modestly, but significantly (1.5- to 2-fold), increased. Endoxifen, however, displayed a 9-fold higher brain penetration at 4 h after administration. Endoxifen was transported by P-gp in vitro. Upon direct oral administration of endoxifen (20 mg/kg), systemic exposure was slightly decreased in Abcb1a/1b(-/-) mice, but brain accumulation of endoxifen was dramatically increased (up to 23-fold at 4 h after administration). Shortly after high-dose intravenous administration (5 or 20 mg/kg), endoxifen brain accumulation was increased only 2-fold in Abcb1a/1b(-/-) mice compared with wild-type mice, suggesting a partial saturation of P-gp at the blood-brain barrier. Endoxifen, the clinically most relevant metabolite of tamoxifen, is a P-gp substrate in vitro and in vivo, where P-gp limits its brain penetration. P-gp might thus be relevant for tamoxifen/endoxifen resistance of P-gp-positive breast cancer and tumors positioned behind a functional blood-brain barrier.     

P-glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2) restrict brain accumulation of the active sunitinib metabolite N-desethyl sunitinib

N-desethyl sunitinib is a major and pharmacologically active metabolite of the tyrosine kinase inhibitor and anticancer drug sunitinib. Because the combination of N-desethyl sunitinib and sunitinib represents total active drug exposure, we investigated the impact of several multidrug efflux transporters on plasma pharmacokinetics and brain accumulation of N-desethyl sunitinib after sunitinib administration to wild-type and transporter knockout mice. In vitro, N-desethyl sunitinib was a good transport substrate of human ABCB1 and ABCG2 and murine Abcg2, but not ABCC2 or Abcc2. At 5 μM, ABCB1 and ABCG2 contributed almost equally to N-desethyl sunitinib transport. In vivo, the systemic exposure of N-desethyl sunitinib after oral dosing of sunitinib malate (10 mg/kg) was unchanged when Abcb1 and/or Abcg2 were absent. However, brain accumulation of N-desethyl sunitinib was markedly increased (13.7-fold) in Abcb1a/1b(-/-)/Abcg2(-/-) mice, but not in Abcb1a/1b(-/-) or Abcg2(-/-) mice. In the absence of the ABCB1 and ABCG2 inhibitor elacridar, brain concentrations of N-desethyl sunitinib were detectable only in Abcb1a/1b(-/-)/Abcg2(-/-) mice after sunitinib administration. Combined elacridar plus N-desethyl sunitinib treatment increased N-desethyl sunitinib plasma and brain exposures, but not brain-to-plasma ratios in wild-type mice. In conclusion, brain accumulation of N-desethyl sunitinib is effectively restricted by both Abcb1 and Abcg2. The effect of elacridar treatment in improving brain accumulation of N-desethyl sunitinib in wild-type mice was limited compared with its effect on sunitinib brain accumulation.     

Ixabepilone, a novel microtubule-targeting agent for breast cancer, is a substrate for P-glycoprotein (P-gp/MDR1/ABCB1) but not breast cancer resistance protein (BCRP/ABCG2)

Ixabepilone is the first epothilone to be approved for clinical use. Current data suggest the epothilones have a role in treating taxane-resistant cancers and ixabepilone is unaffected by at least some of the mechanisms underlying chemoresistance. Here, we report a series of cytotoxicity and transport studies to assess the potential role of P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) in ixabepilone resistance. A significant decrease in ixabepilone-mediated cytotoxicity was observed in Madin-Darby canine kidney cells transfected with human multidrug resistance 1 (MDR1) comparative with the parental cells (IC(50) > 2000 nM versus 90 nM). Overexpression of P-gp also resulted in significantly decreased cell susceptibility to docetaxel, paclitaxel, and vinblastine. Bidirectional transport of ixabepilone across monolayers of porcine kidney-derived cells expressing human MDR1 showed a significantly increased efflux ratio relative to the parental cells. A BCRP-overexpressing cell line was developed by transfecting human embryonic kidney (HEK)-293 cells with BCRP cDNA and confirmed by immunoblotting and bodipy prazosin and mitoxantrone uptake. Neither P-gp nor multidrug resistance protein 2 was detected in the cells by corresponding polyclonal antibodies. This HEK-BCRP cell line demonstrated resistance to docetaxel, paclitaxel, vinblastine, and mitoxantrone, in comparison with the parental cell line (7.3, 4.3, 2.9, and 11.9 resistance factor, respectively). Transport inhibition by BCRP inhibitor fumitremorgin C and broad efflux inhibitor N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl]-phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide (GF120918) restored drug sensitivity. In contrast, ixabepilone was far less susceptible to BCRP-mediated resistance, resulting in a resistance factor of only 1.2-fold. In summary, these results suggest that P-gp could cause resistance to ixabepilone in tumors and affect the disposition of the drug, but it is unlikely that BCRP mediates any drug resistance to ixabepilone.     

Inhibition of ABCB1 (MDR1) and ABCB4 (MDR3) expression by small interfering RNA and reversal of paclitaxel resistance in human ovarian cancer cells

Ovarian cancer is currently the most lethal gynecologic malignancy in developed countries, and paclitaxel is a cornerstone in the treatment of this malignancy. Unfortunately, the efficacy of paclitaxel is limited by the development of drug resistance. Clinical paclitaxel resistance is often associated with ABCB1 (MDR1) overexpression, and in vitro paclitaxel resistance typically demonstrates overexpression of the ABCB1 gene. In this study, we demonstrate that paclitaxel-resistant cell lines overexpress both ABCB1 and ABCB4 (MDR3). To evaluate the role of these transporters in paclitaxel-resistant ovarian cancer cells, small interference RNAs (siRNAs) were used to target ABCB1 and ABCB4 RNA in the paclitaxel-resistant SKOV-3TR and OVCAR8TR ovarian cancer cell lines. Treatment of these lines with either chemically synthesized siRNAs or transfection with specific vectors that express targeted siRNAs demonstrated decreased mRNA and protein levels of ABCB1 or ABCB4. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays of siRNA-treated cells demonstrated 7- to 12.4-fold reduction of paclitaxel resistance in the lines treated with the synthesized siRNA of ABCB1 and 4.7- to 7.3-fold reduction of paclitaxel resistance in the cell lines transfected with siRNA of ABCB1 expressing vectors. ABCB4 siRNA-treated cell lines showed minor reduction in paclitaxel resistance. These results indicate that siRNA targeted to ABCB1 can sensitize paclitaxel-resistant ovarian cancer cells in vitro and suggest that siRNA treatment may represent a new approach for the treatment of ABCB1-mediated drug resistance.     

Tacrolimus pharmacokinetics and pharmacogenetics: influence of adenosine triphosphate-binding cassette B1 (ABCB1) and cytochrome (CYP) 3A polymorphisms

Tacrolimus, an immunosuppressant used after organ transplantation, has a narrow therapeutic range and its pharmacokinetic variability complicates its daily dose assessment. P-glycoprotein (P-gp), encoded by the adenosine triphosphate-binding cassette B1 (ABCB1) and the cytochrome (CYP) 3A4 and 3A5 enzymes appears to play a role in the tacrolimus metabolism. In the present study, two different renal transplant recipient groups were used to examine the influence of ABCB1 and CYP3A polymorphisms on the daily tacrolimus dose and several pharmacokinetic parameters. In total 63 Caucasian renal transplant recipients divided into 26 early [median (range) of the days since transplantation - 16 (3-74)] and 37 late [median (range) of the days since transplantation - 1465 (453-4128)] post-transplant recipients were genotyped for ABCB1 and CYP3A polymorphisms. The pharmacokinetic parameters of tacrolimus were determined for all renal transplant recipients and correlated with their corresponding genotypes. A significant difference in allele frequencies of the CYP3A4*1B (P = 0.028) and CYP3A5*1 (P = 0.022) alleles was observed between the early and late post-transplant recipient groups. Significantly higher dose-normalized trough levels (dnC(0)), dose-normalized area under the curve (dnAUC(0-12)), and dose-normalized maximum concentration (dnC(max)) were observed for carriers of the CYP3A5*3 variant allele in both renal transplant patient groups. Except for the daily tacrolimus dose (P = 0.025) no significant differences were observed for carriers of the CYP3A4*1B variant allele. Neither the individual ABCB1 polymorphisms nor the ABCB1 haplotypes were associated with any pharmacokinetic parameter. We noticed that patients carrying a CYP3A5*1 allele require a twofold higher tacrolimus dose compared with homozygous carriers of the CYP3A5*3 variant allele to maintain the target dnAUC(0-12). Therefore, genotyping for the CYP3A5*3 variant allele can contribute to a better and more individualized immunosuppressive therapy in transplant patients.     

Polymorphisms in human MDR1 (P-glycoprotein): recent advances and clinical relevance

Drug transporters are increasingly recognized to be important to drug disposition and response. P-glycoprotein, the encoded product of the human MDR1 (ABCB1) gene, is of particular clinical relevance in that this transporter has broad substrate specificity, including a variety of structurally divergent drugs in clinical use today. Moreover, expression of this efflux transporter in certain tissue compartments such as the gastrointestinal tract and brain capillary endothelial cells limits oral absorption and central nervous system entry of many drugs. Recently, a number of single-nucleotide polymorphisms (SNPs) in MDR1 have been identified. An increasing number of studies have also implicated certain commonly occurring SNPs in MDR1 in problems including altered drug levels and host susceptibility to diseases such as Parkinson's disease, inflammatory bowel disease, refractory seizures, and CD4 cell recovery during human immunodeficiency virus therapy. However, in many such cases, the reported effects of MDR1 SNPs have been inconsistent and, in some cases, conflicting. In this review SNPs in MDR1 in relation to population frequencies, drug levels, and phenotypes are outlined. In addition, issues relating to MDR1 haplotypes, environmental factors, and study design, as potential confounding factors of the observed MDR1 polymorphism effect in vivo, are also discussed.     

Bayes Library简介与诊断试验系统评价方法

本文介绍的诊断试验系统评价方法是在Bayes Library手册编写组提供的文本基础上写成。     

Immunophenotypic analysis of mast cells in mastocytosis: When and how to do it. Proposals of the Spanish Network on Mastocytosis (REMA)

BACKGROUND: One of the best characterized resistance mechanisms of leukemias is multidrug resistance (MDR) mediated by P-glycoprotein (Pgp) and multidrug-resistant related protein (MRP). In addition to Pgp and MRP, p53 mutation or inactivation might play a relevant role in therapeutic failure. Some studies have demonstrated that Pgp and MRP may be activated in association with overexpression of mutant or inactivated p53 protein. The aim of this study was to investigate the association between p53 expression and MDR functional phenotype analyzed by flow cytometry (FCM). METHODS: Rhodamine-123 assay analyzed by FCM was used to detect the MDR phenotype that was positive in 18 out of 41 (43.9%) cases of chronic myeloid leukemia (CML), 16 out of 28 (57.1%) chronic lymphoid leukemia (CLL) cases, 11 out of 28 (39.3%) acute myeloid leukemia (AML) cases, and four out of 22 (18.2%) acute lymphoid leukemia (ALL) cases. RESULTS: Variable levels of p53 expression were observed in leukemic cells: 12 out of 41 (29.2%) in CML, nine out of 28 (32.1%) in CLL, 15 out of 28 (53.6%) in AML, and eight out of 22 (36.4%) in ALL samples. CONCLUSIONS: In our study, no significant association between p53 expression and MDR functional phenotype was observed in ALL, CLL, and AML. On the other hand, a significant association (P = 0.0003) of the coexpression was observed in CML. The p53 overexpression was more frequently seen in the accelerated phase and the blastic phase of this disease. Our results suggest that an MDR functional phenotype could be associated with p53 mutation in the advanced stage of leukemias.     

Correction: Affinity binding of chicken apolipoprotein A1 to a novel flax orbitide (linusorb)

Correction for ‘Affinity binding of chicken apolipoprotein A1 to a novel flax orbitide (linusorb)’ by Pramodkumar D. Jadhav, et al., RSC Adv., 2018, 8, 17702–17709.

The authors regret the omission of the following conflict of interest statement.Dr Martin J. T. Reaney is the founder of, and has an equity interest in, Prairie Tide Diversified Inc. (PTD, Saskatoon, SK, Canada: previous company name is Prairie Tide Chemicals Inc.). Dr Youn Young Shim is a Market Consultant for PTD in Korea. The terms of this arrangement have been reviewed and approved by the University of Saskatchewan in accordance with its conflict of interest policies.The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Expression of P-glycoprotein in human placenta: relation to genetic polymorphism of the multidrug resistance (MDR)-1 gene

To evaluate whether mutations in the human multidrug resistance (MDR)-1 gene correlate with placental P-glycoprotein (PGP) expression, we sequenced the MDR-1 cDNA and measured PGP expression by Western blotting in 100 placentas obtained from Japanese women. Nine single nucleotide polymorphisms (SNPs) were observed with an allelic frequency of 0.005 to 0.420. Of these SNPs, G2677A (allelic frequency = 0.18) and G2677T (0.39) in exon 21 were associated with an amino acid conversion from Ala to Thr and to Ser, respectively. Sixty-one of 65 samples (93.8%), which had a C3435T allele, also had a mutant G2677(A,T) allele, suggesting an association between the two SNPs. Correlations of mutations with expression levels were observed; individuals having the G2677(A,T) and/or T-129C (p < 0.05) allele had less placental PGP. Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP)-based genotyping tests were developed for the detection of these SNPs. The PCR, in which genomic DNAs obtained from healthy subjects (n = 48) are used as samples, was successful. The frequency of mutations in placental cDNA was identical with that in genomic DNA. When genotype results were compared between Caucasians and Japanese, ethnic differences in the frequency of polymorphism in the MDR-1 gene were suspected. Although it remains to be determined whether these SNPs influence the pharmacokinetic and dynamic properties of clinically useful drugs that are substrates of PGP, the polymorphism of the MDR-1 gene presented here may provide useful information in in vivo study of these issues.