Breast Cancer Resistance Protein Function Research Articles

Breast Cancer Resistance Protein: Structure, Localization, Functions, Significance for Rational Pharmacotherapy

INTRODUCTION: Currently, investigation of efflux transport systems of an organism is an important scientific and practical task permitting to more deeply investigate the pharmacokinetics of medical drugs and to optimize pharmacotherapy of a number of diseases. The super family of ABC transporters plays a significant role in transport of biobiotics, the processes of absorption, distribution and excretion of medical drugs from an organism, in realization of undesired drug-drug interactions and development of pharmacoresistance. An important representative of this super family is breast cancer resistance protein (BCRP). AIM: Systematization of the data on BCRP structure, localization, functions, substrates and modulators of its activity. This literature review presents modern data on the molecular and spatial structure of BCRP, its localization in the cell, in organs and tissues. The data from studies of the functions of BCRP in an organism, of its role in the development of undesired drug-drug interactions at different stages of pharmacokinetics are summarized. An up-to-date list of medicinal drugs that are substrates and inhibitors of BCRP is given. Modern approaches to testing medical drugs for belonging to BCRP substrates or modulators of its activity are disclosed. CONCLUSION: The significance of BCRP consists in the existence of a wide range of drugs that are its substrates or modulators of its activity. Upon that, of increasing significance is the investigation both of new and long-known medicinal substances for their belonging to substrates, inducers or inhibitors of breast cancer resistance protein, in order to increase the effectiveness of pharmacotherapy and reduce the risk of undesired drug interactions. Search for non-drug substrates and modulators of BCRP activity permits to obtain new markers for conducting effective studies of safe pharmacokinetics both in vitro and in vivo.

Regulation of BCRP expression and sulfasalazine pharmacokinetics by the nuclear receptor REV-ERBα

BCRP (breast cancer resistance protein) is a crucial efflux transporter involved in the regulation of the pharmacokinetics and pharmacodynamics of a wide range of drugs. Herein, we aimed to investigate a potential role for the nuclear receptor REV-ERBα in the regulation of BCRP expression and sulfasalazine (a BCRP probe substrate) pharmacokinetics. Regulation of BCRP expression by REV-ERBα was assessed using Rev-erbα -/- mice and AML12 and CT26 cells. Pharmacokinetic analysis was performed with Rev-erbα -/- and wild-type mice after sulfasalazine administration. We found that the expression levels of BCRP mRNA and protein were downregulated in the liver and small intestine of Rev-erbα-dificient mice. In line with this, Rev-erbα ablation increased the systemic exposures of oral sulfasalazine. Positive regulation of BCRP expression and function by REV-ERBα was furtherly confirmed in AML12 and CT26 cells. Moreover, indirect regulation of Bcrp expression by REV-ERBα was potentially mediated by a negative transcription factor DEC2, which is a downstream target of REV-ERBα. In conclusion, REV-ERBα positively regulates BCRP expression in mice, thereby affecting sulfasalazine pharmacokinetics.

Quantitative Comparison of Breast Cancer Resistance Protein (BCRP/ABCG2) Expression and Function Between Maternal Blood-Brain Barrier and Placental Barrier in Mice at Different Gestational Ages

Breast cancer resistance protein (BCRP) is expressed by brain capillary endothelial cells and at the interface between two placental syncytiotrophoblast layers in rodents and serves to suppress drug distribution to the brain and the fetus. The purpose of the present study is to determine and compare the apparent impact of a single BCRP molecule on drug transfer between the maternal blood-brain barrier and placental barrier in pregnant mice at different gestation ages. BCRP protein was quantified by liquid chromatography-tandem mass spectrometry. Genistein or dantrolene was continuously administered to pregnant Bcrp−/− or wild-type (WT) mice, and the brain-to-plasma concentration ratio in the mother (Kp,brain) and the fetal-to-maternal ratio of plasma concentrations (Kp,fp) were determined. At gestational day 15.5 (GD15.5), the protein amount of BCRP at the murine placental barrier was estimated to be approximately three times higher than at the maternal blood-brain barrier, but the levels were approximately the same at GD17.5 due to the decline of placental BCRP expression during gestation. On the other hand, the values of Bcrp−/−/WT ratio of Kp,brain for genistein and dantrolene were 6.1 and 3.8, respectively, while the Kp,fp ratios were all less than 2.0. These results indicate that the apparent impact of a single placental BCRP molecule on the restriction of drug distribution is much less than that of a single brain BCRP molecule, probably because the function of placental BCRP is attenuated by bypass transfer through the connexin26 gap junctions between adjacent syncytiotrophoblast layers. The present study also found that the expression amount of BCRP protein at the human placental barrier formed by the monolayer of syncytiotrophoblasts was lower than that in mice, but this species difference appears to be functionally compensated by the murine-specific bypass route through gap junctions, at least in part.

Fetal Membranes Contribute to Drug Transport across the Feto-Maternal Interface Utilizing the Breast Cancer Resistance Protein (BCRP).

During pregnancy, the placenta is established as a primary organ for drug transport at the maternal-fetal interface. The fetal membranes (FM) also form an interface with maternal tissues; however, their role in drug transport has not been previously investigated. Knowledge of drug transport across this feto-maternal interface along with the placenta can improve new drug development and testing for use during pregnancy. We also hypothesize that extracellular vesicles (exosomes 30–160 nm) released from the FM and placental cells may also contain drug transport proteins and might impact drug trafficking across the feto-maternal interfaces. The objectives were to (1) localize the breast cancer resistance protein (BCRP) in human FM; (2) determine the drug transport function of BCRP in chorion trophoblast cells (CTCs) of the FM; and (3) investigate the presence of BCRP in FM cell-derived exosomes, as a paracrine modifier of the tissue environment for transport functions. The gene and protein expressions of ABCG2/BCRP in FMs were determined by quantitative real-time PCR (qRT-PCR) and western blotting (WB) and were localized by immunohistochemistry (IHC). The surface expression of BCRP in FM cells was determined by flow cytometry. The functional role of BCRP was assessed by an EFFLUX dye multidrug resistance assay. The presence of BCRP in exosomes derived from CTCs and BeWo cells was examined using ExoView®. Data derived from CTCs are compared with placental trophoblast cells (BeWo). BCRP is expressed and localized in the fetal membrane, primarily in the chorion trophoblast cell layer and scarcely in the amnion epithelial layer (AEC), and primarily localized on both AEC and CTC cell surfaces. Efflux assay data showed that FM cells have similar drug resistance activity as BeWo cells, suggesting that FM also have drug transportation capabilities. BeWo- and CTC-derived exosomes expressed limited BCRP protein on the surface, so it was predominantly contained in the exosomal lumen. As far as we are aware, this is the first study to report BCRP expression in fetal membrane cells and as cargo in fetal membrane-derived exosomes. We report that fetal membrane cells are capable of drug transportation. Based on these results, investigational drug trials should include the FM and its exosomes as possible drug transportation routes in pregnancy.

Magnolol and Honokiol Inhibited the Function and Expression of BCRP with Mechanism Exploration.

Breast cancer resistance protein (BCRP), one of the ATP-binding cassette (ABC) transporters, was associated with the multidrug resistance (MDR) of chemotherapy. Magnolol (MN) and honokiol (HK) are major bioactive polyphenols of Magnolia officinalis. This study investigated the effects of MN and HK on the function and expression of BCRP for the purpose of developing BCRP inhibitor to overcome MDR. Cell lines including MDCKII-BCRP and MDCKII-WT were used for evaluating the function and expression of BCRP. The results showed that MN (100–12.5 µM) and HK (100–12.5 µM) significantly decreased the function of BCRP by 80~12% and 67~14%, respectively. In addition, MN and HK were verified as substrates of BCRP. Furthermore, MN and HK reduced the protein expression of BCRP, and inhibited the phosphorylation of epidermal growth factor receptor (EGFR) and phosphatidylinositol 3-kinase (PI3K). In conclusion, both MN and HK decreased the function and expression of BCRP via EGFR/PI3K signaling pathway. Therefore, both compounds were promising candidates for reversing the MDR of chemotherapy.

Bisphenol A Inhibits the Transporter Function of the Blood-Brain Barrier by Directly Interacting with the ABC Transporter Breast Cancer Resistance Protein (BCRP).

The breast cancer resistance protein (BCRP) is an important efflux transporter in the blood-brain barrier (BBB), protecting the brain from a wide range of substances. In this study, we investigated if BCRP function is affected by bisphenol A (BPA), a high production volume chemical used in common consumer products, as well as by bisphenol F (BPF) and bisphenol S (BPS), which are used to substitute BPA. We employed a transwell-based in vitro cell model of iPSC-derived brain microvascular endothelial cells, where BCRP function was assessed by measuring the intracellular accumulation of its substrate Hoechst 33342. Additionally, we used in silico modelling to predict if the bisphenols could directly interact with BCRP. Our results showed that BPA significantly inhibits the transport function of BCRP. Additionally, BPA was predicted to bind to the cavity that is targeted by known BCRP inhibitors. Taken together, our findings demonstrate that BPA inhibits BCRP function in vitro, probably by direct interaction with the transporter. This effect might contribute to BPA’s known impact on neurodevelopment.

Identification of molecular switch regulating tyrosine phosphorylation of Intestinal breast cancer resistance protein (BCRP) mediated mucosal wound repair and barrier functions in obesity

Breast cancer resistance protein (BCRP) is a member of ATP-binding cassette (ABC) transporter proteins whose primary function is to efflux substrates bound to the plasma membrane. In our previous study, we reported that obese individuals have compromised intestinal BCRP functions and that diet-induced obese mice recapitulate these outcomes. Furthermore we demonstrated that the compromised BCRP functions during obesity are because of loss of Janus kinase 3 (JAK3)-mediated tyrosine phosphorylation of BCRP. Janus kinase 3 (Jak3) is a non receptor tyrosine kinase expressed in both hematopoietic and nonhematopoietic cells. Although mutations that abrogate Jak3 functions cause different immunological disorders, its constitutive activation leads to various types of inflammatory diseases. Mechanistically, JAK3-mediated phosphorylation of BCRP promoted its interactions with membrane-localized β-catenin essential not only for BCRP expression and surface localization, but also for the maintenance of BCRP-mediated intestinal drug efflux and barrier functions. In the present study, we demonstrate that, BCRP interacted with Jak3, thereby facilitating intestinal barrier function and drug efflux function. Furthermore, we characterized the structural determinants that regulate the interactions between BCRP and Jak3 and pBCRP and β-catenin. Functional reconstitution of kinase activity by recombinant full-length (wt) Jak3 using Jak3-wt or BCRP-wt as substrate showed that Jak3 autophosphorylation was the rate-limiting step during interactions between Jak3 and drug transporter protein. Determination of kinetic parameters showed that phosphorylated (P) Jak3-wt binds to p-BCRP-wt with a dissociation constant K(d)) of 15 nM and a Hill's coefficient of 2.5. Pairwise binding between Jak3 mutants and P-BCRP-wt showed that the FERM domain of Jak3 was sufficient for binding to p-BCRP with a K(d) of 20.0 nM whereas NBD domain of BCRP was contributing more towards it's binding to pJak3 with a K(d) value of 30 nM. Furthermore, Phosphorylated form of F2-subdomain of FERM was responsible for binding of FERM with BCRP. On the other hand NBD domain of BCRP was sufficient to bind to pβ-catenin with K(d)of 22nM. Physiologically, Jak3-mediated phosphorylation of BCRP increased IL2-mediated mucosal wound repair and also facilitated epithelial barrier functions. Our results also show that both BCRP and β-catenin bind to FERM domain of Jak3 non-competitively. We demonstrate that mutation (Y-F) in the tyrosine residue at 123 position of NBD domain of BCRP prevented Jak3 and β-catenin significantly from binding to BCRP. Results from cell culture: Thus, we demonstrate the molecular mechanism of interactions between Jak3 and BCRP and pBCRP and further we are investigating to determine the molecular mechanism involved in BCRP phosphorylation mediated mucosal wound repair.

Bile duct ligation causes opposite impacts on the expression and function of BCRP and P-gp in rat brain partly via affecting membrane expression of ezrin/radixin/moesin proteins.

Breast cancer resistance protein (BCRP) and P-glycoprotein (P-gp) are co-located at blood-brain barrier (BBB) cells, preventing their substrates from entering brain. Accumulating evidence demonstrates that liver failure impairs P-gp and BCRP expression and function in the brain. In the current study, we investigated how liver failure influenced the expression and function of brain BCRP and P-gp in rats subjected to bile duct ligation (BDL). The function of BCRP, P-gp and BBB integrity was assessed using distribution of prazosin, rhodamine 123 and fluorescein, respectively. We showed that BDL significantly decreased BCRP function, but increased P-gp function without affecting BBB integrity. Furthermore, we found that BDL significantly downregulated the expression of membrane BCRP and upregulated the expression of membrane P-gp protein in the cortex and hippocampus. In human cerebral microvascular endothelial cells, NH4Cl plus unconjugated bilirubin significantly decreased BCRP function and expression of membrane BCRP protein, but upregulated P-gp function and expression of membrane P-gp protein. The decreased expression of membrane BCRP protein was linked to the decreased expression of membrane radixin protein, while the increased expression of membrane P-gp protein was related to the increased location of membrane ezrin protein. Silencing ezrin impaired membrane location of P-gp, whereas silencing radixin impaired membrane location of BCRP protein. BDL rats showed the increased expression of membrane ezrin protein and decreased expression of membrane radixin protein in the brain. We conclude that BDL causes opposite effects on the expression and function of brain BCRP and P-gp, attributing to the altered expression of membrane radixin and ezrin protein, respectively, due to hyperbilirubinemia and hyperammonemia.

Functional Alterations of Multidrug Resistance-Associated Proteins 2 and 5, and Breast Cancer Resistance Protein upon Snail-Induced Epithelial-Mesenchymal Transition in HCC827 Cells.

Our previous report indicated that Snail-induced epithelial-mesenchymal transition (EMT) enhanced P-glycoprotein (P-gp) function and drug resistance to P-gp substrate anticancer drug in a human non-small cell lung cancer (NSCLC) cell line, HCC827. Our objective is to evaluate the changes in the mRNA and protein expression levels and the functions of multidrug resistance-associated protein (MRP) 2, MRP5 and breast cancer resistance protein (BCRP). Snail-expressing HCC827 cells showed increased mRNA levels of Snail and a mesenchymal marker vimentin, and decreased mRNA levels of an epithelial marker E-cadherin after transduction, indicating that Snail had induced EMT consistent with our previous reports. The mRNA level of MRP2 was significantly decreased, while that of MRP5 remained unchanged, in Snail-expressing cells. The expression levels of MRP2 and MRP5 proteins in whole-cell homogenate were unchanged in Snail-expressing cells, but MRP5 protein showed significantly increased membrane localization. Snail-transduction increased the efflux transport of 5-(and-6)-carboxy-2',7'-dichlorofluorescein (CDCF), a substrate of MRP2, 3 and 5. This increase was blocked by MK571, which inhibits MRP1, 2, and 5. Toxicity of cisplatin, a substrate of MRP2 and 5, was significantly decreased in Snail-expressing cells. BCRP mRNA and protein levels were both decreased in Snail-expressing cells, which showed an increase in the intracellular accumulation of 7-ethyl-10-hydroxycamptothecin (SN-38), a BCRP substrate, resulting in reduced viability. These results suggested that MRP5 function appears to be increased via an increase in membrane localization, whereas the BCRP function is decreased via a decrease in the expression level in HCC827 cells with Snail-induced EMT.

Interactions of the major effective components in Shengmai formula with breast cancer resistance protein at the cellular and vesicular levels

Shengmai Formula (SMF) is one of the traditional Chinese medicine representative formulas and is widely used for the treatment of cardio- and cerebrovascular disease. Previous studies demonstrated that the major effective ingredients in SMF can interact with each other based on some uptake transporters. However, the role of the efflux transporter breast cancer resistance protein (BCRP) in these interactions involving SMF remains unclear. The purpose of this study was to investigate the interactions of the major active components of SMF with BCRP and the compatibility mechanism of these complex components in SMF based on BCRP. We selected 4 main fractions, including ginseng total saponins (GTS), ophiopogon total saponins (OTS), ophiopogon total flavonoids (OTF), and fructus schisandrae total lignans (STL), and 12 bioactive components, including ginsenosides Re, Rd, Rb1, and Rg1, ophiopogonins D and Dˊ, methylophiopogonanones A and B, schizandrins A and B, and schizandrols A and B to explore the interactions of SMF with BCRP in LLC-PK1 and LLC-PK1/BCRP cells and BCRP membrane vesicles. The results showed that ginsenosides Re and Rg1, methylophiopogonanone B, and schizandrin A can be transported by BCRP into LLC-PK1/BCRP cells. Schisandrol B exhibited a markedly inhibitory effect on the transport function of BCRP and can significantly inhibit the uptake of methylophiopogonanone B and schizandrin A into LLC-PK1/BCRP cells. In “Inside-Out” BCRP membrane vesicles, BCRP mediated the transport of ginsenosides Re and Rg1, methylophiopogonanone B, and schizandrin A, with Km values of 111.9 ± 31.26 μM, 82.01 ± 16.72 μM, 57.06 ± 8.789 μM, and 37.19 ± 6.512 μM, respectively. GTS, STL, ginsenosides Rd and Rb1, and schisandrol B were potent inhibitors of BCRP and showed different degrees of inhibition on the transport of ginsenosides Re and Rg1, methylophiopogonanone B, and schizandrin A via BCRP. In conclusion, GTS, STL, ginsenosides Rd and Rb1, and schizandrol B are potential inhibitors of BCRP. Ginsenosides Re and Rg1, methylophiopogonanone B, and schizandrin A are potential substrates of BCRP, and their transport, which is mediated by BCRP, may be inhibited by potential inhibitors in SMF. There are potential interactions of these main effective components of SMF at the cellular and vesicular levels that are mediated by BCRP. The interplay of these bioactive components based on BCRP may be an important compatibility mechanism in SMF.

Short-chain fatty acids exert opposite effects on the expression and function of p-glycoprotein and breast cancer resistance protein in rat intestine.

P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) are involved in intestinal barrier. Short-chain fatty acids (SCFAs) play important roles in maintaining intestinal barrier. In this study we explored how SCFAs affected the expression and function of intestinal P-gp and BCRP in rats. Rats received 150 mM acetate, propionate or butyrate in drinking water for 4 weeks. In SCFA-treated rats, the expression and function of intestinal P-gp were decreased, but those of intestinal BCRP were increased; intestinal p-p65 was also decreased, which was positively related to P-gp protein expression. Among the three SCFAs tested, butyrate exhibited the strongest induction or inhibitory effect, followed by propionate and acetate. Similar results were observed in mouse primary enterocytes and Caco-2 cells treated with acetate (5 mM), propionate (2 mM), or butyrate (1 mM). In Caco-2 cells, addition of butyrate, vorinostat, and valproate (two classic HDAC inhibitors), Bay117082 (selective inhibitor of NF-κB activation) or NF-κB p65 silencing significantly decreased the expression of P-gp and the level of phosphorylated p65 (p-p65). Furthermore, butyrate attenuated the expression of P-gp and p-p65 induced by TNF-α (NF-κB activator) and theophylline (HDAC activator). However, vorinostat, valproate, Bay117082, TNF-α or p65 silencing hardly affected BCRP protein expression. But GW9662 (selective PPARγ antagonist) or PPARγ silencing abolished BCRP induction by butyrate and troglitazone (PPARγ agonist). SCFAs-treated rats showed higher intestinal protein expression of PPARγ, which was positively related to BCRP protein expression. Butyrate increased plasma exposure of fexofenadine but decreased that of rosuvastatin following oral dose to rats. In conclusion, SCFAs exert opposite effects on the expression and function of intestinal P-gp and BCRP; butyrate downregulated P-gp expression and function possibly via inhibiting HDAC/NF-κB pathways; butyrateinduced BCRP expression and function partly via PPARγ activation.

A Combination of Clioquinol, Zinc and Copper Increases the Abundance and Function of Breast Cancer Resistance Protein in Human Brain Microvascular Endothelial Cells

Modulating the abundance of the blood-brain barrier (BBB) efflux transporter breast cancer resistance protein (BCRP) has the potential to impact brain levels of drugs and endogenous substrates. Studies have demonstrated that the metal ionophore clioquinol (CQ) increases BBB abundance of P-glycoprotein (P-gp), an effect associated with increased endothelial cell levels of Cu2+. This study therefore assessed whether human brain endothelial (hCMEC/D3) cell abundance and function of BCRP is modulated by CQ. hCMEC/D3 cells were treated with CQ, Zn2+ and Cu2+ (CZC) (0.5 μM, 0.5 μM, 0.1 μM, respectively) for 24 h and BCRP mRNA and protein abundance was determined by Western blot and qPCR, respectively. After a series of optimisation studies assessing specificity of bodipy prazosin (BP) and Ko143 as a substrate and inhibitor of BCRP, respectively, the impact of CZC on BP uptake was assessed. While CZC did not increase mRNA expression of BCRP, BCRP abundance was increased 1.8 ± 0.1-fold; this was associated with a 68.1 ± 3.3% reduction in accumulation of BP in hCMEC/D3 cells. This is the first study to demonstrate that augmenting metal ion availability enhances protein abundance and function of BCRP at the BBB, which may be exploited to modulate CNS access of therapeutics and endogenous substrates.

Identification of Functional Transcriptional Binding Sites within Chicken Abcg2 Gene Promoter and Screening Its Regulators.

Breast cancer resistance protein (BCRP), an ATP-binding cassette (ABC) half transporter encoded by the Abcg2 gene, is reported to influence the pharmacokinetics of substrate drugs during clinical therapy. The aim of this study was to clarify the mechanisms that regulate the transcription of the chicken Abcg2 gene through cloning and characterization of its promoter region. Results showed that the Abcg2 gene is transcribed by a TATA-less promoter with several putative Sp1 sites upstream from two putative CpG islands. A luciferase reporter assay conducted both in chicken leghorn male hepatoma (LMH) cells and chicken primary hepatocytes mapped a basal promoter to nucleotides −110 to +30, which is responsible for the constitutive expression of Abcg2. The 5′-region upstream of the basal promoter was characterized by both positive and negative regulatory domains. Further, using the cell-based reporter gene assay combined with RT-PCR and drug accumulation analysis, we found that four xenobiotics, daidzein, clotrimazole, ivermectin, and lipopolysaccharide (LPS), influence the expression and function of BCRP through significant regulation of the Abcg2 gene promoter. Interaction sites with the Abcg2 gene promoter of these four selected regulators were clarified by progressive deletions and mutation assays. This study shed some light on the regulatory mechanisms involved in chicken Abcg2 gene expression and the results may have far-reaching significance regarding the usage and development of veterinary drugs.

Regulation of breast cancer resistance protein and P-glycoprotein by ezrin, radixin and moesin in lung, intestinal and renal cancer cell lines.

Ezrin (Ezr), radixin (Rdx) and moesin (Msn) (ERM) proteins anchor other proteins to the cell membrane, serving to regulate their localization and function. Here, we examined whether ERM proteins functionally regulate breast cancer resistance protein (BCRP) and P-glycoprotein in cell lines derived from lung, intestinal and renal cancers. ERM proteins were each silenced with appropriate siRNA. BCRP and P-gp functions were evaluated by means of efflux and uptake assays using 7-ethyl-10-hydroxycamptothecin (SN-38) and rhodamine123 (Rho123) as specific substrates, respectively, in non-small cell lung cancer HCC827 cells, intestinal cancer Caco-2 cells and renal cancer Caki-1 cells. In HCC827 cells, the efflux rates of SN-38 and Rho123 were significantly decreased by knockdown of Ezr or Msn, but not Rdx. However, BCRP function was unaffected by Ezr or Rdx knockdown in Caco-2 cells, which do not express Msn. In Caki-1 cells, Rdx knockdown increased the intracellular SN-38 concentration, while knockdown of Ezr or Msn had no effect. Our findings indicate that regulation of BCRP and P-gp functions by ERM proteins is organ-specific. Thus, if the appropriate ERM protein(s) are functionally suppressed, accumulation of BCRP or P-gp substrates in lung, intestine or kidney cancer tissue might be specifically increased.

The effect of green tea catechins on breast cancer resistance protein activity and intestinal efflux of aflatoxin B1 via breast cancer resistance protein in Caco-2 cells.

Aflatoxin B1 (AFB1), a mycotoxin produced by Aspergillus spp., was proved as one of the major causes of human hepatocellular carcinoma (HCC) when chronically consumed. An efflux of AFB1 was reported to be associated with breast cancer resistance protein (BCRP) whose activity could also be modulated by green tea catechins. The purpose of this study was, therefore, to examine the impacts of green tea catechins on BCRP activity in Caco-2 cells by H33342 (bis-benzamide, BCRP substrate) accumulation and AFB1 efflux. Results showed a significant decrease (p < 0.05) of AFB1 in the efflux ratio following the incubation with Ko143, a specific BCRP inhibitor, and sodium fluoride, confirming the association of BCRP in AFB1 efflux transport across the cells. Pre-incubation with green tea and gallate catechins (ECG and EGCG) significantly reduced the efflux ratio of AFB1 (p < 0.05) and significantly increased the intracellular H33342 substrate (p < 0.05) in Caco-2 cells, clearly indicating the inhibitory effects of green tea and gallate catechins on BCRP function. Further study on H33342 accumulation revealed a dose-dependent increment of intracellular H33342 when co-administered with increasing concentrations of AFB1. This result implied a possible role of AFB1 as a BCRP competitive inhibitor. The findings from this study concluded the roles of BCRP as an efflux transporter for AFB1 and could be modulated by the exposure of green tea catechins. Owing to a reduction of its efflux, an inhibitory effect of BCRP when pre-exposed with green tea catechins could be crucial for AFB1 cellular accumulation.

Imaging of hepatic drug transporters with [131I]6-\u03b2-iodomethyl-19-norcholesterol

We examined whether [131I]6-β-iodomethyl-19-norcholesterol (NP-59), a cholesterol analog, can be used to measure function of hepatic drug transporters. Hepatic uptake of NP-59 with and without rifampicin was evaluated using HEK293 cells expressing solute carrier transporters. The stability of NP-59 was evaluated using mouse blood, bile, and liver, and human liver S9. Adenosine triphosphate-binding cassette (ABC) transporters for bile excretion were examined using hepatic ABC transporter vesicles expressing multidrug resistance protein 1, multidrug resistance-associated protein (MRP)1-4, breast cancer resistance protein (BCRP), or bile salt export pump with and without MK-571 and Ko143. Single photon emission computed tomography (SPECT) was performed in normal mice injected with NP-59 in the presence or absence of Ko143. Uptake of NP-59 into HEK293 cells expressing organic anion transporting polypeptide (OATP)1B1 and OATP1B3 was significantly higher than that into mock cells and was inhibited by rifampicin. NP-59 was minimally metabolized in mouse blood, bile, and liver, and human liver S9 after 120 min of incubation. In vesicles, NP-59 was transported by MRP1 and BCRP. Excretion of NP-59 into bile via BCRP was observed in normal mice with and without Ko143 in the biological distribution and SPECT imaging. NP-59 can be used to visualize and measure the hepatic function of OATP1B1, OATP1B3, and BCRP.

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

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

Bile duct ligation enhances AZT CNS toxicity partly by impairing the expression and function of BCRP in rat brain.

Breast cancer resistance protein (BCRP) is one of ATP-binding cassette (ABC) transporters in brain microvessel endothelial cells that transport their substrates from brain to blood, thus limiting substrates to crossing into brain through blood–brain barrier. Our previous works show that bile duct ligation (BDL) impairs expression and function of brain BCRP in rats. Since zidovudine (AZT) is BCRP substrate, we investigated whether impaired expression and function of BCRP increased brain distribution and toxicity of AZT in BDL-D7 rats. After administration of AZT (10 mg/kg, i.v.), BDL markedly increased brain AZT concentrations, compared with sham-operated (SO) rats. The ratio of AZT brain-to-plasma area under concentration curve (AUC) in BDL rats was increased to 1.6-folds of SO rats. After treatment with AZT (100 mg/kg every day, i.v.) for 7 days, BDL significantly impaired cognitive functions compared with SO rats, evidenced by the significantly decreased percentage of alternation in Y-maze test and prolonged escaped latency in two-way passive avoidance trial. Furthermore, AZT treatment caused significant decrease in copies of mitochondrial DNA and mitochondrial membrane potential in hippocampus of BDL rats. Moreover, AZT treatment caused a significant decrease of cortex microtubule-associated protein 2 and hippocampus synaptophysin levels in BDL rats. AZT-induced CNS adverse alterations in BDL rats were not observed in SO rats treated with AZT. In conclusion, BDL decreases the function and expression of brain BCRP in rats, leading to increased brain distribution of AZT, which in turn enhances AZT CNS toxicity, leading to mitochondrial dysfunction, neuronal damage, and ultimately cognitive dysfunction.

Novel inhibitors of ABC transporters increase accumulation of transport substrates in multidrug resistant cancer cells and blood brain barrier cells

Multidrug resistance (MDR) is a major cause of chemotherapy failure. Overexpression of ATP‐binding cassette (ABC) transporters, P‐glycoprotein (P‐gp) and breast cancer resistance protein (BCRP) are two well‐studied drug transporters which are associated with MDR. These two transporters also act as a major functional unit of the blood brain barrier to protect the brain from xenobiotics and toxins. Lack of clinically approved P‐gp and BCRP inhibitors renders chemotherapy treatments of many MDR cancers ineffective and obstructs drug uptake into the brain. Using computational methods, we previously identified a novel class of P‐gp inhibitors that were not transport substrates of the pump. Here we describe the effects of chemical variants of the previously identified P‐gp inhibitor, SMU‐29. The variants were generated using computational approaches or by structure‐based design to improve protein binding interactions. All variants showed improved efficacy in reversing paclitaxel resistance in the P‐gp over‐expressing DU145 TXR prostate cancer cell line and their ability of increasing P‐gp substrate calcein in these cells. Five of these variants were not transported by P‐gp and three of them were substrates of the pump. Four variants only affected P‐gp, but not BCRP function, making them more selective than the parental compound, SMU 29. The three variants that affected BCRP reversed MDR in a BCRP over‐expressing breast cancer cell line, MCF‐7 M100, and increased accumulation of BCRP substrates such as Hoechst 33342, mitoxantrone and daunorubicin in these cells, indicating the potential to be used as BCRP inhibitors. The variants that affected both P‐gp and BCRP also showed higher accumulation of P‐gp and BCRP substrates in a blood brain barrier model cell line, hCMEC/D3, showing the potential to open the blood brain barrier for increased drug uptake into the brain.Support or Funding InformationThis work was supported by NIH NIGMS [R15GM094771‐02] to PVD and JGW, SMU University Research Council, the SMU Center for Drug Discovery, Design and Delivery, the Communities Foundation of Texas, and a private gift from Ms. Suzy Ruff of Dallas, Texas.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Optimization of Breast Cancer Resistance Protein (BCRP) Purification from PichiaPinkTM

The breast cancer resistance protein (BCRP) is an ATP Binding Cassette (ABC) transporter responsible for the export of many toxins across cellular membranes. Overexpression of these ABC transporters is often correlated to multidrug resistances in cancer and decrease in the success of chemotherapy. We have performed high‐throughput in silico ligand docking studies to find drug‐like compounds that are predicted to inhibit the function of BCRP and the related transporter, P‐glycoprotein. A number of drug like molecules were identified that reversed multidrug resistance of a BCRP‐overexpressing breast cancer cell line generated in our lab. Biochemical and biophysical analyses of these inhibitors are needed to evaluate the inhibition mechanism of these drug‐like compounds. For that purpose, relatively large amounts of the purified protein are required. We previously generated a gene for human BCRP that was codon optimized for expression in the yeast, Pichia Pastoris, and cloned into the new expression system PichiaPinkTM. BCRP purification proved to be challenging as reported previously by others. Optimization of growth and BCRP expression in the PichiaPinkTM cells revealed highest cell density and satisfactory BCRP expression after methanol induction when the cells were fed with their carbon source, methanol, more frequently than originally described. Protein purification techniques including cell breakage and solubilization conditions were optimized to achieve a consistent 60% membrane solubilization. Here we report our attempts to purify BCRP into detergent mixed micelles using Ni‐NTA affinity and ion exchange chromatography. Our attempts to assemble BCRP into native‐like membrane nanodiscs to achieve maximum ATP‐hydrolysis activity are also reported. Obtaining BCRP in a near native like environment with high biological activity will be necessary for the assessment of efficiency as well as the mechanism of BCRP inhibition of our newly found drug‐like compounds.Support or Funding InformationThis work was supported by NIH NIGMS [R15GM094771‐02] to PVD and JGW, SMU University Research Council, SMU Hamilton Undergraduate Research Scholars and Undergraduate Research Assistantship Programs, the SMU Center for Drug Discovery, Design and Delivery, the Communities Foundation of Texas, and a private gift from Ms. Suzy Ruff of Dallas, Texas. The authors wish to thank Ms. Lynn McBee and New England Biolabs for their generous support.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.