Molecular modeling of the human multidrug resistance protein 1 (MRP1/ABCC1)

Multidrug resistance protein 1 (MRP1/ABCC1) is a 190 kDa member of the ATP-binding cassette (ABC) superfamily of transmembrane transporters that is clinically relevant for its ability to confer multidrug resistance by actively effluxing anticancer drugs. Knowledge of the atomic structure of MRP1 is needed to elucidate its transport mechanism, but only low resolution structural data are currently available. Consequently, comparative modeling has been used to generate models of human MRP1 based on the crystal structure of the ABC transporter Sav1866 from Staphylococcus aureus. In these Sav1866-based models, the arrangement of transmembrane helices differs strikingly from earlier models of MRP1 based on the structure of the bacterial lipid transporter MsbA, both with respect to packing of the twelve helices and their interactions with the nucleotide binding domains. The functional importance of Tyr³²⁴ in transmembrane helix 6 predicted to project into the substrate translocation pathway was investigated.     

Kuguacin J isolated from Momordica charantia leaves inhibits P-glycoprotein (ABCB1)-mediated multidrug resistance

Multidrug resistance (MDR) is a major factor in the failure of chemotherapy in cancer patients. Resistance to chemotherapy has been correlated to the overexpression of ABC drug transporters including P-glycoprotein (P-gp) that actively efflux chemotherapeutic drugs from cancer cells. Our previous study showed that bitter melon (Momordica charantia) leaf extract (BMLE) was able to reverse the MDR phenotype by increasing the intracellular accumulation of chemotherapeutic drugs. In the present study, bioguided fractionation was used to identify the active component(s) of BMLE that is able to modulate the function of P-gp and the MDR phenotype in a human cervical carcinoma cell line (KB-V1). We found that kuguacin J, one of the active components in BMLE, increased sensitivity to vinblastine and paclitaxel in KB-V1 cells. A flow cytometry assay indicated that kuguacin J inhibits the transport function of P-gp and thereby significantly increases the accumulation of rhodamine 123 and calcein AM in the cells. These results were confirmed by [³H]-vinblastine transport assay. Kuguacin J significantly increases intracellular [³H]-vinblastine accumulation and decreased the [³H]-vinblastine efflux in the cells. Kuguacin J also inhibited the incorporation of [¹²⁵I]-iodoarylazidoprazosin into P-gp in a concentration-dependent manner, indicating that kuguacin J directly interacts with the drug-substrate-binding site on P-gp. These results indicate that kuguacin J modulates the function of P-gp by directly interacting at the drug-substrate-binding site, and it appears to be an effective inhibitor of P-gp activity in vitro and thus could be developed as an effective chemosensitizer to treat multidrug-resistant cancers.     

Modulation of function of three ABC drug transporters, P-glycoprotein (ABCB1), mitoxantrone resistance protein (ABCG2) and multidrug resistance protein 1 (ABCC1) by tetrahydrocurcumin, a major metabolite of curcumin

Many studies have been performed with the aim of developing effective resistance modulators to overcome the multidrug resistance (MDR) of human cancers. Potent MDR modulators are being investigated in clinical trials. Many current studies are focused on dietary herbs due to the fact that these have been used for centuries without producing any harmful side effects. In this study, the effect of tetrahydrocurcumin (THC) on three ABC drug transporter proteins, P-glycoprotein (P-gp or ABCB1), mitoxantrone resistance protein (MXR or ABCG2) and multidrug resistance protein 1 (MRP1 or ABCC1) was investigated, to assess whether an ultimate metabolite form of curcuminoids (THC) is able to modulate MDR in cancer cells. Two different types of cell lines were used for P-gp study, human cervical carcinoma KB-3-1 (wild type) and KB-V-1 and human breast cancer MCF-7 (wild type) and MCF-7 MDR, whereas, pcDNA3.1 and pcDNA3.1-MRP1 transfected HEK 293 and MXR overexpressing MCF7AdrVp3000 or MCF7FL1000 and its parental MCF-7 were used for MRP1 and MXR study, respectively. We report here for the first time that THC is able to inhibit the function of P-gp, MXR and MRP1. The results of flow cytometry assay indicated that THC is able to inhibit the function of P-gp and thereby significantly increase the accumulation of rhodamine and calcein AM in KB-V-1 cells. The result was confirmed by the effect of THC on [³H]-vinblastine accumulation and efflux in MCF-7 and MCF-7MDR. THC significantly increased the accumulation and inhibited the efflux of [³H]-vinblastine in MCF-7 MDR in a concentration-dependent manner. This effect was not found in wild type MCF-7 cell line. The interaction of THC with the P-gp molecule was clearly indicated by ATPase assay and photoaffinity labeling of P-gp with transport substrate. THC stimulated P-gp ATPase activity and inhibited the incorporation of [¹²⁵I]-iodoarylazidoprazosin (IAAP) into P-gp in a concentration-dependent manner. The binding of [¹²⁵I]-IAAP to MXR was also inhibited by THC suggesting that THC interacted with drug binding site of the transporter. THC dose dependently inhibited the efflux of mitoxantrone and pheophorbide A from MXR expressing cells (MCF7AdrVp3000 and MCF7FL1000). Similarly with MRP1, the efflux of a fluorescent substrate calcein AM was inhibited effectively by THC thereby the accumulation of calcein was increased in MRP1-HEK 293 and not its parental pcDNA3.1-HEK 293 cells. The MDR reversing properties of THC on P-gp, MRP1, and MXR were determined by MTT assay. THC significantly increased the sensitivity of vinblastine, mitoxantrone and etoposide in drug resistance KB-V-1, MCF7AdrVp3000 and MRP1-HEK 293 cells, respectively. This effect was not found in respective drug sensitive parental cell lines. Taken together, this study clearly showed that THC inhibits the efflux function of P-gp, MXR and MRP1 and it is able to extend the MDR reversing activity of curcuminoids in vivo.     

Genomic structure,gene expression,and promoter analysis of human multidrug resistance-associated protein 7

The multidrug resistance-associated protein (MRP) subfamily transporters associated with anticancer drug efflux are attributed to the multidrug-resistance of cancer cells. The genomic organization of human multidrug resistance-associated protein 7 (MRP7) was identified. The human MRP7 gene, consisting of 22 exons and 21 introns, greatly differs from other members of the human MRP subfamily. A splicing variant of human MRP7, MRP7A, expressed in most human tissues, was also characterized. The 1.93-kb promoter region of MRP7 was isolated and shown to support luciferase activity at a level 4- to 5-fold greater than that of the SV40 promoter. Basal MRP7 gene expression was regulated by 2 regions in the 5'-flanking region at -1,780-1,287 bp, and at -611 to -208 bp. In Madin-Darby canine kidney (MDCK) cells, MRP7 promoter activity was increased by 226% by genotoxic 2-acetylaminofluorene and 347% by the histone deacetylase inhibitor, trichostatin A. The protein was expressed in the membrane fraction of transfected MDCK cells.     

Transport of antimony salts by Arabidopsis thaliana protoplasts over-expressing the human multidrug resistance-associated protein 1 (MRP1/ABCC1)

ABC transporters from the multidrug resistance-associated protein (MRP) subfamily are glutathione S-conjugate pumps exhibiting a broad substrate specificity illustrated by numerous xenobiotics, such as anticancer drugs, herbicides, pesticides and heavy metals. The engineering of MRP transporters into plants might be interesting either to reduce the quantity of xenobiotics taken up by the plant in the context of “safe-food” strategies or, conversely, in the development of phytoremediation strategies in which xenobiotics are sequestered in the vacuolar compartment. In this report, we obtained Arabidopsis transgenic plants overexpressing human MRP1. In these plants, expression of MRP1 did not increase plant resistance to antimony salts (Sb(III)), a classical glutathione-conjugate substrate of MRP1. However, the transporter was fully translated in roots and shoots, and targeted to the plasma membrane. In order to investigate the functionality of MRP1 in Arabidopsis, mesophyll cell protoplasts (MCPs) were isolated from transgenic plants and transport activities were measured by using calcein or Sb(III) as substrates. Expression of MRP1 at the plasma membrane was correlated with an increase in the MCPs resistance to Sb(III) and a limitation of the metalloid content in the protoplasts due to an improvement in Sb(III) efflux. Moreover, Sb(III) transport was sensitive to classical inhibitors of the human MRP1, such as MK571 or glibenclamide. These results demonstrate that a human ABC transporter can be functionally introduced in Arabidopsis, which might be useful, with the help of stronger promoters, to reduce the accumulation of xenobiotics in plants, such as heavy metals from multi-contaminated soils.     

Triterpenoids from Momordica balsamina: Reversal of ABCB1-mediated multidrug resistance

The ability as P-glycoprotein (P-gp, ABCB1) modulators of thirty (1–30) triterpenoids of the cucurbitane-type was evaluated on human L5178 mouse T-lymphoma cell line transfected with the human MDR1 gene, through the rhodamine-123 exclusion assay. Compounds (1–26, and 29, 30) were previously obtained from the African medicinal plant Momordica balsamina, through both isolation (1–15) and molecular derivatization (16–26 and 29, 30). Compounds 27–28 are two new karavilagenin C (34) derivatives having succinic acid moieties. Apart from 4, 6, 8, 10 and 11, most of the isolated compounds (1–15) displayed strong MDR reversing activity in a dose-dependent mode, exhibiting a many-fold activity when compared with verapamil, used as positive control. At the lowest concentration tested, compounds 2 and 7 were the most active. However, a decrease of activity was found for the acyl derivatives (16–30). In a chemosensitivity assay, the MDR reversing activity of some of the most active compounds (1–3, 5, 7, 12–15) was further assessed on the same cell model. All the tested compounds, excepting 15, corroborated the results of the transport assay, revealing to synergistically interact with doxorubicin. Structure–activity relationship studies, taking into account previous results, showed that different substitution patterns, at both the tetracyclic nucleus and the side chain, play important role in ABCB1 reversal activity. An optimal lipophilicity was also recognized.     

Tetrandrine and fangchinoline,bisbenzylisoquinoline alkaloids from Stephania tetrandra can reverse multidrug resistance by inhibiting P-glycoprotein activity in multidrug resistant human cancer cells

The overexpression of ABC transporters is a common reason for multidrug resistance (MDR) in cancer cells. In this study, we found that the isoquinoline alkaloids tetrandrine and fangchinoline from Stephania tetrandra showed a significant synergistic cytotoxic effect in MDR Caco-2 and CEM/ADR5000 cancer cells in combination with doxorubicin, a common cancer chemotherapeutic agent. Furthermore, tetrandrine and fangchinoline increased the intracellular accumulation of the fluorescent P-glycoprotein (P-gp) substrate rhodamine 123 (Rho123) and inhibited its efflux in Caco-2 and CEM/ADR5000 cells. In addition, tetrandrine and fangchinoline significantly reduced P-gp expression in a concentration-dependent manner. These results suggest that tetrandrine and fangchinoline can reverse MDR by increasing the intracellular concentration of anticancer drugs, and thus they could serve as a lead for developing new drugs to overcome P-gp mediated drug resistance in clinic cancer therapy.     

A 4-aminobenzoic acid derivative as novel lead for selective inhibitors of multidrug resistance-associated proteins

We present a novel lead for inhibitors of multidrug resistance-associated proteins (MRPs). Compound 1 (4-[(5,6,7,8-tetrahydro-4-oxo-4H-[1]benzothieno[2,3-d][1,3]thiazin-2-yl)amino]benzoic acid) was about six times more potent than the known inhibitor MK571 at MRP1, while at MRP2 its effect was similar to that of MK571. Structural analogs were also evaluated. Among them, compound 2, sharing the 4-aminobenzoic acid substructure with 1, also inhibited MRP1. Both derivatives were inactive against P-gp. It can be concluded that their carboxyl group is needed for inhibition of MRPs and accounts for the selectivity of these compounds.     

Involvement of multidrug resistance proteins (MDR) in the modulation of glucocorticoid response

Glucocorticoid resistance is a problem in the treatment of many diseases. One possible factor involved in the modulation of a glucocorticoid response is the export of glucocorticoids out of the cell. It has been shown that multidrug resistance protein 1 (MDR1, ABCB1), a member of the ABC family, is capable of transporting some glucocorticoids. This paper uses a mouse cell line, LMCAT in which the glucocorticoid response can be modulated by inhibitors of multidrug resistance proteins. Glucocorticoids fall into three categories. Firstly, those that are transported by an Abcb1a/Abcb1b transporter and whose transport can be inhibited by inhibitors of ABCB1 activity. Functional Abcb1a/Abcb1b was detected by inhibition of rhodamine efflux by these drugs and mRNA for Abcb1a and Abcb1b were detected in these cells. Secondly, those that are not transported. Finally, those that are transported by an Abcc1a transporter. Calcein transport out of these cells was blocked by treatment with probenecid indicating a functional Abcc1a transporter. Abcc1a mRNA was also detected in these cells. Thus, this paper provides insight into the mechanisms of glucocorticoid transport in cells and demonstrates a diversity of two independent mechanisms of transport of glucocorticoids by Abcb1a/Abcb1b and Abcc1a with individual patterns of steroid specificity.     

Functional expression of a multidrug P-glycoprotein transporter of Leishmania

P-glycoprotein (Pgp) transporters play an important role in multidrug resistance in eukaryotic cells and in protozoan parasites such as Leishmania. To search for new reversal agents of the Leishmania tropica Pgp, we developed a screening assay using the Baculovirus-insect cell expression system. We demonstrated a MgATP-dependent, vanadate-sensitive transport of Hoechst 33342 in membrane preparations of Sf9 insect cells expressing Pgp. We have found that dihydro-beta-agarofuran sesquiterpenes from Maytenus cuzcoina inhibited Hoechst 33342 transport that correlates with their reversal effect in a multidrug-resistant L. tropica line overexpressing Pgp. The results suggest that Sf9 cell membrane Hoechst 33342 transport system represents an efficient tool for examining the interactions of Leishmania Pgp with pharmacological agents.     

Nitensidine A,a guanidine alkaloid from Pterogyne nitens,is a novel substrate for human ABC transporter ABCB1

The Pterogyne nitens (Fabaceae) tree, native to South America, has been found to produce guanidine alkaloids as well as bioactive flavonols such as kaempferol, quercetin, and rutin. In the present study, we examined the possibility of interaction between human ATP-binding cassette (ABC) transporter ABCB1 and four guanidine alkaloids isolated from P. nitens (i.e., galegine, nitensidine A, pterogynidine, and pterogynine) using human T cell lymphoblast-like leukemia cell line CCRF-CEM and its multi-drug resistant (MDR) counterpart CEM/ADR5000. In XTT assays, CEM/ADR5000 cells were resistant to the four guanidine alkaloids compared to CCRF-CEM cells, although the four guanidine alkaloids exhibited some level of cytotoxicity against both CCRF-CEM and CEM/ADR5000 cells. In ATPase assays, three of the four guanidine alkaloids were found to stimulate the ATPase activity of ABCB1. Notably, nitensidine A was clearly found to stimulate the ATPase activity of ABCB1 as strongly as the control drug, verapamil. Furthermore, the cytotoxic effect of nitensidine A on CEM/ADR5000 cells was synergistically enhanced by verapamil. Nitensidine A inhibited the extrusion of calcein by ABCB1. In the present study, the possibility of interaction between ABCB1 and two synthetic nitensidine A analogs (nitensidine AT and AU) were examined to gain insight into the mechanism by which nitensidine A stimulates the ATPase activity of ABCB1. The ABCB1-dependent ATPase activity stimulated by nitensidine A was greatly reduced by substituting sulfur (S) or oxygen (O) for the imino nitrogen atom (N) in nitensidine A. Molecular docking studies on human ABCB1 showed that, guanidine alkaloids from P. nitens dock to the same binding pocket as verapamil. Nitensidine A and its analogs exhibit similar binding energies to verapamil. Taken together, this research clearly indicates that nitensidine A is a novel substrate for ABCB1. The present results also suggest that the number, binding site, and polymerization degree of the isoprenyl moiety in the guanidine alkaloids and the imino nitrogen atom cooperatively contribute to their stimulation of ABCB1's ATPase activity.     

Interaction of ivermectin with multidrug resistance proteins (MRP1, 2 and 3)

Ivermectin is a potent antiparasitic drug from macrocyclic lactone (ML) family, which interacts with the ABC multidrug transporter P-glycoprotein (Pgp). We studied the interactions of ivermectin with the multidrug resistance proteins (MRPs) by combining cellular and subcellular approaches. The inhibition by ivermectin of substrate transport was measured in A549 cells (calcein or 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein, BCECF) and in HL60-MRP1 (calcein). Ivermectin induced calcein and BCECF retention in A549 cells (IC(50) at 1 and 2.5microM, respectively) and inhibited calcein efflux in HL60-MRP1 (IC(50)=3.8microM). The action of ivermectin on the transporters ATPase activity was followed on membranes from Sf9 cells overexpressing human Pgp, MRP1, 2 or 3. Ivermectin inhibited the Pgp, MRP1, 2 and 3 ATPase activities after stimulation by their respective activators. Ivermectin showed a rather good affinity for MRPs, mainly MRP1, in the micromolar range, although it was lower than that for Pgp. The transport of BODIPY-ivermectin was followed in cells overexpressing selectively Pgp or MRP1. In both cell lines, inhibition of the transporter activity induced intracellular retention of BODIPY-ivermectin. Our data revealed the specific interaction of ivermectin with MRP proteins, and its transport by MRP1. Although Pgp has been considered until now as the sole active transporter for this drug, the MRPs should be taken into account for the transport of ivermectin across cell membrane, modulating its disposition in addition to Pgp. This could be of importance for optimizing clinical efficacy of ML-based antiparasitic treatments. This offers fair perspectives for the use of ivermectin or non-toxic derivatives as multidrug resistance-reversing agents.     

Effects of phosphorylation of P-glycoprotein on multidrug resistance

Cells expressing elevated levels of the membrane phosphoprotein P-glycoprotein exhibit a multidrug resistance phenotype. Studies involving protein kinase activators and inhibitors have implied that covalent modification of P-glycoprotein by phosphorylation may modulate its biological activity as a multidrug transporter. Most of these reagents, however, have additional mechanisms of action and may alter drug accumulation within multidrug resistant cells independent of, or in addition to their effects on the state of phosphorylation of P-glycoprotein. The protein kinase(s) responsible for P-glycoprotein phosphorylation has(ve) not been unambiguously identified, although several possible candidates have been suggested. Recent biochemical analyses demonstrate that the major sites of phosphorylation are clustered within the linker region that connects the two homologous halves of P-glycoprotein. Mutational analyses have been initiated to confirm this finding. Preliminary data obtained from phosphorylation- and dephosphorylation-defective mutants suggest that phosphorylation of P-glycoprotein is not essential to confer multidrug resistance.     

A novel class of highly potent multidrug resistance reversal agents: Disubstituted adamantyl derivatives

Novel disubstituted adamantyl derivatives were synthesized and evaluated in a P-glycoprotein dependent multidrug resistance cancer cell line. The hit to lead optimization provided potent MDR reversal agents. Some potent adamantyl derivatives were more than 10-fold more potent than verapamil without considerable intrinsic cytotoxicity. The 3-trifluorophenyl derivative 14f did not affect the metabolism of CYP450 3A4, whereas most of MDR revertants had a weak inhibitory effect.     

Analysis of the inhibition potential of zosuquidar derivatives on selected bacterial and fungal ABC transporters

Abstract

The increasing number of multidrug-resistant pathogenic microorganisms is a serious public health issue. Among the multitude of mechanisms that lead to multidrug resistance, the active extrusion of toxic compounds, mediated by MDR efflux pumps, plays an important role. In our study we analyzed the inhibitory capability of 26 synthesized zosuquidar derivatives on three ABC-type MDR efflux pumps, namely Saccharomyces cerevisiae Pdr5 as well as Lactococcus lactis LmrA and LmrCD. For Pdr5, five compounds could be identified that inhibited rhodamine 6G transport more efficiently than zosuquidar. One of these is a compound with a new catechol acetal structure that might represent a new lead compound. Furthermore, the determination of IC₅₀ values for rhodamine 6G transport of Pdr5 with representative compounds reveals values between 0.3 and 0.9 μM. Thus the identified compounds are among the most potent inhibitors known for Pdr5. For the ABC-type efflux pumps LmrA and LmrCD from L. lactis, seven and three compounds, which inhibit the transport activity more than the lead compound zosuquidar, were found. Interestingly, transport inhibition for LmrCD was very specific, with a drastic reduction by one compound while its diastereomers showed hardly an effect. Thus, the present study reveals new potent inhibitors for the ABC-type MDR efflux pumps studied with the inhibitors of Pdr5 and LmrCD being of particular interest as these proteins are well known model systems for their homologs in pathogenic fungi and Gram-positive bacteria.     

Veliparib overcomes multidrug resistance in liver cancer cells

Overexpression of ATP-binding cassette (ABC) transporter is one of the most important factors taking responsibility for the progress of multidrug resistance (MDR) in multiple cancers. In this study, we investigated that veliparib, a PARP inhibitor which is in clinical development, could overcome ABCB1-mediated MDR in liver cancer cells. Veliparib could significantly enhance the cytotoxic effects of a series of conventional chemotherapeutic drugs in ABCB1-overexpression liver cancer cells. Mechanism study showed that veliparib could significantly enhance the accumulation of doxorubicin in ABCB1-overexpression liver cancer cells, without down-regulating the expression level of ABCB1. Finally, veliparib could significantly inhibit the ATPase activity of ABCB1 transporter. This study could provide information that combine veliparib with other chemotherapeutic drugs may benefit liver cancer patients.     

Estimation of ABCB1 concentration in plasma membrane

The interaction between ABCB1 transporter and its substrates takes place in cell membranes but the available data precludes quantitative analysis of the interaction between transporter and substrate molecules. Further, the amount of transporter is usually expressed as a number of ABCB1 molecules per cell. In contrast, the substrate concentration in cell membranes is estimated by determination of substrate-lipid partition coefficient, as examples. In this study, we demonstrate an approach, which enables us to estimate the concentration of ABCB1 molecules within plasma membranes. For this purpose, human leukemia K562 cells with varying expression levels of ABCB1 were used: drug selected K562/Dox and K562/HHT cells with very high transporter expression, and K562/DoxDR2, K562/DoxDR1, and K562/DoxDR05 cells with gradually decreased expression of ABCB1 derived from K562/Dox cells using RNA interference technology. First, we determined the absolute amount of ABCB1 in cell lysates using immunoblotting and recombinant ABCB1 as a standard. We then determined the relative portion of transporter residing in the plasma membrane using immunohistochemistry in nonpermeabilized and permeabilized cells. These results enabled us to estimate the concentration of ABCB1 in the plasma membrane in resistant cells. The ABCB1 concentrations in the plasma membrane of drug selected K562/Dox and K562/HHT cells containing the highest amount of transporter reached millimolar levels. Concentrations of ABCB1 in the plasma membrane of resistant K562/DoxDR2, K562/DoxDR1, and K562/DoxDR05 cells with lower transporter expression were proportionally decreased.     

The 5-aromatic hydantoin-3-acetate derivatives as inhibitors of the tumour multidrug resistance efflux pump P-glycoprotein (ABCB1): Synthesis,crystallographic and biological studies

A series of arylpiperazine derivatives of hydantoin-3-acetate, including previously obtained 5,5-diphenylhydantoin (1–7) and new-synthesized spirofluorene-hydantoin derivatives (8–12), were investigated in the search for new inhibitors of the tumour multidrug resistance (MDR) efflux pump P-glycoprotein (P-gp, ABCB1) overexpressed in mouse T-lymphoma cells. Synthesis of new compounds (8–12) was performed. Crystal structures of two compounds (8 and 11) were determined by X-ray diffraction method. The conformations of the investigated molecules (8 and 11) in the crystalline samples are different. The bent conformation seems to be more favourable for biological activity than the extended one. The efflux pump inhibitory properties of the compounds 1–12 were evaluated in the fluorescence uptake assay using rhodamine 123 dye in mouse T-lymphoma model in vitro. Their cytotoxic action was examined, too. All compounds with methyl acetate moiety displayed high potency to inhibit the MDR efflux pump. The most active compound, methyl 2-(1-(4-(4-(2,3-dichlorophenyl)piperazin-1-yl)butyl)-5,5-diphenylhydantoin-3-yl)acetate (5), tested at 1/10 of verapamil concentration displayed the 9-fold higher P-gp inhibitory action.