The role of emodin on cisplatin resistance reversal of lung adenocarcinoma A549/DDP cell

Exploring drugs that reverse drug resistance and increase the sensitivity of chemotherapy drugs could significantly improve treatment effect of cancer. Our study explored the reversal effect and possible molecular mechanisms of emodin on cisplatin resistance in A549/DDP cells. The IC50 and resistance index of cells were determined by Cell Counting Kit-8 assay. The ability of cell proliferation was evaluated by wound healing assay. Transwell assay was used to detect cell invasion and migration. Apoptosis induction rate was determined by flow cytometry assay and 4',6- diamidino- 2-phenylindole staining. Intracellular concentration was determined by HPLC. Western blot analysis was applied to determine expressions of nuclear factor kappa beta (NF-κB) and its downstream proteins. In this study, we found that the growth inhibitory effect of cisplatin was significantly enhanced by emodin in A549/DDP cells. The combined use of emodin with DDP can effectively promote lung cancer cells apoptosis and inhibit cell migration and invasion. Further investigation indicated that reinforcement effect of emodin and DDP may be associated with inhibition of NF-κB pathway and drug efflux-related proteins such as P-glycoprotein (P-gp), multidrug resistance-associated protein (MRP) and Glutathione S-transferase (GST). The key role of NF-κB was further confirmed by the application of NF-κB inhibitor Ammonium pyrrolidinedithiocarbamate. The intervention of both can significantly increase A549/DDP cell apoptosis and inhibit DDP-induced upregulation of P-gp, MRP and GST. Emodin reverses the cisplatin resistance of tumor cells by down-regulating expression of P-gp, MRP and GST, increasing the intracellular accumulation in A549/DDP cells, and the effect may be associated with the NF-κB pathways.

Tanshinone IIA attenuates acetaminophen-induced hepatotoxicity through HOTAIR-Nrf2-MRP2/4 signaling pathway

Tanshinone IIA (Tan IIA), an active component in S. miltiorrhiza, has been reported to have excellent antioxidant and detoxifying activity. Here, we prove that Tan IIA attenuates acetaminophen-induced hepatotoxicity from a pharmacokinetic perspective. Compared with acetaminophen (APAP, 200 mg/kg) treated mice, Tan IIA pretreatment (30 mg/kg/d) not only reduced the plasma level of the toxic metabolite N-acetyl-p-benzoquinone imine (NAPQI) but also increased its bile level. After Tan IIA pretreatment, significant induction of nuclear factor E2-related factor 2 (Nrf2), multidrug resistance-associated protein 2 (Mrp2), and multidrug resistance-associated protein 4 (Mrp4) mRNA and protein expression was detected in Nrf2+/+ mouse liver, however, much lower increase of Mrp2 and Mrp4 mRNA and protein expression was observed in Nrf2-/- mouse liver. Luciferase reporter and chromatin immunoprecipitation assays demonstrated that Nrf2 bounds to antioxidant responsive elements (AREs) of the MRP2 and MRP4 promoter, thus regulating the expression of MRP2 and MRP4. in vitro experiments revealed that Tan IIA increase Nrf2, MRP2, and MRP4 expression through a mechanism of inhibiting the expression of HOX transcript antisense RNA (HOTAIR) which belongs to long non-coding RNAs. Collectively, the present results demonstrated that Tan IIA could protect against APAP-induced hepatotoxicity by altering the pharmacokinetic characteristics of APAP and its metabolites via HOTAIR-Nrf2-MRP2/4 signaling pathway, and HOTAIR plays a pivotal role in the MRP2 and MRP4 expression regulated by Nrf2.

Modulation of the multixenobiotic resistance mechanism in Danio rerio hepatocyte culture (ZF-L) after exposure to glyphosate and Roundup®

The presence of the transmembrane proteins of the ATP-binding cassette (ABC) family, which perform the efflux of several substances, contributes to the survival of aquatic organisms in a contaminated environmental. Those proteins provide a phenotype named the multixenobiotic resistance mechanism (MXR) by performing the efflux of a wide range of endogenous and exogenous compounds (ABCB) and biotransformation products and anionic compounds (ABCC). The aim of the present study was to evaluate the cellular defense pathway of an established culture from zebrafish hepatocytes (ZF-L) after 24 and 48 h of exposure to glyphosate and Original Roundup®, an herbicide used globally. Through abcb4, abcc1, abcc2 and abcc4 gene expression, ABCB and ABCC2 protein expression and ABC pump activity in ZF-L cells exposed to glyphosate and Roundup®. The results showed an increase in ABCB gene and protein expression; however, although ABCC2 showed an increase in gene expression, its protein expression was lower than in the control group. Regarding ABC activity, only exposure to Roundup® at the lowest concentration showed an increase at 48 h, but in the presence of inhibitors, both glyphosate and Roundup® appeared to modulate ABC activity, reducing its inhibition and returning activity to levels without inhibitor.

Resveratrol mediated cancer cell apoptosis, and modulation of multidrug resistance proteins and metabolic enzymes

BACKGROUND

The degree of intracellular drug accumulation by specific membrane transporters, i.e., MDR1, BCRP, and MRP, and the degree of detoxification by intracellular metabolic enzymes, i.e., CYP3A4 and GST, provide control for cancer chemotherapy through diminishing the propensity of cancer cells to undergo apoptosis which in turn modulates the unresolved and complex phenomenon of multidrug resistance (MDR) for the cancer cells.

HYPOTHESIS/PURPOSE

This study dwells into the interaction details involving ABC-transporters, CYP3A4, GST and cytotoxic effects of resveratrol on different cell lines.

METHODS

Resveratrol was evaluated for its ability modulating the expression and efflux functions of P-gp /MDR1, MRP1, and BCRP in the multidrug-resistant human colon carcinoma cell line, Caco-2, and CEM/ADR5000 cells through flow cytometry and RTPCR technique.

RESULTS

The resveratrol influenced P-gp and MRP1 efflux functions whereby it increased rhodamine 123 with calcein accumulation in concentration-dependent manner (1 - 500 µM) in the Caco-2 cell lines and inhibited the effluxes of both the substrates also as concentration-dependent phenomenon (10 - 100 µM) in the p-gp overexpressing CEM/ADR5000 cells through FACS (full form). The treatment of drug-resistant Caco-2, and CEM/ADR5000 cells with doxorubicin (DOX) along with 20 µM of resveratrol in the mixture. It increased the cell sensitivity DOX towards the DOX and enhanced the cytotoxicity. The resveratrol inhibited both CYP3A4 and GST enzymatic activity in a concentration-dependent way and induced apoptosis in the resistance cell lines because of increased levels of caspase-3, -8,-6/9 and incremental phosphatidyl serine (PS) exposure as detected by flow cytometry. The treatment of Caco-2 cells with resveratrol showed significantly lower p-gp, MRP1, BCRP, CYP3A4, GST, and hPXR mRNA levels in a 48 h observation.

CONCLUSION

The result confirmed resveratrol mediated inhibition of ABC-transporters' overall efflux functions, and its expression, and apoptosis as well as metabolic enzymes GST and CYP3A4 activity.

Renal Drug Transporters and Drug Interactions

Transporters in proximal renal tubules contribute to the disposition of numerous drugs. Furthermore, the molecular mechanisms of tubular secretion have been progressively elucidated during the past decades. Organic anions tend to be secreted by the transport proteins OAT1, OAT3 and OATP4C1 on the basolateral side of tubular cells, and multidrug resistance protein (MRP) 2, MRP4, OATP1A2 and breast cancer resistance protein (BCRP) on the apical side. Organic cations are secreted by organic cation transporter (OCT) 2 on the basolateral side, and multidrug and toxic compound extrusion (MATE) proteins MATE1, MATE2/2-K, P-glycoprotein, organic cation and carnitine transporter (OCTN) 1 and OCTN2 on the apical side. Significant drug-drug interactions (DDIs) may affect any of these transporters, altering the clearance and, consequently, the efficacy and/or toxicity of substrate drugs. Interactions at the level of basolateral transporters typically decrease the clearance of the victim drug, causing higher systemic exposure. Interactions at the apical level can also lower drug clearance, but may be associated with higher renal toxicity, due to intracellular accumulation. Whereas the importance of glomerular filtration in drug disposition is largely appreciated among clinicians, DDIs involving renal transporters are less well recognized. This review summarizes current knowledge on the roles, quantitative importance and clinical relevance of these transporters in drug therapy. It proposes an approach based on substrate-inhibitor associations for predicting potential tubular-based DDIs and preventing their adverse consequences. We provide a comprehensive list of known drug interactions with renally-expressed transporters. While many of these interactions have limited clinical consequences, some involving high-risk drugs (e.g. methotrexate) definitely deserve the attention of prescribers.

[MiR-145 inhibits drug resistance to Oxaliplatin in colorectal cancer cells through regulating G protein coupled receptor 98]

OBJECTIVE

To predict and identify the target gene of miR-145, and to explore the underlying mechanism of the inhibition of miR-145 on drug resistance to Oxaliplatin (L-OHP) in human colorectal cancer cells.

METHODS

L-OHP-resistant human colorectal cancer cell line (HCT116/L-OHP) was established in vitro by exposing to increased concentrations of L-OHP in cell culture medium. MiR-145-mimics and its negative control (NC-miRNA) were transfected into HCT116/L-OHP cells using liposome to establish HCT116/L-OHP^mimics over-expressing miR-145 and HCT116/L-OHP^NC. The target genes of miR-145 were predicted by bioinformatic analysis, and validated by dual luciferase activity assay. After determination of G protein coupled receptor 98(GPR98) as target gene, corresponding plasmids were constructed and transfected to establish HCT116/L-OHP^GPR98 over-expressing GPR98 and HCT116/L-OHP^control. HCT116/L-OHP cells over-expressing both GPR98 and miR-145 (HCT116/L-OHP^mimics+GPR98) were acquired through modification of the binding sites of GPR98 cDNA with miR-145. CCK-8 assay was used to assess the proliferation (A value) and sensitivity to L-OHP (the lower the IC50, the stronger the sensitivity) in HCT116/L-OHP cells. Real-time quantitative PCR was used to measure the mRNA expression of miR-145 and GPR98. Western blot was used to examine the protein expression of GPR98 and drug-resistant associated protein, such as P-glycoprotein (gp), multiple drug-resistance protein 1(MRP1), cancer-inhibition gene PTEN.

RESULTS

HCT116/L-OHP cell line was successfully established with IC₅₀ of (42.34±1.05) mg/L and miR-145 mRNA expression of 0.27±0.04, which was higher than (9.81±0.95) mg/L (t=39.784, P=0.000) and lower than 1.00±0.09 (t=13.021, P=0.000) in HCT116 cells. Based on HCT116/L-OHP cells, HCT116/L-OHP^mimics cells were established successfully, with relative miR-145 expression of 10.01±1.05, which was higher than 1.06±0.14 in HCT116/L-OHP^NC and 1.00±0.16 in HCT116/L-OHP (F=161.797, P=0.000). GPR98 was identified to be the target gene of miR-145. The relative mRNA and protein expressions of GPR98 in HCT116/L-OHP^GPR98 cells were 8.48±0.46 and 1.71±0.09, respectively, which were higher than those in HCT116/L-OHP^control (mRNA: 3.65±0.40, protein: 1.21±0.10) and HCT116/L-OHP (mRNA: 3.49±0.35, protein: 1.22±0.08; all P<0.05). The A value was 1.31±0.10, and the relative protein expressions of P-gp and MRP1 were 1.53±0.18 and 1.49±0.20 in HCT116/L-OHP^GPR98 cells, which were higher than those in HCT116/L-OHP (A value: 0.82±0.08, relative protein expression: 1.00±0.06 and 1.21±0.13, all P<0.05). The A value was 0.89±0.08, and the relative protein expressions of P-gp and MRP were 1.02±0.24 and 1.38±0.25 in HCT116/L-OHP^mimics+GPR98 cells, which were higher than those in HCT116/L-OHP^mimics(A value: 0.20±0.05, relative protein expression: 0.20±0.07, 0.55±0.10, all P<0.05). The relative protein expression of PTEN in HCT116/L-OHP^GPR98 cells was 0.12±0.03, which was lower than 1.25±0.14 in HCT116/L-OHP cells(P<0.05). In addition, relative protein expressions of P-gp and MRP1 were 1.02±0.24 and 1.38±0.25 in HCT116/L-OHP^mimics+GPR98 cells, which were higher than those in HCT116/L-OHP^mimics cells (0.20±0.07 and 0.55±0.10), while PTEN expression in HCT116/L-OHP^mimics+GPR98 cells was lower as compared to HCT116/L-OHP^mimics cells (1.41±0.16 vs. 1.98±0.13, P<0.05).

CONCLUSION

MiR-145 inhibits drug resistance to L-OHP of HCT116 cells through suppressing the expression of target gene GPR98.

Regulation of expression and activity of multidrug resistance proteins MRP2 and MDR1 by estrogenic compounds in Caco-2 cells. Role in prevention of xenobiotic-induced cytotoxicity

ABC transporters including MRP2, MDR1 and BCRP play a major role in tissue defense. Epidemiological and experimental studies suggest a cytoprotective role of estrogens in intestine, though the mechanism remains poorly understood. We evaluated whether pharmacologic concentrations of ethynylestradiol (EE, 0.05pM to 5nM), or concentrations of genistein (GNT) associated with soy ingestion (0.1-10μM), affect the expression and activity of multidrug resistance proteins MRP2, MDR1 and BCRP using Caco-2 cells, an in vitro model of intestinal epithelium. We found that incubation with 5pM EE and 1μM GNT for 48h increased expression and activity of both MRP2 and MDR1. Estrogens did not affect expression of BCRP protein at any concentration studied. Irrespective of the estrogen tested, up-regulation of MDR1 and MRP2 protein was accompanied by increased levels of MDR1 mRNA, whereas MRP2 mRNA remained unchanged. Cytotoxicity assays demonstrated association of MRP2 and MDR1 up-regulation with increased resistance to cell death induced by 1-chloro-2,4-dinitrobenzene, an MRP2 substrate precursor, and by paraquat, an MDR1 substrate. Experiments using an estrogen receptor (ER) antagonist implicate ER participation in MRP2 and MDR1 regulation. GNT but not EE increased the expression of ERβ, the most abundant form in human intestine and in Caco-2 cells, which could lead in turn to increased sensitivity to estrogens. We conclude that specific concentrations of estrogens can confer resistance against cytotoxicity in Caco-2 cells, due in part to positive modulation of ABC transporters involved in extrusion of their toxic substrates. Although extrapolation of these results to the in vivo situation must be cautiously done, the data could explain tentatively the cytoprotective role of estrogens against chemical injury in intestine.

Let-7c sensitizes acquired cisplatin-resistant A549 cells by targeting ABCC2 and Bcl-XL

Cancer cells that develop resistance to cisplatin (DDP) are a major clinical obstacle to the successful treatment of cancer, including non-small cell lung cancer (NSCLC). Recent studies have implicated dysregulation of microRNAs (miRNAs) function in chemoresistance. Here, we explored the role of let-7c in the acquisition of DDP-resistant phenotype in A549 cells. Let-7c was downregulated in A549/DDP cell compared with A549 cells. Modulation of let-7c altered the sensitivity of A549/DDP cells to DDP through regulating DDP-induced apopotis. Furthermore, ABCC2 and Bcl-XL were identified as targets of let-7c. ABCC2 and Bcl-XL knockdown increased DDP sensitivity and DDP-induced apoptosis in A549/DDP cells. In conclusion, our findings suggested for the first time that let-7c modulate DDP response in A549/DDP cells, and one of the mechanisms was through targeting ABCC2 and Bcl-XL. Thus, let-7c could be considered for potential therapeutic application for modulating DDP-based therapy.

Drug metabolism and transport during pregnancy: how does drug disposition change during pregnancy and what are the mechanisms that cause such changes?

There is increasing evidence that pregnancy alters the function of drug-metabolizing enzymes and drug transporters in a gestational-stage and tissue-specific manner. In vivo probe studies have shown that the activity of several hepatic cytochrome P450 enzymes, such as CYP2D6 and CYP3A4, is increased during pregnancy, whereas the activity of others, such as CYP1A2, is decreased. The activity of some renal transporters, including organic cation transporter and P-glycoprotein, also appears to be increased during pregnancy. Although much has been learned, significant gaps still exist in our understanding of the spectrum of drug metabolism and transport genes affected, gestational age-dependent changes in the activity of encoded drug metabolizing and transporting processes, and the mechanisms of pregnancy-induced alterations. In this issue of Drug Metabolism and Disposition, a series of articles is presented that address the predictability, mechanisms, and magnitude of changes in drug metabolism and transport processes during pregnancy. The articles highlight state-of-the-art approaches to studying mechanisms of changes in drug disposition during pregnancy, and illustrate the use and integration of data from in vitro models, animal studies, and human clinical studies. The findings presented show the complex inter-relationships between multiple regulators of drug metabolism and transport genes, such as estrogens, progesterone, and growth hormone, and their effects on enzyme and transporter expression in different tissues. The studies provide the impetus for a mechanism- and evidence-based approach to optimally managing drug therapies during pregnancy and improving treatment outcomes.

PI3K inhibition enhances doxorubicin-induced apoptosis in sarcoma cells

We searched for a drug capable of sensitization of sarcoma cells to doxorubicin (DOX). We report that the dual PI3K/mTOR inhibitor PI103 enhances the efficacy of DOX in several sarcoma cell lines and interacts with DOX in the induction of apoptosis. PI103 decreased the expression of MDR1 and MRP1, which resulted in DOX accumulation. However, the enhancement of DOX-induced apoptosis was unrelated to DOX accumulation. Neither did it involve inhibition of mTOR. Instead, the combination treatment of DOX plus PI103 activated Bax, the mitochondrial apoptosis pathway, and caspase 3. Caspase 3 activation was also observed in xenografts of sarcoma cells in nude mice upon combination of DOX with the specific PI3K inhibitor GDC-0941. Although the increase in apoptosis did not further impact on tumor growth when compared to the efficient growth inhibition by GDC-0941 alone, these findings suggest that inhibition of PI3K may improve DOX-induced proapoptotic effects in sarcoma. Taken together with similar recent studies of neuroblastoma- and glioblastoma-derived cells, PI3K inhibition seems to be a more general option to sensitize tumor cells to anthracyclines.

In vitro sensitivity of Plasmodium falciparum from China-Myanmar border area to major ACT drugs and polymorphisms in potential target genes

Drug resistance has always been one of the most important impediments to global malaria control. Artemisinin resistance has recently been confirmed in the Greater Mekong Subregion (GMS) and efforts for surveillance and containment are intensified. To determine potential mechanisms of artemisinin resistance and monitor the emergence and spread of resistance in other regions of the GMS, we investigated the in vitro sensitivity of 51 culture-adapted parasite isolates from the China-Myanmar border area to four drugs. The 50% inhibitory concentrations (IC₅₀s) of dihydroartemisinin, mefloquine and lumefantrine were clustered in a relatively narrow, 3- to 6-fold range, whereas the IC₅₀ range of artesunate was 12-fold. We assessed the polymorphisms of candidate resistance genes pfcrt, pfmdr1, pfATP6, pfmdr6 and pfMT (a putative metabolite/drug transporter). The K76T mutation in pfcrt reached fixation in the study parasite population, whereas point mutations in pfmdr1 and pfATP6 had low levels of prevalence. In addition, pfmdr1 gene amplification was not detected. None of the mutations in pfmdr1 and pfATP6 was associated significantly with in vitro sensitivity to artemisinin derivatives. The ABC transporter gene pfmdr6 harbored two point mutations, two indels, and number variations in three simple repeats. Only the length variation in a microsatellite repeat appeared associated with altered sensitivity to dihydroartemisinin. The PfMT gene had two point mutations and one codon deletion; the I30N and N496- both reached high levels of prevalence. However, none of the SNPs or haplotypes in PfMT were correlated significantly with resistance to the four tested drugs. Compared with other parasite populations from the GMS, our studies revealed drastically different genotype and drug sensitivity profiles in parasites from the China-Myanmar border area, where artemisinins have been deployed extensively for over 30 years.

Genetic knockdown and pharmacological inhibition of parasite multidrug resistance transporters disrupts egg production in Schistosoma mansoni

P-glycoprotein (Pgp) and multidrug resistance-associated proteins (MRPs) are ATP-dependent transporters involved in efflux of toxins and xenobiotics from cells. When overexpressed, these transporters can mediate multidrug resistance (MDR) in mammalian cells, and changes in Pgp expression and sequence are associated with drug resistance in helminths. In addition to the role they play in drug efflux, MDR transporters are essential components of normal cellular physiology, and targeting them may prove a useful strategy for development of new therapeutics or of compounds that enhance the efficacy of current anthelmintics. We previously showed that expression of Schistosoma mansoni MDR transporters increases in response to praziquantel (PZQ), the current drug of choice against schistosomiasis, and that reduced PZQ sensitivity correlates with higher levels of these parasite transporters. We have also shown that PZQ inhibits transport by SMDR2, a Pgp orthologue from S. mansoni, and that PZQ is a likely substrate of SMDR2. Here, we examine the physiological roles of SMDR2 and SmMRP1 (the S. mansoni orthologue of MRP1) in S. mansoni adults, using RNAi to knock down expression, and pharmacological agents to inhibit transporter function. We find that both types of treatments disrupt parasite egg deposition by worms in culture. Furthermore, administration of different MDR inhibitors to S. mansoni-infected mice results in a reduction in egg burden in host liver. These schistosome MDR transporters therefore appear to play essential roles in parasite egg production, and can be targeted genetically and pharmacologically. Since eggs are responsible for the major pathophysiological consequences of schistosomiasis, and since they are also the agents for transmission of the disease, these results suggest a potential strategy for reducing disease pathology and spread.

Schistosomes are parasitic flatworms that are the causative agents of schistosomiasis, a major tropical disease. As adults, schistosomes reside within the host vasculature, taking up nutrients, evading host defenses, and expelling wastes and toxins. Multidrug resistance transporters are involved in removal of toxins and foreign compounds, including drugs, from cells. These transporters have broad selectivity, and when upregulated or mutated, can confer resistance to a wide spectrum of drugs against mammalian tumor cells. They are also associated with drug resistance in various parasites, including helminths. In this report, we have used knockdown of expression of these proteins and pharmacological inhibition of their transport function to dissect their physiological role in the schistosome life cycle. We find that either reducing transporter expression or pharmacologically inhibiting transporter function leads to disruption of egg production by adult worms. Eggs deposited within the host are the major cause of disease pathology, and eggs excreted by the host are the means of continuation of the life cycle and transmission of the disease. The capability to interfere with schistosome egg production could have major implications for development of new treatment strategies.

Synergy-directed fractionation of botanical medicines: a case study with goldenseal (Hydrastis canadensis)

It is often argued that the efficacy of herbal medicines is a result of the combined action of multiple constituents that work synergistically or additively. Determining the bioactive constituents in these mixtures poses a significant challenge. We have developed an approach to address this challenge, synergy-directed fractionation, which combines comprehensive mass spectrometry profiling with synergy assays and natural products isolation. The applicability of synergy-directed fractionation was demonstrated using the botanical medicine goldenseal (Hydrastis canadensis) as a case study. Three synergists from goldenseal were identified, sideroxylin, 8-desmethyl-sideroxylin, and 6-desmethyl-sideroxylin. These flavonoids synergistically enhance the antimicrobial activity of the alkaloid berberine (also a constituent of H. canadensis) against Staphylococcus aureus by inhibition of the NorA multidrug resistance pump. The flavonoids possess no inherent antimicrobial activity against S. aureus; therefore, they could have been missed using traditional bioactivity-directed fractionation. The flavonoid synergists are present at higher concentration in extracts from H. canadensis leaves, while the antimicrobial alkaloid berberine is present at higher levels in H. canadensis roots. Thus, it may be possible to produce an extract with optimal activity against S. aureus using a combination of goldenseal roots and leaves.

Norlignans, acylphloroglucinols, and a dimeric xanthone from Hypericum chinense

Two new norlignans, hyperiones A (1) and B (2), three new acylphloroglucinols, aspidinol C (3) and hyperaspidinols A (5) and B (6), the known compound aspidinol D (4), and the symmetrical dimeric xanthone hyperidixanthone (7) were isolated from Hypericum chinense. Their structures were established by spectroscopic analysis. In an antibacterial assay using a panel of multidrug-resistant (MDR) strains, compounds 3 and 4 exhibited promising activity against the NorA efflux protein overexpressing MDR Staphylococcus aureus strain SA-1199B with a minimum inhibitory concentration (MIC) of 2 μg/mL (8.4 μM) and 4 μg/mL (16.8 μM), respectively. The positive control antibiotic norfloxacin showed activity at MIC 32 μg/mL (100 μM).

Characterization of a xylose containing oligosaccharide, an inhibitor of multidrug resistance in Staphylococcus aureus, from Ipomoea pes-caprae

Pescaprein XVIII (1), a type of bacterial efflux pump inhibitor, was obtained from the CHCl(3)-soluble resin glycosides of beach morning glory (Ipomoea pes-caprae). The glycosidation sequence for pescaproside C, the glycosidic acid core of the lipophilic macrolactone 1 containing D-xylose and L-rhamnose, was characterized by means of several NMR techniques and FAB mass spectrometry. Recycling HPLC also yielded eight non-cytotoxic bacterial resistance modifiers, the two pescapreins XIX (2) and XX (3) as well as the known murucoidin VI (4), pecapreins II (6) and III (7), and stoloniferins III (5), IX (8) and X (9), all of which contain simonic acid B as their oligosaccharide core. Compounds 1-9 were tested for in vitro antibacterial and resistance-modifying activity against strains of Staphylococcus aureus possessing multidrug resistance efflux mechanisms. All of the pescapreins potentiated the action of norfloxacin against the NorA over-expressing strain by 4-fold (8 microg/mL from 32 microg/mL) at a concentration of 25 microg/mL.

[Advances in the study of the microbial efflux pumps and its inhibitors development]

Drug resistant bacteria is an increasingly urgent challenge to public health. Bacteria adaptation and extensive abuse of antibiotics contribute to this dilemma. Active efflux of antibiotics is employed by the bacteria to survive the antibiotic pressure. Efflux pump is one of the hot spots of current drug related studies and ideal targets for the improvement of treatment. The efflux pumps and related mechanisms of action, regulation of expression and methodologies were summarized. Comparative genomics analyses were employed to elucidate the underlying mechanisms of action and evolution of efflux pump as exemplified by the Mycobacterium in our lab, which is a crucial re-emerging threat to global public health. The pathway and state-of-art drug development of efflux pump related drugs are included too.

Antibiotic exposure does not influence MRP2 functional expression in Caco-2 cells

Multidrug resistance-associated protein 2 (MRP2) is associated with active drug efflux and may influence oral bioavailability of common classes of drugs. MRP2 expression demonstrates plasticity. Caco-2 cells, a routine in vitro model for predicting oral bioavailability, are often cultured in media containing antibiotics. We have investigated whether exposure of Caco-2 cells to two common antibiotic regimes alters MRP2 functional expression. Caco-2 cells were grown in the presence or absence of either gentamicin or penicillin-streptomycin for up to 9 weeks. MRP2 functional activity was assessed by calcein efflux across the apical membrane. MRP2 protein expression was determined by immunoblots. Neither antibiotic regime resulted in consistent changes in calcein efflux across the apical membrane (reflecting MRP2 activity) or basolateral membrane (reflecting MRP3 and possibly MRP6 activity) of Caco-2 cells. MRP2 protein expression also showed no change in response to antibiotic exposure. Routine exposure of Caco-2 cells to penicillin-streptomycin or gentamicin does not affect apical MRP2 functional activity in intestinal enterocytic Caco-2 cells. Extrapolating these results to the situation in vivo suggests that the oral bioavailability of MRP substrates is not predicted to be influenced by recent courses of antibiotics.

The influence of exposure history on arsenic accumulation and toxicity in the killifish, Fundulus heteroclitus

Exposure to arsenic is known to cause adverse effects in aquatic biota and wildlife and is of major concern to human health. Although numerous studies have investigated the toxicity of arsenic, little is known about the effects of acquired tolerance on arsenic accumulation and toxicity outside of cell culture models. Accordingly, studies were conducted on the estuarine fish, Fundulus heteroclitus, that were preexposed to nontoxic concentrations of arsenic (as sodium arsenite; 0.7 and 106 micromol As/L) for 96 h or naïve to elevated arsenic to determine the effects of acclimation on arsenic toxicity and accumulation. Tolerance to arsenic was rapidly (96 h) acquired in killifish that were preexposed. In toxicity tests with arsenic-acclimated killifish, preexposure to 106 micromol As/L resulted in a reduction in toxicity when compared to naïve animals. Toxicity in arsenic-acclimated fish also was distinguished by a delayed onset of mortality that manifested in dose-dependent fashion and was significant even for the lower acclimation concentration (0.7 micromol As/L). The increase tolerance acquired following preexposure to 106 micromol As/L for 96 h was associated with lower concentrations of arsenic in all monitored tissues (e.g., gill, liver, kidney) and the whole body when fish were exposed to 240 micromol As/L for an additional 96 h. In accordance with these observations, expression of the multidrug resistance- associated protein (MRP)-2 gene, which is responsible for transporting arsenic conjugated to glutathione out of cells, was increased in the liver of arsenic-acclimated fish.

ATP-binding cassette multidrug transporters in Indian-rock oyster Saccostrea forskali and their role in the export of an environmental organic pollutant tributyltin

ATP-binding cassette (ABC) multidrug transporters confer resistance in human cancer cells as well as in pathogenic microorganisms by mediating the extrusion of various chemotherapeutic drugs out of the cell. In aquatic invertebrates, the presence of ABC transporters which are involved in the multi-xenobiotic resistance has been demonstrated. However, most studies have been confined to the MDR1 subfamily. In the present study, we characterized the expression and localization of the ABC multidrug transporters including MDR1, MRP1 and BCRP subfamily in the Indian-rock oyster Saccostrea forskali. To our knowledge, these data represent one of the first reports on the orthologues of MRP1 and BCRP in marine invertebrates. Furthermore, the observations of (i) the expression of the ABC multidrug proteins in detoxifying tissues; (ii) the induction of these transporters upon exposure to an environmental organic pollutant tributyltin (TBT); and (iii) the concentration-dependent inhibition of rhodamine efflux by TBT imply a possible role of these proteins in the export of TBT. Our findings along with previous studies suggest that the ABC multidrug transporters act as a detoxifying mechanism of various toxic agents including TBT in aquatic organisms.

ABCC2 (MRP2, cMOAT) can be localized in the nuclear membrane of ovarian carcinomas and correlates with resistance to cisplatin and clinical outcome

PURPOSE

Cisplatin resistance is a major obstacle in the treatment of ovarian carcinoma. ABCC2 is commonly localized in apical cell membranes and could confer cisplatin resistance. Here, we show that ABCC2 can be localized in the cytoplasmic membrane as well as in the nuclear membrane of various human tissues including ovarian carcinoma cells.

EXPERIMENTAL DESIGN

For the subcellular detection of ABCC2, immunohistochemistry was done using 41 Federation Internationale des Gynaecologistes et Obstetristes stage III ovarian carcinoma specimens prepared before treatment with cisplatin-based schemes and 35 specimens from the same group after chemotherapy. Furthermore, 11 ovarian carcinoma cell lines as well as tissue microarrays consisting of various human tissues were analyzed.

RESULTS

Nuclear membranous localization of ABCC2 was associated with response to first-line chemotherapy at primary (P = 0.0013) and secondary surgery (P = 0.0060). Cases with relapse showed higher nuclear membrane expression at primary (P = 0.0003) and secondary surgery (P = 0.0024). Kaplan-Meier analyses showed that weak nuclear membrane ABCC2 expression before treatment was associated with significantly longer overall (P = 0.04) and progression-free survival (P = 0.001); following chemotherapy, it correlated with significantly longer progression-free survival (P = 0.038). Tissue microarrays confirmed nuclear membranous localization of ABCC2, in particular, in poorly differentiated cells. In ovarian carcinoma cells, it correlated with resistance against cisplatin, whereas localization in the cytoplasmic membrane did not.

CONCLUSIONS

ABCC2 confers resistance to cisplatin of ovarian carcinoma in cell culture systems and in clinics when expressed in the nuclear membrane. Thus, ABCC2 localization can predict platinum therapy outcome. Furthermore, expression of ABCC2 in nuclear membranes in human tissues is specific for poorly differentiated cells including stem cells.

Disruption of function and localization of tight junctional structures and Mrp2 in sustained estradiol-17beta-D-glucuronide-induced cholestasis

Estradiol-17beta-D-glucuronide (E(2)17G) induces immediate and profound but transient cholestasis in rats when administered as a single bolus dose. Here, we examined the consequence of sustained E(2)17G cholestasis and assessed the function and localization of the tight junctional proteins zonula occludens-1 (ZO-1) and occludin and of the canalicular transporter multidrug resistance-associated protein-2 (Mrp2). An initial dose of E(2)17G (15 mumol/kg iv) followed by five subsequent doses of 7.5 mumol/kg from 60 to 240 min induced a sustained 40-70% decrease in bile flow. Following their biliary retrograde administration, cholera toxin B subunit-FITC or horseradish peroxidase were detected at the sinusoidal domain, indicating opening of the paracellular route; this occurred as early as 15 min after the first dose as well as 15 min after the last dose of E(2)17G, but not following the administration of vehicle in controls. Localization of ZO-1 and occludin was only slightly affected under acute cholestatic conditions but was severely disrupted under sustained cholestasis, with their appearance suggesting a fragmented structure. Endocytic internalization of Mrp2 to the pericanalicular region was apparent 20 min after a single E(2)17G administration; however, Mrp2 was found more deeply internalized and partially redistributed to the basolateral membrane under sustained cholestasis. In conclusion, acute E(2)17G-induced cholestasis increased permeability of the tight junction, while sustained cholestasis provoked a significant redistribution of ZO-1, occludin, and Mrp2 in addition to increased permeability of the tight junction. Altered tight junction integrity likely contributes to impaired bile secretion and may be causally related to changes in Mrp2 localization.

Uncoupling by (--)-epigallocatechin-3-gallate of ATP-sensitive potassium channels from phosphatidylinositol polyphosphates and ATP

Of green tea catechins, (--)-epigallocatechin-3-gallate (EGCG) and (--)-epicatechin-3-gallate (ECG), but not (--)-epicatechin and (--)-epigallocatechin, inhibit the activity of ATP-sensitive potassium (K(ATP)) channels at tens of micromolar concentrations, ECG being three times more effective than EGCG. Further, we found that by using cloned beta cell-type K(ATP) channels, only EGCG at 1 microM, a readily achievable plasma concentration by oral intake in humans, but not other epicatechins, significantly blocked channel reactivation after ATP wash-out, suggesting that interaction of phosphatidylinositol polyphosphates (PIP) with the channel was impaired by EGCG. In addition, a 10-fold higher concentration of EGCG reduced the channel sensitivity to ATP, but not AMP and ADP. This effect of EGCG was greater in the channel with the sulfonylurea receptor (SUR) than with the inwardly rectifying K(+) channel (Kir6.2) alone. Neomycin, a polycation, profoundly suppressed the effect of EGCG. Expectedly, glucose-stimulated cytosolic Ca(2+) elevation in rat pancreatic beta cells, and insulin secretory responses to high glucose loading in vivo were impaired by EGCG. In rabbit cardiac myocytes, dinitrophenol-induced opening of the channel was delayed by 1 microM EGCG. These results suggest that EGCG may interact with PIP-binding sites on the Kir6.2 subunit. SUR further endows EGCG with an ability to interfere with an interaction of the gamma-phosphate tail of ATP with Kir6.2. The specificity of EGCG possibly implies that 5'-OH of the B-ring on the pyrogallol moiety in the EGCG molecule may be critical for these actions of EGCG on the K(ATP) channel.

Effects of standard chemotherapy on tumor growth and regulation of multidrug resistance genes and proteins in childhood rhabdomyosarcoma

The prognosis of rhabdomyosarcoma (RMS) in advanced stages is still sobering. Therapy is limited due to local tumor recurrence, development of metastases and multidrug resistance. The aim of this study was to investigate the development of multidrug resistance in cell lines and in xenografts of alveolar and embryonal RMS treated according to the German Soft Tissue Sarcoma Study (CWS). Alveolar and embryonal RMS cell lines were treated with Vincristine, Topotecan, Carboplatin, Actinomycin D, or Ifosfamide. Expression levels of resistance-associated genes were assessed using Real time-PCR. Nude mice (NMRI nu/nu, n = 10 per group) underwent xenotransplantation of human embryonal or alveolar RMS. Animals were treated with standard chemotherapeutic drugs Vincristine, Topotecan, Carboplatin, Actinomycin D, or Ifosfamide according to treatment schedules of the CWS-study. Tumor sizes were measured and relative tumor volumes were calculated. Animals were sacrificed after 20 days and standard histology, Real-time-PCR for MDR1-, MRP-, LRP- and MDM2-gene as well as immunohistochemistry for MDR1-, LRP-, and MRP-protein were performed. In the cell lines, an up-regulation of MDR-1 gene was found in alveolar rhabdomyosarcoma. In embryonal rhabdomyosarcoma, an up-regulation of LRP and MRP was found. Standard chemotherapy of alveolar rhabdomyosarcoma resulted in a significant reduction of tumor growth (P < 0.05) in all groups. In embryonal rhabdomyosarcoma strongest effects were found after treatment with Ifosfamide, Vincristine and Carboplatin (P < 0.05). RT-PCR revealed a MDR1-dependent mechanism in alveolar rhabdomyosarcoma. In embryonal rhabdomyosarcoma, MDR1 occurred to a lower degree. Immunohistochemistry revealed correlating expression levels of multidrug resistance-associated proteins. The use of established chemotherapy on human RMS in vivo had strong effects on xenografts compared to their controls. In all cases, there was only a reduction of tumor growth, but not a complete eradication of the tumors. Chemotherapy seemed to upregulate the expression of resistance-associated genes in vitro and in vivo. The mechanism of multidrug resistance depends on the tumor subtype. Therefore, further investigations will be required to evaluate multidrug resistance in patients and to investigate new modalities for a reversal of multidrug resistance.

Flavonoids inhibit breast cancer resistance protein-mediated drug resistance: transporter specificity and structure–activity relationship

PURPOSE

ATP-binding cassette (ABC) transporters, such as P-glycoprotein (P-gp), breast cancer resistance protein (BCRP), and multidrug resistance-related protein 1 (MRP1), confer resistance to various anticancer agents. We previously reported that some flavonoids have BCRP-inhibitory activity. Here we show the reversal effects of an extensive panel of flavonoids upon BCRP-, P-gp-, and MRP1-mediated drug resistance.

METHODS

Reversal effects of flavonoids upon BCRP-, P-gp-, or MRP1-mediated drug resistance were examined in the BCRP- or MDR1-transduced human leukemia K562 cells or in the MRP1-transfected human epidermoid carcinoma KB-3-1 cells using cell growth inhibition assays. The IC(50) values were determined from the growth inhibition curves. The RI(50) values were then determined as the concentration of inhibitor that causes a twofold reduction of the IC(50) in each transfectant. The reversal of BCRP activity was tested by measuring the fluorescence of intracellular topotecan.

RESULTS

The BCRP-inhibitory activity of 32 compounds was screened, and 20 were found to be active. Among these active compounds, 3',4',7-trimethoxyflavone showed the strongest anti-BCRP activity with RI(50) values of 0.012 microM for SN-38 and 0.044 muM for mitoxantrone. We next examined the effects of a panel of 11 compounds on P-gp- and MRP1-mediated drug resistance. Two of the flavones, 3',4',7-trimethoxyflavone and acacetin, showed only low anti-P-gp activity, with the remainder displaying no suppressive effects against P-gp. None of the flavonoids that we tested inhibited MRP1.

CONCLUSION

Our present results thus indicate that many flavonoids selectively inhibit BCRP only. Moreover, we examined the structure-BCRP inhibitory activity relationship from our current study.

ATP-sensitive potassium currents reduce the PGE2-mediated enhancement of excitability in adult rat sensory neurons

Behavioral studies have shown that the hyperalgesia arising from inflammatory agents, such as prostaglandin E(2) (PGE(2)), can be antagonized by activators of the ATP-sensitive potassium current (K(ATP)). This observation raises questions as to whether this suppression results from a direct action on sensory neurons and what are the cellular mechanisms giving rise to this inhibition. We found that small to medium diameter sensory neurons isolated from the L4-6 DRGs expressed the mRNAs for Kir6.1, Kir6.2, and SUR1. In perforated-patch clamp recordings from acutely dissociated sensory neurons from the young adult rat, exposure to 300 microM diazoxide, a K(ATP) channel agonist, significantly hyperpolarized the resting membrane potential, reduced the number of action potentials evoked by a ramp of depolarizing current, and increased the amplitude of inward K(ATP) currents evoked by the voltage ramp. Similar results were obtained with the protonophore FCCP, which is known to reduce the levels of intracellular ATP and lead to the activation of K(ATP). Only a subpopulation of sensory neurons was sensitive to diazoxide whereas other neurons were unaffected. Treatment with 1 microM PGE(2) significantly enhanced the excitability of these small to medium diameter capsaicin-sensitive sensory neurons; this enhancement was reversed by subsequent exposure to diazoxide in a subpopulation of neurons. Similar to diazoxide, exposure to 8-Br-cyclic GMP antagonized the PGE(2)-induced increase in excitability. The effects of 8-Br-cyclic GMP could be reversed by exposure to glibenclamide, an antagonist of K(ATP) channels. As with diazoxide, only a subpopulation of sensory neurons were affected by 8-Br-cyclic GMP. These results demonstrate that activation of K(ATP) can reverse the sensitization produced by PGE(2) and may be an important means to modulate the enhanced excitability that results from inflammatory or injury conditions.

LmrCD is a major multidrug resistance transporter in Lactococcus lactis

When Lactococcus lactis is challenged with drugs it displays a multidrug resistance (MDR) phenotype. In silico analysis of the genome of L. lactis indicates the presence of at least 40 putative MDR transporters, of which only four, i.e. the ABC transporters LmrA, LmrC and LmrD, and the major facilitator LmrP, have been experimentally associated with the MDR. To understand the molecular basis of the MDR phenotype in L. lactis, we have performed a global transcriptome analysis comparing four independently isolated drug-resistant strains of L. lactis with the wild-type strain. The results show a strong and consistent upregulation of the lmrC and lmrD genes in all four strains, while the mRNA levels of other putative MDR transporters were not significantly altered. Deletion of lmrCD renders L. lactis sensitive to several toxic compounds, and this phenotype is associated with a reduced ability to secrete these compounds. Another gene, which is strongly upregulated in all mutant strains, specifies LmrR (YdaF), a local transcriptional repressor of lmrCD that belongs to the PadR family of transcriptional regulators and that binds to the promoter region of lmrCD. These results demonstrate that the heterodimeric MDR ABC transporter LmrCD is a major determinant of both acquired and intrinsic drug resistance of L. lactis.

Iptakalim modulates ATP-sensitive K(+) channels in dopamine neurons from rat substantia nigra pars compacta

Iptakalim, a novel cardiovascular ATP-sensitive K(+) (K(ATP)) channel opener, exerts neuroprotective effects on dopaminergic (DA) neurons against metabolic stress-induced neurotoxicity, but the mechanisms are largely unknown. Here, we examined the effects of iptakalim on functional K(ATP) channels in the plasma membrane (pm) and mitochondrial membrane using patch-clamp and fluorescence-imaging techniques. In identified DA neurons acutely dissociated from rat substantia nigra pars compacta (SNc), both the mitochondrial metabolic inhibitor rotenone and the sulfonylurea receptor subtype (SUR) 1-selective K(ATP) channel opener (KCO) diazoxide induced neuronal hyperpolarization and abolished action potential firing, but the SUR2B-selective KCO cromakalim exerted little effect, suggesting that functional K(ATP) channels in rat SNc DA neurons are mainly composed of SUR1. Immunocytochemical staining showed a SUR1-rather than a SUR2B-positive reaction in most dissociated DA neurons. At concentrations between 3 and 300 microM, iptakalim failed to hyperpolarize DA neurons; however, 300 microM iptakalim increased neuronal firing. In addition, iptakalim restored DA neuronal firing during rotenone-induced hyperpolarization and suppressed rotenone-induced outward current, suggesting that high concentrations of iptakalim close neuronal K(ATP) channels. Furthermore, in human embryonic kidney 293 cells, iptakalim (300-500 microM) closed diazoxide-induced Kir6.2/SUR1 K(ATP) channels, which were heterologously expressed. In rhodamine-123-preloaded DA neurons, iptakalim neither depolarized mitochondrial membrane nor prevented rotenone-induced mitochondrial depolarization. These data indicate that iptakalim is not a K(ATP) channel opener in rat SNc DA neurons; instead, iptakalim is a pm-K(ATP) channel closer at high concentrations. These effects of iptakalim stimulate further pharmacological investigation and the development of possible therapeutic applications.

Estimation of efflux mediated multi-drug resistance and its correlation with expression levels of two major efflux pumps in mycobacteria

Multidrug resistance has been posing an increasing problem in the treatment of tuberculosis. Mutations in the genomic targets of drugs have been identified as the major mechanism behind this resistance. However, high degree of resistance in some isolates towards major drugs like rifampicin, isoniazid, ethambutol and streptomycin can not be explained solely on the basis of mutations. Besides this, certain other mechanisms like efflux pumps have also been considered as alternative mechanisms in the drug resistant isolates where there is no mutation and these mechanisms are specially important for drug resistance in non-tuberculous mycobacteria (NTM). In this study, we have estimated efflux pump mediated drug resistance in different mycobacterial species with the help of efflux pump inhibitors. All major anti-tuberculous drugs have been shown to be extruded by efflux pumps and the degree to which these drugs are extruded, vary in different mycobacterial species and isolates. The correlation of this resistance with functional activity of two major efflux pump genes pstB and Rv1258c was also assessed by reverse transcription PCR. Besides the significant role of these pumps observed, other efflux pumps, present in mycobacteria, may also be involved in drug resistance and need to be investigated.

In vitro andin vivo evaluation of WK-X-34, a novel inhibitor of P-glycoprotein and BCRP, using radio imaging techniques

Overexpression of the multidrug resistance proteins P-glycoprotein (Pgp) and breast cancer resistance protein (BCRP) results in treatment failure of many malignancies including ovarian cancer. Dual inhibition of Pgp and BCRP may restore the sensitivity of resistant cells to anticancer drugs. We report the synthesis and characterization of a novel anthranilic-acid based Pgp and BCRP modulator, WK-X-34. In vitro inhibition of Pgp activity was evaluated using 99mTc-Sestamibi and daunorubicin accumulation in Pgp overexpressing human ovarian cancer cells (A2780/Adr) and its sensitive counterpart (A2780/wt). Interaction with BCRP was examined with a mitoxantrone-efflux assay in BCRP-overexpressing MCF7/mx cells, with flow cytometry. Interactions with the multidrug resistance associated proteins (MRP) were evaluated in transfected MRP1, MRP2 and MRP3 cell lines, using a 5-CFDA efflux assay. In vivo 99mTc-Sestamibi imaging of human ovarian cancer xenografts was used to evaluate the in vivo efficacy of WK-X-34 in mice. Daunorubicin accumulation in A2780/Adr cells was inhibited by WK-X-34 at nanomolar concentrations (IC50: 82.1 +/- 6 nM). WK-X-34 inhibited mitoxantrone accumulation in BCRP-overexpressing cells at micromolar concentrations (IC50 = 26.5 +/- 4.6 microM), whereas WK-X-34 did not significantly alter 5-CFDA accumulation in MRP transfected cells. In vivo, uptake of 99mTc-Sestamibi was significantly increased in A2780/Adr xenograft tumors, brain and intestine (AUCs(0-4h) 136%, 147% and 138%; p < 0.05) in mice dosed with WK-X-34 (20 mg/kg i.p.). WK-X-34 selectively modulates Pgp and BCRP in vitro and in vivo in multidrug resistant ovarian cancer cells, and thus may have potential utility in the treatment of multidrug resistant tumors.

[Mechanisms of drug resistance in epilepsy]

Epilepsy can be classified as a multifactor neurological disease which affects ca. 1% of the world's population. Approximately 30% of epileptic patients do not favourably respond to antiepileptic drug treatment, but--on the other hand--the mechanism of drug-resistance has not been satisfactorily elucidated so far. Cortical dysplasia, hippocampal sclerosis, ion channel and receptor mutations and autoimmune processes can all contribute to the development of drug-resistant epilepsy. Furthermore, a crucial role of the overexpression of ABC transporters in eliminating rapidly antiepileptic drugs from the central nervous system and, on the other hand, the insensitivity of the epileptogenic tissue to some sodium channel blockers and GABA-mimetic agents have been strongly suggested. Further progress in elucidating the molecular basis of epilepsy and a rational polytherapy with novel and classic antiepileptic drugs, along with the development of diagnostic tools, may significantly contribute to better prognostication in this disease. The present paper briefly summarizes contemporary views on drug resistance in epilepsy, being particularly concerned with its neurobiological background.

Role of Lymphocyte Multidrug Resistance Protein 1 in HIV Infection

The multidrug resistance protein 1 (MRP1) is a drug transporter that protects cells from oxidative stress, which increases HIV-1 replication. The aim of this study was to characterize the expression, function, and role of lymphocyte MRP1 in HIV-1 infection and its modulation by antiretroviral drugs such as the protease inhibitors (PIs). Peripheral blood mononuclear cells (PBMCs) from HIV-positive individuals do not show significant alterations of MRP1 expression despite highly active antiretroviral therapy and HIV plasma viral load levels; however, they exhibit different intracellular MRP1 expression as compared with healthy subjects. By contrast, MRP efflux function is increased in subjects with primary HIV infection and becomes defective in later stages of the infection. PI- and probenecid (PBCD)-mediated inhibition of MRP lowers the in vitro stress-induced response of lymphoid cells by reducing the level of the specific reactive oxygen species superoxide anion and hydrogen peroxide. Finally, the blockade of MRP by PBCD and PIs down-modulates HIV-1 replication by a mechanism independent of inhibition of the HIV-1 protease. Our results are consistent with a model wherein HIV replication is favored by the MRP1-related oxidative stress and inhibition of MRP1 may contribute to the antiviral activity of PIs.

Long-term azithromycin in cystic fibrosis: another possible mechanism of action?

Azithromycin is used for the treatment of cystic fibrosis lung disease, although its mechanisms of action are not completely understood. Besides its antiinflammatory and antimicrobial activities, one possibility could be the overexpression induction of the multidrug resistance-associated protein (MRP), which could affect chloride transport, thus overcoming the ion transport defect of cystic fibrosis. Seven patients were evaluated before and after 4 weeks of azithromycin treatment (500 mg once daily). Ion transport was studied in vivo by measuring nasal potential difference (NPD). MRP mRNA expression was studied in nasal cells by an internal standard-based semiquantitative RT-PCR assay. NPD was consistent with cystic fibrosis before treatment. After azithromycin treatment, sodium transport was still impaired, whereas a significant increase in chloride conductance was observed (p = 0.03). A significant direct correlation was found between MRP mRNA expression levels and NPD chloride response after azithromycin treatment (p = 0.04, r = 0.78). In conclusion, azithromycin may induce MRP overexpression and restore chloride conductance in the airways of cystic fibrosis patients. These findings suggest a new potential role of azithromycin in the treatment of cystic fibrosis pulmonary disease, i.e. the possibility to upregulate proteins whose function may, at least in part, compensate for the basic defect of cystic fibrosis.

Interactions of mefloquine with ABC proteins, MRP1 (ABCC1) and MRP4 (ABCC4) that are present in human red cell membranes

Human erythrocyte membranes express the multidrug resistance-associated proteins, MRP1, MRP4 and 5, that collectively can efflux oxidised glutathione, glutathione conjugates and cyclic nucleotides. It is already known that the quinoline derivative, MK-571, is a potent inhibitor of MRP-mediated transport. We here examine whether the quinoline-based antimalarial drugs, amodiaquine, chloroquine, mefloquine, primaquine, quinidine and quinine, also interact with erythrocyte MRPs with consequences for their access to the intracellular parasites or for efflux of oxidised glutathione from infected cells. Using inside-out vesicles prepared from human erythrocytes we have shown that mefloquine and MK-571 inhibit transport of 3 microM [(3)H]DNP-SG known to be mediated by MRP1 (IC(50) 127 and 1.1 microM, respectively) and of 3.3 microM [(3)H]cGMP thought but not proven to be mediated primarily by MRP4 (IC(50) 21 and 0.41 microM). They also inhibited transport in membrane vesicles prepared from tumour cells expressing MRP1 or MRP4 and blocked calcein efflux from MRP1-overexpressing cells and BCECF efflux from MRP4-overexpressing cells. Both stimulated ATPase activity in membranes prepared from MRP1 and MRP4-overexpressing cells and inhibited activity stimulated by quercetin or PGE(1), respectively. Neither inhibited [alpha-(32)P]8-azidoATP binding confirming that the interactions are not at the ATP binding site. These results demonstrate that mefloquine and MK-571 both inhibit transport of other substrates and stimulate ATPase activity and thus may themselves be substrates for transport. But at concentrations achieved clinically mefloquine is unlikely to affect the MRP1-mediated transport of GSSG across the erythrocyte membrane.

A nuclear receptor-mediated choleretic action of fibrates is associated with enhanced canalicular membrane fluidity and transporter activity mediating bile acid-independent bile secretion

Fibrates are commonly used lipid-lowering agents that act via PPARalpha, a member of the nuclear hormone receptor superfamily. The mechanism(s) of fibrate-induced changes in the hepatic canalicular membrane and bile lipids are still unknown. Therefore, the aim of this study was to investigate the influence of fibrates on hepatic lipid metabolism and to assess the hepatocellular cytoprotective effect on hepatocyte canalicular membrane. Male ICR mice were fed standard chow with or without bezafibrate (100 mg/kg) for 6 days. The expression of canalicular membrane transporters (Mdr2 and Mrp2) was evaluated by RT-PCR and Western blotting. Canalicular membrane fluidity was also investigated. Canalicular membrane fluidity was markedly increased by fibrates. The expression of mdr 2 and mrp2 mRNA and protein showed a significant increase in fibrate-treated mice. These results suggested that fibrates improve liver function by enhancing bile secretion. The mechanism of the choleretic action of fibrate therapy might involve the enhancement of bile acid-independent bile secretion, since increased expression of Mdr2 and Mrp2 was found in fibrate-treated animals. These changes were very likely mediated by PPARalpha, and the increase of canalicular membrane fluidity may have been partly associated with enhancement of this transporter activity.

Multiple flavonoid-binding sites within multidrug resistance protein MRP1

Recombinant nucleotide-binding domains (NBDs) from human multidrug resistance protein MRP1 were overexpressed in bacteria and purified to measure their direct interaction with high-affinity flavonoids, and to evaluate a potential correlation with inhibition of MRP1-mediated transport activity and reversion of cellular multidrug resistance. Among different classes of flavonoids, dehydrosilybin exhibited the highest affinity for both NBDs, the binding to N-terminal NBD1 being prevented by ATP. Dehydrosilybin increased vanadate-induced 8-N3-[alpha-32P]ADP trapping, indicating stimulation of ATPase activity. In contrast, dehydrosilybin strongly inhibited leukotriene C4 (LTC4) transport by membrane vesicles from MRP1-transfected cells, independently of reduced glutathione, and chemosensitized cell growth to vincristine. Hydrophobic C-isoprenylation of dehydrosilybin increased the binding affinity for NBD1, but outsite the ATP site, lowered the increase in vanadate-induced 8-N3-[alpha-32P]ADP trapping, weakened inhibition of LTC4 transport which became glutathione dependent, and induced some cross-resistance. The overall results indicate multiple binding sites for dehydrosilybin and its derivatives, on both cytosolic and transmembrane domains of MRP1.

Unique inhibition of bile salt-induced apoptosis by lecithins and cytoprotective bile salts in immortalized mouse cholangiocytes

Bile duct epithelium is physiologically exposed to high concentrations of bile salts, suggesting the presence of a cytoprotective mechanism(s). The aim of this study was to clarify whether bile salts cause bile duct cell damage and to elucidate the mechanism(s) providing protection against such an action of bile salts. Immortalized mouse cholangiocytes were incubated with taurocholate, taurochenodeoxycholate, glycochenodeoxycholate (GCDC), taurodeoxycholate, and tauroursodeoxycholate (TUDC), followed by flow-cytometric analysis and caspase activity assay to evaluate the induction of apoptosis. GCDC time-dependently induced caspase 3 (3.4-fold)- and caspase 9 (1.4-fold)-mediated apoptosis of cholangiocytes, but this was inhibited by lecithins and TUDC. Further, expression of cholangiocyte bile salt transporters (apical sodium-dependent bile salt transporter [Asbt] and multidrug resistance protein 3 [Mrp3]) was examined by RT-PCR and western blotting, and cholangiocyte bile salt uptake was determined using radiolabeled bile salts. Expression of cholangiocyte Asbt and Mrp3 was increased by bile salts, whereas lecithins interestingly reduced bile salt uptake to inhibit cholangiocyte apoptosis. In conclusion, bile salts themselves cause cholangiocyte apoptosis when absorbed by and retained inside the cell, but this is inhibited by washing out cytotoxic bile salts according to Mrp3, a rescue exporting molecule. Biliary lecithin is seemingly another cytoprotective player against cytotoxic bile salts, reducing their uptake, and this is associated with a reduced expression of Mrp3.

Modulation of MRP1-like efflux activity in human erythrocytes caused by membrane perturbing agents

The effect of membrane perturbing agents on the efflux (37 degrees C, 60 min) of the fluorescent probe 2', 7'-bis-(carboxypropyl)-5(6)-carboxyfluorescein (BCPCF) from human erythrocytes was studied. Several anionic amphiphiles (detergents) markedly inhibited BCPCF efflux (IC50 < or = 40 microM). Most zwitter-ionic amphiphiles were inefficient inhibitors. Non-ionic and cationic amphiphiles had minor effects or increased efflux. Of the aliphatic inhibitors, C12-homologues were the most efficient. Hexanol, ethanol, methyl-beta-cyclodextrin (MbetaCD) and diamide (+ washing) did not influence BCPCF efflux. It is suggested that amphiphiles affect BCPCF efflux by modulating multi-drug resistance protein 1 (MRP1, ABCC1) activity. A negative charge of amphiphiles is essential for the inhibitory effect, while alkyl chain length modulates inhibition. MRP1-mediated BCPCF efflux appears to be relatively insensitive to non-specific plasma membrane modification.

Characterisation of the brain multidrug resistance protein (BMDP/ABCG2/BCRP) expressed at the blood-brain barrier

The blood-brain barrier (BBB) plays the predominant role in controlling the passage of endogenous and xenobiotic substances between the circulating blood and the extracellular fluid environment of the brain. The transfer of compounds is strictly regulated by brain capillary endothelial cells (BCEC), which are interconnected to each other by well developed tight junctions, without fenestrations. Although hydrophobic molecules such as nicotine and ethanol readily cross the BBB by diffusion, the brain microvasculature shows a highly restrictive permeability to hydrophobic antitumor agents. So far, this multidrug resistance has been almost exclusively attributed to the most prominent member of the ATP-binding cassette (ABC) transporter family, P-glycoprotein located in the luminal membrane of brain capillary endothelial cells and to a minor extent to the multidrug resistance-associated proteins (MRPs). The brain multidrug resistance protein (BMDP) has recently been discovered at the porcine BBB and was shown to be highly homologous to the human breast cancer resistance protein (BCRP/ABCG2). Here, we demonstrate by northern blot and RT-PCR analysis that BMDP mRNA is more highly expressed in the capillary endothelial cells compared to other cell types of the brain. Immunocytochemistry of porcine BCEC showed a clear plasma membrane localisation of BMDP. Analysis of the total mRNA pool revealed that BMDP is more strongly expressed than P-glycoprotein and MRP1. Consistently, first transport studies indicate that active exclusion of the chemotherapeutic drug daunorubicin from the central nervous system is mediated mainly by this new transporter compared to P-glycoprotein or MRP1. Thus, we hypothesise that BMDP might play an important role in the exclusion of xenobiotics from the porcine brain.

Interaction of ochratoxin A with human intestinal Caco-2 cells: possible implication of a multidrug resistance-associated protein (MRP2)

Ochratoxin A (OTA), a nephrotoxic mycotoxin, is absorbed from small intestine and, in plasma, binds to serum albumin. Prolonged half-live results from reabsorption by proximal tubules and enterohepatic circulation. The mechanism whereby OTA crosses intestine was investigated by means of a cell culture system consisting of Caco-2 cells, as in vitro model of human intestinal epithelium. Cytotoxicity assays on proliferating Caco-2 cells showed that 0.4 microM OTA inhibits MTT reduction by 50%. Transepithelial transport and intracellular accumulation of OTA were studied in Caco-2 cells, differentiated in bicameral inserts. At pH 7.4, OTA is transported preferentially in basolateral (BL) to apical (AP) direction, suggesting a net secretion. Conditions closer to in vivo situation in duodenum (AP pH 6.0, BL pH 7.4) increase intracellular accumulation and transepithelial transport. AP to BL transport becomes higher than BL to AP transport, suggesting OTA absorption. Addition of serum albumin in BL compartment further increases OTA absorption across Caco-2 cells and suggests that in vivo OTA transport from serosal to luminal side of enterocytes is prevented, due to its binding to plasma proteins. Competition experiments showed that carrier systems for large neutral amino acids, H(+)/dipeptides cotransporter, organic anion (p-aminohippurate) carrier and organic anion transporter (oatp) are not implicated in OTA transport across Caco-2 cells, in contrast to what was reported in kidney and liver. AP and BL transport and intracellular accumulation of OTA are increased in the presence of non specific inhibitors of MRPs (indomethacin, genistein and probenecid) and of 1-chloro-2,4-dinitrobenzene (biotransformed into 2,4-dinitrophenyl-gluthatione, a specific inhibitor of MRPs), but are affected by verapamil, an inhibitor of P-gp. This suggests that the multidrug resistance-associated protein (MRP2) could be implicated in transepithelial transport. Therefore, absorption of OTA across the intestinal mucosa would be limited thanks to its excretion through MRP2 at the apical pole of enterocytes.

Co-induction of glutathione-S-transferases and multidrug resistance associated protein by xenobiotics in wheat

Herbicide safeners are known to protect monocotyledonous crops from herbicide injury by accelerating the metabolism of herbicides. We have investigated the effects of the safener cloquintocetmexyl, which protects small-grain cereals against the graminicidal herbicide, clodinafop-propargyl. Subtractive suppression hybridisation was used to identify wheat genes which are up-regulated by treatment not only with cloquintocet-mexyl but also with phenobarbital, which is known to stimulate xenobiotic metabolism in animals and plants. DNA sequences of five glutathione transferases (GSTs) belonging to three different classes and a multidrug resistance associated protein (MRP) homologue were identified in the screen. The chemical inducibility of these clones was confirmed by Northern analysis. The MRP protein was shown to be induced by treatments with cloquintocet-mexyl and phenobarbital and to be localised to the tonoplast. Since clodinafop-propargyl is not known to be metabolised by glutathionylation, the significance of GST induction is interpreted in terms of a generalised response to chemical stress, particularly the generation of active oxygen species. This work establishes herbicide safeners as useful tools for the identification of genes encoding herbicide-metabolising enzymes.

Xenobiotic export pumps, endothelin signaling, and tubular nephrotoxicants--a case of molecular hijacking

This article is a review on recent studies in intact renal proximal tubules that link tubular nephrotoxicants with endothelin (ET) regulation of xenobiotic export pump function. The data show that transport on p-glycoprotein and Mrp2 decreases rapidly when ET signals through an ET(B) receptor, NO synthase (NOS), and protein kinase C (PKC). Surprisingly, nephrotoxicants, such as radiocontrast agents, aminoglycoside antibiotics, and heavy metal salts, "hijack" this signaling pathway, causing ET release from the tubules, hormone binding to its receptor, activation of NOS and PKC, and reduced xenobiotic transport. These findings suggest a new common mechanism by which nephrotoxicants may act to disrupt renal tubular function.

The protease inhibitor ritonavir inhibits the functional activity of the multidrug resistance related-protein 1 (MRP-1)

BACKGROUND

Efflux pumps situated on the plasma membrane, such as P-glycoprotein (Pgp) and the multidrug resistance related-protein 1 (MRP-1), have been shown to extrude HIV protease inhibitors from the cell. MRP-1 is present on many barrier sites throughout the body, such as the blood-brain and blood-testis interfaces and could reduce the concentration of protease inhibitors in these sanctuary sites for HIV-1 replication. Factors that modulate efflux pump function in vivo are poorly defined.

OBJECTIVE

To analyze the inhibitory potential of the anti-retroviral drugs indinavir, amprenavir, ritonavir, lamivudine or zidovudine to modulate MRP-1 function.

METHODS

Effect of anti-HIV drugs on the efflux pump activity of MRP-1 was evaluated in the presence of increasing concentrations of human plasma, using UMCC-1/VP cells which stably over-express MRP-1. MRP-1 activity was abrogated by probenecid. The potential of blocking MRP-1 function for an extended (3 day) time period, was also examined in MRP-1 over-expressing cells cultured with either probenecid or the anti-retroviral drugs and a cytotoxic compound (etoposide) that is transported by MRP-1.

RESULTS

Ritonavir inhibited the functional activity of MRP-1 similarly to probenecid, as demonstrated by re-sensitization of MRP-1 over-expressing cells to cytotoxic effects of etoposide. Inhibition by ritonavir was inversely related to the concentration of human plasma added to the cells (r2 = 0.89). Other anti-HIV drugs didn't affect the MRP-1 mediated efflux of etoposide.

CONCLUSIONS

These data may be exploitable to further improve sanctuary site concentrations of anti-HIV or anti-cancer drugs by using ritonavir as a lead compound to develop more potent MRP-1 inhibitors.

Interaction of tyrosine kinase inhibitors with the human multidrug transporter proteins, MDR1 and MRP1

Specific tyrosine kinase inhibitors (TKIs) are rapidly developing clinical tools applied for the inhibition of malignant cell growth and metastasis formation. Most of these newly developed TKI molecules are hydrophobic, thus rapidly penetrate the cell membranes to reach intracellular targets. However, a large number of tumor cells overexpress multidrug transporter membrane proteins, which efficiently extrude hydrophobic drugs and thus may prevent the therapeutic action of TKIs. In the present work, we demonstrate that the most abundant and effective cancer multidrug transporters, MDR1 and MRP1, directly interact with several TKIs under drug development or already in clinical trials. This interaction with the transporters does not directly correlate with the hydrophobicity or molecular structure of TKIs, and shows a large variability in transporter selectivity and affinity. We suggest that performing enzyme- and cell-based multidrug transporter interaction tests for TKIs may greatly facilitate drug development, and allow the prediction of clinical TKI resistance based on this mechanism. Moreover, diagnostics for the expression of specific multidrug transporters in the malignant cells, combined with information on the interactions of the drug transporter proteins with TKIs, should allow a highly effective, individualized clinical treatment for cancer patients.

Inhibition of transport across the hepatocyte canalicular membrane by the antibiotic fusidate

Hyperbilirubinemia is a frequent side effect induced by long-term therapy with the antibiotic fusidate. The aim of this study was to elucidate the molecular mechanisms of fusidate-induced hyperbilirubinemia by investigating its influence on hepatic transport systems in the canalicular membrane. Using canalicular membrane vesicles from rat liver, we determined the effect of fusidate on the adenosine 5'-triphosphate (ATP)-dependent transport of substrates of the apical conjugate export pump, multi-drug resistance protein 2 (Mrp2, symbol Abcc2) and the bile salt export pump (Bsep, symbol Abcb11). Fusidate inhibited the ATP-dependent transport of the Mrp2 substrates 17beta-glucuronosyl estradiol and leukotriene C4, and the transport of cholyltaurine by Bsep with Ki values of 2.2+/-0.3, 7.6+/-1.3, and 5.5+/-0.8 microM, respectively. To elucidate the in vivo implication of these findings, the effect of fusidate treatment on the elimination of intravenously administered tracer doses of 17beta-glucuronosyl estradiol and cholyltaurine into bile was studied in rats. Treatment with fusidate (100 micromol/kg body weight) reduced the biliary excretion rate of 17beta-glucuronosyl [3H]estradiol and [3H]cholyltaurine by 75 and 80%, respectively. Extended treatment of rats with fusidate (100 micromol/kg body weight, three times daily i.p. for 3 days) reduced hepatic Mrp2 protein levels by 61% (P<0.001). Our data suggest that there are at least two different mechanisms involved in the impairment of transport processes and hepatobiliary elimination by fusidate, direct inhibition of transport of Mrp2 and Bsep substrates by competitive interaction and impairment by a decreased level of hepatic Mrp2.

S-decyl-glutathione nonspecifically stimulates the ATPase activity of the nucleotide-binding domains of the human multidrug resistance-associated protein, MRP1 (ABCC1)

The human multidrug resistance-associated protein(MRP1) is an ATP-dependent efflux pump that transports anionic conjugates, and hydrophobic compounds in a glutathione dependent manner. Similar to the other, well-characterized multidrug transporter P-gp, MRP1 comprises two nucleotide-binding domains (NBDs) in addition to transmembrane domains. However, whereas the NBDs of P-gp have been shown to be functionally equivalent, those of MRP1 differ significantly. The isolated NBDs of MRP1 have been characterized in Escherichia coli as fusions with either the glutathione-S-transferase (GST) or the maltose-binding domain (MBP). The nonfused NBD1 was obtained by cleavage of the fusion protein with thrombin. The GST-fused forms of NBD1 and NBD2 hydrolyzed ATP with an apparent K(m) of 340 microm and a V(max) of 6.0 nmol P(I) x mg-1 x min-1, and a K(m) of 910 microm ATP and a V(max) of 7.5 nmol P(I) x mg-1 x min-1, respectively. Remarkably, S-decyl-glutathione, a conjugate specifically transported by MRP1 and MRP2, was able to stimulate the ATPase activities of the isolated NBDs more than 2-fold in a concentration-dependent manner. However,the stimulation of the ATPase activity was found to coincide with the formation of micelles by S-decyl-glutathione. Equivalent stimulation of ATPase activity could be obtained by surfactants with similar critical micelle concentrations.

Homocamptothecin-daunorubicin association overcomes multidrug-resistance in breast cancer MCF7 cells

The multidrug-resistance (MDR) status of a novel camptothecin analogue, homocamptothecin (hCPT), was investigated in human colon adenocarcinoma HT29 cells, myelogenous leukemia K562 cells and breast carcinoma MCF7 cells. The cytotoxicity of hCPT was not sensitive to the MDR status in K562 cell lines. However, its cytotoxicity was altered by MRP1, but not Pgp, in naturally MRP1-expressing HT29 cells, and etoposide- and doxorubicin-resistant MCF7/VP and MCF7/DOX cells, respectively. These cells were sensitized to hCPT in presence of MK571, probenecid but not verapamil. These results led to consider hCPT as a substrate for MRP1 and a potential modulator of MRP1 activity. The relationship between the cytotoxic effect of anthracyclines and their nuclear localization had been previously demonstrated. We show that MRPI mediated the daunorubicin (DNR) efflux in MCF7/VP and MCF7/DOX cells. The combination of sub-toxic doses of hCPT with DNR resulted in the potentiation of DNR activity, well-correlated with an increase in its nuclear accumulation in MCF7/VP cells. Simultaneous pattern was shown to provide higher cytotoxic response than sequential one. In agreement, hCPT increased also the DNR nuclear accumulation in low MRP1-expressing MCF7/DOX cells. However, the enhancement of cytotoxicity in the DNR-hCPT combination was poorly correlated with the nuclear concentration of DNR in MCF7/DOX cells. In addition to the increase in DNR accumulation, the potentiation of DNR activity by hCPT in MCF7/DOX cells implied a synergistic mechanism between both drugs. These data suggest that the present topoisomerase I/II inhibitors combination may be of clinical interest to overcome MDR phenotype in DNR-treated breast cancer patients.

Activity of drugs from traditional Chinese medicine toward sensitive and MDR1- or MRP1-overexpressing multidrug-resistant human CCRF-CEM leukemia cells

There is considerable interest among basic and clinical researchers in novel drugs with activity against leukemia. The vast history of experience of traditional Chinese medicine (TCM) with medicinal plants may facilitate the identification of novel antileukemic compounds. In the present investigation, we tested 22 drugs for their activity toward CCRF-CEM cell lines: artesunate, artemisinin, baicalein, baicalin, berberine, bufalin, cantharidin, cephalotaxine, curcumin, daidzein, daidzin, diallyl disulfide, ginsenoside Rh2, glycyrrhizic acid, isonardosinon, homoharringtonine, nardosinon, nardofuran, puerarin, quercetin, tannic acid, and tetrahydronardosinon. As compounds from folk medicinal remedies are sometimes looked upon as alternative medicine with some hesitation or criticism, we investigated only chemically pure compounds and tested the drugs independently in two different laboratories in Germany and Australia. We used CCRF-CEM parental cells and doxorubicin-selected P-glycoprotein (P-gp)/MDR1-expressing CEM/ADR5000, vinblastine-selected P-gp/MDR1-expressing CEM/VLB(100), and epirubicin-selected multidrug resistance-related protein 1 (MRP1)-expressing CEM/E1000 sublines thereof. While CEM/ADR5000, CEM/VLB(100), and CEM/E1000 cells were highly resistant to the corresponding selecting agents, no or only minimal degrees of cross-resistance were observed to TCM drugs in both growth inhibition assay and MTT assay (range from 0.4- to 8-fold). Homoharringtonine, artesunate, and bufalin were most active among this panel of compounds. As shown by flow cytometry, artesunate significantly increased daunorubicin accumulation in CEM/E1000 cells, but not in CEM/VLB(100) or CCRF-CEM parental cells. Bufalin caused a small, but significant increase in daunorubicin accumulation in CEM/VLB(100) and CEM/E1000 cells. As artesunate and bufalin showed both antileukemic activity if applied alone and modulation activity in combination with daunorubicin in multidrug-resistant (MDR) cells, these two drugs may be suitable for novel combination treatment regimens to improve leukemia cell killing.

Budesonide reduces multidrug resistance-associated protein 1 expression in an airway epithelial cell line (Calu-1)

The objective of this study was to determine the expression and activity of multidrug resistance-associated protein (MRP1) in a human airway epithelial cell line (Calu-1) and to further assess whether budesonide, a potent antiasthma corticosteroid, alters the expression and activity of MRP1 in these cells. Reverse transcriptase polymerase chain reaction (RT-PCR) and the Western blot analysis demonstrated the MRP1 mRNA and MRP1 protein in Calu-1 cells. Indomethacin, probenecid, and verapamil significantly enhanced the fluorescein accumulation and reduced the fluorescein efflux, consistent with the MRP1 activity in the Calu-1 cells. Following 14-day budesonide treatment, fluorescein accumulation increased and fluorescein efflux decreased, consistent with the inhibition of MRP1 activity by budesonide. At a concentration (10 microM) devoid of cytotoxicity, budesonide treatment decreased MRP1 mRNA and MRP1 protein expression in Calu-1 cells by 38% and 42%, respectively. In addition, budesonide (10 microM) enhanced the sensitivity of the MRP1 overexpressing COR-L23R cells to vincristine, suggesting the chemosensitizing effect of budesonide. Thus, budesonide inhibits MRP1 expression and may be useful as a chemosensitizer in tumor chemotherapy.