Presence Of MK571 Research Articles

Molecular evidence and functional expression of multidrug resistance associated protein (MRP) in rabbit corneal epithelial cells

Multidrug resistance associated protein (MRP) is a major family of efflux transporters involved in drug efflux leading to drug resistance. The objective of this study was to explore physical barriers for ocular drug absorption and to verify if the role of efflux transporters. MRP-2 is a major homologue of MRP family and found to express on the apical side of cell membrane. Cultured Rabbit Corneal Epithelial Cells (rCEC) were selected as an in vitro model for corneal epithelium. [ 14C]-erythromycin which is a proven substrate for MRP-2 was selected as a model drug for functional expression studies. MK-571, a known specific and potent inhibitor for MRP-2 was added to inhibit MRP mediated efflux. Membrane fraction of rCEC was used for western blot analysis. Polarized transport of [ 14C]-erythromycin was observed in rCEC and transport from B → A was significantly high than from A → B. Permeability's increased significantly from A → B in the presence of MK-571 and ketoconozole. Uptake of [ 14C]-erythromycin in the presence of MK-571 was significantly higher than control in rCEC. RT-PCR analysis indicated a unique and distinct band at ∼498 bp corresponding to MRP-2 in rCEC and MDCK11-MRP-2 cells. Immunoprecipitation followed by Western Blot analysis indicated a specific band at ∼190 kDa in membrane fraction of rCEC and MDCK11-MRP-2 cells. For the first time we have demonstrated high expression of MRP-2 in rabbit corneal epithelium and its functional activity causing drug efflux. RT-PCR, immunoprecipitation followed by Western blot analysis further confirms the result.

Glucuronidation and the Transport of the Glucuronide Metabolites in LLC-PK1 Cells

Formation and transport of glucuronide metabolites were studied in LLC-PK1 cells. Glucuronidation of 17beta-estradiol, 1-naphthol, mycophenolic acid, and 4-methylumbelliferone was examined in microsomes prepared from LLC-PK1 cells, human livers, human kidneys, and human intestines. The rate of glucuronide metabolite formation observed with LLC-PK1 microsomes was comparable to rates observed with various human tissue microsomes. The fate of the glucuronide metabolite formed in the LLC-PK1 cells was studied by examining its extracellular transport using mycophenolic acid as a model substrate. After administration of mycophenolic acid, the amount of the glucuronide metabolite exiting to the extracellular compartments significantly decreased in the presence of MK-571, an inhibitor for the multidrug resistance-associated protein (MRP) transporter. However, the intracellular levels of the glucuronide metabolite did not change, suggesting that MK-571 was probably blocking metabolite efflux. In summary, these results suggest that the glucuronidating enzyme(s) expressed in the LLC-PK1 cells are capable of sufficient glucuronidation activity and that endogenous transporter(s) in LLC-PK1 cells are active and determine the distribution of the formed metabolites. Since these cells have been previously used to study drug transport, they may be a useful tool in future studies to explore the effect of drug transporters on glucuronidation.

Transport of dietary phenethyl isothiocyanate is mediated by multidrug resistance protein 2 but not P-glycoprotein

We demonstrated recently that phenethyl isothiocyanate (PEITC), a potent anticarcinogen present in cruciferous vegetables, inhibited P-glycoprotein (P-gp) and multidrug resistance protein 1 (MRP1) and that MRP1 can transport PEITC and/or its metabolites. In this study, we have examined whether PEITC is transported by P-gp and MRP2, two transporters with high expression in human intestine, liver and kidney. Using 14C-PEITC, no significant difference was observed for the intracellular accumulation of PEITC in human breast cancer MCF-7/sensitive (control) and MCF-7/ADR (P-gp overexpressing) cells at PEITC concentrations of 1, 10 and 50 μM. Moreover, the presence of verapamil or PSC833, two P-gp inhibitors, had no significant effect on the intracellular accumulation of PEITC in P-gp overexpressing MCF-7/ADR and MDA435/LCC6MDR1 cells, indicating that PEITC may not be a substrate for P-gp. In contrast, 14C-PEITC intracellular accumulation in the kidney epithelial MDCK II/MRP2 cells (transfected with human MRP2) was significantly lower than in the wild-type MDCK II/wt cells at PEITC concentrations of 1, 5, 10 and 50 μM. The presence of MK571, an MRP inhibitor, significantly enhanced 14C-PEITC accumulation in MDCK II/MRP2 but not MDCK II/wt cells. Furthermore, depletion of intracellular glutathione (GSH) following treatment with buthionine sulphoximine, an inhibitor of GSH biosynthesis, significantly increased 14C-PEITC intracellular accumulation in a concentration-dependent manner. Transcellular transport studies also demonstrated that depletion of intracellular GSH reduced the mean ratio of basal-to-apical transport to apical-to-basal transport of PEITC in MDCK II/MRP2, but not MDCK II/wt cell monolayers. These results indicate that GSH plays an important role in the MRP2-mediated transport of PEITC. The findings provide new information concerning the interactions between PEITC and membrane transporters and suggest the possibility of PEITC interactions with xenobiotics that are MRP2 substrates.

Effects of grapefruit juice and orange juice components on P‐glycoprotein‐ and MRP2‐mediated drug efflux

We investigated the effects of grapefruit juice (GFJ) and orange juice (OJ) on drug transport by MDR1 P-glycoprotein (P-gp) and multidrug resistance protein 2 (MRP2), which are efflux transporters expressed in human small intestine. We examined the transcellular transport and uptake of [(3)H]vinblastine (VBL) and [(14)C]saquinavir in a human colon carcinoma cell line (Caco-2) and in porcine kidney epithelial cell lines transfected with human MDR1 cDNA and human MRP2 cDNA, LLC-GA5-COL150, and LLC-MRP2, respectively. In Caco-2 cells, the basal-to-apical transports of [(3)H]VBL and [(14)C]saquinavir were greater than those in the opposite direction. The ratio of basal-to-apical transport to apical-to-basal transport of [(3)H]VBL and [(14)C]saquinavir by Caco-2 cells was reduced in the presence of MK571 (MRPs inhibitor), verapamil (P-gp inhibitor), cyclosporin A (inhibitor of both), 50% ethyl acetate extracts of GFJ and OJ, or their components (6',7'-dihydroxybergamottin, bergamottin, tangeretin, hepatomethoxyflavone, and nobiletin). Studies of transport and uptake of [(3)H]VBL and [(14)C]saquinavir with MDR1 and MRP2 transfectants showed that VBL and saquinavir are transported by both P-gp and MRP2. GFJ and OJ components inhibited the transport by MRP2 as well as P-gp. However, their inhibitory potencies for P-gp or MRP2 were substrate-dependent. The present study has revealed that GFJ and OJ interact with not only P-gp but also MRP2, both of which are expressed at apical membranes and limit the apical-to-basal transport of VBL and saquinavir in Caco-2 cells.

Investigation of intestinal absorption and disposition of green tea catechins by Caco-2 monolayer model

The current study was designed to investigate the absorption mechanism and identify the possible disposition pathways of green tea catechins (GTC), including epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECG) and epigallocatechin gallate (EGCG), during their absorption across small intestine by Caco-2 monolayer model. The transport of each GTC from both apical to basolateral and basolateral to apical directions was measured in the absence and the presence of MK571, an MRP inhibitor. HPLC and LC/MS were employed to identify the possible metabolites of the four GTC formed during their bidirectional transport processes. The results indicated that the four GTC showed limited transepithelial absorption with relatively small P app values. However, significant efflux mediated by MRP was observed during the secretion of GTC, especially the non-gallated catechins. Methylation and sulfation were the main biotransformation pathways of GTC during their secretion transport and the efflux of the related metabolites seem to be mediated by MRP.

Transport of parthenolide across human intestinal cells (Caco-2).

This study examined the intestinal epithelial membrane transport of the sesquiterpene lactone parthenolide, a bioactive compound present in the migraine prophylactic herb feverfew. The Caco-2 human colonic cell line was used as an in vitro model of the human intestinal mucosal barrier. The bidirectional transport (apical to basolateral and basolateral to apical) of parthenolide was investigated using Caco-2 monolayers grown on Transwell inserts. Quantitation of parthenolide was performed using high performance liquid chromatography (HPLC). Apical to basolateral and basolateral to apical permeability coefficients and percent transport were calculated and a potential bioavailability of parthenolide was determined. Sodium fluorescein was used as a marker for paracellular leakage. Parthenolide, at a concentration of 250 microM, demonstrated substantial linear transport across the monolayer. The transport parameters were not affected by the presence of MK-571, an inhibitor of multidrug resistance transporter P-glycoprotein (MRP). Upon comparison of the transport parameters of parthenolide with atenolol under identical conditions and the reported values for model compounds like mannitol and propranolol, it is concluded that parthenolide is effectively absorbed through the intestinal mucosa via a passive diffusion mechanism.

THE β-d-GLUCOSIDE AND SODIUM-DEPENDENT GLUCOSE TRANSPORTER 1 (SGLT1)-INHIBITOR PHLORIDZIN IS TRANSPORTED BY BOTH SGLT1 AND MULTIDRUG RESISTANCE-ASSOCIATED PROTEINS 1/2

Phloridzin, a glucoside of the flavonoid-like polyphenol phloretin, has long been known to be a specific nontransportable inhibitor of the sodium-dependent glucose transporter SGLT1. The objective of this study was to determine whether efflux by multidrug resistance-associated protein (MRP) transporters might have masked the absorption by SGLT1 in previous studies. Various cells used as transport models were incubated with phloridzin (50 microM) in the absence and presence of 50 microM 3-[[3-[2-(7-chloroquinolin-2-yl)vinyl]phenyl]-(2-dimethylcarbamoylethylsulfanyl)methylsulfanyl] propionic acid (MK-571), a highly selective MRP1/MRP2 inhibitor, and the cellular uptake of phloridzin was measured by high performance liquid chromatography. The uptake of phloridzin by SGLT1-transfected Chinese hamster ovary (CHO) (G6D3) cells was 1.7-fold higher than that by parent CHO cells (p < 0.01). In the presence of MK-571, the uptake of phloridzin by CHO cells increased 3.7-fold (p < 0.001). MK-571 caused an 8.0-fold increase in the uptake of phloridzin by G6D3 cells (p < 0.0001). Thus, in the absence of MRP1 efflux, transport of phloridzin by SGLT1 was clearly demonstrated. Similar results were obtained for the glycosides of the flavonoids quercetin, genistein, and diosmetin. A significantly lower accumulation of phloridzin in MRP2-transfected Madin-Darby canine kidney (MDCK) cells compared with parent MDCK cells demonstrated that phloridzin was a substrate also for MRP2 (p < 0.05). This conclusion was further strengthened when MK-571 increased the uptake by MRP2-MDCK cells as much as 3.6-fold (p < 0.01). These results demonstrate that phloridzin, in contrast to previous notions, is transported by SGLT1. In addition, they demonstrate that this and other flavonoid glycosides unexpectedly are efficiently effluxed by both MRP1 and MRP2.

Involvement of multidrug resistance-associated proteins in regulating cellular levels of (−)-epigallocatechin-3-gallate and its methyl metabolites

(−)-Epigallocatechin-3-gallate (EGCG), a major polyphenol of green tea, has many interesting biological activities. The uptake of EGCG and involvement of specific efflux pumps were studied in MDCKII cells transfected with hPgp, hMRP1, and hMRP2 genes. Total cell associated [ 3H]EGCG increased 7-fold in the presence of the MRP inhibitors, indomethacin and probenecid, in MDCKII/MRP1 cells, compared to a 2-fold increase in wild-type cells. Intracellular levels of EGCG, 4 ′′- O-methyl EGCG, and 4 ′,4 ′′-di- O-methyl EGCG were increased by 13-, 11-, and 3-fold, respectively, by indomethacin in MDCKII/MRP1 cells. Accumulation of EGCG and its methyl metabolites was also increased ∼10-fold in the presence of MK-571 in MDCKII/MRP2 cells. Co-treatment with isoflavones, curcumin and tetrahydrocurcumin, increased [ 3H]EGCG accumulation significantly in MDCKII/MRP1 and HT-29 cells. The results indicate that EGCG and its methyl metabolites are substrates for MRP1 and MRP2, but not for Pgp. MRP type efflux pumps may limit the bioavailability of EGCG.

Evidence for a non-MDR1 component in digoxin secretion by human intestinal Caco-2 epithelial layers

Caco-2 epithelial layers were used as a model to re-evaluate the mechanism(s) by which intestinal digoxin absorption is limited by its active secretion back into the lumen. It is widely recognised that intestinal secretion of digoxin is mediated by the ATP-binding cassette (ABC) transporter Multidrug Resistance 1, MDR1. In MDR1-transfected Madin-Darby canine kidney, MDCKII , cell monolayers, digoxin secretion was reduced by the MDR1 inhibitor cyclosporin A, whereas no inhibition was seen in the presence of MK-571, 3-([(3-(2-[7-chloro-2-quinolinyl]ethyl)phenyl]-[(3-dimethylamino-3-oxoprphyl)-thio)-methyl]-thio) propanoic acid, a Multidrug Related Protein (MRP) inhibitor. In contrast, digoxin secretion by Caco-2 epithelia was significantly inhibited by both cyclosporin A and MK-571, suggesting that an additional non-MDR1 component may contribute to this transport. Since digoxin secretion by MRP2-transfected MDCKII monolayers was increased by only 1.2-fold relative to controls, it is likely that the contribution of MRP2 to digoxin secretion by Caco-2 cells is negligible. An additional MK-571-sensitive secretory pathway for digoxin, together with MDR1, is likely to mediate digoxin secretion in Caco-2 epithelia.

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.