Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.6.3.44 (P-glycoprotein)
13,344 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

P-glycoprotein (P-gp), the MDR1 multidrug transporter, is known to be expressed in several human organs and tissues, including the apical membrane of the renal proximal tubular cells. It has been reported that human immunodeficiency virus 1 (HIV-1) can trigger the expression of P-gp in cultured cells (i.e., H9, a T-lymphocyte cell line, and U937, a monocyte cell line), which may render the cells resistant to antiretrovirals. Since multiple membrane transport systems (i.e., organic cation, organic anion, and nucleoside systems) can be involved in the renal tubular transport of dideoxynucleoside analog drugs (DADs) (i.e., zidovudine and zalcitabine), we have questioned if P-gp is involved in the renal transport of DADs. Chinese hamster ovary colchicine-resistant cells (CH(R)C5), a cell line that is well known to highly express P-gp, and continuous renal epithelial cell lines (LLC-PK1 and OK), which have also been shown to express P-gp, were used. The accumulation of [3H]vinblastine (20 nM), an established P-gp substrate, by the monolayer cells was significantly enhanced in the presence of two P-gp inhibitors (i.e., verapamil and cyclosporin A) and nucleoside transport inhibitors (i.e., dipyridamole and dilazep). In contrast, DADs (i.e., zidovudine, lamivudine, didanosine, and zalcitabine) did not significantly affect vinblastine accumulation by these cell lines. These data suggest that P-gp does not play a significant role in the renal tubular transport of DADs. Dipyridamole and dilazep, two nucleoside membrane transport inhibitors, appear to be P-gp inhibitors.
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PMID:Role of P-glycoprotein in the renal transport of dideoxynucleoside analog drugs. 1054 26

The subcellular distribution of doxorubicin was evaluated in living non-fixed LLC-PK1 cells, which maintain the structural and functional characteristics of the kidney proximal tubule epithelium and also express P-glycoprotein. After 10 min incubation, doxorubicin fluorescence was detectable in the nucleus. The intensity of nuclear fluorescence progressively increased, reaching the maximum at the end of the first hour. Then, the nuclear signal started to decrease and, at 2 h, doxorubicin fluorescence disappeared almost completely from the cell nucleus. Cytoplasmic fluorescent vesicles first appeared in the perinuclear region after 10 min doxorubicin exposure and increased in number and size over a period of 2 h. From 2 to 5 h, fluorescent vesicles moved unidirectionally to the cell periphery. Disappearance of doxorubicin punctate fluorescence in LLC-PK1 cells treated with methylamine or monensin demonstrated that drug accumulation occurred inside acidic compartments. In addition, the cytoplasmic pattern of doxorubicin fluorescence was very similar to that observed upon exposure to the acidotropic tracer LysoSensor Blue. Involvement of P-glycoprotein in doxorubicin handling by LLC-PK1 cells was suggested by modified intracellular doxorubicin distribution after cell incubation with verapamil and vinblastine. Moreover, the fluorescent P-glycoprotein substrate Bodipy FL Verapamil was shown to accumulate in LLC-PK1 cells in a manner that is quite similar to that observed for doxorubicin. P-glycoprotein expression was evaluated by immunoblot using the JSB-1 and C219 monoclonal antibodies. Immunofluorescence analysis was performed using the JSB-1 monoclonal antibody. P-glycoprotein immuno-reactivity was found both on the plasma membrane and intracytoplasmically in a perinuclear position. Reverse transcriptase-polymerase chain reaction (RT-PCR) analysis revealed that MDR1 gene was expressed. This study indicates that a rapid intracellular redistribution accompanies the process of doxorubicin uptake by LLC-PK1 cells. Although these cells are non-tumour cells derived from the normal epithelium of the proximal renal tubule, they display a model of doxorubicin redistribution which is characteristic of doxorubicin-resistant tumour cells.
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PMID:Kinetics of doxorubicin handling in the LLC-PK1 kidney epithelial cell line is mediated by both vesicle formation and P-glycoprotein drug transport. 1057 12

Sister of P-glycoprotein (SPGP), a novel murine cDNA and member of the ATP-binding cassette superfamily highly homologous to P-glycoprotein (Pgp), was cloned. Moreover, its genomic clone was isolated and localized to chromosome 2 by fluorescence in situ hybridization. SPGP was functionally evaluated relative to MDR1 after subcloning SPGP cDNA into a retroviral bicistronic vector capable of expressing both SPGP and the green fluorescent protein. LLC-PK1 and MDCKII cells were transduced with this retrovirus and SPGP-positive clones were isolated. Drug uptake and efflux was compared in cells ectopically expressing either SPGP or human MDR1. SPGP cells had decreased uptake of taurocholate and vinblastine compared with LLC-PK1 cells. Additional studies revealed that vinblastine efflux was accelerated by SPGP compared with LLC-PK1. Further comparison revealed that although MDR1 easily impaired uptake of vincristine, daunomycin, paclitaxel, and digoxin, SPGP had no effect on uptake of these drugs. However, further studies demonstrated that, like MDR1, SPGP effluxed calcein-acetoxymethyl ester (AM). Unlike MDR1, SPGP was incapable of effluxing rhodamine 123. Although cyclosporine A and reserpine blocked calcein-AM transport by MDR1, these drugs had either minimal or no effect, respectively, on blocking SPGP efflux of calcein-AM. In contrast, ditekiren, a linear hexapeptide, readily and preferentially inhibited SPGP efflux of calcein-AM. Further studies with three structural analogs of ditekiren revealed that one analog inhibited SPGP efflux of calcein-AM, although not as potently as ditekiren. These are the first studies to reveal that SPGP has distinct transport properties compared with MDR1.
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PMID:Cloning and expression of murine sister of P-glycoprotein reveals a more discriminating transporter than MDR1/P-glycoprotein. 1061 75

We have previously shown that cloned rat multidrug resistance-associated protein 3 (Mrp3) has the ability to transport organic anions such as 17beta-estradiol 17-beta-D-glucuronide (E(2)17betaG) and has a different substrate specificity from MRP1 and MRP2 in that glutathione conjugates are poor substrates for Mrp3 (Hirohashi, T., Suzuki, H., and Sugiyama, Y. (1999) J. Biol. Chem. 274, 15181-15185). In the present study, the involvement of Mrp3 in the transport of endogenous bile salts was investigated using membrane vesicles from LLC-PK1 cells transfected with rat Mrp3 cDNA. The ATP-dependent uptake of [(3)H]taurocholate (TC), [(14)C]glycocholate (GC), [(3)H]taurochenodeoxycholate-3-sulfate (TCDC-S), and [(3)H]taurolithocholate-3-sulfate (TLC-S) was markedly stimulated by Mrp3 transfection in LLC-PK1 cells. The extent of Mrp3-mediated transport of bile salts was in the order, TLC-S > TCDC-S > TC > GC. The K(m) and V(max) values for the uptake of TC and TLC-S were K(m) = 15.9 +/- 4.9 microM and V(max) = 50.1 +/- 9.3 pmol/min/mg of protein and K(m) = 3.06 +/- 0.57 microM and V(max) = 161.9 +/- 21.7 pmol/min/mg of protein, respectively. At 55 nM [(3)H]E(2)17betaG and 1.2 microM [(3)H]TC, the apparent K(m) values for ATP were 1.36 and 0.66 mM, respectively. TC, GC, and TCDC-S inhibited the transport of [(3)H]E(2)17betaG and [(3)H]TC to the same extent with an apparent IC(50) of approximately 10 microM. TLC-S inhibited the uptake of [(3)H]E(2)17betaG and [(3)H]TC most potently (IC(50) of approximately 1 microM) among the bile salts examined, whereas cholate weakly inhibited the uptake (IC(50) approximately 75 microM). Although TC and GC are transported by bile salt export pump/sister of P-glycoprotein, but not by MRP2, and TCDC-S and TLC-S are transported by MRP2, but not by bile salt export pump/sister of P-glycoprotein, it was found that Mrp3 accepts all these bile salts as substrates. This information, together with the finding that MRP3 is extensively expressed on the basolateral membrane of human cholangiocytes, suggests that MRP3/Mrp3 plays a significant role in the cholehepatic circulation of bile salts.
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PMID:ATP-dependent transport of bile salts by rat multidrug resistance-associated protein 3 (Mrp3). 1064 59

The interaction of docetaxel ("Taxotere") with P-glycoprotein (P-gp) was examined using porcine kidney epithelial LLC-PK1 and LLC-GA5-COL150 cells, overexpressing human P-gp selectively on the apical plasma membrane by transfection of human MDR1 cDNA into the LLC-PK1 cells. The basal-to-apical transport of [14C]docetaxel in LLC-GA5-COL150 cells significantly exceeded that in LLC-PK1 cells, but the apical-to-basal transport was decreased in LLC-GA5-COL150 cells. The intracellular accumulation after its basal or apical application to LLC-GA5-COL150 cells was 4- to 20-fold lower than that of LLC-PK1 cells. Multidrug resistance (MDR) modulators, i.e., cyclosporin A and SDZ PSC 833, inhibited the basal-to-apical transport and increased the apical-to-basal transport of [14C]docetaxel in LLC-GA5-COL150 cells, but verapamil affected only apical-to-basal transport. The intracellular accumulation after basal or apical application to LLC-GA5-COL150 cells was also increased by these three MDR modulators. These observations demonstrated that docetaxel is a substrate for human P-gp, suggesting that docetaxel-drug interactions occur via P-gp. The inhibition of [14C]docetaxel transport by the MDR modulators, as well as daunorubicin and vinblastine, was also found in LLC-PK1 cells, which endogenously express P-gp at lower levels, and concentrations showing similar levels of inhibition were lower than those in the case of LLC-GA5-COL150 cells. These observations indicate that it is necessary to consider the pharmacokinetic and pharmacodynamic interactions of docetaxel via P-gp.
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PMID:Interaction of docetaxel ("Taxotere") with human P-glycoprotein. 1066 57

MDR results from overexpression of P-glycoprotein (Pgp) and multidrug resistance protein (MRP or MRP1) that function as ATP-dependent efflux pumps. Lung resistance related protein (LRP) is also supposed to be involved in MDR. The human canalicular multispecific organic anion transporter (cMOAT) gene that is responsible for the defects in Dubin-Johnson syndrome was isolated. cMOAT is homologous to MRP1 and supposed to be involved in drug resistance. Human cMOAT cDNA transfected LLC-PK1 cells, LLC/cMOAT-1, have increased resistance to vincristine (VCR), 7-ethyl-10-hydroxycamptothecin (SN-38), and cisplatin. The multidrug resistance (MDR)-reversing agents, cyclosporin A (CsA) and PAK-104P, almost completely reversed the resistance to VCR, SN-38 and cisplatin of LLC/cMOAT-1 cells by interacting with the substrate binding site of cMOAT. Treatment of human colorectal carcinoma SW-620 cells with sodium butyrate(NaB) induced LRP in the cells and conferred resistance to Adrianycin(ADM), VCR, VP-16, gramicidin D and taxol. Two LRP-specific ribozymes inhibited the NaB-induced expression of LRP in SW-620 cells and almost completely abolished their acquisition of the MDR phenotype. The accumulation of ADM, VCR and taxol was not decreased in NaB-treated cells, suggesting that ATP-binding cassette transporters are not involved in the MDR of NaB-treated cells. ADM was mainly located in the nuclei of untreated and the cytoplasm of NaB-treated cells. The accumulation level of ADM in the nuclei isolated from untreated cells or those from treated cells in the presence of anti-LRP polyclonal antibody was higher than that from treated cells in the absence of the antibody. Efflux of ADM from nuclei isolated from NaB-treated cells was enhanced compared with those from untreated cells and NaB-treated cells transfected with a LRP-specific ribozyme. The polyclonal antibody against LRP inhibited the enhanced efflux of ADM from nuclei isolated from NaB-treated cells. These findings indicate that LRP is involved in resistance to ADM, VCR, VP-16, taxol and gramicidin D, and has an important role in the transport of ADM from the nucleus to the cytoplasm.
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PMID:[Mechanisms for resistance to anticancer agents and the reversal of the resistance]. 1069 15

The reversal effect of itraconazole on P-glycoprotein (P-gp)-mediated resistance of vinblastine, daunorubicin and doxorubicin was analyzed from a cellular pharmacokinetic point of view, namely by [3H]azidopine photoaffinity labeling, intracellular accumulation and transcellular transport experiments. The LLC-GA5-COL150 cells, which expressed human P-gp selectively on the apical membrane due to transfection of MDR1 cDNA into the porcine kidney epithelial cells (LLC-PK1 cells), was used here, since this cell line constructs the monolayer with tight junction, being able to characterize the cellular pharmacokinetics. In LLC-GA5-COL150 cells, itraconazole caused a reversal from resistance as shown by a growth inhibition assay. [3H]Azidopine photoaffinity labeling demonstrated that itraconazole, vinblastine, daunorubicin and doxorubicin showed higher binding ability for P-gp compared with digoxin, suggesting the following results were via P-gp. The intracellular accumulation of [3H]vinblastine, [3H]daunorubicin and [14C]doxorubicin after their application on the basal and apical sides was increased by itraconazole. These changes were similar to the dose modifying factors determined by the growth inhibition assay. However, their basal-to-apical transport was hardly affected by itraconazole, and this was explained by the fact that itraconazole inhibited P-gp, and subsequently increased their intracellular concentration and then the non-P-gp mediated transport from the intracellular space to apical side. The apical-to-basal transport of [3H]vinblastine, [3H]daunorubicin and [14C]doxorubicin was increased by itraconazole, and this was reasonably explained by the inhibition of P-gp, and partly also by the increase of their intracellular concentration via the inhibition of P-gp.
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PMID:Cellular pharmacokinetic aspects of reversal effect of itraconazole on P-glycoprotein-mediated resistance of anticancer drugs. 1074 69

The interaction of the novel anticancer drug KRN5500, a spicamycin derivative, with human P-glycoprotein (P-gp) was analyzed from the viewpoint of cellular pharmacokinetics, i.e. by means of [3H]azidopine photoaffinity labeling, cellular accumulation and transcellular transport experiments. In this study, P-gp-overexpressing LLC-GA5-COL150 cells, porcine kidney epithelial LLC-PK1 cells transformed with human MDR1 cDNA, were used, since this cell line constructs monolayers with tight junctions, and would provide sufficient information for analyzing the cellular pharmacokinetics. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay revealed that the growth-inhibitory effect of KRN5500 in LLC-GA5-COL150 cells was comparable to that in LLC-PK1 cells (IC50 = 79.4 and 72.7 nM, respectively), but the inhibition of [3H]azidopine binding by KRN5500 was concentration-dependent in the membrane fraction of LLC-GA5-COL150 cells. The cellular accumulation of [14C]KRN5500 after its basal application in LLC-GA5-COL150 cells was slightly lower than that in LLC-PK1 cells, and was restored by the multidrug resistance (MDR) modulator SDZ PSC 833. The basal-to-apical transport of [14C]KRN5500 in LLC-GA5-COL150 cells was also slightly higher than that in LLC-PK1 cells, and was inhibited by SDZ PSC 833. However, the basal-to-apical transport of [14C]KRN5500 in LLC-GA5-COL150 cells was only a little higher than the apical-to-basal transport. Consequently, these results demonstrated that KRN5500 interacted with, but was hardly transported via, P-gp. These observations suggested that KRN5500 may be useful even for the treatment of tumors exhibiting P-gp-mediated MDR.
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PMID:The novel anticancer drug KRN5500 interacts with, but is hardly transported by, human P-glycoprotein. 1076 13

Verapamil is subject to extensive oxidative metabolism mediated by cytochrome P450 enzymes with less than 5% of an oral dose being excreted unchanged in urine. Furthermore, verapamil is known to be a potent inhibitor of P-glycoprotein function. There is evidence from in vivo investigations that some verapamil metabolites might be actively transported. The aim of the present study was to investigate P-glycoprotein-mediated transport and inhibition properties of verapamil and its metabolites norverapamil, D-620, D-617, and D-703. Polarized transport of these compounds was assessed in P-glycoprotein-expressing Caco-2 and L-MDR1 cells (LLC-PK1 cells stably transfected with human MDR1-P-glycoprotein). Inhibition of P-glycoprotein-mediated transport by these compounds was determined using digoxin as P-glycoprotein substrate. At concentrations of 5 microM, significant differences between basal-to-apical and apical-to-basal apparent permeability coefficients were observed for D-617 and D-620 in all P-glycoprotein-expressing cell monolayers, indicating that both are P-glycoprotein substrates. In contrast, no P-glycoprotein-dependent transport was found for verapamil, norverapamil, and D-703 in Caco-2 cells and for D-703 in L-MDR1 cells. Moreover, verapamil, norverapamil, and D-703 inhibited P-glycoprotein-mediated digoxin transport with IC(50) values of 1.1, 0.3, and 1.6 microM, respectively, whereas D-617 and D-620 did not (at concentrations up to 100 microM). We conclude that verapamil phase I metabolites exhibit different P-glycoprotein substrate and inhibition characteristics, with the N-dealkylated metabolites D-617 and D-620 being P-glycoprotein substrates and norverapamil and D-703 being inhibitors of P-glycoprotein function, which may influence P-glycoprotein-dependent drug disposition and elimination.
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PMID:Characterization of the major metabolites of verapamil as substrates and inhibitors of P-glycoprotein. 1077 5

Mibefradil, a calcium T- and L-channel blocker developed for use in hypertension, was recently removed from the market after reports of severe drug-drug interactions. Mibefradil is known to inhibit various cytochrome P450 enzymes involved in drug metabolism, particularly CYP3A. However, the extent and the severity of the observed drug interactions in humans suggest that inhibition of additional systems important to drug disposition, such as the drug transporter P-glycoprotein (P-gp), may also have contributed to the severity of the mibefradil interactions. A polarized epithelial cell line, LLC-PK1, which does not express P-gp, and the derived L-MDR1 cell line, which overexpresses human P-gp, were used to study the effects of mibefradil on drug transport. A markedly greater basal-to-apical versus apical-to-basal transport of [H3]mibefradil was seen in the L-MDR1, but not in the LLC-PK1 cells, suggesting that the drug is a substrate of P-gp. Using a human intestinal cancer-derived cell line Caco-2, which constitutively expresses P-gp, mibefradil was shown to be a potent inhibitor of P-gp-mediated digoxin transport, with an IC50 of 1.6 microM. Additionally, the effect of mibefradil on CYP3A was assessed using human liver microsomes. Mibefradil inhibited CYP3A-mediated nifedipine oxidase activity with an IC50 of 0.8 microM, and a Ki of 0.6 microM. Thus, mibefradil is not only a P-gp substrate, but also a potent inhibitor of both P-gp and CYP3A. These data suggest that the severity of drug interactions seen with mibefradil use is due to the dual inhibition of both P-gp and CYP3A.
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PMID:Mibefradil is a P-glycoprotein substrate and a potent inhibitor of both P-glycoprotein and CYP3A in vitro. 1090 97


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