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

---

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

The endothelium both initiates and responds to a cascade of events triggered by cytokines. Enhanced formation of NO, especially by inducible nitric oxide- synthase (i NOS), is largely stimulated by tumor necrosis factor (TNF). Nitrogen oxides are reactive intermediate molecules functioning in neural transmission, and vasodilatation. The aim of our study was to investigate the effect of TNF and Staphylococcus aureus, a TNF inducing agent on the NO production of brain endothelial cells in vitro. The effect of the same agent was investigated on the MDR expression of endothelial cells. Both TNF and Staphylococcus aureus resulted in enhanced NO production. Western blot analysis showed enhanced expression of iNOS, which could be inhibited by pentoxifylline, an inhibitor of TNF synthesis. Flow cytometric analysis revealed that the brain capillary endothelial cells exerted P-glycoprotein expression, which was not influenced by TNF. However, the mdr function itself in these cells was decreased by TNF. Cultured endothelial cells are excellent tools for the investigation of the possible connection between the NO production and MDR function, and for the estimation the effect of different agents influencing these activities, which might be important in blood-brain barrier function.
...
PMID:Nitric oxide production and MDR expression by human brain endothelial cells. 971 8

Resistance to multiple natural product drugs associated with reduced drug accumulation in human tumor cells may be conferred by either the 170 kDa P-glycoprotein or the 190 kDa multidrug resistance protein, MRP. Both MRP and P-glycoprotein belong to the large and ancient ATP-binding cassette (ABC) superfamily of transport proteins but share only 15% amino acid identify. Unlike P-glycoprotein, MRP actively transports conjugated organic anions such as the cysteinyl leukotriene C4 and glutathione-conjugated aflatoxin B1. Transport of unconjugated chemotherapeutic agents appears to require cotransport of glutathione. MRP and several more recently discovered ABC proteins contain an additional NH2-proximal membrane-spanning domain not found in previously characterized ABC transporters. This domain, whose NH2-terminus is extracytosolic, is essential for MRP-mediated transport activity. This review summarizes current knowledge of the structural and transport characteristics of MRP which suggest that the physiologic functions of this protein could range from a protective role in chemical toxicity and oxidative stress to mediation of inflammatory responses involving cysteinyl leukotrienes.
...
PMID:Multidrug resistance mediated by the ATP-binding cassette transporter protein MRP. 987 59

Substrate specificity and pH dependence of the transport system for diphenhydramine were investigated in Caco-2 cell monolayers. Diphenhydramine uptake was not affected by any typical substrate for the renal organic cation transport system except procainamide. Along with procainamide, tertiary amine compounds with N-dimethyl or N-diethyl moieties in their structures inhibited the diphenhydramine uptake. Moreover, accumulation of diphenhydramine was stimulated by preloading the Caco-2 cells with these tertiary amines (trans-stimulation effect), indicating the existence of the specific transport system for tertiary amines with N-dimethyl or N-diethyl moieties. Efflux of diphenhydramine from monolayers was enhanced by medium acidification. In addition, intracellular acidification resulted in marked stimulation of diphenhydramine accumulation. ATP depletion of the cells caused an enhancement of diphenhydramine accumulation, suggesting the involvement of an active secretory pathway. However, P-glycoprotein did not mediate the diphenhydramine transport. These findings indicate that a novel pH-dependent tertiary amine transport system that recognizes N-dimethyl or N-diethyl moieties is involved in diphenhydramine transport in Caco-2 cells.
...
PMID:Diphenhydramine transport by pH-dependent tertiary amine transport system in Caco-2 cells. 1076 10

Peptides and peptidomimetics often exhibit poor oral bioavailability due to their metabolic instability and low permeation across the intestinal mucosa. N-Methylation has been used successfully in peptide-based drug design in an attempt to improve the metabolic stability of a peptide-based lead compound. However, the effect of N-methylation on the absorption of peptides through the intestinal mucosa is not well understood, particularly when transporters, i.e. the oligopeptide transporter (OPT) and P-glycoprotein (P-gp), modulate the passive diffusion of these types of molecules. To examine this, terminally free and terminally modified (N-acetylated and C-amidated) analogs of H-Ala-Phe-Ala-OH with N-methyl groups on either the Ala-Phe or Phe-Ala peptide bond were synthesized. Transport studies using Caco-2 cell monolayers, an in vitro model of the intestinal mucosa, showed that N-methylation of the Ala-Phe peptide bond of H-Ala-Phe-Ala-OH stabilized the molecule to protease degradation, and the resulting analog exhibited significant substrate activity for OPT. However, N-methylation of the Phe-Ala peptide bond of H-Ala-Phe-Ala-OH did not stabilize the molecule to protease degradation, and the substrate activity of the resulting molecule for OPT could not be determined. Interestingly, N-methylation of the Phe-Ala peptide bond of the terminally modified tripeptide Ac-Ala-Phe-Ala-NH2 decreased the substrate activity of the molecule for the efflux transporter P-gp. In contrast, N-methylation of the Ala-Phe peptide bond of the terminally modified tripeptide Ac-Ala-Phe-Ala-NH2 increased the substrate activity of the molecule for P-gp.
...
PMID:Transport characteristics of peptides and peptidomimetics: I. N-methylated peptides as substrates for the oligopeptide transporter and P-glycoprotein in the intestinal mucosa. 1132 89

In an attempt to find clinically useful modulators of multidrug resistance (MDR), a series of 19 N(10)-substituted-2-methoxyacridone analogues has been synthesized. 2-Methoxyacridone and its derivatives (1-19) were synthesized. Compound 1 was prepared by the Ullmann condensation of o-chlorobenzoic acid and p-anisidine followed by cyclization using polyphosphoric acid. This compound undergoes N-alkylation in the presence of phase transfer catalyst (PTC). Stirring of 2-methoxy acridone with 1-bromo-3-chloropropane or 1-bromo-4-chlorobutane in a two-phase system consisting of organic phase (tetrahydrofuran) and 6N potassium hydroxide in the presence of tetrabutylammonium bromide leads to the formation of compounds 2 and 11 in good yield. N-(omega-Chloroalkyl) analogues were found to undergo iodide catalyzed nucleophilic substitution reaction with various secondary amines. Products were characterized by UV, IR, 1H and 13C NMR, mass-spectral data and elemental analysis. The lipophilicity expressed in log(10) P and pK(a) of compounds have been determined. All compounds were examined for their ability to increase the uptake of vinblastine (VLB) in MDR KBCh(R)-8-5 cells and the results showed that the compounds 7, 10, 12, and 15-19 at 100 microM caused a 1.05- to 1.7-fold greater accumulation of vinblastine than did a similar concentration of the standard modulator, verapamil (VRP). However, the effects on VLB uptake were specific because these derivatives had little effect in the parental drug sensitive line KB-3-1. Steady state accumulation of VLB, a substrate for P-glycoprotein (P-gp) mediated efflux, was studied in the MDR cell line KBCh(R)-8-5 in the presence and absence of novel MDR modulators. Results of the efflux experiment showed that VRP and each of the modulators (1-19) significantly inhibited the efflux of VLB, suggesting that they may be competitors for P-gp. From among the compounds examined, 14 except 1, 2, 4, 8, and 11, exhibited greater efflux inhibiting activity than VRP. All the 19 compounds effectively compete with [(3)H] azidopine for binding to P-gp, pointed out this transport membrane protein as their likely site of action. Cytotoxicity has been determined and the IC(50) values lie in the range 8.00-18.50 microM for propyl and 4-15 microM for butyl derivatives against KBCh(R)-8-5 cells suggesting that the antiproliferative activity increases as chain length increases from 3 to 4 carbons at N(10)-position. Compounds at IC(10) were evaluated for their efficacy to modulate the cytotoxicity of VLB in KBCh(R)-8-5 cells and found that the modulators enhanced the cytotoxicity of VLB by 5- to 35-fold. Modulators 12, 14-16, and 19 like VRP, were able to completely reverse the 24-fold resistance of KBCh(R)-8-5 cells to VLB. Examination of the relationship between lipophilicity and antagonism of MDR showed a reasonable correlation suggesting that hydrophobicity is one of the determinants of potency for anti-MDR activity of 2-methoxyacridones.
...
PMID:Synthesis and chemical characterization of 2-methoxy-N(10)-substituted acridones needed to reverse vinblastine resistance in multidrug resistant (MDR) cancer cells. 1198 34

Oligopeptides are generally thought to have poor permeability across biological membranes. Recent studies, however, suggest significant distribution of [Dmt1]DALDA (Dmt-D-Arg-Phe-Lys-NH2; Dmt is 2',6'-dimethyltyrosine), a 3+ net charge opioid peptide, to the brain and spinal cord after subcutaneous administration. Peptide transporters (PEPT1 and PEPT2) play a major role in the uptake of di- and tripeptides across cell membranes, but their ability to transport tetrapeptides is not clear. The purpose of this study was to determine whether [Dmt1]DALDA can translocate across Caco-2 cell monolayers and whether PEPT1 plays a role in the uptake process. Our results show that [3H][Dmt1]DALDA can readily translocate across Caco-2 cells, with a permeability coefficient estimated to be 1.24 x 10(-5) cm/s. When incubated with Caco-2 cells, [3H][Dmt1]DALDA was detected in cell lysates by 5 min. The internalization of [Dmt1]DALDA was confirmed visually with a fluorescent [Dmt1]DALDA analog (H-Dmt-D-Arg-Phe-dnsDap-NH2; dnsDap is beta-dansyl-L-alpha,beta-diaminopropionic acid). The uptake of [3H][Dmt1]DALDA was concentration-dependent but temperature- and pH-independent. Treatment with diethylpyrocarbonate (DEPC) inhibited [14C]glycine-sarcosine uptake but increased [3H][Dmt1]DALDA uptake 34-fold. These findings suggest that PEPT1 is not involved in [Dmt1]DALDA internalization. [Dmt1]DALDA uptake was also observed in SH-SY5Y, human embryonic kidney 293, and CRFK cells, and was independent of whether the cells expressed opioid receptors. The efflux of [3H][Dmt1]DALDA from Caco-2 cells was temperature-dependent and was inhibited by DEPC, but was not affected by verapamil, an inhibitor of P-glycoprotein. These data show transcellular translocation of a highly polar 3+ charge tetrapeptide and suggest that [Dmt1]DALDA may not only distribute across the blood-brain barrier but also it may even have reasonable oral absorption.
...
PMID:Transcellular transport of a highly polar 3+ net charge opioid tetrapeptide. 1249 Jun 19

P-glycoprotein (Pgp) is a drug-translocating ATPase responsible for multidrug resistance in cancer. Although it is well-established that Pgp exhibits drug-dependent ATPase and ATP-dependent drug transport functions, the mechanism by which these two reactions are coupled remains unclear. We have shown recently that proteolytic cleavage of the linker region, which joins the NH2 and COOH halves of the Pgp molecule, results in a Pgp form that exhibits drug-independent and -dependent ATPase activities (Nuti et al., (2000) Biochemistry 39, 3424-3432; Nuti, S. L., and Rao, U. S. (2002) J. Biol. Chem. 277, 29417-29423). To understand the mechanism underlying this phenomenon, we used the procedure of vanadate-mediated trapping of the Pgp transport cycle intermediates to determine the steps in the catalytic cycle that are being regulated by the linker region. We show that vanadate stably traps Pgp under two different conditions, one in the presence of ATP alone and the other in the presence of ATP and drug, suggesting the existence of two Pgp conformations. These two conformations, one mediating basal and the other drug-stimulated ATPase reactions, represent different transport cycle intermediates of Pgp, because arresting Pgp in either conformation prevents the catalytic cycle from proceeding to completion. The results also show that these two conformations are uncoupled and appear simultaneously in Pgp that was cleaved in the linker region. These results together suggest that Pgp assumes at least two distinct conformational states, which catalyze two ATP hydrolysis events in the drug transport cycle, and the linker region mediates the transition between these two states of Pgp.
...
PMID:Identification of two different states of P-glycoprotein in its catalytic cycle: role of the linker region in the transition between these two states. 1296 25

Development of new therapeutic agents for colon cancer is highly desirable. To this end, we screened a chemical library for new anticancer agents and identified a synthetic compound, 5-(2,4-dihydroxybenzylidene)-2-(phenylimino)-1,3-thiazolidin (DBPT), which kills cancer cells more effectively than it kills normal human fibroblasts. The molecular mechanism of the antitumor action of DBPT was further analyzed in three human colorectal cancer cell lines. DBPT effectively inhibited the growth of colorectal cancer cells, independent of p53 and P-glycoprotein status, whereas normal fibroblasts were unaffected at the same IC50. Over time, DLD-1 cancer cells treated with DBPT underwent apoptosis. The general caspase inhibitor benzyloxycarbonyl-valine-alanine-aspartate-fluoromethylketone partially blocked DBPT-induced apoptosis in a dose-dependent manner. DBPT-induced apoptosis, including cytochrome c release and caspase activation, was abrogated when c-Jun NH2-terminal kinase (JNK) activation was blocked with either a specific JNK inhibitor or a dominant-negative JNK1 gene. However, constitutive JNK activation alone did not replicate the effects of DBPT in DLD-1 cells, and excessive JNK activation by adenovirus encoding MKK7 had little influence on DBPT-induced apoptosis. Our results suggested that DBPT induces apoptosis in colorectal cancer cell lines through caspase-dependent and caspase-independent pathways and that JNK activation was crucial for DBPT-induced apoptosis. DBPT and its analogues might be useful as anticancer agents.
...
PMID:Identification of a novel synthetic thiazolidin compound capable of inducing c-Jun NH2-terminal kinase-dependent apoptosis in human colon cancer cells. 1602 41

A significant impediment to the success of cancer chemotherapy is multidrug resistance (MDR). A typical form of MDR is attributable to the overexpression of membrane transport proteins, such as P-glycoprotein, resulting in an increased drug efflux. In this study, we show that adenovirus-mediated enhancement of the c-Jun NH2-terminal kinase (JNK) reduces the level of P-glycoprotein in a dose- and time-dependent manner. Protein turnover assay shows that the decrease of P-glycoprotein is independent of its protein stability. Instead, this occurs primarily at the mRNA level, as revealed by reverse transcription-PCR analysis. We find that P-glycoprotein down-regulation requires the catalytic activity of JNK and is mediated by the c-Jun transcription factor, as either pharmacologic inhibition of JNK activity or dominant-negative suppression of c-Jun remarkably abolishes the ability of JNK to down-regulate P-glycoprotein. In addition, electrophoretic mobility shift assay reveals that adenoviral JNK increases the activator protein binding activity of the mdr1 gene in the MDR cells. We further show that the decrease of P-glycoprotein level is associated with a significant increase in intracellular drug accumulation and dramatically enhances the sensitivity of MDR cancer cells to chemotherapeutic agents. Our study provides the first direct evidence that enhancement of the JNK pathway down-regulates P-glycoprotein and reverses P-glycoprotein-mediated MDR in cancer cells.
...
PMID:Reversal of P-glycoprotein-mediated multidrug resistance in cancer cells by the c-Jun NH2-terminal kinase. 1639 60

ATP-dependent drug transport by human P-glycoprotein (Pgp, ABCB1) involves a coordinated communication between its drug-binding site (substrate site) and the nucleotide binding/hydrolysis domain (ATP sites). It has been demonstrated that the two ATP sites of Pgp play distinct roles within a single catalytic turnover; whereas ATP binding or/and hydrolysis by one drives substrate translocation and dissociation, the hydrolytic activity of the other resets the transporter for the subsequent cycle (Sauna, Z. E., and Ambudkar, S. V. (2000) Proc. Natl. Acad. Sci. U. S. A. 97, 2515-2520; Sauna, Z. E., and Ambudkar, S. V. (2001) J. Biol. Chem. 276, 11653-11661). Trapping of ADP (or 8-azido-ADP) and vanadate (ADP.Vi or 8-azido-ADP.Vi) at the catalytic site, following nucleotide hydrolysis, markedly reduces the affinity of Pgp for its transport substrate [125I]iodoarylazidoprazosin ([125I]IAAP), resulting in dissociation of the latter. Regeneration of the [125I]IAAP site requires an additional round of nucleotide hydrolysis. In this study, we demonstrate that certain thioxanthene-based allosteric modulators, such as cis-(Z)-flupentixol and its closely related analogs, induce regeneration of [125I]IAAP binding to vanadate-trapped (or fluoroaluminate-trapped) Pgp without any further nucleotide hydrolysis. Regeneration was facilitated by dissociation of the trapped nucleotide and vanadate. Once regenerated, the substrate site remains accessible to [125I]IAAP even after removal of the modulator from the medium, suggesting a modulator-induced relaxation of a constrained transition state conformation. Consistent with this, limited trypsin digestion of vanadate-trapped Pgp shows protection by cis-(Z)-flupentixol of two Pgp fragments (approximately 60 kDa) recognizable by a polyclonal antiserum specific for the NH2-terminal half. No regeneration was observed in the Pgp mutant F983A that is impaired in modulation by flupentixols, indicating involvement of the allosteric modulator site in the phenomenon. In summary, the data demonstrate that in the nucleotide-trapped low affinity state of Pgp, the allosteric site remains accessible and responsive to modulation by flupentixol (and its closely related analogs), which can reset the high affinity state for [125I]IAAP binding without any further nucleotide hydrolysis.
...
PMID:Allosteric modulation bypasses the requirement for ATP hydrolysis in regenerating low affinity transition state conformation of human P-glycoprotein. 1650 85


<< Previous 1 2 3 4 Next >>

---