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)

The mechanism of action of 2-chlorpromazine (2-chloro-10-(3-dimethylaminopropyl)-phenothiazine) as a reversal agent for P-glycoprotein-mediated multidrug resistance was investigated using inside out-orientated membrane vesicles prepared from vinblastine-resistant human CCRF-CEM leukaemia cells (VBL1000). 2-Chlorpromazine (10 microM) completely inhibited ATP-dependent P-glycoprotein-mediated vinblastine accumulation in the vesicles. Whereas in the absence of added ligands VBL transport was described by a hyperbolic function of vinblastine concentration, in the presence of 2-chlorpromazine vinblastine transport was a sigmoidal function. 2-Chlorpromazine was shown previously [Syed SK, Christopherson RI and Roufogalis BD (1996) Biochem Mol Biol Int 39: 687-696] to be actively transported into vesicles from multidrug-resistant cells. Colchicine (10 microM) and phenoxybenzamine (10 microM) blocked vinblastine transport but had no effect on 2-chlorpromazine transport into vesicles. The results were consistent with a two-state concerted model in which P-glycoprotein exists in two conformational states, P(A) and P(B), where 2-chlorpromazine is transported by the conformer, P(A), and vinblastine by the conformer, P(B). In the presence of 2-chlorpromazine, the conformer P(A) predominates and vinblastine transport is inhibited. Addition of 2-chlorpromazine during the steady state of vinblastine accumulation blocked uptake and resulted in enhanced vinblastine efflux from the vesicles. The findings were similar when vinblastine was added at the steady state of 2-chlorpromazine transport. We propose a minimal kinetic model whereby in these preloaded vesicles the complex VV.P(A).CC is formed, where two internal binding sites of P-glycoprotein (P(A)) are occupied by vinblastine (V) and the two external sites are occupied by 2-chlorpromazine (C). When the two binding sites on both the inside and outside of P-glycoprotein are saturated with ligands vinblastine is effluxed at a very rapid rate, and vice versa when vesicles are preloaded with 2-chlorpromazine and vinblastine is added outside. These unexpected observations and the concerted model developed provide an alternative mechanism of action for reversal agents that sensitize multidrug-resistant cancer cells to anti-cancer drugs.
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PMID:Reversal of vinblastine transport by chlorpromazine in membrane vesicles from multidrug-resistant human CCRF-CEM leukaemia cells. 970 77

Colchicine is an alkaloid drug commonly used in familial Mediterranean fever (FMF), gout, Behcet's syndrome, psoriasis and Sweet's syndrome. The exact mechanism of its action in these diseases is not entirely known. However, it has been shown that colchicine may inhibit neutrophil chemotaxis, thereby decreasing the inflammatory process. Recently, it was shown that colchicine accumulates in neutrophils in higher concentrations than in lymphomonocytes. Studies dealing with the multiple drug resistance (MDR) issue disclosed that neutrophils lack the P-glycoprotein (P-gly) membranal pump (encoded by the MDR1 gene). We propose that the preferential accumulation of colchicine in neutrophils compared with lymphomonocytes is due to the absence of the P-gly efflux pump in the former. This may explain the effectiveness of colchicine in diseases where increased chemotaxis is evident. The hypothesis may also provide an explanation for FMF patients who do not respond to the drug.
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PMID:Does the lack of the P-glycoprotein efflux pump in neutrophils explain the efficacy of colchicine in familial Mediterranean fever and other inflammatory diseases? 984 64

We have obtained a novel multidrug resistant cell line, derived from HT29 G(+) human colon carcinoma cells, by selection with gradually increasing concentrations of the anti-mitotic, microtubule-disrupting agent colchicine. This HT29(col) cell line displayed a 25-fold increase in colchicine resistance and exhibited cross-resistance to doxorubicin, VP16, vincristine and taxol. Immunoblotting, combined with RT-PCR showed that the multidrug resistance phenotype was conferred by specific overexpression of the multidrug resistance protein 1. Confocal scanning laser microscopy revealed that multidrug resistance protein 1 specifically localized in the plasma membrane of HT29(col) cells. In a functional assay, using the fluorescent multidrug resistance protein 1 substrate 5-carboxyfluorescein, an increased efflux activity of HT29(col) cells was measured, as compared to the wild-type HT29 G(+) cells. MK571, a specific inhibitor of multidrug resistance protein 1, blocked the 5-carboxyfluorescein efflux, but only partially reversed resistance to colchicine, indicating that additional multidrug resistance mechanisms operate in HT29(col) cells. In conclusion, these results show for the first time overexpression of a functional multidrug resistance protein 1 under colchicine pressure, indicating that colchicine is not a P-glycoprotein-specific substrate. Colchicine-induced overexpression of multidrug resistance protein 1 is accompanied by a changed sphingolipid composition, i.e., enhanced levels of glucosylceramide and galactosylceramide. In addition, ceramide, a lipid messenger molecule involved in apoptosis-related signal transduction processes, was much more abundant in HT29(col) cells, which is indicative of a stress response.
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PMID:Differential expression of sphingolipids in MRP1 overexpressing HT29 cells. 1086 70

The multidrug transporter P-glycoprotein (Pgp) is an ATPase efflux pump for multiple cytotoxic agents, including vinblastine and colchicine. We have found that resistance to vinblastine but not to colchicine in cell lines derived from different types of tissues and expressing the wild-type human Pgp correlates with the Pgp density. Vinblastine induces a conformational change in Pgp, evidenced by increased reactivity with a conformation-sensitive monoclonal antibody UIC2, in all the tested cell lines. In contrast, colchicine increases the UIC2 reactivity in only some of the cell lines. In those lines where colchicine alone did not affect UIC2 reactivity, this drug was, however, able to reverse the vinblastine-induced increase in UIC2 reactivity. The magnitude of the increase in UIC2 reactivity in the presence of saturating concentrations of colchicine correlates with the relative ability of Pgp to confer colchicine resistance in different cell lines, suggesting the existence of some cell-specific factors that have a coordinate effect on the ability of colchicine to induce conformational transitions and to be transported by Pgp. Colchicine, like vinblastine, reverses the decrease in UIC2 reactivity produced by nonhydrolyzable nucleotides, but unlike vinblastine, it does not reverse the effect of ATP at a high concentration. Colchicine, however, decreases the Hill number for the effect of ATP on the UIC2 reactivity from 2 to 1. Colchicine increases the UIC2 reactivity and reverses the effect of ATP in ATPase-deficient Pgp mutants, but not in the wild-type Pgp expressed in the same cellular background, suggesting that ATP hydrolysis counteracts the effects of colchicine on the Pgp conformation.
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PMID:P-glycoprotein-mediated colchicine resistance in different cell lines correlates with the effects of colchicine on P-glycoprotein conformation. 1128 88

The anti-mitotic drugs colchicine and paclitaxel increase transfection efficiency of cationic liposomes. Using combined lipid-mediated transfection with anti-mitotic agents for gene therapy of cancer has been limited due to the likely development of multi-drug resistance (MDR). We treated human cancer cell lines and normal liver cells with glucocorticoids in combination with the antimitotics paclitaxel or colchicine before transient, cationic lipid-mediated transfection. Colchicine and paclitaxel each enhanced transgene expression in several cell lines. Moreover, glucocorticoid, combined with paclitaxel or colchicine, significantly increased reporter gene expression above that seen in cells treated with each drug alone. P-glycoprotein (PGP), a drug exporter encoded by ABCB1, exports both paclitaxel and colchicine. To determine the influence of PGP in colchicine- or paclitaxel-mediated enhancement of transgene expression, cells were treated with a histone deacetylase inhibitor, trichostatin A (TSA), known to induce ABCB1 expression, before treatment with colchicine or paclitaxel. TSA significantly reduced colchicine-mediated increases in reporter gene expression. Addition of glucocorticoid to colchicine pretreatment significantly attenuated TSA-mediated inhibition of colchicine-induced increases in transgene expression. TSA accelerated and glucocorticoid blocked export of rhodamine 123, a molecule known to be exported by PGP. The glucocorticoid/paclitaxel combination also increased reporter gene expression in BE(2)C cells, which constitutively express high levels of PGP. Thus, the degree of enhancement of transgene expression mediated by these anti-mitotics seems to be dependent on PGP activity. Glucocorticoids augment colchicine- or paclitaxel-mediated enhancement of transgene expression most likely by reducing drug egress through PGP.
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PMID:Enhancement of transgene expression by combining glucocorticoids and anti-mitotic agents during transient transfection using DNA-cationic liposomes. 1194 73

Colchicine is a relatively safe and effective medication when given at appropriate doses to patients with normal kidney and liver function. A clinical picture of multiple organ failure has been described in cases of colchicine poisoning and in kidney graft recipients treated with usual doses of colchicine during cyclosporine therapy. We report a case of multiple organ failure in a renal transplant patient who received appropriate doses of colchicine in combination with cyclosporine therapy. Interaction between colchicine and cyclosporine is postulated but boosting of CSA toxicity was excluded because of the low CSA blood through levels before and throughout the episode, in the presence of relatively stable renal function and for the prompt CSA withdrawal. Mechanism of toxicity and modulation of the P-glycoprotein by cyclosporine are reviewed. Although the proscription of the drug in cyclosporine-treated patients is not justified, caution is recommended in prescribing colchicine to patients receiving cyclosporine therapy, particularly in the presence of suboptimal kidney graft function.
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PMID:Multiple organ failure in a kidney transplant patient receiving both colchicine and cyclosporine. 1283 45

Understanding mechanisms associated with flavonoid neuroprotection is complicated by the lack of information on their ability to enter the CNS. This study examined naringenin and quercetin permeability across the blood-brain barrier (BBB), using in vitro (ECV304/C6 coculture) and in situ (rat) models. We report measurable permeabilities (P(app)) for both flavonoids across the in vitro BBB model, consistent with their lipophilicity. Both flavonoids showed measurable in situ BBB permeability. The rates of uptake (K(in)) into the right cerebral hemisphere were 0.145 and 0.019 ml min(-1) g(-1) for naringenin and quercetin, respectively. Quercetin K(in) was comparable to that of colchicine (0.006 ml min(-1) g(-1)), a substrate for P-glycoprotein (P-gp). Preadministration of the P-gp inhibitor PSC833 or GF120918 (10 mg/kg body wt) significantly increased colchicine K(in), but only GF120918 (able to inhibit breast cancer resistance protein, BCRP) affected K(in) for quercetin. Naringenin K(in) was not affected. The influence of efflux transporters on flavonoid permeability at the BBB was further studied using MDCK-MDR1 and immortalized rat brain endothelial cells (RBE4). Colchicine, quercetin, and naringenin all showed measurable accumulation (distribution volume, V(d) (microl/mg protein)) in both cell types. The V(d) for colchicine increased significantly in both cell lines following coincubation with either PSC833 (25 microM) or GF120918 (25 microM). Both inhibitors also caused an increase in naringenin V(d); by contrast only GF120918 coincubation significantly increased quercetin V(d). In conclusion, the results demonstrate that flavonoids are able to traverse the BBB in vivo. However, the permeability of certain flavonoids in vivo is influenced by their lipophilicity and interactions with efflux transporters.
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PMID:Flavonoid permeability across an in situ model of the blood-brain barrier. 1498 Jul 3

During the course of a mechanism-based screening program aimed at identifying new antimitotic agents, a novel microtubule depolymerizing piperazine derivative, 1-(5-chloro-2-methoxybenzoyl)-4-(3-chlorophenyl) piperazine, was identified. The compound, designated CB694, caused inhibition of proliferation of a wide range of cancer cell lines, with an average IC50 of 85 nM. A multidrug-resistant cell line was sensitive to inhibition by CB694, suggesting that this compound is a poor substrate for transport by P-glycoprotein. CB694 caused formation of abnormal mitotic structures in HeLa cells. Specifically, CB694 caused a concentration-dependent increase in bipolar spindles with lagging chromosomes and, with slightly higher concentrations, formation of multipolar mitotic spindles. These mitotic abnormalities occurred at concentrations that did not cause significant changes in the appearance or quantity of interphase microtubules. Coincident with the formation of abnormal mitotic spindles, CB694 caused G2/M arrest. CB694 inhibited the assembly of purified tubulin with an IC50 of 2.3 microM. Colchicine binding was strongly inhibited by CB694, suggesting that it binds to tubulin at the colchicine site. Bcl-2 phosphorylation and activation of ERK and JNK and caspase 3-dependent cleavage of PARP were observed in MDA-MB-435 cells treated with CB694. CB694 caused phosphorylation of Aurora A within 8 hr of treatment, and increases in Aurora A protein levels were coincident with mitotic accumulation. The efficacy of CB694 against a syngeneic murine transplantable solid tumor, Mammary 16/C, was also evaluated. CB694 was well tolerated and showed antitumor activity.
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PMID:CB694, a novel antimitotic with antitumor activities. 1615 90

Multidrug resistance (MDR) mediated by over-expression of P-glycoprotein (Pgp) is one of the major causes of failure of chemotherapy in cancer treatment. Colchicine, a naturally occurring alkaloid, is a Pgp substrate and acts as an antimitotic agent by binding to microtubules. Hence, Colchicine and its analogues radiolabeled with 99mTc may have potential for visualization of MDR in tumors. Here we report 99mTc-labeling of colchicine derivatives using [99mTc(CO)3(H2O)3]+ and [99mTc triple bond N]2+ cores. Trimethylcolchicinic acid synthesized from colchicine was used as the precursor to prepare iminodiacetic acid and dithiocarbamate derivatives which were then radiolabeled with [99mTc(CO)3(H2O)3]+ and [99mTc triple bond N]2+ cores, respectively. Radiolabeling yield for both the complexes was > 98% as observed by HPLC and TLC patterns. In vitro studies in tumor cell lines showed significant uptake for 99mTc-carbonyl as well as for 99mTc-nitrido colchicine complexes. Biodistribution studies in Swiss mice bearing fibrosarcoma tumor showed 4.1 +/- 1.2% ID/g of uptake at 30 min pi for 99mTc(CO)3-complex as against 0.42 +/- 0.24% ID/g for the 99mTcN-complex. 99mTc(CO)3-colchicine complex exhibited better pharmacokinetics with lower liver accumulation as compared to the 99mTcN-complex. Thus, colchicine radiolabeled with [99mTc(CO)3(H2O)3]+ core is more promising with respect to in vivo distribution characteristics in tumor model.
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PMID:99mTc-labeling of colchicine using [99mTc(CO)3(H2O)3]+ and [99mTc triple bond N]2+ core for the preparation of potential tumor-targeting agents. 1628 54

This study investigates the P-glycoprotein (Pgp)-mediated transport of its substrates in accumulation or efflux modes under steady-state conditions. The kinetics of colchicine uptake and efflux, a substrate of both Pgp and intracellular tubulin, were studied in HL60 and HL60/DNR cells; HL60/DNR cells contain 25 times more Pgp than do HL60 cells. HL60/DNR cells in a medium containing 6.25 nM colchicine, which mimics therapeutic conditions, reached steady-state twice as rapidly as did HL60 cells, and accumulated 24-times less colchicine than did HL60 cells. The Pgp inhibitor GF120918, increased colchicine uptake by HL60 cells 1.2-fold and that of HL60/DNR cells 17-fold, while it had no effect on colchicine efflux from either cell line that had been incubated with colchicine for 24 h. Colchicine kinetics fitted well a two closed-compartment model, showing that the low intracellular accumulation of colchicine in HL60/DNR cells resulted from a 11-fold decrease in colchicine uptake and a 2.3-fold increase in colchicine efflux, that could be attributed to Pgp-mediated efflux activity in HL60/DNR cells. Intracellular colchicine was mainly and similarly distributed in the cytosol in both cell lines. These data demonstrate that the kinetics of the intracellular colchicine accumulation depend on the density of Pgp and that Pgp is more a phase 0 (preventing cellular uptake) than a phase 3 (effluxing intracellular substrate) transporter under steady-state conditions, although the situation is reversed after a short incubation time (30 min), when intracellular free colchicine concentration is probably high enough for it to be removed from the cell by Pgp.
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PMID:Is P-glycoprotein (ABCB1) a phase 0 or a phase 3 colchicine transporter depending on colchicine exposure conditions? 1697 77


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