Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.6.3.44 (P-glycoprotein)
 13,344 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cyclosporin A (CSA) is an effective inhibitor of the P-glycoprotein (P-gp) activity and has been shown to modulate multidrug resistance (MDR) in in vitro experimental models. During degradation of CSA, the metabolites arising from the parental compound reach high levels in the serum of patients, and it is not clear whether these metabolites maintain the reversal activity of the parental compound, like the metabolites of verapamil. In an in vitro experimental model, we compared the reversal activity of CSA and 3 CSA metabolites (M1, M17, and M21) in the range of concentrations obtained in whole blood during a clinical trial with CSA used as a revertant agent. As experimental model we used LoVo-resistant cells. Our in vitro studies indicated that the metabolic hydroxylation and demethylation of CSA lead to molecules that greatly differ from the parent drug in their reversal activity. In the range of concentration detected in the whole blood of the patients (1-3 microM), CSA had a significant reversal activity. It decreased the IC50 of antineoplastic drugs involved in MDR (vincristine, taxol, doxorubicin and etoposide) but not the IC50 of platinum or methotrexate. CSA increased intracellular doxorubicin content and inhibited P-gp 3[H]azidopine photolabeling. Conversely, CSA metabolite concentrations superimposable to those observed in the patients (0.5-2.2 microM) had no sensitizing effects on the cytotoxicity of MDR-related anti-neoplastic drugs, nor did they affect 3[H]azidopine photolabeling or doxorubicin uptake. This study demonstrates that, during degradation of CSA, metabolite derivatives arise that have a very different reversal activity from that of the parental compound.
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PMID:Reversal activity of cyclosporin A and its metabolites M1, M17 and M21 in multidrug-resistant cells. 918 Jan 63

Transmembrane segments (TM) 6 and 12 are directly connected to the ATP-binding domain in each homologous half of P-glycoprotein and are postulated to be important for drug-protein interactions. Cysteines introduced into TM6 (L332C, F343C, G346C, and P350C) were oxidatively cross-linked to cysteines introduced into TM12 (L975C, M986C, G989C, and S993C, respectively). The pattern of cross-linking was consistent with a left-handed coiled coil arrangement of the two helices. To detect conformational changes between the helices during drug-stimulated ATPase activity, we tested the effects of substrates and ATP on cross-linking. Cyclosporin A, verapamil, vinblastine, and colchicine inhibited cross-linking of mutants F343C/M986C, G346C/G989C, and P350C/S993C. By contrast, ATP promoted cross-linking between only L332C/L975C. Enhanced cross-linking between L332C/L975C was due to ATP hydrolysis, since cross-linked product was not observed in the presence of ATP and vanadate, ADP, ADP and vanadate, or AMP-PNP. Cross-linking between P350C/S993C inhibited verapamil-stimulated ATPase activity by about 75%. Drug-stimulated ATPase activity, however, was fully restored in the presence of dithiothreitol. These results show that TM6 and TM12 undergo different conformational changes upon drug binding or during ATP hydrolysis, and that movement between these two helices is essential for drug-stimulated ATPase activity.
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PMID:Drug-stimulated ATPase activity of human P-glycoprotein requires movement between transmembrane segments 6 and 12. 926 Oct 97

Multidrug resistance in leukemic cells is associated with decreased drug accumulation. A resistant cell line and cells from 11 patients with chronic lymphoid leukemia B were used for the evaluation of intracellular accumulation of daunorubicin (DNR), idarubicin (IDA), epirubicin (EPI) and rhodamine-123 (Rh-123). Cyclosporin A (CSA) and verapamil were used to test their modulatory effects on anthracyclines and the fluorescent dye. In leukemic samples there was a tendency for a lower accumulation index in samples tested with Rh-123 as compared to anthracyclines. IDA was a poorer substrate to P-glycoprotein (Pgp) than two of its analogues, e.g. DNR and EPI. A good correlation (80%) was found between Rh-123 accumulation and Pgp expression by phosphatase-anti-alkaline phosphatase. A strict correlation (100%) was found between modulation by CSA of Rh-123 accumulation and immunoreactivity to Pgp. Two discordant results were seen suggesting that other mechanisms of resistance could be present. The Rh-123 accumulation test seems to give a better indication than anthracyclines, however, it is not selective and may allow the detection of other drug-transport pumps.
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PMID:Comparison between anthracyclines and rhodamine-123 accumulation in chronic lymphoid leukemia: effect of cyclosporin A and verapamil. 942 81

The response of T cells in relation to the cell cycle has not been extensively studied. We have attempted to address this question using Jurkat T cells treated with cytostatic drugs known to arrest cells at various transition points of their cycle. We tested several concentrations of drugs that act at G1/S (hydroxyurea, lovastatin, thymidine), early S (aphidicolin, cyclosporin A, rapamycin) or G2+M (colchicine, nocodazole) in 24 h cultures. Cytofluorimetric analyses showed that cycling Jurkat cells were equally distributed between the G1 (44.9 +/- 6.5%) and S (42.3 +/- 8.0%) phases. Cell distribution in G2+M was 12.7 +/- 2.8%. Hydroxyurea but not lovastatin increased the percentage of cells in S phase to approximately 60-70% and both drugs decreased it to approximately 30% in G1. Thymidine had no effects. Aphidicolin increased the distribution in S phase to approximately 70% with a decrease in G1 to approximately 30%. Cyclosporin A and rapamycin increased the percentage of the cells in G1 to approximately 70% and decreased it to approximately 25% in S phase. Nocodazole increased cell distribution in G2+M to approximately 60% and induced a decrease in G1 to approximately 10%. The effects of the drugs were not related to their toxicity and their limited efficiency raised the possibility that Jurkat cells possessed an intrinsic resistance to these xenobiotics. Time-course analysis showed (scanning electron microscopy) that the early morphological changes induced by colchicine were reversible. Drug efflux experiments (vinblastine) suggested that an ATP-dependent process could be involved. However, Northern blot analyses showed a weak signal for MDR1 (P-glycoprotein). In contrast, a probe for MRP (P-190) showed a strong signal in Jurkat and peripheral lymphocytes. The presence of drugs (cyclosporin A, nocodazole, thymidine) (24 h) did not upregulate its message and cell treatment with DL-butathione (S,R)-sulfoximine only moderately affected the efficiency of the glutathione S-conjugate MRP transporter. Our data suggest that the intrinsic multidrug resistance of leukemic Jurkat T cells does not appear to involve the MDR1 and MRP members of the ABC family of reverse drug transporters and these observations raise the possibility of the involvement of multifaceted mechanisms.
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PMID:The MDR1 (P-glycoprotein) and MRP (P-190) transporters do not play a major role in the intrinsic multiple drug resistance of Jurkat T lymphocytes. 944 42

The basic distinguishing feature of all cells expressing functional P-glycoprotein-multidrug resistance is a decrease of steady state drug levels as compared to those in drug-sensitive controls. A variety of small molecules, such as verapamil and cyclosporin A, bind to P-glycoprotein and inhibit its ability to pump out antitumor drugs. The kinetics of P-glycoprotein-mediated efflux of various anthracycline derivatives was measured in multidrug-resistant (MDR) K562 cells in the presence of verapamil. Used for the purpose were daunorubicin, idarubicin and 8-S-fluoro-idarubicin which have the same pKa of deprotonation equal to 8.4, but different lipophilicity, 4'-epi-2'-bromo-daunorubicin which has a lipophilicity which is comparable to that of daunorubicin but a pKa equal to 6.3, pirarubicin with pKa equal to 7.7 and lipophilicity different from that of these derivatives were used. Our data show (1) that verapamil is unable to completely block the P-glycoprotein-mediated efflux of anthracyclines and that 10% of its functionality remains even with high verapamil concentrations, (2) that the ability of verapamil to restore intracellular accumulation of anthracyclines in MDR cells depends on the kinetics of their uptake. With fast kinetics uptake, as is the case for idarubicin, 8-S-fluoro-idarubicin, 4'-epi-2'-bromo-daunorubicin and pirarubicin (which have either a low pKa and/or high lipophilicity), verapamil can restore in multidrug resistant cells an intracellular drug level which is comparable to that observed in sensitive cells. This is not possible when the kinetics of uptake is low as is the case for daunorubicin. Cyclosporin A is a more potent modulator and is able to fully restore daunorubicin accumulation in multidrug resistant cells.
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PMID:The ability of verapamil to restore intracellular accumulation of anthracyclines in multidrug resistant cells depends on the kinetics of their uptake. 957 Apr 81

Cyclosporin A (CsA) is a widely-used immunosuppressant drug whose therapeutic and toxic actions are mediated through inhibition of calcineurin (CN), a calcium- and calmodulin-dependent phosphatase. Inhibition of CN by CsA requires drug binding to its protein cofactor in the inhibition, cyclophilin. Because cyclophilin is a high affinity target for CsA it is expected that this protein can act as a reservoir for the drug in the cell and may be able to inhibit cellular efflux of CsA. P-glycoprotein (P-gp) is known to increase the rate of CsA efflux from CsA loaded cells but it is not clear if the P-gp drug efflux pump can compete effectively with cyclophilin at therapeutically relevant concentrations of CsA. To test the hypothesis that increased expression of P-gp confers protection against CsA-dependent inhibition of CN phosphatase activity, KB-V cells expressing varying levels of P-gp were analyzed to determine the potency of CsA as a CN inhibitor. When intact cells were treated with CsA, a positive correlation was observed between P-gp expression and resistance to CsA-dependent inhibition of CN: the IC50 is approximately 20-fold higher in the multidrug resistant epidermal carcinoma cell line, KB-V, which expresses P-gp at a high level than in the parental, KB, cell line expressing very low levels of P-gp. The resistance displayed by KB-V cells is abrogated by co-administration of the P-gp inhibitor verapamil, whereas verapamil has no effect on CsA potency in control KB cells. In cell lysates from KB-V cells with different amounts of P-gp CsA exhibits equivalent potency, indicating that the difference in sensitivity to CsA among the cell types requires maintenance of cell integrity. These observations support the view that resistance to CN inhibition by CsA occurs in cells with moderately elevated P-gp activity. Therefore, P-gp activity appears to be an important determinant of CsA cellular specificity for both therapeutic and toxic effects.
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PMID:Cyclosporin A has low potency as a calcineurin inhibitor in cells expressing high levels of P-glycoprotein. 965 Nov 11

P-glycoprotein (Pgp)-related multidrug resistance (MDR) is frequently observed in acute non-lymphocytic leukemia (ANLL) and is associated with a poor response to standard chemotherapy. Cyclosporin A (CsA) is an effective downmodulator of Pgp-related MDR in vitro and has already been tested for that purpose in vivo also. Since Pgp is expressed in several normal cells and tissues, the modulation of Pgp can also modify total body exposure to antileukemic drugs and can alter and increase the toxicity of the antileukemic treatment. We report here the results of a study where 46 consecutive adult patients with ANLL were assigned to receive the same standard chemotherapy regimen of arabinosyl cytosine and idarubicin (IDA) for remission induction or consolidation, without or with CsA. Twenty-eight patients received 36 courses of chemotherapy without CsA and 18 patients received 32 courses of chemotherapy with CsA. CsA dose was 10-12.5 mg/kg/day and was given as a continuous i.v. infusion for 72 h. Whole blood CsA steady-state concentration ranged between 0.61 and 1.14 microM. The IDA area-under-the-curve was about twice as high in the cases that received CsA than in the other cases. CsA had no detectable effects on renal function and fluid balance, but significantly increased systemic blood diastolic pressure and conjugated bilirubine concentration. Furthermore, CsA-treated patients had greater, and more severe, oral and intestinal mucosal toxicity, with more severe adverse events, including more cases of gram-negative bacteremia, and with a delayed hemopoietic recovery. In conclusion, this study showed that an attempt at an effective downmodulation of Pgp-mediated MDR would substantially increase the hemopoietic and mucosal toxicity of antileukemic treatment and that the increase is accounted for, at least in part, by an increase of total body exposure to IDA.
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PMID:Adjuvant treatment with cyclosporin A increases the toxicity of chemotherapy for remission induction in acute non-lymphocytic leukemia. 969 78

1. Homozygously mdr1a gene disrupted mice (mdr1a(-/-) mice) and wild type mice (mdr1a(+/+) mice) were used to develop a method for P-glycoprotein (P-gp) function imaging non-invasively and to study the effect of a P-gp reversal agent on its function in vivo. 2. [11C]verapamil (0.1 mg/kg) was administered and the changes in tissue concentrations were determined ex vivo by organ extirpation and in vivo with PET. To block P-gp function, cyclosporin A was administered. 3. Biodistribution studies revealed 9.5-fold (P < 0.001) and 3.4-fold (P < 0.001) higher [11C]verapamil in the brain and testes of mdr1a(-/-) mice than in mdr1a(+/+) mice. Cyclosporin A (25 mg/kg) increased [11C]verapamil levels in the brain and testes of mdr1a(+/+) mice in both cases 3.3-fold (P < 0.01 (brain); P < 0.001 (testes)). Fifty mg/kg cyclosporin A increased [11C]verapamil in the brain 10.6-fold (P < 0.01) and in the testes 4.1-fold (P < 0.001). No increases were found in the mdr1a(-/-) mice. This indicates complete inhibition of P-gp mediated [11C]verapamil efflux. 4. Positron camera data showed lower [11C]verapamil levels in the brain of mdr1a(+/+) mice compared to those in mdr1a(-/-) mice. [11C]verapamil accumulation in the brain of mdr1a(+/+) mice was increased by cyclosporin A to levels comparable with those in mdr1a(-/-) mice, indicating that reversal of P-gp mediated efflux can be monitored by PET. 5. We conclude that cyclosporin A can fully block the P-gp function in the blood brain barrier and the testes and that PET enables the in vivo measurement of P-gp function and reversal of its function non-invasively.
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PMID:Complete in vivo reversal of P-glycoprotein pump function in the blood-brain barrier visualized with positron emission tomography. 972 52

Multidrug resistance mediated by P-glycoprotein may be an important cause of chemotherapy failure. Renal cell carcinoma is a disease known to demonstrate a high degree of intrinsic chemotherapy drug resistance, and this has been shown to be related to intrinsic overexpression of P-glycoprotein. Cyclosporine A and tamoxifen have been shown to reverse multidrug resistance in renal cell carcinoma cell lines in vitro. Phase I studies have defined appropriate doses of cyclosporine A and tamoxifen that can be combined with continuous-infusion vinblastine and safely achieve serum levels associated in vitro with resistance reversal. A randomized Phase II study was carried out by the Cancer and Leukemia Group B to evaluate the potential of high doses of cyclosporine A or tamoxifen to modulate clinical vinblastine resistance in patients with advanced renal cell carcinoma. Patients were treated initially with continuous-infusion vinblastine alone (1.2 mg/m2/day for 4 days or 1.5 mg/m2/day for 5 days); patients with stable or progressive disease were then treated with the same vinblastine regimen, combined with a high-dose regimen of either cyclosporine A (12.5 mg/kg/day for 5 days) or tamoxifen (400 mg/m2 as a loading dose and 300 mg/m2/day for 13 days). Sixty-three patients were randomized to each arm. Eighty patients on both arms were evaluable for response to vinblastine alone; of these, only one patient achieved a partial response. Thirty-three patients went on to be treated with vinblastine and high-dose cyclosporine A. No responses were observed, although four patients with progressive disease on prior vinblastine achieved stabilization of disease after cyclosporine A was added. Addition of cyclosporine resulted in more leukopenia (5% versus 25%) and in transient hyperbilirubinemia (24%) and neurocortical changes (11%). No significant azotemia was observed. Thirty-five patients received high-dose tamoxifen with continuous-infusion vinblastine. One complete remission was seen in a patient who had stable disease only with prior vinblastine alone; no other responses were observed. Leukopenia was not more severe with the addition of tamoxifen to vinblastine, nor was hyperbilirubinemia observed. However, 9% of patients developed transient ataxia with or without neurocortical changes as a result of high-dose tamoxifen therapy, and 11% developed phlebitis. We conclude that advanced renal cell carcinoma is a highly chemoresistant tumor, that continuous-infusion vinblastine has no appreciable activity in the therapy of this disease, and that addition of high doses of cyclosporine A or tamoxifen was not able to modulate this resistance in these patients. Suggestions regarding study design for future drug resistance modulation trials were made based on the design and conduct of this study.
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PMID:Modulation of vinblastine resistance in metastatic renal cell carcinoma with cyclosporine A or tamoxifen: a cancer and leukemia group B study. 981 87

P-glycoprotein (Pgp) has been widely associated with the multidrug resistance phenotype. Nevertheless, this protein has been detected in many normal tissues and cells, including liver, kidney, endothelial cells that constitute the hematological barrier of the brain and testes, and cells from the immune system. Many in vitro models have been used to study drugs that modulate Pgp activity and the multidrug resistance phenomenon. In the present work, we investigate the in vivo effects of resistance-modulating agents on lymphoid organs. Rhodamine 123 (Rho123), a well-known Pgp substrate, was administered to mice, and the fluorescence level in thymus and lymph node cells measured. The fluorescence level on these organs showed a dose-dependent response. Cyclosporin A (CSA), Verapamil (VP) and Trifluoperazine (TFP), three resistance-modulating agents, were administered to mice 1 h prior to 1 mg/kg Rho123 administration. Surprisingly, VP (10 mg/kg) and TFP (750 microg/kg) did not modulate Rho123 retention by thymus and lymph node cells. CSA (50 mg/kg) was the only drug that increased the fluorescence level in both organs. These results point out to the need of a wider study on the in vivo effects of resistance-modulating agents in different organs and systems.
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PMID:The in vivo effect of the administration of resistance-modulating agents on rhodamine 123 distribution in mice thymus and lymph nodes. 1037 99


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