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)

Small cell lung cancer (SCLC) is treated primarily with combination chemotherapy. Despite high initial response rates, most patients eventually die with drug resistant disease. In some tumours, resistance to multiple chemotherapeutic agents is attributed to overexpression of P-glycoprotein (P-gp). However, this does not appear to be a frequent occurrence in drug resistant SCLC. Increased levels of glutathione (GSH) and related enzymes may play a role in resistance to alkylating agents as well as natural product drugs. We measured levels of GSH, glutathione S-transferase (GST), glutathione reductase (GSH Red), glutathione peroxidase (GSH Px), and gamma-glutamyl transpeptidase (gamma-GT) in a panel of 20 SCLC cell lines. Most of these lines were established from patients treated at this centre. Each cell line had a characteristic and reproducible profile of GSH and related enzyme levels. Immunoblot analysis indicated that the predominant GST in the cell lines was the anionic pi isoenzyme. The relative sensitivity of each of these cell lines to 16 different chemotherapeutic agents was measured using a modified MTT assay. Spearman rank correlation analysis was used to determine the relationships between the relative chemosensitivity of these cell lines and the levels of GSH and related enzymes. The number of positive correlations was no greater than expected by chance alone. Furthermore, there was no correlation with the treatment history of the patients from whom the cell lines were derived. These data suggest that alterations in glutathione metabolism do not play a major role in resistance to chemotherapeutic agents in these human SCLC cell lines.
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PMID:Do glutathione and related enzymes play a role in drug resistance in small cell lung cancer cell lines? 810 44

Methylmercury transport across liver canalicular membranes into bile, a major route of excretion of this toxic compound, is dependent upon intracellular GSH, and a glutathione-methylmercury complex (CH3Hg.SG) has been detected in liver tissue and bile. To examine whether the CH3Hg.SG complex is itself transported across the canalicular membrane and to identify the transport system involved, studies were performed in isolated rat liver canalicular plasma membrane vesicles. Uptake of CH3(203)Hg.SG (10 microM) into an osmotically active space was temperature-sensitive and unaffected by either ATP (5 mM) or an inwardly directed Na+ gradient (100 mM); however, CH3Hg.SG uptake was enhanced by a valinomycin-induced K+ diffusion potential (inside-positive) indicating that its transport was electrogenic. Transport of CH3Hg.SG exhibited saturation kinetics with both high affinity (Km = 12 +/- 2 microM, Vmax = 0.23 +/- 0.02 nmol.mg-1.20 s-1) and low affinity (Km = 1.47 +/- 0.22 mM, Vmax = 1.23 +/- 0.14 nmol.mg-1.20 s-1) components. Uptake of this complex was inhibited by GSH, the GSH analog ophthalmic acid, S-methyl, S-ethyl, S-butyl, S-hexyl, S-octyl, and S-dinitrophenyl glutathione, but not by GSSG, bile acids, amino acids, and P-glycoprotein inhibitors. Furthermore, GSH competitively inhibited (Ki = 83 microM) and trans-stimulated CH3Hg.SG uptake into the canalicular vesicles. These studies provide the first kinetic characterization of a transport system for glutathione-mercaptides and indicate that CH3Hg.SG is not a substrate for the ATP-dependent, canalicular GSSG or glutathione S-conjugate carriers, but appears to be a substrate for canalicular carriers that also transport GSH. Because efflux systems for GSH are found in all mammalian cells, transport of glutathione-metal complexes by such carriers may be a common mechanism for the removal of methylmercury and possibly other metals from cells.
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PMID:Transport of the glutathione-methylmercury complex across liver canalicular membranes on reduced glutathione carriers. 814 67

We studied the potentiation of doxorubicin (DOX) activity in multidrug-resistant (MDR) cells by buthionine sulfoximine (BSO), a specific inhibitor of gamma-glutamylcysteine synthetase, and by cepharanthine (CE), which interacts with P-glycoprotein. The glutathione (GSH) of MDR cells was approximately 1.5-fold greater than that of the parental cell line. BSO reduced GSH content of MDR cells compared to that of the sensitive ones. The BSO treatment (50 microM) enhanced the effect of DOX by 1.8-fold, while CE caused a greater reversal of drug resistance. The combination of BSO with CE produced further potentiation of DOX activity in an antiproliferative effect. Pretreatment of cells with BSO did not alter the cellular accumulation of DOX in the absence or presence of CE. The addition of BSO (30 mM) to the drinking water of mice reduced the tissue levels of GSH in tumor cells, suggesting that the marked decrease in GSH might diminish the ability of that tumor to resist DOX. Combined administration of CE and DOX resulted in enhancement of DOX antitumor activity and prolongation of survival time. The survival of mice treated with BSO and CE as a supplement to DOX treatment was superior that of mice receiving DOX alone. These studies demonstrated that the combinations of BSO with CE may be useful for killing drug-resistant tumor cells.
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PMID:Combined effects of buthionine sulfoximine and cepharanthine on cytotoxic activity of doxorubicin to multidrug-resistant cells. 855 53

The role of the glutathione (GSH) system in vivo or in drug resistance has received much attention, since GSH is a major component of the cellular detoxification system. We Studied the effect of GSH depletion by buthionine sulfoximine (BSO), a potent inhibitor of gamma-glutamylcysteine synthetase, on doxorubicin (DOX) toxicity in mice. The administration of BSO (30 mM in drinking water for 5 days) significantly decreased the tissue GSH. The GSH depletion in various tissues by BSO was associated with a decrease in the detoxification of DOX in mice. A single dose of 20 mg/kg of DOX significantly reduced body weight and rectal temperature in mice 3 days after injection. The combination with BSO and cepharanthine (biscoclaurine alkaloid), a P-glycoprotein (P-gp) inhibitor, significantly potentiated decrease in body and hypothermia induced by DOX. The study demonstrates that BSO markedly increases the toxicological effect of DOX with the alterations in GSH of tissues and Suggests that the intracellular accumulation of DOX is not a factor.
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PMID:Effect of glutathione depletion by buthionine sulfoximine on doxorubicin toxicity in mice. 868 Aug 8

An in vitro study was designed to evaluate the uptake of sestamibi (MIBI) in P-glycoprotein (Pgp) and glutathione-associated (GSH) multidrug-resistant (MDR) cell lines. MIBI uptake was studied in various human breast carcinoma cell lines, i.e. in wild-type (MCF7/wt) cells, in adriamycin-resistant (MCF7/adr) cells which express Pgp and in melphalan-resistant (MCF7/mph) cells with increased levels of GSH. The effects of buthiomine sulphoximine (BSO) and verapamil on MIBI uptake were also studied in the MCF7/mph and MCF7/adr cells respectively. The cells were incubated for 1 h with a dose of 0.1 MBq thallium-201 and technetium-99m MIBI. Both MIBI and 201Tl uptakes were higher for MCF7/mph cells than for the other cells studied. The mean MIBI uptake in MCF7/adr cells was significantly lower than that in MCF7/wt cells (1.9%+/-0.5% vs 3. 1%.0.6%; P <0.01). Verapamil treatment increased the MIBI uptake in MCF7/adr cells (to 2.6%.0.3%; P <0.05). Treatment of MCF7/mph cells with BSO resulted in a significant reduction in GSH content (from 243.2+/-81.1 nmol/mg protein to 17.6+/-4.4 nmol/mg protein; P <0. 001). However, MIBI uptake in BSO-treated and untreated MCF7/mph cells was similar (4.43%+/-0.5% and 5.93%+/-1.7%, respectively; P >0. 1). This study suggests that the uptake of MIBI is not diminished by glutathione-associated drug resistance and that MIBI uptake in a tumour sample does not necessarily indicate that a cancer is sensitive to drugs.
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PMID:Technetium-99m sestamibi uptake in human breast carcinoma cell lines displaying glutathione-associated drug-resistance. 869 63

We have measured the cytotoxic effect of 1 h exposure to doxorubicin (DOX) on a panel of tumor cell lines. Cellular effects were measured by monolayer colony-forming assay and a colorimetric cytotoxicity assay. As parameters of chemosensitivity we used two different end-points: the dose of DOX that reduces to 50% the number of colonies (ID50) and the dose of DOX that reduces the final optical density to 50% of the control value (IC50). There was a significant correlation between both chemosensitivity indices (r = 0.886, p = 0.0034). DOX-induced DNA double-strand breaks (dsb) were evaluated using pulsed-field gel electrophoresis (PFGE) and compared with cellular effects, P-glycoprotein expression (P-170) and intracellular glutathione (GSH) levels. Our results showed a relationship between the slope of DNA dsb dose-response curves and the percentage of cells that express P-170 (r = -0.957, p = 0.0002). Our study also detects a positive relationship between cellular chemosensitivity parameters and GSH content [ID50 versus GSH (r = 0.794, p = 0.0186), IC50 versus GSH (r = 0.790, p = 0.0198)] in our panel of cell lines.
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PMID:Relationship between doxorubicin cell sensitivity, drug-induced DNA double-strand breaks, glutathione content and P-glycoprotein in mammalian tumor cells. 884 87

Cells exposed to calcein acetoxymethyl ester (calcein AM) in the growth medium become fluorescent following cleavage of calcein AM by cellular esterases to produce the fluorescent derivative calcein. It has previously been shown by others that multidrug resistant cells which overexpress P-glycoprotein accumulate much less fluorescent calcein than the corresponding parental cells. We have now examined the transport of calcein in multidrug resistant cells which overexpress an alternative transporter, the multidrug resistance-associated protein (MRP). Accumulation of calcein fluorescence was greatly reduced in the MRP-overexpressing human lung cancer cell lines COR-L23/R and MOR/R compared with their parental lines. Energy depletion resulted in a considerably increased accumulation in the resistant lines. Treatment of resistant cells with buthionine sulfoximine (BSO), which depletes cellular glutathione (GSH), did not affect calcein accumulation, in marked contrast to our previous results for daunorubicin or the fluorescent probe rhodamine 123. Genistein, verapamil, cyclosporin A and ouabain were also each able to modify, to some extent, accumulation of daunorubicin, whilst having essentially no effect on calcein accumulation. However, the organic anion transport inhibitor probenecid was able to increase accumulation of both calcein and daunorubicin in the resistant cells. Genistein and verapamil treatment preferentially reduced the GSH content of resistant cells, whilst probenecid did not. However, probenecid caused a clear decrease in release of GSH from resistant cells into the medium.
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PMID:On the relationship between the probenecid-sensitive transport of daunorubicin or calcein and the glutathione status of cells overexpressing the multidrug resistance-associated protein (MRP). 884 45

Drug resistance often results in failure of anticancer chemotherapy in leukemias. Several mechanisms of drug resistance are known with multidrug resistance (MDR) being the best characterized one. MDR can be due to enhanced expression of certain genes (MDR1, MRP or LRP), alterations in glutathione-S-transferase activity or GSH levels and to reduction of the amount or the activity of topoisomerase II. Here we review the current status of the clinical significance of the various mechanisms of MDR in leukemias and also discuss possibilities for the reversal of MDR. MDR1 gene expression has been seen in many leukemias, notably in acute myeloid leukemia (AML) and blast crisis of chronic myeloid leukemia. Both MDR1 RNA and P-glycoprotein expression of the leukemic cells have been shown to correlate with poor clinical outcome in AML. However, preliminary results indicate that the MRP gene as well as the LRP gene can be expressed in AML. Thus, drug resistance in leukemias appears to be multifactorial. P-glycoprotein-mediated MDR can be reversed by several drugs. These resistance modifiers are currently evaluated with regard to their clinical efficacy. Despite some encouraging results, reversal of drug resistance and subsequent improvement in clinical outcome remains to be shown.
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PMID:Multidrug resistance in leukemias and its reversal. 903 Oct 75

A recent study has suggested that degraded adducts smaller than 2 kDa in molecular weight of bovine serum albumin (BSA)-conjugated doxorubicin (DXR) (BSA-DXR) might exhibit cytotoxicity against multidrug resistant (MDR) cells. To investigate this notion further, intracellular accumulation and cytotoxicity of DXR coupled to several small peptides, such as glycylglycine (diGly), glycylglycylglycine (triGly), reduced glutathione (GSH) and oxidized glutathione (GSSG), were investigated using DXR-sensitive (AH66P) and DXR-resistant (AH66DR) rat hepatoma cell lines. Against both AH66P and AH66DR cells, diGly-conjugated DXR (diGly-DXR) and triGly-conjugated DXR (triGly-DXR) demonstrated the same cytotoxic activity as DXR, and the accumulation of both conjugates in the two cell lines was almost similar to that of DXR. After treatment of AH66DR cells with 5 microM verapamil [an inhibitor of P-glycoprotein (Pgp)], the intracellular levels of diGly-DXR and triGly-DXR were markedly increased and consequent cytotoxicity was improved. On the other hand, GSH-conjugated DXR (GSH-DXR) showed 9- and 7.5-fold more cytotoxic activity than BSA-DXR against AH66P and AH66DR cells, respectively. GSH-DXR accumulated rapidly in AH66DR cells, probably by the same mechanism as in AH66P cells, because the treatment of AH66DR cells with verapamil did not cause a significant increase in the intracellular drug level as compared with that in cells treated without verapamil. The levels of cytotoxicity and accumulation of GSSG-DXR were the same as those of BSA-DXR for both cell lines. These results indicate that GSH-DXR exerts potent cytotoxicity against both cell lines among the peptide DXR conjugates examined because of the rapid uptake and high accumulation of GSH-DXR similar to that of DXR without efflux.
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PMID:Drug conjugate of doxorubicin with glutathione is a potent reverser of multidrug resistance in rat hepatoma cells. 907 16

Ethyldeshydroxy-sparsomycin (EdSm) is a ribosomal protein synthesis inhibitor which synergistically enhances the antitumor activity of cisplatin against L1210 leukemia in vivo. Because cellular glutathione (GSH) and glutathione S-transferases (GST) are reported to interfere with the antitumor activity of cisplatin, we analyzed the effect of EdSm and cisplatin on GSH and GST activity in selected tumor cells. For this purpose we used three murine leukemia tumors with different sensitivities towards EdSm and cisplatin: L1210-WT, sensitive to both drugs, L1210-Sm, resistant to EdSm, and L1210-CDDP, resistant to cisplatin. No significant differences were detectable between these three cell lines regarding the population doubling time, the cell size, and the cellular level of protein and glutathione. Neither of the resistant L1210 subclones showed P-glycoprotein expression. Drug exposure, however, changed the intracellular dynamics. Exposure to EdSm strongly decreased the amount of cellular protein, decreased the overall GST activity and led to GSH depletion, whereas exposure to cisplatin induced a rise in the amount of protein, in GSH, and in the total GST activity. These effects are dose-dependent and correlate well with the sensitivity of the tumor cells for EdSm or cisplatin. In addition, exposure to EdSm lowered the V(max) of GST in L1210-WT and L1210-Sm; however, in L1210-CDDP both the V(max) and the K(m) were increased. That this was not a direct effect of EdSm on GST was shown in a cell-free system, where EdSm did not influence the GST activity nor could it act as a substrate for GST. Our results suggest that the synergistic combination of EdSm and cisplatin might be explained by EdSm switching off the cellular detoxification mechanism for cisplatin, i.e. by inhibition of de novo synthesis and subsequent depletion of GSH and GST.
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PMID:The effect of ethyldeshydroxy-sparsomycin and cisplatin on the intracellular glutathione level and glutathione S-transferase activity. 918 Mar 88


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