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)

Native resistance to conventional chemotherapy remains an important cause of treatment failure in the adult acute leukemias. Delineation of cellular mechanisms of drug resistance therefore represents a prerequisite to the development of more effective treatment strategies. The multidrug resistance (MDR) phenotype represents one such mechanism of resistance with direct clinical relevance. This phenotype occurs normally in certain mammalian tissues, and is detectable in tumor cell lines selected for resistance to naturally occurring antineoplastics. The mdr1 gene or its glycoprotein product, P-glycoprotein, is detected with high frequency in secondary acute myeloid leukemia (AML) and poor-risk subsets of acute lymphoblastic leukemia. In prospective studies in AML, MDR overexpression is an independent determinant of response to treatment and overall survival with conventional-dose induction regimens. Investigations of mdr1 regulation in normal hematopoietic elements has shown a pattern which corresponds to its regulation in acute leukemia, explaining the linkage of mdr1 to specific cellular phenotypes. Therapeutic trials are now in progress to test the ability of various MDR-reversal agents to restore chemotherapy sensitivity in high-risk acute leukemias.
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PMID:Multidrug resistance in acute leukemia: a conserved physiologic function. 128 51

In many cell systems, resistance to cytotoxic drugs is acquired by the amplification and/or overexpression of the multidrug resistance (mdr) gene, which codes for the glycoprotein, p170 (P-glycoprotein). Moreover, in a variety of malignant tumours there is increasing evidence of the relationship between the DNA ploidy pattern of patients and their prognosis. In this study we aimed to evaluate these two potential indicators of constitutive drug resistance in human colorectal tumours. We employed a method to quantify simultaneously, on a per cell basis, mdr gene expression (using the C219 monoclonal antibody for P-glycoprotein) and nuclear DNA content with high-resolution bivariate flow cytometry. The study was performed on a human colon-carcinoma-derived cell line (LoVo) and its doxorubicin-resistant variant (LoVo/Dx) and on tumour samples and adjacent normal mucosa from 35 untreated patients with colon cancer. The P-glycoprotein was found in both LoVo and LoVo/Dx cells with levels slightly lower in the parental than in the resistant subline (P, NS). A multi-drug-resistant specific probe for mRNA expression and Western blot assay confirmed the specificity of p170 expression. All of the colon cancer with unimodal diploid DNA distribution and all the normal colonic mucosa samples showed P-glycoprotein expression, without a statistically significant difference in median values between tumours and normal samples. Tumours with bimodal DNA distribution showed median values of P-glycoprotein expression of their hyperdiploid cell clones significantly higher than those of their diploid clones and of the tumours with unimodal DNA distribution (P less than 0.005). Our results show the feasibility of bivariate flow-cytometric analysis of P-glycoprotein expression and DNA content on clinical material and support the hypothesis that the MDR phenotype and DNA ploidy together may influence the biological behaviour of colon cancer in vivo.
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PMID:Flow cytometric analysis of multidrug-resistance-associated antigen (P-glycoprotein) and DNA ploidy in human colon cancer. 135 83

The morphologic distinction between thyroid carcinoma and certain benign thyroid conditions can be difficult in selected cases. P-glycoprotein (Pgp), a glycoprotein associated with tumor multidrug resistance, has been reported to be expressed in thyroid carcinoma but not in benign thyroid conditions. To determine the specificity of immunostaining for Pgp in the diagnosis of thyroid carcinoma, we studied formalin-fixed, paraffin-embedded tissue from 69 cases of various thyroid lesions using a commercially available monoclonal antibody to Pgp (C219, Centocor, Malvern, PA) and an avidin-biotin-peroxidase complex technique. Positive reactivity was seen in 15 of 37 (41%) benign thyroid conditions and in 23 of 32 (72%) thyroid carcinomas. We conclude that immunostaining for Pgp is not specific in the diagnosis of thyroid carcinoma.
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PMID:Immunostaining for P-glycoprotein in the diagnosis of thyroid carcinomas. 136 65

Cellular multidrug resistance, a common side-effect of anticancer chemotherapy frequently leading to failure of the treatment, has been characterized as an acquired resistance to several antimitotic drugs simultaneously. Multidrug resistance could mainly be attributed to the overexpression of the P-170 glycoprotein, considered as a drug-efflux pump encoded by the mdr 1 gene. Overexpression of this protein can be induced either by an accidental amplification or activation or both of the mdr 1 gene. Recent investigations focused on these mechanisms, aiming at a better understanding of the appearance of multidrug resistance during a chemotherapy. P-glycoprotein mediated drug resistance, however, is only one, albeit quite an important detoxification pathway, and some observations revealed genetic interactions with other systems. On the basis of this new knowledge, the development of novel therapeutic strategies to circumvent this clinical side-effect of cancer treatment has already begun.
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PMID:The genetic basis of multidrug resistance. 143 45

The conventional laboratory approach to study the mechanisms of drug resistance has been the selection of drug-resistant cell lines by continuous exposure to cytotoxic agents. Such lines, which are selected for resistance to a single agent, frequently display cross-resistance to a number of cytotoxic agents that are unrelated in both structure and proposed mechanism of action. Multidrug-resistant cells display reduced drug accumulation, which is the result of overexpression of a surface glycoprotein (P170). Although resistance to multiple antitumor agents is a common clinical problem in the treatment of cancer, the precise role of the P-glycoprotein-mediated mechanism in human tumors remains to be established. Many alterations in multidrug-resistant cells selected in vitro have been identified. The concomitant expression of multiple phenotypic differences, which appear to be favored by continued and prolonged drug exposure, makes analysis of critical individual resistance pathways more difficult. However, multiple factors may also be involved in the development of clinical resistance. Recent studies have identified alterations in DNA topoisomerase II activity and function as an alternative mechanism that contributes to the multidrug-resistance phenomenon or is responsible for a different type of drug resistance. The precise nature of these changes remains unclear. Available evidence supports the view that expression of the enzyme is an important determinant of cell sensitivity to DNA topoisomerase poisons, but that other changes involved in regulation of enzyme function and/or in the cellular processing of drug-induced DNA damage may be critical in determining the differential pattern of cell response to antitumor agents.
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PMID:The role of topoisomerase II in drug resistance. 164 58

One of the phenotypes of multidrug resistance is characterized by a decrease in the intracellular concentration of drug in resistant cells as compared to sensitive cells. This is correlated with the presence in the membrane of resistant cells of a 150-180-kDa glycoprotein, P-glycoprotein, responsible for an active efflux of the drug. The fluorescence emission spectra from anthracycline-treated cells suspended in buffer have been used to compare the membrane transport of five anthracycline derivatives: adriamycin, daunorubucin, 4'-o-tetrahydropyranyladriamycin, carminomycin and aclacinomycin in drug-sensitive and drug-resistant K562 cells. The initial rate of uptake of these five drugs has been measured as a function of the extracellular pH, pHe. The data show that the uptake occurs through free permeation of the neutral form of the drug. For each drug an influx coefficient kpHe, characteristic of the drug and of the cell type has been defined and calculated: k+(7.2) = V+/[D]e.n where V+ and [D]e are the initial rate of uptake and the concentration of drug in the medium at pHe = 7.2 respectively and n is the number of cells. This coefficient is characteristic of a passive diffusion of the neutral form of the drug through the lipid bilayer. Efflux coefficients k-(7.2)- at pHi = 7.2 (the intracellular pH value) have also been calculated. In the case of sensitive cells, k+(7.2) and k-(7.2)- are equal. For resistant cells, the efflux coefficient is composed of two terms: (a) (k-)p corresponding to the passive diffusion of the neutral form of the drug and (k-)p = k+; (b) (k-)a corresponding to an active efflux mediated by the P-glycoprotein. Our data suggest that the anthracycline derivatives efflux actively in the neutral form.
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PMID:Comparison of the membrane transport of anthracycline derivatives in drug-resistant and drug-sensitive K562 cells. 167 20

One strategy to overcome multidrug resistance in neoplasia is to inhibit the gp170 glycoprotein (relative molecular mass, 170,000) that functions as a plasma membrane, energy-dependent, drug-efflux pump. The human colon cancer cell line HT-29, which grows as an ascitic tumor in athymic NCr-nu/nu nude mice, was made multidrug resistant by infection with an MDR1 (also known as PGY1) retrovirus. Referred to as HT-29mdr1, it was used to study reversal of drug resistance in vivo by the anti-P-glycoprotein monoclonal antibody MRK-16. Flow cytometry and radioimmunoassay demonstrated a marked increase in MRK-16 reactivity on HT-29mdr1 cells as compared with its reactivity on the parental, uninfected cell line (HT-29par). The 50% inhibitory concentrations (IC50) of vincristine on HT-29par and HT-29mdr1 cells were 2.5 and 15 ng/mL, respectively. The MRK-16 monoclonal antibody did not affect the vincristine sensitivity of the HT-29par cells. Pretreatment of HT-29mdr1 cells with 10 micrograms/mL MRK-16 in tissue culture partially restored the vincristine sensitivity (IC50 = 7 ng/mL). This modulation of vincristine sensitivity by MRK-16 was then tested in vivo. The median survival times of mice given intraperitoneal transplants of 5 x 10(6) HT-29par or HT-29mdr1 were 37 and 39 days, respectively. Treatment of mice with 1 mg/kg vincristine weekly for 3 weeks, beginning 10 days after tumor injection, resulted in a significant increase in the median survival time of the HT-29par tumor-bearing mice (68 days, P less than .0001), but it had no effect on the HT-29mdr1 tumor-bearing mice. However, treatment of mice bearing the HT-29mdr1 tumor with MRK-16 before vincristine therapy reversed the resistance to the drug (median survival time = 64 days, P less than .0001). The MRK-16 monoclonal antibody alone had no effect on the median survival time of mice given an injection of either HT-29par or HT-29mdr1 cells. These results suggest that strategies employing monoclonal antibody against gp170 may be clinically useful to reverse multidrug resistance.
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PMID:Reversal of drug resistance in a human colon cancer xenograft expressing MDR1 complementary DNA by in vivo administration of MRK-16 monoclonal antibody. 168 Nov 10

The development of resistance to chemotherapy is a major problem in the treatment of malignant tumors. Clinically, this is characterized by short periods of remission and failure to respond to subsequent therapy. Multidrug-resistance or pleiotropic resistance describes the simultaneous expression of cellular resistance to a vide range of structurally unrelated drugs (e.g. alkaloids, anthracyclines, antibiotics, etc.). The most frequently reported alteration of multidrug-resistant cells is the overexpression of a 170 kD glycoprotein (P--170 or P-glycoprotein) encoding by the MDR gene family. A great deal of evidence has suggested that the P-glycoprotein is, in fact, an energy-dependent drug efflux pump. Pharmacological overcome of MDR may indicate to circumvent clinically observed drug resistance.
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PMID:[Multidrug resistance of malignant tumors]. 168 63

The glycoproteins on the surface of HL-60/S wild-type, drug-sensitive human leukemia cells and HL-60/AR anthracycline-resistant cells which do not overexpress the P-glycoprotein, were characterized by labeling with [35S]-methionine, NaB[3H4], phosphorus 32, or sodium iodide I 125. HL-60/S and HL-60/AR cell lysates and membrane fractions tagged with [35S]-methionine or phosphorus 32 showed no significant differences in their protein patterns as analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and by autoradiography. HL-60/S cells labeled with NaB[3H4] yielded glycoproteins that were smeared predominantly in the molecular-weight range of 210,000 and 160,000 Da, with pI values ranging between pH 4 and pH 4.4. In contrast, NaB[3H4]-labeled HL-60/AR cells showed 7-8 discrete glycoproteins within a molecular-weight range of 170,000 and 140,000 Da, with pI values also ranging between pH 4 and pH 4.4. In addition, [3H]-glucosamine incorporation into HL-60/S and HL-60/AR cells revealed that the latter showed lower uptake of [3H]-glucosamine than did the former. Following treatment with tunicamycin, [3H]-glucosamine uptake in HL-60/S cells decreased, whereas that in HL-60/AR cells remained unchanged. Surface-membrane radioiodination of HL-60/S and HL-60/AR cells showed two distinct protein electrophoretic patterns, with differences being observed in both the high-(220-95 kDa) and low-molecular-weight ranges (21 kDa). Flow cytometric analysis of HL-60/S and HL-60/AR cells using myeloid and lymphoid antigen-specific antibodies demonstrated no antigenic differences between HL-60/S and HL-60/AR cells. HL-60/S cells incubated in the presence of tunicamycin, an inhibitor of N-linked glycosylation, or the protein kinase C agonist phorbol 12-myristate 13-acetate (PMA) developed a glycoprotein pattern similar to that observed in HL-60/AR cells. In addition, tunicamycin treatment of HL-60/S cells decreased daunorubicin (DNR) retention and altered its intracellular distribution as compared with that in HL-60/AR cells. These data indicate that HL-60/AR cells do not possess either de novo or amplified high-molecular-weight surface-membrane proteins; instead, existing proteins are hypoglycosylated. These results also show that HL-60/AR cells exhibit the multidrug-resistant phenotype in association with altered membrane glycoproteins of both high (220-95 kDa) and low molecular weight (21 kDa), but without overexpression of the P-glycoprotein. Furthermore, in HL-60/S cells, the multidrug-resistant phenotype is partially inducible by inhibition of N-linked glycosylation of cell-surface proteins.
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PMID:Membrane glycoprotein changes associated with anthracycline resistance in HL-60 cells. 171 35

Direct photoaffinity labeling of liver plasma membrane subfractions enriched in sinusoidal and canalicular membranes using [35S]adenosine 5'-O-(thiotriphosphate) ([35S]ATP gamma S) allows the identification of ATP-binding proteins in these domains. Comparative photoaffinity labeling with [35S]ATP gamma S and with the photolabile bile salt derivative (7,7-azo-3 alpha, 12 alpha-dihydroxy-5 beta-[3 beta-3H]-cholan-24-oyl-2'- aminoethanesulfonate followed by immunoprecipitation with a monoclonal antibody (Be 9.2) revealed the identity of the ATP-binding and the bile salt-binding canalicular membrane glycoprotein with the apparent Mr of 110,000 (gp110). The isoelectric point of this glycoprotein was 3.7. Transport of bile salt was studied in vesicles enriched in canalicular and sinusoidal liver membranes. Incubation of canalicular membrane vesicles with [3H] taurocholate in the presence of ATP resulted in an uptake of the bile salt into the vesicles which was sensitive to vanadate. ATP-dependent taurocholate transport was also observed in membrane vesicles from mutant rats deficient in the ATP-dependent transport of cysteinyl leukotrienes and related amphiphilic anions. Substrates of the P-glycoprotein (gp170), such as verapamil and doxorubicin, did not interfere with the ATP-dependent transport of taurocholate. Reconstitution of purified gp110 into liposomes resulted in an ATP-dependent uptake of [3H]taurocholate. These results demonstrate that gp110 functions as carrier in the ATP-dependent transport of bile salts from the hepatocyte into bile. This export carrier is distinct from hitherto characterized ATP-dependent transport systems.
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PMID:ATP-dependent transport of taurocholate across the hepatocyte canalicular membrane mediated by a 110-kDa glycoprotein binding ATP and bile salt. 191 7


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