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)

We have previously shown that phenothiazines sensitize multidrug resistant (MDR) cells to chemotherapeutic drugs in a manner related to specific structural features, and have identified structurally related thioxanthenes with increased anti-MDR activity. We have now studied the structure-activity relationships of 16 thioxanthenes in the human breast cancer line MCF-7 AdrR. trans-Thioxanthene stereoisomers were 2- to 7-fold more potent than cis-thioxanthenes for antagonizing MDR. The most potent thioxanthenes possessed a halogenated tricyclic ring connected by a 3-carbon alkyl bridge to a piperazinyl or piperadinyl side group. The chemosensitizing effects of the lead compound, trans-flupenthixol, its stereoisomer cis-flupenthixol, its phenothiazine homologue fluphenazine, and the calcium channel blocker verapamil, were further studied in a series of sensitive and MDR cell lines. trans-Flupenthixol caused a greater reversal of cellular resistance to doxorubicin, vinblastine, vincristine, and colchicine in MCF-7 AdrR, KB-V1, and P388/DOX MDR cells than the other chemosensitizers. In particular, trans-flupenthixol was 2- to 3-fold more potent for reversing MDR than equimolar concentrations of verapamil. Furthermore, trans-flupenthixol fully reversed resistance to doxorubicin, vincristine, and colchicine in MDR MCF-7 and NIH 3T3 cells transfected with the mdr1 gene. None of these agents altered MDR in a non-P-glycoprotein expressing MCF-7 cell line selected with mitoxantrone, nor in any of the parental cell lines. The stereoselective antagonism of the flupenthixol isomers on several putative cellular targets was studied to explore the mechanism of their chemosensitizing activity. cis- and trans-flupenthixol were equally active inhibitors of protein kinase C and calmodulin. Both cis- and trans-flupenthixol were also potent inhibitors of [3H]azidopine binding to P-glycoprotein. The apparent lack of clinical toxicity of trans-flupenthixol makes it an attractive drug for possible use in the modulation of tumor resistance in vivo if appropriate tissue concentrations can be achieved.
...
PMID:Cellular and biochemical characterization of thioxanthenes for reversal of multidrug resistance in human and murine cell lines. 196 58

Development of multidrug resistance due to overexpression of P-glycoprotein (Pgp), a cell membrane drug efflux pump, occurs commonly during in vitro selections with adriamycin (Adr). Pgp-mediated drug resistance can be overcome by the calcium channel blocker verapamil (Vp), which acts as a competitive inhibitor of drug binding and efflux. In order to identify other mechanisms of Adr resistance, we isolated an Adr-resistant subline by selecting the human breast cancer cell line MCF-7 with incremental increases of Adr in the presence of 10 microgram/ml verapamil. The resultant MCF-7/AdrVp subline is 900-fold resistant to Adr, does not overexpress Pgp, and does not exhibit a decrease in Adr accumulation. It exhibits a unique cross-resistance pattern: high cross-resistance to the potent Adr analogue 3'-deamino-3'-(3-cyano-4-morpholinyl)doxorubicin, lower cross-resistance to the alkylating agent melphalan, and a sensitivity similar to the parental cell line to vinblastine. The levels of glutathione and glutathione S-transferase are similar in the parental line and the Adr-resistant subline. Topoisomerase II-DNA complexes measured by the potassium-sodium dodecyl sulfate precipitation method shows a 2-3 fold decrease in the resistant subline. The MCF-7/AdrVp cells overexpress a novel membrane protein with an apparent molecular mass of 95 kDa. Polyclonal antibodies raised against the P-95 protein demonstrate a correaltion between the level of expression and Adr resistance. Removal of Adr but not verapamil from the selection media results in a decline in P-95 protein levels that parallels a restoration of sensitivity to Adr. Immunohistochemistry demonstrates localization of the P-95 protein on the cell surface. The demonstration of high levels of the protein in clinical samples obtained from patients refractory to Adr suggests that this protein may play a role in clinical drug resistance.
...
PMID:Characterization of adriamycin-resistant human breast cancer cells which display overexpression of a novel resistance-related membrane protein. 197 54

To characterize the membrane changes related to adriamycin (ADM) resistance in tumor cells, we have developed monoclonal antibodies against an ADM-resistant subline of human myelogenous leukemia K562 (K562/ADM), and reported the overexpression of P-glycoprotein and 85-kDa protein as determined by the antibodies. In the present study, we have established a monoclonal antibody, MRK18, with higher reactivity to K562/ADM than to K562. MRK18 also showed higher reactivity to other human ADM-resistant lines, 2780AD and Hattori/ADM, than the corresponding parental lines. MRK18 also reacted to human breast cancer MCF-7 and human T-lymphoma CCRF-CEM which have never been exposed to anticancer agents in culture. MRK18 recognized a 300-kDa membrane protein of K562/ADM and MCF-7 and inhibited the growth of these cell lines in culture. These results indicate an induction of the 300-kDa protein during the development of ADM resistance.
...
PMID:Detection of 300-kilodalton membrane protein in adriamycin-resistant human tumor cells by a monoclonal antibody MRK18. 197 22

The interaction of etoposide (VP-16), Vinca alkaloids, and verapamil with the P-glycoprotein (P-gp) was studied in human breast (MCF-7) and Chinese hamster lung (DC3F) cell lines and the corresponding multidrug-resistant MCF-7/ADR and DC3F/ADX tumor cell lines, selected for resistance to Adriamycin and actinomycin D, respectively, and overexpressing P-gp. Verapamil (10 microM) markedly reversed resistance to vincristine (11-fold in DC3F/ADX and 125-fold in MCF-7/ADR; 1-hr exposure), but it had a very modest effect on resistance to VP-16 (3- to 4-fold; 1-hr exposure). Resistant cells accumulated 2- to 4-fold less VP-16 and vincristine than the parental cell lines. Verapamil (10 microM) significantly increased accumulation and retention of vincristine, but not of VP-16, in resistant cell lines. Photoaffinity labeling of resistant cell lines with radioactive analogs of verapamil [N(p-azido-3-125I-salicyl)-N'-beta-aminoethylverapamil (NASVP)] and vinblastine[N-(p-azido-3-125I-salicyl)-N'-beta-aminoethylvindesine (NASV)] showed distinctly labeled P-gp bands in both resistant cell lines, compared with wild-type cells. Excess nonradioactive vinblastine or verapamil effectively competed with the P-gp photolabeling by either NASVP or NASV, with IC50 levels of 0.6 and 10 microM, respectively. In contrast, nonradioactive VP-16 was 100- to 500-fold less potent than vinblastine in competing with P-gp photolabeling, suggesting that VP-16 has significantly lower affinity for P-gp than Vinca alkaloids have. Taken together, our data indicate that P-gp glycoprotein by itself may not be important in the transport/efflux of VP-16 and, thus, in the mechanism of resistance to VP-16 in these cells.
...
PMID:P-glycoprotein-independent mechanism of resistance to VP-16 in multidrug-resistant tumor cell lines: pharmacokinetic and photoaffinity labeling studies. 197 71

The nucleotide sequence of the mdr1 gene encoding a putative drug efflux pump (P-glycoprotein) is homologous to a class of bacterial membrane-associated transport proteins. These bacterial proteins are part of a multicomponent system that includes soluble periplasmic proteins that bind substrates, channeling them through the membrane in an energy-dependent manner. We have investigated the possibility that a similar multicomponent transport system exists in a multidrug-resistant human MCF-7 breast cancer cell line that was initially selected for resistance to doxorubicin (AdrR MCF-7). AdrR MCF-7 cells overexpress both the mdr1 gene and the pi class isozyme of glutathione S-transferase (GST-pi) (EC 2.5.1.18). The latter is one of several isozymes known to have a ligand-binding function in addition to drug-metabolizing capabilities. Although we have recently shown that transfection of a functional GST-pi expression vector is insufficient to confer resistance to doxorubicin in cells that lack P-glycoprotein expression [Mol. Pharmacol. 36:22-28 (1989)], we examined the possibility that GST-pi interacts with P-glycoprotein to alter multidrug resistance. To do this, we have cloned cDNAs encoding these proteins from AdrR MCF-7 cells, constructed expression vectors containing these two genes, and transfected these vectors sequentially into drug-sensitive MCF-7 cells. The human mdr1 cDNA isolated from AdrR MCF-7 is a variant gene whose sequence differs from that isolated previously from vinblastine-resistant KB cells [Cell 53:519-529 (1989)], resulting in an amino acid substitution of alanine to serine at position 893 (mdr1/893ala). Transfection of eukaryotic expression vectors containing the mdr1 gene isolated from AdrR MCF-7 cells produced a multidrug-resistant phenotype in recipient cells, with a cross-resistance pattern similar to that in the AdrR MCF-7 cells. To determine whether GST-pi expression could augment resistance provided by mdr1, two clones transfected with mdr1, one with high levels (153% of mdr1 RNA in AdR MCF-7 cells) and one with low levels (10% of mdr1 RNA in AdrR MCF-7 cells), were subsequently cotransfected with a GST-pi expression vector and pSVNeo and selected for resistance to G418. Six of these clones contained levels of GST-pi that were 8- to 18-fold greater than GST levels found in mdr1-expressing clones transfected with nonspecific DNA. We found no difference in the degree of resistance to doxorubicin, actinomycin D, and vinblastine between the clones expressing mdr1 only and the clones expressing both mdr1 and GST-pi.(ABSTRACT TRUNCATED AT 400 WORDS)
...
PMID:Multidrug resistance in cells transfected with human genes encoding a variant P-glycoprotein and glutathione S-transferase-pi. 197 72

Resistance of tumor cells to chemotherapeutic drugs may be due to several mechanisms within a single cell line. Resistance to doxorubicin in the human multidrug resistant breast cancer cell line, MCF-7 AdrR, has been attributed to increased glutathione (GSH) S-transferase and GSH peroxidase activity, as well as to increased expression of the mdr1 gene product, P-glycoprotein. We studied the potentiation of doxorubicin activity in these cells by buthionine sulfoximine (BSO), a specific inhibitor of gamma-glutamylcysteine synthetase, and by verapamil and trans-flupenthixol, agents which interact with P-glycoprotein. Treatment with BSO enhanced the effect of doxorubicin by 1.5-fold, while verapamil or transflupenthixol caused a greater reversal of drug resistance. The combination of BSO with trans-flupenthixol produced no further potentiation of doxorubicin activity. However, the combination of BSO with verapamil and doxorubicin caused up to a 10-fold increment in antiproliferative effect. To explore the mechanism by which BSO interacted with this drug combination, we determined whether or not BSO might potentiate the effects of verapamil. These studies demonstrated that the effects of BSO were predominantly due to an increase in verapamil toxicity rather than to doxorubicin toxicity. In addition, when mice received concentrations of BSO in their drinking water sufficient to deplete GSH and were treated with verapamil, the calcium channel blocker was lethal to 9 of 12 mice receiving BSO compared to 1 of 10 control animals receiving verapamil alone. These studies demonstrate that BSO does not markedly increase the pharmacological effect of doxorubicin against MCF-7 AdrR cells and suggest that alterations in GSH and related enzymes are not a major factor in drug resistance in this cell line. Furthermore, BSO can increase the toxicity of verapamil, a finding which may have important implications for clinical trials.
...
PMID:Effect of buthionine sulfoximine on toxicity of verapamil and doxorubicin to multidrug resistant cells and to mice. 198 8

In order to identify changes in 31P nuclear magnetic resonance (NMR) spectra associated with multiple drug resistance (MDR), a number of wild type and drug-resistant cancer cell lines were studied. The resistant cells included cells selected with various drugs, mainly Adriamycin, as well as cells transfected with the human multidrug resistance gene (MDR1 gene), which encodes P-glycoprotein. In most cases, 31P NMR spectra were significantly different from those of parental, drug-sensitive lines. The spectra of resistant cells generally indicated increased levels of ATP and phosphocreatine in the cytoplasm. These changes are compatible with the increased glucose utilization rate previously described for resistant cells. Major changes were also observed in the levels of glycerophosphocholine and glycerophosphoethanolamine. Changes in cellular metabolism reflected by 31P NMR spectra depend on the drug used to select the cells for MDR. The direction of these changes was not consistent for all cell lines studied and could not be directly attributed to expression of P-glycoprotein, suggesting that the changes may be related to alterations in metabolism and membrane function associated with other mechanisms of MDR. The results demonstrate the suitability of 31P NMR for studies of biochemical changes associated with MDR. The toxicity of 2-deoxyglucose, a glucose antimetabolite, was investigated in addition to the NMR studies and was found to be consistently higher in multidrug-resistant cells than in the parental drug-sensitive lines. For MCF-7 breast cancer cells, where several sublines with different levels of resistance were available, the toxicity was highest for the most resistant lines.
...
PMID:The multidrug resistance phenotype: 31P nuclear magnetic resonance characterization and 2-deoxyglucose toxicity. 199 55

An MCF-7 human breast cancer cell line was selected which was 200-fold more resistant to Adriamycin than the wild type cell line. This Adriamycin-resistant (AdrR) cell line exhibited a multidrug-resistant phenotype and was cross-resistant to a wide range of antineoplastic agents including Vinca alkaloids, anthracyclines, and epipodophyllotoxins. Cytogenetic analysis of the AdrR cell line showed the presence of homogeneously staining regions on several chromosomes which were not present in the parental cell line. Using the technique of in-gel renaturation, DNA sequences which were amplified 50- to 100-fold in the AdrR cell line and which covered a total of over 140 kilobases were isolated. In addition, AdrR cells were found to contain amplified and overexpressed sequences which were homologous to hamster P-glycoprotein gene sequences. A hamster cDNA P-glycoprotein gene probe was used to screen a lambda gt10 cDNA library made from human AdrR cell line mRNA and human cDNA sequences homologous to the P-glycoprotein gene were isolated. Hybridization studies with the cloned human cDNA (pADR1) showed that the AdrR MCF-7 cell line contained a 60-fold amplification of this DNA sequence and that polyadenylated mRNA from the AdrR cell line contained a 4.8-kilobase transcript which was overexpressed 45-fold. There was a direct correlation between DNA and RNA copy number of this sequence and level of resistance among several MCF-7 Adriamycin-resistant cell lines. In situ hybridization studies demonstrated that the human P-glycoprotein gene sequence was found on chromosome 7q21.1 in normal human lymphocytes and that amplified DNA sequences isolated from the AdrR MCF-7 cells by the in-gel hybridization technique were linked to the human P-glycoprotein sequences in the homogeneously staining regions in the AdrR cells.
...
PMID:Isolation of amplified and overexpressed DNA sequences from adriamycin-resistant human breast cancer cells. 244 61

Multidrug resistance (MDR) in an MCF-7 human breast cancer cell line (MCF7/Adr) is associated with decreased drug accumulation and overexpression of P-glycoprotein as well as alterations in the levels of specific drug-metabolizing enzymes, including decreased activity of the phase I drug-metabolizing enzyme aryl hydrocarbon hydroxylase (AHH) and increased expression of the anionic form of the phase II drug-metabolizing enzyme glutathione S-transferase. Since the development of MDR in this MCF-7 cell line is also associated with a loss of estrogen receptors (ER), we have examined the expression of cytochrome P450IA 1, the gene encoding AHH activity, in other breast cancer cell lines not selected for drug resistance but expressing various levels of ER. These studies show that a relationship exists between 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-inducible AHH activity and the ER content in a series of breast cancer cell lines. In these cell lines expression of AHH activity is regulated, at least in part, at the level of P450IA 1 RNA. While TCDD-specific binding proteins (Ah receptors) were found in each of the breast cancer cell lines, there was no apparent relation between the level of nuclear TCDD-binding proteins and the level of TCDD-inducible P450IA 1 expression. Previous studies from our laboratory have described an inverse relationship between levels of the anionic form of glutathione S-transferase and ER in breast cancer.(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:Relation between cytochrome P450IA1 expression and estrogen receptor content of human breast cancer cells. 246 54

The development of multidrug resistance in MCF-7 human breast cancer cells and the acquisition of broad resistance to xenobiotics in rat hyperplastic nodules are both associated with increased P-glycoprotein (mdr) gene expression as well as changes in activities of intracellular detoxication enzymes; among these changes is a significant increase in the activity of the anionic isozyme of glutathione-S-transferase (GST). We have isolated a cDNA encoding the human anionic glutathione-S-transferase, GST pi-1, from a cDNA library constructed from multidrug-resistant MCF-7 cells. The deduced amino acid sequence of GST pi-1 shows that while the human anionic GST displays 85% nucleotide and amino acid sequence homology to the rat anionic isozyme, it is markedly less related to human basic GST isozymes. We have examined the expression of GST pi and P-glycoprotein in 170 specimens of human tissues and tumors. P-Glycoprotein RNA expression was positive in eight of 23 lymphomas and two of 12 colon tumors; however, many other normal and malignant tissues, including lung, bladder, and breast tumors, had low or undetectable levels of P-glycoprotein RNA expression. In contrast, GST pi was readily detected in a wide variety of normal and malignant tissues. The level of GST pi mRNA expression in normal tissues was heterogeneous, with lowest levels found in liver and the highest levels found in lung, esophagus, and placenta. GST pi was also variably expressed in human tumors, with the lowest relative levels occurring in lymphoma and breast cancer and the highest levels found in lung cancer and head and neck tumors. In addition, comparison of paired specimens from the same patient indicated that GST pi expression was increased in many tumors relative to matched normal tissue.
...
PMID:Expression of anionic glutathione-S-transferase and P-glycoprotein genes in human tissues and tumors. 246 54


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---