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)

This report investigated whether the calmodulin inhibitor, trifluoperazine, can circumvent multi-drug resistance both in primary tissue cultures of human kidney and kidney carcinoma. For detection of inherent multi-drug resistance, the expression of P-glycoprotein was determined by immunofluorescence and immunocytochemistry using the monoclonal antibody C219. For detection of doxorubicin resistance and reversal of this resistance by trifluoperazine, the incorporation of nucleic acid precursor was measured after addition of doxorubicin and trifluoperazine, respectively. Both P-glycoprotein expressing resistant normal and malignant kidney tissue cultures could be modified by trifluoperazine. However, sensitive normal kidney and kidney carcinoma cultures were little affected by trifluoperazine. Thus, circumvention of primary resistance to doxorubicin is not limited to tumor cells. This might have important implications for the use of resistance modifiers in the clinical setting.
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PMID:Circumvention of multi-drug resistance in human kidney and kidney carcinoma in vitro. 167 84

The molecular characteristics of two human doxorubicin-resistant cell lines were examined specifically for MDR1 gene amplification by Southern analysis and for overexpression of its messenger RNA. The 285-fold doxorubicin-resistant colon adenocarcinoma subline, LoVo/DR5, was found to overexpress the mRNA for P-glycoprotein without the concomitant requirement of MDR1 gene amplification, suggesting that relatively high levels of P-glycoprotein mediated multiple drug resistance may occur by transcriptional activation of the gene. Despite a similar in vitro selection strategy and in contrast to LoVo/DR cells, the 220-fold doxorubicin-resistant fibrosarcoma subline, HT1080/DR4, did not overexpress P-glycoprotein mRNA nor was the MDR1 gene amplified. In-gel renaturation studies were performed to determine the nature of a putative HSR-bearing chromosome 7 found in HT1080/DR4 cells; however, at a level of sensitivity nearing 20 copies of an amplified DNA fragment per haploid genome, no amplified sequences could be detected. These results suggest that doxorubicin resistance is multifactorial and alternative mechanisms of multiple drug resistance remain to be determined. LoVo/DR5 cells should prove to be a useful model for investigating transcriptional activation of the MDR1 gene; HT1080/DR4 cells should be an excellent model for the study of non-P-glycoprotein mediated multiple drug resistance.
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PMID:Molecular analysis of two human doxorubicin-resistant cell lines: evidence for differing multidrug resistance mechanisms. 167 31

Cross-resistance to anticancer drugs, termed multidrug resistance (mdr), has been functionally associated with the expression of a plasma membrane energy-dependent efflux pump, termed P-glycoprotein, the product of the mdr1 gene. When MCF-7 breast carcinoma cells were transfected with the human mdr1 gene (BC-19 cells), they expressed levels of P-glycoprotein equivalent to those of cells selected for resistance to doxorubicin (MCF-7/ADR) but exhibited 10- to 50-fold less resistance to doxorubicin and vinblastine. We have now demonstrated that when BC-19 cells were stably transfected with protein kinase C alpha (PKC alpha), resistance to doxorubicin and vinblastine was increased; wild-type MCF-7 cells transfected with PKC alpha did not exhibit any change in drug resistance. Increased resistance in PKC alpha-transfected BC-19 cells was associated with enhanced PKC activity and phosphorylation of P-glycoprotein and decreased drug accumulation. The PKC activator, phorbol dibutyrate, further increased resistance to doxorubicin and stimulated P-glycoprotein phosphorylation. These results demonstrate that transfection of P-glycoprotein-expressing cells with PKC resulted in increased mdr and that PKC may have served as an important modulator of this process.
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PMID:Transfection with protein kinase C alpha confers increased multidrug resistance to MCF-7 cells expressing P-glycoprotein. 167 75

Specific protein domains and amino acids responsible for the apparent capacity of P-glycoprotein (mdr) to recognize and transport a large group of structurally unrelated drugs have not been identified. We have introduced a single Ser----Phe substitution within the predicted TM11 domain of mdr1 (position 941) and mdr3 (position 939) and analyzed the effect of these substitutions on the drug-resistance profiles of these two proteins. Mutations at this residue drastically altered the overall degree of drug resistance conveyed by mdr1 and mdr3. The modulating effect of this mutation on mdr1 and mdr3 varied for the drugs tested: it was very strong for colchicine and adriamycin and moderate for vinblastine. For mdr1, the Ser941----Phe941 substitution produced a unique mutant protein that retained the capacity to confer vinblastine resistance but lost the ability to confer adriamycin and colchicine resistance. These results strongly suggest that the predicted TM11 domain of proteins encoded by mdr and mdr-like genes plays an important role in the recognition and transport of their specific substrates.
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PMID:A single amino acid substitution strongly modulates the activity and substrate specificity of the mouse mdr1 and mdr3 drug efflux pumps. 167 20

Multidrug resistance (MDR) in mammalian cells is associated with the expression of the MDR1 gene encoding P-glycoprotein (P-gp), an and active efflux pump for various lipophilic compounds. MDR transfectants can be isolated after MDR1 gene transfer and selection with cytotoxic drugs; low levels of drug resistance have also been observed in unselected NIH 3T3 mouse cells after retrovirus-mediated transfer of mouse mdr1 cDNA. MDR cell lines possess multiple phenotypic changes, suggesting that P-gp function could be complemented by some additional mechanisms associated with cytotoxic selection. To determine whether cytotoxic selection contributes to the MDR phenotype of MDR1-expressing cells, NIH 3T3 cells infected with a recombinant retrovirus carrying the human MDR1 gene were selected by two different procedures: (i) noncytotoxic selection for increased P-gp expression on the cell surface by multiple rounds of immunofluorescence labeling and flow sorting or (ii) one or more steps of selection with a cytotoxic drug. The levels of MDR in both types of infectants showed an excellent correlation with the P-gp density in the plasma membrane, expressed as immunoreactivity with a P-gp-specific antibody normalized by reactivity with an antibody against an unrelated antigen. Cytotoxic selection conferred no additional increase in resistance relative to P-gp density. These results indicate that P-gp density in the plasma membrane may be sufficient to determine the level of MDR.
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PMID:Multidrug resistance after retroviral transfer of the human MDR1 gene correlates with P-glycoprotein density in the plasma membrane and is not affected by cytotoxic selection. 167 23

The multidrug transporting cell membrane molecule P-glycoprotein can be spontaneously expressed in human glioma cells. Transcripts of mdr genes were detected in glial tumor cells by polymerase chain reaction and Northern blotting, expression of P-glycoprotein was analyzed by immunocytochemistry and functional activity by cytofluorometry of fluorescent probe transport. In vitro treatment of glioma cells with vincristine induced coordinate over-expression of both mdr1 and mdr3 genes associated with very high P-glycoprotein-mediated multidrug transport, resistant to the inhibitory activity of chemosensitizers like verapamil. The physiological modulators of multidrug transport are as yet unknown. We therefore initiated a screening program to analyze the effects of cytokines on multidrug transport. We observed, that transforming growth factors (TGF)-beta 1, -beta 2, and -beta 1.2-but not the related bone morphogenetic protein (BMP) 2--inhibited multidrug transport. Interestingly, BMP 2 antagonized the TGF-beta induced inhibition of multidrug transport.
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PMID:Spontaneous multidrug transport in human glioma cells is regulated by transforming growth factors type beta. 167 77

Development of resistance to cytotoxic agents is a common problem in the treatment of acute leukemia. In cell lines having multidrug resistance (MDR) phenotype, a decrease in the intracellular accumulation of drugs has been closely related to the overexpression of P-glycoprotein/mdr1 genes. We analyzed the relationship between the cytotoxicity of adriamycin (ADR) in vitro, intracellular accumulation of ADR, and the expression of P-glycoprotein on fresh leukemic cells from 19 patients at their initial presentation and from 9 relapsed patients. Pretreatment patients showed significantly higher ratio of complete remission than relapsed patients, and mean value of IC50 for adriamycin in initial presentation was higher than at relapse. But we found no significant relationship between in vitro cytotoxicity and drug transport. In addition, only 2 of the 5 relapsed patients examined by monoclonal antibody C219 expressed the P-glycoprotein. These results suggest that the acquisition of clinical drug resistance may involve various mechanisms other than the reduction of drug accumulation with P-glycoprotein expression.
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PMID:Absence of correlation between cytotoxicity and drug transport by P-glycoprotein in clinical leukemic cells. 167 20

P-glycoprotein expression was demonstrated in two human intestinal adenocarcinoma cell-lines (HCT-8, ileocaecal and T84, colonic) by immunoprecipitation of a 170-180 kDa protein with monoclonal antibody JSB-1. Both HCT-8 and T84 formed functional epithelial cell layers of high transepithelial electrical resistance (greater than 700 omega.cm2) when grown on permeable matrices. These epithelial layers demonstrated vectorial secretion (net vinblastine fluxes in the basal-to-apical direction of 0.135 and 0.452 pmol h-1 cm-2 in HCT-8 and T84 cell layers, respectively, from bathing solutions containing 10 nM vinblastine). These vectorial vinblastine secretions were sensitive to inhibition by verapamil. Passive transepithelial vinblastine permeation was limited by the presence of intercellular (tight) junctions, as demonstrated by the high transepithelial electrical resistance, and verapamil increased this passive vinblastine permeation concomitant with a reduction in the electrical resistance. Cellular vinblastine loading was significantly greater from the basal side, and this was also susceptible to inhibition by basal verapamil. The demonstration of vectorial transport of vinblastine in human intestinal colonic adenocarcinoma cell layers is direct evidence in favour of the hypothesis that the function of mdr1 in epithelial from the gastrointestinal tract is to promote detoxification by a process of epithelial secretion. This study also highlights that cellular vinblastine accumulation depends not only upon P-glycoprotein function, but also upon differential apparent membrane permeabilities and the presence of intercellular (tight) junctions that may restrict drug permeation and cellular accumulation to apical or basal membrane domains.
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PMID:Epithelial secretion of vinblastine by human intestinal adenocarcinoma cell (HCT-8 and T84) layers expressing P-glycoprotein. 168 Mar 66

Ninety-four human non-small cell lung carcinomas (NSCLC) of previously untreated patients were analysed for the presence of P-glycoprotein (P-170) and glutathione S-transferase-pi (GST-pi) by means of immunohistochemistry. The expression of P-170 and GST-pi was compared with the results of doxorubicin resistance of the tumours in vitro and the smoking habits of the patients. A significant relationship between smoking habits of the patients and resistance of NSCLC was found (P = 0.007). Of the 72 tumours of smokers 57 (= 79%) were resistant, whereas of the 22 tumours of non-smokers only 11 (= 50%) showed resistance. Identical results were obtained when the analysis was restricted to patients with epidermoid lung carcinomas (P = 0.004). In contrast to these data, there exists no relationship between resistance and smoking for adenocarcinomas of the lung. Forty-two (= 58%) out of the 72 NSCLC of smokers expressed P-170, whereas out of 22 tumours of non-smokers only two tumours (= 9%) showed P-170 expression (P less than 0.0001). Similar results were obtained with epidermoid carcinomas (P = 0.004) and adenocarcinomas (P = 0.027). Fifty (= 69%) of 72 NSCLC of smokers revealed expression of GST-pi, whereas only nine (= 41%) of 22 tumours of non-smokers showed GST-pi expression (P = 0.015). Significant correlations also exist between resistance in vitro and expression of P-170 (P less than 0.0001) or expression of GST-pi (P less than 0.0001). Furthermore, a significant relationship between both proteins could be demonstrated (P less than 0.0001).
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PMID:Overexpression of P-glycoprotein and glutathione S-transferase-pi in resistant non-small cell lung carcinomas of smokers. 168 Mar 67

We examined the ability of dipyridamole (DPM) to act synergistically with vinblastine (VBL) in HT1080 fibrosarcoma cells and a drug-resistant variant, HT1080/DR4, which lacks mdr1 expression, in order to determine whether DPM requires P-glycoprotein to modulate drug sensitivity. Median effect analysis of clonogenic assay was used to produce the combination index (CI50, values less than 1 indicate synergy). DPM was mildly synergistic with VBL producing a CI50 of 0.83 +/- 0.13 for HT1080 cells and 0.80 +/- 0.16 for HT1080/DR4 cells. HT1080 and HT1080/DR4 cells accumulated 6.7 +/- 0.7 and 5.6 +/- 0.9 pmol 3H-VBL mg cells-1 at steady state (Css) and 20 microM DPM elevated the Css by 1.8 and 2.9-fold, respectively. In comparison, the CI50 was 1.1 +/- 0.2 in parental KB-3-1 cells and 0.1 +/- 0.1 in mdr1-expressing KB-GRC1 cells. The KB-3-1 and KB-GRC1 cells had a Css of 3.8 +/- 0.8 and 0.7 +/- 0.2 pmol 3H-VBL mg cells-1, respectively, and DPM elevated the Css by 9.2-fold in KB-GRC1 cells. These studies demonstrate that DPM can produce synergy independently of mdr1 expression but that much greater levels of synergy are achievable in mdr1-expressing tumour cells.
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PMID:Modulation of vinblastine sensitivity by dipyridamole in multidrug resistant fibrosarcoma cells lacking mdr1 expression. 168 Mar 68


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