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)

The effect of osmotic stress on Cl- permeability in human squamous lung carcinoma epithelial (S1) cells was investigated using a macroscopic 125I efflux assay. Hypotonic challenge of monolayers led to a significant (P < 0.01) dose-related increase in efflux from pre-loaded cells, returning to pre-activation rates within 10 min. A similar magnitude of response could be produced by challenge with an isotonic low chloride-containing solution. Neither 100 mM dideoxy-forskolin nor 100 mM verapamil inhibited the increase in Cl- secretion after hypotonic challenge, whereas 100 mM DIDS inhibited volume-activated Cl- secretion by 55%. Both Northern and Western blot analysis confirmed the absence of MDR1 mRNA and P-glycoprotein in the S1 cells. We conclude that these cells have a volume-regulated Cl- secretory pathway that is independent of the ABC transporter, P-glycoprotein.
Biochim Biophys Acta 1994 Dec 30
PMID:Lack of inhibition by dideoxy-forskolin and verapamil of DIDS-sensitive volume-activated Cl- secretion in human squamous lung carcinoma epithelial cells. 780 88

P-glycoprotein (P-gly) is the transmembrane efflux pump responsible for multidrug resistance in tumor cells. Functional P-gly activity can be conveniently assessed microfluorometrically using the fluorescent dye rhodamine 123 (Rh123), which is an artificial substrate for the P-gly transporter. Here we assess P-gly activity in subsets of mouse peripheral T lymphocytes using the Rh123 efflux assay. Our data indicate that virtually all CD8+ cells extrude Rh123 efficiently, whereas only a subset of CD4+ cells exhibit P-gly activity. Correlation of P-gly activity in CD4+ cells with the expression of a panel of surface markers revealed that cells bearing an "activated/memory" phenotype (CD45RB-, CD44hi, CD62L-, CD25+, CD69+) were exclusively found in the fraction that can extrude Rh123. In contrast "naive" phenotype CD4+ cells (CD45RB+, CD44lo, CD62L+, CD25-, CD69-) could be further subdivided into two major subsets based on P-gly activity. In functional studies of sorted cell populations the Rh123-extruding subset of "naive" CD4+ cells proliferated more strongly and secreted higher levels of interleukin (IL)-2 than its Rh123-retaining counterpart when activated by a variety of polyclonal stimuli. Furthermore, this subset produced detectable levels of interferon (IFN)-gamma upon stimulation but no IL-4 or IL-10. As expected, the Rh123-retaining "naive" subset produced only IL-2 after stimulation, whereas the "memory" subset produced IFN-gamma, IL-4 and IL-10 in addition to low levels of IL-2. Collectively, our data indicate that P-gly activity is a novel parameter that can be used to distinguish a subset of "preactivated" CD4+ cells that would be considered as naive on the basis of their surface phenotype.
Eur J Immunol 1994 Dec
PMID:Heterogeneity in P-glycoprotein (multidrug resistance) activity among murine peripheral T cells: correlation with surface phenotype and effector function. 780 24

Hydroxyrubin (OH-Dox), a neutral doxorubicin derivative that is only slightly cross-resistant to doxorubicin (Dox), can be actively pumped out of resistant K562 cells by P-glycoprotein (P-gp). This efflux is saturable and can be inhibited by verapamil. The Michaelis constant is equal to 2 +/- 0.5 microM. However, the efficiency of P-gp in pumping out the drugs is 2.5 times less for OH-Dox than for Dox. This shows that in order to be pumped out by P-gp a molecule does not necessarily have to have a basic center. The mean influx coefficient for the drug is 5 times higher for OH-Dox than for Dox. In conclusion, the degree of resistance of analogs is related not only to their ability to be recognized and transported by P-gp but also, and probably essentially, to their kinetics of uptake. Both parameters have to be taken into account in the rational design of new compounds capable of overcoming multidrug resistance.
FEBS Lett 1994 Dec 19
PMID:P-glycoprotein-mediated efflux of hydroxyrubicin, a neutral anthracycline derivative, in resistant K562 cells. 780 56

P-glycoprotein is though to mediate the energy-dependent efflux of many structurally and functionally unrelated lipophilic compounds. Presently, the molecular mechanism underlying the binding and efflux of drugs by P-glycoprotein is not well understood. However, it has been suggested that two planar benzene ring structures and a cationic charge are commonly found in many drugs that interact with P-glycoprotein. The benzimidazoles (BZs) are potent anti-tumour, anti-fungal and anti-parasitic agents, whose mode of action is thought to result from their inhibition of microtubule functions. Although other classes of microtubule inhibitors, such as colchicine and vinblastine, have been studied extensively with respect to their interaction and efflux by P-glycoprotein, the BZ group of drugs has not been characterized. In this study, we have characterized the interaction of BZ with multidrug-resistant cells and found that resistant cells accumulated substantially less BZ compared with drug-sensitive cells. Furthermore, BZ was more toxic to sensitive than to drug-resistant cells, suggesting that BZ is likely to be a substrate for the P-glycoprotein drug efflux pump. In addition, we used a photoactive analogue of BZ ([125I]ASA-BZ) to demonstrate a direct binding between BZ and P-glycoprotein. Results showing that a molar excess of vinblastine, unmodified BZ, verapamil and rhodamine 123, but not colchicine, inhibited the photoaffinity labelling of P-glycoprotein by [125I]ASA-BZ confirmed the binding specificity of BZ to P-glycoprotein. Protease digestion of [125I]ASA-BZ photoaffinity labelled P-glycoprotein yielded two peptides that were similar to those obtained with other P-glycoprotein-associated drugs, e.g. azidopine and iodoaryl azidoprazosin. Taken together, these results demonstrate a direct and specific interaction between P-glycoprotein and BZ in a manner that is probably similar to other previously characterized P-glycoprotein-associated drugs.
Biochem Pharmacol 1994 Dec 16
PMID:Benzimidazoles, potent anti-mitotic drugs: substrates for the P-glycoprotein transporter in multidrug-resistant cells. 781 3

The intracellular distribution of the anthracyclinic antibiotic adriamycin in living cultured cells has been investigated by confocal microscopy. In human melanoma cells (M14), adriamycin was localized inside the nuclei. When adriamycin-treated M14 cells were allowed to recover in drug-free medium, a complete efflux of the drug from the nucleus was revealed. In recovered cells, a weakly fluorescent signal was observed in the perinuclear region. When M14 cells were recovered in a medium containing colcemid, a microtubule depolymerizing agent, the drug transport from the nucleus to the cell periphery appeared to be inhibited, suggesting that the microtubule network is strongly involved in drug transport mechanisms. In multidrug-resistant (MDR) cells the intracellular location of adriamycin was shown to be noticeably different from that of the parental wild-type cells. In particular, in resistant human breast carcinoma cells (MCF-7), adriamycin appeared to be exclusively located within the cytoplasm whereas the nuclei were shown to be completely negative. When adriamycin treatment was performed in association with MDR revertants, such as Lonidamine (inhibitor of the energy metabolism) or verapamil (inhibitor of the P-glycoprotein efflux pump), a marked enhancement of the cytoplasmic signal was observed in resistant cells. Under these conditions, adriamycin appeared concentrated in the perinuclear region, but the nuclei were still negative. Confocal microscopy proved to be a very useful method for the study of the intracellular transport of fluorescent substances, such as anthracyclinic antibiotics, and for the investigation of the multidrug resistance phenomenon in tumour cells.
J Microsc 1994 Dec
PMID:Intracellular localization of the antitumour drug adriamycin in living cultured cells: a confocal microscopy study. 786 63

Determination of intracellular calcium levels in Chinese hamster ovary (CHO) cells using the fluorescent calcium probe indo-1AM was hindered by the low level of accumulation of indo-1 in these cells. CHO cells are known to express basal levels of the multidrug resistance efflux pump P-glycoprotein (P-gp). Rhodamine-123, which is a known substrate of P-gp, was used to confirm the presence of P-gp in CHO cells. Verapamil and cyclosporin (CsA), both inhibitors of P-gp, enhanced accumulation of indo-1 in these cells and therefore allowed for improved intracellular calcium measurements. P-gp overexpressing colchicine-resistant CHO cells (CHRC5) also displayed enhanced indo-1AM loading with P-gp inhibitors. Nondetectable levels of P-gp activity were found in wild-type CEM-CCRF cells (human T lymphoblasts), and these cells did not show any difference in indo-1AM loading in the presence or absence of P-gp inhibitors. Loading of a second calcium fluorescent probe fluo-3AM was improved in CHO cells by P-gp inhibition, whereas the structurally related pH probe BCECF-AM was minimally affected. Because low levels of P-gp may be expressed by a range of cell lines and normal tissues, it is suggested that this be considered if difficulties are encountered in loading fluorescent calcium probes.
Cytometry 1994 Dec 01
PMID:Constitutive expression of P-glycoprotein as a determinant of loading with fluorescent calcium probes. 787 42

The novel anthracycline N-benzyladriamycin-14-valerate (AD 198) circumvents P-glycoprotein (P-gp)- and altered topoisomerase II-mediated drug resistance. Nevertheless, AD 198-resistant (AD 198R) murine J774.2 cells overexpressed P-gp, were cross-resistant to other drugs through reduced accumulation and were rendered sensitive by continuous exposure to verapamil. Intracellular AD 198 was, however, similar in sensitive and resistant cells. Consequently, the ability of P-gp to confer AD 198 resistance was examined. It was observed that (i) AD 198 resistance in AD 198R cells grown without drug for 15 months declined by 60% with only a 10-15% loss of vinblastine cross-resistance and P-gp expression; (ii) a cloned AD 198R P388 mouse leukemic cell line did not express P-gp; and (iii) verapamil did not attenuate resistance against high-dose, short-term exposure to AD 198. Therefore, AD 198 resistance appeared to be P-gp-independent despite P-gp overexpression. Antioxidant enzyme and topoisomerase II activities remained unchanged between sensitive and resistance cells. These results suggest that AD 198 resistance was conferred by a novel mechanism.
Anticancer Drugs 1994 Dec
PMID:P-glycoprotein overexpression in mouse cells does not correlate with resistance to N-benzyladriamycin-14-valerate (AD 198). 788 99

A growing body of evidence indicates that expression of the mdr1 gene, which encodes the multidrug transporter, P-glycoprotein, contributes to chemotherapeutic resistance of human cancers. Expression of this protein in normal tissues such as the biliary tract, intestines, and renal tubules suggests a role in the excretion of toxins. Modulation of P-glycoprotein function in normal tissues may lead to decreased excretion of drugs and enhanced toxicities. A clinical trial of etoposide with escalating doses of cyclosporine (CsA) as a modulator of multidrug resistance was performed. CsA was delivered as a 2-hour loading dose followed by a 60-hour intravenous infusion, together with etoposide administered as a short infusion daily for 3 days. Patients received one or more courses of etoposide alone before the combined therapy to establish their clinical resistance to etoposide and to study etoposide pharmacokinetics without and then with CsA. Plasma and urinary etoposide was measured by high-performance liquid chromatography and plasma CsA by a nonspecific immunoassay. Conclusions from the initial phase I trial with the use of CsA as a modulator of etoposide are: (1) Serum CsA steady-state levels of up to 4800 ng/ml (4 microM) could be achieved with acceptable toxicity. (2) Toxicities caused by the combined treatment included increased nausea and vomiting, increased myelosuppression, and hyperbilirubinemia, consistent with modulation of P-glycoprotein function in the blood-brain barrier, hematopoietic stem cell, and biliary tract. Renal toxicity was uncommon, but severe in two patients with steady-state plasma CsA levels above 6000 ng/ml. (3) CsA administration had a marked effect on the pharmacokinetics of etoposide, with a doubling of the area under the concentration-time curve as a result of both decreased renal and nonrenal clearance, necessitating a 50% dose reduction in patients with normal renal function and hepatic function. (4) The recommended dose of CsA is a 6-7 mg/kg loading dose administered as a 2-hour intravenous infusion followed by a continuous infusion of 18-21 mg/kg/day for 60 hours with adjustments in the infusion rate to maintain steady-state serum levels of 3000-4800 ng/ml (2.5-4.0 M). We are performing additional phase I trials combining CsA with single-agent doxorubicin and taxol, and the CsA analog PSC-833 with various multidrug-resistant-related cytotoxins.
Cancer 1993 Dec 01
PMID:Clinical trials of modulation of multidrug resistance. Pharmacokinetic and pharmacodynamic considerations. 790 6

The blood-testis barrier is believed to be constituted by tight junctions between Sertoli cells in seminiferous tubules and possibly by myoid cells that encircle these tubules. We now show that testis microvessels are endowed with several markers of barrier properties of brain microvessels, such as the glucose transporter, P-glycoprotein, and gamma-glutamyl transpeptidase. Quantitative EM studies show that the endothelium in testis, as in brain, is continuous and has long junctional profiles and few vesicles. However, a small proportion of testis capillaries have expansions in their junctional clefts suggestive of patent paracellular channels, which may explain their higher permeability. Because barrier features are thought to be induced and/or maintained in brain microvessels by astrocytes, we assessed whether astrocyte-like cells exist in the testis. We found that the intertubular Leydig cells, adjacent to microvessels, express the astrocyte markers: glial fibrillary acidic protein, glutamine synthetase, and S-100 protein. We suggest that the testis endothelium contributes to the blood-testis barrier and that these endothelial barrier features are influenced by Leydig cells. We believe that the endothelial and the epithelial (Sertoli) components of the blood-testis barrier are "in series" and complement each other in achieving a stable milieu for spermatogenesis.
Proc Natl Acad Sci U S A 1993 Dec 01
PMID:Barrier properties of testis microvessels. 790 79

Conflicting reports of MDR1 gene expression in human tumours are observed according to whether studies are performed at the mRNA or P-glycoprotein level. We have investigated this expression in 22 clinically drug-resistant sarcomas at the mRNA level by Northern blot (NB), Dot blot (DB), in situ hybridisation (ISH), and at the protein level by immunohistochemistry (IHC) using three monoclonal antibodies (MoAbs): C219, JSB1, MRK16. Increased MDR1 mRNA expression was detected by NB, DB, and ISH in 1/22 sarcoma (an Ewing's sarcoma). ISH was perfectly correlated with DB hybridisation and confirmed the expression of tumoral cells alone. Specific staining of 100% of tumoral cells was obtained with the three MoAbs in the same sarcoma. Expression in tumoral cells of 12 other sarcomas was detected with MRK16, and positive staining of stromal cells with both C219 (1/22) and MRK16 (8/22) was observed. This study confirms that MDR1 overexpression occurs in human sarcomas but is not the principal mechanism of drug-resistance. Furthermore, positivity with one antibody does not necessarily imply the presence of P glycoprotein (P-gp) and a disparity may exist between the levels of P-gp and its mRNA in the same sample. So care must be taken in interpreting results and more sensitive techniques such as the polymerase chain reaction (PCR) could prove useful.
Br J Cancer 1993 Dec
PMID:Expression of MDR1/P glycoprotein in human sarcomas. 790 54


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