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)

A major obstacle to successful chemotherapy is the development of multidrug resistance (MDR) by cancer cells. MDR is characterized by enhanced cellular efflux of many structurally and functionally diverse compounds, including many anticancer drugs, due to overexpression of the MDR-1 gene product, P-glycoprotein. We hypothesized that the phytochemical, indole-3-carbinol (I3C), and some of its acid-condensation derivatives may inhibit P-glycoprotein-mediated transport due to their aromatic and nitrogen components, thus increasing the accumulation and efficacy of anticancer drugs and acting as a dietary adjuvant to conventional chemotherapy. I3C was subjected to acid conditions similar to those occurring in the stomach following ingestion and three acid-condensation products; a dimer, a noncyclic trimer, and a cyclic trimer were isolated and purified by high-performance liquid chromatography. The ability of I3C and its acid-condensation derivatives to reverse MDR was investigated using murine B16 melanoma cells that were transfected with the human MDR-1 gene (B16/hMDR-1 cells) and were cross-resistant to vinblastine and doxorubicin. The I3C acid-condensation product mixture, but not I3C, sensitized B16/hMDR-1 transfectants to the toxicity of vinblastine and doxorubicin. All three I3C acid-condensation products also increased the accumulation of the P-glycoprotein substrate, doxorubicin, in B16/hMDR-1 transfectants to levels comparable to parental B16 cells. The I3C acid-condensation product mixture competed with azidopine for binding to P-glycoprotein, suggesting that the observed MDR-reversing effect of the acid-condensation products was due to direct interaction with P-glycoprotein. The ability of p.o. administered I3C to reverse MDR was also tested in vivo. The resistance of B16/hMDR-1 transfectants to vinblastine and doxorubicin was preserved after i.p. injection and growth in nude mice. Tumor mass in mice that were provided with 333 or 500 mg/kg mouse/day I3C in their diet and injected s.c. with the anticancer drugs doxorubicin or vinblastine was significantly reduced as compared to tumor mass in mice provided with standard diet and injected with these anticancer drugs or mice provided with 500 mg/kg mouse/day I3C and not injected with anticancer compound. The concentrations of I3C used had no effect on survival or the general appearance and behavior of the mice. Collectively, these results indicate that ingestion of the common dietary constituent I3C results in its conversion to acid-condensation derivatives that sensitized MDR tumors to chemotherapeutic drugs without eliciting direct toxicity to the host.
...
PMID:Reversal of multidrug resistance in vivo by dietary administration of the phytochemical indole-3-carbinol. 856 74

A reasonably facile and effective procedure is described for the preparation of inside-out plasma membrane vesicles from tumor cells. The method incorporates nitrogen cavitation, optimized with respect to the applied N2 pressure, in the absence of added divalent cations followed by differential centrifugation and discontinuous, sucrose gradient centrifugation. With the three tumor cell types utilized, multidrug-resistant (MEL/VCR-6) and parental (MEL/O) murine erythroleukemia cells and methotrexate-resistant (L1210/R24) L1210 leukemia cells, yields were in the range of 8-12 mg of plasma membrane vesicles/10(10) cells at a purity of 87-94% with average inside-out sidedness among preparations varying from 65 to 93% depending upon the cell type. Inside-out plasma membrane vesicles so derived were capable of sustaining ATP-dependent transport inward of two common antitumor cytotoxic agents, vinblastine and methotrexate. The former was demonstrated with inside-out vesicles from only P-glycoprotein-overexpressing, multidrug-resistant MEL/VCR-6 cells, while the latter was readily demonstrated in inside-out vesicles from all three cell types.
...
PMID:Facile preparation of inside-out plasma membrane vesicles from tumor cells for functional studies of pharmacologically relevant translocating ATPases. 857 99

Estramustine phosphate (EMP) is thought to form a chemical link between estradiol and non-nitrogen mustard. An estramustine-binding protein has been isolated in prostate, breast, and brain cancers as well as in malignant melanoma cells. Estramustine phosphate's ability to bind to microtubular-associated proteins and to interfere with mdr-mediated drug efflux are thought to result in its enhancement of paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) activity in cell lines and in its ability to affect hormone-resistant prostate cancer. This phase I study administered combined paclitaxel and EMP to 25 women with ovarian, breast, and other tumors and assessed efficacy and toxicity. Estramustine phosphate was administered at two dose levels, 900 or 1,200 mg/m2 daily on days 1, 2, and 3 in 3-week cycles. On day 3, paclitaxel (150, 180, 210, or 225 mg/m2) was given concomitantly by 3-hour infusion. Therapeutic effects were noted in all patients. Partial responses were noted in three of eight patients with breast cancer who had failed to improve on paclitaxel alone. Three other patients experienced prolonged stable disease. Only moderate toxicities were noted until EMP levels of 1,200 mg/m2 were reached. At these dose levels, gastrointestinal toxicities became more prominent. The addition of EMP to paclitaxel allowed patients to receive paclitaxel for longer periods, and may have enhanced the therapeutic effects of paclitaxel. If so, the mechanisms of such enhancement warrant investigation. The two drugs may work on different aspects of microtubular function, for example, or may reduce efflux of paclitaxel in P-glycoprotein overexpressed tumors.
...
PMID:Response to estramustine phosphate and paclitaxel in patients with advanced breast cancer: a phase I study. 907 37

A Chinese hamster ovary cell line resistant to okadaic acid (OA), OAR2-3 has a mutation of the protein phosphatase (PP) 2A alpha gene and expresses a multi-drug resistance (MDR) phenotype. In the present work, we isolated two additional OA-resistant variants, also showing MDR with a cross-resistance profile similar to that of OAR2-3, and with increased and decreased expressions of the P-glycoprotein (Pgp) and DNA topoisomerase (topo) II protein, respectively. Unlike OAR2-3, however, they had no mutation in the same region of the PP2A alpha gene. Except for OA-resistance in OAR2-3, the MDR was found to decrease in the absence of OA, and this decrease was again associated with changes in topo II- and Pgp-expressions. Thus, we conclude that 1) OA regulates the expressions of Pgp and topo II positively and negatively, respectively, resulting in reversible expression of MDR irrespective of genetic changes and 2) in OAR2-3, the mutation in the PP2A alpha gene confers stable resistance to OA. The MDR was also linked with collateral sensitivity to some drugs, like cisplatin and nitrogen mustard.
...
PMID:Unstable expression of the multi-drug-resistant phenotype in Chinese hamster ovary cells resistant to okadaic acid. 912 89

The purpose of this study was to clarify the clinical efficacy of multidrug chemotherapy for aggressive adult T-cell leukemia (ATL). We report the therapeutic results of treatment of patients with aggressive ATL undertaken between 1986 and 1995. A total of 120 newly diagnosed patients with a performance status of 0-3 and aged < 70 years at diagnosis were entered into the study. Clinical features, including clinical subtypes, serum levels of lactate dehydrogenase and blood urea nitrogen, the response to chemotherapy, and doses of individual chemotherapeutic agents, were evaluated. Of the 120 patients enrolled, 97 had acute-type and 23 lymphoma-type ATL. The complete response rate and median survival of these patients were 25.3% and 9 months, respectively. The 2- and 5-year survival rates were 18.4% and 8%, respectively, and five patients have been alive for > 5 years and are disease-free. These long-term survivors had good prognostic factors at diagnosis. There was no correlation between the doses of the various chemotherapeutic agents and the survival duration. These results indicate that ordinary combined chemotherapy has limited ability to improve the prognosis of aggressive ATL. Our previous study indicated that expression of P-glycoprotein in ATL cells might be involved in resistance to chemotherapeutic agents, particularly doxorubicin, vincristine, and etoposide. Therefore, new therapeutic strategies will be necessary to improve the prognosis of ATL patients.
...
PMID:Treatment for adult T-cell leukemia. 927 34

Compound LY335979 is a P-glycoprotein inhibitor currently entering phase I clinical trials for potential reversal of multidrug resistance to cancer chemotherapy. In early exploratory studies, LY335979 was found to be rapidly transformed in incubations with liver microsomes from rats, dogs, monkeys, and humans. Although the parent compound was completely metabolized, no prominent metabolite peaks were observed. One peak did appear early in the time course, but it did not increase over time. In another preliminary experiment, rats were treated iv with [3H]LY335979 (prepared for pharmacology studies), and urine and bile fractions were collected. Analysis of the urine by reverse-phase HPLC with UV and radioactivity detection revealed that almost all of the material eluted with the solvent front. More than half the radioactivity in bile was accounted for by two peaks eluting earlier than the parent compound (the rest eluted at the solvent front). With both bile and the incubations with microsomes, initial attempts to isolate metabolites were not successful. There was also evidence in both systems of products derived from cleavage of LY335979 (by both further metabolism and degradation). LC/NMR was thus used to analyze materials directly in their respective matrices. An N-oxide metabolite (LY389551) formed by oxidation of the quinoline nitrogen was identified in the microsomal incubations; in bile, three glucuronide metabolites were identified, all of which were conjugates of products formed by oxidation of the quinoline ring of LY335979. There have been few reports in the literature of LC/NMR analysis of bile, which is a more complex matrix than either urine or microsomal suspensions. However, the HPLC techniques developed in this work for the HPLC/UV and LC/MS analyses of LY335979 metabolites in the microsomal matrix and in bile proved readily adaptable for LC/NMR. Using a 500-MHz instrument, basic 1H NMR spectra could be obtained in 2-3 hr with approximately 100 ng of material in the LC/NMR microprobe. With approximately 1.5 microg of material injected onto the column, 1H-1H correlation spectroscopy spectra could be acquired overnight. Along with LC/MS data, the LC/NMR technique facilitated direct identification of a number of metabolites of LY335979 at a point at which their identification by traditional methods would not have been pursued.
...
PMID:Liquid chromatography/nuclear magnetic resonance spectroscopy and liquid chromatography/mass spectrometry identification of novel metabolites of the multidrug resistance modulator LY335979 in rat bile and human liver microsomal incubations. 944 51

The endothelium both initiates and responds to a cascade of events triggered by cytokines. Enhanced formation of NO, especially by inducible nitric oxide- synthase (i NOS), is largely stimulated by tumor necrosis factor (TNF). Nitrogen oxides are reactive intermediate molecules functioning in neural transmission, and vasodilatation. The aim of our study was to investigate the effect of TNF and Staphylococcus aureus, a TNF inducing agent on the NO production of brain endothelial cells in vitro. The effect of the same agent was investigated on the MDR expression of endothelial cells. Both TNF and Staphylococcus aureus resulted in enhanced NO production. Western blot analysis showed enhanced expression of iNOS, which could be inhibited by pentoxifylline, an inhibitor of TNF synthesis. Flow cytometric analysis revealed that the brain capillary endothelial cells exerted P-glycoprotein expression, which was not influenced by TNF. However, the mdr function itself in these cells was decreased by TNF. Cultured endothelial cells are excellent tools for the investigation of the possible connection between the NO production and MDR function, and for the estimation the effect of different agents influencing these activities, which might be important in blood-brain barrier function.
...
PMID:Nitric oxide production and MDR expression by human brain endothelial cells. 971 8

To clarify renal handling of rhodamine 123, a substrate for P-glycoprotein, in normal and diseased states, in-vivo clearance studies were performed with normal rats and rats with glycerol-induced acute renal failure. For normal rats the excretion ratio of unbound rhodamine 123-to-inulin was 3.25, indicating the presence of the renal tubular secretion of rhodamine 123. Co-administration of cyclosporin, a P-glycoprotein inhibitor, significantly reduced tubular secretion of rhodamine 123. Administration of glycerol induced both an increase in blood urea nitrogen and a reduction in the glomerular filtration rate, confirming the induction of acute renal failure. Total plasma, renal, and tubular secretory clearances of rhodamine 123 were significantly lower for rats with acute renal failure than for control rats. There was no difference between the ATP content of the renal cortex in control rats and those with acute renal failure. In addition to the decrease in renal clearance, a decrease in the biliary clearance of rhodamine 123 was also observed in rats with acute renal failure. These results imply that rhodamine 123 is secreted via P-glycoprotein in renal tubules and that the renal secretory clearance of rhodamine 123 was reduced after acute renal failure, probably because of impairment of P-glycoprotein.
...
PMID:Renal excretion of rhodamine 123, a P-glycoprotein substrate, in rats with glycerol-induced acute renal failure. 982 64

A series of dihydrobenzopyrans and tetrahydroquinolines was synthesized and pharmacologically tested for their ability to inhibit P-glycoprotein mediated daunomycin efflux in multidrug resistant CCRF-CEM vcr1000 cells. Several compounds exhibit activities in the range of the reference compounds verapamil and propafenone. Preliminary structure-activity relationship studies propose the importance of high molar refractivity values of the compounds and the presence of an additional basic nitrogen atom.
...
PMID:Synthesis and in vitro multidrug resistance modulating activity of a series of dihydrobenzopyrans and tetrahydroquinolines. 1035

The presence of a nitrogen atom, charged at physiological pH, has frequently been considered to be a hallmark of P-glycoprotein (PGP) inhibitors, although certain steroids, such as progesterone, lack a nitrogen atom and still are active modulators of PGP. The present study was aimed at investigating the role the nitrogen atom plays in the activity of PGP inhibitors. Propafenone-related amines, anilines, and amides that cover a broad range of pK(a) values, as well as an ester, were synthesized and tested for multidrug resistance-reverting activity. The sum of the hydrogen bond acceptor strengths was calculated and correlated with EC(50) values for PGP inhibition. For the complete set of 12 compounds, an excellent correlation between these two parameters was found; this included the ester GP570, which lacks a nitrogen atom but contains the strong hydrogen bond-accepting ester unit. The interaction of the nitrogen atom with PGP therefore is nonional and is determined by the sum of the hydrogen acceptor strengths of the region. The high predictivity of the obtained model is demonstrated in a leave-one-out cross-validation procedure.
...
PMID:The importance of a nitrogen atom in modulators of multidrug resistance. 1049 63


<< Previous 1 2 3 4 5 6 7 Next >>

---