Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.6.3.44 (P-glycoprotein)
 13,344 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Tenidap [5-chloro-2,3-dihydro-3-(hydroxy-2-thienylmethylene)-2-oxo-1H- indole-1-carboxamide], a novel antirheumatic agent, produces a rapid and sustained intracellular acidification when applied to cells in culture. To investigate the mechanism by which this change in ionic homeostasis is achieved, the acidification activities of structural analogs of tenidap were determined, and the movements of [14C]tenidap into and out of cells were explored. The acidification activity of tenidap was enhanced by lowering extracellular pH, suggesting that the free acid species was required for this process. Consistent with this requirement, a non-acidic analog of tenidap did not produce a change in intracellular pH (pHi). In contrast, multihalogenated derivatives of tenidap produced greater changes in pHi than did tenidap, and one analog produced a transient acidification from which the cell recovered; this recovery, however, was blocked by an inhibitor of the Na+/H+ antiporter. Fibroblasts incubated with [14C]tenidap achieved within 5 min a level of cell-associated drug that remained constant during longer incubations. Simultaneous addition of the electrogenic ionophore valinomycin or the P-glycoprotein inhibitor 4-(3,4-dihydro-6,7-dimethoxy-2(1H)-isoquinolinyl)-N-[2-(3,4-dimethoxyphe nyl) ethyl]-6,7-dimethoxy-2-quinazolinamine (CP-100,356) caused a time- and concentration-dependent increase in the level of cell-associated [14C]tenidap; other agents tested did not promote this enhanced cellular accumulation. [14C]Tenidap accumulated by fibroblasts in the presence of CP-100,356 subsequently was released when these cells were placed in a tenidap- and CP-100,356-free medium. Importantly, several agents that are known to inhibit anion transport processes, including alpha-cyano-beta-(1-phenylindol-3-yl) acrylate, 5-nitro-2(3-phenylpropylamino)-benzoic acid, and meclofenamic acid, inhibited efflux of [14C]tenidap. In contrast, ethacrynic acid and 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid did not impair the efflux process. Likewise, tenidap analogs that produced a sustained intracellular acidification blocked the efflux of [14C]tenidap, but non-acidifying species did not. These data suggest that movements of tenidap into and/or out of cells is a facilitated process subject to pharmacological intervention. Together, the structural selectivity of the acidification response and the evidence of facilitated transport suggest that the pHi modulating activity of tenidap is dependent on its unique physicochemical properties. Due to the dependence of these physicochemical properties on environmental and cellular conditions, in vivo expression of the acidification activity is likely to occur only within restricted environments that favor this tenidap-induced process.
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PMID:Reduction of intracellular pH by tenidap. Involvement of cellular anion transporters in the pH change. 750 93

In this study we have investigated the effects of the multidrug-resistance (MDR) modifiers verapamil (VPM), cyclosporin A (CsA) and tamoxifen (TMX) on the intracellular pH(pHi) of four colon carcinoma-derived cell lines with low P-glycoprotein expression (CaCo-2, HT-29, SW 620 and SW 480). Addition of VPM (1 mu M), CsA (1 microgram/ml) or TMX (2 microM) in HEPES- or bicarbonate/CO2-buffered Ringer's solution was followed by dose-dependent and reversible decreases of the pHi (0.1-0.3 units) of all cell lines, as measured ratiometrically by the changes in the pH-dependent fluorescence of bis(carboxyethyl)carboxyfluorescein (BCECF). Testing the effects of the resistance modifiers on the Na+/H+ antiporter and bicarbonate trans-porters under appropriate buffer conditions and addition of inhibitors (amiloride, DIDS) revealed that the chemomodulator-induced acidification does not interfere with the function of these major pHi-regulating acid-base transporters. The induction of changes in pHi shows no correlation with MDR-reversing activity of the drugs and our data do not support the P-gp-inhibition-mediated accumulation of acidic substrates as underlying mechanism. In addition to the P-gp-directed MDR-reversal, chemomodulator-induced intracellular acidification may enhance the chemosensitivity of the cells especially under alkaline extracellular conditions, and contribute to the decreased efficacy of MDR-modifiers in acidic extracellular environments and to the chemosensitising effect of VPM in P-gp-negative cell lines.
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PMID:The multidrug-resistance modifiers verapamil, cyclosporine A and tamoxifen induce an intracellular acidification in colon carcinoma cell lines in vitro. 790 52

Although multidrug resistance (mdr) may arise through a variety of mechanisms, the most widely studied and accepted form is associated with an increased concentration of P-glycoprotein (P-gp), a 170 kd protein found in the membrane fraction of a number of mammalian cells. Since mdr seems to be related to the ability of resistant cells to extrude drugs and the circumvention of mdr is supposed to be due to the restored ability to accumulate drugs, membrane has been regarded as the crucial site for such a regulation and an important role for membrane ion exchangers has been suggested. The aim of this work was to elucidate whether the Na+/H+ antiporter is involved in the mechanism of regulation and circumvention of mdr and if 5-(N-ethyl-N-isopropyl) amiloride (EIPA), a selective inhibitor of the Na+/H+ exchanger, can modulate the functional expression of the mdr phenotype. The effect of EIPA on doxorubicin (DX) resistant cells (LoVo/DX) obtained from a human colon adenocarcinoma cell line (LoVo) was studied. EIPA at concentrations ranging from 10 to 50 mu M was able to increase the antibiotic cytotoxicity in the resistant Lovo/DX cells. The reversal of DX resistance paralleled an increase of the ability of the cells to accumulate the drug. Both drug loading and sensitivity to the inhibitory effect of DX on cell proliferation were restored by EIPA in a dose-dependent way. These results suggest a new mechanism of mdr reversal and indicate that amiloride and its derivatives may be useful in reversing DX resistance and in enhancing the clinical effectiveness of chemotherapeutics.
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PMID:Reversal of doxorubicin resistance by the amiloride analogue EIPA in multidrug resistant human colon carcinoma cells. 890 49