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)

An overexpression of plasma membrane 170-180 kDa P-glycoproteins is consistently found in multidrug-resistant (MDR) cell lines. In this study MRK-16, a monoclonal antibody (mAb) reacting with P-glycoprotein is used to study the putative functional role of this protein in vincristine (VCR) and daunorubicin (DNR) cellular accumulation in the MDR human ovarian carcinoma cell line 2780AD. We established that this cell line is highly cross-resistant to vincristine and daunomycin, related to a greatly reduced drug accumulation. Verapamil (Vp) (8 microM) caused a 3.6-fold increase in DNR as well as VCR accumulation. Exposition of 2780AD cells to MRK-16 led to an increase of 30% in cellular accumulation of VCR, both in normal growth medium as well as in medium without added glucose and with sodium azide, which largely depleted cellular ATP levels. No increase in DNR accumulation was found under these conditions. However, in the presence of 8 microM Vp, MRK-16 increased not only VCR but also DNR accumulation with about 30%. The relative increase of DNR accumulation was constant in a concentration range of 0.2-4 microM DNR. These data indicate that mAbs against P-glycoprotein might potentiate the action of calcium antagonists like Vp to increase cellular anthracycline accumulation.
...
PMID:Increase of daunorubicin and vincristine accumulation in multidrug resistant human ovarian carcinoma cells by a monoclonal antibody reacting with P-glycoprotein. 289 43

Two vincristine-resistant Chinese hamster ovary cell lines have been shown previously to be hypersensitive to the calcium channel blocker, verapamil. They are now shown to be hypersensitive to the membrane-active agent quinidine sulfate and to the calcium channel blockers diltiazem and nicardipine. Hypersensitivity to quinidine sulfate implies that calcium channels are not the primary target for these drug effects on these cell lines and is consistent with our previous observation that their calcium accumulation is normal in the presence and absence of verapamil. The two cell lines have elevated levels of membrane P-glycoprotein and of two cytosolic proteins, Mr 27,000 and pI 6.0 and 6.4. Revertants have normal levels of these cytosolic proteins, suggesting that these proteins may play a role in conferring resistance. [3H]Verapamil accumulation by the two cell lines is lower than in controls. One of the cell lines has been hybridized to normal cells and the vincristine resistance and verapamil sensitivity of three hybrid clones has been determined. Vincristine resistance is semidominant but verapamil hypersensitivity is completely recessive.
...
PMID:Properties of verapamil-hypersensitive multidrug-resistant Chinese hamster ovary cells. 289 55

Verapamil, a phenylalkylamine calcium channel blocker, has been shown to reverse multidrug resistance in tumor cells, possibly by increasing drug retention through interaction with an outward drug transporter of the resistant cells. In this study two photoactive radioactive analogs of verapamil, N-(p-azido[3,5-3H]benzoyl)aminomethyl verapamil and N-(p-azido[3-125I]salicyl)aminomethyl verapamil, were synthesized and used to identify the possible biochemical target(s) for verapamil in multidrug-resistant DC-3F/VCRd-5L Chinese hamster lung cells selected for resistance to vincristine. The results show that a specifically labeled 150- to 180-kDa membrane protein in resistant cells was immunoprecipitated with a monoclonal antibody specific for P-glycoprotein. Phenylalkylamine binding specificity was established by competitive blocking of specific photolabeling with the nonradioactive photoactive analogs as well as with verapamil. Photoaffinity labeling was also inhibited by 50 microM concentrations of the calcium channel blockers nimodipine, nifedipine, nicardipine, azidopine, bepridil, and diltiazem and partially by prenylamine. Bay K8644, a calcium channel agonist, also inhibited P-glycoprotein photolabeling. Moreover, P-glycoprotein labeling was inhibited in a dose-dependent manner by vinblastine with half-maximal inhibition at 0.2 microM compared to that by verapamil at 8 microM. Photolabeling was also partially inhibited by two of the drugs to which these cells are cross-resistant, doxorubicin and actinomycin D, at 100 microM, but not by colchicine. These data provide direct evidence that P-glycoprotein has broad drug recognition capacity and that it serves as a molecular target for calcium channel blocker action in reversing multidrug resistance.
...
PMID:Photoaffinity labeling of the multidrug-resistance-related P-glycoprotein with photoactive analogs of verapamil. 290 25

Verapamil reversed resistance to doxorubicin in a human multiple myeloma cell line selected for multiple drug resistance. The drug-resistant cell line 8226/DOX40 is known to have reduced intracellular drug accumulation associated with the overexpression of P-glycoprotein when compared to the sensitive parent cell line 8226/S. Verapamil alone was minimally cytotoxic in both cell lines, but reversed doxorubicin resistance in a dose-related manner in 8226/DOX40. A similar dose-response relationship was observed for verapamil in increasing net intracellular doxorubicin accumulation. This increased net accumulation was secondary to block of enhanced doxorubicin efflux by verapamil from resistant cells. In contrast, verapamil did not alter initial doxorubicin accumulation over the first 60 s when incubated with resistant cells. Addition of verapamil to the 8226/DOX40 cells enhanced the formation of doxorubicin-induced DNA single strand breaks, double strand breaks, and DNA-protein cross-links. Verapamil had no effect on these lesions in the drug-sensitive cells. In addition, verapamil did not affect chemotherapeutic cytotoxicity or transport in the drug-sensitive cell line. Verapamil appears to reverse doxorubicin resistance in this human myeloma cell line by blocking enhanced drug efflux, leading to increased drug accumulation and enhanced DNA damage.
...
PMID:Verapamil reversal of doxorubicin resistance in multidrug-resistant human myeloma cells and association with drug accumulation and DNA damage. 318 56

Resistance of human cancer cells to multiple cytotoxic hydrophobic agents (multidrug resistance) is due to overexpression of the "MDR1" gene, whose product is the plasma membrane P-glycoprotein. Plasma membrane vesicles partially purified from multidrug-resistant human KB carcinoma cells, but not from drug-sensitive cells, accumulate [3H]vinblastine in an ATP-dependent manner. This transport is osmotically sensitive, with an apparent Km of 38 microM for ATP and of approximately equal to 2 microM for vinblastine. The nonhydrolyzable analog adenosine 5'-[beta, gamma-imido]triphosphate does not substitute for ATP but is a competitive inhibitor of ATP for the transport process. Vanadate, an ATPase inhibitor, is a potent noncompetitive inhibitor of transport. These results indicate that hydrolysis of ATP is probably required for active transport of vinblastine. Several other drugs to which multidrug-resistant cell lines are resistant inhibit transport, with relative potencies as follows: vincristine greater than actinomycin D greater than daunomycin greater than colchicine = puromycin. Verapamil and quinidine, which reverse the multidrug-resistance phenotype, are good inhibitors of the transport process. These results confirm that multidrug-resistant cells express an energy-dependent plasma membrane transporter for hydrophobic drugs, and establish a system for the detailed biochemical analysis of this transport process.
...
PMID:ATP-dependent transport of vinblastine in vesicles from human multidrug-resistant cells. 336 66

Using four cell lines including drug-sensitive K562/Parent cells, P-glycoprotein (Pgp)-mediated multidrug resistant (MDR) K562/VCR, K562/ADR and revertant K562/ADR-R cells, two fluorescent agents, Fluo-3 and rhodamine-123 (Rh-123), were compared as indicators in a functional assay of MDR. Cells were incubated with 4 microM Fluo-3 or 1 microM Rh-123 for 45 min and then the intracellular accumulation of the agent was measured using a flow cytometer. Verapamil (20 microM) or cepharanthine (biscoclaurine alkaloid, 10 microM) was added just before the fluorescent agents. Efflux patterns were also studied 60 min after incubation with or without verapamil and cepharanthine. Increased intracellular accumulation and a delayed efflux pattern of Fluo-3 by verapamil and cepharanthine were demonstrated in multidrug resistant K562/VCR and K562/ADR cells, indicating that Fluo-3 is another good indicator of MDR. However, a similar, but lower, increase in uptake and a delayed efflux pattern of Fluo-3 by verapamil and cepharanthine were also demonstrated even in Pgp-non-overexpressed K562/Parent cells. In contrast, accumulation of Rh-123 was not affected by verapamil and cepharanthine. To further study the Pgp dependency of Fluo-3, another cell line, K562/NC16 expressing minimum MDR1 mRNA, was cloned. Increased uptake and a delayed efflux pattern of Fluo-3, but not Rh-123, with verapamil or cepharanthine were again demonstrated in K562/NC16 cells, indicating that intracellular accumulation of Fluo-3 may be non-specifically influenced by verapamil and cepharanthine at very low levels of Pgp-related MDR, while the influx and efflux patterns of Rh-123 may be specifically affected by Pgp overexpression.
...
PMID:Flow cytometric functional analysis of multidrug resistance by Fluo-3: a comparison with rhodamine-123. 748 25

P-glycoprotein (PGP), responsible for multidrug resistance (MDR) in cancer cells, is normally expressed in kidney proximal tubules and mesangium. PGP expression and function were studied in human mesangial cell cultures. MDR1 gene expression was demonstrated by reverse transcription-polymerase chain reaction. PGP expression was determined using MRK16 monoclonal antibody and its function was assessed by the efflux of rhodamine-123 (R123). R123 efflux had a half time of 25 +/- 5 s. Efflux was inhibited by cyclosporin A (10 microM), verapamil (10 microM), and vinblastine (100 microM) with half times of 380, 535, and 312 s, respectively. Incubation with MDR1-antisense oligonucleotide decreased R123 efflux (half time = 304 s). Verapamil, cyclosporin A, and PSC-833 augmented the cytotoxicity of Adriamycin by reducing the 50% maximal growth-inhibitory dose from 730 nM to 130, 110, and 90 nM, respectively. We conclude that human mesangial cells express MDR1 and demonstrate xenobiotic transport inhibitable by several known PGP substrates. Concomitant exposure of mesangial cells to PGP-transported drugs causes intracellular accumulation of toxic PGP substrates and ultimately damages the mesangial cells.
...
PMID:Expression and function of P-glycoprotein in human mesangial cells. 752 96

We have used a new methodology to measure the activity of P-glycoprotein (P-gp) in multidrug-resistant (MDR) tumor cells. This activity leads to a lower cytosolic concentration and a lower cytotoxicity of the classical anthracyclines, daunorubicin (DNR), and doxorubicin (DOX). It has been reported that the anthracycline idarubicin (IDA), which is more lipophilic, has a higher clinical efficacy in acute myeloid leukemias (AML) than DNR and DOX. In our study, the aim was to determine for a series of anthracyclines how variations in the passive drug influx rate as well as the P-gp-mediated drug pumping rate affect their cytosolic free drug concentrations and how these parameters are related to drug cytotoxicity. We selected six anthracyclines: DOX, DNR, epidoxorubicin (EPI), IDA, cyano-morpholino-doxorubicin (CMD), and carminomycin (CAR), ordered according to their increasing octanol/PBS buffer concentration ratios, respectively. To measure the passive permeation coefficient, the P-gp-mediated drug pumping rate, and the cytosolic free drug concentration, we used a flow-through system in which cells were exposed to a flowing medium containing drugs. We used the MDR P-gp-containing cell line KB8-5. It was shown that the passive drug permeation coefficient as well as the drug pumping rate of P-gp increased with increasing lipophilicity in this series of anthracyclines. The cytosolic free drug concentration was lowered by P-gp to a similar extent in KB8-5 cells for all drugs tested (40-50% of the extracellular drug concentration). CMD, IDA, and CAR had lower IC50 values and lower resistance factors in comparison to DOX, DNR, and EPI. Verapamil reversed the resistance for all anthracyclines tested. In conclusion, for several anthracyclines the activity of P-gp leads to a similar relative decrease in the cytosolic free drug concentration; consequently, the reported lower resistance factor of IDA compared to that of DNR is not due to the inability of P-gp to export IDA from cells.
...
PMID:The P-glycoprotein-mediated relative decrease in cytosolic free drug concentration is similar for several anthracyclines with varying lipophilicity. 757 81

Multidrug resistance is a major obstacle to cancer treatment. Using an expression cDNA library transfer approach to elucidating the molecular basis of non-P-glycoprotein-mediated multidrug resistance, we previously established that expression of multidrug resistance protein (MRP), an ATP-binding cassette superfamily transporter, confers multidrug resistance (G. D. Kruh et al., Cancer Res., 54: 1649-1652, 1994). In the present study, we generated NIH/3T3 MRP transfectants without using chemotherapeutic drugs to facilitate the pharmacological analysis of the MRP phenotype. MRP transfectants displayed increased resistance to several lipophilic drugs, including doxorubicin, daunorubicin, etoposide, actinomycin D, vincristine, and vinblastine. However, increased resistance was not observed for Taxol, a drug for which transfection of MDR1 confers high levels of resistance. Verapamil increased the sensitivity of MRP transfectants relative to control transfectants, but reversal was incomplete for doxorubicin and etoposide, the drugs for which MRP conferred the highest resistance levels. For the latter two drugs, MRP transfectants, which were approximately 8- and approximately 10-fold more sensitive than control cells in the absence of verapamil, exhibited 3.8- and 3.3-fold relative sensitization with 10 microM verapamil, respectively, but remained approximately 2 and approximately 3-fold more resistant than control cells. Analysis of drug kinetics using radiolabeled daunorubicin revealed decreased accumulation and increased efflux in MRP transfectants. Confocal microscopic analysis of intracellular daunorubicin in MRP transfectants was consistent with reduced intracellular drug concentrations, and also revealed an altered pattern of intracellular drug distribution characterized by the initial accumulation of drug in a perinuclear location, followed by the development of a punctate pattern of drug scattered throughout the cytoplasm. This pattern was suggestive of a process of drug sequestration, possibly followed by vesicle transport. Both increased drug efflux and perinuclear drug accumulation are consistent with the reported localization of MRP in plasma and cytosolic membranes (N. Krishnamachary and M. S. Center, Cancer Res., 53: 3658-3663, 1993; M. J. Flens et al., Cancer Res., 54: 4557-4563, 1994). These results thus indicate that the drug specificity of MRP is quite similar to that of MDR1, but also suggest potential differences in Taxol specificity and the level of verapamil sensitivity. In addition, these results indicate that MRP functions to extrude drug from the cell, but additionally suggest the intriguing possibility that drug sequestration contributes to drug resistance by protecting cellular targets and/or contributing to drug efflux.
...
PMID:Expression of multidrug resistance-associated protein in NIH/3T3 cells confers multidrug resistance associated with increased drug efflux and altered intracellular drug distribution. 758 98

Azatoxin (NSC 640737), a synthetic molecule, was rationally designed as a topoisomerase-II inhibitor and was shown to be a potent cytotoxic agent that inhibits both tubulin and topoisomerase II. A structure-activity relationship study allowed to select 3 derivatives that inhibit either tubulin (methylazatoxin) only or topoisomerase II (fluoroanilinoazatoxin and nitroanilino-azatoxin) in MTT assays performed on K562 and K562/ADM cells; the latter, expressing P-glycoprotein, indicated cross-resistance of K562/ADM cells to all 4 compounds. DNA double-strand breaks induced by the 3 azatoxins that inhibit topoisomerase II in vitro were decreased in K562/ADM as compared with K562 cells. Nitroanilino-azatoxin was the only compound for which resistance and reduced DNA damage observed in K562/ADM cells was partially reversed by verapamil, suggesting that nitroanilinoazatoxin was a substrate for P-glycoprotein. These results were confirmed by testing the cytotoxic activity of azatoxins on P-glycoprotein-expressing rat colon-carcinoma DHDK12/TRb cells in the absence and the presence of verapamil. Cell-cycle and mitotic-index studies indicated that azatoxin- and methyl-azatoxin-induced M-phase arrest was less in K562/ADM than in K562 cells. The G2 block induced by fluoro- and nitroanilinoazatoxins was delayed in K562/ADM cells. Verapamil increased cell-cycle inhibition induced by nitroanilinoazatoxin in K562/ADM cells without modifying cell-cycle effects of fluoroanilinoazatoxin. These results (i) are consistent with the specific inhibition of topoisomerase II or tubulin by azatoxin derivatives in cells; (ii) indicate that the nitro group of nitroanilinoazatoxin allows recognition and efflux by the P-glycoprotein; and (iii) suggest that cross-resistance of K562/ADM cells to other azatoxin derivatives is not mediated by P-glycoprotein.
...
PMID:Cellular pharmacology of azatoxins (topoisomerase-II and tubulin inhibitors) in P-glycoprotein-positive and -negative cell lines. 759 Dec 16


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

---