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

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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)

Cytochalasins are a family of structurally related natural product cytotoxins that selectively depolymerize microfilaments. In this study, the interaction between several cytochalasins and the drug transporter P-glycoprotein was investigated. Dihydrocytochalasin B and cytochalasin E consistently sensitized P-glycoprotein-overexpressing human breast carcinoma cells (MCF-7/ADR) to daunomycin, vinblastine, and actinomycin D without affecting the cytotoxicity of cisplatin. These compounds did not affect the sensitivities of the parental MCF-7 cells to anticancer drugs, indicating that their effects are due to P-glycoprotein inhibition. Effects of dihydrocytochalasin B and cytochalasin E were observed at concentrations as low as 2.5 and 5 microM, respectively. In contrast, cytochalasins A, B, C, D, H, and J did not sensitize MCF-7/ADR cells to any of the drugs. The accumulation of [3H]-vinblastine by MCF-7/ADR cells and by drug-resistant human ovarian carcinoma cells (SKVLB1) was increased to the greatest extent by verapamil, followed by dihydrocytochalasin B > cytochalasin E > cytochalasin B, whereas cytochalasins A, C, D, H, and J did not alter intracellular accumulation of the drug. Similarly to verapamil, dihydrocytochalasin B significantly stimulated the ATPase activity of P-glycoprotein, while other cytochalasins were ineffective. These results demonstrate that very closely related compounds can differentially interact with P-glycoprotein. For example, the only difference between cytochalasin B and dihydrocytochalasin B is the saturation of a carbon-carbon double bond in dihydrocytochalasin B. These structural differences may provide important insight into chemical determinants for drug interaction with P-glycoprotein.
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PMID:Differential interactions of cytochalasins with P-glycoprotein. 883 87

The new lipophilic anthracycline N-benzyl-adriamycin-14-valerate (AD198) was evaluated for its activity in comparison to doxorubicin in P-glycoprotein (Pgp)-positive and -negative cell lines. AD198 and doxorubicin showed comparable antitumor activity in the Pgp-negative breast cancer cell line MCF-7 and the Pgp-negative ovarian carcinoma cell line A2780. By contrast, AD198 was significantly more active than doxorubicin in the Pgp-positive breast cancer cell line MCF7AD (IC50 values 2.5 and 0.15 microM for 96 h continuous exposure) and the Pgp-positive ovarian carcinoma cell line A2780 DX5 (IC50 values 0.6 and 0.07 microM, respectively). Unlike doxorubicin, the activity of AD198 was not increased by concommittant application of cyclosporin A in cell line MCF7AD. Flow cytometry studies showed that, in contrast to doxorubicin, AD198 was not transported by Pgp and that verapamil did not change the intracellular pharmacokinetics of this new anthracycline. These data provide evidence that AD198 possesses high activity in human solid tumor cell lines expressing the classical multidrug resistant phenotype. Its further clinical development appears to be warranted.
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PMID:Activity of N-benzyl-adriamycin-14-valerate (AD198), a new anthracycline derivate, in multidrug resistant human ovarian and breast carcinoma cell lines. 884 78

Multidrug resistance (MDR) has been related to two members of the ABC-superfamily of transporters, P-glycoprotein (Pgp) and Multidrug Resistance-associated Protein (MRP). We have described a 110 kD protein termed the Lung Resistance-related Protein (LRP) that is overexpressed in several non-Pgp MDR cells lines of different histogenetic origin. Reversal of MDR parallels a decrease in LRP expression. In a panel of 61 cancer cell lines which have not been subjected to laboratory drug selection, LRP was a superior predictor for in vitro resistance to MDR-related drugs when compared to Pgp and MRP, and LRP's predictive value extended to MDR unrelated drugs, such as platinum compounds. LRP is widely distributed in clinical cancer specimens, but the frequency of LRP expression inversely correlates with the known chemosensitivity of different tumour types. Furthermore, LRP expression at diagnosis has been shown to be a strong and independent prognostic factor for response to chemotherapy and outcome in acute myeloid leukemia and ovarian carcinoma (platinum-based treatment) patients. Recently, LRP has been identified as the human major protein. Vaults are novel cellular organelles broadly distributed and highly conserved among diverse eukaryotic cells, suggesting that they play a role in fundamental cell processes. Vaults localise to nuclear pore complexes and may be the central plug of the nuclear pore complexes. Vaults structure and localisation support a transport function for this particle which could involve a variety of substrates. Vaults may therefore play a role in drug resistance by regulating the nucleocytoplasmic transport of drugs.
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PMID:Relationship of LRP-human major vault protein to in vitro and clinical resistance to anticancer drugs. 886 6

The sensitivity of tumor cells to lysis by natural killer (NK) and interleukin-2 (IL-2)-activated killer (LAK) cells was studied in three ovarian carcinoma cell lines (2780.9S, SKOV-3, and CHOAUXB1), four multidrug-resistant (MDR) variants, and a melphalan-resistant line. The antitumor activity of LAK cells was evaluated both by 51Cr release and by conjugate formation assays. Four of four P-glycoprotein-positive (P-gp+) MDR ovarian carcinoma cell line variants were lysed by human LAK cells to a greater extent than were their drug-sensitive counterparts. In contrast, a melphalan-resistant ovarian carcinoma cell line that does not overexpress P-gp (P-gp-) did not exhibit an increased susceptibility to LAK cells relative to its parental cell line. Two of the four P-gp+ MDR ovarian carcinoma cell line variants were tested for human NK cell susceptibility and this was found to be unchanged or decreased. The P-gp+ MDR ovarian carcinoma cell line 2780.AD645 showed a higher frequency of tumor cell binding to LAK cells than did the drug-sensitive parental line. A monoclonal antibody (mAb) against a cell surface epitope of P-gp, MRK16, used at 1 microgram/ml, enhanced the LAK susceptibility of P-gp+ MDR ovarian carcinoma cell lines. However, when incubation with 10 micrograms/ml MRK-16 antibody (Ab) was followed by 12.5 micrograms/ml F(ab')2 goat anti-mouse (GAM) immunoglobulin (Ig), the increased LAK susceptibility of P-gp+ MDR cell lines was inhibited. These data strongly suggest that P-glycoprotein-positive MDR ovarian carcinoma cells not only are targets for LAK cells, but are more sensitive than their drug-sensitive parental lines. This is in contrast to their susceptibility to NK cells, which is low to start with and remains unchanged or even decreased in MDR cells. It is postulated here that P-gp or associated changes result in a greater frequency of effector-target cell binding, leading to increased LAK cell cytotoxicity.
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PMID:P-glycoprotein-mediated multidrug resistance and lymphokine-activated killer cell susceptibility in ovarian carcinoma. 894 80

Taxol-resistant clones from a human ovarian carcinoma cell line (2008) were selected by an initial exposure to 0.05 microM (2008/13) or 0.5 microM (2008/17) taxol. Thereafter, a series of clones with increasing taxol resistance were derived from the 2008/17 and 2008/13 cells by stepwise sequential exposure to increasing concentrations of taxol. The 2008/17 clones displayed a classical P-glycoprotein-mediated drug-resistance phenotype. In contrast, the 2008/13 clones followed the classical P-glycoprotein-mediated resistance phenotype until a 245-fold taxol-resistant clone (2008/13/2) was obtained, which was followed by a further increase in the degree of resistance but significant down-regulation of P-glycoprotein expression in the 252-fold taxol-resistant 2008/13/4 cells. This clone (2008/13/4) also accumulated significantly higher intracellular levels of taxol than those expressing the P-glycoprotein. No correlation between the expression of the multidrug resistance-associated protein and taxol resistance was observed. Verapamil increased the sensitivity of all drug-resistant clones to taxol, and this was probably related to the ability of verapamil to increase the intracellular concentration of taxol (except in the case of 2008/13/4 cells). The 2008/17 clones were highly cross-resistant to Adriamycin, etoposide, and vincristine. They also displayed a low level of cross-resistance to camptothecin but were not cross-resistant to cisplatin. The taxol-resistant 2008/13 clones displayed a similar pattern of cross-resistance for all drugs (except Adriamycin). The 2008/13 clones were only 2-to 4-fold cross-resistant Adriamycin. The levels of alpha-tubulin and beta-tubulin were similar in the parental 2008 and taxol-resistant 2008/13/4 cells. Furthermore, the in vitro binding of [3H]taxol to semipurified microtubule preparations derived from the parental 2008 and the taxol-resistant 2008/13/2 and 2008/13/4 cells was similar. These results show that in human ovarian carcinoma cells resistance to taxol can be acquired via as yet undescribed mechanisms.
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PMID:Acquisition of taxol resistance via P-glycoprotein- and non-P-glycoprotein-mediated mechanisms in human ovarian carcinoma cells. 910 96

Acquired resistance to paclitaxel can be mediated by P-glycoprotein or by alterations involving tubulin. We report two paclitaxel-resistant sublines derived from 1A9 human ovarian carcinoma cells. Single-step paclitaxel selection with verapamil yielded two clones that are resistant to paclitaxel and collaterally sensitive to vinblastine. The resistant sublines are not paclitaxel-dependent, and resistance remained stable after 3 years of drug-free culture. All cell lines accumulate [3H]paclitaxel equally, and no MDR-1 mRNA was detected by polymerase chain reaction following reverse transcription. Total tubulin content is similar, but the polymerized fraction increased in parental but not in resistant cells following the paclitaxel addition. Purified tubulin from parental cells demonstrated paclitaxel-driven increased polymerization, in contrast to resistant cell tubulin, which did not polymerize under identical conditions. In contrast, epothilone B, an agent to which the resistant cells retained sensitivity, increased assembly. Comparable expression of beta-tubulin isotypes was found in parental and resistant cells, with predominant expression of the M40 and beta2 isotypes. Sequence analysis demonstrated acquired mutations in the M40 isotype at nucleotide 810 (T --> G; Phe270 --> Val) in 1A9PTX10 cells and nucleotide 1092 (G --> A; Ala364 --> Thr) in 1A9PTX22 cells. These results identify residues beta270 and beta364 as important modulators of paclitaxel's interaction with tubulin.
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PMID:Paclitaxel-resistant human ovarian cancer cells have mutant beta-tubulins that exhibit impaired paclitaxel-driven polymerization. 920 30

The expression of the MDR1 gene has been shown to correlate with tumor aggressiveness and oncogenic activation both in experimental tumor models and in human clinical specimens In order to verify whether this association also takes place in ovarian carcinoma, we studied tumor samples from 39 patients by means of immunohistochemistry for the overexpression of P-glycoprotein (MDR1), nm23, c-erb-B2 and p53. MDR1 (p = 0.023), nm 23 (p = 0.037) and c-erb-B2 (p = 0.015) were expressed significantly more in specimens from patients with advanced stage of disease. There were no differences in p53 expression between both groups of patients. Furthermore, we found a significant coexpression of MDR1 and nm23 (p = 0.028), and of MDR1 and c-erb-B2 (p = 0.0077). There was no association between the expression of the MDR1 gene and p53. These results parallel those previously reported by us for mammary carcinoma, and seem to indicate that expression of the multidrug resistance gene (MDR1) is inherent to the development of the malignant phenotype in several human tumors.
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PMID:Correlation of MDR1 expression and oncogenic activation in human epithelial ovarian carcinoma. 921 79

Intrinsic and acquired multidrug resistance (MDR) in many human cancers may be due to expression of the multidrug transporter P-glycoprotein (Pgp), which is encoded by the mdr1 gene. There is substantial evidence that Pgp is expressed both as an acquired mechanism (e.g., in leukemias, lymphomas, myeloma, and breast and ovarian carcinomas) and constitutively (e.g., in colorectal and renal cancers) and that its expression is of prognostic significance in many types of cancer. Clinical trials of MDR modulation are complicated by the presence of multiple-drug-resistance mechanisms in human cancers, the pharmacokinetic interactions that result from the inhibition of Pgp in normal tissues, and, until recently, the lack of potent and specific inhibitors of Pgp. A large number of clinical trials of reversal of MDR have been undertaken with drugs that are relatively weak inhibitors and produce limiting toxicities at doses below those necessary to inhibit Pgp significantly. The advent of newer drugs such as the cyclosporin PSC 833 (PSC) provides clinicians with more potent and specific inhibitors for MDR modulation trials. Understanding how modulators of Pgp such as PSC 833 affect the toxicity and pharmacokinetics of cytotoxic agents is fundamental for the design of therapeutic trials of MDR modulation. Our studies of combinations of high-dose cyclosporin (CsA) or PSC 833 with etoposide, doxorubicin, or paclitaxel have produced data regarding the role of Pgp in the clinical pharmacology of these agents. Major pharmacokinetic interactions result from the coadministration of CsA or PSC 833 with MDR-related anticancer agents (e.g., doxorubicin, daunorubicin, etoposide, paclitaxel, and vinblastine). These include increases in the plasma area under the curve and half-life and decreases in the clearance of these cytotoxic drugs, consistent with Pgp modulation at the biliary lumen and renal tubule, blocking excretion of drugs into the bile and urine. The biological and medical implications of our studies include the following. First, Pgp is a major organic cation transporter in tissues responsible for the excretion of xenobiotics (both drugs and toxins) by the biliary tract and proximal tubule of the kidney. Our clinical data are supported by recent studies in mdr-gene-knockout mice. Second, modulation of Pgp in tumors is likely to be accompanied by altered Pgp function in normal tissues, with pharmacokinetic interactions manifesting as inhibition of the disposition of MDR-related cytotoxins (which are transport substrates for Pgp). Third, these pharmacokinetic interactions of Pgp modulation are predictable if one defines the pharmacology of the modulating agent and the combination. The interactions lead to increased toxicities such as myelosuppression unless doses are modified to compensate for the altered disposition of MDR-related cytotoxins. Fourth, in serial studies where patients are their own controls and clinical resistance is established, remissions are observed when CsA or PSC 833 is added to therapy, even when doses of the cytotoxin are reduced by as much as 3-fold. This reversal of clinical drug resistance occurs particularly when the tumor cells express the mdr1 gene. Thus, tumor regression can be obtained without apparent increases in normal tissue toxicities. In parallel with these trials, we have recently demonstrated in the laboratory that PSC 833 decreases the mutation rate for resistance to doxorubicin and suppresses activation of mdr1 and the appearance of MDR mutants. These findings suggest that MDR modulation may delay the emergence of clinical drug resistance and support the concept of prevention of drug resistance in the earlier stages of disease and the utilization of time to progression as an important endpoint in clinical trials. Pivotal phase III trials to test these concepts with PSC 833 as an MDR modulator are under way or planned for patients with acute myeloid leukemias, multiple myeloma, and ovarian carcinoma.
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PMID:Modulation and prevention of multidrug resistance by inhibitors of P-glycoprotein. 927 28

Methoxymorpholino doxorubicin (MMRDX) is an anthracycline analogue that is able to overcome tumor cell resistance to classical anthracyclines. Mechanisms for increased MMRDX cytotoxicity were analyzed in a small cell lung carcinoma cell line (GLC4), its 300-fold doxorubicin-resistant and multidrug resistance-associated protein (MRP)-over-expressing subline (GLC4/ADR), an ovarian carcinoma cell line (A2780) and its 100-fold doxorubicin resistant and P-glycoprotein (P-gp)-overexpressing subline A2780AD. Cross-resistance, measured with the MTT assay at MMRDX concentration resulting in 50% growth inhibition, was 1.8-fold in GLC4/ADR and 4.5-fold in A2780AD compared to their respective parental cell lines. Cellular MMRDX accumulation was equal in GLC4 and GLC4/ADR and 2-fold lower in A2780AD compared to A2780. Doxorubicin fluorescence was analyzed with confocal laser scan microscopy. Fluorescence was nuclear in sensitive, and cytoplasmic in resistant, cell lines, while MMRDX fluorescence was found in the nucleus in all cell lines. Pre-incubation with the MRP blocker MK 571 restored in GLC4/ADR cells the nuclear doxorubicin fluorescence pattern, as observed in GLC4 cells. MMRDX, thus, can largely overcome cross-resistance in these P-gp- and MRP-overexpressing doxorubicin-resistant cell lines. Our results suggest that MMRDX is not a substrate for MRP-mediated resistance.
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PMID:Mechanisms for high methoxymorpholino doxorubicin cytotoxicity in doxorubicin-resistant tumor cell lines. 935 83

The lactone-bearing polyhydroxylated alkatetraene (+)-discodermolide, which was isolated from the sponge Discodermia dissoluta, induces the polymerization of purified tubulin with and without microtubule-associated proteins or GTP, and the polymers formed are stable to cold and calcium. These effects are similar to those of paclitaxel (Taxol), but discodermolide is more potent. We confirmed that these properties represent hypernucleation phenomena; we obtained lower tubulin critical concentrations and shorter polymers with discodermolide than paclitaxel under a variety of reaction conditions. Furthermore, we demonstrated that discodermolide is a competitive inhibitor with [3H]paclitaxel in binding to tubulin polymer, with an apparent Ki value of 0.4 microM. Multidrug-resistant human colon and ovarian carcinoma cells overexpressing P-glycoprotein, which are 900- and 2800-fold resistant to paclitaxel, respectively, relative to the parental lines, retained significant sensitivity to discodermolide (25- and 89-fold more resistant relative to the parental lines). Ovarian carcinoma cells that are 20-30-fold more resistant to paclitaxel than the parental line on the basis of expression of altered beta-tubulin polypeptides retained nearly complete sensitivity to discodermolide. The effects of discodermolide on the reorganization of the microtubules of Potorous tridactylis kidney epithelial cells were examined at different times. Intracellular microtubules were reorganized into bundles in interphase cells much more rapidly after discodermolide treatment compared with paclitaxel treatment. A variety of spindle aberrations were observed after treatment with both drugs. The proportions of the different types of aberration were different for the two drugs and changed with the length of drug treatment.
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PMID:The microtubule-stabilizing agent discodermolide competitively inhibits the binding of paclitaxel (Taxol) to tubulin polymers, enhances tubulin nucleation reactions more potently than paclitaxel, and inhibits the growth of paclitaxel-resistant cells. 938 24


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