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)

Trifluoperazine (TFP) is effective in modulating DNA damage/repair in doxorubicin (DOX) treated cells. In the present study we have characterised the resistance phenotype of parental sensitive L1210 mouse leukaemia cells (L1210/S) adapted to grow in the presence of 0.017 microns DOX+5 microM TFP (L1210/DT). Although with prolonged exposure, 0.017 microM DOX alone produced < 35% cell kill in L1210/S cells, similar cytotoxicity was achieved at 0.43 microM DOX in L1210/S cells selected in the presence of 0.017 microM DOX+5 microM TFP. L1210/DT cells were > 30-fold resistant to DOX following a 3 h drug exposure in a soft agar colony assay. In contrast, DOX sensitivity in cells adapted to grow in 5 microM TFP alone was comparable to L1210/S cells. Resistance to other inhibitors of topoisomerase II in L1210/DT cells was > 30-fold to etoposide and > 6-fold to amsacrine. The levels of the 170 kDa and 180 kDa isoforms of topoisomerase II in an immunoblot were comparable between the L1210/S and L1210/DT cells. Cross resistance to vincristine in the L1210/DT cells was accompanied by the overexpression of plasma membrane P-glycoprotein. Although a 1.5-2-fold decrease in accumulation of etoposide and DOX was observed in the L1210/DT cells, drug levels for equivalent DNA damage in the alkaline elution assay were > 5-fold higher in the L1210/DT versus L1210/S cells. No abrogation in the modulating effects of TFP on DOX, VP-16 or amsacrine induced cytotoxicity was apparent in the L1210/DT cells. Results suggest that: (a) TFP in combination with low concentrations DOX can induce the selection of cells with the multidrug resistant phenotype; and (b) characteristics of cells selected for resistance to DOX or DOX plus TFP are comparable.
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PMID:Calmodulin inhibitor trifluoperazine in combination with doxorubicin induces the selection of tumour cells with the multidrug resistant phenotype. 809 6

The H209/V6 cell line was derived from the H209 small cell lung cancer cell line by selection in etoposide (VP-16). Cytogenetic analysis indicates that the sensitive and resistant cell lines share 20 marker chromosomes and thus are clearly related. However, the H209/V6 cell line has four additional structurally altered chromosomes and a 2 N-modal chromosome number, while the H209 cell line is hypotetraploid (4 N-). H209/V6 cells are cross-resistant to some drugs that interact with topoisomerase II but not mitoxantrone. H209/V6 cells are also not cross-resistant to vincristine, trimetrexate, or cisplatin. The rates of VP-16 efflux are the same in the resistant and sensitive cell lines, which is consistent with the observation that P-glycoprotein mRNA is not detectable in either cell line. Fewer VP-16-induced DNA-protein complexes are observed in H209/V6 cells, and immunoblot analysis shows that levels of topoisomerase II alpha are reduced in H209/V6 cells compared to the sensitive H209 cells. Furthermore, the topoisomerase II alpha-related protein in H209/V6 cells has an increased electrophoretic mobility, with an apparent M(r) of 160,000. The levels of the topoisomerase II alpha 6.1-kilobase mRNA in H209/V6 cells are reduced > 10-fold. In addition, a second topoisomerase II alpha-related mRNA of approximately 4.8 kilobases is observed in H209/V6 cells but not in H209 cells. The quantity and electrophoretic mobility of the M(r) 180,000 topoisomerase II beta protein and its 6.1-kilobase mRNA are the same in the sensitive and resistant cell lines. The topoisomerase II strand-passing activity in H209/V6 nuclear extracts is reduced about 2-fold, but this activity is not more resistant to inhibition by VP-16 than the activity in H209 cells. However, band depletion immunoblot experiments show that the topoisomerase II alpha-related M(r) 160,000 protein in H209/V6 cells is not bound to DNA in the presence of concentrations of VP-16 that deplete the M(r) 170,000 topoisomerase II alpha in H209 cells and the M(r) 180,000 topoisomerase II beta in both the resistant and sensitive cells. We conclude that quantitative and qualitative alterations in topoisomerase II alpha have occurred in H209/V6 cells and are likely to contribute to its resistance phenotype.
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PMID:Altered topoisomerase II alpha in a drug-resistant small cell lung cancer cell line selected in VP-16. 810 87

In tumour cells the pharmacological basis for multidrug resistance (MDR) often appears to be a reduced cellular cytostatic drug accumulation caused by the drug efflux protein, P-glycoprotein (Pgp MDR), or by other drug transporters (non-Pgp MDR). Here we report the reversal of the decreased daunorubicin (DNR) accumulation in five non-Pgp MDR cell lines (GLC4/ADR, SW-1573/2R120, HT1080/DR4, MCF7/Mitox and HL60/ADR) by genistein. Genistein inhibited the enhanced DNR efflux in the GLC4/ADR cells. In these cells the decreased VP-16 accumulation was also reversed by genistein. Three other (iso)flavonoids biochanin A, apigenin and quercetin also increased the DNR accumulation in the GLC4/ADR cells. In contrast to the effects on non-Pgp MDR cells, 200 microM genistein did not increase the reduced DNR accumulation in three Pgp MDR cell lines (SW-1573/2R160, MCF7/DOX40 and KB8-5) or in the parental cell lines. In conclusion the use of genistein provides a means to probe non-Pgp related drug accumulation defects.
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PMID:Genistein modulates the decreased drug accumulation in non-P-glycoprotein mediated multidrug resistant tumour cells. 810 67

Previous reports from this laboratory have demonstrated that novobiocin produces supraadditive cytotoxicity and increases the formation of drug-stabilized topoisomerase II-DNA covalent complexes in WEHI-3B myelomonocytic leukemia and A549 lung carcinoma cells when combined with etoposide (VP-16). Inhibition of the efflux of VP-16 by novobiocin is responsible for the increase in VP-16 accumulation, which in turn leads to increased formation of VP-16-stabilized topoisomerase II-DNA covalent complexes and increased cytotoxicity. We now report that novobiocin synergistically enhanced the sensitivity of the multidrug resistant variants, WEHI-3B/NOVO and A549(VP)28, to VP-16, causing almost complete reversal of the resistance to the epipodophyllotoxin. These two tumor cell variants are resistant to several topoisomerase II-targeted drugs, particularly VP-16, but not to Vinca alkaloids; this finding corresponds to the fact that they do not overexpress the P-glycoprotein. The effects of novobiocin in these resistant sublines are mediated through the intracellular accumulation of VP-16, resulting in an increase in the formation of lethal VP-16-induced topoisomerase II-DNA covalent complexes. In the P-glycoprotein expressing multidrug resistant HCT116(VM)34 colon carcinoma and L1210/VMDRC0.06 leukemia cell lines, the latter being transfected with the human mdr-1 gene, novobiocin did not potentiate the cytotoxic activity of VP-16 nor increase the intracellular accumulation of VP-16 and the formation of covalent complexes, whereas their normal counterparts were sensitive to the potentiating activity of novobiocin when used in combination with VP-16. These results indicate that the action of novobiocin on the intracellular transport of VP-16 is not directed at the level of the P-glycoprotein, but that the action of novobiocin is antagonized by the presence of the P-glycoprotein. Since novobiocin is a clinically available antibiotic, has numerous structural analogues available for comparative studies, and has a relatively low toxicity profile, this drug, as well as structurally related agents, would appear to have significant clinical potential in combination with an epipodophyllotoxin for the treatment of non-P-glycoprotein expressing multidrug resistant tumors.
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PMID:Reversal of etoposide resistance in non-P-glycoprotein expressing multidrug resistant tumor cell lines by novobiocin. 810 48

K562 leukaemia cells were selected for resistance using 0.5 microM etoposide (VP-16). Cloned K/VP.5 cells were 30-fold resistant to growth inhibition by VP-16 and 5- to 13-fold resistant to m-AMSA, adriamycin and mitoxantrone. K/VP.5 cells did not overexpress P-glycoprotein; VP-16 accumulation was similar to that in K562 cells. VP-16-induced DNA damage was reduced in cells and nuclei from K/VP.5 cells compared with K562 cells. Topoisomerase II protein was reduced 3- to 7-fold and topoisomerase II alpha and topoisomerase II beta mRNAs were each reduced 3-fold in resistant cells. After drug removal, VP-16-induced DNA damage disappeared 1.7 times more rapidly and VP-16-induced DNA-topoisomerase II adducts dissociated 1.5 times more rapidly in K/VP.5 cells than in K562 cells. ATP (1 mM) was more effective in enhancing VP-16-induced DNA damage in nuclei isolated from sensitive cells than in nuclei from resistant cells. In addition, ATP (0.3-5 mM) stimulated VP-16-induced DNA-topoisomerase II adducts to a greater extent in K562 nuclei than in K/VP.5 nuclei. Taken together, these results indicate that resistance to VP-16 in a K562 subline is associated with a quantitative reduction in topoisomerase II protein and, in addition, a distinct qualitative alteration in topoisomerase II affecting the stability of drug-induced DNA-topoisomerase II complexes.
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PMID:Altered stability of etoposide-induced topoisomerase II-DNA complexes in resistant human leukaemia K562 cells. 814 56

Simultaneous occurrence of resistance to many chemotherapeutic agents, termed multidrug resistance (MDR), is a complex phenotype. MDR occurs due to several reasons, including over-expression of a 170-kDa membrane-bound protein, called P-glycoprotein (P-gp), which apparently participates in active drug efflux. Multidrug-resistant cells also frequently exhibit an altered pattern of intracellular drug distribution, resulting in a reduction in the nuclear level of drugs such as doxorubicin (DOX). In this study, the effect of dipyridamole (DP) on drug resistance and on intracellular as well as nuclear levels of DOX in multidrug-resistant melanoma cells has been examined. For this purpose, drug-sensitive murine melanoma cells (B16V) and their multidrug-resistant variant cells, (B16VDXR; selected for resistance to DOX) which over-produce P-gp, were employed. B16VDXR cells were cross-resistant to several anti-cancer agents including etoposide (VP-16) and mitoxantrone (Mitox). DP (10 microM) significantly potentiated the cytotoxicity of DOX, VP-16 and Mitox towards multidrug-resistant B16VDXR cells but not in parental drug-sensitive B16V cells. The presence of DP resulted in a 3.7-fold increase in the total cellular level and a 4.2-fold increase in the nuclear content of DOX in the resistant cells. Isobologram analysis indicates that DP at several pharmacologically relevant concentrations synergistically potentiates the activity of DOX in B16VDXR cells.
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PMID:Dipyridamole modulates multidrug resistance and intracellular as well as nuclear levels of doxorubicin in B16 melanoma cells. 826 66

Amplification of the gene encoding multidrug resistance-associated protein (MRP) and overexpression of its cognate mRNA have been detected in multidrug-resistant cell lines derived from several different tumor types. To establish whether or not the increase in MRP is responsible for drug resistance in these cell lines, we have transfected HeLa cells with MRP expression vectors. The transfectants display an increase in resistance to doxorubicin that is proportional to the levels of a M(r) 190,000, integral membrane protein recognized by anti-MRP antibodies. The transfectants are also resistant to vincristine and VP-16 but not to cisplatin. The results demonstrate that MRP overexpression confers a multidrug resistance phenotype similar to that formerly associated exclusively with elevated levels of P-glycoprotein.
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PMID:Overexpression of multidrug resistance-associated protein (MRP) increases resistance to natural product drugs. 827 68

A drug-resistant human small cell lung cancer cell line, H209/V6, selected in the presence of increasing concentrations of 9-(4,6-O-ethylidene-beta-D-glucopyranosyl)-4'-demethylepipodophylloto xin (VP-16) from parental H209 cells, is 22-, 9-, and 4-fold resistant to VP-16, 4'-(9-acridinyl-amino)methanesulfon-m-anisidide, and doxorubicin, respectively, but not cross-resistant to 1,4-dihydroxy-5,8-bis((2-[(2-hydroxyethyl)amino] ethyl]-amino)-9,10-anthracenedione. These cells do not overexpress P-glycoprotein or the multidrug resistance-associated protein. Immunoblotting demonstrates that H209 cells contain the M(r) 170,000 isoform of topoisomerase II (topo II), while H209/V6 cells have a M(r) 160,000 enzyme but none of the M(r) 170,000 isoform. The cell lines have equal amounts of topo II beta. The H209/V6 cells have a 5-fold decrease in total immunoreactive topo II alpha. The catalytic and VP-16-induced DNA cleavage activities of the topo II present in 0.35 M NaCl nuclear extracts are decreased 2- to 3-fold in the drug-resistant cell line. This decrease in enzymatic activity is not consistent with either the 22-fold VP-16 resistance of the H209/V6 cell line or the approximately 5-fold decrease in immunoreactive topo II alpha in the cells. The M(r) 160,000 isoform from the H209/V6 cell line and the M(r) 170,000 enzyme from the parental cell line were purified so that the enzymatic activity of the 2 isoforms could be evaluated. The catalytic activities of the purified isoforms were found to be very similar. The drug-induced DNA cleavage activity of the M(r) 160,000 enzyme was reduced compared to the M(r) 170,000 enzyme. However, as with the nuclear extracts, the differences in enzymatic activity of the purified enzymes are considerably less than the level of drug resistance. Investigations of the subcellular localization of topo II by immunocytochemical techniques and cytoplasm/nuclear fractionation studies demonstrated that the M(r) 160,000 topo II alpha-related enzyme is primarily localized in the cytoplasm, while the M(r) 170,000 topo II alpha enzyme and topo II beta are located in the nucleus. These data imply that the deleted sequence in the M(r) 160,000 enzyme is not necessary for catalytic activity but is required to facilitate nuclear localization.
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PMID:Altered subcellular distribution of topoisomerase II alpha in a drug-resistant human small cell lung cancer cell line. 830 38

The Adriamycin-resistant small cell lung carcinoma cell line, GLC4/ADR, showed large differences in cross-resistance to drugs such as Adriamycin, etoposide (VP-16), teniposide (VM-26), 4'-(9-acridinylamino)-methanesulfon-m-anisidide (m-AMSA), and mitoxantrone, which stimulate the formation of topoisomerase (Topo) II-DNA complexes. GLC4/ADR cells demonstrated a reduced Topo II activity and no detectable levels of the P-glycoprotein compared to the parental GLC4 cells (S. De Jong et al., Cancer Res., 50: 304-309, 1990). In the present study, the resistance to VM-26 (59.5-fold) and to m-AMSA (4-fold) of GLC4/ADR after a 1-h incubation was further analyzed. Using the K(+)-sodium dodecyl sulfate precipitation assay, a reduction in VM-26- and m-AMSA-induced cleavable complex formation was found in GLC4/ADR cells compared to GLC4 cells that was related to the degree of resistance to each drug. Cellular accumulation of the VM-26 analogues VP-16 was 3- to 8-fold less and the accumulation of m-AMSA 1- to 2-fold less in GLC4/ADR cells than in the parental cells. Following the removal of VM-26, the cleavable complexes in GLC4/ADR cells disappeared at least 2-fold faster than in GLC4 cells, while the efflux of VP-16 was also enhanced in the resistant cells. On the contrary, no differences in cleavable complex disappearance or drug efflux between these cell lines were observed with m-AMSA. Efflux of both drugs, however, occurred at a much higher rate than cleavable complex disappearance. Using isolated nuclei, a reduction in cleavable complexes in GLC4/ADR was still observed with VM-26 as well as m-AMSA compared to GLC4. The resistant nuclei and nuclear extracts showed a 3-fold decrease in M(r) 170,000 Topo II by immunoblotting. No differences in cleavable complex formation were found between nuclear extracts of both cell lines, when the Topo II activities were equalized. These findings suggest that the cross-resistance to m-AMSA is due to a decreased amount of Topo II and decreased drug accumulation, while in addition to these mechanisms an increased rate of cleavable complex disappearance is involved in the cross-resistance to VM-26 of the GLC4/ADR cell line.
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PMID:Topoisomerase II as a target of VM-26 and 4'-(9-acridinylamino)methanesulfon-m-aniside in atypical multidrug resistant human small cell lung carcinoma cells. 838 51

This study examined whether levels of estrogen receptor (ER), progesterone receptor (PR), and expression of estrogen regulated pS2 and/or heat shock protein (hsp) 27 were associated with drug resistance in a series of MCF-7 sublines expressing modest (i.e. 3- to 14-fold), yet clinically relevant, levels of resistance to vincristine (VCR). These sublines were variously derived following pulsed exposures to VCR, to fractionated X-irradiation, or to alternating drug and X-ray treatments. This selection procedure more closely reflects the clinical treatment of breast tumors than the use of continuous drug exposures. The drug-selected sublines exhibited the classical multidrug resistance phenotype (MDR) characterized by cross-resistance to vinblastine (VLB), etoposide (VP-16), and Adriamycin (ADR), overexpression of P-glycoprotein (Pgp), impaired accumulation of [3H]-VCR and of Rhodamine-123 (Rh 123), and altered activities of certain drug detoxification enzymes. This classic MDR phenotype was associated with a lack of mitogenic response to estrogen or antiestrogen, related to loss of detectable ER and PR; consistent with these data, neither pS2 nor hsp27 expression was detectable. In contrast, X-ray-pretreated VCR-resistant cells (MCF/DXR-10) cells exhibited a distinctive resistance phenotype proving cross-resistant to VLB and VP-16 but not to ADR, and Pgp overexpression was not detectable. Furthermore, these VCR-resistant DXR-10 cells retained parental levels of ER and PR, exhibited sensitivity to estrogen and 4-hydroxytamoxifen, and expressed detectable levels of pS2 and hsp27. Comparable characteristics to these MCF-7/DXR-10 cells were also identified in a similarly-derived X-ray-pretreated VCR-resistant subline of the ZR-75-1 human breast tumor cell line. These data therefore indicate that functional ER are frequently, but not invariably, modified in tumor cells which express resistance to multiple drugs.
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PMID:Differential expression of steroid receptors, hsp27, and pS2 in a series of drug resistant human breast tumor cell lines derived following exposure to antitumor drugs or to fractionated X-irradiation. 840 Mar 21


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