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)

The epothilones (Epos) are a group of natural products isolated from the myxobacterium, Sorangium cellulosum. They have a mechanism of action similar to that of Taxol, i.e., they stabilize microtubules and induce the formation of microtubule bundles in cells. Because they are simpler in structure than Taxol and preserve their activity in P-glycoprotein-expressing cells, they are being studied as potential antitumor drugs. In this work, a series of Epo-resistant A549 and HeLa cell lines have been selected and analyzed. Class I beta-tubulin, the major isotype of beta-tubulin in these Epo-resistant cell lines, has been sequenced in a search for mutations. In the Epo B-resistant A549 cells, there is a mutation at beta 292 from Gln to Glu, in the Epo A-resistant HeLa cell line there is a mutation at beta 173 from Pro to Ala, and in the Epo B-resistant HeLa cell line there is a heterozygous mutation at beta 422 from Tyr to a mixture of Tyr and Cys. These mutations are close to the M-loop, the nucleotide-binding site, and the microtubule-associated protein binding sites, respectively. It is likely that these mutations in beta-tubulin provide cells with a mechanism of resistance to the Epos and taxanes. Among these resistant cell lines, A549.EpoB40 is hypersensitive to microtubule-destabilizing drugs, such as vinblastine and colchicine, and HeLa.EpoB1.8 is dependent on the Epos or taxanes for growth. Our studies provide evidence that the M-loop, the GTP binding site, and the microtubule-associated protein binding sites at the COOH terminus in beta-tubulin are critical for the regulation of microtubule stability.
 ...
PMID:Mutations in beta-tubulin map to domains involved in regulation of microtubule stability in epothilone-resistant cell lines. 1246 33

Inappropriate expression of the multidrug resistance (MDR1) gene encoding the P-glycoprotein (Pgp) has been frequently implicated in resistance to different chemotherapeutic drugs. We have previously generated chronic myeloid leukemia (CML) cell lines resistant to the tyrosine kinase inhibitor imatinib mesylate (STI571), and one line (LAMA84-r) showed overexpression not only of the Bcr-Abl protein but also of Pgp. In the present study, we investigated this phenomenon in other cell lines overexpressing exclusively Pgp. Thus, cells from the K562/DOX line, described as resistant to doxorubicin due to MDR1 gene overexpression, grew continuously in the presence of 1 microM imatinib, but died in 4 to 5 days if the Pgp pump modulators verapamil or PSC833 were added to the imatinib-treated culture. Analysis of cell proliferation by the MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) assay confirmed the differential sensitivity of K562/DOX to imatinib, which was also reversed by verapamil or PSC833. Flow cytometric analysis of the total phosphotyrosine content by intracytoplasmic staining after a 2-hour incubation with escalating doses of imatinib showed that the inhibitory concentrations of 50% (IC(50)) for inhibition of cellular protein tyrosine phosphorylation were 15, 10, and 5 microM for K562/DOX, K562/DOX plus verapamil, and K562, respectively. Retroviral-mediated transfection of the BCR-ABL(+) AR230 cell line with the MDR1 gene decreased its sensitivity to imatinib, an effect that was also reversed by verapamil. The possible role of MDR overexpression in clinical resistance to imatinib remains to be defined. We therefore confirm that imatinib should be added to the extensive list of drugs that can be affected by the MDR phenomenon.
 ...
PMID:MDR1 gene overexpression confers resistance to imatinib mesylate in leukemia cell line models. 1286 89

STI571, an Abl-specific tyrosine kinase inhibitor, selectively kills Bcr-Abl-containing cells in vitro and in vivo. However, some chronic myelogenous leukemia (CML) cell lines are resistant to STI571. We evaluated whether STI571 interacts with P-glycoprotein (P-gp) and multidrug resistance protein 1 (MRP1), and examined the effect of agents that reverse multidrug resistance (MDR) on the resistance to SI571 in MDR cells. STI571 inhibited the [(125)I]azidoagosterol A-photolabeling of P-gp, but not that of MRP1. K562/MDR cells that overexpress P-gp were 3.67 times more resistant to STI571 than the parental Philadelphia-chromosome-positive (Ph +) CML K562 cells, and this resistance was most effectively reversed by cepharanthine among the tested reversing agents. The concentration of STI571 required to completely inhibit tyrosine phosphorylation in K562/MDR cells was about 3 times higher than that in K562 cells, and cepharanthine abolished the difference. In KB-G2 cells that overexpress P-gp, but not Bcr-Abl, 2.5 micro M STI571 partly reversed the resistance to vincristine (VCR), paclitaxel, etoposide (VP-16) and actinomycin D (ACD) but not to Adriamycin (ADM) or colchicine. STI571 increased the accumulation of VCR, but not that of ADM in KB-G2 cells. STI571 did not reverse resistance to any agent in KB/MRP cells that overexpress MRP1. These findings suggest that STI571 is a substrate for P-gp, but is less efficiently transported by P-gp than VCR, and STI571 is not a substrate for MRP1. Among the tested reversing agents that interact with P-gp, cepharanthine was the most effective agent for the reversal of the resistance to STI571 in K562/MDR cells. Furthermore, STI571 itself was a potent reversing agent for MDR in P-gp-expressing KB-G2 cells.
 ...
PMID:Reversal of the resistance to STI571 in human chronic myelogenous leukemia K562 cells. 1282 82

Elevated expression of multidrug efflux pumps such as P-glycoprotein (Pgp) have been associated with resistance to cytotoxic drugs used in the treatment of leukemias and other cancers. Imatinib mesylate (STI-571 or Gleevec) is a potent inhibitor of the BCR/ABL and c-KIT tyrosine kinases. It has displayed considerable efficacy in treatment of patients with Philadelphia-positive acute lymphoblastic leukemia and chronic myelogenous leukemia and those with gastrointestinal stromal tumors (GISTs). However, recently imatinib-resistant relapse has emerged as a significant problem. Although a major cause of resistance appears to be point mutation in the kinase domain of the target enzyme, the potential contribution of elevated multidrug efflux activity has not been systematically evaluated. The imatinib-sensitive human leukemic cell line K562, which is dependent on the activity of BCR/ABL for survival and growth, provides a convenient system for evaluating modulation of drug activity. By expressing Pgp at high levels in these cells, we have demonstrated that this pump provides minimal protection against cell growth inhibition and apoptosis induced by imatinib. In contrast, overexpression of Bcl-xL, which blocks apoptosis, resulted in partial protection against the drug. We conclude that Pgp up-regulation is not likely to be a significant contributor to imatinib resistance.
 ...
PMID:Overexpression of P-glycoprotein in K562 cells does not confer resistance to the growth inhibitory effects of imatinib (STI571) in vitro. 1288 21

Immunophenotyping of acute and chronic leukaemias has revealed many lineage- and differentiation-specific antigens. It has now become possible to classify leukaemias according to their unique antigenic expression pattern. Among many lineage- and differentiation-specific antigens, disease-specific antigens are increasingly recognized because of their specific prognostic or therapeutic relevance. Expression of the multidrug resistance proteins of the ABC transporter family is associated with a poor response to treatment and a grave clinical prognosis. Recently, attempts to reverse refractory disease by using P-glycoprotein inhibitors have been performed in acute myeloid leukaemia, so far without evidence of clinical benefit. Other new leads to use antigen expression as a way of designing tumour-specific therapy have resulted in imatinib and Flt3 inhibitors which target tyrosine kinases in the leukaemic cell. Clinical trials are underway to investigate the effect of these new agents. The development of an antibody-calicheamycin complex directed against the myeloid-specific antigen CD33 has shown clinical activity in patients with relapsed acute myeloid leukaemia. The further development of these approaches is discussed.
 ...
PMID:Immunophenotyping as a guide for targeted therapy. 1459 47

The most common cause of cystic fibrosis is misfolding of the cystic fibrosis transmembrane conductance regulator (CFTR) protein because of deletion of residue Phe-508 (DeltaF508). P-glycoprotein (P-gp) is an ideal model protein for studying how mutations disrupt folding of ATP-binding cassette proteins such as CFTR because specific chemical chaperones can be used to correct folding defects. Interactions between the nucleotide binding domains (NBDs) are critical because ATP binds at the interface between the NBDs. Here, we used disulfide cross-linking between cysteines in the Walker A sites and the LSGGQ signature sequences to test whether processing mutations located throughout P-gp disrupted interactions between the NBDs. We found that mutations present in the cytoplasmic loops, transmembrane segments, and linker regions or deletion of Tyr-490 (equivalent to Phe-508 in CFTR) inhibited cross-linking between the NBDs. Deletion of Phe-508 in the P-gp/CFTR chimera also inhibited cross-linking between the NBDs. Cross-linking was restored, however, when the mutants were expressed in the presence of the chemical chaperone cyclosporin A. The "rescued" mutants exhibited drug-stimulated ATPase activity, and cross-linking between the NBDs was inhibited by vanadate trapping of nucleotide. These results together with our previous findings (Loo, T. W., Bartlett, M. C., and Clarke, D. M. (2002) J. Biol. Chem. 277, 27585-27588) indicate that processing mutations disrupt interactions among all four domains. It appears that cross-talk between the cytoplasmic and the transmembrane domains is required for establishment of proper domain-domain interactions that occur during folding of ATP-binding cassette protein transporters.
 ...
PMID:Processing mutations located throughout the human multidrug resistance P-glycoprotein disrupt interactions between the nucleotide binding domains. 1524 15

Multidrug resistance (MDR) is a phenomenon by which cancer cells evade the cytotoxic effects of chemotherapeutic agents. It may occur through different mechanisms, but it often correlates with the overexpression of integral membrane transporters, such as P-glycoprotein (Pgp) and MDR-associated proteins (MRPs), with resulting decrease of drug accumulation and cellular death. Doxorubicin is a substrate of Pgp; it has been suggested that its ability to induce synthesis of nitric oxide (NO) could explain, at least in part, its cytotoxic effects. Culturing the human epithelial colon cell line HT29 in the presence of doxorubicin, we obtained a doxorubicin-resistant (HT29-dx) cell population: these cells accumulated less intracellular doxorubicin, were less sensitive to the cytotoxic effects of doxorubicin and cisplatin, overexpressed Pgp and MRP3, and exhibited a lower NO production (both under basal conditions and after doxorubicin stimulation). The resistance to doxorubicin could be reversed when HT29-dx cells were incubated with inducers of NO synthesis (cytokines mix, atorvastatin). Some NO donors increased the drug accumulation in HT29-dx cells in a guarosine-3':5'-cyclic monophosphate-independent way; this effect was associated with a marked reduction of doxorubicin efflux rate in HT29 and HT29-dx cells, and tyrosine nitration in the MRP3 protein. Our results suggest that onset of MDR and impairment of NO synthesis are related; this finding could point to a new strategy to reverse doxorubicin resistance in human cancer.
 ...
PMID:Nitric oxide reverts the resistance to doxorubicin in human colon cancer cells by inhibiting the drug efflux. 1569 94

Human malignant mesothelioma (HMM) is resistant to many anticancer drugs, including doxorubicin. Mevastatin and simvastatin, 2 inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMGCoA) reductase, potentiated the intracellular accumulation and the cytotoxicity of doxorubicin in HMM cells constitutively expressing P-glycoprotein and multidrug resistance-associated protein 3. This effect of statins was nitric oxide (NO)-dependent, since it was reverted by either an NO synthase inhibitor or an NO scavenging system. The NO synthase up-regulation in HMM and other cells is known to be associated with the activation of the transcription factor NF-kappaB: in HMM cells statins increased the NF-kappaB translocation into the nucleus, decreased the level of the NF-kappaB inhibitor IkBalpha and increased the phosphorylation/activation of IkB kinase alpha (IKKalpha). IKKalpha is under the negative control exerted by RhoA in its prenylated (active) form: incubation of HMM cells with statins lowered the amount of active RhoA and the level of Rho-associated kinase activity. All statins' effects were reverted by mevalonic acid, thus suggesting that they were mediated by the inhibition of HMGCoA reductase and were likely to be subsequent to the reduced availability of precursor molecules for RhoA prenylation. Both the Rho kinase inhibitor Y27632 and the RhoA inhibitor toxin B (from Clostridium difficile) mimicked the statins' effects, enhancing doxorubicin accumulation, NO synthesis and IKKalpha phosphorylation and decreasing the amount of IkBalpha in HMM cells. Simvastatin, Y27632 and toxin B elicited tyrosine nitration in the P-glycoprotein, thus providing a likely mechanism by which NO reverts the doxorubicin resistance in HMM cells.
 ...
PMID:Statins revert doxorubicin resistance via nitric oxide in malignant mesothelioma. 1645 Mar 90

Alteration of the epidermal growth factor (EGF) signaling pathway occurs frequently in human cancer cells and may subsequently affect the cell survival towards anti-cancer agents. To elucidate the effect of long-term EGF treatment on the chemo-sensitivity of human cancer cells, human squamous carcinoma A431 cells (AP) were incubated continuously with 50 ng/ml EGF for 30 weeks and these cells were designated as the AC cells. The long-term EGF treatment did not alter the EGFR level and the EGF-induced protein tyrosine phosphorylation pattern in the AC cells. By MTT assay, the AC cells were shown to be more resistant than the AP cells to doxorubicin, etoposide and amsacrine but not to cisplatin. Among the drug-resistant proteins, topoisomerase IIalpha (topoII) was downregulated in the AC cells while there was no apparent change in the levels of P-glycoprotein, MRP-1 or glutathione- S-transferase-pi as compared to the AP cells. Furthermore, knockdown of topoII by antisense topoII oligonucleotide transfection decreased the sensitivity to doxorubicin, etoposide and amsacrine in the A431 cells. Results from the present study support an idea that long-term treatment with EGF may induce drug resistance in cells through the downregulation of topoII.
 ...
PMID:Epidermal growth factor induction of resistance to topoisomerase II toxins in human squamous carcinoma A431 cells. 1696 95

Microtubules are crucial targets for cancer chemotherapeutic drugs, and new microtubule-directed agents are of continued interest in drug development. A novel microtubule-directed agent, ethyl-2-[N-rho-chlorobenzyl-(2'-methoxy)]-anilino-4-oxo -4, 5-dihydro-furan-3-carboxylate, was identified. The compound, designated K2154, inhibited cell proliferation, with IC(50) values of 10.3, 15.3, 9.6, 11.2, 12.8 and 12.1 muM in prostate cancer PC-3, hepatocellular carcinoma Hep3B, non-small cell lung cancer A549, colorectal cancer HT29 and HCT116, and P-glycoprotein-rich breast cancer NCI/ADR-RES cells, respectively. Because NCI/ADR-RES cells were susceptible to inhibition by K2154, it indicated that this compound is a poor substrate for P-glycoprotein. In this study, PC-3 cells were used to identify the anticancer mechanisms of K2154. K2154 induced an arrest of the cell cycle at G2/M phase and a subsequent increase of hypodiploid phase in PC-3 cells, whereas it only induced a moderate level of G2/M arrest with little increase of hypodiploid phase in normal prostate cells. K2154 inhibited microtubule assembly in both in vitro turbidity assay and in vivo microtubule spin-down experiment. Immunochemical examination showed that K2154 caused formation of abnormal mitotic characteristics with bipolar spindles, particularly, in beta(II)- and beta(III)-tubulin staining. It also induced several pathways, including cyclin B1 up-regulation, dephosphorylation on Tyr(15) and phosphorylation on Thr(161) of Cdk1 and Cdc25C phosphorylation, and roscovitine (a Cdk1 inhibitor) significantly inhibited K2154-induced apoptosis, suggesting a pro-apoptotic role of Cdk1. Phosphorylation of Bcl-2 and Bcl-xL and cleavage of Mcl-1, together with activation of caspase-9 and -3, indicated that mitochondrial pathway played a central role in K2154-mediated apoptotic cell death. Additionally, AIF contributed to a late phase of K2154-induced apoptotic pathway. In conclusion, it is suggested that K2154 displays an anticancer activity through a target on microtubules and a subsequent signaling cascade on cell cycle regulation and apoptotic machinery.
 ...
PMID:Investigation of anti-tumor mechanisms of K2154: characterization of tubulin isotypes, mitotic arrest and apoptotic machinery. 1710 38


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