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)

There are two broad categories of drug resistance encountered during cancer chemotherapy, i.e. intrinsic and acquired. They are observed in virtually every type of tumor with every known anticancer chemotherapeutic drug. As such there is an urgent need to develop innovative approaches of preventing or reversing these types of resistance. One strategy to do so is to develop completely new drugs which may be resistance free, such as direct acting angiogenesis inhibitors (T. Boehm, J. Folkman, T. Browder, M.S. O'Reilly, Antiangiogenic therapy of experimental cancer does not induce acquired drug resistance, Nature 390 (1997) 404-407; R.S. Kerbel, Inhibition of tumor angiogenesis as a strategy to circumvent acquired resistance to anti-cancer therapeutic agents, BioEssays 13 (1991) 31-36; R.S. Kerbel, A cancer therapy resistant to resistance, Nature 390 (1997) 335-336). Another is to devise methods which will improve significantly the effectiveness of those conventional drugs already in use, such as adriamycin, cyclophosphamide and taxol. We have directed efforts towards the latter. They depend on the discovery of a new class of chemosensitizers which act as antiadhesive agents rendering solid tumors more susceptible to such conventional cytotoxic therapeutic drugs. Examples of this concept are illustrated with bovine testicular hyaluronidase and a mouse mammary tumor called EMT-6. When this enzyme preparation is used to treat intact multicellular spheroids of the EMT-6 tumor, the spheroids are substantially disaggregated. Dispersed spheroids are more susceptible to the cytotoxic effects of cyclophosphamide than intact spheroids. Moreover, this antiadhesive chemosensitizing effect can actually be reproduced in BALB/c mice when EMT-6 cells are grown intraperitoneally as an ascites tumor (consisting mostly of multicellular aggregates) and the mice are given injections of hyaluronidase and cyclophosphamide. In a similar fashion, the indifference of P-glycoprotein-positive multidrug-resistant EMT-6 spheroids to the P-glycoprotein reversal agent PSC-833 (a cyclosporin A analogue) can be reversed by disaggregation of the intact spheroids by hyaluronidase. This renders the treated cells highly sensitive to a combination of adriamycin and PSC-833 in a manner similar to the striking chemosensitization effects commonly observed in monolayer culture systems. Thus, hyaluronidase has the potential to reverse forms of both intrinsic and acquired drug resistance in solid tumors, such as EMT-6, which are sensitive to its antiadhesive effects.
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PMID:Reversal of intrinsic and acquired forms of drug resistance by hyaluronidase treatment of solid tumors. 983 18

Targeting the tyrosine kinase activity of Bcr-Abl with STI571 is an attractive therapeutic strategy in chronic myelogenous leukemia (CML). A few CML cell lines and primary progenitors are, however, resistant to this compound. We investigated the mechanism of this resistance in clones of the murine BaF/3 cells transfected with BCR-ABL and in 4 human cell lines from which sensitive (s) and resistant (r) clones were generated by various methods. Although the resistant cells were able to survive in the presence of STI571, their proliferation was approximately 30% lower than that of their sensitive counterparts in the absence of the compound. The concentration of STI571 needed for a 50% reduction in viable cells after a 3-day exposure was on average 10 times higher in the resistant (2-3 micromol/L) than in the sensitive (0.2-0.25 micromol/L) clones. The mechanism of resistance to STI571 varied among the cell lines. Thus, in Baf/BCR-ABL-r, LAMA84-r, and AR230-r, there was up-regulation of the Bcr-Abl protein associated with amplification of the BCR-ABL gene. In K562-r, there was no Bcr-Abl overexpression, but the IC(50) for the inhibition of Bcr-Abl autophosphorylation was increased in the resistant clones. Sequencing of the Abl kinase domain revealed no mutations. The multidrug resistance P-glycoprotein (Pgp) was overexpressed in LAMA84-r, indicating that at least 2 mechanisms of resistance operate in this cell line. KCL22-r showed neither Bcr-Abl up-regulation nor a higher threshold for tyrosine kinase inhibition by STI571. We conclude that BCR-ABL-positive cells can evade the inhibitory effect of STI571 by different mechanisms, such as Bcr-Abl overexpression, reduced intake mediated by Pgp, and, possibly, acquisition of compensatory mutations in genes other than BCR-ABL.
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PMID:Selection and characterization of BCR-ABL positive cell lines with differential sensitivity to the tyrosine kinase inhibitor STI571: diverse mechanisms of resistance. 1091 Sep 24

Chronic myeloid leukaemia (CML) is characterized by marked expansion of the myeloid series, and is thought to arise as a direct result of the bcr-abl fusion-gene. The BCR-ABL oncoprotein is a constitutively active protein tyrosine kinase (PTK), which results in altered cell signalling and is responsible for the changes that characterize the malignant cells of CML. It has been shown that the increased tyrosine kinase activity of BCR-ABL is a requirement for transformation and is, therefore, a legitimate target for pharmacological inhibition. Several compounds have now been identified as relatively selective inhibitors of BCR-ABL, including members of the tyrphostin family, herbimycin A and most importantly the 2-phenylaminopyrimidine ST1571. Having established the efficacy of this agent in vitro, phase I trials using an oral formulation were commenced in the USA in mid 1998. Early data from an interferon-alpha (IFN) resistant/refractory or intolerant cohort demonstrated good patient tolerance and effective haematological control at doses above 300 mg. More promising was its ability to induce cytogenetic responses in this pretreated group of patients. Phase II data, albeit far from complete, appear to confirm its efficacy even in the context of advanced disease and phase III clinical trials are currently underway in many countries. Recent laboratory evidence, however, suggests that the development of drug resistance is a possibility (via amplification of the bcr-abl fusion gene, overexpression of P-glycoprotein or binding of ST1571 to alpha1 acid glycoprotein) and that combination therapy including ST1571 should be considered.
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PMID:Tyrosine kinase inhibitors in the treatment of chronic myeloid leukaemia: so far so good? 1140 8

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.
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PMID:MDR1 gene overexpression confers resistance to imatinib mesylate in leukemia cell line models. 1286 89

Imatinib (Glivec), STI571) is an intracellular acting drug that demonstrates high activity against BCR-ABL-positive chronic myelogenous leukemia (CML) or acute lymphoblastic leukemia (ALL). However, many patients, especially with advanced disease, develop drug resistance. Here, we show by a novel high-performance liquid chromatography-based method that intracellular levels of imatinib decrease in P-glycoprotein (Pgp)-positive leukemic cells. In a model of K562 cells with gradually increasing Pgp expression, a Pgp-dependent decline of intracellular imatinib levels was observed. Decreased imatinib levels were associated with a retained phosphorylation pattern of the Bcr-Abl target Crkl and loss of effect of imatinib on cellular proliferation and apoptosis. The modulation of Pgp by cyclosporin A (CSA) readily restored imatinib cytotoxicity in these cells. Finally, we provide first data showing a biological effect of Pgp modulation in the imatinib treatment of a patient with BCR-ABL-positive ALL. MDR1 overexpression must therefore be considered as an important clinical mechanism in the diversity of resistance development to imatinib treatment.
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PMID:P-glycoprotein-mediated drug efflux is a resistance mechanism of chronic myelogenous leukemia cells to treatment with imatinib mesylate. 1472 52

Chemotherapeutic agents have been used for the treatment of patients with osteosarcoma (OS). However, inherent or acquired resistance to these agents is a serious problem in the management of OS patients. The emergence of the multidrug resistance (MDR) phenotype in cancer cells is often associated with the overexpression of P-glycoprotein, encoded by the multidrug resistance gene MDR-1. The administration of some of the most common chemotherapeutic agents to these cells becomes ineffective because of their P-gp-driven efflux from the cell. Apo2L/TRAIL is a member of the tumor necrosis factor (TNF) family of cytokines that is considered to induce death of cancer cells but not normal cells. Its powerful apoptotic activity is mediated through its cell surface death domain-containing receptors, TRAIL-R1/DR4 and TRAIL-R2/DR5, which in turn spread the signal in the cytosol through the activation of the caspase cascade. The Akt/PKB kinase is an important cell survival protein which is regulated by D3-phosphoinositides. High Akt expression and activity levels are well documented in many types of tumors, which very often show an altered PI3-K/Akt/PTEN pathway. In this study the U2OS human osteosarcoma cell line and its multidrug resistant (MDR) subline that overexpresses MDR-1 gene, MDR-U2OS, have been analyzed for their responsiveness to TRAIL. In conflict with the presence of active DR4 and DR5 receptors in both clones, U2OS cells exhibited only a low responsiveness to TRAIL, while the MDR-U2OS subline did exhibit a marked TRAIL sensitivity. An analysis of the post-receptor events showed that TRAIL responsiveness correlates with a reduced expression of endogenous Akt. In fact, expression in MDR-U2OS cells of a constitutively active Akt strongly decreased their sensitivity to TRAIL. The identification of Akt as a key modulator of TRAIL responsiveness could help to design TRAIL-based combinations for treatment of osteosarcoma. Moreover, the discovery that multidrug resistant osteosarcomas are highly sensitive to TRAIL-induced apoptosis indicates TRAIL as a new candidate for the treatment of multidrug resistant bone malignancies.
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PMID:Sensitization of multidrug resistant human ostesarcoma cells to Apo2 Ligand/TRAIL-induced apoptosis by inhibition of the Akt/PKB kinase. 1554 96

Overexpression of BCR-ABL and P-glycoprotein (Pgp) are two of the known mechanisms of imatinib resistance. As combination therapy may allow to overcome drug resistance, we investigated the effect of combination treatment with imatinib and 17-allylamino-17-demethoxygeldanamycin (17-AAG), a heat-shock protein 90 (Hsp90) inhibitor, on different imatinib-sensitive and imatinib-resistant CML cell lines. In imatinib-sensitive cells, combination index (CI) values obtained using the method of Chou and Talalay indicated additive (CI=1) or marginally antagonistic (CI>1) effects following simultaneous treatment with imatinib and 17-AAG. In imatinib-resistant cells both drugs acted synergistically (CI<1). In primary chronic-phase CML cells additive or synergistic effects of the combination of imatinib plus 17-AAG were discernible. Annexin V/propidium iodide staining showed that the activity of imatinib plus 17-AAG is mediated by apoptosis. Combination treatment with imatinib plus 17-AAG was more effective in reducing the BCR-ABL protein level than 17-AAG alone. Monotherapy with 17-AAG decreased P-glycoprotein activity, which may increase intracellular imatinib levels and contribute to the sensitization of CML cells to imatinib. The results suggest that combination of imatinib and 17-AAG may be useful to overcome imatinib resistance in a clinical setting.
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PMID:Synergistic activity of imatinib and 17-AAG in imatinib-resistant CML cells overexpressing BCR-ABL--Inhibition of P-glycoprotein function by 17-AAG. 1590 98

Central nervous system (CNS) relapse accompanying the prolonged administration of imatinib mesylate has recently become apparent as an impediment to the therapy of Philadelphia chromosome-positive (Ph+) leukemia. CNS relapse may be explained by limited penetration of imatinib mesylate into the cerebrospinal fluid because of the presence of P-glycoprotein at the blood-brain barrier. To overcome imatinib mesylate-resistance mechanisms such as bcr-abl amplification, mutations within the ABL kinase domain, and activation of Lyn, we developed a dual BCR-ABL/Lyn inhibitor, INNO-406 (formerly NS-187), which is 25 to 55 times more potent than imatinib mesylate in vitro and at least 10 times more potent in vivo. The aim of this study was to investigate the efficacy of INNO-406 in treating CNS Ph+ leukemia. We found that INNO-406, like imatinib mesylate, is a substrate for P-glycoprotein. The concentrations of INNO-406 in the CNS were about 10% of those in the plasma. However, this residual concentration was enough to inhibit the growth of Ph+ leukemic cells which expressed not only wild-type but also mutated BCR-ABL in the murine CNS. Furthermore, cyclosporine A, a P-glycoprotein inhibitor, augmented the in vivo activity of INNO-406 against CNS Ph+ leukemia. These findings indicate that INNO-406 is a promising agent for the treatment of CNS Ph+ leukemia.
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PMID:INNO-406, a novel BCR-ABL/Lyn dual tyrosine kinase inhibitor, suppresses the growth of Ph+ leukemia cells in the central nervous system, and cyclosporine A augments its in vivo activity. 1695 4

The majority of chronic phase chronic myeloid leukemia (CML) patients treated with the tyrosine kinase inhibitor (TKI) imatinib mesylate maintain durable responses to the drug. However, most patients relapse after withdrawal of imatinib and advanced stage patients often develop drug resistance. As CML is considered a hematopoietic stem cell cancer, it has been postulated that inherent protective mechanisms lead to relapse in patients. The ATP binding-cassette transporters ABCB1 (MDR-1; P-glycoprotein) and ABCG2 are highly expressed on primitive hematopoietic stem cells (HSCs) and have been shown to interact with TKIs. Herein we demonstrate a dose-dependent, reversible inhibition of ABCG2-mediated Hoechst 33342 dye efflux in primary human and murine HSC by both imatinib and nilotinib (AMN107), a novel aminopyrimidine inhibitor of BCR-ABL. ABCG2-transduced K562 cells were protected from imatinib and nilotinib-mediated cell death and from downregulation of P-CRKL. Moreover, photoaffinity labeling revealed interaction of both TKIs with ABCG2 at the substrate binding sites as they compete with the binding of [(125)I] IAAP and also stimulate the transporter's ATPase activity. Therefore, our evidence suggests for the role of ABC transporters in resistance to TKI on primitive HSCs and CML stem cells and provides a rationale how TKI resistance can be overcome in vivo.
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PMID:Imatinib mesylate and nilotinib (AMN107) exhibit high-affinity interaction with ABCG2 on primitive hematopoietic stem cells. 1751 60

We compared the growth-inhibitory effects and inhibition profile of the SRC family kinases (SFKs) of imatinib, dasatinib, nilotinib and INNO-406. Dasatinib exhibited the strongest potency against BCR-ABL with little selectivity over SFKs. Nilotinib exhibited a weaker affinity than the other inhibitors, but was highly specific for ABL and may be useful for the treatment of P-glycoprotein overexpressing leukemic cells. INNO-406 had an intermediate affinity for BCR-ABL between that of dasatinib and nilotinib, and inhibited only SFKs LCK and LYN among SFKs. Both nilotinib and INNO-406 were potent inhibitors of the dasatinib-resistant T315A, F317L and F317V BCR-ABL mutations.
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PMID:Comparison of imatinib, dasatinib, nilotinib and INNO-406 in imatinib-resistant cell lines. 1819 50


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