Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.13 (protein kinase C)
 49,245 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Drugs that interfere with the action of P-glycoprotein (P-gp), the membrane efflux pump responsible for multidrug resistance (MDR), should be valuable in the treatment of patients with drug-resistant cancer. We have used one class of drug, the phenothiazines, to study the structural features required for optimum interference with the function of P-gp. The structure-activity relationships revealed three important components including the hydrophobicity of the tricyclic ring, the length of the alkyl bridge and the charge on the terminal amino group. Trans-flupenthixol is a lead compound that conforms to these structural requirements and demonstrates significant activity as a sensitizer of MDR cell lines to drugs affected by the MDR phenotype. Based on these data, we have proposed a model for the binding of modulators to P-gp and have speculated on the structure of the drug-binding domain. We have developed pre-clinical models of MDR that may help predict clinical activity of chemo-modulators. L1210/VMDRC.06 is a murine lymphocytic leukemia line transformed by a retroviral expression vector containing a full-length cDNA for the human mdr1 gene. K562/VBL1-3 are clones of human myeloid blast cells that were transformed with the same vector. Resistance in these lines is not complicated by changes in the cellular content of glutathione or alterations in topoisomerase II. The transformed L1210 line grows in mice as a slowly proliferating non-metastatic peritoneal implant. Both MDR lines are restored to sensitivity by cyclosporin A or trans-flupenthixol, and the K562 clones are induced to differentiate by hemin. These lines should provide simple, sensitive screens for new drugs for use against cancers expressing P-gp. We have proposed a model to explain how the pumping activity of P-gp is activated in response to toxic drugs. In this schema, basal activity of P-gp is modulated through phosphorylation/dephosphorylation reactions mediated by protein kinase C (PKC) and calcium sensitive phosphatases. In response to the activation of phospholipase C by toxic drugs and the local production of 1,2-diacylglycerol, PKC is translocated to the cell membrane where it phosphorylates P-gp. Following the extrusion of drug from the cell membrane, phospholipase C activity returns to baseline, diacylglycerol is metabolized, PKC returns to the cytosol and serine/threonine phosphatases dephosphorylate P-gp returning it to the basal state.
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PMID:Rational design and pre-clinical pharmacology of drugs for reversing multidrug resistance. 134 93

Cross-resistance to anticancer drugs, termed multidrug resistance (MDR), is functionally associated with the expression of a plasma membrane, energy-dependent, drug efflux pump termed P-glycoprotein (PGP), the product of the mdr1 gene. We have shown previously that MCF-7 breast carcinoma cells transfected with the human mdr1 gene (BC-19 cells) exhibit greater MDR when stably transfected with protein kinase C alpha (PKC alpha). We now demonstrate that transfection of BC-19 cells with the gamma isoform of PKC (BC-19/PKC gamma cells), which is not normally present in BC-19 cells, does not confer increased resistance to doxorubicin, despite a 19-fold increase in PKC activity. All of the increased PKC activity is accounted for by PKC gamma and it is rapidly down-regulated by phorbol dibutyrate, within 15 min of treatment. Endogenous PKC alpha and PKC epsilon activities are not affected by phorbol dibutyrate. The cytotoxicity of doxorubicin was similar in BC-19/neo or BC-19/PKC gamma cells after either 2-hr or continuous drug exposure, and co-treatment with phorbol dibutyrate increased resistance to doxorubicin 4-fold in both cell lines. Phosphorylation of PGP was similar in both cell lines and drug accumulation was not affected by overexpression of PKC gamma. These results demonstrate that transfection of PGP-expressing cells with an atypical isoform of PKC does not confer increased MDR, and they suggest that the regulation of PGP is phenotype specific with respect to the isoform of PKC.
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PMID:Role of protein kinase C in the modulation of multidrug resistance: expression of the atypical gamma isoform of protein kinase C does not confer increased resistance to doxorubicin. 136 42

The induction of murine erythroleukemia cells (MELC; DS19/Sc9) to terminal differentiation by hexamethylenebisacetamide (HMBA) is characterized by a latent period of 10-12 hr before onset of commitment to terminal-cell division and increased transcription of globin genes. MELC variants, derived from this parental cell line, selected for resistance to vincristine (VC), can be induced to differentiate with little or no latent period. This study shows that accelerated HMBA-induced commitment is characteristic of MELC with a low level (2- to 5-fold) of VC resistance in four independently derived cell lines. Both resistance to VC and accelerated differentiation are stable phenotypes for at least 50 passages (approximately 5 months) in the absence of VC. Low-level VC-resistant MELC do not display increased levels of P-glycoprotein or mdr1, mdr2, and mdr3 mRNAs, nor do they exhibit cross-resistance to colchicine or doxorubicin. These cells do show (i) increased level of protein kinase C activity, (ii) reduced accumulation of [3H]VC, and (iii) restoration of VC sensitivity in the presence of verapamil. MELC selected for higher levels of VC resistance (approximately 500-fold) do express high levels of P-glycoprotein and the mdr3 gene. During HMBA-induced differentiation, DS19/Sc9 decrease [3H]VC accumulation, but P-glycoprotein content does not change. A VC-transport-associated protein, also critical for the process of induced differentiation, may be constitutively present in VC-resistant MELC, accounting for their enhanced sensitivity to inducer. This protein accumulates by exposure of VC-sensitive cells to HMBA, contributing to their differentiation and decreased level of VC accumulation.
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PMID:Characteristics of erythroleukemia cells selected for vincristine resistance that have accelerated inducer-mediated differentiation. 167 43

Cross-resistance to anticancer drugs, termed multidrug resistance (mdr), has been functionally associated with the expression of a plasma membrane energy-dependent efflux pump, termed P-glycoprotein, the product of the mdr1 gene. When MCF-7 breast carcinoma cells were transfected with the human mdr1 gene (BC-19 cells), they expressed levels of P-glycoprotein equivalent to those of cells selected for resistance to doxorubicin (MCF-7/ADR) but exhibited 10- to 50-fold less resistance to doxorubicin and vinblastine. We have now demonstrated that when BC-19 cells were stably transfected with protein kinase C alpha (PKC alpha), resistance to doxorubicin and vinblastine was increased; wild-type MCF-7 cells transfected with PKC alpha did not exhibit any change in drug resistance. Increased resistance in PKC alpha-transfected BC-19 cells was associated with enhanced PKC activity and phosphorylation of P-glycoprotein and decreased drug accumulation. The PKC activator, phorbol dibutyrate, further increased resistance to doxorubicin and stimulated P-glycoprotein phosphorylation. These results demonstrate that transfection of P-glycoprotein-expressing cells with PKC resulted in increased mdr and that PKC may have served as an important modulator of this process.
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PMID:Transfection with protein kinase C alpha confers increased multidrug resistance to MCF-7 cells expressing P-glycoprotein. 167 75

The plant diterpene forskolin reverses acquired resistance to doxorubicin in variants of the murine sarcoma S180 cell line. Because forskolin is known to elevate intracellular cAMP levels, investigations were performed to determine whether this reversal of resistance resulted from effects on signal transduction. Two analogues of forskolin, dideoxyforskolin, which does not elevate cAMP, and a water-soluble analogue, were also investigated. Although all three diterpenes elevated levels of either cAMP or protein kinase C, these effects were not consistently associated with reversal of doxorubicin resistance. Likewise, all three diterpenes were capable of displacing [3H]azidopine from P-glycoprotein, but reversal of doxorubicin resistance was observed only with forskolin and dideoxyforskolin, suggesting that binding to P-glycoprotein may be a necessary, but not sufficient, condition for reversing doxorubicin resistance. The hydrophobicity of the compounds appeared to be the single factor most consistently related to reversal of doxorubicin resistance in this cell system, with the hydrophilic compound water-soluble forskolin failing to produce this result, even at concentrations 10-fold higher than effective concentrations of the hydrophobic diterpenes.
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PMID:Reversal of doxorubicin resistance by hydrophobic, but not hydrophilic, forskolins. 168 37

We have previously shown that phenothiazines sensitize multidrug resistant (MDR) cells to chemotherapeutic drugs in a manner related to specific structural features, and have identified structurally related thioxanthenes with increased anti-MDR activity. We have now studied the structure-activity relationships of 16 thioxanthenes in the human breast cancer line MCF-7 AdrR. trans-Thioxanthene stereoisomers were 2- to 7-fold more potent than cis-thioxanthenes for antagonizing MDR. The most potent thioxanthenes possessed a halogenated tricyclic ring connected by a 3-carbon alkyl bridge to a piperazinyl or piperadinyl side group. The chemosensitizing effects of the lead compound, trans-flupenthixol, its stereoisomer cis-flupenthixol, its phenothiazine homologue fluphenazine, and the calcium channel blocker verapamil, were further studied in a series of sensitive and MDR cell lines. trans-Flupenthixol caused a greater reversal of cellular resistance to doxorubicin, vinblastine, vincristine, and colchicine in MCF-7 AdrR, KB-V1, and P388/DOX MDR cells than the other chemosensitizers. In particular, trans-flupenthixol was 2- to 3-fold more potent for reversing MDR than equimolar concentrations of verapamil. Furthermore, trans-flupenthixol fully reversed resistance to doxorubicin, vincristine, and colchicine in MDR MCF-7 and NIH 3T3 cells transfected with the mdr1 gene. None of these agents altered MDR in a non-P-glycoprotein expressing MCF-7 cell line selected with mitoxantrone, nor in any of the parental cell lines. The stereoselective antagonism of the flupenthixol isomers on several putative cellular targets was studied to explore the mechanism of their chemosensitizing activity. cis- and trans-flupenthixol were equally active inhibitors of protein kinase C and calmodulin. Both cis- and trans-flupenthixol were also potent inhibitors of [3H]azidopine binding to P-glycoprotein. The apparent lack of clinical toxicity of trans-flupenthixol makes it an attractive drug for possible use in the modulation of tumor resistance in vivo if appropriate tissue concentrations can be achieved.
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PMID:Cellular and biochemical characterization of thioxanthenes for reversal of multidrug resistance in human and murine cell lines. 196 58

Safingol is a lysosphingolipid protein kinase C (PKC) inhibitor that competitively interacts at the regulatory phorbol binding domain of PKC. We investigated the effects of safingol on antineoplastic drug sensitivity and PKC activity of MCF-7 tumor cell lines. Safingol treatment of 32P-labeled MCF-7 WT and MCF-7 DOXR cells inhibited phosphorylation of the myristoylated alanine-rich protein kinase C substrate in both cell lines, suggesting inhibition of cellular PKC. However, only in MCF-7 DOXR cells did safingol treatment increase accumulation of [3H]vinblastine and enhance toxicity of Vinca alkaloids and anthracyclines. Drug accumulation changes in MCF-7 DOXR cells treated with safingol were accompanied by inhibition of basal and phorbol 12,13-dibutyrate-stimulated phosphorylation of P-glycoprotein (P-gp). Expression of P-gp and levels of mdr1 message in MCF-7 DOXR cells were not altered by safingol treatment alone or in combination with vinblastine. Treatment of MCF-7 DOXR cell membranes with safingol did not inhibit [3H]vinblastine binding or [3H]azidopine photoaffinity labeling of P-gp. Furthermore, safingol did not stimulate P-gp ATPase activity in membranes prepared from MCF-7 DOXR cells. We conclude that enhanced drug accumulation and sensitivity in MCF-7 DOXR cells treated with safingol are correlated with inhibition of PKC rather than competitive interference with P-gp drug binding through direct interaction with P-glycoprotein.
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PMID:Partial inhibition of multidrug resistance by safingol is independent of modulation of P-glycoprotein substrate activities and correlated with inhibition of protein kinase C. 759 89

We compared the influence of exogenous N-ras oncogene and treatment with PKC agonist 12-O-tetradecanoylphorbol-13-acetate (TPA) on P-glycoprotein (Pgp) function in various human, rat and dog cell lines. Two approaches were used: (a) flow cytometry analysis of Rhodamine 123 (Rh123) exclusion; and (b) sensitivity to cytotoxic action of colchicine. We have found that in Rat1 fibroblasts, rat IAR2 epithelial cells and rat McA RH 7777 (hepatoma), ras activates Pgp function, while in MDCK (dog kidney), K562 (human chronic myelogenous leukaemia) and LIM1215 (human colon carcinoma) cells it either has no effect or even acts in opposite direction. TPA-induced Pgp function shows dissimilar pattern of cell specificity. It is assumed that PKC and ras oncogene regulate mdr1 gene expression through at least partially distinct signalling pathways.
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PMID:Cell-specific effects of RAS oncogene and protein kinase C agonist TPA on P-glycoprotein function. 762 41

The ability of malignant cells to develop resistance to chemotherapeutic drugs is a major obstacle to the successful treatment of clinical tumors. The phenomenon multidrug resistance (MDR) in cancer cells results in cross-resistance to a broad range of structurally diverse antineoplastic agents, due to outward efflux of cytotoxic substrates by the mdr1 gene product, P-glycoprotein (P-gp). Numerous pharmacologic agents have been identified which inhibit the efflux pump and modulate MDR. The biochemical, cellular and clinical pharmacology of agents used to circumvent MDR is analyzed in terms of their mechanism of action and potential clinical utility. MDR antagonists, termed chemosensitizers, may be grouped into several classes, and include calcium channel blockers, calmodulin antagonists, anthracycline and Vinca alkaloid analogs, cyclosporines, dipyridamole, and other hydrophobic, cationic compounds. Structural features important for chemosensitizer activity have been identified, and a model for the interaction of these drugs with P-gp is proposed. Other possible cellular targets for the reversal of MDR are also discussed, such as protein kinase C. Strategies for the clinical modulation of MDR and trials combining chemosensitizers with chemotherapeutic drugs in humans are reviewed. Several novel approaches for the modulation of MDR are examined.
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PMID:Pharmacologic circumvention of multidrug resistance. 776 25

Multidrug resistance is functionally associated with the expression of a plasma membrane energy-dependent drug efflux pump termed P-glycoprotein, the product of the mdr1 gene. Transfection of P-glycoprotein-expressing doxorubicin-resistant MCF-7 cells with an expression vector containing the cDNA for protein kinase C alpha in the antisense orientation reduces protein kinase C alpha levels and decreases total protein kinase C activity by 75%. This is accompanied by reduced phosphorylation of P-glycoprotein, a 2-fold increase in drug retention, and a 3-fold increase in doxorubicin cytotoxicity. These results provide further evidence that protein kinase C alpha can positively regulate multidrug resistance in MCF-7 cells through posttranslational phosphorylation of P-glycoprotein.
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PMID:Expression of the antisense cDNA for protein kinase C alpha attenuates resistance in doxorubicin-resistant MCF-7 breast carcinoma cells. 810 Mar 51


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