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MESH Headings
- ATP Binding Cassette Transporter, Subfamily B, Member 1/chemistry
- ATP Binding Cassette Transporter, Subfamily B, Member 1/isolation & purification
- ATP Binding Cassette Transporter, Subfamily B, Member 1/metabolism
- Affinity Labels/chemical synthesis
- Affinity Labels/chemistry
- Affinity Labels/pharmacokinetics
- Animals
- Binding Sites
- Cell Line
- Cell Membrane/metabolism
- Cell Membrane/ultrastructure
- Centrifugation, Density Gradient/methods
- Chromatography, High Pressure Liquid/methods
- Cricetinae
- Cricetulus
- Drug Resistance, Multiple
- Electrophoresis, Polyacrylamide Gel/methods
- Humans
- Iodine Radioisotopes
- Molecular Structure
- Photochemistry
- Tumor Cells, Cultured
- Vinblastine/pharmacokinetics
- Vinblastine/pharmacology
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Affiliation(s)
- A R Safa
- Department of Experimental Oncology, Medical University of South Carolina, Charleston 29425, USA
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Nare B, Lubega G, Prichard RK, Georges E. p-Azidosalicyl-5-amino-6-phenoxybenzimidazole photolabels the N-terminal 63-103 amino acids of Haemonchus contortus beta-tubulin 1. J Biol Chem 1996; 271:8575-81. [PMID: 8621485 DOI: 10.1074/jbc.271.15.8575] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Benzimidazoles (BZ) are broad spectrum anthelmintics thought to exert their effects by interacting with and disrupting the functions of microtubules. However, direct biochemical evidence for binding between BZ and tubulin has not been shown nor is it known what sequences in tubulin interact with BZ. In this study, a photoactive analogue of 2-acetamido-5-(3-aminophenoxy)benzimidaz ole that has biological activity similar to other benzimidazoles was synthesized and used to photoaffinity label cell lysates from the parasitic nematode of sheep Haemonchus contortus. The photoactive analogue, 2-acetamido-5-[3-(4-azido-3-125I-salicyl amido)phenoxy]benzimida zol e or 125I-ASA-BZ, was shown to photolabel a 54-kDa protein that was specifically immunoprecipitated with anti-tubulin monoclonal antibodies. Tubulin photoaffinity labeling by 125I-ASA-BZ was also inhibited with molar excess of various BZ analogues and colchicine. Interestingly, 125I-ASA-BZ photoaffinity-labeled the beta- and not the alpha-subunits of tubulin. Proteolytic digestion of 125I-ASA-BZ-labeled tubulin with Staphylococcus aureus V8 proteinase revealed one major peptide with an apparent molecular mass of 3.5 kDa. Exhaustive digestion of 125I-ASA-BZ-labeled beta-tubulin with trypsin resulted in two fractions containing radioactive peptides. Protein sequencing of the high performance liquid chromatography-purified tryptic ASA-BZ-photolabeled peptides identified the N-terminal 63-77 and 78-103 sequences as the BZ binding domain.
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Affiliation(s)
- B Nare
- Institute of Parasitology of McGill University, Macdonald Campus, Ste Anne de Bellevue, Quebec H9X 3V9, Canada
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Safa AR, Agresti M, Bryk D, Tamai I. N-(p-azido-3-[125I]iodophenethyl)spiperone binds to specific regions of P-glycoprotein and another multidrug binding protein, spiperophilin, in human neuroblastoma cells. Biochemistry 1994; 33:256-65. [PMID: 7904476 DOI: 10.1021/bi00167a034] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
P-glycoprotein (P-gp) is an energy-dependent drug extrusion pump with broad specificity for diverse hydrophobic anticancer agents and compounds known to reverse multidrug resistance (MDR). Among MDR reversing agents, phenothiazines (PTZs) and related compounds may sensitize MDR by interacting with a specific binding site(s) on P-gp and by other mechanisms. In order (1) to identify a binding site for PTZs and related compounds on P-gp, (2) to examine whether these compounds and other MDR modulators bind to the same domains of P-gp, and (3) to identify proteins with high specificity for these neuroleptic agents and other MDR modulators, we used a butyrophenone D2-dopamine receptor photoaffinity probe, N-(p-azido-3-[125I]iodophenethyl)spiperone ([125I]NAPS). [125I]NAPS was actively effluxed from vincristine (VCR)-resistant SH-SY5Y/VCR human neuroblastoma cells, and nonradioactive I-NAPS was a potent chemosensitizing agent. After photolabeling, the probe bound specifically and with high efficiency to P-gp and to another multidrug binding 17-kDa membrane-bound protein, spiperophilin, in these cells. The efficiency of [125I]NAPS binding to P-gp was 5-6-fold more than [3H]azidopine and [125I]arylazidoprazosin ([125I]AAP), known photoaffinity analogs for P-gp. [125I]NAPS photolabeling of P-gp was preferentially competed by MDR-related drugs, with vinblastine > VCR > colchicine > doxorubicin > actinomycin D. Many drugs that are known to reverse MDR were potent inhibitors of [125I]NAPS binding to P-gp. While PTZs and related compounds were potent inhibitors of [125I]NAPS binding to P-gp, most of them enhanced the binding of [125I]AAP significantly. cis-Flupentixol increased the binding of [125I]AAP to P-gp 9-fold more than did trans-flupentixol, but both were potent inhibitors of [125I]NAPS binding, suggesting their stereoselective effect on the [125I]AAP binding site. Proteolysis of [125I]NAPS-bound P-gp with Staphylococcus aureus V8 protease revealed that this probe binds to two major peptides, 6 and 8 kDa, and a number of minor ones, while [125I]AAP binds to only an 8-kDa peptide. These results suggest that modulators of MDR may interact with separate or overlapping domains. Furthermore, most MDR modulators, dopaminergic drugs, and beta-adrenergic antagonists used also inhibited binding of [125I]-NAPS to spiperophilin, suggesting that this protein may be a target for these drugs.
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Affiliation(s)
- A R Safa
- Department of Medicine, University of Chicago, Illinois 60637-1470
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Nakamura S, Wakusawa S, Tajima K, Miyamoto K, Hagiwara M, Hidaka H. Effects of isoquinolinesulphonamide compounds on multidrug-resistant P388 cells. J Pharm Pharmacol 1993; 45:268-73. [PMID: 8098366 DOI: 10.1111/j.2042-7158.1993.tb05551.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The effects of eight isoquinolinesulphonamide compounds on resistance to vinblastine in adriamycin-resistant mouse leukaemia cells (P388/ADR) which overexpress the relative molecular weight (M(r)) 140 kDa P-glycoprotein in the plasma membrane were investigated. N-[2-(Methylamino)ethyl]-5-isoquinolinesulphonamide (H-8) and N-(2-aminoethyl)-5-isoquinolinesulphonamide (H-9) did not reverse vinblastine resistance. N-[2-[N-[3-(4-Chlorophenyl)-2-propenyl]amino] ethyl]-5-isoquinolinesulphonamide (H-86) and N-[2-[N-[3-(4-chlorophenyl)-1-methyl-2-propenyl] amino]ethyl]-5-isoquinolinesulphonamide (H-87) caused accumulation of intracellular vinblastine and inhibition of vinblastine efflux from the cells and reversed the resistance. Addition of an aminoethyl group to the nitrogen atom of the sulphonamide group (W-66) or a formyl group at the terminal amino group (H-85) of H-86 reduced those activities. Conversion of the chlorophenyl group of H-87 to pyridinyl (H-31) or furanyl (H-34) markedly decreased activities against the drug resistance. The activity against vinblastine accumulation closely correlated with the apparent partition coefficient of compounds. These compounds dose-dependently inhibited photoaffinity labelling of a photosensitive analogue of vinblastine, N-(p-azido-(3-[125I)salicyl)-N'-beta-aminoethyl-vindesine ([125I]NASV), and there was a good correlation between inhibition of [125I]NASV-photolabelling and hydrophobicity. Although these isoquinolinesulphonamides inhibited protein kinase A with different magnitudes, this activity did not correlate with the effect on the drug resistance. These results indicate that isoquinolinesulphonamide compounds with a hydrophobic group interact with antitumour drugs on P-glycoprotein and reverse multidrug resistance without involvement of their activity on protein kinase A.
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Affiliation(s)
- S Nakamura
- Third Division, Hokuriku University, Kanazawa, Japan
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Affiliation(s)
- A R Safa
- Department of Medicine, University of Chicago, Illinois 60637
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Hodgson ST, Con Jenkins D, Knick V, Rapson E, Watts SD. Synthesis and biological properties of 1069C: a new synthetic antitumour agent with very low cross-resistance potential. Bioorg Med Chem Lett 1992. [DOI: 10.1016/s0960-894x(00)80225-5] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Fleming GF, Amato JM, Agresti M, Safa AR. Megestrol acetate reverses multidrug resistance and interacts with P-glycoprotein. Cancer Chemother Pharmacol 1992; 29:445-9. [PMID: 1348973 DOI: 10.1007/bf00684845] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
We evaluated the multidrug resistance (MDR)-modulating effects of progesterone (PRG) and an orally active, structurally related compound, megestrol acetate (MA), in several MDR human cell lines. At 100 microM, both steroids inhibited the binding of a Vinca alkaloid photoaffinity analog to P-glycoprotein (P-gp) in MDR human neuroblastic SH-SY5Y/VCR cells [which show greater than 1500-fold resistance to vincristine (VCR) in the tetrazolium dye (MTT) assay]. However, 100 microM MA markedly enhanced the binding of [3H]-azidopine to P-gp in both SH-SY5Y/VCR cells and the MDR human epidermoid KB-GSV2 cell line (which displays 250-fold resistance to VCR in the MTT assay). PRG had little effect on the binding of [3H]-azidopine to P-gp. MA at low doses was more effective than PRG in sensitizing cells to VCR and enhancing their accumulation of [3H]-VCR. The highly resistant SH-SY5Y/VCR subline exhibited significant collateral sensitivity to both steroids. These data suggest that MA may be a clinically useful modulator of MDR.
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Affiliation(s)
- G F Fleming
- Department of Medicine, University of Chicago, Ill
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Tamai I, Safa A. Azidopine noncompetitively interacts with vinblastine and cyclosporin A binding to P-glycoprotein in multidrug resistant cells. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)55371-0] [Citation(s) in RCA: 132] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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Abstract
The dimeric Vinca alkaloids represent a group of important anti-tumor compounds whose intracellular target is tubulin, the protein monomer of microtubules. In this review data on the binding of these drugs to tubulin and microtubules in vitro are examined. The binding to tubulin is linked to a protein self-association reaction described by Na and Timasheff (1986a) as a ligand-induced plus ligand-mediated isodesmic self-association reaction. The simplest model which fits the binding data is one in which there is one intrinsic site which is linked to the self-association process. Effects of solution variables on the binding and self-association explain the wide variation of reported apparent binding constants for Vinca alkaloids to tubulin. The Vinca drugs also bind to microtubules via a low number of sites at the ends of microtubules with apparent high affinity and which are involved in the inhibition of tubulin dimer addition to the microtubule ends, and to sites along the microtubule wall with apparent low affinity which are involved in the disruption of the microtubules into spiraled protofilaments. This review also compares available binding data for different natural and semi-synthetic Vinca alkaloids.
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Affiliation(s)
- R H Himes
- Department of Biochemistry, University of Kansas, Lawrence 66045-2106
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Nasioulas G, Grammbitter K, Himes RH, Ponstingl H. Interaction of a new photosensitive derivative of vinblastine, NAPAVIN, with tubulin and microtubules in vitro. EUROPEAN JOURNAL OF BIOCHEMISTRY 1990; 192:69-74. [PMID: 2401298 DOI: 10.1111/j.1432-1033.1990.tb19196.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
We have synthesized a new photoreactive vinblastine derivative, 3-[[2-amino(4-azido-2-nitrophenyl)ethyl]-amino)-carbonyl)-O4-deceatyl -3-de (methoxycarbonyl)-vincaleukoblastine (NAPAVIN), which can be photoactivated with light in the 455-nm region as well as with ultraviolet irradiation. Previous studies had shown that photoactivated NAPAVIN is much more effective than vinblastine in inhibiting cell proliferation of multidrug resistant cell lines. The experiments reported here demonstrate that the unirradiated derivative is very similar to vinblastine in its interactions with brain tubulin and microtubules, regarding inhibition of in vitro assembly, binding, aggregation, and production of protofilament spirals. Irradiation of [3H]NAPAVIN in the presence of tubulin led to covalent binding of the drug to both subunits of the protein. Labeling also occurred when NAPAVIN was first irradiated, then incubated with tubulin in the dark, indicating the production of a fairly stable reactive species with a half-life of about 400 min. We conclude that labeling by this compound, under some conditions, occurs not by a nitrene but by an electrophilic photoproduct.
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Affiliation(s)
- G Nasioulas
- Project Molecular Biology of Mitosis, Institute of Cell and Tumor Biology, German Cancer Research Center, Heidelberg
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McGrath T, Latoud C, Arnold ST, Safa AR, Felsted RL, Center MS. Mechanisms of multidrug resistance in HL60 cells. Analysis of resistance associated membrane proteins and levels of mdr gene expression. Biochem Pharmacol 1989; 38:3611-9. [PMID: 2573357 DOI: 10.1016/0006-2952(89)90134-2] [Citation(s) in RCA: 95] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
HL60 cells isolated for resistance to Adriamycin do not contain P-glycoprotein, as determined with immunological probes. These cells, however, are multidrug resistant and defective in the cellular accumulation of drug. In view of these findings, we have examined in greater detail certain properties of the HL60/Adr cells and have compared these properties to an HL60 drug-resistant isolate (HL60/Vinc) which contains high levels of P-glycoprotein. The results of these studies demonstrated that verapamil induces a major increase in cellular drug accumulation in both HL60/Adr and HL60/Vinc isolates. An 125I-labeled photoaffinity analog of verapamil labeled P-glycoprotein contained in membranes of HL60/Vinc cells. In contrast, this agent did not label any protein selectively associated with drug resistance in membranes of the HL60/Adr isolate. The photoactive dihydropyridine calcium channel blocker [3H]azidopine and [125I]NASV, a photoaffinity analog of vinblastine, labelled P-glycoprotein in membranes from HL60/Vinc cells, whereas in experiments with the HL60/Adr isolate there was no detectable labeling of a drug resistance associated membrane protein. Additional studies have been carried out to analyze membrane proteins of HL60/Adr cells labeled with the photoaffinity agent 8-azido-alpha-[32P]ATP (AzATP32). The results demonstrate that this agent labeled a resistance associated membrane protein of 190 kilodaltons (P190). P190 is essentially absent in membranes of drug-sensitive cells. Labeling of P190 with AzATP32 in membranes of resistant cells was blocked completely when incubations were carried out in the presence of excess unlabeled ATP. Additional studies were carried out to analyze mdr gene amplification and expression in sensitive and resistant cells. Experiments carried out with human 5',mdr1 (1.1 kb) and mdr3 (1.0 kb) cDNAs demonstrate that both of these sequences were highly amplified in the HL60/Vinc isolate. Only the mrd1 gene sequence however, was overexpressed. In contrast, there was no detectable amplification or overexpression of mdr1 or mdr3 sequences in HL60/Adr cells. The results of this study thus identify a new nucleotide binding protein which is overexpressed in membranes of HL60 cells isolated for resistance to Adriamycin. P190, which exhibits properties distinct from P-glycoprotein, possibly functions in the energy-dependent drug efflux system contained in the HL60/Adr resistant isolate.
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Affiliation(s)
- T McGrath
- Division of Biology, Kansas State University, Manhattan 66506
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Safa AR, Mehta ND, Agresti M. Photoaffinity labeling of P-glycoprotein in multidrug resistant cells with photoactive analogs of colchicine. Biochem Biophys Res Commun 1989; 162:1402-8. [PMID: 2569869 DOI: 10.1016/0006-291x(89)90830-9] [Citation(s) in RCA: 55] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Two photoactive radiolabeled analogs of colchicine, N-(p-azido[3,5-[3H]benzoyl)aminohexanoyldeacetylcolchicine ([3H]NABC]) and N-(p-azido-[3-125I]salicyl)aminohexanoyldeacetylcolchicine ([125I]NASC) were synthesized and used to identify colchicine-specific acceptor(s) in membrane vesicles from multidrug resistant (MDR) variant DC-3F/VCRd-5L Chinese hamster lung cells. Both [3H]NABC and [125I]NASC specifically photolabeled a prominent 150-180 kDa polypeptide in membrane vesicles from DC-3F/VCRd-5L cells. The photolabeled polypeptide was immunoprecipitated by monoclonal antibody C219 specific for the MDR-related P-glycoprotein (P-gp) indicating the identity of this protein with P-gp. Colchicine at 1000 microM reduced [3H]NABC photolabeling of P-gp by 72%. Furthermore, 100 microM of colchicine, vincristine, vinblastine, doxorubicin and actinomycin D inhibited [125I]NASC photolabeling by 45, 88.8, 91.1, 61.5, and 51% respectively. However, methotrexate did not affect the [125I]NASC photolabeling of P-gp, indicating the multidrug specificity of the P-gp colchicine acceptor for drugs to which these cells are resistant.
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Affiliation(s)
- A R Safa
- Joint Section of Hematology/Oncology, University of Chicago Medical Center, IL 60637
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Asoh K, Saburi Y, Sato S, Nogae I, Kohno K, Kuwano M. Potentiation of some anticancer agents by dipyridamole against drug-sensitive and drug-resistant cancer cell lines. Jpn J Cancer Res 1989; 80:475-81. [PMID: 2568984 PMCID: PMC5917755 DOI: 10.1111/j.1349-7006.1989.tb02339.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
In this study, we have used two different vincristine (VCR)-resistant variants, VJ-300 and HC-7-5/VCR. VJ-300 was isolated from a human cancer KB cell line and HC-7-5/VCR from a human cancer HC-7-5 cell line. VJ-300 and HC-7-5/VCR are both multidrug-resistant (MDR) variants, showing resistance to multiple anticancer drugs such as VCR, adriamycin, actinomycin D and daunomycin. Dipyridamole, a specific inhibitor of nucleoside transport, potentiated these anticancer drugs about 2- to 10-fold against KB and VJ-300. Dipyridamole almost completely reversed drug resistance to actinomycin D in VJ-300 cells with about a 70-fold higher resistance to actinomycin D. Dipyridamole inhibited the efflux of actinomycin D and VCR from VJ-300 cells. Dipyridamole enhanced the uptake of VCR but not that of actinomycin D in VJ-300 and KB. Dipyridamole at 10-100 microM inhibited photoaffinity labeling with [3H]azidopine of the cell-surface protein P-glycoprotein in VJ-300 cells. Dipyridamole potentiated 5-fluorouracil and hexylcarbamoyl-5-fluorouracil in cultured KB and VJ-300, but it annihilated the cytotoxic action of 5-fluorouridine. Potentiation of 5-fluorouracil by dipyridamole against HC-7-5 and HC-7-5/VCR was also observed, but appeared to be less than in VJ-300 and KB cells. Dipyridamole almost completely inhibited the cellular accumulation of 5-fluorouridine, but not that of 5-fluorouracil. Thus, dipyridamole appeared to potentiate anticancer agents through pleiotropic action sites, one of which is inhibition of enhanced efflux of MDR cell lines and the other of which is inhibition of nucleoside transport. Dipyridamole might be a useful and potent agent to potentiate anticancer agents and reverse drug-resistance.
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Affiliation(s)
- K Asoh
- Department of Biochemistry, Oita Medical School
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Nogae I, Kohno K, Kikuchi J, Kuwano M, Akiyama S, Kiue A, Suzuki K, Yoshida Y, Cornwell MM, Pastan I. Analysis of structural features of dihydropyridine analogs needed to reverse multidrug resistance and to inhibit photoaffinity labeling of P-glycoprotein. Biochem Pharmacol 1989; 38:519-27. [PMID: 2563655 DOI: 10.1016/0006-2952(89)90393-6] [Citation(s) in RCA: 66] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Synthetic dihydropyridine analogs were screened to determine whether they would reverse multidrug resistance of a multidrug-resistant human KB carcinoma cell line, KB-C1. Among twenty-four dihydropyridine analogs examined, thirteen almost completely overcame drug resistance (group A), nine partially overcame resistance (group B) and two did not reverse resistance (group C). The twenty-two compounds that reversed drug-resistance (groups A and B) were hydrophobic dihydropyridine derivatives. Three compounds that reversed resistance, NK-113, NK-138 and NK-194, increased the accumulation of [3H]vincristine in the resistant KB-C1 cells, but not in the parental KB cells, nor in a revertant cell line, KB-C1-R2. NK-101 (group C), which did not reverse resistance, had no effect on drug accumulation. Enhanced efflux of vincristine from the resistant cells was inhibited completely by NK-194, but NK-194 did not affect vincristine influx. Nine of the twenty-four compounds were screened to determine whether they inhibited photoaffinity labeling of the cell surface protein gp170 (P-glycoprotein) in KB-C1 cells by N-(p-azido-[3-125I]-salicyl)-N'-beta-aminoethylvindesine [( 125I]NASV). All five compounds of group A, NK-138, NK-194, NK-200, NK-203 and NK-220, inhibited the photoaffinity labeling of gp170 at less than 10-100 microM, whereas NK-113 and NK-196 of group B inhibited the labeling at 100-200 microM. By contrast, NK-101 and NK-102 of group C did not inhibit labeling even at 2000 microM. These studies confirm the relationship among reversal of multidrug resistance, decreased efflux of vincristine, and inhibition of [125I]NASV labeling of P-glycoprotein.
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Affiliation(s)
- I Nogae
- Department of Biochemistry, Oita Medical School, Japan
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Sempuku K. Photoinactivation of the thiamin transport system in Saccharomyces cerevisiae with azidobenzoyl derivatives of thiamin. BIOCHIMICA ET BIOPHYSICA ACTA 1988; 944:177-84. [PMID: 3052587 DOI: 10.1016/0005-2736(88)90430-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
In an attempt to obtain a potent inhibitor for thiamin transport of Saccharomyces cerivisiae three novel thiamin derivatives having an arylazido substituent in the thiazole moiety have been synthesized. The derivatives prepared were 4-azidobenzoylthiamin (ABT), 4-azidobenzoylthiamin disulfide (ABTD), and 4-azido-2-nitrobenzoylthiamin disulfide (ANBTD). Among the newly prepared photoreactive azidobenzoyl derivatives of thiamin, ANBTD showed the strongest competitive inhibition with an apparent Ki of 7.9 nM against thiamin uptake by S. cerevisiae IFO-2375. The Ki values for ABT, 4-azido-2-nitrobenzoylthiamin (ANBT), and ABTD were 187 nM, 83 nM, and 15 nM, respectively. When exposed to visible light, ANBTD inactivated in a time- and concentration-dependent manner the uptake of [14C]thiamin by yeast protoplasts as well as intact cells. Remaining activities of the thiamin uptake by the intact cells were 71.9%, 27.3%, 40.1%, and 15.0% after visible light irradiation for 15 min in the presence of 1 microM ABT, ANBT, ABTD, and ANBTD, respectively. The inactivation by ANBTD (0.05 microM) was partially prevented by previous addition of an excessive amount of thiamin (5 microM). Furthermore, it was found that ANBTD (0.5 microM) irreversibly inactivated 70.6% of the thiamin-binding activity of the membrane fraction from S. cerevisiae IFO-2375. These results suggest that ANBTD can inhibit yeast thiamin transport by photoinactivation of membrane-bound thiamin-binding protein in the plasma membrane which may be a functional component involved in the thiamin transport system of S. cerevisiae.
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Affiliation(s)
- K Sempuku
- Department of Biochemistry, Kyoto Prefectural University of Medicine, Japan
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