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British Journal of Cancer Oct 1988Puromycin-resistant (PurR) mutants/variants of a human carcinoma cell line (HeLa), which show greatly reduced cellular uptake of 3H-puromycin and 3H-daunomycin have been...
Puromycin-resistant (PurR) mutants/variants of a human carcinoma cell line (HeLa), which show greatly reduced cellular uptake of 3H-puromycin and 3H-daunomycin have been isolated after one- and two-step selections in presence of the drug. The cross-resistance pattern of these mutant cell lines towards numerous anticancer drugs and other inhibitors has been examined. Both the first- and the second-step mutants exhibited increased resistance to a number of antimitotic drugs (viz. vinblastine, vincristine, colchicine, taxol and maytansine), several protein synthesis inhibitors (viz. chalcomycin, bruceantin, harringtonine, homoharringtonine), a large number of DNA interactive compounds (viz. aclacinomycin A, actinomycin D, adriamycin, m-AMSA, chromomycin A3, coralyne sulphoacetate, daunomycin, ellipticine, mithramycin, mitoxantrone, 5-methoxysterigmatocystin, rubidazone, variamycin, VM26 and VP16-213) and a number of other drugs acting via other mechanisms (viz. Baker's antifol, nitidine chloride and rhodamine 123). Whereas the first-step mutants showed stable resistance to these drugs, the second-step lines partially reverted upon growth in non-selective medium. Further, treatment of these mutant lines with non-cytotoxic doses of the calcium channel blocker verapamil reverted or abolished their resistance to the above drugs in a dose-dependent manner. In contrast to the above compounds, the PurR mutants showed no significant cross-resistance to a large number of other drugs which included asaley, AT-125, 5-azacytidine, azaserine, cyclocytidine, cis-platin, cytosine arabinoside, chlorambucil, chlorpromazine, alpha-difluoromethyl ornithine, 5-fluorouracil, ftorafur, gallium nitrate, hydroxyurea, ICRF-159, ICRF-187, imipramine, methotraxate, 6-methylmercaptopurine riboside, mycophenolic acid, melphalan, mitomycin C, methyl GAG, nafoxidine, reumycin, 6-selenoguanosine, 6-thioguanine, tiazofurin, tamoxifen, thalicarpine, tiapamil and verapamil). These cross-resistance data should prove useful in developing suitable drug combinations to which cellular resistance would not develop readily.
Topics: Animals; Antineoplastic Agents; Cricetinae; Daunorubicin; Dose-Response Relationship, Drug; Drug Resistance; HeLa Cells; Humans; Mice; Mutation; Puromycin; Verapamil
PubMed: 3207599
DOI: 10.1038/bjc.1988.237 -
The Journal of Biological Chemistry Sep 2004The protozoan parasite Cryptosporidium parvum causes severe enteritis with substantial morbidity and mortality among AIDS patients and young children. No fully effective...
The protozoan parasite Cryptosporidium parvum causes severe enteritis with substantial morbidity and mortality among AIDS patients and young children. No fully effective treatment is available. C. parvum relies on inosine 5'-monophosphate dehydrogenase (IMPDH) to produce guanine nucleotides and is highly susceptible to IMPDH inhibition. Furthermore, C. parvum obtained its IMPDH gene by lateral transfer from an epsilon-proteobacterium, suggesting that the parasite enzyme might have very different characteristics than the human counterpart. Here we describe the expression of recombinant C. parvum IMPDH in an Escherichia coli strain lacking the bacterial homolog. Expression of the parasite gene restores growth of this mutant on minimal medium, confirming that the protein has IMPDH activity. The recombinant protein was purified to homogeneity and used to probe the enzyme's mechanism, structure, and inhibition profile in a series of kinetic experiments. The mechanism of the C. parvum enzyme involves the random addition of substrates and ordered release of products with rate-limiting hydrolysis of a covalent enzyme intermediate. The pronounced resistance of C. parvum IMPDH to mycophenolic acid inhibition is in strong agreement with its bacterial origin. The values of Km for NAD and Ki for mycophenolic acid as well as the synergistic interaction between tiazofurin and ADP differ significantly from those of the human enzymes. These data suggest that the structure and dynamic properties of the NAD binding site of C. parvum IMPDH can be exploited to develop parasite-specific inhibitors.
Topics: Amino Acid Sequence; Animals; Binding Sites; Cryptosporidium parvum; Dose-Response Relationship, Drug; Drug Design; Escherichia coli; Gene Transfer Techniques; Genetic Complementation Test; Humans; IMP Dehydrogenase; Kinetics; Models, Biological; Models, Chemical; Molecular Sequence Data; Mycophenolic Acid; Phylogeny; Protein Conformation; Recombinant Proteins; Ribavirin; Sequence Homology, Amino Acid; Time Factors
PubMed: 15269207
DOI: 10.1074/jbc.M407121200 -
Cell May 2004NAD+ is essential for life in all organisms, both as a coenzyme for oxidoreductases and as a source of ADPribosyl groups used in various reactions, including those that...
NAD+ is essential for life in all organisms, both as a coenzyme for oxidoreductases and as a source of ADPribosyl groups used in various reactions, including those that retard aging in experimental systems. Nicotinic acid and nicotinamide were defined as the vitamin precursors of NAD+ in Elvehjem's classic discoveries of the 1930s. The accepted view of eukaryotic NAD+ biosynthesis, that all anabolism flows through nicotinic acid mononucleotide, was challenged experimentally and revealed that nicotinamide riboside is an unanticipated NAD+ precursor in yeast. Nicotinamide riboside kinases from yeast and humans essential for this pathway were identified and found to be highly specific for phosphorylation of nicotinamide riboside and the cancer drug tiazofurin. Nicotinamide riboside was discovered as a nutrient in milk, suggesting that nicotinamide riboside is a useful compound for elevation of NAD+ levels in humans.
Topics: Chromosomes, Human, Pair 9; Energy Metabolism; Evolution, Molecular; Fungi; Gene Expression Regulation, Enzymologic; Gene Expression Regulation, Fungal; Humans; Intracellular Signaling Peptides and Proteins; Molecular Sequence Data; NAD; Niacinamide; Nucleosides; Phosphorylation; Phosphotransferases (Alcohol Group Acceptor); Pyridinium Compounds; Ribavirin; Saccharomyces cerevisiae Proteins; Sequence Homology, Amino Acid; Sequence Homology, Nucleic Acid
PubMed: 15137942
DOI: 10.1016/s0092-8674(04)00416-7 -
The Journal of Biological Chemistry Mar 1993Incubation of HeLa cells with the IMP dehydrogenase inhibitors: ribavirin (100 microM, 4 h), tiazofurin (100 microM, 4 h), selenazofurin (100 microM, 4 h), or...
Incubation of HeLa cells with the IMP dehydrogenase inhibitors: ribavirin (100 microM, 4 h), tiazofurin (100 microM, 4 h), selenazofurin (100 microM, 4 h), or mycophenolic acid (10 microM, 4 h) resulted in approximately 70% reduction in cellular GTP pools and shifting of nucleophosmin/B23 from nucleoli to nucleoplasm as detected by immunofluorescence (B23-translocation). Enzyme-linked immunosorbent assay and Western blot assay showed there is no loss or degradation of nucleophosmin/B23 protein during drug treatment. This translocation effect could be prevented by co-incubation with guanosine (100 microM) or reversed by addition of guanosine (100 microM) to the culture medium after B23-translocation had been induced by these inhibitors. Under these conditions of guanosine supplementation, cellular GTP pool concentrations were maintained at the control level. These results indicate that localization of nucleophosmin/B23 into the nucleolus is dependent on the cellular GTP level.
Topics: Biological Transport; Cell Nucleolus; Guanosine Triphosphate; HeLa Cells; Humans; IMP Dehydrogenase; Nuclear Proteins; Nucleophosmin; Phosphoproteins; Ribavirin
PubMed: 8095498
DOI: No ID Found -
British Journal of Cancer Feb 1992The antibiotic drug novobiocin was evaluated for its anti-tumour properties in B16 melanoma cells. Novobiocin is shown to inhibit melanoma B16 cell proliferation. The...
The antibiotic drug novobiocin was evaluated for its anti-tumour properties in B16 melanoma cells. Novobiocin is shown to inhibit melanoma B16 cell proliferation. The anti-proliferative effect was gradually reversible upon removal of novobiocin from the culture medium. Growth inhibition by novobiocin was accompanied by phenotypic alterations, that included morphological changes, lipid accumulation and marked increases in the activities of NADPH cytochrome c reductase and gamma glutamyl transpeptidase. In vivo administration of repeated i.p. doses of novobiocin, to mice implanted with B16 melanoma cells resulted in growth retardation. The combined treatment of the B16 melanoma cells with novobiocin and other chemical inducers of differentiation was examined in a cell growth assay. Novobiocin and sodium butyrate inhibited cell growth in a near additive manner, while combination of novobiocin with the GTP-depleting agents, tiazofurin or mycophenolic acid resulted in a synergistic decrease in cell growth. Our results support the contention further that novobiocin and other differentiating agents might be of potential value in melanoma therapy.
Topics: Animals; Antineoplastic Agents; Cell Count; Cell Differentiation; Cell Division; Drug Screening Assays, Antitumor; Melanoma, Experimental; Mycophenolic Acid; Novobiocin; Phenotype; Ribavirin
PubMed: 1739614
DOI: 10.1038/bjc.1992.38 -
Journal of Virology Nov 2007The broad spectrum of antiviral activity of ribavirin (RBV) lies in its ability to inhibit IMP dehydrogenase, which lowers cellular GTP. However, RBV can act as a potent...
The broad spectrum of antiviral activity of ribavirin (RBV) lies in its ability to inhibit IMP dehydrogenase, which lowers cellular GTP. However, RBV can act as a potent mutagen for some RNA viruses. Previously we have shown a lack of correlation between antiviral activity and GTP repression for Hantaan virus (HTNV) and evidence for RBV's ability to promote error-prone replication. To further explore the mechanism of RBV, GTP levels, specific infectivity, and/or mutation frequency was measured in the presence of RBV, mycophenolic acid (MPA), selenazofurin, or tiazofurin. While all four drugs resulted in a decrease in the GTP levels and infectious virus, only RBV increased the mutation frequency of viral RNA (vRNA). MPA, however, could enhance RBV's mutagenic effect, which suggests distinct mechanisms of action for each. Therefore, a simple drop in GTP levels does not drive the observed error-prone replication. To further explore RBV's mechanism of action, we made a comprehensive analysis of the mutation frequency over several RBV concentrations. Of importance, we observed that the viral population reached a threshold after which mutation frequency did not correlate with a dose-dependent decrease in the level of vRNA, PFU, or [RTP]/[GTP] (where RTP is ribavirin-5'-triphosphate) over these same concentrations of RBV. Modeling of the relationship of mutation frequency and drug concentration showed an asymptotic relationship at this point. After this threshold, approximately 57% of the viral cDNA population was identical to the wild type. These studies revealed a lethal threshold, after which we did not observe a complete loss of the quasispecies structure of the wild-type genome, although we observed extinction of HTNV.
Topics: Animals; Antiviral Agents; Chlorocebus aethiops; Dose-Response Relationship, Drug; Gene Frequency; Genome, Viral; Guanosine Triphosphate; Hantaan virus; Mutation; Mycophenolic Acid; Organoselenium Compounds; RNA, Viral; Ribavirin; Ribonucleosides; Vero Cells
PubMed: 17699579
DOI: 10.1128/JVI.00874-07 -
The Journal of Biological Chemistry Jan 1998Tissue transglutaminase (tTG) is a calcium-dependent enzyme that catalyzes the posttranslational modification of proteins by transamidation of specific polypeptide-bound...
Tissue transglutaminase (tTG) is a calcium-dependent enzyme that catalyzes the posttranslational modification of proteins by transamidation of specific polypeptide-bound glutamine residues. Previous in vitro studies have demonstrated that the transamidating activity of tTG requires calcium and is inhibited by GTP. To investigate the endogenous regulation of tTG, a quantitative in situ transglutaminase (TG) activity assay was developed. Treatment of human neuroblastoma SH-SY5Y cells with retinoic acid (RA) resulted in a significant increase in tTG levels and in vitro TG activity. In contrast, basal in situ TG activity did not increase concurrently with RA-induced increased tTG levels. However, stimulation of cells with the calcium-mobilizing drug maitotoxin (MTX) resulted in increases in in situ TG activity that correlated (r2 = 0.76) with increased tTG levels. To examine the effects of GTP on in situ TG activity, tiazofurin, a drug that selectively decreases GTP levels, was used. Depletion of GTP resulted in a significant increase in in situ TG activity; however, treatment of SH-SY5Y cells with a combination of MTX and tiazofurin resulted in significantly less in situ TG activity compared with treatment with MTX alone. This raised the possibility of calcium-dependent proteolysis due to the effects of tiazofurin, because in vitro GTP protects tTG against proteolysis by trypsin. Studies with a selective membrane permeable calpain inhibitor indicated that tTG is likely to be an endogenous substrate of calpain, and that depletion of GTP increases tTG degradation after elevation of intracellular calcium levels. TG activity was also increased in response to activation of muscarinic cholinergic receptors, which increases intracellular calcium through inositol 1,4,5-trisphosphate generation. The results of these experiments demonstrate that selective changes in calcium and GTP regulate the activity and levels of tTG in situ.
Topics: 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; Antineoplastic Agents; Calcium; Calcium Channel Agonists; Calpain; Carbachol; Diazomethane; Guanosine Triphosphate; Humans; IMP Dehydrogenase; Ionomycin; Ionophores; Marine Toxins; Muscarinic Agonists; Oligopeptides; Oxocins; Receptors, Retinoic Acid; Retinoid X Receptors; Ribavirin; Thapsigargin; Transcription Factors; Transglutaminases; Tumor Cells, Cultured
PubMed: 9442073
DOI: 10.1074/jbc.273.4.2288 -
Carbohydrate Research Oct 1993Synthesis of an analogue 3 of thiazole-4-carboxamide adenine-dinucleotide (TAD) in which the beta-oxygen atom of the pyrophosphate bridge is replaced by a...
Synthesis of an analogue 3 of thiazole-4-carboxamide adenine-dinucleotide (TAD) in which the beta-oxygen atom of the pyrophosphate bridge is replaced by a difluoromethylene group has been achieved. Likewise, 2'-deoxy-2'-fluoroadenosine containing analogues of TAD (4) and its difluoromethylenediphosphonate congener (5) have been synthesized. Adenosine 5'-difluoromethylenediphosphonate (8) was prepared from 5'-O-tosyladenosine (6) and tris(tetra-n-butylammonium)difluoromethylenediphosphonate (7) by a modified procedure of Poulter's. Compound 8 was converted into the 2',3'-cyclic carbonate 9 by treatment with triethyl orthoformate. Treatment of 9 with 2',3'-O-isopropylidenetiazofurin (10) in pyridine in the presence of DCC gave a mixture of dinucleotide 11 and the isopropylidene-protected diadenosine tetraphosphonate 12. After deprotection of 11, the desired beta-difluoromethylene TAD (3) was separated by HPLC as the minor product. The diadenosine tetraphosphonate 12, an analogue of Ap4A, was obtained as the major component. Alternatively, 2',3'-O-isopropylidenetiazofurin (10) was tosylated, and the product 13 was further converted into the corresponding difluoromethylenediphosphonate 14 by coupling with 7. DCC-catalyzed coupling of 14 with 2'-deoxy-2'-fluoroadenosine (15) followed by deisopropylidenation afforded the analogue 5. Again the corresponding tetraphosphonate analogue of tiazofurin 17 was the predominant product. Dinucleotide 4 was obtained by coupling of the carbonyldiimidazole-activated tiazofurin 5'-monophosphate with 2'-deoxy-2'-fluoroadenosine 5'-monophosphate. 2'-Deoxy-2'-fluoroadenosine (15) was prepared efficiently from the known N6-benzoyl-3'-O-tetrahydropyranyladenosine (18), which was converted into 3'-O-tetrahydropyranyl-2'-O-triflyl-5'-O-trityladenosine (20) by tritylation and triflation. Treatment of 20 with sodium acetate in hexamethylphosphoric triamide, followed by deacetylation afforded 9-(3-O-tetrahydropyranyl-5-O-trityl-beta-D- arabinofuranosyl)-N6-benzoyladenine (22), which was then treated with DAST. After deprotection of the product, 15 was obtained in good yield.
Topics: Adenine Nucleotides; Adenosine; Fluorine; Indicators and Reagents; Magnetic Resonance Spectroscopy; Molecular Structure; Spectrometry, Mass, Fast Atom Bombardment; Thiazoles
PubMed: 8252557
DOI: 10.1016/0008-6215(93)84063-c -
The Journal of Biological Chemistry Oct 1992GTP cyclohydrolase I exhibits a positive homotropic cooperative binding to GTP, which raises the possibility of a role for GTP in regulating the enzyme reaction...
IMP dehydrogenase inhibitors reduce intracellular tetrahydrobiopterin levels through reduction of intracellular GTP levels. Indications of the regulation of GTP cyclohydrolase I activity by restriction of GTP availability in the cells.
GTP cyclohydrolase I exhibits a positive homotropic cooperative binding to GTP, which raises the possibility of a role for GTP in regulating the enzyme reaction (Hatakeyama, K., Harada, T., Suzuki, S., Watanabe, Y., and Kagamiyama, H. (1989) J. Biol. Chem. 264, 21660-21664). We examined whether or not the intracellular GTP level is within the range of affecting GTP cyclohydrolase I activity, using PC-12 rat pheochromocytoma and IMR-32 human neuroblastoma cells. Since GTP cyclohydrolase I was the rate-limiting enzyme for the biosynthesis of tetrahydrobiopterin in these cell lines, the intracellular activities of this enzyme were reflected in the tetrahydrobiopterin contents. We found that the addition of guanine or guanosine increased GTP but not tetrahydrobiopterin in these cells. On the other hand, three IMP dehydrogenase inhibitors, tiazofurin, 2-amino-1,3,4-thiadiazole, and mycophenolic acid, decreased both GTP and tetrahydrobiopterin in a parallel and dose-dependent manner, and these effects were reversed by the simultaneous addition of guanine or guanosine. There was no evidence suggesting that these inhibitors inhibited other enzymes involved in the biosynthesis and regeneration of tetrahydrobiopterin. Comparing intracellular activities of GTP cyclohydrolase I in the inhibitor-treated cells with its substrate-velocity curve, we estimated that the intracellular concentration of free GTP is 150 microM at which point the activity of GTP cyclohydrolase I is elicited at its maximum velocity. Below this GTP concentration, GTP cyclohydrolase I activity is rapidly decreased. Therefore GTP can be a regulator for tetrahydrobiopterin biosynthesis.
Topics: Animals; Antineoplastic Agents; Biopterins; GTP Cyclohydrolase; Guanine; Guanosine; Guanosine Triphosphate; Humans; IMP Dehydrogenase; Kinetics; Mycophenolic Acid; Neuroblastoma; PC12 Cells; Ribavirin; Thiadiazoles; Tumor Cells, Cultured
PubMed: 1356983
DOI: No ID Found -
Blood Apr 1991The physiologically active form of vitamin D, 1,25 dihydroxyvitamin D3 [1,25(OH)2D3], was found to inhibit erythroid differentiation of human leukemic K562 cells....
The physiologically active form of vitamin D, 1,25 dihydroxyvitamin D3 [1,25(OH)2D3], was found to inhibit erythroid differentiation of human leukemic K562 cells. Differentiation was induced by 1 mumol/L arabinocytosine (Ara-C), 40 mumol/L tiazofurin, 1 mumol/L aphidicolin, or 1 mumol/L hydroxyurea, and was monitored daily by the appearance of hemoglobin in an increasing proportion of cells. Pretreatment for 48 hours with 2.4 x 10(-8) mol/L 1,25(OH)2D3, a concentration that is also optimal for induction of monocytic differentiation of HL-60 cells, reproducibly inhibited subsequent induction of erythroid differentiation by all of the above inducers, and modified the morphologic changes that Ara-C produced in these cells. The inhibition of hemoglobinization was approximately 50% irrespective of the degree of differentiation produced by the various inducers, but growth inhibition associated with exposure to the inducers was not affected by 1,25(OH)2D3. Similar inhibition of differentiation by 1,25(OH)2D3 was observed in mouse erythroleukemia cells MEL-D1B treated with 5 mmol/L hexamethylenebisacetamide. The inhibitory effect of 1,25(OH)2D3 on erythroid differentiation of K562 cells was abrogated by cyclohexamide (20 micrograms/mL), an inhibitor of protein synthesis. The mRNA for 1,25(OH)2D3 receptor (VDR) was detected in K562 cells, and was downregulated by a 96-hour exposure to 1,25(OH)2D3 or a 48-hour exposure to Ara-C. The presence of VDR mRNA suggests a physiologic role for 1,25(OH)2D3 in K562 cells that are precursors of erythroid cells. This role is perhaps to shift the pathways of differentiation from the erythroid to the monocytic lineage.
Topics: Animals; Calcitriol; Cell Differentiation; Cell Division; Cell Line; Cytarabine; Humans; Kinetics; Leukemia, Experimental; Leukemia, Myelogenous, Chronic, BCR-ABL Positive; Mice; RNA, Messenger; Receptors, Calcitriol; Receptors, Steroid; Ribavirin; Time Factors
PubMed: 1849032
DOI: No ID Found