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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 -
The Biochemical Journal Nov 1992A rapid and convenient method has been developed to monitor the inhibition of inosinate (IMP) dehydrogenase by antimetabolites in intact human CEM lymphocytes. This...
A rapid and convenient method has been developed to monitor the inhibition of inosinate (IMP) dehydrogenase by antimetabolites in intact human CEM lymphocytes. This method is based on the determination of 3H release from [2,8-3H]hypoxanthine ([2,8-3H]Hx) or [2,8-3H]inosine ([2,8-3H]Ino). The validity of this procedure was assessed by evaluating IMP dehydrogenase inhibition in intact CEM cells by the well-known IMP dehydrogenase inhibitors ribavirin, mycophenolic acid and tiazofurin. As reference materials, several compounds that are targeted at other enzymes in de novo purine nucleotide anabolism (i.e. hadacidine, acivicin) or catabolism (i.e. 8-aminoguanosine, allopurinol) were evaluated. There was a strong correlation between the inhibitory effects of the IMP dehydrogenase inhibitors (ribavirin, mycophenolic acid, tiazofurin) on 3H release from [2,8-3H]Hx and [2,8-3H]Ino in intact CEM cells and their ability to decrease intracellular GTP pool levels. The other compounds (hadacidine, acivicin, 8-aminoguanosine, allopurinol) had no marked effect on 3H release from [2,8-3H]Hx. Using this method, we demonstrated that the novel ribavirin analogue, 5-ethynyl-1-beta-D-ribofuranosylimidazole-4-carboxamide, is a potent inhibitor of IMP dehydrogenase in intact cells.
Topics: Adenosine Triphosphate; Antimetabolites; Cell Line; Guanosine Triphosphate; Humans; Hypoxanthine; Hypoxanthines; IMP Dehydrogenase; Inosine; Inosine Monophosphate; Kinetics; Lymphocytes; Ribonucleosides
PubMed: 1359876
DOI: 10.1042/bj2870785 -
The Journal of Biological Chemistry Nov 1993EICAR (5-ethynyl-1-beta-D-ribofuranosylimidazole-4-carboxamide) is a cytostatic agent that inhibits murine leukemia L1210 and human lymphocyte CEM cells at a 50%...
EICAR (5-ethynyl-1-beta-D-ribofuranosylimidazole-4-carboxamide) is a cytostatic agent that inhibits murine leukemia L1210 and human lymphocyte CEM cells at a 50% inhibitory concentration of 0.80-1.4 microM, respectively. EICAR causes a rapid and marked inhibition of inosinate (IMP) dehydrogenase (EC 1.1.1.205) activity in intact L1210 and CEM cells reflected by a concentration-dependent accumulation of IMP and depletion of GTP and dGTP levels. EICAR 5'-monophosphate is a potent inhibitor of purified L1210 cell IMP dehydrogenase (Ki/Km 0.06). Inhibition of IMP dehydrogenase by EICAR 5'-monophosphate is competitive with respect to IMP. L1210 cells that were selected for resistance to the cytostatic action of EICAR proved to be adenosine kinase-deficient. Also, studies with other mutant L1210 and CEM cell lines revealed that adenosine kinase, as well as an alternative pathway, may be responsible for the conversion of EICAR to its 5'-monophosphate. Purified 2'-deoxycytidine kinase, 2'-deoxyguanosine kinase, cytosolic 5'-nucleotidase, and nicotinamide dinucleotide (NAD) pyrophosphorylase do not seem to be markedly involved in the metabolism of EICAR.
Topics: Adenosine; Animals; Antineoplastic Agents; Cell Division; Deoxyguanine Nucleotides; Guanine; Guanosine; Guanosine Triphosphate; Humans; IMP Dehydrogenase; Leukemia L1210; Lymphocytes; Mice; Mycophenolic Acid; Purine Nucleotides; Ribavirin; Ribonucleosides; Ribonucleotides; Tumor Cells, Cultured
PubMed: 7901217
DOI: No ID Found -
Proceedings of the National Academy of... Mar 1999Inosine monophosphate dehydrogenase (IMPDH) controls a key metabolic step in the regulation of cell growth and differentiation. This step is the NAD-dependent oxidation...
Inosine monophosphate dehydrogenase (IMPDH) controls a key metabolic step in the regulation of cell growth and differentiation. This step is the NAD-dependent oxidation of inosine 5' monophosphate (IMP) to xanthosine 5' monophosphate, the rate-limiting step in the synthesis of the guanine nucleotides. Two isoforms of IMPDH have been identified, one of which (type II) is significantly up- regulated in neoplastic and differentiating cells. As such, it has been identified as a major target in antitumor and immunosuppressive drug design. We present here the 2.9-A structure of a ternary complex of the human type II isoform of IMPDH. The complex contains the substrate analogue 6-chloropurine riboside 5'-monophosphate (6-Cl-IMP) and the NAD analogue selenazole-4-carboxamide adenine dinucleotide, the selenium derivative of the active metabolite of the antitumor drug tiazofurin. The enzyme forms a homotetramer, with the dinucleotide binding at the monomer-monomer interface. The 6 chloro-substituted purine base is dehalogenated, forming a covalent adduct at C6 with Cys-331. The dinucleotide selenazole base is stacked against the 6-Cl-IMP purine ring in an orientation consistent with the B-side stereochemistry of hydride transfer seen with NAD. The adenosine end of the ligand interacts with residues not conserved between the type I and type II isoforms, suggesting strategies for the design of isoform-specific agents.
Topics: Adenosine Diphosphate; Amino Acid Sequence; Antineoplastic Agents; Binding Sites; Crystallography, X-Ray; Drug Design; Humans; IMP Dehydrogenase; Immunosuppressive Agents; Inosine Monophosphate; Ligands; Macromolecular Substances; Models, Molecular; Molecular Sequence Data; Organoselenium Compounds; Protein Isoforms; Protein Structure, Secondary; Recombinant Proteins
PubMed: 10097070
DOI: 10.1073/pnas.96.7.3531 -
Organic Letters Sep 2005[reaction: see text] A tandem dimerization-macrocyclization approach using 1,3-dipolar azide-alkyne cycloaddition reactions has been employed in the facile and...
[reaction: see text] A tandem dimerization-macrocyclization approach using 1,3-dipolar azide-alkyne cycloaddition reactions has been employed in the facile and convergent solution phase syntheses of C2 symmetric cyclic peptide scaffolds bearing triazole epsilon2-amino acids as dipeptide surrogates.
Topics: Heterocyclic Compounds; Molecular Structure; Peptides, Cyclic; Ribavirin
PubMed: 16178569
DOI: 10.1021/ol0518028 -
Blood Jan 1987We have shown previously that induced maturation of the human myeloid leukemia cell line, HL-60, is associated with a selective down-regulation of guanine ribonucleotide...
We have shown previously that induced maturation of the human myeloid leukemia cell line, HL-60, is associated with a selective down-regulation of guanine ribonucleotide synthesis and depletion of intracellular guanosine triphosphate (GTP) and guanosine diphosphate (GDP) pools. We showed, furthermore, that inhibitors of the enzyme, inosine monophosphate (IMP) dehydrogenase, which catalyzes the initial rate-limiting step of guanylate synthesis from the central intermediate IMP, are potent inducers of myeloid maturation in these cells. We now show that induced maturation of HL-60 cells is prevented or impaired if intracellular concentrations of guanine ribonucleotides are maintained at high levels. HL-60 cells can utilize exogenous guanine and guanosine to maintain GTP and GDP pools through a salvage pathway that bypasses guanylate synthesis from IMP. Moreover, incubation of HL-60 cells with guanosine or guanine (10(-6) to 10(-4) mol/L) prevents both the depletion of intracellular guanine ribonucleotides and the induction of myeloid maturation caused by the IMP dehydrogenase inhibitor, tiazofurin. These findings provide strong additional support for the concept that terminal myeloid differentiation is influenced by a guanine ribonucleotide-dependent regulatory system.
Topics: Cell Differentiation; Cell Line; Dimethylformamide; Guanine; Guanine Nucleotides; Guanosine; Hematopoiesis; Humans; IMP Dehydrogenase; Leukemia, Myeloid, Acute; Ribavirin; Tretinoin
PubMed: 2878694
DOI: No ID Found