inosinic-acid and Leukemia

Cytotoxic nucleoside analogs (NA) are important in the treatment of hematologic malignancies. The NA in routine clinical use include the pyrimidine analog cytosine arabinoside (ara-c), which is extensively used in the treatment of acute leukemias, and the purine analogs, cladribine and fludarabine. These drugs have mostly been used in the treatment of low grade hematological malignancies. NA become therapeutically effective only after phosporylation to the triphosphate level. The 5'-nucleotidases (5'-NTs) dephosphorylate the monophosphate form of NA and, therefore, may affect the pharmacological activity of these antimetabolites in the clinic. Several 5'-NTs attached to membranes or present in the cytosol or in mitochondria are present in mammalian cells. cN-II, an IMP-selective 5'-NT, participates in the regulation of purine deoxyribonucleotide metabolism. cN-II opposes the action of the salvage enzymes by dephosphorylating purine nucleoside mononphosphates to purine nucleosides. Due to its phosphotransferase activity, cN-II can also phosphorylate inosine and 2',3'-dideoxyribonucleosides utilizing IMP as a phosphate donor. The observation that cytosolic cN-II is able to phosphorylate purine nucleosides has initiated studies on its potential participation in the metabolism of anticancer agents and in the development of cN-II inhibitory substances. In this review, we highlight the current knowledge concerning cN-II activity and regulation of intracellular deoxyribonucleotide pools and it role in hematological malignancies.

Topics: 5'-Nucleotidase; Animals; Cytosol; Humans; Inosine Monophosphate; Leukemia; Phosphotransferases

Topics: Antimetabolites, Antineoplastic; Deoxyguanine Nucleotides; Guanosine Triphosphate; Humans; IMP Dehydrogenase; Inosine Monophosphate; Leukemia; Neoplasms; Purines; Ribavirin; Signal Transduction

Topics: Animals; Breast Neoplasms; Chromatography, High Pressure Liquid; Chromatography, Ion Exchange; Deficiency Diseases; Female; Fluorouracil; Guanine; Humans; Inosine Monophosphate; Lesch-Nyhan Syndrome; Leukemia; Nucleosides; Nucleotides; Sarcoma 180; Skin; Thioinosine

The catalytic mechanism for the enzyme, IMP cyclohydrolase, may involve a reaction intermediate with negative charge in the 2-position of the purine ring (Szabados, E., Hindmarsh, E., Phillips, L., Duggleby, R.G. & Christopherson, R.I. (1994) Biochemistry 33, 14237-14245). Three analogues of IMP have been synthesised where fluorine, chlorine or bromine has been substituted in the 2-position on the purine ring. These analogues with an electronegative substituent may resemble a reaction intermediate for IMP cyclohydrolase; 2-fluoro IMP is a potent inhibitor of the enzyme with a Ki value of 0.19 microM, while 2-chloro IMP has a Ki of 1.9 microM and 2-bromo IMP is not inhibitory. However, IMP cyclohydrolase is not inhibited in human CCRF-CEM leukaemia cells exposed to 2-fluoro inosine although it is toxic to these cells with an IC50 value of 4.9 microM.

Topics: Bromine; Cell Division; Chlorine; Deoxyguanine Nucleotides; Deoxyribonucleosides; Enzyme Inhibitors; Fluorine; Humans; Inosine Monophosphate; Leukemia; Nucleosides; Nucleotide Deaminases; Phosphates; Purines; Structure-Activity Relationship; Tumor Cells, Cultured

The synthesis and biological activity of selenophenfurin (5-beta-D-ribofuranosylselenophene-3-carboxamide, 1), the selenophene analogue of selenazofurin, are described. Glycosylation of ethyl selenophene-3-carboxylate (6) under stannic chloride-catalyzed conditions gave 2- and 5-glycosylated regioisomers, as a mixture of alpha- and beta-anomers, and the beta-2,5-diglycosylated derivative. Deprotected ethyl 5-beta-D-ribofuranosylselenophene-3-carboxylate (12 beta) was converted into selenophenfurin by ammonolysis. The structure of 12 beta was determined by 1H- and 13C-NMR, crystallographic, and computational studies. Selenophenfurin proved to be antiproliferative against a number of leukemia, lymphoma, and solid tumor cell lines at concentrations similar to those of selenazofurin but was more potent than the thiophene and thiazole analogues thiophenfurin and tiazofurin. Incubation of K562 cells with selenophenfurin resulted in inhibition of IMP dehydrogenase (IMPDH) (76%) and an increase in IMP pools (14.5-fold) with a concurrent decrease in GTP levels (58%). The results obtained confirm the hypothesis that the presence of heteroatoms such as S or Se in the heterocycle in position 2 with respect to the glycosidic bond is essential for both cytotoxicity and IMP dehydrogenase inhibitory activity in this type of C-nucleosides.

Topics: Animals; Antineoplastic Agents; Cell Division; Computer Simulation; Crystallography, X-Ray; Enzyme Inhibitors; Guanosine Triphosphate; Humans; IMP Dehydrogenase; Inosine Monophosphate; Leukemia; Lymphoma; Magnetic Resonance Spectroscopy; Mice; Models, Molecular; Molecular Structure; Neoplasms; Organoselenium Compounds; Ribavirin; Ribonucleosides; Tumor Cells, Cultured

Tiazofurin was demonstrated to be an effective inhibitor of the growth of human cultured blast cells, and the high specific activities of IMP dehydrogenase (EC 1.1.1.205) were observed in all the cell extracts tested. IMP dehydrogenase has been purified to homogeneity from MOLT 4F human T-lymphoblast, and the Km values for IMP and NAD were 29 and 54 microM, respectively. The inhibitory mechanisms of thiazole-4-carboxamide adenine dinucleotide (TAD) and ribavirin 5'-monophosphate (RMP), the active forms of the antimetabolites tiazofurin and ribavirin, were investigated on the purified enzyme. RMP inhibits competitively with respect to IMP as well as XMP, and the inhibition by TAD was similar to that by NADH, which was uncompetitive with NAD. However, the Ki values of RMP (0.58 microM) and TAD (0.075 microM) were several orders of magnitude lower than those of XMP (85 microM) and NADH (94 microM). Thus, the drugs interact with the two distinct sites of IMP dehydrogenase with much higher affinities than the natural substrates and products. Preincubation of the purified enzyme with RMP enhanced its inhibitory effect in a time-dependent manner, and the enhancement was further increased by the addition of TAD. The combination of tiazofurin and ribavirin exerted a synergistic effect on the growth inhibition in MOLT 4F cells.

Topics: Adenine Nucleotides; Antimetabolites, Antineoplastic; Cell Division; Cell Line; Humans; IMP Dehydrogenase; Inosine Monophosphate; Ketone Oxidoreductases; Kinetics; Leukemia; NAD; Ribavirin; Ribonucleosides

Methyl 2,3-O-isopropylidene-D-ribofuranoside (1) was converted to 1-O-acetyl-5-bromo-5-deoxy-2,3-di-O-benzoyl-D-ribofuranose (6) in five steps with good yield. The Arbuzov condensation of compound 6 with triethyl phosphite resulted in the synthesis of 1-O-acetyl-2,3-di-O-benzoyl-5-deoxy-5-(diethoxyphosphinyl)-D-ribofuranos e (7). Compound 7 was used for direct glycosylation of both purine and pyrimidine bases. The glycosylation was accomplished with the dry silylated heterocyclic base in the presence of trimethylsilyl triflate. Deblocking of the glycosylation products gave exclusively the beta anomer of the 5'-phosphonate analogues of 9-[5'-deoxy-5'-(dihydroxyphosphinyl)-beta-D-ribofuranosyl]adenine (13), 9-[5'-deoxy-5'-(dihydroxyphosphinyl)-beta-D-ribofuranosyl]guanosin e (16), 9-[5'-deoxy-5'-(dihydroxyphosphinyl)-beta-D-ribofuranosyl]hypoxant hine (17), and 9-[5'-deoxy-5'-(dihydroxyphosphinyl)-beta-D-ribofuranosyl]cytosine (15), described here for the first time. The target compounds as well as their intermediates showed no in vitro antiviral or antitumor activity, although phosphorylation of 15 and 16 to di- and triphosphate analogues was demonstrated with use of isolated cellular enzymes.

Topics: Adenosine Monophosphate; Animals; Chemical Phenomena; Chemistry; Colonic Neoplasms; Cytidine Monophosphate; Cytosine Nucleotides; Guanine Nucleotides; Guanosine Monophosphate; Humans; Inosine Monophosphate; Inosine Nucleotides; Leukemia; Leukemia L1210; Magnetic Resonance Spectroscopy; Mice; Molecular Structure; Neoplasms; Phosphorylation; Spectrophotometry, Ultraviolet; Structure-Activity Relationship; Tumor Cells, Cultured; Viruses

A highly sensitive reversed-phase high-performance liquid chromatographic assay, with ultraviolet detection, for 6-thioinosinic acid and the 6-thioguanine nucleotides (6TGNs) was developed. The 6TGNs are major red blood cell metabolites of the immunosuppressive agent azathioprine and the cytotoxic drugs 6-thioguanine and 6-mercaptopurine. The assay is based on the specific extraction, via phenyl mercury adduct formation, of the thiopurine released on acid hydrolysis of the thionucleotide metabolite. Red blood cell 6TGN concentrations in eighteen leukaemic children receiving chronic 6-mercaptopurine chemotherapy were measured and compared to a previously published spectrophotofluorometric assay. Linear regression analysis gave r = 0.991; P less than 0.001; y = 40 + 0.94x.

Topics: Chromatography, High Pressure Liquid; Drug Stability; Erythrocytes; Humans; Inosine Monophosphate; Inosine Nucleotides; Leukemia; Mercaptopurine; Nucleotides; Spectrometry, Fluorescence; Thioguanine; Thionucleotides

The PRPP concentrations, PRPP formation, and phosphorylation of 6-mercaptopurine in leukocyte suspensions and homogenates prepared from leukemic patients were studied...

Topics: Amidophosphoribosyltransferase; Animals; Humans; Hypoxanthine Phosphoribosyltransferase; Hypoxanthines; In Vitro Techniques; Inosine; Inosine Monophosphate; Leukemia; Leukemia L1210; Leukemia, Myeloid, Acute; Leukocytes; Mercaptopurine; Phosphoribosyl Pyrophosphate; Purine-Nucleoside Phosphorylase