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Biomedical subjects

A P Kimball

Publications and source records attributed to A P Kimball.

At least 19 recordsLinked to original sources
PubMed1984

Dipyridamole enhancement of toxicity to L1210 cells by deoxyadenosine and deoxycoformycin combinations in vitro.

The combination of 2'-deoxyadenosine and deoxycoformycin is known to be markedly toxic to T-lymphocyte cell lines relative to B-cell lines, and this difference appears to be related to the capacity of the cells to accumulate deoxyadenosine triphosphate (dATP). In the presence of dipyridamole and 2'-deoxyadenosine and when adenosine deaminase was inhibited with deoxycoformycin, the L1210 leukemia cell which is a non-T-, non-B-cell type accumulated dATP like a T-cell type. The intracellular L1210 concentration of dATP using the triple combination (1.1 microM deoxycoformycin-40 microM deoxyadenosine-10 microM dipyridamole) reached 400 microM at which concentration ribonucleotide reductase specific activity was reduced by 80%. While this degree of enzyme may be significant, complete inhibition might have been expected, since 400 microM dATP is approximately 40 times the concentration to give 50% inhibition in some purified systems.

Animals↗
PubMed1982

Probes of eukaryotic DNA-dependent RNA polymerase II-I. Binding of 9-beta-D-arabinofuranosyl-6-mercaptopurine to the elongation subsite.

9-beta-D-Arabinofuranosyl-6-mercaptopurine (ara-6-MP) was used to affinity-label wheat germ DNA-dependent RNA polymerase II (or B) (nucleosidetriphosphate:RNA nucleotidyltransferase, EC 2.7.7.6). This nucleoside analogue was found to be a competitive inhibitor with respect to [3H]UMP incorporation. Natural substrates protected the enzyme from inactivation by ara-6-MP when the enzyme was preincubated with excess concentrations of substrates, suggesting that the inhibitor binds at the elongation subsite. The inhibitor bound the catalytic center of the enzyme with a stoichiometry of 0.6:1. The sulfhydryl reagent, dithiothreitol, reversed the inhibition by ara-6-MP, suggesting that the 6-thiol group of the inhibitor was interacting closely with an essential cysteine residue in the catalytic center of the enzyme. Chromatographic analysis of the pronase-digestion products of the RNA polymerase II-ara-6-MP complex also showed that ara-6-MP had bound a cysteine residue. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the denatured [6-35S]ara-6-MP-labeled RNA polymerase II revealed that over 80% of the radioactivity was associated with the IIb subunit of the enzyme.

Affinity Labels↗
PubMed1982

Probes of eukaryotic DNA-dependent RNA polymerase II-II. Covalent binding of two purine nucleoside dialdehydes to the initiation subsite.

The catalytic center of wheat germ DNA-dependent RNA polymerase II (nucleosidetriphosphate:RNA nucleotidyltransferase, EC 2.7.7.6) as a model eukaryotic enzyme system was probed with two purine nucleoside dialdehydes, 6-methylthioinosinedicarboxaldehyde (MMPR-OP) and a derivative 6-[(acetylaminoethyl)-1-naphthylamine-5-sulfonyl]thioinosinedicarboxaldehyde (AMPR-OP). Both drugs gave noncompetitive inhibition with respect to [3H]UMP incorporations into RNA, and inhibitor bindings were reversed with initiation substrates. The Ki values for MMPR-OP and AMPR-OP were determined to be 0.64 mM and 1.0 muM respectively. The drugs were covalently bound to the catalytic center by NaBH4 reduction. Both were found bound to the largest enzyme subunit, IIa. It is tentatively concluded that MMPR-OP and AMPR-OP inhibit RNA polymerase II by binding to an essential lysine in the initiation subsite of the catalytic center located on the IIa subunit.

DNA-Directed RNA Polymerases↗
PubMed1980

Affinity labeling of a cysteine at or near the catalytic center of Escherichia coli B DNA-dependent RNA polymerase.

9-beta-D-Arabinofuranosyl-6-thiopurine was used to affinity label DNA-dependent RNA polymerase isolated from Escherichia coli B. This substrate analogue displayed competitive type inhibition which could be reversed by addition of a thiol reagent, such as dithiothreitol, while exposure to hydrogen peroxide, a mild oxidizing agent, caused an increase in both the inhibitory and enzyme binding capability of arabinofuranosyl thiopurine. Chromatographic analysis of the products obtained by pronase digestion of the 9-beta-D-arabinofuranosyl-6-[35S]thiopurine-enzyme complex suggests that disulfide bond formation occurs between the inhibitor and a cysteine residue located in or near the active center of the enzyme. In addition, polyacrylamide gel electrophoresis indicated that the arabinofuranosyl thiopurine moeity was bound to the beta' subunit of the enzyme.

Affinity Labels↗
PubMed1980

Cyclophosphamide potentiation and aldehyde oxidase inhibition by phosphorylated aldehydes and acetals.

Fourteen phosphorylated acetals and aldehydes were synthesized for testing in vitro as inhibitors or substrates of aldehyde oxidase, an enzyme involved in the conversion of aldophosphamide to inactive carboxyphosphamide, and for concurrent in vivo administration with cyclophosphamide to mice bearing L1210 ascites tumor cells. Five phosphorus derivatives gave Ki values of 0.1--0.3 mM compared to 0.03 mM for pyridoxal, as determined in aldehyde oxidase assays using N-methylnicotinamide as the substrate. The most active phosphorus inhibitor, ethyl phenyl(2-formylethyl)phosphinate (2b), and pyridoxal were further shown to give competitive and mixed inhibition, respectively. Three aldehydes, administered concurrently with cyclophosphamide, produced greater increases in life span of L1210-implanted mice than did pyridoxal. All four agents gave an average increase in life span greater than 50% over that shown by cyclophosphamide alone.

Acetals↗
PubMed1979

Subunit localizations of zinc(II) in DNA-dependent RNA polymerase from Escherichia coli B.

RNA Polymerase holoenzyme and core enzyme from Escherichia coli B have been shown to contain two zinc ions. Flameless atomic absorption spectroscopy of the isolated core subunits indicated that one zinc ion is localized on the beta subunit and the other is bound on the beta' subunit. Atomic fluorescence spectroscopy showed that prolonged dialysis of the metalloenzyme against 0.01 M o-phenanthroline resulted in the removal of both zinc(II) ions with accompanying loss of enzymatic activity. The activity of the apoenzyme was observed to be completely restored by readdition of zinc(II) and partially restored by cobalt(II).

Apoenzymes↗
PubMed1979

Mechanism of action of tetra-mu-carboxylatodirhodium(II) in L1210 tumor suspension culture.

The effect of tetrakis-mu-methoxyacetato, tetra-mu-acetato, tetra-mu-propionato, and tetra-mu-butyratodirhodium(II) on the proliferation and macromolecular synthesis of leukemia L1210 cells in suspension culture was evaluated. The cytotoxicity of these dimeric rhodium(II) complexes to tumor cells in suspension culture follows the same trend as observed in vivo, i.e., butyrato greater than propionato greater than acetato greater than methoxyacetato. The cellular synthesis of DNA and protein was found to be strongly inhibited by tetra-mu-propionatodirhodium(II), whereas minimal inhibition of RNA synthesis was observed. Flow microfluorometric analysis of the drug-treated cells revealed an arrest of cellular development during the G2 phase of the cell cycle. The inhibition of DNA synthesis was attributed at least in part to the arrest in G2 which is consistent with the observed inhibition of protein synthesis.

Animals↗
PubMed1977

Hydrophobicity of several rhodium(II) carboxylates correlated with their biologic activity.

Rhodium(II) carboxylates differ greatly in antitumor activity and toxicity depending on the properties of the carboxylate group (methoxyacetate, propionate, butyrate, etc.) involved. The solubility characteristics of rhodium(II) carboxylates correlate well with both the antitumor activity and toxicity that these compounds display. The amount of rhodium which is adsorbed by tumor cells in vitro also correlates with the partition coefficient of the rhodium(II) compounds studied. Survival and toxicity studies show rhodium(II) pentanoate to possess the highest therapeutic index against the Ehrlich ascites tumor strain and also show that lengthening the carboxylate R chain beyond the pentanoate reduces the drugs' therapeutic efficacy.

Animals↗
PubMed1977

Therapeutic effects of 9-beta-D-arabinofuranosyladenine and 2'-deoxycoformycin combinations on intracerebral leukemia.

Drug combinations of 9-beta-D-arabinofuranosyladenine and 2'-deoxycoformycin were active in the therapy of mice with intracerebral implants of the L1210 tumor. In in vivo mouse brain adenosine deaminase studies, inhibition of 9-beta-D-arabinofuranosyladenine deamination for periods of up to 24 hr was found after a single i.p. dose of 0.002 mmole/kg.

Adenosine Deaminase Inhibitors↗
PubMed1977

Effects of 2'-deoxycoformycin, 9-beta-D-arabinofuranosyladenine 5'-phosphate, and 1-beta-D-arabinofuranosylcytosine triple combination therapy on intracerebral leukemia 1210.

The triple combination of 2'-deoxycoformycin (2'-dCF), 9-beta-D-arabinofuranosyladenine 5'-phosphate, and 9-beta-D-arabinofuranosylcytosine was found to be very effective in the therapy of C57BL X DBA/2 F1 mice with intracerebral L1210. At the dosages and dosage scheduling used, the double combination of 2'-dCF and 9-beta-D-arabinofuranosyladenine 5'-phosphate gave minimal but significant increases in life-span. When 9-beta-D-arabinofuranosylcytosine was given at suboptimal dosage to mice with intracerebral L1210, the host toxicity caused by 2'-dCF and 9-beta-D-arabinofuranosyladenine 5'-phosphate in combination was decreased by a factor of 2, allowing a more prolonged therapy. "Cures" were obtained with the triple combination at dosages of 9-beta-D-arabinofuranosylcytosine that did not "cure". The supernatant adenosine deaminase from C57BL X DBA/2 F1 mouse brains was purified and the Ki for 2'-dCF using 9-beta-D-arabinofuranosyladenine as substrate was determined to be not more than 2 X 10(-11) M.

Adenosine Deaminase↗
PubMed1976

The affinity labeling of amino acids in or about the active center of DNA-dependent DNA polymerase I.

The use of an affinity label and an inhibitor that shows relative specificity for one amino acid has led to the identification of two amino acid residues in or near the active center of DNA-dependent DNA polymerase I. [35S]-beta-D-Ribosyl-6-methylthiopurine periodate oxidation product ([35S]MMPR-OP) and [14C]phenylglyoxal ([14C]PG) were used to elucidate the presence of a single lysine and arginine in or about the active center of the enzyme.

Amino Acids↗
PubMed1976

The metabolism of rhodium(II) acetate in tumor-bearing mice.

Rhodium(II) acetate has been shown to have carcinostatic activity in Swiss mice bearing Ehrlich ascites tumors. For metabolic studies, single therapeutic doses of rhodium(II) [1-14C]acetate that had been given i.p. implantations 3 days previously of 50-fold 10(6) Ehrlich ascites tumor cells. The tissue distribution and excretion of the rhodium (measured by atomic absorption spectrometry) and the acetate (measured by 14C label) were followed at designated time intervals up to 24 hr after injection. Rhodium(II) acetate, a neutral cage complex, breaks down to rhodium and acetate ionic species within 2 hr after i.p. injection, as measured by the rapid exhalation of 14CO2. Both the rhodium and 14C label disappear rapidly from the ascites fluid, with a small but variable amount of each species being incorporated into the tumor cells. Both species were detected mainly in the blood plasma, and the primary organ of deposition was the liver. No measurable quantity of rhodium was found in the brain tissue. During the first 24 hr following drug administration, only 5% rhodium was eliminated in the urine.

Acetates↗
PubMed1976

Enhancement of the antitumor activity of arabinofuranosyladenine of 2'-deoxycoformycin.

The 6C3HED lymphosarcoma, a tumor cell line very sensitive to 9-beta-D-arabinofuranosyladenine (ara-A), and 6C3HED/ara-A, a line resistant to ara-A, were studied. Both were responsive to 9-beta-D-arabinofuranosylcytosine (ara-C). Two lines of cells. L1210 and L1210/ara-C, are both resistant to ara-A and have very high levels of the deaminase that inactivates ara-A. When an effective inhibitor of the deaminase, 2'-deoxycoformycin, was combined with ara-A in the treatment of mice bearing L1210 or L1210/ara-C tumors, both became responsive to ara-A. Studies are reported on the extent of effects of 2'-deoxycoformycin at several dose levels and the duration of its effect in tumor cells and normal tissues. Single doses produce essentially complete inhibition of the deaminase, and little recovery was seen before 24 hr. However, DNA synthesis in normal tissues recovered more quickly. It is suggested that ara-A and ara-C, the former as a new derivative (9-beta-D-arabinofuranosyladenine 5'-phosphate) and possibly combined with 2'-deoxycoformycin, be regarded as potentially alternative drugs for the treatment of neoplasms.

Adenosine Deaminase↗