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G F Whitmore

Publications and source records attributed to G F Whitmore.

At least 37 records · Page 2Linked to original sources
PubMed1984

Detection of a reactive metabolite of misonidazole in human urine.

Chemical studies have indicated that, following reduction of misonidazole to the hydroxylamine derivative, reaction with guanosine leads to the formation of a 2-carbon addition product of guanosine. In this study, the formation of the guanosine product is used to detect the presence of a reactive metabolite of misonidazole in the urine of patients treated with misonidazole. Urine samples were incubated with [14C]guanosine and the guanosine product was separated by HPLC analysis. The quantities of product vary as much as 10-fold from patient to patient and it is suggested that the assay might be useful as a predictor of patients susceptible to the development of peripheral neuropathy or other effects of misonidazole.

Combined Modality Therapy↗
PubMed1984

Detection of a reactive metabolite of misonidazole in hypoxic mammalian cells.

A misonidazole metabolite capable of reacting with guanosine has been detected in extracts of Chinese hamster ovary cells exposed to misonidazole under hypoxic conditions. A misonidazole metabolite with identical chromatographic properties and reactivity with guanosine has been detected in earlier studies with misonidazole reduced to the hydroxylamine state by chemical, radiolytic, or electrolytic means. The proposed structure of the guanosine product involves the addition of a two-carbon fragment between the N1 and N2 positions of guanosine. Rearrangement of the N-hydroxy derivative of misonidazole to a C-hydroxy derivative is postulated as the initial step in the reaction scheme.

Animals↗
PubMed1983

Modification of guanine derivatives by reduced 2-nitroimidazoles.

Misonidazole, after reduction to the hydroxylamine derivative, was found to react with guanosine in aqueous solution at pH 7. The guanosine product was isolated and was assigned a structure having a new 5-membered ring with a -CHOH-CHOH-linkage between the N-1 and N-2 positions of guanine. Removal of the sugar residue from the guanosine product by acid hydrolysis resulted in the corresponding guanine derivative, which was also made by reacting guanine with reduced misonidazole. In aqueous solution at pH 11, the guanine product was quantitatively converted to guanine within 20 min. A number of N-1-substituted 2-nitroimidazoles and 2-nitroimidazole reacted with guanosine in an analogous manner, giving rise to the same product as misonidazole, indicating that the C-4-C-5 fragment from the imidazoles is involved in the modification. Neither misonidazole nor its amine or hydrazo derivatives reacted with guanosine. Reduced misonidazole reacted with N-2-methyl guanosine, whereas with N-1-methyl guanosine a reaction was not detected. The identity of Structure I was confirmed by comparison with an authentic sample of Structure I that was prepared by reacting guanosine with glyoxal. Reactions such as the modification of guanine provide a possible molecular mechanism for the cytotoxic and neurotoxic properties of misonidazole.

Chemical Phenomena↗
PubMed1981

Cellular and chemical reduction products of misonidazole.

Misonidazole is readily reduced by zinc dust in aqueous solution in the presence of ammonium chloride. High pressure liquid chromatographic (HPLC) separation of the reduction mixture revealed the presence of three products. These were identified as the hydroxylamine, amine and the hydrazo derivative of misonidazole. There is evidence that the azoxy derivative was an intermediate in the reduction process. When the reduction was carried out in dilute solution (0.1 mg/ml), the hydroxylamine was the only product. In concentrated solution (20 mg/ml), the hydrazo derivative was the major product. When misonidazole was reduced with hydrogen using palladium as catalyst, the amine was the only detectable product. Of the three products, only the hydroxylamine was found to bind covalently to bovine albumin. In Chinese hamster ovary (CHO) cells under hypoxic conditions the amine was confirmed as one of the metabolites. There was no evidence for the presence of detectable amounts of the hydroxylamine in the cell extracts. These studies suggest that the hydroxylamine is probably the reactive reduction metabolite responsible for the in vivo and in vitro binding of misonidazole to cellular macromolecules.

Animals↗
PubMed1981

Toxicity of 4'-(9-acridinylamino)methanesulfon-m-anisidide in exponential- and plateau-phase Chinese hamster cell cultures.

The antitumor acridine derivative 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA) is at present being evaluated in Phase 2 clinical trials. Exposure of exponential-phase Chinese hamster V79-171b cells to physiologically attainable concentrations of m-AMSA for 60 min generates survival curves with little or no threshold region and an initial D0 of 0.245 +/- 0.019 (S.D.) microM under standard conditions of assay. A minor subpopulation of apparently drug-resistant cells is revealed at low survivals, but these cells on culturing do not display a stable drug-resistant phenotype. m-AMSA survival curves for Chinese hamster ovary cells display features similar to the above. Sensitivity of V79-171b cells to m-AMSA is maximal near pH 7.2 and is markedly reduced by the presence of fetal calf serum. Hypoxia has little effect on the toxicity of m-AMSA, and repair of potentially lethal damage has not been observed after treatment with this agent. Noncycling plateau-phase V79-171b or Chinese hamster ovary cells are markedly less sensitive to m-AMSA than are early log-phase cells. This resistance to m-AMSA appears to be related to the slowly cycling or noncycling status of plateau-phase cells, suggesting that the cytokinetic character of cell populations in vivo will be a major determinant of their sensitivity to this drug. However, the increase in resistance to m-AMSA during growth into plateau-phase appears to commence well before departure from exponential growth can be detected and may thus be a consequence of metabolic changes more subtle than the transition from a cycling to a noncycling state.

Aminoacridines↗
PubMed1981

Activity of 4'-(9-acridinylamino)methanesulfon-m-anisidide against Chinese hamster cells in multicellular spheroids.

The cytotoxic activity of 4'-(9-acridinylamino)methanesulfon-m-anisidide (m-AMSA), a novel acridine derivative with clinical antitumor activity, has been examined in multicellular spheroids grown from Chinese hamster V79-171b cells. m-AMSA is much less effective against cells within these tumor-like structures than it is against exponential-phase V79-171b cells in monolayer cultures, the initial D0 of the survival curve for the latter being approximately 10-fold lower than for the former following a 60-min exposure to the drug. The resistance of spheroid cells to m-AMSA appears to be at least partially a result of the noncycling or slowly cycling state of the majority of these cells, although they are more sensitive than cells in plateau-phase monolayers. A further component of resistance in spheroids requires the presence of an intact spheroid structure and may be due to drug transport limitations. The use of sequential trypsinization techniques to recover cells at varying depths within spheroids demonstrates that a 60-min m-AMSA treatment preferentially kills cells nearest the spheroid surface, suggesting that tumor cells at a distance from the vasculature may limit the efficacy of m-AMSA in vivo.

Aminoacridines↗
PubMed1980

A screening method for isolating DNA repair-deficient mutants of CHO cells.

A simple procedure for isolating mutagen-sensitive clones of CHO cells was developed and applied in mutant hunts in which colonies were screened for hypersensitivity to killing by ultraviolet radiation (UV, ethyl methanesulfonate (EMS), or mitomycin C (MMC). Each of two UV-sensitive clones studied in detail had a D37 dose of 1.0 J/m2 compared to 7.0 J/m2 for the wild-type cells, and each was shown to have no detectable repair replication following exposure to UV doses of up to 26 J/m2. Although these mutants resemble xeroderma pigmentosum human mutants with respect to their repair defect and cross-sensitivity to the carcinogen 4-nitroquinoline-1-oxide, one of two clones (UV-20) is characterized by extreme hypersensitivity to MMC (80-fold as compared to the wild type). Clones having hypersensitivity to alkylating agents, but not UV, were obtained using MMC and EMS. In the latter case the two clones had significantly increased sensitivity to the killing action of 60Co gamma-rays.

Animals↗
PubMed1980

Binding to cellular macromolecules as a possible mechanism for the cytotoxicity of misonidazole.

Reduction of the nitro group occurred when [14C]misonidazole was treated with zinc dust in aqueous solution in the presence of ammonium chloride. When the reduction mixture was allowed to react with calf thymus DNA or bovine albumin, radioactivity was bound to both DNA and protein. Under the same conditions, misonidazole did not bind to these macromolecules. Analysis of the reduction mixture indicated that the hydroxylamine, amine, and hydrazo derivatives of mizonidazole were the major products. In a number of tissues of C3H mice after administration of [14C]misonidazole, radioactivity was detected in the DNA, RNA, and protein fractions. Similar results were also obtained with Chinese hamster ovary cells incubated with the drug in the absence of oxygen. It is postulated that nitroreduction and binding of the nitroreduction products to macromolecules is a probable mechanism for the mutagenic and cytotoxic properties of misonidazole.

Ammonium Chloride↗
PubMed1980

Binding of nitroreduction products of misonidazole to nucleic acids and protein.

[14C]Misonidazole was reduced with zinc dust in aqueous solution in the presence of ammonium chloride. When the reduction mixture was allowed to react with calf thymus DNA and the reaction mixture was dialyzed, radioactivity was detected in the DNA fraction. Bovine albumin, after reaction with the reduction mixture and subsequent Bio-Gel P-2 column chromatography, was also found to be radioactive. The hydroxylamine derivative of misonidazole was detected in the reduction mixture. It is postulated that binding of nitroreduction products of misonidazole to cellular macromolecules is a probable mechanism for the cytotoxicity of misonidazole.

Ammonium Chloride↗
PubMed1977

Segregation studies in CHO hybrid cells: I. Spontaneous and mutagen-induced segregation events of two recessive drug-resistant loci.

The process of segreation or phenotypic expression of two recessive drug-resistant loci from heterozygous Chinese hamster ovary hybrid lines is examined. The spontaneous segregation rates of phytohaemagglutinin resistance (Phar) and a temperature-dependent 8-azaguanine-resistant locus (Azarts) from heterozygous quasitetraploid lines using Luria-Delbruck fluctuation analysis were 5 X 10(-5) and 10(-5) events/cell/generation, respectively. In quasihexaploid lines, the latter rates increased 40- and 200-fold, respectively, and were dependent on the number of presumptive drug-sensitive allelel. The mutagens EMS, MNNG, ICR-170, ICR-191, and gamma rays significantly increased the frequency of segregation events. The mutagen-induced frequency of dominant mutations to ouabain (Ouar) and alpha-amanitin (Amar) rsistance in the same hybrid line was much lower in comparison to segregation events and was mutagen specific. The chromosome number per metaphase cell was more variable than DNA content in quasitetraploid lines. These properties of marker segregation are consistent with mechanisms of either restricted chromosome loss, rearrangement, or mutation.

Azaguanine↗
PubMed1975

The potential for radiation sensitizers and possible strategy for use.

The search for radiation sensitzers for use in radiotherapy is based on the assumption that proper use of these compounds will provide a differential sensitization of tumor and normal tissue. Based on the evidence that hypoxic cells exist within human tumors but not within normal cell populations, there is reason to believe that specific sensitizers of hypoxic cells might provide useful therapeutic benefit. This paper discusses the possible advantages of such sensitizers, over reliance on the phenomenon of reoxygenation, and describes very briefly the current status of hypoxic cell sensitizers. Finally a proposal is made concerning the way in which such sensitizers might be tested for their efficacy in human radiotherapy.

Animals↗
PubMed1975

Mechanism of growth inhibition by methotrexate.

The effect of methotrexate on the growth of Chinese hamster cells was examined under a variety of conditions. The experiments suggest that the important biological effects of methotrexate are the result of direct inhibition of thymidylate synthetase and one or both of the folate-dependent enzymes involved in a purine biosynthesis. In addition, analysis of the distribution of intracellular folate derivatives following methotrexate treatment gives no indication of accumulation of dihydrofolate, and accumulation that would be expected if inhibition of dihydrofolate reductase were the principal site of methotrexate action.

Animals↗