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Biomedical subjects

T A Connors

Publications and source records attributed to T A Connors.

At least 37 records · Page 2Linked to original sources
PubMed1987

Effects of substituted 2-nitroimidazoles and related compounds on unscheduled DNA synthesis in rat hepatocytes and in non-transformed (BL8) and transformed (JB1) rat liver epithelial derived cell lines.

1. Using unscheduled DNA synthesis as an index, the possible interaction of a number of substituted nitroimidazoles, e.g. misonidazole, with cellular DNA has been investigated. Transformed (JB1), non-transformed (BL8) rat liver epithelial derived cell lines and freshly prepared rat hepatocytes have been used. 2. Under anaerobic or aerobic conditions, relative to cells exposed to a nitroquinoline-N-oxide standard, misonidazole and related nitroimidazoles were very poor at stimulating unscheduled DNA synthesis in JB1 or BL8 cells or in hepatocytes, even at the highest concentrations tested (10 mM). Under anaerobic conditions, metabolic activation did occur as judged from the time-dependent depletion of cellular reduced glutathione in all three cell types. 3. It was concluded that in hypoxic cells an important mode of action of such nitroimidazoles as chemotherapeutic sensitisers may be by their interaction with cellular thiols rather from their interaction with DNA. 4. Functionalisation of the nitroimidazole ring with a side chain containing an aziridine function, e.g. RSU-1069 (1-(2-nitro-1-imidazolyl)-3-(1-aziridinyl)-2-propanol), results in the induction of unscheduled DNA synthesis in cells exposed under both aerobic and anaerobic conditions. On a molar basis, however, this induction was not so great as that caused by the simple monofunctional alkylating agent 1-aziridineethanol itself. Methyl-substitution of the aziridine ring in RSU-1069 reduced the extent of unscheduled DNA synthesis. 5. With all the compounds tested, unscheduled DNA synthesis was greater in JB1 cells than in BL8s or in hepatocytes.

Animals↗
PubMed1987

Preliminary investigations into the involvement of the intestinal microflora in CNS toxicity induced by 1,3-dinitrobenzene in male F-344 rats.

Administration of a single oral dose of 20 mg/kg of 1,3-dinitrobenzene caused ataxia in germ-free male F-344 rats but not in conventional rats. Repeated oral dosing of 20 mg/kg, 1,3-DNB was required to cause ataxia in conventional rats. Considerable differences were observed between the uptake, tissue distribution and excretion of DNB in germ-free and conventional rats.

Administration, Oral↗
PubMed1985

In vitro covalent binding of cismethrin, bioresmethrin, and their common alcohol to hepatic proteins.

When [14C]Alcohol-labeled cismethrin, bioresmethrin, and 5-benzyl-3-furylmethyl alcohol (BFA) were incubated with rat liver S 9 homogenates or microsomes, a proportion of the radioactive compounds was covalently bound to proteins. The covalent binding was greater with phenobarbital-pretreated rats, and dependent on a NADPH-generating system. When a S 9 homogenate was used, the bound compounds were twofold higher for cismethrin than for bioresmethrin and BFA. Inversely, when microsomes were used more covalent binding occurred with bioresmethrin and BFA than with cismethrin. The inhibition of esterases by tetraethyl pyrophosphate (TEPP) in a S 9 homogenate did not alter the amount of covalent binding to the three compounds whereas malathion inhibited this binding. Treatment of a S 9 homogenate with piperonyl butoxide, however, greatly reduced covalent binding. Covalent binding was inhibited when the microsomes were incubated with carbon monoxide or modified by thermal denaturation. It is suggested that oxidative metabolism was responsible for the covalent binding.

Animals↗
PubMed1984

Synthesis and preliminary characterization of a novel substrate for gamma-glutamyl transferase. A potential anti-hepatoma drug.

9he synthesis and chemical characterization of the gamma-glutamyl adduct of phenylenediamine mustard is reported. The activity of this compound, gamma-[N,N-bis(2-chloroethyl)-p-phenylenediamine]-glutamate, as a substrate for gamma-glutamyl transferase is demonstrated and compared with the activity of glutathione. The possible use of this material as a directed anti-hepatoma agent is discussed.

Aniline Mustard↗
PubMed1981

Methylation of cysteine in hemoglobin following exposure to methylating agents.

In addition to reacting with biologically important nucleophilic sites in DNA, alkylating agents also interact with amino acids in proteins. Measurements of the extent of formation of these alkyl amino acids may be used as a means of determining exposure to these compounds. The degree of S-methylation of cysteine in hemoglobin was studied following in vivo exposure of rats to methyl methanesulfonate, dimethylnitrosamine, and 5-(3,3-dimethyl-1-triazeno)imidazole-4-carboxamide. A linear dose-response curve was observed for methyl methanesulfonate over a 100-fold dose range. For dimethylnitrosamine, there was a threshold of doses where no methylation could be detected, and a curved dose-response curve was obtained. At high doses, the degree of methylation of hemoglobin cysteine was 7-fold lower than that with methyl methanesulfonate. In vivo, no alkylation could be observed with 5-(3,3-dimethyl-1-triazeno)imidazole-4-carboxamide; however, the existence of naturally occurring S-methylcysteine in the rat hemoglobin may have overshadowed small increases in alkylation arising from exposure to this compound. The natural occurrence of S-methylcysteine was studied in 13 species, and amounts ranging from 5.6 nmol/g globin (hamster) to 481 nmol/g globin (partridge) were observed. The reason for its occurrence is unknown but is under investigation.

Alkylating Agents↗
PubMed1977

Preparation and antitumor activity of 1-aryl-3,3-dimethyltriazene derivatives.

Several 1-aryl-3,3-dimethyltriazene derivatives have been synthesized and tested for their antitumor activity against the TLX5 lymphoma in mice. These compounds are characterized by the presence of a carbonyl group bound to the benzene nucleus in the para position to the triazene funciton. Three p-sulfamoyl derivatives have also been included and proved to be inactive. Among the carbonyl derivatives compounds 1 and 20, which can be used as reference, cause ILS of about 50%, respectively, at four and three dose levels. Compound 16, the o-nitro-phenylhydrazone of the hydrazide 1, is active at all six dose levels studied. The adduct 19, obtained from the same hydrazide and p-nitrobenzaldehyde, is active at four dose levels, and the ILS values at two optimum doses are significantly greater than those caused by compound 1.

Animals↗