The third UKEMS collaborative trial.
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Biomedical subjects
M F Cross
Publications and source records attributed to M F Cross.
Microwell mutation assays: evaluation of ethylmethanesulphonate, benzo[a]pyrene and benzidine using the tk locus in L5178Y mouse lymphoma cells.
As part of the third UKEMS collaborative trial, ICI Central Toxicology Laboratory (CTL) tested the three study chemicals ethylmethanesulphonate (EMS), benzo[a]pyrene (B[a]P) and benzidine (BZD) in a microwell adaptation of the L5178Y gene mutation assay using the thymidine kinase (tk) locus. Cofactors for metabolic activation were optimized prior to testing the chemicals under differing expression times (48 and 72 h) and S9 levels (2,5 and 10%). The results for zero hour survival, relative total growth and mutant frequency were subjected to extensive statistical analyses. It was concluded that the methods described produce a robust and reliable assay and that for routine use a single 72 h expression time and 5% S9 level are sufficient, provided true independent replicates are used.
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Determination of benzidine--DNA adduct formation in CHO, HeLa, L5178Y, TK6 and V79 cells.
Using 32P-postlabelling, evidence of DNA adduct formation was sought in six mammalian cell lines, namely Chinese hamster ovary (CHO), human cervical carcinoma (HeLa S3), mouse lymphoma L5178Y tk +/- and L5178Y wild-type, human lymphoblastoid TK6 and Chinese hamster V79, following treatment with benzidine (BZD) in the presence of S-9. Adduct formation was also determined in calf thymus DNA reacted in vitro with N-hydroxy-N'-acetyl-BZD, and in liver DNA from mice given a single intraperitoneal injection of BZD. DNA adducts were detected in the calf thymus DNA sample and in mouse liver DNA, but not in DNA from any of the six cell lines. The absence of adduct formation is consistent with the lack of mutagenicity of BZD in CHO, and V79 and in L5178Y cells at the hprt locus, and in TK6 cells at the tk and hprt loci. These results also suggest that the observed mutagenicity of BZD at the tk locus in L5178Y cells may be due to a mechanism(s) not involving covalent binding to DNA.
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Activity of bromochlorodifluoromethane (BCF) in three mutation tests.
The halocarbon BCF was tested in 3 assays to assess its mutagenicity and clastogenicity. It produced a positive response in Salmonella typhimurium strain TA1535 but was negative in TA1537, TA1538, TA98 and TA100. In an L5178Y mouse lymphoma microwell assay (TK locus), BCF was negative. BCF was administered at 5000 and 50 000 ppm in air for 6 h to groups of C57B1/6J mice of both sexes. Animals were killed at 24, 48 and 72 h after cessation of exposure and the incidence of bone marrow micronuclei per 1000 PCEs determined. There was no significant difference in the incidences of micronuclei between untreated animals and those exposed to either concentration of BCF at any of the sampling times. These results suggest that BCF is mutagenic in vitro in only one strain of Salmonella; in mammalian cells the compound induced no gene mutation in vitro nor clastogenic activity in vivo at doses that also produced clear evidence of toxicity.
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Suitability of the P388F mouse lymphoma system for detecting potential carcinogens and mutagens.
The P388F mouse lymphoma (TK +/-) system has been evaluated further for use as a primary mammalian-cell test and as a complementary assay to the Ames Salmonella reverse-mutation assay. The system showed a clear dose response with three alkylating agents of previously demonstrated genotoxic potential and gave the anticipated positive result with benzo[a]pyrene in the presence of S-9 mix. In addition, while giving the expected negative result with sugar, the assay detected genotoxic activity in hexamethylphosphoramide, acrylonitrile and formaldehyde, all of which are known to give negative results in the Ames test.
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