The in vivo rat micronucleus test: integration with a 14-day study.

A 14-day subchronic toxicity study is routinely conducted in Fischer 344 rats at the Lilly Research Laboratories. This study is done to gather preliminary toxicological information about chemical entities showing efficacy in various pharmacological screens. This manuscript describes the validation of a method for evaluating micronuclei in the bone marrow polychromatic erythrocytes of animals from this test in order to obtain additional information about the genotoxic potential of these compounds without incurring the cost of additional animals or the use of additional test article, which is often in limited supply. Compounds selected for evaluation were acetylsalicylic acid, mitomycin C, cyclophosphamide, colchicine, 6-mercaptopurine, and etoposide. With the exception of colchicine, the results obtained were as expected with acetylsalicylic acid yielding negative results and the other compounds yielding positive results. These findings are consistent with those published for mice (MacGregor et al., Fund. Appl. Toxicol., 14, 513-522, 1990) and show that a bone marrow micronucleus test can be successfully integrated into a routine subchronic rat toxicology study.

Localization of the xanthine guanine phosphoribosyl transferase gene (gpt) of E. coli in AS52 metaphase cells by fluorescence in situ hybridization.

The purpose of this study was to localize the xanthine guanine phosphoribosyl transferase gene (gpt) to a specific chromosome to investigate its proposed autosomal location in the AS52 cell line. AS52 cells are hgprt-deficient Chinese hamster ovary (CHO) cells which carry a single functional copy of the E. coli gpt gene. Fluorescence in situ hybridization (FISH) and digoxigenin-labeled probes, as small as 673 bp, were used in an attempt to localize the 456 bp gpt gene to a specific chromosome. Chi-square analysis of 13 metaphases showed significant labeling on autosomal chromosomes 6 or 7, which are indistinguishable without further banding analysis. Furthermore, a majority of the signals were on the q arm, proximal to the centromere. The data collected supports incorporation of the gpt gene into an acrocentric autosome of the AS52 cell line.