THE USE OF L5178Y MOUSE LYMPHOMA-CELLS TO ASSESS THE MUTAGENIC, CLASTOGENIC AND ANEUGENIC PROPERTIES OF CHEMICALS

Guidelines have been proposed to assess the potential of chemicals to affect human health, Written into these guidelines is the requirement that information be submitted on mutagenic activity, Although regulato ry agencies accept mutagenicity data from both the hprt and tk loci in mammalian cells, many studies suggest that the L5178Y mouse lymphoma assay at the thymidine kinase locus is likely to detect a greater spec trum of mutagenic lesions, Thus, there is increasing emphasis being pl aced on this assay in many proposed and published guidelines, The L517 8Y mouse lymphoma suspension protocol produces both small and large co lonies which are the products of mutants growing at different rates, T here is a reduction in the proportion of slowly growing mutants with r espect to the total population of cells when expression is carried out in suspension, This potentially leads to quantitatively inaccurate as sessments of the mutagenic activity of chemicals, Therefore an in situ procedure was developed that more accurately assesses the mutagenic a ctivity of chemicals by maximizing the detection of small colonies, Ma ny guidelines recommend tests that assess the clastogenic activity of chemicals. Some regulatory agencies accept data from the mouse lymphom a mutation assay to detect clastogens if the protocol is optimized for the detection of small colonies or if colony sizing data are submitte d, The conventional suspension assay protocol is not sufficiently vali dated for this purpose. The in situ protocol has greater potential to meet these requirements, However, although this strategy might be suit able for detecting compounds that induce gene mutations and chromosoma l aberrations in cells, it should not be used to distinguish these two responses from each other because there are insufficient data showing that small and large colony populations always represent the inductio n of chromosome aberrations and gene mutations, respectively, It is, n evertheless, possible to infer not only mutation and clastogenesis but also aneugenesis in one culture using mouse lymphoma cells, To achiev e this, we recommend an assessment of micronucleus formation with an a nalysis of micronuclei for the presence of whole chromosomes and chrom osomal fragments in mouse lymphoma cells coupled with the measurement of TFT resistance using the in situ protocol with these same cells, Th is should result in eventual validation of a simpler and more accurate method for ascertaining these endpoints.