Induced Mutation with Standard Mutagens 
The standard mutagens, EMS and BrdU, were evaluated for mutagenic 
activity at several doses. Data pertinent to the mutagenicity of these 
compounds are presented in terms of the parameters of equation [2] in Table 
7-2. The estimated number of mutants per 10 6 viable cells (7) is plotted in 
Figure 7-6 as a function of relative dose. By expressing the mutagenesis data in 
terms of mutant cell frequencies per 10^ viable cells, meaningful comparisons 
between different compounds or different doses of the same compound could 
be made. Applying the data to equation [3], EMS was mutagenic at all doses 
tested (a< 0.05). BrdU was mutagenic at five of seven doses tested, and 
produced a complex dose-response pattern similar to those observed with 
hycanthone methanesulfonate, and other compounds in different assays (12, 
13 ). 
Induced Mutation with Other Compounds 
Forward mutation experiments employing doses of toxicant generally 
yielding 20 percent survival or greater were carried out in replica with several 
inorganic compounds, and an aqueous extract of JP-5 jet fuel. The data are 
presented in Table 7-3 in terms of the parameters of equation [2]. These 
compounds or mixtures were selected for evaluation as mutagens because they 
were either known to have, or were suspected of having, carcinogenic 
properties. Their mutagenic response in the CHO Cell/BrdU-VL system can be 
divided into three classes: (1) Experiments with the oxides of arsenic and 
selenium, lead acetate, and the chloride salts of cobalt and nickel, failed to 
produce any auxotrophs; (2) tests with beryllium and chromium usually 
produced auxotrophs, but never in sufficient numbers to support a conclusion 
of induced mutation; (3) Experiments with cadmium chloride, manganese 
chloride, and an aqueous extract of JP-5 jet fuel, also produce auxotrophs, 
sometimes in sufficient numbers to suggest induced mutation by these 
compounds. As indicated in Table 7-3, it was possible to obtain relatively large 
numbers of auxotrophs with CdCl->. Usually, however, observed mutant 
frequencies were low. Cadmium chloride was found to be significantly 
mutagenic in about 20 percent of experiments, as was the extract of JP-5 jet 
fuel. Manganous chloride was observed to be mutagenic in approximately 50 
percent of experiments. 
Isolation of Nonauxotrophic Variants 
Two classes of variants, other than auxotrophs, were isolated from cell 
populations treated with known genetic toxicants. One class consists of cells 
exhibiting a rounded morphology, and represents cells unable to stretch out on 
88 
