Suspension cultures of Chinese hamster (CHO) cells, containing 10 μM bromodeoxyuridine (BrdU), were exposed to ethyl methanesulfonate (EMS) 4.0-20 x 10-4 M) or mitomycin-C (MMC) (1.5-7.5 x 10-8 M) for 18 hr. For each dose the cultures were then divided. One fraction was grown in normal medium and then plated on days 4 and 5 into medium containing 15 μg/ml azaguanine for selection of resistant mutants. The second fraction of each dose was further divided into smaller replicate cultures, containing 10 μM BrdU, which were used to prepare chromosomes at 4-hr intervals between 18-32 hr. This sampling, combined with a 4-hr Colcemid block of each culture before harvesting, insured collection of the entire population of second division cells. Because the frequency of sister chromatid exchanges (SCEs) induced by EMS or MMC was not constant over the collection intervals a weighted average frequency was used. Both drugs produced a linear increase in SCEs as a function of dose; MMC was 104 times more effective on a molar basis. Mutation frequencies determined after 4 and 5 days expression were the same, indicating the achievement of plateaus for the induced frequencies. EMS exhibited a linear dose-response for mutation induction while MMC produced only a slight increase over background for the concentration range examined. Comparison of the slopes from a linear regression analysis showed that EMS was 1.6 times more efficient in producing mutations than SCEs. On the other hand, MMC was 11 times more efficient in producing SCEs than mutations. These preliminary results suggest that SCEs are a qualitative predictor of induced mutations for testing chemical agents.
|Original language||English (US)|
|Title of host publication||Mutation Research|
|State||Published - 1978|
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