Characterization of the uptake and toxicity of a fluorescent thiol reagent

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Abstract
3‐(4‐Maleimidylphenyl)‐4‐methyl‐7‐diethylamino coumarin (CPM), is a fluorescent thiol‐binding agent. CPM is nontoxic to Chinese hamster V‐79 cells (2 × 105 cells/milliliter) exposed to 2.5 μg/milliliter for 30 minutes. However, both toxicity and cellular binding were directly dependent on the drug:cell ratio. Using flow cytometry, cellular binding of CPM correlated with inhibition of DNA synthesis. In cells pretreated with the thiol binding drugs N‐ethylmaleimide, diamide and diethylmaleate or the carcinogens 4‐nitroquinoline‐1‐oxide and AF‐2 (furylfuramide), the subsequent binding of CPM was reduced by 40% or more.