Cytosine arabinoside as a suicide agent for human colony forming cells

The fractional reduction of cloning efficiency, otherwise known as in vitro suicide, produced by HU or 3H-TdR, is considered equivalent to the fraction of colony forming cells (CFC) in S phase and is used for the evaluation of proliferation in this population. The accuracy of both agents has been discussed. We tested cytosine arabinoside (Ara-C) on normal and pathological human bone marrow GM-CFC on different parameters. A plateau of concentrations between 1 and 5 X 10(-6) M was found to be as effective as 3H-TdR in diminishing 7 to 9 day colonies. Ara-C solutions were equally effective up to 18 weeks of storage at 4 degrees C; suicide levels were unchanged between 2 X 10(5) and 5 X 10(6) cells/ml; incubation with Ara-C was not critical between 1 and 2 h. Unlike HU, Ara-C does not require strict conditions of cell concentration, incubation time or extemporaneous preparation. Compared with 3H-TdR, Ara-C is easy to handle and does not show a decrease in cell cloning with the duration of the culture suggesting a prolonged action of the drug. Results on cell killing are comparable with the three drugs on day 7 to 9 colonies and we conclude that Ara-C is a reliable agent for suicide studies on human bone marrow GM-CFC.