A comparison of two methods for determining the sensitivity of human myeloid colony-forming units to cytosine arabinoside.

Studies were carried out to determine the optimal method for measuring the sensitivity of myeloid clonogenic cells to cytosine arabinoside (ara C). Bone marrow or peripheral blood cells were either exposed to different concentrations of ara C for 1 h in vitro and then after washing were plated in agar and cultured for 7 d in vitro, or were directly plated in agar containing different concentrations of the drug. The 3H-TdR suicide index of the clonogenic cells was also determined. Washing the specimens under study subsequent to incubation with ara C prior to plating in agar provided the most accurate measure of the ara C sensitivity of the clonogenic cells. When carried out in conjunction with the 3H-thymidine suicide index, the 'wash' method permitted the simultaneous determination of both the kinetic and metabolic sensitivity of these cells to ara C. Using this combined method, it was observed that the differences between the ara C sensitivity of the CFUc of different individuals resulted from differences in the proportion of clonogenic cells synthesizing DNA in the different marrow specimens.