In vitro sensitivity of CFU-L to cytosine arabinoside (Ara-C)

The in vitro sensitivity of leukemic colony-forming cells to Cytosine arabinoside (Ara-C) was assessed in acute myeloid leukemia, by means of a clonogenic assay using methyl-cellulose with phyto-hemagglutinin (PHA)-leukocyte conditioned medium. Bone marrow clonogenic cells were more sensitive to Ara-C than blood clonogenic cells. Also a continuous exposure to Ara-C induced a higher reduction of the leukemic colonies than one hour exposure. Patients were, according to the in vitro results, divided into 3 groups: eight patients had a dose-responsive curve for all the tested drug concentrations and were characterized by a marked sensitivity to the induction treatment combining Ara-C and Adriamycin. Three patients had a = 50% reduction of colonies with the 3 concentrations; two achieved complete remissions. Seven patients were in vitro insensitive to the drug; four of them had a relative or absolute resistance to the induction treatment.