Cytosine arabinoside (Ara-C) is the major drug in the treatment of acute myelogenous leukemia, but human leukemic cells are heterogenous with respect to their response to the drug.
We measured in vitro suppression by Ara-C of 3H-thymidine incorporation into leukemic cells which obtained from children with relapsed acute leukemia.
1∼2×105 leukemic cells suspended in RPMI 1640 with 25 mM Hepes buffer and 30% patient's serum were placed in wells of microtiter plates with Ara-C at final concentration of 30 ng/ml. After 5 and 24 hours of incubation, 0.2 μCi of 3H-thymidine were added to each well and, after 3-hour labelling period, counts of 3H-thymidine uptake were made on aliquots of cells drawn from the well with automated cell harvestor.
In the leukemic cells of 3 children who achieved complete remission by low dose Ara-C therapy, the degree of suppression of 3H-thymidine incorporation at 5 hours after incubation with Ara-C remained until 24 hours. In contrast, the patient whose cells showed the recovery of 3H-thymidine uptake at 24 hours, though revealed the suppression at 5 hours, did not achieved remission.
These experience suggests that this in vitro sensitivity test reliably predicts the effectiveness of low dose Ara-C therapy in patients with relapsed acute leukemia.
