In vitro sensitivity and metabolism of ara-C in myeloblasts from AML patients. DS myeloblasts were significantly more sensitive to both ara-C (A) and daunorubicin (B) compared with non-DS myeloblasts (P < .0001 and P < .0001, respectively). ³H-Ara-CTP generation in DS myeloblasts was significantly higher compared with non-DS myeloblasts after incubation with ³H-ara-C (P < .0001; C).