Cytoplasmic nucleoside kinase activity is elevated in AML. (A) Relative quantification of total intracellular ddC and ddCTP by LC-MS/MS in primary human AML (samples B1-B6) and normal hematopoietic progenitor samples following treatment with 2 µM ddC for 6 days. ddC and ddCTP content were normalized to total protein input and represented as mean ± SD (n = 2) of technical replicates within each independent experiment. Levels of ddC and ddCTP in each panel represent semiquantitative values. Each panel represents a separate experiment. Differences between ddC or ddCTP levels in each AML sample compared with mean of normal samples within an experiment was assessed using the Bonferroni posttest after 1-way ANOVA or the Student t test. *P < .05, ***P < .001. (B) Correlation between levels of ddC and ddCTP from samples in panel A was determined using the Pearson correlation method. BLQ, below the limit of quantification.