Establishment of ara-G-resistant CEM variant, CEM/ara-G. (a) The growth inhibition curve. Cells were incubated with various concentrations of ara-G for 72 h, and the IC50 was then determined by using the XTT assay. (b) Doubling time for CEM cells and CEM/ara-G cells. (c) Intracellular ara-GTP concentrations. CEM cells and CEM/ara-G cells were incubated for 6 h with 10 μM ara-G, followed by an extraction of the nucleotide pool and subsequent measurement of ara-GTP by using HPLC. *P = 0.0006 determined by unpaired T test. (d) Apoptotic cell death induced by ara-G. CEM cells and CEM/ara-G cells were incubated with 10 μM ara-G for 72 h, followed by the evaluation of annexin V positivity by flow cytometry. *P = 0.002 determined by unpaired T test. The values shown are the mean ± SD of at least three independent experiments.