Effect of drug withdrawal on cell resistance. (A) Parental sensitive CCRF-CEM cells, resistant R10, and long-term drug withdrawn resistant (R10 longWD) cells were treated and cell death determined by annexin V-FITC/propidium iodide staining at the selected time points. Values represent the percentage of cells in each quadrant. Representative data from two independent experiments are shown. (B) A portion of each sample for SL profile analysis (Figure 5) was saved for XTT assay estimation of resistance. Briefly, R10 cells after 48 h and long-term drug withdrawal were subjected to 48 h treatment with 3 or 10 μM 4-HPR. All data were related to the corresponding untreated cells. Statistical analysis was related to R10 data. Data are average ± SD of 12 values from to three independent experiments. *P < 0.05; **P < 0.01; ANOVA plus Tamhane post-hoc test.