Comparison of residual viable cells after treatment with F-ara-A or PEITC. (A) Representative cell viability curves of F-ara-A–sensitive CLL cells treated with various concentrations of F-ara-A or PEITC for 72 hours and cell viability was measured by MTT assay. (B) Representative cell viability curves of F-ara-A–resistant CLL cells treated with various concentrations of F-ara-A or PEITC for 72 hours. (C) Quantitative comparison of percentage of viable cells after treatment with 20 μM F-ara-A or 10 μM PEITC (72 hours, MTT assay) in F-ara-A–sensitive and –resistant CLL cells. Each data point represents the mean of triplicate measurements for each patient sample. (D) Comparison of cellular thiols in control (untreated) CLL cells and in the residual viable CLL cells after treatment with 20 μM F-ara-A for 72 hours, using CMFDA and annexin V–PE dual staining flow cytometric analysis. Viable cells were defined as annexin V–negative subpopulation, which was gated as R1 (D left and middle panels). Cellular thiol levels in the R1 cell population of the control sample and the F-ara-A–treated sample were shown on the right panel. Representative plots of 3 different patients are shown.