Synergism between Nutlin-3a and F-ara-A is maintained in low Atm cases. Results of annexin V–binding assay in 30 Nutlin-sensitive samples (Figure 1) were separately analyzed with regard to Atm expression levels. Cells were incubated with the indicated concentrations of Nutlin-3a or F-ara-A, and the annexin V–positive fractions were measured by flow cytometry at 24 hours. Results are expressed as mean ± SEM. □ indicates Nutlin-3a; ▦, F-ara-A; and ▪, combination.