Effects of E21R and cytosine arabinoside. (A) Effect of E21R or cytosine arabinoside (Ara-c) on the survival of AML blasts. Primary AML blasts were incubated with increasing concentrations of E21R for the indicated times or with increasing concentrations of cytosine arabinoside for 48 hours. Samples were assayed in duplicate by the MTS technique for viable cell number, and the data are presented as the mean ± SEM activity as a percentage of the result obtained with cells incubated without additives. For E21R, n = 15 at 24 hours (□), 23 at 48 hours (▦), and 14 at 72 hours (▪). For Ara-c, n = 21 at 48 hours (▨). (B) Effect of E21R combined with Ara-c on the survival of AML blasts. Primary AML blasts were incubated with Ara-c alone (at 10 ng/mL or 100 ng/mL) or in combination with E21R (10 μg/mL) for 48 hours and cell survival measured by MTS assay (mean ± SEM of 21 samples).