Cytotoxic effect of MDM2 antagonists on B-CLL cells. (A) Dose response of enantiomers of nutlin-3 on B-CLL cells. Cells from 5 patients were incubated for 48 hours with various doses of the active (nutlin-3a: ▪, •) or the inactive (nutlin-3b: □, ○) enantiomers. The figure shows results from 2 representative patients (patient 1, ▪, □; patient 2, •, ○). (B) Time course of nutlin-3a–induced apoptosis. Cells from patients 11 and 18 were incubated for different times with (▪, •) or without (□, ○)5 μM nutlin-3a (patient 11, ▪, □; patient 18, •, ○). (C) Cells from 26 patients were incubated for 48 hours with or without 5 μM nutlin-3a. ○ represent 6 patients with ATM alterations (patients 3, 11, 15, 20, 26, and 25); □ and discontinuous lines represent 2 resistant patients (patients 16 and 17). Viability was measured by analysis of phosphatidylserine exposure and PI uptake as described in “Patients, materials, and methods,” and is expressed as the percentage of nonapoptotic cells. (D) Dose response of nutlin-3a on B-CLL cells with TP53 (□, ○) or ATM (•, ▪, ▴, ♦) alterations. Cells were incubated for 48 hours with various doses of nutlin-3a. Viability was expressed as the percentage of the viability of untreated cells.