Evaluation of cytotoxicity by Nutlin-3 and γ-secretase inhibitors used alone or in combination in leukemic cells. OCI and SKW6.4 cells were exposed for 24 hours to Nutlin-3 (10 μM), DAPT (20 μM), or L-685,458 (20 μM), used either alone or in combination, as indicated. Cell viability was calculated as percentage with respect to the control (vehicle) cultures. Data are reported as means ± SD of results from 3 independent experiments. *P < .05 with respect to cultures treated with vehicle + Nutlin-3. (B) Leukemic cells were exposed to serial doses of Nutlin-3 or L-685,458, used either alone or in combination, with a fixed ratio, for 24 hours. Dose-effect plots to determine drug efficacy are shown for SKW6.4, OCI, representative TP53^wild-type B-CLL samples, and for one TP53^mutated B-CLL (patient no. 1). The decrease of cell viability, labeled “effect” on the y-axis, was determined in assays done at least twice in duplicate.