Nutlin-3 induces cytotoxicity toward B-CLL cells via apoptosis. After exposure to nutlin-3 for 24 hours, B-CLL samples were analyzed by flow cytometry, after staining with annexin V–FITC/PI (A) and by Western blot on cell lysates (B). (A) Induction of apoptosis in nutlin-3–treated B-CLL samples, calculated with respect to control cultures (vehicle alone). For selected samples (nos. 6, 9, 12, 15, 16), aliquots of frozen B-CLL cells were thawed and retested for response to nutlin-3 (▦). Results are expressed as mean plus or minus SD of assays each performed in triplicate. (B) Western blot analysis for PARP and procaspase-3 after 24 hours of treatment with increasing doses of nutlin-3 of representative B-CLL cultures. The proform of PARP (115 kDa) and the cleaved form (80 kDa; arrowhead) are shown. The dose-dependent PARP cleavage in B-CLL cultures is concurrent with the decrease in the procaspase-3. Error bars indicate SD.