Cytotoxic interactions between oxaliplatin and fludarabine. (A) Apoptosis was compared in untreated CLL lymphocytes (i) or after incubation with 2.5 μM fludarabine (ii), 5 μM oxaliplatin (iii), or the combination (iv) for 24 hours. Apoptotic cell death was measured by Annexin V binding. Viable cells not undergoing apoptosis are Annexin V-FITC and PI negative; cells undergoing apoptosis are Annexin V-FITC positive and PI negative; cells already dead are Annexin V-FITC and PI positive. (B) Lymphocytes from healthy donors were incubated with 2.5 μM fludarabine, 5 μM oxaliplatin, or the combination for 24 hours. (C) Lymphocytes from patients with CLL were treated as in panel B. Values for Annexin V positivity are presented as the percentage of apoptotic cell death and expressed as the mean ± SE (n = 3). *P < .05 between the combination and the sum of fludarabine and oxaliplatin.