Type 5/6 PDE inhibitors induce apoptosis of CLL PBMCs in vitro.

(A) PBMCs isolated from 14 patients with CLL were cultured for 24 hours in the presence (░) or absence (□) of sildenafil (50 μg/mL). (B) Differential induction of apoptosis in CLL PBMCs by various phosphodiesterase inhibitors (mean percentages ± SEMs). Apoptosis was determined by double staining with FITC-labeled annexin V and PI analysis by flow cytometry. Percentage annexin V⁺ cells are calculated as described in “Patients, materials, and methods.” Statistical analysis was performed using the paired Student t test (*P < .05; **P < .01; ***P < .001).