Comparison of cytotoxic activity of apoossypol and gossypol against human B-cell malignancies. NHL B-cell lines bearing t(14;18) translocations (DoHH2, RS11846, and 380) (top) and primary CLL specimens (bottom) were cultured at 10⁶ cells/mL for 48 hours in the absence (vehicle control [white squares]) or presence of various concentrations (log-scale) of gossypol (black circles) or apogossypol (white circles). Percentage viability was determined by staining with FITC–annexin V and PI, scoring viable cells as annexin V negative/PI negative. Data for NHL are representative of several experiments. For CLLs, primary data are shown for 3 patient specimens that had low spontaneous rates of cell death in culture (Rai stage II [n = 1]; Rai stage I [n = 2]), derived from previously untreated patients. Differences in percentage viability between CLLs treated with apogossypol versus gossypol were statistically significant (P < .025 by 2-way ANOVA analysis). An additional 3 CLL specimens were also tested and showed similar sensitivity to gossypol and apogossypol, but higher levels of background cell death precluded determination of LD50 (not shown).