Figure 6

Sensitivity to DRB-induced apoptosis in prototypic leukaemia/lymphoma cell lines. (A) DRB induces HL60 cell death. HL60 cells were cultured in medium alone or containing 10–100 μM DRB, harvested at 24, 48 and 72 hr and analysed by flow cytometry after staining with PI. p < 0.005 with the test of independence at doses above 40 μM, compared to untreated cells. (B) DRB induces HL60 caspase activation and translocation of phosphatidylserine to the external leaflet of the cell membrane. Left panel: HL60 cells were kept for 24 hr in medium alone or containing 10–100 μM DRB, then harvested and stained with anti-active caspase-3 antibody. Histograms show the percentage of active caspase-3⁺ cells (mean ± S.D. of two independent experiments). Right panel: HL60 cells were kept for 24 hr in medium alone or containing 10–100 μM DRB, harvested and stained with annexin V and PI. Percentages of PI- annexin V+ cells are indicated. (C, D) The same experiments were performed on Namalwa cells. (E, F) The same experiments were performed on Raji cells, analysing caspase activation and translocation of phosphatidylserine to the external leaflet of the cell membrane 48 hr after treatment.