Bryostatin 1 potentiates paclitaxel-induced apoptosis in leukemic cell lines.

(A) U937 cells were exposed to 5 nM paclitaxel (Tax) in combination with increasing concentrations of bryostatin 1 (Bry; 10 to 100 nM) for 24 hours, after which the percentage of apoptotic cells was determined by flow cytometric analysis of annexin V/PI–stained cells as described in “Materials and methods.” (B) U937 cells were treated with 10 nM bryostatin 1 combined with the indicated concentrations of paclitaxel for 24 hours, after which apoptosis was monitored as described in “Materials and methods.” (C) HL-60 cells were treated with 10 nM paclitaxel with or without 10 nM bryostatin 1 for 24 hours, after which apoptosis was determined as described in “Materials and methods.” (D) THP-1 cells were treated with 10 nM paclitaxel with or without 10 nM bryostatin 1 for 24 hours. Values for panels A-D represent the means for 3 separate experiments (± SE). *Significant difference compared with the sum of the effects of each agent administered alone (P < .05 in each case).