Time-dependent potentiation of the ATRA-dependent induction of NBT-reducing activity by ST1346 in NB4 cells.

NB4 cells were seeded (200 000/mL) and treated with vehicle, ST1346 (5 μM), ATRA (0.1 μM), or the combination of ATRA + ST1346 for 3 days (panel B) for various lengths of time, as indicated (panels A,C). Aliquots of cells were used for the determination of NBT-reducing activity (panel A), the number of cells scoring positive for NBT-reducing activity (panel B), and the total number of viable cells (panel C). In all cases the cellular viability was above 90%, as assessed by the erythrosin exclusion test. The results are the means ± SD of 3 separate cultures. *Significantly higher than the corresponding group treated with vehicle (P < .01 according to the Student t test). °Significantly higher than the sum of the effects observed in the corresponding ST1346- and ATRA-treated groups, following 2-way analysis of variance and measurement of the F of interaction (P < .01 according to Tukey test).