Effects of TT and 9CTT on the NBT-reducing activity of myeloid leukemia cells. Effects of TT (○, ▵) and 9CTT (•, ▴) on APL-derived NB4 (○, •) and HT93 (▵, ▴) cells (A) are compared with those of ATRA (○, ▵) and 9CRA (•, ▴) on NB4 (○, •) and HT93 (▵, ▴) cells (B). Cells (5 × 10⁴ cells/mL) were treated with TT, 9CTT, ATRA, or 9CRA for 4 days. Values represent the means ± SD of three separate experiments.