ATO/ATRA exert antileukemic activity in human primary NPM1-mutated AML cells. (A) Apoptosis rates (Annexin V/7AAD) of human primary AML cells from 36 patients (n = 18 NPM1 mutated; n = 18 NPM1 wild-type), untreated (NT) vs treated with 3 μM ATO for 24 hours. (B) Graph expressing ATO-induced apoptosis from experiments in panel A as fold of induction, relative to control (mean ± SD), with statistics between NPM1-mutated and NPM1 wild-type cells (2-tailed paired Student t test P value: P = .02). (C) Graph expressing ATO-induced apoptosis from experiments in panel A (left) as fold of induction, relative to control (mean ± SD), with statistics between FLT3 wild-type (FLT3 wt) (n = 5) and FLT3-ITD (n = 9) NPM1-mutated AML (2-tailed paired Student t test P value: P = .03). (D) Effects of ATRA (1 μM) treatment on apoptosis at 48 hours in primary human NPM1-mutated AML samples (n = 11): n = 8 nonresponders (left) and n = 3 responders (right). Effect of ATO/ATRA combination on ATRA responders is also shown (right).