Effect of ATO/ATRA on DNR sensitization of human AML cell lines. (A-B) Apoptosis rate (relative to untreated) by flow cytometric evaluation (Annexin V/7AAD) upon DNR treatment in OCI/AML3 (DNR 0.05 μM, 48 hours) (A) and IMS-M2 (DNR 0.075 μM, 48 hours) (B) NPM1-mutated AML cell lines pretreated with ATO, ATRA, and ATO/ATRA for 24 hours. (C,D) Apoptosis rate (relative to untreated) upon DNR treatment in U937 (DNR 0.075 μM, 48 hours) (C) and OCI/AML2 (DNR 0.01 μM, 48 hours) (D) NPM1 wild-type AML cell lines pretreated with ATO, ATRA, and ATO/ATRA for 24 hours. (A-D) Means of 3 independent experiments ± SD. Two-tailed paired Student t test significant P values are indicated (P < .05).