VE-821-mediated ATR inhibition potentiates the cytotoxic effects of HU and Gem in mononuclear cells isolated from AML patients. (A-B) Bone marrow mononuclear cells from up to 6 AML patients (3 de novo AML, 1 relapsed AML, and 2 t-AML patients) were treated with (A) HU or (B) Gem in combination with 5 µM VE-821 (blue circles) or DMSO control (red circles). Cell survival (relative to respective vehicle controls) was determined after 72 hours by addition of resazurin sodium salt. (C-D) CD34⁺ cells from 2 healthy donors were treated with (C) HU or (D) Gem, and cell survival was determined as above. See supplemental Figure 5C.