Evaluation of G4723A ADCs with monoimine or diimine IGN payloads. (A) Chemical structures of IMGN632 and X-ADC. Imine is highlighted in red; amine is highlighted in blue, and peptide linker is highlighted in green. (B) In vitro potency of IMGN632 and X-ADC toward CD123-positive HNT-34, MOLM-13, and KG-1 cells without and with blocking antibody. (C) Potency of IMGN632, X-ADC, and their control nonbinding ADCs toward leukemic progenitors from AML patients with various treatment and MDR status in CFU assays. (D) Potency of IMGN632 and X-ADC toward normal myeloid progenitors from healthy donors in CFU assays.