PIWIL4 depletion and ATR inhibition act synergistically to target AML cells. (A) Fifty percent inhibitory concentration (IC₅₀) of ATRi in scrambled and PIWIL4-depleted AML cells at 72 hours after treatment. (B) Percentage difference in clonogenicity in CFU assay of scrambled and shPIWIL4-transduced AML cell lines treated with respective IC₅₀ concentrations (scrambled/shPIWIL4-A/shPIWIL4-B: THP-1-712/50/64 nM; NB-4-240/61/71 nM) of ATRi. (C) Flow cytometry analysis of human engraftment in BM of NSG mice sacrificed 12 weeks after transplantation with cells from patients with AML transduced with shRNA or scrambled, sorted and treated with dimethyl sulfoxide (DMSO) or respective IC₅₀ concentrations of ATRi (712 nM for scrambled and 50 nM for shPIWIL4-A) for 48 hours. (D) Kaplan Meier plot depicting survival of NSG mice that underwent transplantation with scrambled control or shPIWIL4-transduced THP-1 cells treated with DMSO or respective IC₅₀ concentrations of ATRi (712 nM for scrambled and 50 nM for shPIWIL4-A).