WEE1 and acute lymphoblastic leukemia: Consistent with the ALL cell lines, exposure to IC50 concentrations of adavosertib significantly reduced phospho-CDK-Tyr15 levels relative to total CDK1 levels in the PDX samples (N = 6, p = 0.009), which was further diminished at higher adavosertib concentrations (p < 0.0001), confirming on-target WEE1 kinase inhibition in these cells (Fig. 2D).