DNA-PK inhibitor IV is an inhibitor of DNA-dependent protein kinase (DNA-PK) with an IC50 value of 400 nM for the DNA-PK-dependent phosphorylation of a p53 peptide substrate. It also inhibits the phosphatidylinositol 3-kinase (PI3K) isoforms p110β, p110δ, and p110γ (IC50s = 2.8, 5.1, and 37 nM, respectively) but not p110α (IC50 = ~10 µM) or class II PI3Ks, PI4Kβ, ATM, ATR, mTOR, CK2, or GRK2 (IC50s = >50 µM). It enhances radiation-induced cytotoxicity of HCT116 cells when used at a concentration of 100 µM.