A fluorescently-labeled substrate (500 nM) was used to determine whether M3814 can inhibit Artemis (10 nM) by inhibiting DNA-PKcs (10 nM) (4). Reactions were performed in 25 mM Tris−HCl, pH 8.0, 10 mM KCl, 10 mM MgCl2, and 1 mM DTT incubated for 30 min at 37 °C. DNA-PKcs was treated with M3814, and inhibition was measured by comparing substrate-to-product conversion relative to the DMSO control (Lane 3). A visual description of substrates and products is provided on the right-hand side of the figure, and the sequences are in the Methods.