Prexasertib is a potent and selective Chk1/Chk2 inhibitor. Prexasertib increases the effectiveness of conventional therapy in B-/T- cell progenitor acute lymphoblastic leukemia. LY2606368 causes replication catastrophe and antitumor effects through CHK1-dependent mechanisms. Treatment of cells with LY2606368 results in the rapid appearance of TUNEL and pH2AX-positive double-stranded DNA breaks in the S-phase cell population.