Development of inhibitors to antagonize the activities of antiapoptoticBcl-2familyproteins is of particular interest in cancer chemotherapy. We discovered a quinazoline-2(1H)-thione derivative (DCBL55) as a new Bcl-xL, Bcl-2, and Mcl-1 inhibitor by virtual database screening. We systematically modified the structure of compound 1 by chemical synthesis. The interactions of the compounds with Bcl-xL