CP-461 is an orally bioavailable second-generation apoptotic antineoplastic drug and analog of the nonsteroidal anti-inflammatory drug sulindac. CP-461 is an inhibitor of monophosphate-phosphodiesterase, an enzyme that inhibits the normal apoptosis signal pathway. Inhibition of cGMP-PDE permits the apoptotic signal pathway to proceed unopposed, resulting in apoptotic cell death. CP-461 was initially developed by OSI Pharmaceuticals, and in the early 2000s, CP-461 was investigated in phase I and phase 2 clinical trials for the treatment of chronic lymphocytic leukemia, Crohn's disease, malignant melanoma, renal cell carcinoma, and prostate cancer, both alone and in combination with other chemotherapeutic agents. The coadministration of CP-461 with other agents, however, did not increase the response rate. CP-461 was licensed to Celek Pharmaceuticals, where the compound was repurposed for the treatment of bladder cancer, but no development was reported.