GDC-0917 (CUDC-427) is an orally available, monovalent mimetic of the second mitochondrial-derived activator of caspases (Smac/DIABLO) and inhibitor of IAPs (Inhibitor of Apoptosis Proteins) with potential antineoplastic activity. Smac mimetic GDC-0917 binds to the Smac binding groove on IAPs, including the direct caspase inhibitor X chromosome-linked IAP (XIAP) and the cellular IAPs 1 and 2. This inhibits the activities of these IAPs and promotes the induction of apoptosis through apoptotic signaling pathways. GDC-0917 demonstrated single-agent antitumor activity in mouse xenograft models bearing subcutaneous MDA-MB-231 tumors. In addition, CUDC-427 demonstrated additive activity in combination with chemotherapeutic agents and tumor necrosis factor apoptosis-inducing ligand (TRAIL) receptor targeting antibodies in xenograft tumor models. Preclinical safety and pharmacokinetic testing established an expected therapeutic range of doses as well as elucidated possible toxicities including inflammatory cytokine and chemokine proteins that could cause an inflammatory reaction, and reversible mild to moderate inflammation in the lungs and liver. GDC-0917 had been in phase I clinical trials by Genentech, Inc. for the treatment of Refractory Solid Tumors or Lymphoma. The principal toxicities related to CUDC-427 were mild to moderate in severity and included fatigue, nausea, vomiting, and rash.