AT-406 (formerly known as SM-406) is an orally bioavailable potent IAP (inhibitor of apoptosis protein) of XIAP, cIAP1, and cIAP2 with Ki of 66.4 nM, 1.9 nM, and 5.1 nM, respectively. This may restore and promote the induction of apoptosis through apoptotic signaling pathways. AT-406 may work synergistically with cytotoxic drugs to overcome tumor cell resistance to apoptosis. IAPs are overexpressed by many cancer cell types, suppressing apoptosis by binding and inhibiting active caspases-3, -7 and -9 via their BIR (baculoviral lAP repeat) domains. AT-406 is currently in Phase I clinical trial in patients with advanced solid tumors and lymphomas.