An orally bioavailable inhibitor of IAP (Inhibitor of Apoptosis Protein) family of proteins with potential apoptotic inducing and antineoplastic activity. IAP inhibitor AT-406 selectively inhibits the biological activity of IAP proteins, including X chromosome-linked IAP (XIAP), the cellular IAPs 1 (c-IAP1) and 2 (c-IAP2) and melanoma inhibitor of apoptosis protein (ML-IAP). 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.