AT406 (SM-406) is a potent small-molecule inhibitor that targets inhibitor of apoptosis proteins (IAPs), particularly cIAP1, cIAP2, and XIAP. It functions by mimicking the action of Smac (Second Mitochondria-derived Activator of Caspases), a natural protein that promotes apoptosis. By binding to IAPs, AT406 disrupts their ability to suppress caspase activity, thereby restoring programmed cell death in cancer cells. This compound is widely used in cancer research to induce apoptosis in tumor cells, especially those resistant to conventional therapies. It has shown promising activity in preclinical studies against various cancers, including leukemia, lymphoma, and solid tumors. AT406 can sensitize cancer cells to other apoptotic stimuli such as TNF-α and chemotherapeutic agents, making it a valuable tool for combination therapy strategies. In addition to its direct pro-apoptotic effects, AT406 has been shown to activate the NF-κB signaling pathway through cIAP degradation, leading to production of pro-inflammatory cytokines and modulation of the tumor microenvironment. This dual mechanism enhances immune recognition of tumor cells and supports its investigation in immuno-oncology contexts. Overall, AT406 serves as a critical research compound for understanding IAP-mediated survival pathways and developing novel anticancer therapeutics.