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    • AT-406 (SM-406): Orally Bioavailable IAP Inhibitor for Ca...

    2026-01-15

    AT-406 (SM-406): Orally Bioavailable IAP Inhibitor for Cancer Apoptosis Pathway Activation

    Executive Summary: AT-406 (SM-406) is a small-molecule, orally bioavailable antagonist of multiple inhibitor of apoptosis proteins (IAPs), including XIAP, cIAP1, and cIAP2, with sub-100 nM affinity for each target (APExBIO product page). It functions by disrupting IAP-mediated suppression of caspases 3, 7, and 9, leading to activation of programmed cell death in cancer cells (Yang et al., 2024). AT-406 demonstrates in vitro IC50 values between 0.05–0.5 μg/mL in ovarian cancer cell lines and enhances sensitivity to carboplatin chemotherapy. In vivo, the compound reduces tumor burden and prolongs survival in mouse xenograft models of ovarian and breast cancer. Clinically, oral doses up to 900 mg are well tolerated, affirming its translational potential for targeting IAP signaling in cancer therapy (Yang et al., 2024).

    Biological Rationale

    Inhibitor of apoptosis proteins (IAPs) are a family of endogenous regulators that suppress cell death by binding and inhibiting caspases, notably caspase 3, 7, and 9 (Yang et al., 2024). XIAP, cIAP1, and cIAP2 are the principal IAPs implicated in resistance to apoptosis in cancer cells. IAPs are critical for regulating tissue homeostasis, immune responses, and cell cycle progression. Aberrant upregulation of IAPs is frequently observed in cancer, contributing to chemoresistance and tumor survival. Disrupting IAP function restores caspase activity and re-engages intrinsic and extrinsic apoptosis pathways (AT-406: Structural Disruption of IAP Signaling), extending established structural insights into death-effector domain (DED) assembly in FADD-procaspase-8-cFLIP complexes (Yang et al., 2024). This article extends previous reviews by providing an updated, atomic-level dossier on AT-406’s mechanism, distinguishing itself from prior literature by detailing pharmacological, biochemical, and translational parameters.

    Mechanism of Action of AT-406 (SM-406)

    AT-406 is a bivalent small molecule that binds to the BIR3 domain of XIAP, cIAP1, and cIAP2. The measured Ki values are 66.4 nM (XIAP), 1.9 nM (cIAP1), and 5.1 nM (cIAP2), confirming high target selectivity and potency (APExBIO). Upon binding, AT-406 disrupts the interaction between IAPs and caspases, leading to caspase activation. In particular, binding to cIAP1 induces its rapid ubiquitination and proteasomal degradation. Loss of cIAP1 relieves NF-κB-mediated survival signaling and shifts the cellular environment toward apoptosis (Yang et al., 2024). Additionally, AT-406 indirectly promotes the assembly of death-inducing signaling complexes (DISC) and secondary cytosolic complexes (complex II), leading to caspase-8 activation and execution of apoptosis (AT-406: Orally Bioavailable IAP Inhibitor for Apoptosis). This mechanistic pathway directly modulates the balance between cell survival and programmed cell death in cancer cells.

    Evidence & Benchmarks

    • AT-406 binds XIAP (Ki = 66.4 nM), cIAP1 (Ki = 1.9 nM), and cIAP2 (Ki = 5.1 nM) as determined by competitive binding assays (APExBIO product page).
    • In vitro, AT-406 induces apoptosis in human ovarian cancer cell lines with IC50 values between 0.05–0.5 μg/mL (24 h, standard culture conditions) (APExBIO).
    • Combination treatment with AT-406 and carboplatin synergistically increases cancer cell death compared to either agent alone (Yang et al., 2024).
    • In vivo, AT-406 demonstrates good oral bioavailability and significantly reduces tumor growth in mouse xenograft models of ovarian and breast cancer (Yang et al., 2024).
    • Clinical studies report that oral doses up to 900 mg are well tolerated, with manageable side effects in cancer patients (APExBIO).
    • AT-406 induces rapid cIAP1 degradation, activates caspases 3/7/9, and modulates NF-κB signaling in preclinical models (AT-406: Unlocking IAP Inhibitor Potential).

    This article provides an updated synthesis of these benchmarks by mapping them to specific use-case protocols and mechanistic checkpoints, whereas AT-406 and the Translational Frontier offers a broader translational perspective.

    Applications, Limits & Misconceptions

    AT-406 is used in basic and translational cancer research to study apoptosis modulation, evaluate IAP signaling pathways, and develop new therapeutic strategies. The compound’s high selectivity and oral bioavailability make it suitable for in vitro and in vivo experiments. AT-406 is especially valuable for investigating chemoresistance in ovarian and breast cancers. Additionally, it is used to study the structural and functional consequences of IAP inhibition in the context of cell death regulation and immune responses (AT-406: Advanced IAP Inhibition and the Future). This article clarifies the experimental boundary conditions and mechanistic checkpoints, extending the systems-level analysis presented in prior reviews.

    Common Pitfalls or Misconceptions

    • AT-406 is not effective in cell lines lacking functional caspase 3/7/9 expression.
    • It does not directly inhibit necroptosis; its effect is limited to apoptosis pathways mediated via IAP modulation.
    • AT-406 is insoluble in water and must be dissolved in DMSO or ethanol at ≥27.65 mg/mL for experimental use.
    • Long-term storage of AT-406 solutions is not recommended; solutions should be freshly prepared and stored at -20°C for short-term use only.
    • Clinical efficacy in humans is still under investigation; preclinical results may not directly translate to all cancer types.

    Workflow Integration & Parameters

    For in vitro studies, treat cancer cell lines with 0.1–3 μM AT-406 for 24 hours to induce apoptosis and measure caspase activation. Use DMSO or ethanol as a solvent; do not use water. For in vivo experiments, oral dosing regimens should be established based on prior pharmacokinetic studies, with attention to species-specific bioavailability and maximum tolerated dose. Store the solid compound at -20°C. Monitor for cIAP1 degradation, caspase activation, and cell death markers as primary readouts. When integrating AT-406 into combinatorial regimens, such as with carboplatin, optimize timing and concentration for maximal synergistic efficacy. Refer to the A3019 kit documentation for detailed experimental parameters and safety notes.

    Conclusion & Outlook

    AT-406 (SM-406) is a validated, potent, orally bioavailable IAP inhibitor that restores apoptosis in cancer cells by targeting XIAP, cIAP1, and cIAP2. Its robust performance in preclinical models highlights its value for apoptosis pathway activation, particularly in overcoming chemoresistance. Ongoing clinical studies will further elucidate its therapeutic potential. For validated protocols, refer to the AT-406 (SM-406) product page by APExBIO. For a systems-level perspective, see AT-406: Structural Disruption of IAP Signaling (this article provides atomic-level and workflow-specific updates beyond that review).