Birinapant (TL32711) is a synthetic small molecule that is both a peptidomimetic of second mitochondrial-derived activator of caspases (SMAC) and inhibitor of IAP (Inhibitor of Apoptosis Protein) family proteins, with potential antineoplastic activity.

XIAP:45 nM(Kd), CIAP1:<1 nM(Kd)

Birinapant binds with XIAP and cIAP1 with Kd of 45 and <1 nM, respectively. Birinapant induces cell death as a single agent in TRAIL-insensitive SUM190 (ErbB2-overexpressing) cells (IC50, ~300 nM), and significantly increases potency of TRAIL-induced apoptosis in TRAIL-sensitive SUM149 (triple-negative, EGFR-activated) cells. Birinapant causes rapid cIAP1 degradation, caspase activation, PARP cleavage, and NF-κB activation. [1] Birinapant in combination with TNF-α exhibits a strong antimelanoma effect in vitro. Birinapant in combination with TNF-α(1 ng/mL) inhibits the growth of human melanoma cell lines WTH202, WM793B, WM1366 and WM164 with IC50s of 1.8, 2.5, 7.9 and 9 nM, respectively, while neither compound is effective individually. Birinapant singly treatment induces inhibition on proliferation of WM9 cells with IC50 of 2.4 nM. Birinapant significantly inhibits the target protein cIAP1 and cIAP2 in these cell lines.[2]

Birinapant (30 mg/kg) treatment significantly induces abrogation of tumor growth in melanoma xenotransplantation models 451Lu with. [2]

Fluorescence polarization assay: The binding affinities of compounds to XIAP and cIAP1 are determined using a fluorogenic substrate and are reported as Kd values. Initially, the dissociation constant (Kd) for the fluorescently labeled modified Smac peptide (AbuRPF-K(5-Fam)-NH2; FP pep-tide) is determined using a fixed concentration of peptide (5 nM) and titrating varying concentrations of protein (0.075–5 μM in half log dilutions). The dose–response curves are produced by a nonlinear least squares fit to a single-site binding model using GraphPad Prism, with 5 nM of FP peptide and 50 nM of XIAP used in the assay. Various concentrations of Smac mimetics (100–0.001 μM in half log dilutions) are added to FP peptide:protein binary complex for 15 min at room temperature in 100μL of 0.1 M potassium phosphate buffer, pH 7.5, containing 100 mg/mL bovine c -globulin. Following incubation, the polarization values are measured on a multi-label plate reader using a 485 nm excitation filter and a 520 nm emission filter.

Cells are allowed to attach for 24 hours and subsequently incubated with Birinapant and/or TNF-α for 24 or 72 hours. Then MTS assay is conducted(Only for Reference)