sm-164 and birinapant

Smac mimetics, or IAP antagonists, are a class of drugs currently being evaluated as anti-cancer therapeutics. These agents antagonize IAP proteins, including cIAP1/2 and XIAP, to induce cell death via apoptotic or, upon caspase-8 deficiency, necroptotic cell death pathways. Many cancer cells are unresponsive to Smac mimetic treatment as a single agent but can be sensitized to killing in the presence of the cytokine TNFα, provided either exogenously or via autocrine production. We found that high concentrations of a subset of Smac mimetics could provoke death in cells that did not produce TNFα, despite sensitization at lower concentrations by TNFα. The ability of these drugs to kill did not correlate with valency. These cells remained responsive to the lethal effects of Smac mimetics at high concentrations despite genetic or pharmacological impairments in apoptotic, necroptotic, pyroptotic, autophagic and ferroptotic cell death pathways. Analysis of dying cells revealed necrotic morphology, which was accompanied by the release of lactate dehydrogenase and cell membrane rupture without prior phosphatidylserine exposure implying cell lysis, which occurred over a several hours. Our study reveals that cells incapable of autocrine TNFα production are sensitive to some Smac mimetic compounds when used at high concentrations, and this exposure elicits a lytic cell death phenotype that occurs via a mechanism not requiring apoptotic caspases or necroptotic effectors RIPK3 or MLKL. These data reveal the possibility that non-canonical cell death pathways can be triggered by these drugs when applied at high concentrations.

Topics: Acetylcysteine; Antineoplastic Agents; Apoptosis; Apoptosis Regulatory Proteins; Azocines; Benzhydryl Compounds; Bridged Bicyclo Compounds, Heterocyclic; Caspase 3; Caspase 7; Cell Line, Tumor; Cyclohexylamines; Dipeptides; Ferroptosis; Gene Expression Regulation, Neoplastic; Humans; Imidazoles; Indoles; Mitochondrial Proteins; Molecular Mimicry; Necroptosis; Oligopeptides; Phenylenediamines; Protein Kinases; Receptor-Interacting Protein Serine-Threonine Kinases; Signal Transduction; Triazoles; Tumor Necrosis Factor-alpha

Chronic active B cell receptor (BCR) signaling, a hallmark of the activated B cell-like (ABC) subtype of diffuse large B cell lymphoma (DLBCL), engages the CARD11-MALT1-BCL10 (CBM) adapter complex to activate IκB kinase (IKK) and the classical NF-κB pathway. Here we show that the CBM complex includes the E3 ubiquitin ligases cIAP1 and cIAP2, which are essential mediators of BCR-dependent NF-κB activity in ABC DLBCL. cIAP1/2 attach K63-linked polyubiquitin chains on themselves and on BCL10, resulting in the recruitment of IKK and the linear ubiquitin chain ligase LUBAC, which is essential for IKK activation. SMAC mimetics target cIAP1/2 for destruction, and consequently suppress NF-κB and selectively kill BCR-dependent ABC DLBCL lines, supporting their clinical evaluation in patients with ABC DLBCL.

Topics: Adaptor Proteins, Signal Transducing; Animals; Apoptosis Regulatory Proteins; B-Cell CLL-Lymphoma 10 Protein; B-Lymphocytes; Baculoviral IAP Repeat-Containing 3 Protein; Bridged Bicyclo Compounds, Heterocyclic; CARD Signaling Adaptor Proteins; Caspases; Cell Line, Tumor; CRISPR-Cas Systems; Dipeptides; Enzyme Activation; Gene Dosage; Gene Expression Profiling; Gene Expression Regulation, Neoplastic; Guanylate Cyclase; Humans; I-kappa B Kinase; Indoles; Inhibitor of Apoptosis Proteins; Intracellular Signaling Peptides and Proteins; Lymphoma, Large B-Cell, Diffuse; Mice; Mice, Inbred NOD; Mice, SCID; Mitochondrial Proteins; Mucosa-Associated Lymphoid Tissue Lymphoma Translocation 1 Protein; Multiprotein Complexes; Neoplasm Proteins; NF-kappa B; Protein Processing, Post-Translational; Receptors, Antigen, B-Cell; Triazoles; Ubiquitin-Protein Ligases; Ubiquitination; Xenograft Model Antitumor Assays