Abstract 6221: Targeting IAP in cancer: BI 891065 a potent small molecule SMAC mimetic that synergizes with immune checkpoint inhibition
Authors: Aichinger Martin , Santoro Valeria , Slavic-Obradovic Ksenija , Ruhland Stefanie , Wernitznig Andreas , Neudolt Andrea , Schaefer Markus , Kallenda Sabine , Zach Daniel , Olt Sabine , Salomon Carina , Rieser Sarah , Weissenboeck Martina , Ebner Florian , Schlattl Andreas , De Almeida Melanie Talata , Langlois Rebecca , Sykora Martina , Reschke Markus , Zichner Thomas , Gerlach Daniel , Jude Julian , Fellner Michaela , Scharn Dirk , Kraut Norbert , Moll Juergen , Zuber Johannes , Carotta Sebastian , Impagnatiello Maria Antonietta , Tontsch-Grunt Ulrike 
Published: September 2020

Abstract
Background: Engagement of Tumor Necrosis Factor-α (TNF-α) with its receptor can lead to dramatically different cellular outcomes ranging from regulating cell survival and inflammation to induction of programmed forms of cell death. A critical proximal checkpoint determining the nature of TNF-α signaling is put in place by the cellular inhibitor of apoptosis proteins (cIAPs). In the context of cancer therapy these constitute an attractive target as they (1) block the TNF-α induced activation of apoptotic/necroptotic cues and (2) are negatively regulated by a highly selective endogenous ligand (i.e. SMAC), which served as a blueprint for the development of small molecule inhibitors of IAP (so called SMAC mimetics).
Methods: Here we investigated the efficacy of SMAC mimetic BI891065 in enhancing targeted and chemotherapeutic approaches in preclinical mouse cancer models and describe immune-modulatory effects in syngeneic settings. To identify responding indications, a large pan-cancer cell line panel screening comprising 246 cell lines was performed (Eurofins). Proliferation of cells treated with increasing concentrations of BI 891065 combined with a fixed concentration of TNF-α was assessed by high-content screening. Furthermore, to gain a better understanding of the molecular determinants associated with sensitivity to SMAC mimetic treatment, genome-wide CRISPR/Cas9 drug modifier screens were performed.
Results: Here we present key data demonstrating antitumor activity of BI891065 in preclinical models, our efforts towards understanding of genetic determinants of SMAC sensitivity and of potential responsive indications. By using genome-wide CRISPR/Cas9 drug modifier screens we not only demonstrated the feasibility of such unbiased approaches, as we identified many known (e.g. TNF Receptor 1, RIPK1, Caspase 8 and members of the NFκB signaling pathways) - but also potentially novel - regulators of TNF-α/SMAC mimetic induced cell death. In addition, to identify potential responsive indications to BI891065, extensive profiling of in vitro drug sensitivity across a large set of cancer cell types was performed. As a result of this, colorectal cancer (n=56) was identified as a promising indication: 5% of cell lines were found to be sensitive to BI 891065 single treatment. This could be further extended by the exogenous supply of TNF-α to BI 891065, increasing the number of sensitive cells to 21%.
Conclusion: The presented data demonstrate the potential of BI 891065 to facilitate tumor cell death and to enhance anti-tumor immune responses, and nominate the compound as an attractive combination partner in cancer therapy. Our results led to the identification of potentially novel modulators of SMAC mimetic sensitivity via genome-wide CRISPR/Cas9 drug sensitizer screens and suggest colorectal cancer as a promising indication for clinical positioning.
Citation Format: Martin Aichinger, Valeria Santoro, Ksenija Slavic-Obradovic, Stefanie Ruhland, Andreas Wernitznig, Andrea Neudolt, Markus Schaefer, Sabine Kallenda, Daniel Zach, Sabine Olt, Carina Salomon, Sarah Rieser, Martina Weissenboeck, Florian Ebner, Andreas Schlattl, Melanie Talata De Almeida, Rebecca Langlois, Martina Sykora, Markus Reschke, Thomas Zichner, Daniel Gerlach, Julian Jude, Michaela Fellner, Dirk Scharn, Norbert Kraut, Juergen Moll, Johannes Zuber, Sebastian Carotta, Maria Antonietta Impagnatiello, Ulrike Tontsch-Grunt. Targeting IAP in cancer: BI 891065 a potent small molecule SMAC mimetic that synergizes with immune checkpoint inhibition [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 6221.