Abstract C4: Development and pre-clinical assessment of a first-in-class small molecule inhibitor of FLIP for treatment of NSCLC

Background Evasion of cell death is a major cause of resistance to cancer therapy, making proteins that regulate cell death clinically relevant therapeutic targets. The anti-apoptotic protein FLIP is frequently overexpressed in a number of cancers, including non-small cell lung cancer (NSCLC), and has been shown by us and others to be a major mediator of drug resistance. FLIP and procaspase-8 form complexes with the adaptor protein FADD in response to a variety of clinically relevant stimuli, including ligation of death receptors, such as TRAIL-R1 and R2, and treatment with chemotherapeutic agents. In these complexes, FLIP modulates the activation of procaspase-8, and thereby apoptosis and necroptosis - two major cell death mechanisms. We recently reported that there are important differences between FLIP and procaspase-8 in terms of both their binding affinities and preferred modes of interaction with FADD that are potentially therapeutically exploitable [1]. We now report our subsequent work leading to the development and pre-clinical characterisation of first-in-class inhibitors of FLIP. Methods Molecular modelling of the FLIP-FADD complex; virtual small molecule library screening; cell-free screening assays; cell-based activity assays; biophysical binding assays; in vivo anti-tumor studies. Results Molecular modelling of the FLIP-FADD complex identified a putative drug-binding pocket on FLIP against which a virtual small-molecule screen was carried out. Subsequent biochemical screening of selected compounds using a FLIP-FADD protein-protein interaction assay identified hits with on-target activity. Medicinal chemistry optimisation of these hits afforded lead and back-up series with nanomolar activity in cell-based assays (i.e. caspase activation, cell death and cell survival), which is in line with their binding affinity in an orthogonal biophysical assay (isothermal calorimetry). The pro-apoptotic effects of these FLIP inhibitors were enhanced upon addition of death ligands, such as TRAIL, and lead-molecules have been shown to potentiate the effects of the standard-of-care chemotherapeutic cisplatin. FLIP overexpression and procaspase-8 depletion abrogated the effects of these novel inhibitors consistent with the expected mechanism-of-action. Lead molecules have been identified with ADME profiles suitable for in vivo evaluation. Using these compounds, single-agent anti-tumor effects have been demonstrated in NSCLC xenograft models. Conclusions The novel first-in-class inhibitors of FLIP developed in this study have the potential for broad application in treatment of NSCLC, either as monotherapy or in combination with other agents. Acknowledgements This work was supported by a Seeding Drug Discovery award from the Wellcome Trust (reference: 099470). 1. Majkut, J., et al., Differential affinity of FLIP and procaspase 8 for FADD9s DED binding surfaces regulates DISC assembly. Nat Commun, 2014. 5 : p. 3350. Citation Format: Joanna Majkut, Catherine Higgins, Adnan Malik, Zsusannah Nemeth, Peter Blurton, Ray J. Boffey, Trevor R. Perrior, David Haigh, Timothy Harrison, Daniel B. Longley. Development and pre-clinical assessment of a first-in-class small molecule inhibitor of FLIP for treatment of NSCLC. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C4.