SMAC Mimetic Birinapant plus Radiation Eradicates Human Head and Neck Cancers with Genomic Amplifications of Cell Death Genes FADD and BIRC2

Comparison of tumors from The Cancer Genome Atlas (TCGA) reveals that head and neck squamous cell carcinomas (HNSCC) harbor the most frequent genomic amplifications of Fas-associated death domain (FADD), with or without Baculovirus inhibitor of apoptosis repeat containing BIRC2 (cIAP1), affecting about 30% of patients in association with worse prognosis. Here, we identified HNSCC cell lines harboring FADD/BIRC2 amplifications and overexpression by exome sequencing, RT-PCR, and Western blotting. In vitro, FADD or BIRC2 siRNA knockdown inhibited HNSCC displaying amplification and increased expression of these genes, supporting their functional importance in promoting proliferation. Birinapant, a novel SMAC mimetic, sensitized multiple HNSCC lines to cell death by agonists TNF alpha or TRAIL and inhibited cIAP1 > XIAP > IAP2. Combination of birinapant and TNF alpha induced sub-G(0) DNA fragmentation in sensitive lines and birinapant alone also induced significant G2-M cell-cycle arrest and cell death in UM-SCC-46 cells. Gene transfer and expression of FADD sensitized resistant UM-SCC-38 cells lacking FADD amplification to birinapant and TNF alpha, supporting a role for FADD in sensitization to IAP inhibitor and death ligands. HNSCC varied inmechanisms of cell death, as indicated by reversal by inhibitors or protein markers of caspase-dependent apoptosis and/or RIPK1/MLKL-mediated necroptosis. In vivo, birinapant inhibited tumor growth and enhanced radiation-induced TNF alpha, tumor responses, and host survival inUM-SCC-46 and -11B xenograft models displaying amplification and overexpression of FADD+/- BIRC2. These findings suggest that combination of SMAC mimetics such as birinapant plus radiation may be particularly active in HNSCC, which harbor frequent FADD/BIRC2 genomic alterations. (C) 2016 AACR.