Head and neck cancer is the sixth most common cancer worldwide, over 90% of which are squamous cell carcinoma (HNSCC). Despite advances in treatment options, the 5-year survival remains approximately 50%. Recent findings from The Cancer Genome Atlas (TCGA) have revealed that cell death signaling pathways are frequently altered, in up to 60% of HNSCC tumors. Among these, FADD or BIRC2 (cIAP1) amplifications (∼30%) or CASP8 mutations (∼10%) occur in mutually exclusive subsets. Because resistance of tumor cells to programmed cell death and chemotherapy or radiation-induced cytotoxicity is a significant challenge in HNSCC treatment, we hypothesized that these cell death pathways could serve as critical targets for therapeutic intervention. In this study, we investigate the in vitro and in vivo effects of birinapant, a novel small molecule peptidomimetic of the second mitochondria-derived activator of caspases (SMAC) that targets and promotes degradation of certain Inhibitor of Apoptosis Proteins (IAPs), the products of BIRCs. Quantitative Real-time PCR and western blot analyses on a panel of 11 genomically-characterized HNSCC cell lines (UM-SCC) revealed a subset with altered expression of FADD, cIAP1, or CASP8, which was consistent with the TCGA findings. Functional knockdown of FADD and/or cIAP1 or re-expression of wild-type CASP8 in altered lines inhibited cell density in XTT assays. Birinapant had inhibitory activity alone in a cell line overexpressing FADD but not cIAP1. Co-treatment with TNF or TRAIL sensitized multiple cell lines to birinapant treatment, reducing cell density by XTT assay, with a corresponding increase in sub-G0 cell death as assessed by flow cytometry, and increased caspase-3 and -8 activities by colorimetric assays. These effects were blocked by caspase inhibitors in the majority of cell lines tested. However, in the cell line overexpressing FADD, birinapant-induced cell death was unaffected by caspase inhibitors but blocked by RIPK1 inhibition, supporting an alternate mechanism of cell death by RIPK1-mediated necroptosis. Birinapant treatment significantly inhibited tumor growth and prolonged host survival in human HNSCC xenografts, consistent with the cytotoxic effects seen in vitro. Collectively, molecular alterations of cell death signaling pathways including FADD or BIRC2/cIAP1 amplification and overexpression or CASP8 mutations could be important targets for personalized therapeutic intervention in HNSCC. This warrants further investigation of SMAC-mimetics in HNSCC patients with these alterations. Supported by NIH Medical Research Scholars Program (DFE, GES) and NIDCD intramural project ZIA-DC-000016,73, 74 (ZC, CVW).
Citation Format: Danielle F. Eytan, Grace E. Snow, Zhong Chen, Carter Van Waes. Novel SMAC-mimetic birinapant demonstrates preclinical antitumor activity in human xenograft head and neck cancer models exhibiting alterations in cell death pathway components FADD, BIRC2, or CASP8. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2771. doi:10.1158/1538-7445.AM2014-2771