Abstract POSTER-TECH-1102: Caspase 8 cooperates with IKKβ to protect ovarian cancer cells from necroptosis
Authors: Hernandez Lidia , Noonan Anne M. , Sagher Ethan , Kohlhammer Holger , Wright George , Reed L. Tiffany , Steeg Patricia S. , Anver Miriam , Bowtell David D. , Annunziata Christina M. 
Published: August 2015

Ovarian cancer is a leading cause of cancer death in women, and identification of factors determining clinical outcome is essential to enable pathway-directed therapeutic advances. We recently showed that NF-κB signaling is constitutively active in a subset of ovarian cancer patients. Over-expression of the critical IκBα-regulatory kinase IKKβ, and its defined NF-κB gene signature, correlated with poor overall survival in that population. In order to identify cooperating pathways engaging in compensatory signaling in NF-κB-dependent ovarian cancer cells, genome-wide RNA interference was used as a loss-of-function genetic screen for key regulators of cell survival in response to IKKβ inhibition. The pro-apoptotic protease CASPASE 8 was identified. Ovarian cancer cells became more sensitive to killing with IKKb inhibitor when CASPASE 8 was depleted by shRNA. In agreement, co-expression of CASPASE 8 and NF-κB gene signature was observed in two large cohorts of primary ovarian cancer patient samples, and was largely confined to immune-related subtypes. In vitro, TNFα stimulation of Ovcar3 cells required CASPASE 8 for apoptotic cell death induced by IKKβ or cIAP1 inhibition, suggesting that both enzymatic activity of CASPASE 8 and its association with TNFR-induced cIAP protein complexes are mechanistically involved. However, CASPASE 8 depletion combined with IKKβ inhibition and cIAP1 depletion produced additional, CASPASE 8-independent cell death, in a RIP1-dependent manner. The data presented herein demonstrate our novel finding that Caspase 8 signals in conjunction with IKKβ to maintain viability of a subtype ovarian cancer cells, especially in the presence of TNFα stimulation. Ovarian cancer is known to be a heterogeneous disease, prone to developing resistance to chemotherapies designed primarily to induce apoptosis. The NF-kB pathway is one means by which tumors survive. Our findings point towards a new avenue for treatment of this disease, namely that cancers may be therapeutically susceptible to inducers of necroptosis, in addition to IKKβ blockade. The current data link our in vitro findings to primary patient samples, underscoring the relevance of our findings to future clinical application. Therefore, dual therapy with an IKKβ inhibitor and apoptosis- or necroptosis-inducing treatments may add together in molecularly selected ovarian cancer patient subsets.

Citation Format: Lidia Hernandez, Anne M. Noonan, Ethan Sagher, Holger Kohlhammer, George Wright, L. Tiffany Reed, Patricia S. Steeg, Miriam Anver, David D. Bowtell, Christina M. Annunziata. Caspase 8 cooperates with IKKβ to protect ovarian cancer cells from necroptosis [abstract]. In: Proceedings of the 10th Biennial Ovarian Cancer Research Symposium; Sep 8-9, 2014; Seattle, WA. Philadelphia (PA): AACR; Clin Cancer Res 2015;21(16 Suppl):Abstract nr POSTER-TECH-1102.