Ovarian cancer is the most lethal gynecological malignancy in the United States with high morbidity and mortality due to recurrence and chemoresistance. Our data suggest tumor-initiating cells (TICs) play an important role in disease biology. We previously showed that a subset of ovarian cancer cells depends on NF-kappaB signaling, and that expression of NF-kappaB proteins is associated with poor survival. Given that NF-kappaB expression correlates with a poor outcome in ovarian cancer, and NF-kappaB activity supports drug resistance and tumorigenicity, we hypothesize that NF-kappaB supports a TIC program responsible for ovarian cancer relapse. To investigate this pathway in TICs, we designed a novel method to enrich for TICs from cell lines and patient samples by culturing non-adherent, floating cells in stem cell conditions defined by low attachment flasks and serum free media. Preliminary data confirm that these cells have higher stem cell marker expression, are chemoresistant, and are more tumorigenic in nude mice compared to their adherent counterparts. These TIC-enriched culture conditions enhance NF-kappaB expression and activity. More specifically, alternative NF-kappaB signaling through the RelB transcription factor supports TIC populations by regulating aldehyde dehydrogenase (ALDH), an enzyme with high activity in TICs. Using an inducible shRNA targeting RelB we show that spheroid formation, ALDH expression and activity, chemoresistance, and tumorigenesis in both subcutaneous and intrabursal xenograft models, significantly decreased in the absence of RelB. Interestingly, loss of classical NF-kappaB signaling, through an shRNA targeting the RelA transcription factor, was less effective in targeting TICs, but more effective at targeting a proliferative subpopulation with high Ki67 staining. We conclude that classical and alternative NF-kappaB signaling support ovarian tumor cells with distinct phenotypes and the collaboration of these pathways may be critical for supporting tumor repopulation following chemotherapy. Current studies will measure system level changes induced by these shRNAs, and identify a gene signature specific to each NF-kappaB pathway in ovarian TICs. Clarifying the nuances of NF-kappaB signaling in TICs will increase our understanding of ovarian cancer recurrence and further focus therapeutic strategies to prevent relapse.

Citation Format: Carrie D. House, Christina M. Annunziata. NF-kappaB classical versus alternative pathways support distinct populations of ovarian cancer tumor-initiating cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1910. doi:10.1158/1538-7445.AM2017-1910