Abstract 99: Identification of genes involved in NFκB driven resistance to endocrine treatment in breast cancer.
Authors: Sas Leen , Van Dam Peter , Dirix Luc , Vermeulen Peter , Lardon Filip , Van Laere Steven 
Published: August 2014

Introduction: Breast cancer is a heterogeneous disease exemplified by patients with Estrogen Receptor (ER) positive and negative breast cancer. Treatment of patients with breast cancer is increasingly governed by this notion of heterogeneity. For example, patients with ER+ breast cancer are treated with endocrine therapy. Although endocrine treatment is the mainstay of therapy for patients with ER+ breast cancer, resistance to endocrine therapy is a major clinical problem. Recently we identified a 6-gene signature predictive of Tamoxifen sensitivity. In addition, our earlier work has shown the importance of the NFkB transcription factor family in determining ER function. In this study, we aim to elucidate the role of NFkB in endocrine therapy response.

Materials and methods: Public gene expression data sets of breast cancer patients and cell lines have been analyzed. ER- (PAM50-model) and NFkB-activation signatures (Annunziata et al, Cancer Cell, 2007) were calculated for all samples. In addition, samples were classified using our Tamoxifen response gene signature. We selected 11 cell lines with presumed strong or weak activation of NFkB based on the analysis of NFkB target gene expression. These cell lines were analyzed for NFkB DNA-binding using the TransAM ELISA kits (Active Motif). ER and NFkB target gene expression was determined using qRT-PCR. In addition, the expression of the 6 endocrine therapy responsive genes (ABAT, ADAMDEC1, CLEC7A, ETS1, ITK and STC2) was evaluated.

Results: When analyzing the NFkB activation signature in ∼700 samples from patients with breast cancer, we clearly observed an inverse correlation with the ER activation signature (R=-0.65, P&lt;0.01). Also, we observed NFkB hyperactivation in ER- breast cancers (P&lt;0.01). When restricting our analysis to ER+ samples, we demonstrated NFkB hyperactivation in samples from patients predicted by our 6-gene signature to be resistant to endocrine therapy. NFkB DNA-binding experiments confirmed the gene expression based NFkB activation status of eleven selected cell lines. In addition, NFkB DNA-binding was associated with elevated expression of ADAMDEC1 and ETS1 and reduced expression of ABAT (All Ps&lt;0.05). Finally, the 6-gene signature predictive of Tamoxifen response showed an increased expression in cell lines with increased NFkB DNA-binding (P&lt;0.01).

Conclusion: In the present study we demonstrate that NFkB activation is associated with attenuated response to endocrine treatment in patients with breast cancer. Our data suggest that this association is due to a repressive effect of NFkB on ER but mechanistic data in support of this view are currently lacking. We propose that the panel of cell lines evaluated in part of the present study will prove to be helpful instrument in elucidating the role of the interaction between ER and NFkB in endocrine treatment resistance.

Citation Format: Leen Sas, Peter Van Dam, Luc Dirix, Peter Vermeulen, Filip Lardon, Steven Van Laere. Identification of genes involved in NFκB driven resistance to endocrine treatment in breast cancer. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 99. doi:10.1158/1538-7445.AM2013-99