Introduction:Endocrine treatment is the mainstay of therapy for patients with Estrogen Receptor positive (ER+) breast cancer.Unfortunately, primary and secondary resistance to endocrine therapy are a major clinical problem. Previous studies have suggested a possible role for NFkB transcription factor family members in this resistance due to their effect on ER signaling. In this study, we aim to elucidate the interaction between both transcription factor families (ER and NFkB) and the consequence thereof on the growth pattern of ER+ cell lines.

Materials and methods:For this study, 2 ER+ breast cancer cell lines (i.e. MCF7 and MDA-MB-361) were selected based on a documented attenuated NFkB activity in these cell lines and a different ErbB2 status.Prior to treatment with estrogen (E2), TNFα (NFkB activation) and/or parthenolide (NFkB inhibition), cells were seeded in 48 well plates. Proliferation was measured by means of a crystal violet assay. ELISA experiments to measure NFkB DNA-binding in nuclear protein extracts and qRT-PCR for NFkB target genes was performed.

Results:Treatment of MCF7cells with different concentrations of TNFα initially increased cell proliferation, but after 48hrs, apoptosis occurred. Evaluation of NFkB DNA-binding showed a clear increase in RelA (p65), RelB (p62) and NFkB1 (p50) DNA-binding after 4hrs and up until but no longer than 24hrs of treatment. Results were confirmed by qRT-PCR for NFkB target genes.Due to the dynamics of NFkB activation secondary to TNFα treatment, we limited further experiments to 24hrs of treatment. Combination of E2and TNFα gave an additive effect in MCF7 cell proliferation compared to E2 alone, an effect counteracted by parthenolide in a concentration dependent manner. In the ErbB2+ cell line MDA-MB-361 our initial results suggest that addition of TNFα does not affect E2-driven cell proliferation.

Conclusion: Our results so far suggest a different, ErbB2-dependent role for NFkB on the proliferation of ER+ breast cancer cells. Interestingly, the effect of NFkB seems to depend on both RelA- and RelB-dependent pathways. Experiments are currently being performed to elaborate on the present results.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P5-09-04.