Activation of nuclear factor-κB (NFκB) identifies a high-risk subset of hormone-dependent breast cancers

Activation of nuclear factor-κB (NFκB) has been linked to the development of hormone-independent, estrogen receptor (ER)-negative human breast cancers. To explore the possibility that activated NFκB marks a subset of clinically more aggressive ER-positive breast cancers, NFκB DNA-binding was measured in ER-positive breast cancer cell lines and primary breast cancer extracts by electrophoretic mobility shift assay and ELISA-based quantification of specific NFκB p50 and p65 DNA-binding subunits. Oxidant (menadione 100 μM × 30 min) activation of NFκB was prevented by pretreatment with various NFκB inhibitors, including the specific IκB kinase (IKK) inhibitor, parthenolide (PA), which was found to sensitize MCF-7/HER2 and BT474 but not MCF-7 cells to the antiestrogen tamoxifen. Early stage primary breast cancers selected a priori for lower ER content (21-87 fmol/mg; n = 59) and known clinical outcome showed two- to four-fold increased p50 and p65 NFκB DNA-binding over a second set of primary breast cancers with higher ER content (>100 fmol/mg; n = 22). Breast cancers destined to relapse (13/59) showed significantly higher NFκB p50 (but not p65) DNA-binding over those not destined to relapse (46/59; p = 0.04). NFκB p50 DNA-binding correlated positively with several prognostic biomarkers; however, only NFκB p50 DNA-binding (p = 0.04), Activator Protein-1 DNA-binding (AP-1; p ≤ 0.01) and urokinase-type plasminogen activator expression (uPA; p = 0.0014) showed significant associations with metastatic relapse and disease-free patient survival. These clinical findings indicate that high-risk ER-positive breast cancers may be prognostically identified by increased NFκB p50 DNA-binding, and support preclinical models suggesting that therapeutic inhibition of NFκB activation may improve the endocrine responsiveness of high-risk ER-positive breast cancers.