Nuclear factor-κB activation: a molecular therapeutic target for estrogen receptor–negative and epidermal growth factor receptor family receptor–positive human breast cancer

Sindhu Singh,Debajit K Biswas,Marek J Palczewski,Qian Shi,Arthur B Pardee,Shannon T Bailey,J Dirk Iglehart

doi:10.1158/1535-7163.mct-07-0063

Abstract

Nuclear factor-kappaB (NF-kappaB), a transcription factor with pleotropic effects, is a downstream mediator of growth signaling in estrogen receptor (ER)-negative and erbB family particularly erbB2 (HER-2/neu) receptor-positive cancer. We previously reported activation of NF-kappaB in ER-negative breast cancer cells and breast tumor specimens, but the consequence of inhibiting NF-kappaB activation in this subclass of breast cancer has not been shown. In this study, we investigated the role of NF-kappaB activation by studying the tumorigenic potential of cells expressing genetically manipulated, inducible, dominant-negative inhibitory kappaB kinase (IKK) beta in xenograft tumor model. Conditional inhibition of NF-kappaB activation by the inducible expression of dominant-negative IKKbeta simultaneously blocked cell proliferation, reinstated apoptosis, and dramatically blocked xenograft tumor formation. Secondly, the humanized anti-erbB2 antibody trastuzumab (Herceptin) and the specific IKK inhibitor NF-kappaB essential modifier-binding domain peptide both blocked NF-kappaB activation and cell proliferation and reinstated apoptosis in two ER-negative and erbB2-positive human breast cancer cell lines that are used as representative model systems. Combinations of these two target-specific inhibitors synergistically blocked cell proliferation at concentrations that were singly ineffective. Inhibition of NF-kappaB activation with two other low molecular weight compounds, PS1145 and PS341, which inhibited IKK activity and proteasome-mediated phosphorylated inhibitory kappaB protein degradation, respectively, blocked erbB2-mediated cell growth and reversed antiapoptotic machinery. These results implicate NF-kappaB activation in the tumorigenesis and progression of ER-negative breast cancer. It is postulated that this transcription factor and its activation cascade offer therapeutic targets for erbB2-positive and ER-negative breast cancer.

Highlights

Human breast cancer is not a single disease but a composite of disorders of mammary epithelial cells, with distinct pathologic characteristics and diverging clinical manifestations [1, 2]
We found that treatment of cells with trastuzumab combined with drugs that inhibit nuclear factor-nB (NF-nB) blocked cell proliferation at concentrations that are incapable of exerting significant inhibitory effects when used singly
An elevated level of activated NF-nB is detected in specific subclasses of human breast cancer cells and tumor tissue specimens, predominantly in erbB2-overexpressing estrogen receptor (ER)-negative breast cancer [5, 6, 12]

Summary

Introduction

Human breast cancer is not a single disease but a composite of disorders of mammary epithelial cells, with distinct pathologic characteristics and diverging clinical manifestations [1, 2]. We propose that inhibitors of NF-nB – activating kinase (IKK) would be potential candidates for combination therapy for ER-negative and erbB2-positive breast cancer patients. NBD peptide, the IKK-specific inhibitor, and trastuzumab, the anti-erbB2 antibody, and the two low molecular weight compounds showed similar patterns of concentration-dependent inhibition (Fig. 2A).

Results

Conclusion