Plumbagin Suppresses the Invasion of HER2-Overexpressing Breast Cancer Cells through Inhibition of IKKα-Mediated NF-κB Activation

HER2-overexpressing breast cancers account for about 30% of breast cancer occurrences and have been correlated with increased tumor aggressiveness and invasiveness. The nuclear factor-κB (NF-κB) is overexpressed in a subset of HER2-positive breast cancers and its upregulation has been associated with the metastatic potential of HER2-overexpressing tumors. The present study aimed at determining the potential of plumbagin, a naturally occurring naphthoquinone, to inhibit the invasion of HER2-overexpressing breast cancer cells and determine the involvement of NF-κB inhibition in plumbagin-mediated cell invasion suppression. In the present research we showed that plumbagin inhibited the transcriptional activity of NF-κB in HER2-positive breast cancer cells. The suppression of NF-κB activation corresponded with the inhibition of NF-κB p65 phosphorylation and downregulation of NF-κB-regulated matrix metalloproteinase 9 (MMP-9) expression. Plumbagin suppressed the invasion of HER2-overexpressing breast cancer cells and the inhibition of cell invasion was associated with the ability of plumbagin to inhibit NF-κB transcriptional activity. The silencing of NF-κB p65 increased the sensitivity of HER2-overexpressing breast cancer cells to plumbagin-induced cell invasion inhibition. NF-κB inhibition was associated with IκB kinase α (IKKα) activity suppression and inhibition of IκBα phosphorylation and degradation. The knockdown of IKKα resulted in increased sensitivity of HER2-positive cells to plumbagin-induced suppression of NF-κB transcriptional activity and expression of MMP-9. In conclusion, plumbagin inhibits the invasion of HER2-overexpressing breast cancer cells through the inhibition of IKKα-mediated NF-κB activation and downregulation of NF-κB-regulated MMP-9 expression.