Targeting HER-2/neu-overexpressing breast cancer cells by an antisense iron responsive element-directed gene expression

Overexpression of HER-2/neu proto-oncogene is found in many human cancers i ncluding 20-30% of breast cancer and is a predictor of poor prognosis. To t arget breast cancer cells that overexpress HER-2/neu mRNA, we previously de scribed a novel strategy that combines the principle of antisense (AS) and translational inhibitory activity conferred by an iron-responsive element ( IRE) (AS-IRE). Here, we showed that three potential AS-IREs, i.e. AS-IRE1, 4, and 5, derived from HER-2/neu antisense sequence could bind endogenous i ron regulatory protein (IRP) and, when placed in 5' untranslated region (5' UTR) of a reporter gene, the gene expression could be translationally repre ssed by recombinant IRP in vitro. Using AS-IRE4 as our model, we demonstrat ed that it is regulated by iron, and importantly, such regulation is impair ed in HER-2/neu-overexpressing breast cancer cells. Furthermore, we showed that AS-IRE4 could preferentially direct the expression of a reporter gene in HER-2/neu-overexpressing breast cancer cells. Interestingly, when AS-IRE 4 was placed in 5'UTR of Bax gene, a pro-apoptotic protein in the Bcl-2 pro tein family, we observed a preferential cell killing in breast cancer cells that overexpress HER-2/neu. Taken together, our results suggest that AS-IR E behaves as a functional IRE and it may direct therapeutic gene expression to preferentially target HER-2/neu-overexpressing breast cancer cells. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.