Suppressing HER2/neu-Mediated Cell Transformation by Transcriptional Repressors

Abstract

Breast and ovarian cancer are two of the leading causes of death for women in the United States. HER2/neu overexpression is an unfavorable prognosis factor associated with low patient survival rate of multiple cancer types including breast and ovarian cancer. Downregulation of the HER2/neu gene expression in cancer cells has been shown to be a useful strategy to significantly reverse the malignant characteristics induced by HER2/neu overexpression. It is possible that HER2/neu overexpression can be repressed through inhibiting the promoter activity of the gene. We have identified a number of potent transcriptional regulators, including the adenovirus type 5 E1A, the SV40 large T antigen, and the ets family member PEA3, and have tested their activity to repress HER2/neu overexpression. Ectopic expression of these transcriptional regulators resulted in downregulation of the HER2/neu promoter activity and reversed the transformed phenotype of the cancer cells in vitro. These observations were followed by a series of studies to investigate whether these HER2/neu repressors could act therapeutically as tumor suppressor genes for cancers overexpressing HER2/neu. The results of these preclinical studies clearly indicated that transcriptional repressors, which downregulate HER2/neu overexpression, can be an effective regimen for cancer treatment in a gene therapy format combined with an appropriate gene delivery system such as the cationic liposome DC-Chol or replication-deficient adenovirus vector. Our results have demonstrated that these delivery systems can effectively transfer the therapeutic genes into the cancer cells in vivo and lead to significant suppressive effects on tumor growth. Furthermore, tumor-free survival rate of treated animals is increased dramatically using nontoxic doses, compared with animals without the treatment. A great body of evidence has revealed the potential of using transcriptional repressors to suppress HER2/neu overexpression and abolish tumor growth. Thus, suppression of oncogenic gene expression using transcription factors can be a novel field for cancer treatment and prevention.