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The tumor suppression activity of E1A in HER-2/neu-overexpressing breast cancer
1Department of Tumor Biology and Breast Cancer Basic Research Program, University of Texas M.D. Anderson Cancer Center, Houston 77030, USA.
Abstract:
The HER-2/neu proto-oncogene is frequently amplified or overexpressed in human breast and ovarian cancers, and is significantly correlated with shorter survival. We have previously reported that the adenovirus type 5 early region 1A (E1A) gene product can repress HER-2/neu overexpression by repressing HER-2/neu promoter activity, and suppress the tumorigenic potential of HER-2/neu-overexpressing ovarian cancer cells. To examine E1A tumor suppressor function in breast cancer, we transduced E1A in vitro by adenovirus into both HER-2/neu-overexpressing and low expressing human breast cancer cell lines. In HER-2/neu-overexpressing cells, E1A greatly inhibited tumor cell growth in vitro. However, in HER-2/neu low expressing cancer cell lines, E1A had no significant effect on cell growth in culture medium. To test the therapeutic efficacy of E1A, we used both adenovirus-mediated and cationic liposome-mediated E1A gene delivery systems in an orthotopic breast cancer animal model. An advanced breast cancer model was established by inoculation of HER-2/neu-overexpressing human breast cancer cells in mammary fat pad and treated by local injections of either replication-deficient adenovirus expressing E1A, Ad.E1A(+) or a liposome-E1A DNA complex. As controls, mice bearing tumors were also treated with Ad.E1A(-) which is virtually the same adenovirus as Ad.E1A(+) except that E1A is deleted, a liposome-E1A frame-shift mutant DNA complex, or just PBS. In mice bearing a HER-2/neu-overexpressing breast cancer cell line, E1A delivered either by adenovirus or liposome significantly inhibited tumor growth and prolonged mouse survival compared with the controls. In fact, 60-80% of E1A-treated mice lived longer than 2 years versus only 0-20% of control mice (P<0.05). Western blot analysis showed that E1A protein was expressed in tumor tissue and immunohistochemical analysis showed that HER-2/neu p185 protein expression was suppressed. Taken together, our results indicated that both adenovirus and cationic liposome delivery systems were effective in transfering E1A gene for tumor suppression in a HER-2/neu-overexpressing breast cancer model.
Insights
The adenovirus type 5 early region 1A (E1A) gene effectively suppressed HER-2/neu-overexpressing breast cancer growth and prolonged survival in mice. Gene therapy using adenovirus or liposome delivery showed significant therapeutic potential for HER-2/neu-positive cancers.
Area of Science:
- Oncology
- Molecular Biology
- Gene Therapy
Background:
- HER-2/neu proto-oncogene amplification/overexpression correlates with poor survival in breast and ovarian cancers.
- Adenovirus type 5 early region 1A (E1A) gene product previously showed potential to repress HER-2/neu and suppress ovarian cancer cell tumorigenicity.
Purpose of the Study:
- To investigate the tumor suppressor function of E1A in breast cancer.
- To evaluate the therapeutic efficacy of E1A gene delivery systems in a HER-2/neu-overexpressing breast cancer model.
Main Methods:
- In vitro transduction of E1A into human breast cancer cell lines (HER-2/neu-overexpressing and low-expressing).
- In vivo orthotopic breast cancer animal model using HER-2/neu-overexpressing cells.
- Adenovirus-mediated (Ad.E1A(+)) and cationic liposome-mediated E1A gene delivery.
- Control groups received Ad.E1A(-), liposome-E1A mutant, or PBS.
Main Results:
- E1A significantly inhibited in vitro growth of HER-2/neu-overexpressing breast cancer cells, with no effect on low-expressing cells.
- Adenovirus or liposome delivery of E1A significantly inhibited tumor growth and prolonged survival in mice with HER-2/neu-overexpressing tumors.
- E1A treatment led to 60-80% long-term survival in mice compared to 0-20% in controls.
- E1A protein expression was detected in tumors, and HER-2/neu p185 expression was suppressed.
Conclusions:
- Adenovirus and cationic liposome delivery systems are effective for E1A gene transfer.
- E1A gene therapy demonstrates significant tumor suppression in a HER-2/neu-overexpressing breast cancer model.
- E1A holds therapeutic promise for HER-2/neu-positive breast cancers.