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E2F-1 and Telomeres: A Combined Strategy for Treatment and Prognosis of Breast Cancer
Background: A crucial need exists for breast cancer patients to improve treatment of metastatic disease and prediction of risk of recurrence. E2F-1 is a transcription factor that directs cell cycle progression, but when overexpressed by an adenovirus can induce apoptosis even in chemoresistant cells. We utilized the selective activity of telomerase in cancer cells to develop AdhTERT-E2F-1 that has a human telomerase reverse transcriptase (hTERT) promoter. We have shown it induces apoptosis of colon cancer cells and inhibits growth of liver metastases in murine colorectal cancer models. Interestingly, the role of E2F-1 and telomere length in predicting breast cancer patient outcomes has yet to be established, but studies suggest telomerase activity and telomere length are associated with tumor aggressiveness.
Objective/Hypothesis: We wish to identify if an hTERT promoter will enable the E2F-1 vector to kill breast cancer cells without harming normal cells. We also wish to test this vector for effectiveness alone and in combination with chemotherapy in a murine model. Finally, we want to examine if E2F-1 and telomere length are useful prognostic markers.
Specific Aims: (1) To determine the ability of AdhTERT-E2F-1 to selectively induce apoptosis in breast cancer cell lines versus normal breast epithelial cell lines; (2) To demonstrate that the AdhTERT-E2F-1 adenoviral vector can be utilized as a therapeutic agent both as a single agent and in combination with chemotherapy in a murine model of human metastatic breast cancer; (3) To establish that E2F-1 and telomere length can predict disease-specific or overall survival in breast cancer patients utilizing archived tissue specimens from patients with stage I through IV disease.
Study Design: First, we will transfect human breast cancer and breast epithelial cells with Ad-hTERT-E2F-1 and analyze apoptosis and expression of E2F-1 and related proteins. Second, hepatic metastases will be counted for mice systemically treated with the vector alone and combined with chemotherapy. Third, using breast cancer specimens from time of diagnosis immunohistochemistry for E2F-1 and fluorescent in situ hybridization for telomere length will be performed.
Potential Outcomes and Benefits of Research: Our proposed studies will allow us to understand if Ad-hTERT-E2F-1 can be developed as an effective therapy for metastatic breast cancer with less toxicity to normal cells. In addition, insight into the role of E2F-1 and telomere length in patient prognosis may provide better risk analysis for disease recurrence.
While significant strides have been made in the care of patients with early stage breast cancer, there is still a vital need to improve our ability to treat patients with metastatic disease and to predict which patients have a higher risk developing of recurrent disease. During a cell cycle cancer cells go through a series of steps that allow them to grow and divide. E2F-1 is a transcription factor which turns on genes that allow cells to synthesize DNA. E2F-1, however, will cause an opposite effect of cell death (apoptosis) if it is present in very high amounts or overexpressed.
It is important to target overexpression of E2F-1 and subsequent cell death to cancer cells. Telomeres are repeats of DNA at the end of chromosomes which allow cells to be resistant to cell death. Telomerase is the enzyme which maintains telomere length, and is active in most cancer cells but not normal cells. Thus, we have made an adenovirus (cold virus) which does not replicate and uses a telomerase promoter to overexpress E2F-1. Importantly, researchers have shown that telomere length and telomerase seem to correlate with tumor aggressiveness, but the role E2F-1 and telomere length in predicting breast cancer patients’ prognosis has not been determined.
We propose to study overexpression of E2F-1 as a treatment for breast cancer. In order to achieve this goal breast cancer and normal breast cells will be infected (transfected) with an adenovirus which has a telomerase promoter that causes overexpression of E2F-1. The amount of cell death and expression of proteins after this treatment will be evaluated. Also mice which are models for human metastatic breast cancer will be injected with the same adenovirus which overexpresses E2F-1, and this treatment as it affects liver metasases will be studied by itself and in combination with chemotherapy. In addition, we propose to study the role of E2F-1 and telomere length in predicting prognosis. This will be accomplished by examining levels of E2F-1 expression and telomere length in previously collected breast cancer specimens. This information will then be correlated with the outcomes of the patients in regards to survival and disease recurrence.
The results generated by our research will help to develop molecular based therapies which can be targeted specifically to cancer cells to minimize toxicities, and that may be effective even when tumors are resistant to other forms of therapy. Also an improved ability to predict risk of recurrence can allow for further customization of therapy based on the aggressiveness of the tumor.