> Research & Grants
> Grants Program
> Research Grants
> Research Grants Awarded
Inhibition of Breast Cancer Growth by a Novel Regulator of EGFR
INHIBITION OF BREAST CANCER GROWTH BY A NOVEL REGULATOR OF EGFR
BACKGROUND: The breast cancer is a complex disease, and its development and progression are influenced by multiple factors. Several critical genes including estrogen receptor (ER), progesterone receptor (PR), retinoic acid receptor (RAR)-b, epidermal growth factor receptor (EGFR) family members, and tumor suppressor p53 are known risk factors for development of disease, predictors of prognosis and response to therapy, and serve as therapeutic targets. EGFR pathway is frequently hyperactivated or dysregulated in human breast carcinoma involving range of mechanisms, including overproduction of ligands, overproduction of the receptor, and/or constitutive activation of the receptor. Thus, EGFR and EGFR-dependent signaling pathways are currently being pursued as potential targets for therapy for many epithelial cancers including human breast carcinoma. Recently, we isolated and characterized ERRP, a negative regulator of EGFR. ERRP has significant homology to the external domain of the EGFR, and is a secretory protein. It is likely that ERRP exerts its action by competing with EGFR for the ligands, thereby attenuating EGFR activation, subsequent cell growth inhibition and apoptosis. Whether ERRP could be an effective therapeutic agent for breast cancer, we generated ERRP fusion protein and studied its effect on the growth of breast cancer cells in vitro. Treatment with purified ERRP caused apoptosis of breast cancer cells.
HYPOTHESIS: ERRP is postulated to be a negative regulator of EGFR. In view of this, we hypothesize that increased activation of EGFR associated with breast cancer could partly be the result of loss of ERRP, a suppressor of EGFR function. The objective of this investigation is to test the hypothesis that ERRP will be effective in inhibiting the growth of estrogen-responsive and estrogen-nonresponsive breast cancers.
SPECIFIC AIMS: We will test our hypothesis by investigating (1) effect of ERRP on subcutaneous tumor growth in SCID mice xenografts of different human breast cancer cell lines, (2) effect of ERRP on proliferation of breast cancer cells and the regulation of this process, and (3) mechanism(s) of ERRP-induced inhibition of EGFR activation.
STUDY DESIGN: In aim 1, purified ERRP protein will be injected either intratumorally or subcutaneously at a site away from the tumors to determine whether ERRP inhibits the growth of the tumors. Whether presence of ERRP prevents tumors from growing will be studied by continuously delivering purified ERRP from the time of subcutaneous implantation of tumors in SCID mice. The effictiveness of ERRP as anti-tumor agent will also be studied by comparing its effects with anti-tumor properties of anti-EGFR antibodies. In aim 2, the growth inhibitory properties of ERRP, including its interference with EGFR activity and inhibition of EGFR signaling, will be studied in vitro by conducting assays for cell proliferation and by measuring tyrosine kinase activity and tyrosine phosphorylation of EGFR. In aim 3, the co-immunoprecipitation, in vitro cross-linking and western immunoblot methods will be utilized to determine whether and to what extent ERRP forms complex with various ligands for EGFR family of receptors, and whether ligand-dependent ERRP interactions with EGFR results in formation of ERRP/EGFR heterodimers.
POTENTIAL OUTCOMES/BENEFITS: Understanding anti-tumor properties of ERRP in in vivo SCID mice tumor model, and delineation of its cancer cell growth inhibitory properties is anticipated to establish ERRP as a potential therapeutic agent against human breast carcinoma. The uniqueness of ERRP as an anti-proliferative agent, however, is specifically related to the fact that it is a widely expressed endogenous secretory protein. Therefore, the likelihood of an immune response mounted against ERRP is very small. Moreover, since ERRP is a secretory protein it could be administered systemically to inhibit EGFR signaling pathways leading to diminution of cancer cell growth.
INHIBITION OF BREAST CANCER GROWTH BY A NOVEL REGULATOR OF EGFR
Breast cancer is the most common cancer among women. It is the second leading cause of cancer death in women, after lung cancer. About 203,500 women in the United States will be found to have breast cancer in 2003 and about 20% of the women diagnosed with breast cancer will die from this disease. Breast cancer death rates declined significantly from 1992 to 1996, with the largest decrease in younger women-- both white and black. This decline is probably the result of earlier detection and improved treatment.
A number of peptide growth factors and their receptors play an important role in normal mammary development and carcinogenesis. Epidermal growth factor receptor (EGFR) family members are known risk factors for development of disease, predictors of prognosis and response to therapy, and are utilized as therapeutic targets against a variety of cancers including breast cancer. There are several strategies under investigation to block binding of growth factor to receptor. A number of antibodies that block the EGFR have been developed. Evidence is emerging which indicates that downstream blocking of EGFR signaling pathway is an effective therapeutic approach for treatment and prevention of many epithelial malignancies, particularly those whose growth is regulated by EGF family of peptides. This may be the most relevant area for utilization of a naturally occurring novel negative regulator of EGFR called epidermal growth factor receptor related protein (ERRP), that we recently isolated, purified and characterized, as a therapeutic and possibly chemopreventive agent against human breast carcinoma. Our preliminary data suggest that treatment of human breast cancer cells with purified ERRP protein causes apoptosis (cell death) and, therefore, serves as an effective inhibitor of breast cancer cell growth.
This investigation is aimed at elucidating tumor-supressor and therapeutic properties of ERRP in inhibiting growth of human breast cancer cell-derived tumors. The primary objective of this investigation is to test the hypothesis that ERRP will be effective in inhibiting the growth of estrogen-responsive and estrogen-nonresponsive breast cancers. Different estrogen-responsive as well as estrogen-nonresponsive breast cancer cells will be utilized to study growth of their tumors in SCID mice in the presence or absence of purified ERRP. We will determine whether and to what extent ERRP inhibits growth of the breast cancer cell-derived tumors in SCID mice. We will also compare effectiveness of ERRP with the monoclonal antibody MoAb225 (that is currently in phase III clinical trial) in inhibiting tumor growth in SCID mice. We will also determine whether continuous presence of ERRP could interfere with establishment of tumors in SCID mice that would indicate a chemopreventive potential of ERRP against breast carcinoma. The regulation of ERRP-dependent growth inhibition of breast cancer cells in vitro, and elucidation of the mechanism(s) of ERRP-induced inhibition of EGFR activation are anticipated to lead to the discovery of new anticancer agents through its use in the development of screening assays, or in the design of small molecules that mimic the action of one or more parts of the ERRP that are critical in inhibition of EGFR activation. This approach could result in an alternative to many toxicotherapies currently available. The success of the most similar treatment approved thus far – Herceptin – gives a strong signal of the receptiveness of the cancer drug market to a similar treatment. The ERRP is, therefore, one of a number of potential therapies emerging from the field of signal transduction research. This is particularly attractive since ERRP is an endogenous, secreted molecule, that can be targeted directly to tumors overexpressing EGFR, thereby reducing the broad cytotoxic effects seen with many others treatments.