Research Grants Awarded
Transphosphorylation Of The Egfr By Met And Other Receptor Tyrosine Kinases In Breast Cancer.
Career Catalyst Research
The epidermal growth factor receptor (EGFR) is overexpressed in over 30% of breast cancers. This overexpression of the EGFR correlates with poor prognosis, however inhibition of the kinase activity of the EGFR fails to improve survival of breast cancer patients. The role EGFR plays in breast cancer progression independent of its kinase activity is unknown. Understanding the kinase-independent signaling through the EGFR will provide insight into the growth and survival pathways activated in EGFR expressing breast cancers. The long-term goal of this research is to improve the treatment of breast cancer patients with poor prognosis correlating with overexpression of the EGFR. The objective of this application is to identify receptor tyrosine kinases that tyrosine phosphorylate the EGFR in breast cancer. Evidence has shown that the EGFR is tyrosine phosphorylated in the absence of EGFR tyrosine kinase activity. In addition, in breast cancer cells when EGFR is tyrosine phosphorylated the cell do not require EGFR kinase activity for growth. One receptor tyrosine kinase found to be constitutively phosphorylated under these conditions is Met. Therefore, the hypothesis of this study is that constitutive activation of Met and other receptor tyrosine kinases regulate EGFR tyrosine phosphorylation in breast cancer. The rationale for the proposed research is that identifying the receptor tyrosine kinases that are constitutively activated and tyrosine phosphorylate the EGFR will provide additional therapeutic targets in the treatment of EGFR expressing breast cancers. This hypothesis will be tested by addressing the following two specific aims: 1) Determine the role of Met in tyrosine phosphorylation of the EGFR in breast cancer; and 2) Identify receptor tyrosine kinases that phosphorylate the EGFR in breast cancer. Preliminary data has indicated that Met is highly tyrosine phosphorylated in breast cancer cell lines that do not require EGFR kinase activity for growth. In addition, in the absence of EGFR kinase activity, inhibiting Met activity abrogates EGFR tyrosine phosphorylation and signaling. Therefore, under the first specific aim, it will be determined if in the absence of EGFR kinase activity, whether Met kinase activity is required for EGFR tyrosine phosphorylation, signaling, and growth. In addition, the mechanism by which Met regulates EGFR tyrosine phosphorylation will be determined and the process by which Met is constitutively phosphorylated will be identified. Preliminary data also demonstrates that Met is not highly phosphorylated in all EGFR expressing breast cancers. Under the second specific aim, phosphoproteomic techniques will be used to identify kinases in breast cancer cell lines demonstrating EGFR tyrosine phosphorylation in the absence of EGFR kinase activity. More specifically, phosphoproteomic arrays, immunoaffinity purification, phage display, and in gel kinase assays will be used to identify receptor tyrosine kinases that are highly phosphorylated, determine which receptor tyrosine kinases associate with and phosphorylate the EGFR, and elucidate the role of these receptor tyrosine kinases in EGFR tyrosine kinase-independent cell growth. This approach is innovative because it will rationally identify kinases that are cooperating with the EGFR to promote tumorigenesis and therefore, will prove to be an effective new way to treat cancer. The significance of addressing these objectives is that alternative therapeutic combinations may be identified for the treatment of breast cancer patients with EGFR overexpression.
Breast cancer is a serious health problem for many women with 212,000 estimated new cases and 40,000 estimated deaths in 2006. The majority of deaths due to breast cancer arise from the cancer spreading away from the breast to lymph nodes and distant sites such as the lung and bone. Once the cancer spreads beyond the breast, the relative 5-year survival rate drops from 98% to 26%. Clearly, these statistics tell physicians and scientists that improvements need to be made in the treatment of patients with advanced disease. In that regard, one molecule found to be overexpressed in about 30% of patients with breast cancer with poor prognosis is the epidermal growth factor receptor (EGFR). Clinical trials using molecules to inhibit the EGFR are not proving to be effective in treating breast cancers. In addition, targeted therapies that have been shown to be useful in treating breast cancers, such as Tamoxifen and Herceptin, are not effective in EGFR expressing breast cancers because they lack expression of the targets for these drugs, the estrogen receptor and HER2. Therefore, the identification of new targets for EGFR expressing breast cancers needs to be established. Recently, activation of another tyrosine kinase receptor, Met, has been shown to occur in a lung cancer cell line made resistant to EGFR kinase inhibitors. The authors of this study suggest that Met expression increases and regulates signaling through the EGFR family of kinases in the presence of the EGFR kinase inhibitors. Our own preliminary data demonstrate that in breast cancer cell lines that do not require EGFR kinase activity for growth, Met is highly activated. However, this activation of Met does not occur in every breast cancer cell line that grows without EGFR kinase activity. Therefore, we hypothesize that growth of EGFR expressing breast cancers that do not require EGFR kinase activity occurs through the co-activation of other receptor tyrosine kinases, including Met. We will test this hypothesis by determining the role of a Met in regulating breast cancer cell growth and survival, as well as by identifying novel EGFR interacting receptor tyrosine kinases. Therefore, this proposal aims to identify and validate receptor tyrosine kinases important for cell growth and survival that are activated in the absence of EGFR kinase activity. In the short term, this study will identify new targets for additional efficacy testing in breast cancer patients and determine if multiple kinase inhibitor treatment may be an alternative approach for inhibition of breast cancer cell growth and survival. In the long term, this study may provide information to improve the treatment of breast cancer patients with advanced disease by adding to the list of targeted therapeutics and biomarkers that may be beneficial to this subset of patients.