Research Grants Awarded
Targeting Notch Signaling And Hepatocyte Growth Factor In Breast Cancer
Investigator Initiated Research
Background: Pharmacogenomics and targeted therapies are at the forefront of cancer research today. Instead of treating all patients the same (?one size fits all?), this approach allows us to tailor treatment options to patients who will most likely benefit while sparing others from the risks of toxic drug therapy. As cancers result from abnormalities in multiple signaling pathways, an emerging approach is simultaneous treatment of cancers to inhibit more than one signaling pathway (multi-targeted therapy). The drugs used in this setting can then be tailored based on the tumor subset and the patient?s genetic makeup (individualized medicine). One of the most promising new approaches for treating breast cancer is inhibition of the Notch signaling pathway. Notch proteins play a fundamental role in cell fate decisions and deregulated Notch signaling is associated with breast cancer. Gamma secretase inhibitors (GSIs, which block Notch activation), are known to kill breast cancer cells in preclinical studies; however, it is unknown how to best utilize them to treat human disease.
In this application, we demonstrate that hepatocyte growth factor (HGF, a cytokine that engages the c-Met receptor tryosine kinase and is involved in tumor progression, angiogenesis and cell survival) is able to preserve Notch expression / activation in breast cancer cells and protects the cells from GSI-induced death. The results suggest we have discovered a new signaling mechanism linking HGF / c-Met and Notch with respect to cell survival. In addition HGF promotes expression of Notch ligands on breast cancer cells that activate Notch on adjacent endothelial cells to promote angiogenesis. As HGF is commonly overexpressed in advanced breast cancer, our findings may have important clinical implications. Patients with advanced / metastatic disease may not benefit from therapies aimed at solely blocking Notch signaling, and a multi-targeted approach attacking both Notch signaling and HGF / c-Met signaling may be necessary for these patients.
Objective/Hypothesis: We hypothesize HGF, a growth factor commonly found in advanced and metastatic breast tumors, plays a key role in breast cancer progression by deregulating Notch signaling. Notch activation in response to HGF promotes tumor cell survival and induces Notch ligand expression on the tumor cells, which can engage and activate Notch receptors on adjacent endothelial cells resulting in angiogenesis. We propose a combined therapeutic approach targeting both Notch and HGF / c-Met signaling may be necessary to kill breast cancer tumor cells in vivo.
Specific Aims: Aim #1. Determine the mechanism(s) by which HGF protects breast cancer cells from the Notch inhibition. Aim #2. Explore the role of HGF-induced Notch signaling in crosstalk between breast cancer cells and endothelial cells resulting in angiogenesis. Aim #3. Determine the effect of HGF-induced Notch signaling in an in vivo model of breast cancer with respect to tumor cell survival and angiogenesis (microvessel density).
Study Design: In Aim 1, we will examine the effect of HGF on Notch expression / activation in breast cancer cell lines and primary tumor samples representing major subsets of disease (ER-alpha+ versus ER-alpha-; ErbB-2 overexpressing, metastatic versus non-metastatic). If only a particular subset follows the pattern seen in our preliminary studies, it is important to identify this group of patients who may benefit from this therapeutic approach. The mechanism by which HGF increases Notch expression / activation and protects breast cancer cells from GSI-induced apoptosis will be determined. We will identify the signal transduction pathways downstream of HGF / c-Met that are involved in Notch expression and then evaluate other plausible mechanisms including altered Notch turnover, changes in endocytosis, altered gamma-secretase expression, activity, or phosphorylation and changes in ABC transporter expression / activity.
In Aim 2, we will explore HGF induction of Notch ligand expression on breast cancer cells from different subsets of disease and determine their role in promoting endothelial cell proliferation and network formation (angiogenesis). These experiments will be performed under normoxic and hypoxic conditions, as angiogenesis in tumors occurs in hypoxic conditions. Angiogenesis is a key factor in tumor progression, and understanding how HGF-Notch interactions play a role in this process is necessary for treatment of the tumors.
In Aim 3, we will translate our in vitro findings into an in vivo model of breast cancer to determine the effect of HGF-induced Notch signaling with respect to tumor cell survival and angiogenesis. A sample of breast cancer cell lines will be chosen from Aims 1 and 2. These will be injected into mice along with fibroblasts that constitutively secrete human HGF. Following tumor characterization, animals will be treated with GSI, c-Met blocking antibodies or both to determine if tumors stabilize or regress.
Breast cancer is a leading cause of death among women. If detected early, it is often treatable, but those suffering from more advanced disease have a 26% 5-year survival. To improve the overall outlook, our efforts should be focused on novel treatments for advanced or relapsed disease. One of the most exciting novel therapeutic targets in breast cancer are the ?Notch? proteins, which are cell membrane receptors that function in close contacts among tumor cells and between tumor cells and normal cells in the body. The Notch signaling pathway has been of interest to breast cancer researchers because Notch signaling is abnormally high in the tumor cells and drugs aimed at blocking this abnormal activity can kill breast cancer cells in the laboratory. In fact, clinical trials have begun to examine the use of drugs targeting Notch signaling in breast cancer. Another promising therapeutic target is a secreted protein called HGF, which enhances tumor cell survival and promotes angiogenesis, that is, the formation of new blood vessels. Growing tumors need to promote angiogenesis so that they have a supply of oxygen and nutrients. Angiogenesis also allows tumor cells to escape their original location and move to distant organs. A recent study in head and neck cancer suggests HGF can stimulate tumor cells to promote their interaction with the cells that make up blood vessels (called endothelial cells) causing them to form structures similar to small blood vessels. This interaction occurs via the Notch proteins, and HGF increased Notch expression to facilitate communication between the tumor and endothelial cells. We have recently discovered that HGF, which is present at high levels in advanced breast cancer, can promote Notch signaling in breast cancer cells, even in the presence of drugs that potently block Notch activity. Therefore, blocking Notch activity alone in patients may not be sufficient to kill the patient?s cancer cells completely unless HGF is also blocked. Here, we propose to determine how HGF protects breast cancer cells from death induced by Notch inhibition and how it stimulates angiogenesis. Finally, we will test our hypothesis that blocking both Notch and HGF activity in breast cancer patients may be the necessary ?one-two punch? needed to effectively kill the tumor cells.
It is unclear if inhibition of Notch signaling will benefit breast cancer patients in general or if a specific subgroup of patients will respond better to these drugs. It is also unknown if HGF alters Notch signaling in all types of breast cancer or only in a certain subset of patients. The proposed studies will address this important issue. ?Pharmacogenomics? and ?Targeted Therapy? are concepts that have come to the forefront of drug development in recent years. Pharmacogenomics refers to the ability to predict or identify patients who will likely benefit (responder) or will not benefit (non-responder) from a particular treatment. Targeted therapy refers to the use of drugs that specifically inhibit proteins that are thought to be essential to tumor growth and survival. In this application, we propose a ?multi-targeted" therapeutic approach for the treatment of advanced or relapsed breast cancer as these patients commonly overexpress HGF in combination with deregulated Notch signaling. Given the recent entry of Notch inhibitors into clinical trials for breast cancer, our findings could have a significant clinical impact and proactively identify breast cancer patients who need multi-targeted therapy.