Defining a Role for Endothelial Precursor Cells in Breast

Institution: La Jolla Institute for Molecular Medicine
Investigator(s): Longchuan Chen, Sc.D. -
Award Cycle: 2002 (Cycle VIII) Grant #: 8IB-0095 Award: $199,174
Award Type: IDEA
Research Priorities
Biology of the Breast Cell>Biology of the Normal Breast: the starting point



Initial Award Abstract (2002)
New blood vessel growth is required for both normal tissue expansion and tumor formation. Blocking this process is a promising way to treat breast cancer. Endothelial cells lining the inner surface of new blood vessels can come from either existing vessels or bone marrow-derived endothelial precursor cells circulating in the blood. The critical role of the latter pathway to building new blood vessels is emerging. The significance of circulating endothelial precursor cells to breast development and breast cancer is currently unknown and therefore requires further investigation.

We hypothesize that, by promoting new vessel growth, endothelial precursor cells could play a significant role in normal breast development and breast cancer. Finding ways to block this pathway may be necessary to completely halt the growth of new blood vessels in breast tumors. We will establish mouse bone marrow transplant models to mark the bone marrow-derived endothelial cells and track them in the breast tissue and tumor blood vessels. We will screen antibodies that specifically recognize endothelial precursor cells from a phage display antibody library. We will try to design ways to block endothelial precursor cells to test if breast tumor growth is inhibited.

This study, to my knowledge, is the first to link endothelial precursor cells to breast development and breast cancer. It will combine the use of mouse bone marrow transplant model and mouse breast cancer models to study the role of endothelial precursor cells in tumor formation. It could lead to new ways to treat breast cancer.


Final Report (2003)
Growing new blood vessels or angiogenesis is a critical step in breast cancer growth. Recent findings show that bone marrow-derived endothelial precursor cells (EPC) can incorporate into new blood vessels during physiological and pathological processes. It is possible the contribution of EPCs to new vessels varies in different tissues and tumor types. The involvement of EPCs in the breast tissue and breast tumors is not clear. Therefore, the importance of this pathway to breast cancer needs to be evaluated.

The first objective was to determine the contribution of EPC in the blood vessels of breast tumors by using a mouse bone marrow transplant model. We tried to answer whether EPC are involved, to what extent and how EPC incorporate into breast tumor vessels. The second objective was to discover reagents and ways to block endothelial precursor cells and angiogenesis. As we know very little about the markers on EPC, we tried to screen antibodies that specifically recognize endothelial precursor cells from a phage display antibody library.

We successfully used mouse bone marrow transplant models to mark the bone marrow derived endothelial cells and track them in the breast tissue and tumor blood vessels. The bone marrow from Tie2-IaCZ transgenic mice was transplanted into female wild type mice and breast tumors were inoculated orthotopically in the mammary fat pads of these animals. Immunohistochemistry methods using endothelial marker CD31 and LacZ staining detected clusters of blue endothelial cells derived from EPC in tumor vessels, albeit at a small percentage of total endothelial cells. This finding is in line with results reported by previous studies in other tissues and tumor types. Using an in vitro screening method, we have successfully screened antibodies against a purified extracellular protein and obtained antibodies against isolated AC133+ endothelial precursor cells from a phage display antibody library. These antibodies can be produced and purified in large quantity for further testing.

Based on our current results, it is critical to know whether the small percentage of endothelial cells derived from bone marrow play an important role in tumor initiation. Toward this goal, we will use a skinfold chamber model to address the role of EPC in the initiation stage of breast tumor development. This model also serves as a convenient system to test the tumor blocking effect by the phage-derived antibodies. We will continue to identify the markers that the phage antibodies binds and test them in angiogenesis and tumor inhibition assays. This study has confirmed the involvement of bone marrow derived in tumor vessels in the breast and we will continue characterizing antibodies for potential imaging and therapeutic uses for breast cancer.