Defining Mammary Cancer Origins in a Mouse Model of DCIS

Institution: University of California, Davis
Investigator(s): Alexander Borowsky, M.D. -
Award Cycle: 2005 (Cycle 11) Grant #: 11IB-0158 Award: $149,950
Award Type: IDEA
Research Priorities
Biology of the Breast Cell>Pathogenesis: understanding the disease



Initial Award Abstract (2005)
Early events in breast cancer progression are critical to the understanding of the disease, and critical to the development of new therapies and strategies for prevention. In mammary cancer, evidence points to early evolutionary cellular divergence and cancer fate commitment. We believe that all of the genetic changes that commit a mammary cell to become a cancer occur before a morphologic lesion is formed. We believe these changes commit the cell to become a cancer with specific “behavioral properties”, and that this commitment does not depend on, nor does it diverge based upon additional molecular "hits". Mouse models of mammary cancer progression permit experimental evaluation of the behavior and biology of disease that is impossible to study in humans.

We have generated and characterized specific genetically engineered and micro-anatomically defined mouse mammary epithelia with properties critical to the understanding of mammary cancer progression. Specifically, these epithelia have precise features of human mammary pre-cancer (DCIS, ductal carcinoma in situ) with consistent progression to invasive carcinoma, and consistent metastatic behavior. The system provides a window to study the early evolution of mammary cancer.

We propose to use our novel mouse model system to define pre-cancer cell populations and characterize their biologic potential. The following specific aims will be pursued: 1. Assess clonal selection and genomic alterations in mammary pre-cancer 2. Characterize the cell types in mammary pre-cancer.

Using time honored techniques of mammary serial transplantation, specific lesions from genetically engineered mice (GEM) will be isolated and the biologic potential experimentally defined. These are defined by the "test-by-transplantation" as mammary intraepithelial neoplasia outgrowths (MIN-Os). Dissected tissues will be characterized for gene expression and DNA content. Using immunohistochemistry (IHC), mammary epithelial dissociation techniques, flow cytometry and cell sorting, specific cell subsets will be isolated and tested by re-transplantation for their biologic potential.

Our future aim is to genetically manipulate pre-cancerous breast cells and test them in our mouse models of mammary pre-cancer. The NCI Breast Cancer Progress Review Group has specified a priority to identify the earliest changes in the initiation of breast cancer. The group highlighted the importance of mammary stem cell biology and the manipulation of mouse mammary tissue in this priority, and recognized the need for experimentally defined assessment of biologic potential using techniques for mouse mammary gland manipulation including transplantation and genetic engineering.


Final Report (2007)
In this CBCRP-funded project we confirmed the clonality and genetic stability of our mouse MINO (mammary intraepithelial neoplasia outgrowths) model system. The purpose of these studies was to explore the earliest stages of breast cancer development. For this we performed “flow cytometry” to analyze the cell population heterogeneity of our MINO cells compared to normal epithelial cells and mammary tumors. Data derived from the flow cytometry experiments suggest that there are significant differences in the ratio of "stem"- like cells in pre-cancer MINO and tumor tissues, and these are also different from normal mammary gland. Published results from other labs show data only for normal, and one particular type of tumor--Wnt pathway induced carcinomas. Errbb2 pathway tumors appear to also be significantly different from Wnt pathway tumors. The “proof of potential” for these various cell subsets resides in the ongoing transplantation experiments. Also, we were also able to re-grow dissociated MINO cells into hollow balls, called “mammospheres”, which contained properties of both normal epithelial cells and tumor-like elements. Finally, we studied potential markers of mammary stem cells in our MINO system. The effort to identify, isolate, and study normal mammary and tumor stem cells is ongoing in many laboratories.

We are now collaborating with the Kent Erickson laboratory at UC Davis in an effort to identify new stem cell markers. He has adapted a "one bead, one peptide" technology from Kit Lam at UC Davis for use in mammary cells. We have agreed to provide FACS sorted cells from a variety of mouse mammary tissues/tumors as the required starting material for these experiments. In addition we are now collaborating with several other laboratories to use the MINO model in a variety of contexts. Our future goals are to evaluate the specific effect on the stem-like precancer cells of various therapies. We have submitted a renewal application to the CBCRP to pursue these new aims.


Symposium Abstract (2005)
Alexander D. Borowsky,1 J. Graeme Hodgson, 2 Jeffrey P.Gregg,1 Larry J. T. Young,1 Qian J. Chen,1 Robert D. Cardiff.1
UC Davis,1 Davis, CA, UCSF,2 San Francisco, CA.

The early origins of breast cancer have become the subject of intense interest. In some cancers, colon cancer, for example, there is a clear stepwise progression with morphologically recognizable intermediate stages correlated to precise molecular alterations. In mammary cancer, epidemiologic and molecular evidence points to early evolutionary divergence and cancer fate commitment. We hypothesize that all of the changes committing a mammary cell to become a cancer occur before a morphologic lesion is detectable. Our evidence shows that these changes commit the cell to become a cancer with specific behavioral properties. We also hypothesize that this commitment does not depend on additional molecular “hits” and that the path of commitment is not altered by additional molecular “hits”. If true, there must be progenitor cells that encode the genetic (or epigenetic) information required for these behavioral properties. The encoded information should be different for progenitor cells with different malignant potentials and all progeny of a given progenitor should show parallel evolution. If not true, the progeny from a given progenitor cell should diverge in specific behavior. Mouse models of mammary cancer progression permit experimental evaluation of the behavior and biology of disease that is impossible to study in humans. We have generated and characterized specific genetically engineered and microanatomically defined mouse mammary epithelia with properties critical to the understanding of mammary cancer progression. Specifically, these epithelia have precise features of human mammary pre-cancer (ductal carcinoma in situ) with consistent progression to invasive carcinoma, and consistent metastatic behavior. We refer to the models as mouse mammary intraepithelial neoplasia outgrowths (MIN-Os) denoting both the in situ neoplasia origin of the tissues, as well as the serially transplantable (outgrowth) behavior of the tissues. This mouse model system provides a window on the early evolution of mammary cancer.

Heterogeneity of mammary lesions represent molecular differences.
Periodical:BMC Cancer
Index Medicus: BMC Cancer
Authors: Namba R, et al , Borowsky AD, Cardiff RD, Gregg JP
Yr: 2006 Vol: 6 Nbr: Abs: Pg:275-294

Rapamycin inhibits growth of premalignant and malignant mammary lesions in a mouse model of ductal carcinoma in situ.
Periodical:Clinical Cancer Research
Index Medicus: Clin Cancer Res
Authors: Namba R, et al , Borowsky AD, Qi J, Tepper CG, MacLeod CL, Cardiff RD, Gregg JP.
Yr: 2006 Vol: 12 Nbr: 8 Abs: Pg:2613-21