Research

My laboratory currently has six main research themes:

1. Characterisation of normal mammary epithelial stem and progenitor cells

Mammary stem and progenitor cells are perceived to be the cell of origin of breast tumours since only these cells have the replicative capacity that allow the multiple mutations required for tumour progression to accumulate. My previous research demonstrated that functionally distinct mammary cells can be purified and detected via the use of flow cytometry and functional assays (Figure 1). We have recently identified two novel types of progenitor cells within the mammary epithelium and are currently determining their properties and how they relate to breast tumours.

Figure 1
Flow cytometry dot plot demonstrating the distribution of epithelial cell adhesion molecule (EpCAM) and alpha 6 integrin (CD49f) among freshly dissociated human mammary epithelial cells. The differentiated luminal (NCL), luminal progenitor (LP) and basal cell populations are indicated. The LP population generates colonies of pure luminal cells, whereas the basal cell population is enriched in bipotent progenitors, which generate mixed lineage colonies in vitro. Re-plating of these mixed colonies demonstrates that they are precursors to myoepithelial-restricted progenitors. Scale bars are 1mm.

2. Determining the cell of origin in breast cancer

Breast cancer is a heterogeneous disease with approximately five molecular subtypes and 18 histological subtypes identified. Our laboratory is interested in elucidating the mechanisms that account for this heterogeneity. One possible mechanism is that different types of breast cancers initiate in, and are propagated by, different types of mammary cells. To test this directly, we are conducting experiments in which we are reverse engineering human breast tumours onto different cellular backgrounds. We will also be examining the influence of a variety of tumour suppressor genes on mammary stem and progenitor cell function to determine if loss of common tumour suppressor genes can impart some properties of stem cells to committed progenitor cells. The tumour suppressor genes that we are focusing on are those associated with basal-like breast tumours, which are very aggressive types of breast cancer.

3. Identification of the molecular mechanisms that regulate stem cell self-renewal

Self-renewal is perceived to be a defining property of stem cells. Cellular pathways that regulate stem cell self-renewal are considered to be good targets for therapeutic intervention since tumours should eventually exhaust their proliferative capacity in the absence of these pathways. Since we have developed strategies that enable us to isolate stem cells to high purities, our approach to identify these pathways is to compare the gene expression patterns of mammary stem cells isolated from different developmental states (e.g. states of stem cell expansion vs. non-expansion).

4. Characterisation of human breast tumour stem cells 

Previous reports in the literature have demonstrated that human breast tumours contain a cancer stem cell component and that these cells can be prospectively isolated on the basis of the expression of certain cell surface markers and intracellular enzymes (reviewed in Stingl and Caldas, Nat Rev Cancer 2007; 7: 791). It is not known if these properties are universal for all breast cancer stem cells or if different types of breast tumours have stem cells with unique properties. To address this issue, we have initiated experiments in which the breast cancer stem cell component of human breast tumours is identified and characterised using flow cytometry in combination with functional assays. We will be able to understand the cellular context of these cancer stem cells by using the markers that we have previously determined to characterise different subsets of normal mammary epithelial cells. Long-term experiments include tracking the evolution of these cancer stem cells over time and examining their functional heterogeneity, both of which have large implications for response to therapy.

(Collaborative project with Carlos Caldas, CRI)

5. Characterisation of human ovarian cancer stem cells 

Serous ovarian cancer is an aggressive disease that initially responds to chemotherapy, but approximately 70% of patients will relapse and become resistant to therapy. It is our hypothesis that this resistance is mediated by the emergence of a subpopulation of ovarian cancer stem cells. We are currently evaluating the proliferative potential of phenotypically distinct subsets of ovarian tumour cells in order to identify the putative cancer stem cells. Future research includes tracking experiments to follow the fate of individual clones during chemotherapy and gene expression profiling of these cells.

(Collaborative project with James Brenton, CRI)

6. Characterisation of the normal and malignant prostate epithelial cell hierarchy

We are applying our expertise in the characterisation of the mammary epithelial cell hierarchy to the human prostate epithelial cell hierarchy. We are particularly interested in characterising progenitor cells within the human prostate and their developmental relationships.

(Collaborative project with David Neal, CRI)