Characterisation of primitive stem cell-like canine cancer cells: identification of therapeutic targets through genomics

Cancer has emerged as a major cause of morbidity and mortality in the dog, with an estimated incidence of 1 in 4. Despite advances in conventional chemotherapy and radiation, complete cures for most cancer types remains elusive, the challenge being to develop highly targeted therapies that kill cancer cells but leave normal cells healthy. For decades the scientific community has accepted a model that most cells in the body have the capacity to undergo genetic changes that ultimately result in them becoming cancerous. However, there has been a recent challenge to this model that suggests that the ability to become a cancer cell is restricted to specific tissue stem cells. These cells give rise to cancer stem cells that drive the production of daughter tumour cells. Daughter cells have the potential to be killed by conventional chemotherapy and radiation in contrast to cells with stem cell capabilities, which are largely resistant to such therapies. The implications of this are immense as it suggests that current therapeutic strategies are not targeting the root of the cancer, the cancer stem cell. There is a growing body of evidence that cancer is a true stem cell disease. Researchers in human medicine have identified putative cancer stem cells from a diverse range of cancers such as breast, colon, pancreas and brain. We have recently applied similar methodologies to the dog and identified a sub-set of cells in bone cancer that have stem cell characteristics. This proposal aims to further characterize these cells and will seek to identify novel signalling pathways in these cells that have the potential to be a therapeutic target. This study will inform the veterinary oncology community of potentially new ways to kill cancer cells. Further, it has the potential to inform similar studies in people and help to further advance the field of stem cell biology.

For decades the advances in molecular techniques has allowed us to continually dissect the mechanisms of carcinogenesis, most work focusing on the accepted model of multistage carcinogenesis underpinned by progressive genetic changes that drive malignant transformation. In this model, any cell in the body has the potential for malignant transformation. More recently, attention has focused on an alternative model where transformation takes place in a tissue stem cell, becoming a cancer stem cell (CSC) and giving rise to a tumour composed mostly of daughter cancer cells and a small number of CS cells that drive tumour growth and expansion. Proof that cancer stem cells exist as a phenotypically different population of cancer cells requires isolation of different populations of cancer cells and demonstration that one or more groups are efficient at producing tumors while other groups lack this ability. However, these cells cannot be definitively called cancer stem cells until it is possible to demonstrate that a single transplanted cancer cell can give rise to a diverse population of cancer cells within a tumour. Using 'sphere' assays we have isolated cancer cells from cell lines and clinical cases that express markers (e.g. Nanog, Oct 3/4) indicative of a primitive phenotype. We have demonstrated that these cells can be passaged multiple times and are phenotypically distinct from daughter populations. This proposal aims to further characterize these cells in vitro and in vivo. In particular we will evaluate to ability of these cells to form tumours in NOD-SCID mice and use microarray to study specific transcriptomic profiles. Finally, we will use the array data, information from the published canine genome sequence, and RNAi to identify and validate potential targets in these cells for therapeutic intervention.