Colorectal cancer (CRC) is the fourth most common cause of cancer related deaths in the UK with the prognosis dependent on the degree of tumour invasion and presence of metastasis at diagnosis. An important step in the invasion and metastasis of solid tumours is the loss of cell-cell junctions and the acquirement of a more motile mesenchymal phenotype which is facilitated by the epithelial-mesenchymal transition (EMT). The presence of EMT is linked with a more aggressive, invasive tumour and subsequent poor prognosis. In addition to roles in motility and invasion, EMT can induce a cancer stem cell phenotype in a subset of tumour cells. Cancer stem cells (CSCs) are a subpopulation of cells capable of self-renewal and maintaining a cellular population whilst displaying increased therapeutic resistance. Induction of EMT and CSCs can be regulated by common signalling pathways with expression of EMT transcription factors inducing CSCs expression. Understanding the signalling pathways regulating EMT and CSC formation in cancer is important for preventing of metastasis and combating therapeutic resistance. Aspirin’s role in cancer prevention has been established for a number of years with aspirin treatment reducing the incidence of CRC. Recently, evidence has emerged suggesting aspirin treatment may have post-diagnosis benefits and increase survival rates of CRC patients. A potential mechanism for the post-diagnosis benefit of aspirin is the inhibition of EMT and CSC formation which both facilitate tumour progression and metastasis. Aspirin has been demonstrated to suppress the migratory and invasive capacity of lung cancer cell lines by inhibiting EMT. Whilst aspirin has been shown to inhibit platelet-induced EMT in CRC, the direct effects of aspirin on EMT in CRC cell lines has not been established. I hypothesis that aspirin inhibits cell migration, invasion and EMT in CRC which results in a reduction in the CSC population and contributes to the clinical benefit of post-diagnosis aspirin. Using CRC cell lines, I have demonstrated that aspirin treatment inhibits cell migration, invasion, motility and promotes an epithelial phenotype. These results have been confirmed in human organoids and mouse intestinal adenoma in vivo models. Aspirin also promotes a budding phenotype in Apc deficient organoids and reduces expression of stem cell markers in both mouse and human tissue. Aspirin inhibits the mTOR and Wnt signalling pathways in vivo which have the ability to regulate EMT and CSCs although signalling dependency has not been determined. Regardless, aspirin is decreasing the cancer stem cell population and promoting a non-invasive epithelial phenotype which may explain some of the previously described post-diagnosis benefits.

Perivascular cells of microvascular niches are the prime candidates for being a reservoire of mesenchymal stem cell (MSC)-like cells in many tissues and organs that could serve as a potential source of cells and a target of novel cell-based therapeutic approaches. In the present study, by utilising typical markers of pericytes (neuronal-glial antigen 2, NG2, a chondroitin sulphate proteoglycan) and those of MSCs (CD146 and CD105) and primitive pluripotent cells (sex-determining region Y-box 2, Sox2), the phenotypic traits and the distribution of murine and rat retinal perivascular cells were investigated in situ. Our findings indicate that retinal microvessels of juvenile rodents are highly covered by NG2-positive branching processes of pericytic (perivascular) cells that are less prominent in mature capillary networks of the adult retina. In the adult rodent retinal vascular bed, NG2 labeling is mainly confined to membranes of the cell body resulting in a pearl-chain-like distribution along the vessels. Retinal pericytes, which were identified by their morphology and NG2 expression, simultaneously express CD146. Furthermore, CD146-positive cells located at small arteriole-tocapillary branching points appear more intensely stained than elsewhere. Evidence for a differential expression of the two markers around capillaries that would hint at a clonal heterogeneity among pericytic cells, however, is lacking. In contrast, the expression of CD105 is exclusively restricted to vascular endothelial cells and Sox2 is detected neither in perivascular nor in endothelial cells. In dissociated retinal cultures, however, simultaneous expression of NG2 and CD105 was observed. Collectively, our data indicate that vascular wall resident retinal pericytes share some phenotypic features (i.e. CD146 expression) with archetypal MSCs, which is even more striking in dissociated retinal cultures (i.e. CD105 expression). These findings might have implications for the treatment of retinal pathologies.

The leading cause of breast cancer-associated death is metastasis. During metastasis, tumor cells metastasize from primary tumors to distant organs via the circulatory and lymphatic systems. However, in 80% of solid tumors, metastasis via the lymphatic system precedes metastasis via the vascular system. There is a lot of information about metastasis through the circulatory system. However, not much information is available about the tumor cell dissemination through the lymphatic system or the lymphatic microenvironment that aids in this process in breast cancer metastasis. In addition, the molecular properties of tumor cells as they exit the primary tumor into the afferent lymphatics en route to the sentinel lymph nodes (SLNs) are not yet known.<br><div><br></div><div>This project aims to determine why and how tumor cells metastasize to the lymphatic system. The proposal is based on the hypothesis that active migration is needed for tumor cells to spread via the lymphatic vessels. Thus, finding and understanding the molecules that contribute to this can be a breakthrough for breast cancer metastasis therapy.<br></div><div><br></div><div>The goals of this thesis are to 1) Examine the molecular, genetic, and proteomic characteristics of circulatory tumor cells and compare these to the primary tumor and lung metastasis, 2) Examine the role of Toll-like receptors in tumor cell migration to the lymph node, and 3) Identify the difference in protein expression among two different types of breast cancer (Triple-Negative and Luminal A) and understand their aggressive biology.<br></div>