Analysis Of Differences Between Metastatic Sarcomas And Carcinomas

Abstract

The tumour microenvironment consists of cancerous and non-cancerous cells with a variety of stromal cells, such as platelets and fibroblasts, and the extracellular matrix (ECM) involved in tumour progression and metastasis. Although there are different types of cancers, in this study, we compared the metastatic behaviours between carcinomas and sarcomas by analysing platelets and fibroblasts. In addition, the effects of a heparanase inhibitor (PI-88) on the metastatic behaviours of carcinomas and sarcomas was investigated. The ability of platelets to promote carcinoma and melanoma progression has been thoroughly studied and occurs in numerous ways. By contrast, the effect of platelets on sarcomas, which are tumours arising from mesenchymal cells, has received very little attention. A novel migration assay was developed using bioluminescent tumour cell lines that is rapid, accurate, and permits the study of the effects of tumour cell-stromal cell interactions on tumour cell migratory behaviour (Chapter 3). The results showed that platelets inhibited the invasion of some murine and all human sarcomas tested in vitro when compared with carcinomas (Chapter 4). Further invasion studies with TGF treatment only partially recapitulated the results seen with whole platelets. In a spontaneous tumour growth and lung metastasis model, platelets promoted mammary carcinoma metastasis but not fibrosarcoma metastasis. Gene expression analysis of the platelet-promoted breast carcinoma and platelet-inhibited fibrosarcoma cell lines revealed that exposure of breast carcinoma to platelets resulted in upregulation of oncogenes and EMT-associated genes. Conversely, a tumour-suppressor gene was significantly upregulated in fibrosarcoma. The experiments described in Chapter 5 determined the metastatic behaviours of sarcomas and carcinomas when co-incubated with fibroblasts. Secreted factors from fibroblasts enhanced the migratory capacity of breast and ovarian carcinomas but inhibited the activity of osteosarcomas in a transwell migration assay. Compared with carcinomas, sarcomas expressed significantly increased levels of TGF-RII and extracellular TGF-1, comparable levels of FGFRII, and decreased levels of extracellular bFGF. In addition, fibroblasts promoted murine mammary gland carcinoma and melanoma growth. Immunohistochemical analysis revealed increased vascularisation. However, these effects were not seen on osteosarcoma and fibrosarcoma growth or vascularisation; however, increased lung metastasis was observed. In Chapter 6, the lung metastasis of murine and human carcinomas and sarcomas in mice following PI-88 treatment, and the effect of pro-coagulation on inhibition, were assessed. The expression of 84 metastasis-associated genes was measured in human lung carcinoma and fibrosarcoma cell lines prior to and following PI-88 treatment. PI-88 does not impact the invasive and metastatic capacity of sarcomas despite its ability to inhibit carcinoma metastasis. A synergistic effect between PI-88 and platelet depletion was detected, resulting in the inhibition of carcinoma metastasis in vivo. PI-88 downregulated pro-metastatic genes in lung carcinoma. This thesis has revealed an exciting new chapter in the field of the tumour microenvironment with cancer cells, conclusively demonstrating the metastatic difference between epithelial and mesenchymal cancers. Moreover, this thesis showed that platelets and fibroblasts have opposing effects on mesenchymal and epithelial cancers. This is an intriguing finding that potentially reflects the 'switch-on and -off' role of platelets and fibroblasts in many aspects of wound healing. These data provide future research directions to further elucidate the phenomena of tumour metastasis of different origins. Show more