Uveal melanoma (UM) is the most common malignancy of the eye in adults and it is the second most common form of melanoma after cutaneous melanoma (CM). The identification of patients who have a... Show moreUveal melanoma (UM) is the most common malignancy of the eye in adults and it is the second most common form of melanoma after cutaneous melanoma (CM). The identification of patients who have a high risk of developing metastases would allow the possibility of providing adjuvant therapies to prevent metastases. The application of FISH on transvitreal fine-needle aspiration biopsies is thought to be a reliable method for assaying genetic parameters such as chromosome 3 loss. However, this is based on the assumption that this chromosomal abnormality is distributed homogeneously throughout the tumor. We show that UM can be heterogeneous for the number of copies of chromosome 3 and investigated whether any evidence can be found for heterogeneity in the regulation of tumor-suppressor genes (TSG). Recently, a segregation study identified a potential locus harboring a TSG. One of the genes in this area, RASEF, was analyzed whether the RASEF gene was affected by mutations or gene silencing due to promoter methylation. The MAPK pathway is involved in the balance between melanocyte proliferation and differentiation. Whereas mutant B-RAF and N-RAS are responsible for the activation of the MAPK pathway in most CM, mutations in these genes are usually absent in UM. Nowadays, an assay with increased potential to identify mutations is available and we set out to reanalyze UM cell lines and primary UM for B-RAF mutations. We set out to explore the MAPK pathway by using MAPK profiling and tyrosine kinase arrays. Finally, conclusions drawn from above mentioned studies are summarized and put into perspective. Show less
Uveal melanoma (UM) is a disease with many faces: ophthalmologists treat the primary tumor, but the patient faces the problem of developing metastases, which are often deadly after a short period.... Show moreUveal melanoma (UM) is a disease with many faces: ophthalmologists treat the primary tumor, but the patient faces the problem of developing metastases, which are often deadly after a short period. Recent insight, indicates the need for knowledge-based treatment of UM. The __pseudohypoxic__ and tumor promoting effects of bevacizumab as described in this thesis is especially relevant. Bevacizumab is frequently used off-label to treat macular edema in UM patients suffering of radiation retinopathy, without the knowledge of possible effect on still viable UM cells. We further observed that specific peptides, such as UMAP1, which can successfully be internalized by targeted UM cells, have demonstrated potential for UM-targeted treatment. These peptides have to be investigated in vivo, to ascertain whether they are a viable clinical tool. Labeling the peptides with radionuclides, and demonstrating specificity for UM cells are some of the challenges which have to be overcome. Another aspect in the patient-specific treatment of UM is the in vitro analysis of primary UM samples to predict treatment responses. In case of Dasatinib, we describe treatment responses associated with monosomy 3 and __kinase__ activity in different primary UM samples. Show less
The p53 tumor suppressor protein plays a key role in cancer and its direct or indirect inactivation is an almost universal feature of human tumors. P53 has a central position in the prevention of... Show moreThe p53 tumor suppressor protein plays a key role in cancer and its direct or indirect inactivation is an almost universal feature of human tumors. P53 has a central position in the prevention of genomic instability and protection of tumorigenesis. This thesis presents novel studies regarding the role of Hdmx in p53 inactivation during tumorigenesis, as well as the use of specific drugs for p53 reactivation as cancer treatment. Chapter 2 shows that constitutive Hdmx overexpression contributes to the neoplastic transformation of human fibroblasts and embryonic retinoblasts, thereby functionally resembling loss of p53. Chapter 3 establishes the importance of Hdmx as an oncogene in a subset of uveal melanomas. Importantly, the results described in this chapter extend the function of Hdmx beyond p53 inhibition. Chapter 4 evaluates the use of the specific p53 activating drugs Nutlin-3 and RITA in synergy studies as potential therapy for uveal melanoma. Chapter 5 is a more detailed analysis of the cellular responses to RITA. In particular, Chk2 is shown to be an essential mediator of the RITA-induced effects. Chapter 6 is a general discussion of the results presented in this thesis, and their implications for clinical exploitation and future research. Show less
