Aspects of Tumour Targeting : Preclinical Studies on Human Malignant Cells in vitro

• Exclusive eradication of tumour cells causing minimal damage to healthy tissue, a concept referred to as targeting, is an interesting approach to improve the outcome for patients afflicted with cancer.The general aim of this thesis was to highlighten aspects that could be of importance in developing novel treatment regimens based on specific targeting of tumour cells. Two variants of targeting strategies, boron neutron capture therapy (BNCT) and platelet-derived growth factor receptor (PDGFR) tumour targeting were studied in vitro.In BNCT, the ability of boron-10, 10B, to capture neutrons is utilized. The capture reaction initiate emission of high linear energy transfer (LET) particles which exerts potential damaging effects on exposed cells. A preferential accumulation of at least 10 μg 10B/g tumour tissue is suggested to be required for effective clinical outcome. Here, the accumulation of boronophenylalanine, BPA, was investigated in human glioma, synovial sarcoma, fibroblast and monocytoid cells in vitro. For the purpose of quick and effective separation of extracellular and cell-associated boron, a rapid cell filtration method was developed. Inductively coupled plasma atomic emission spectroscopy, ICP-AES, was used to analyse the amount of boron associated to the cells.Over-expression of PDGFRs may render the possibility to target certain tumours using PDGF-based conjugates for a specific delivery of cytotoxic agents. PDGF-AA was conjugated to dextran of two different sizes, 10 and 40 kDa, and compared with 125I-radiolabelled PDGF-AA regarding accumulation, retention and localisation in human glioma cells in vitro.A boron concentration of >10 μg 10B/g tumour tissue was found in all human cell lines studied. For the two glioma cell lines, the results extend differences between the two although originating from the same human tumour material. Since fibroblasts and monocytoid cells, here used to represent normal cells, accumulated boron at a clinically relevant amount one may have to consider the role of these cells in/at the tumour site during treatment. Regarding results for the human synovial sarcoma cells, further investigations may state the potential of BNCT as a treatment modality and explore the possibilities of a directed delivery of boron-containing substances to receptors specifically expressed in this malignancy.PDGF-AA-based dextran conjugates, preferentially 10 kDa dextran conjugates, showed in vitro properties that were superior to radiolabelled unconjugated PDGF-AA. A prolonged retention time was observed for the conjugates. Radiolabelled PDGF-AA was mainly determined to be located intracellular but the localisation, internalised or membrane-associated, of radiolabelled conjugates seemed to be dependent on the composition of the conjugate. It is of interest to explore the potential of dextran conjugates carrying toxic substances for therapeutic purpose.

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