The Investigation of Targets for Therapy in Brain Tumours

Gliomas are among the most difficult of tumours to treat. Their highly invasive\ud nature leads to recurrence even after aggressive therapy including surgery,\ud radiotherapy and chemotherapy. A promising target for new therapies are tyrosine\ud kinases, because they regulate a large range of proteins involved in growth,\ud metabolism and differentiation. The receptor tyrosine kinases, epidermal growth\ud factor receptor (EGFR), platelet derived growth factor receptor (PDGFR) and C-Kit,\ud as well as the non-receptor tyrosine kinase C-Abl are often amplified,\ud overexpressed, and/or mutated in gliomas and play an important role in glioma\ud development. A number of tyrosine kinase inhibitors (TKIs) have been developed\ud and tested in clinical trials with mixed results.\ud In collaboration with Beaumont hospital 31 glioma cell cultures were\ud established to identify molecular markers indicative of responsiveness to EGFR and\ud PDGFR blockade. Each culture was characterised with regard to their protein\ud expression profile, their proliferative and invasive behaviour and their\ud responsiveness to three TKIs, erlotinib, gefitinib and imatinib, and two\ud chemotherapy drugs, docetaxel and temozolomide.\ud All data of 26 high-grade gliomas (20 primary glioblastomas, 2 secondary\ud glioblastomas, and 4 grade III astrocytomas including medical history of the patients\ud were analysed using hierarchical clustering analysis (HCA) and principal component\ud analysis (PCA) employing multivariate statistics.\ud Two distinct clusters of samples were found, which separated by the\ud expression of PTEN and PDGFR-a in cluster 1 and predominately PDGFR-b,\ud EGFR, phosphorylated C-Kit (p-C-Kit) and phosphorylated C-Abl (p-C-Abl)\ud expression in cluster 2. Principal components analysis of the culture data captured\ud 55% of the variance in the dataset showing PTEN, PGDFR-a and PGDFR-� loading\ud vectors in approximately the same direction.\ud Imatinib responsiveness was strongly correlated with high expression levels\ud of PTEN and PDGFR-a. Responsiveness to erlotinib was correlated with the lack of\ud expression of all proteins tested, while non-responders showed higher expression of\ud PTEN and PDGFR-a. Responders to gefitinib fit into two groups, the majority\ud (group 1) were influenced by the expression of the proteins tested, while the second\ud smaller group correlated with the lack of protein expression. Non-responders t