Thesis, FRANZEN Rachelle

Abstract

Glioblastoma (GBM) is the most common and aggressive primary brain tumour in adults. Despite standard treatments, including surgery, radiotherapy, and chemotherapy with temozolomide (TMZ), the current median survival rate remains limited to approximately 9 months and is characterised by systematic relapses. This poor prognosis is primarily due to significant intratumoral heterogeneity, an immunosuppressive tumour microenvironnement (TME), limited penetration of treatments through the blood-brain barrier (BBB), and the persistence of glioblastoma stem cells (GSCs), which are implicated in treatment resistance and recurrence. In this context, the laboratory has developed a therapeutic approach aimed at targeting protein tyrosine kinase-7 (PTK7), which is highly expressed by GBM cells. The primary objective of this master thesis was to evaluate the efficacy and specificity of this therapeutic strategy. To achieve it, we characterised the cytotoxicity induced in PTK7+ cell lines, analysed the selectivity of the effect under PTK7+/PTK7- co-culture conditions, and validated these observations in translational models of increasing complexity, including in vivo models. We have also developed a mouse GSC model expressing PTK7, in which we examined protein expression and targeting specificity. The results suggest a preferential induction of cell death in PTK7+ cells exposed to the therapy, associated with the activation of apoptotic markers observed by western blot and flow cytometry. Concurrently, the specificity of the targeting was confirmed in monocultures and co-cultures of PTK7+ and PTK7- cells. These observations were partially validated in intracerebral xenograft tissues, where morphological alterations in the tumour, as well as localised foci positive for a cell death marker were recorded. Finally, a murine model of GBM expressing PTK7 was established and validated for future translational investigations.