PO-295 Heterogeneity of the alpha5 integrin subunit expression in glioblastoma

Abstract

IntroductionGlioblastoma (GBM) is the most aggressive primary brain tumour. Treatment failure and recurrence are explained by intratumoral heterogeneity. Our previous results showed that the integrin α5β1, the fibronectin receptor, is implicated in GBM aggressiveness and represents a pertinent therapeutic target. Recently, we observed that its expression was heterogeneous between patient tumours but also between different areas in a given tumour. We hypothesised that this intratumoral heterogeneity may be linked to different glioma initiating cells (GIC).Material and methodsGICs were grown as neurospheres in stem cell medium and their differentiation was induced by serum. We characterised α5β1 expression in 9 GICs cell lines before and after differentiation. Two cell lines were selected and were genetically modified by depletion (CrisprCas9) or transfection of the α5 integrin gene. Different clones were selected expressing or not the integrin. Aggressiveness of polyclonal lines and individual clones was analysed in vitro before and after differentiation (proliferation, migration, evasion from spheroids) and in vivo (orthotopically xenografted cells).Results and discussionsOur results show that α5 integrin is not expressed in stem cell culture conditions. However, α5 expression is induced after differentiation in about half of the cell lines supporting the notion of inter-tumoral heterogeneity of GICs. Interestingly, single cell-derived clone evaluation showed that intra-tumoral GICs heterogeneity also exists. We noticed that when GICs are programmed or forced to express α5 integrin, differentiated cells became more aggressive. Notably, differentiated cells, expressing the integrin, acquired a fibronectin-dependent motility and a proliferative phenotype. The in vivo assays demonstrated that GICs, programmed to express the integrin, were prone to form larger tumours.ConclusionOur data support the hypothesis that some GICs are programmed to express the α5 integrin subunit to form a more aggressive tumour. Further studies will be needed to explore the implication of such heterogeneity in resistance to anti-integrin therapies but also to conventional chemo/radiotherapies.