OP63
METASTATIC MEDULLOBLASTOMA - ARE DRUG RESISTANT CANCER STEM CELLS TWIST1NG AWAY? Free

INTRODUCTION: Medulloblastoma is an aggressive malignant neuro-ectodermal tumour of the cerebellum that is frequently metastatic resulting in poor outcome. Here we use a 3D model of the tumour microenvironment (TME) to investigate whether an epithelial-mesenchymal transition (EMT)-like process underlies metastasis. METHOD: Expression of EMT genes and the multidrug transporter ABCB1 was assessed by qRT-PCR on cell lines cultured either in 3D, within basement membrane extract for 8 days, or as 2D monolayers. TWIST1 and ABCB1 protein expression were assessed by immunohistochemistry. Time lapse imaging (Cell IQ) was used to investigate cell migration in 3D. RESULTS: Metastatic MED1 formed metabolically active branched interconnecting aggregates in 3D-culture whilst non-metastatic MED6, C17.2WNT and non-tumourigenic C17.2 cells demonstrated low metabolic activity and differentiation. EMT transcription factor TWIST1 expression doubled in MED1 cells grown in 3D compared to 2D, with no increase in expression observed in other cell types. Both TWIST1 and ABCB1 showed high focal positivity in the MED1 primary tumour and were significantly correlated with metastasis in patient samples (p < 0.02 and p < 0.04 respectively). TWIST1 and ABCB1 demonstrated a similar pattern of expression in spinal metastases in a MED1 orthotopic mouse model. The ABCB1 inhibitor vardenafil reduced formation of branched interconnecting aggregates in 3D without affecting MED1 cell metabolism. CONCLUSION: We have identified a TWIST1 controlled EMT-like process in metastatic medulloblastoma. Using a 3D-TME model we have shown that TWIST1 and ABCB1 may be interconnected and that ABCB1 inhibition could be sufficient to block metastatic induction.