MB-92
DO ABCB1 EXPRESSING DRUG RESISTANT CANCER STEM CELLS UNDERLIE MEDULLOBLASTOMA METASTASIS? Free

INTRODUCTION: Metastatic paediatric medulloblastomas (MB) are aggressive chemo-incurable tumours. We have previously demonstrated an association between expression of the multidrug resistance transporter ABCB1, in a subpopulation of cells, with high risk MB. We hypothesise that these ABCB1 expressing cells also underlie MB metastasis. METHODS: ABCB1 protein expression was assessed in patient tissue microarrays, metastatic cell lines (D283Med, D458Med and MED1) and mouse orthotopic xenografts by immunohistochemistry. ABCB1 gene expression was analysed in publically available MB data using the R2: Genomics Analysis and Visualization platform and in metastatic cell lines grown in 2D and 3D cultures by qRT-PCR. The effect of ABCB1 functional inhibition with vardenafil on MB cell migration and invasion was investigated using 3D migration assays. Vardenafil was also used to investigate increased sensitivity to chemotherapy treatment in ABCB1 expressing cells using clonogenic and 3D spheroid assays. RESULTS: ABCB1 expression was significantly upregulated in metastatic MB patients (p < 0.04) particularly in M3 patients with spinal metastases (p < 0.01). ABCB1 expression was also confirmed in both primary tumours and spinal metastases in a group 4 MED1 mouse orthotopic xenograft model. 3/3 metastatic MB cell lines maintained ABCB1 expression in 2D and 3D cultures and demonstrated reduced cell migration when treated with vardenafil (p < 0.005). Vardenafil treatment also significantly increased sensitivity to etoposide in all three metastatic ABCB1 expressing cell lines (p ≤ 0.02). CONCLUSION: Our data supports the hypothesis that ABCB1 expression underlies both drug resistance and metastasis in medulloblastoma.