A novel zebrafish xenograft model for immunotherapeutic drug screening

摘要

Glioblastoma multiforme (GBM) is most aggressive and frequently occurring form of glioma. GBM resists multimodal therapies and has a median survival rate of less than 14 months. Microglia are the resident macrophage of the brain and are the initial myeloid cell type to infiltrate brain tumours. The extent of microglia infiltration into glioblastoma has been directly correlated with glioma grade and invasiveness. Furthermore microglia have been shown to directly support tumour growth, invasion and immunosuppression. Thus microglia represent an attractive immunotherapeutic target in cancer research. Hence, we have developed a novel zebrafish xenograft model as a tool for drug screening in order to identify novel immunotherapeutic compounds. Well established human U87-nls-mKate2 glioblastoma cell lines were xenografted into the brains of transgenic mpeg1:EGFP zebrafish in which all macrophages and microglia are labelled with GFP. Our confocal live imaging results showed distinct interactions between microglia and U87. Importantly these interactions do not appear to be anti-tumoral as zebrafish microglia do not engulf and phagocytose the human glioblastoma cells. Finally, xenotransplants into the irf8-/- zebrafish mutant that lacks microglia, as well as pharmacological inhibition of the CSF-1 receptor on microglia, confirm a prominent role for zebrafish microglia in promoting human glioblastoma cell growth. In addition, we have extended this new xenograft model to test the potential of palladium mediated prodrug into drug conversion in the brain by BioOrthogonal OrganoMetallic (BOOM) reactions. Metallic palladium beads were implanted into the living brains of U87 xenografted zebrafish and the effects of BOOM reactions on tumour cells and microglia could be followed in real time. The proposed zebrafish xenograft model has shown promising potential to be used in compound testing and in the development of future immunotherapeutics within glioma.