Standardized orthotopic xenografts in zebrafish reveal glioma cell line specific characteristics and tumor cell heterogeneity

Abstract

Glioblastoma (GBM) is a deadly brain cancer with few effective drug treatments available. Studies have used zebrafish to study GBM, but a standardize approach to modeling GBM in zebrafish is lacking inhibiting the ability to compare data across studies. To facilitate analysis of glioblastoma tumor cell behavior in real time and for drug screens, we generated and standardized a xenotransplant model of GBM in zebrafish. Dose response survival curves identified the optimal number of cells for tumor formation, techniques were optimized to measure tumor burden and cell spread within the brain over time in-vivo, and mouse neural stem cells were used as control transplants. Using this standardized approach, we transplanted two patient-derived GBM cell lines, serum grown adherent cells (X12) and neurospheres (GBM9) into the midbrain region of embryonic zebrafish. Analysis of larvae over time showed progressive brain tumor growth and premature death with both cell lines, however, fewer GBM9 cells were needed to cause tumor growth and lethality. Approximately half of the cells in both xenotransplants were dividing whereas control mouse neural stem cells failed to engraft and were cleared from the brain. Few GBM9 cells expressed GFAP or vimentin, markers of more differentiated cells, early, but this number increased significantly during tumor growth indicating that GBM9 cells undergo differentiation in-vivo. In contrast the vast majority of serum grown X12 cells expressed GFAP and vimentin at the earliest times examined post transplant. Both cell types produced tumors in the zebrafish brain containing Sox2-positive cells indicative of neural stem cells. To determine whether GBM9 tumors were responsive to currently used therapeutics, we treated transplanted larvae with either temozolomide or bortezomib and found a reduction in tumor volume in-vivo and an increase in survival supporting the use of this standardized model for drug screening.