Malignant transformation of glioma stromal cells induced by glioma stem cells heterotopically inoculated in host liver

Abstract

Tumor stromal cells have the potential of undergoing malignant transformation induced by glioma stem cells (GSCs) in orthotopic glioma model. The purpose of this study was to explore whether malignant transformation of tumor stromal cells induced by GSCs is dependent on specific local microenvironment. Human glioma stem/progenitor cell line SU3 transfected with red fluorescent protein (SU3-RFP) gene were implanted into the liver of nude mice with whole-body expressing green fluorescence protein (GFP). Then hepatic tumors were harvested to prepare single cell suspension and analyzed with routine pathological examinations. GFP cells with high proliferative abilities were obtained from the cultivation of single cell suspension. Immortalized glioma stromal cells only expressing GFP and double expressing GFP/RFP were further monocloned with micro-pipetting techniques and under continuous passages. Cell phenotypic analysis and tumorigenicity tests were also performed. SU3-RFP was transplanted into liver with a tumor formation rate of 83%. Immortalized glioma stromal cells were obtained from re-cultured xenograft tumor tissue. Three monoclonal cell lines B4, B9, B10 were established and proved to be host-derived cells. B4 was found to be a fusion cell co-expressing GFP/RFP and dendritic cell markers CD1 a, CD83 and CD86. Both B9 and B10 were GFP⁺ cells. B9 expressed macrophage markers CD68 and F4/80 while B10 produced fibroblast marker proteins FAP-α, α-SMA and S100. Three cells were all aneuploid with a tumorigenicity rate of 100% in nude mice. Tumor stromal cells have the potential of malignant transformation in a heterotopic xenograft glioma model. Malignant transformation may also occur outside the central nervous system and contribute to tumor heterogeneity. Further studies are warranted for elucidating the relationship between tumorigenesis, evolution and tumor microenvironment.