Abstract
BackgroundOncolytic virotherapy is a novel approach for the treatment of glioblastoma multiforme (GBM) which is still a fatal disease. Pathologic features of GBM are characterized by the infiltration with microglia/macrophages and a strong interaction between immune- and glioma cells. The aim of this study was to determine the role of microglia and astrocytes for oncolytic vaccinia virus (VACV) therapy of GBM.MethodsVACV LIVP 1.1.1 replication in C57BL/6 and Foxn1nu/nu mice with and without GL261 gliomas was analyzed. Furthermore, immunohistochemical analysis of microglia and astrocytes was investigated in non-, mock-, and LIVP 1.1.1-infected orthotopic GL261 gliomas in C57BL/6 mice. In cell culture studies virus replication and virus-mediated cell death of GL261 glioma cells was examined, as well as in BV-2 microglia and IMA2.1 astrocytes with M1 or M2 phenotypes. Co-culture experiments between BV-2 and GL261 cells and apoptosis/necrosis studies were performed. Organotypic slice cultures with implanted GL261 tumor spheres were used as additional cell culture system.ResultsWe discovered that orthotopic GL261 gliomas upon intracranial virus delivery did not support replication of LIVP 1.1.1, similar to VACV-infected brains without gliomas. In addition, recruitment of Iba1+ microglia and GFAP+ astrocytes to orthotopically implanted GL261 glioma sites occurred already without virus injection. GL261 cells in culture showed high virus replication, while replication in BV-2 and IMA2.1 cells was barely detectable. The reduced viral replication in BV-2 cells might be due to rapid VACV-induced apoptotic cell death. In BV-2 and IMA 2.1 cells with M1 phenotype a further reduction of virus progeny and virus-mediated cell death was detected. Application of BV-2 microglial cells with M1 phenotype onto organotypic slice cultures with implanted GL261 gliomas resulted in reduced infection of BV-2 cells, whereas GL261 cells were well infected.ConclusionOur results indicate that microglia and astrocytes, dependent on their activation state, may preferentially clear viral particles by immediate uptake after delivery. By acting as VACV traps they further reduce efficient virus infection of the tumor cells. These findings demonstrate that glia cells need to be taken into account for successful GBM therapy development.
Highlights
Oncolytic virotherapy is a novel approach for the treatment of glioblastoma multiforme (GBM) which is still a fatal disease
Replication of intratumorally injected vaccinia virus (VACV) LIVP 1.1.1 was inhibited in orthotopic GL261 gliomas in mice To analyze VACV progeny in orthotopic GL261 gliomas in vivo, two different mouse strains, immunocompetent C57BL/6 wild-type mice and immunodeficient athymic Foxn1nu/nu mice, were injected intratumorally with 5 × 106 pfu/brain LIVP 1.1.1
This data implicates that VACV LIVP 1.1.1 did not replicate efficiently in orthotopic GL261 gliomas nor did it in healthy brains of immunocompetent and immunodeficient mice
Summary
Oncolytic virotherapy is a novel approach for the treatment of glioblastoma multiforme (GBM) which is still a fatal disease. The aim of this study was to determine the role of microglia and astrocytes for oncolytic vaccinia virus (VACV) therapy of GBM. The success rate of conventional therapy is low and the prognosis for GBM is very poor, with a median survival time of less than 15 months [3], more emphasis on the research and development regarding alternative therapeutical approaches is essential In this respect, the use of oncolytic viruses is an innovative and encouraging strategy in cancer therapy [4,5,6]. Oncolytic viruses can kill tumor cells grown in vitro with high efficiency, they often exhibit reduced replication capacity in vivo, which results in a low therapeutic efficiency in clinical trials [11]. They are a heterogeneous population of cells thought to be involved in almost all aspects of brain functions, e.g. in biochemical support of endothelial cells that form the blood–brain barrier, in providing of nutrients to nervous tissues, as well as in maintenance of extracellular ion balance and transmitters [29, 30]
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