The Up-Regulation of CXCL12-CXCR4 Axis By Radiotherapy Could Accelerate Glioma Progression
Abstract Background: This study investigated whether the effect of changes in the microenvironment of parenchymal brain tissue caused by radiotherapy for malignant brain tumors affect the recurrence and progression of glioma. Methods: 3 months after the same 65-Gy irradiation had been applied to the right hemisphere. Irradiated Fisher rats were divided into three groups for in vitro assay as follows. IR/Ipsi-brain; the right-hemisphere tissue was used for experiments. IR/Contra-brain; the left-hemisphere tissue was used. Sham-IR/Brain; sham-irradiation was applied to the brain, and the right-hemisphere tissue was used. The effects of proteins extracted from the brains directly or indirectly affected by irradiation on the growth of F98 cells, the effect on tube formation, the influence on tumor biology, and the influence on cytokine production were investigated. Additionally, irradiated animals were divided into three groups for in vivo assay as follows. IR/Ipis-tumor; F98 cells (a glioma cell line) were transplanted to the right hemisphere. IR/Contra-tumor; F98 cells were transplanted to the left hemisphere. Sham-IR/Tumor; F98 cells were transplanted to the right hemisphere without irradiation. The median survival time of F98 transplanted rats was also examined. Results: X-ray irradiation promoted the secretion of cytokines such as TNFα, TGF-β1, VEGF-A, and CXCL12 from the irradiated brain. F98 glioma cells implanted in the irradiated brains showed significantly high proliferation and angiogenesis ability, and the post-irradiation F98 tumor-implanted rats showed a shorter median survival time compared to the Sham-irradiation group.Conclusions: These results indicate that the up-regulation of CXCL12-CXCR4 axis by radiotherapy could promote tumor proliferation. Radiation therapy is a standard treatment for malignant gliomas including glioblastoma multiforme, but the current study suggests that the microenvironment around the brain tissue in the chronic phase after exposure to X-ray radiation becomes suitable for glioma cell growth and invasion.