S1.02 SUBLETHAL IRRADIATION ENHANCES INVASIVENESS OF MALIGNANT GLIOMA CELLS; IMPLICATIONS FOR RADIOTHERAPY OF HUMAN GLIOBLASTOMA

PURPOSE: This study explored the effect of irradiation on glioma invasion and also established relation between the infiltrative phenotype of glioma and the expression of p53 and MMP-2. METHODS: Human glioma cell line, U87MG (p53+) was prepared. U2OS (p53+) and SAOS2 (p53-) from osteosarcoma were used as control for p53 positive or negative. Each cell lines received single dose (2-8Gy) of irradiation, and then were analyzed the expression of p53, TIMP-1, 2 by western blot and MMP-2 activity by zymography. In order to confirm p53-MMP2 association, RNAi of p53 was treated into U87MG. The effect of irradiation on malignant glioma invasion was investigated by bioluminescence imaging after implantation U87-Fluc cell line in nude mouse brain, and then immunohistochemistry for p53, MMP-2 and in situ zymography were performed. RESULTS: MMP-2 activity and p53 expression were increased in proportional to irradiation dose in U87-MG and U2OS. TIMP-1, 2 was not changed in u87MG, but was increased in U2OS. In SAOS, TIMP-1, not TIMP-2 was increased after irradiation. Interestingly, MMP-2 began to express in 8 Gy-induced SAOS cells and expression of p53 and TIMP-1 were simultaneously increased. In vivo experiment, tumor margin of irradiated group was changed infiltrative phenotype, while control group was clear. MMP-2 and p53 was highly expressed in marginal area. And also, p53 knockdown decrease MMP-2 activity in irradiation induced u87MG cells. CONCLUSION: Irradiation could enhance glioma invasion, p53 expression and MMP-2 activities. Consequently p53 may regulate MMP-2 activity and high level of MMP-2 activation may play important roles in alteration to invasive growth pattern of U87MG by irradiation. These data suggest that the current involved-field radiotherapy for malignant glioma may need to be reconsidered and that future trials should consider pharmacologic therapies inhibiting invasion concurrently with radiotherapy.