Proton beam irradiation stimulates migration and invasion of human U87 malignant glioma cells

Migration and invasion of malignant glioma play a major role in tumor progression and can be increased by low doses of gamma or X-ray irradiation, especially when the migrated tumor cells are located at a distance from the main tumor mass or postoperative cavity and are irradiated in fractions. We studied the influence of proton beam irradiation on migration and invasion of human U87 malignant glioma (U87MG) cells. Irradiation at 4 and 8 Gy increased cell migration by 9.8% (±4, P = 0.032) and 11.6% (±6.6, P = 0.031) and invasion by 45.1% (±16.5, P = 0.04) and 40.5% (±12.7, P = 0.041), respectively. After irradiation at 2 and 16 Gy, cell motility did not differ from that at 0 Gy. We determined that an increase in proton beam irradiation dose to over 16 Gy might provide tumor growth control, although additional specific treatment might be necessary to prevent the potentially increased motility of glioma cells during proton beam therapy.