Description
【Background and Aims】 Currently, normal tissue sparing and local tumor control at ultra-High Dose Rate (uHDR) irradiation have been reported with particles and photons. Our group is interested in the effect of radiation to metastatic potentials on irradiated cells. We focused on the comparison of cell invasive capabilities between uHDR and normal dose rate (NDR) irradiated cells with carbon ion beams and proton beams on breast cancer cell lines. 【Methods】 MDA-MB-231 (MM231: triple negative human breast cancer cells) and MCF-7 (estrogen receptor positive human breast cancer cells) were used. Cells were irradiated with 1.63, 4.36 and 5.65 Gy by carbon ion under uHDR (> 90 Gy/sec) or NDR (1.16 Gy/sec) at Osaka Heavy Ion Therapy Center (HIMAK), they were irradiated with proton (4.0, 12.0 and 15.0 Gy) under uHDR (250 Gy/sec) and NDR (1 Gy/sec) at Sumitomo Heavy Industries, Ltd. E-cadherin, a type of invasion suppressor protein, was measured by western blotting. Matrigel invasion assays were conducted using living cells after 24 hours of irradiation. 【Results】In the results with carbon ion irradiation, MCF-7 showed increased expression of E-cadherin with 4.36 and 5.65 Gy at 50 keV/µm under uHDR irradiation compared to NDR. When cells were irradiated with 1.6 Gy at 19 keV/µm under uHDR, cell invasion was inhibited by MCF-7 compared to NDR. The dose to 4.36 Gy at 50 keV/µm, cell invasion was suppressed by 83% (MM231) and 58% (MCF-7) with uHDR compared to NDR. This result suggested that Epithelial-mesenchymal transition (EMT) can be suppressed in uHDR irradiation. However, EMT-related invasion was not observed in MM231. In the results with proton irradiation, there were no significant changes to the cell invasive capabilities between uHDR and NDR in MCF-7. However, MM231 showed a trend toward increased cell invasion ability with uHDR compared to NDR in all conditions. 【Conclusions】 Cell types exhibited varying response to EMT, and E-cadherin expression was influenced by uHDR carbon ion irradiation. 【Acknowledgement】 The author is grateful to F-REI (JPFR24040302) for the support of travel expenses.
