Changes of radio resistance by knocking down PTOP. A and B showed the different cell survival curves among the MDA-MB- 435s cell, radio resistant cell lines and PTOP silenced cell lines. Each group was irradiated at the dose of 0 Gy, 1 Gy, 2Gy, 4 Gy, 6 Gy, 8 Gy, 10 Gy, respectively. The same procedures were performed as above. The data was analyzed by single-hit multi-target model and survival curve of each group was described by Graphpad prism 5.0 software.