Abstract: Objective To investigate the effect of solute carrier family 1 member 5 (SLC1A5) on the radiosensitivity of triple⁃negative breast cancer MDA⁃MB⁃231 cell lines and its mechanism. Methods The triple⁃negative breast cancer MDA⁃MB⁃231 cell lines  were treated with X⁃ray and SLC1A5 inhibitor L⁃γ⁃glutamyl⁃p⁃nitroanilide (GPNA). The cells were irradiated with 4 Gy or 8 Gy alone or combined with 3 mmol/L GPNA, and the proliferation ability of cells was detected by CCK⁃8 method. Then the cells treated with 8 Gy irradiation alone or combined with 3 mmol/L GPNA were divided into control (DMSO) group, SLC1A5 inhibitor (GPNA) group, irradiation (IR) group, and combination (IR+GPNA) group. Clone formation test, Scratch assay and Transwell assay were used to detect the clonogenesis ability, migration ability and the invasion ability of cells, respectively. Reactive oxygen species (ROS) fluorescent probe (DCFH⁃DA) was used to detect the contents of ROS in cells. Malondialdehyde (MDA) kits were used to detect the contents of MDA in cells. Mito⁃tracker Red CMXRos staining assay was used to observe mitochondrial morphology. The expression level of PTGS2 gene was detected by RT⁃qPCR. Results Compared with the DMSO group, the cell proliferation ability decreased in the 4 Gy, 8 Gy, 4 Gy+GPNA and 8 Gy+GPNA groups(all P<0.01), the proliferation ability of cells in the 4 Gy+GPNA and 8 Gy+GPNA groups was lower than that of the corresponding simple irradiation groups(all P<0.01), and the decrease was more obvious in the high radiation dose group. Compared with the DMSO group, the cell clone formation ability, migration ability and invasion ability were reduced in the IR, GPNA and IR+GPNA groups, and the reduction was more significant in the IR+GPNA group. Compared with the DMSO group, the GPNA, IR and IR+GPNA groups had increased ROS levels, MDA contents and PTGS2 gene expression (all P<0.05) and reduced mitochondrial morphology (P<0.01), and such changes were most pronounced in the IR+GPNA group. Conclusions SLC1A5 inhibitor can further inhibit the proliferation. clonogenesis migration and invasion, of triple⁃negative breast cancer MDA⁃MB⁃231 cells on the basis of irradiation, and improve the radiosensitivity of cells. The underlying mechanism may be related to the activation of ferroptosis.

Key words: Breast cancer, MDA-MB-231 cells, Radiosensitivity, SLC1A5, Ferroptosis