Evaluation Of Olaparib Enhances Radiosensitivity In Triple-negative Breast Cancer By ¹⁸F-FDG And ¹⁸F-FLT Micro-PET/CT Imaging

ObjectiveEvaluation of Olaparib’s radiosensitizing effect by combination of Olaparib and radiotherapy,and evaluation of Olaparib’s radiosensitizing effect on triple-negative breast cancer by ¹⁸F-deoxyglucose(¹⁸F-FDG)and ¹⁸F-deoxythymidine nucleoside(¹⁸F-FLT)Positron Emission Computed Tomography（PET/CT）Effects.MethodsThe radiosensitization of Olaparib was demonstrated by culturing human breast cancer MDA-MB-231 cells and by MTT,CCK8 and cell cloning assays;In animal experiments,24 BALB/C nude mice MDA-MB-231 breast cancer models were established and divided into 4 groups of 6 animals each according to the random number table method,namely,control group,radiotherapy group,Olaparib group,Olaparib+radiotherapy group.The¹⁸F-FDG and ¹⁸F-FLT micro-PET/CT images were performed on the nude mice before and 24h after radiotherapy and 7 days after radiotherapy,respectively.SUV_max and Tumor muscle ratio（TMR）were compared before and after treatment in the four groups.After imaging,the tumor-bearing nude mice were executed and their tumors were stained with HE,and the expression of Glut-1 and Ki-67 were measured by immunohistochemistry.Paired t-test was used for comparison before and after radiotherapy within each group,and two independent samples t-test was used for comparison between two groups.ResultsIn an in vitro experiment,human breast cancer MDA-MB-231 cells were successfully cultured.In the MTT assay,the semi-inhibitory concentrations（IC50）of Olaparib at 24h,48h and 72h were obtained;In the CCK8 and cell cloning assays,the cell viability of Olaparib+radiotherapy group was significantly lower than that of Olaparib group and radiotherapy group,and the differences were statistically significant（P<0.001,P<0.010）.In cell cloning experiments,the cell survival fraction（SF）of the Olaparib group was significantly lower than that of the control group by different X-ray doses（P<0.001）,and the radiosensitization ratio of the Olaparib group was found to be 1.36,showing that Olaparib had a radiosensitizing effect.In the in vivo experiment,the MDA-MB-231 nude mouse breast cancer model was constructed.SUV_max values by ¹⁸F-FDG Micro PET/CT imaging were 1.475±0.319,1.519±0.493,1.512±0.307,and 1.501±0.232 in the pre-radiotherapy control group,radiotherapy alone group,Olaparib group,and Olaparib+radiotherapy group,respectively,with no statistically significant differences（F=0.018,P=0.996）.At the end of radiotherapy,SUV_max was 2.119±0.353,1.182±0.457,1.919±0.175,and 0.799±0.174 in the four groups,respectively,with statistically significant differences（F=54.413,P<0.001）.The SUV_max values were reduced in the radiotherapy alone and Olaparib+radiotherapy groups compared with those before radiotherapy（t=6.926,P=0.001;t=6.914,P=0.001）.The SUV_max values in the Olaparib+radiotherapy group after radiotherapy were significantly lower than those in the radiotherapy alone and Olaparib groups（P=0.047,P<0.001）.The TMR values in the four groups before radiotherapy were 2.240±0.404,2.272±0.330,2.291±0.478,and 2.215±0.169,respectively,with no statistically significant difference（F=0.052,P=0.984）.At the end of radiotherapy,the TMR values in the four groups were 3.011±0.265,1.804±0.218,2.829±0.355,and 1.361±0.191,respectively,with a statistically significant difference（F=54.413,P<0.001）.TMR values were reduced in the radiotherapy alone and Olaparib+radiotherapy groups compared with those before radiotherapy（t=3.331,P=0.021;t=8.257,P<0.001）.The TMR values in the Olaparib+radiotherapy group were significantly lower than those in the radiotherapy alone and Olaparib groups after radiotherapy（P=0.009,P<0.001）.¹⁸F-FLT Micro PET/CT showed that the SUV_max values of the four groups before radiotherapy were 1.093±0.206,1.117±0.160,1.066±0.213,and 1.087±0.147,respectively,with no statistically significant difference（F=0.077,P=0.972）.At the end of radiotherapy,the SUV_max values in the four groups were 1.420±0.100,0.855±0.161,1.362±0.145,and 0.587±0.092,respectively,with a statistically significant difference（F=59.527,P<0.001）.The SUV_max values were reduced in the radiotherapy alone and Olaparib+radiotherapy groups compared with those before radiotherapy（t=6.634,P=0.001;t=11.327,P<0.001）.The SUV_max values in the Olaparib+radiotherapy group were significantly lower than those in the radiotherapy alone and Olaparib groups after radiotherapy（P=0.002,P<0.001）.HE staining showed that Olaparib+radiotherapy group had fewer tumor cells and saw lamellar necrotic areas.Immunohistochemical results showed that Glut-1 and Ki-67 were expressed in tumor tissues of all four groups,and the mean optical density values of Glut-1 in tumor tissues of control group,radiotherapy-only group,Olaparib group and Olaparib+radiotherapy group were 63.515±5.139,51.198±6.019,61.080±5.766,41.905±8.947,respectively,with statistically significant differences（F=13.372,P<0.001）.The mean optical density values of Ki-67 in the four tumor groups were 63.592±6.573,49.930±9.131,60.068±10.065,and 36.025±7.295,respectively,and the differences were statistically significant（F=13.034,P<0.001）,and the mean optical density values of Glut-1 and Ki-67 in the Olaparib+radiotherapy group were significantly lower in the Olaparib+radiotherapy group than in the radiotherapy alone and Olaparib groups（P=0.025,P<0.001;P=0.009,P<0.001）.ConclusionOlaparib has a radiosensitizing effect and shows good therapeutic effect in combination with radiotherapy.¹⁸F-FDG and ¹⁸F-FLT PET/CT images can be used to evaluate the radiosensitizing effect of Olaparib in a nude mouse breast cancer model by glucose metabolism and cell proliferation levels.