Objective To compare the transparency efficiency of six different optical clearing method on the rat brain tissues. Methods Brain tissue blocks of 14 SD rats were processed with iDISCO, SeeDB, CUBIC, SCALEVIEW-A2,CLARITY-CUBIC, Passive-CLARITY clearing method, respectively. Results The gray value of PBS group was 13.031 ± 0.586,that of iDISCO,SeeDB,CUBIC,SCALEVIEW-A2,CLARITY-CUBIC,passive-CLARITY clearing were 6.447 ± 0.574,11.690 ± 0.909,2.318 ± 0.986,8.118 ± 1.026,8.591 ± 0.384,4.198 ± 0.182, respectively. Except the SeeDB group(P=0.185),the rest groups showed significant differences compared with the PBS group(P< 0.01), and there were significant differences between CUBIC and other groups(P < 0.01). After the clearing treatment, the changes of tissue area ratio in the iDISCO, SeeDB, CUBIC, SCALEVIEW-A2, CLARITY-CUBIC, Passive-CLARITY method were(-30.02 ± 2.39)%,(19.74 ± 4.09)%,(14.7 ± 3.92)%,(10.7 ± 5.55)%,(23.01 ± 4.19)%,(66.51 ± 5.68)%,respectively. Each group showed a significant difference compared with the groups iDISCO and the Passive-CLARITY,P< 0.01. Conclusions Except the SeeDB method,all the clearing methods can achieve a transparent effect, while CUBIC is better than the other groups applied for rat brain tissues. The tissue block volume is shrunken after iDISCO clearing,and expanded after Passive-CLARITY processing.

Radiotherapy is widely used in the treatment of primary and metastatic malignant tumors. It is traditionally believed that the killing effect of radiotherapy on tumor is based on the direct or indirect damage of ionizing radiation to DNA. In recent years, the anti-tumor role and mechanism of anti-tumor immune response induced by ionizing radiation have captivated widespread attention and achieved significant progress. Among them, Cyclic GMP-AMP synthase (cGAS)-stimulator of interference genes (STING) pathway is considered to be one of the key regulatory hubs. cGAS is a cytoplasmic DNA receptor that can bind to tumor-derived double-stranded DNA and activate the downstream STING, thereby activating anti-tumor immune response of the host. In view of the latest progress in this field, the important role and potential mechanism of cGAS-STING pathway in radiotherapy immune effect were mainly summarized, and the application prospect of targeting cGAS-STING pathway in radiotherapy sensitization was explored.