Serum Assisted PD-L1 Aptamer Screening And Robustness Characterization

PD-L1 protein molecule is an important target of cancer diagnosis and treatment drugs,and PD-L1 aptamer can be used for real-time diagnosis and in vivo detection and imaging.Based on the characteristics of strong specificity,high affinity for target substances,low synthesis cost and easy modification,nucleic acid aptamers can be used to design and develop new and efficient cancer diagnosis and detection tools.The activity of aptamer in biological fluid environment is very low,and nuclease will degrade it rapidly.As a result,the cancer diagnosis and detection tool developed based on aptamer will present problems such as insufficient stability,short half-life and too short targeted drug use time when detecting cancer cells in vivo.Therefore,it is necessary to optimize and improve the robustness(half-life)of aptamers in organisms.In order to improve the robustness of aptamers,the strategy of screening aptamers is optimized.The ordinary buffer used in the screening process is replaced with the buffer of real complex sample system containing human serum,so that the aptamers can be screened after adapting to the complex serum environment in advance.The main results are as follows:1.Using this screening strategy,the optimal number of screening rounds was determined to be 8 rounds,which improved the screening efficiency,and obtained the nucleic acid aptamer Apt-S1 which can bind PD-L1 with high specificity.2.The specificity and CD spectrum of Apt-S1(K_d=87.74±12.63 n M)were studied experimentally.When the CD spectrum was analyzed and measured between 220 nm and 260 nm,Apt-S1 combined with PD-L1 would have great slope peak changes and more drastic conformational differences,indicating that Apt-S1 showed more superior specific stability and more utilization value.3.Based on the simulation of normal temperature and p H of human blood,after characterizing the robustness of Apt-S1,it is found that the half-life of Apt-S1 is significantly improved.It means that this screening strategy can increase the retention time of aptamers in tumor cells,which is of great significance for the application of aptamers in the targeted delivery of target drugs and the detection and imaging of aptamers in vivo.