Screening and Application of Serum Aptamer for Colon Cancer Based on Ser-SELEX

Objective Colon cancer is a common malignant tumor of the gastrointestinal tract and the second leading cause of cancer-related death. It is a type of cancer which is difficult to detect in early stage and easy to metastasize in late stage operation. The aim of this work is to solve the difficult problem of early diagnosis of cancer and realize the early detection of colon cancer and provide a new idea for early diagnosis of colon cancer. Methods Serum-SELEX technique was used to screen the specific aptamers of colon cancer serum. The
aptamer sequence with higher affinity and more stable properties can be obtained through the cyclic process of prophase positive screening for colon cancer and prophase positive screening for colon cancer and prophase positive screening for other cancers, and gradually increasing the screening pressure, such as reducing the
incubation time of positive screening targets, increasing the incubation time of reverse screening targets and elution steps. qPCR was used to quantitatively monitor the positive screen template obtained to ensure that the aptamer pool was enriched. In this process, the aptamers of common protein binding of negative and positive targets were continuously reduced, so that the sequences in the pool had high specificity. After 16 rounds of screening, a total of four candidate aptamers were selected. Results The results showed that APT-1, APT-2 and APT-5 had high family homology, and the four candidate aptamers mainly formed stem ring and pseudojunction.
Affinity was tested by qPCR. The Kd values of the four candidate aptamers binding to the serum of colon cancer patients were (4.466 +/- 0.384), (6.122 +/- 0.615), (5.610 +/- 0.202) and (6.964 +/- 0.181) nmol/L, respectively, which were all smaller than 10 nmol/L. The specificity of the serum of about 60 patients was analyzed. It was found that candidate APT-2 had good specificity, and the detection rate of this method was about 82.5%. Conclusion An excellent functional APT-2 was selected, and the APT-2 could be specifically bound to the serum of colon cancer patients with good affinity, so it has a good development prospect for the early diagnosis of colon cancer.