Prediction and Validation of Circulating G-quadruplex as a Novel Biomarker in Colorectal Cancer

Background: G-quadruplex (G4) is a special structure in DNA and RNA. It plays an important biological role in the formation of tumors via the Hoogsteen hydrogen base-pairing to form a planar array structure. G4 mutation prediction in the genome using bioinformatics revealed that the G4 quantity in SW480 cells was lower than that of the reference gene, but it was unclear how the G4 quantity was changed in the actual sample. Methods We detected the G4 content in cells via fluorescence and found that the G4 content in SW480 cells was significantly higher than that in NCM480 ( p  < 0.001). To further confirm the relationship between tumorigenesis and G4, we knocked out the TP53 gene in SW480 cells and found that the G4 content was decreased significantly by 64% ( p  < 0.001), indicating that the difference in G4 content was a key factor for distinguishing between normal and tumor cells. Results G4 was detected in serum samples from 27 normal and 27 CRC patients. The result showed that G4 was significantly increased ( p  = 0.006) in CRC patients by 1.94-fold. Subsequently, we evaluated the G4 model using ROC, with AUC = 0.91, and it was found to have excellent specificity and sensitivity. Conclusion Increased G4 is an important characteristic in CRC patients and has clinical application value as a novel biomarker.