DEVELOPMENT OF ASSAY FOR CTDNA DETECTION USING SPR SENSOR
Sera Park, Daeho Jang, Sehyun Shin
Korea University, South Korea
Early detection of cancer greatly increases the chances for successful treatment. The development of non-invasive methods to detect and monitor tumors continues to be a major challenge in oncology. For most tumors, a tissue biopsy is costly, painful, or potentially risky for the patient. Liquid biopsy with circulating biomarkers such as circulating tumor cells (CTCs), exosomes and circulating tumor DNA (ctDNA) is a simple and non-invasive alternative to surgical biopsies which is easy repetitive sampling and whole mutation representation. These circulating biomarkers can be easily obtained from biofluids such as blood. ctDNA liquid biopsy allows us to understand specifically what kind of mutations are happening in the tumor in real time. Although various methods for detecting ctDNA have been introduced such as NGS (Next Generation Sequencing) and Real-time PCR (Polymerase Chain Reaction), there are still unmet needs; cost, time for the applications.
We applied novel SPR (Surface Plasmon Resonance) based approaches to detect one of the ctDNA; EGFR (Epithermal Growth Factor Receptor) gene mutations with ultra-high sensitivity and multiplexing. SPR used to detect biomolecules without labeling via changes in the refractive index on the sensing film of the SPR sensor in real time. This tool is suitable to detect small molecules; ctDNA. Optimizing the selectivity between mutant and wild-type is challengeable in the case of the ctDNA detection. To provide selectivity enhancement for the sensing approach, we designed the surface of SPR gold chip with various SAM (Self-Assembly Monolayer) considered the steric hindrance between nucleotides. Additionally, we applied proper buffer to control the condition;pH, NaCl for DNA duplex stability. As a result, the limit of detection (LOD) of EGFR mutant in our system was determined to be 500pM without acquiring false-positive wild-type signals.