Clinical application of combined monitoring of cfDNA and CTC in the treatment of lung cancer

1. It has a biological laboratory and a PCR laboratory 2. It has carried out a project of circulating tumor cells (CTC) 3. It has experienced, skilled and qualified technicians 1. It has established a prediction model for evaluating the therapeutic effect of two detection methods of CTC and cfDNA in patients with different stages of lung cancer; 2 Establish standardized test procedures and result interpretation standards. Through the detection of CTC and cfDNA, evaluate the value of the two detection methods to monitor the treatment of lung cancer alone and jointly: 1) clarify the correlation between the detection of CTC and cfDNA and the treatment effect of lung cancer, and establish a prediction model; 2) Published 1-2 SCI papers. The follow-up results will continue to apply for the project as a preliminary basis. The detection of cell free DNA fragments (cfDNA) is a new and fast developing "liquid biopsy" technology in recent years. The study found that the abnormal increase of cfDNA in plasma and serum of cancer patients [1] suggests that cfDNA is related to tumor and may become a biomarker for evaluating prognosis and monitoring curative effect [2]. Up to now, cfDNA has been found to have characteristic gene changes in colorectal cancer, pancreatic cancer, lung cancer and other tumors, including point mutation, microsatellite instability, DNA hypermethylation, loss of heterozygotes, etc. [3]. Many studies have shown that the gene changes of cfDNA are highly consistent with those of primary tumor and circulating tumor cells (CTC) [4,5]. The detection of CTC or circulating tumor cell DNA (ctDNA) cell-free DNA fragments (cfDNA) is a new and rapidly developing "liquid biopsy" technology in recent years. The study found that the abnormal increase of cfDNA in plasma and serum of cancer patients [1] suggests that cfDNA is related to tumor and may become a biomarker for evaluating prognosis and monitoring curative effect [2]. Up to now, cfDNA has been found to have characteristic gene changes in colorectal cancer, pancreatic cancer, lung cancer and other tumors, including point mutation, microsatellite instability, DNA hypermethylation, loss of heterozygotes, etc. [3]. Many studies have shown that the gene changes of cfDNA are highly consistent with those of primary tumor and circulating tumor cells (CTC) [4,5]. CTC or circulating tumor cell DNA (ctDNA) can be used as a new biomarker for tumor diagnosis, treatment and prognosis evaluation [6], but its content in patients' peripheral blood is low, and it is difficult to extract and identify. Because of its complex operation, high cost and long monitoring cycle, its practical application in clinical treatment is limited [7]. Previous data showed that there was a strong positive correlation between cfDNA and ctDNA content [8]. Therefore, we can indirectly monitor the response of tumor to treatment by detecting the level of cfDNA. In addition, normal tissues or cells will also undergo apoptosis or necrosis after being exposed to radiation, and a large amount of cfDNA will be released in a short period of time. The amount of change can indicate the risk of radiation damage [9]. How to detect the change of cfDNA content in blood with high sensitivity, accuracy, speed, convenience and efficiency is the key to develop the clinical application of this "liquid biopsy technology". Our cooperative research unit has developed a set of nucleic acid signal amplification technology (SuperbDNATM), which indirectly reflects the overall level of cfDNA by detecting the content of free Alu sequence in blood. Alu sequence is a highly expressed repetitive sequence, accounting for about 10% of the genome [10], and stably exists in the whole blood [11]. Its expression has a strong correlation with the level of total cfDNA [12]. This technology platform has a sensitivity of 91.7% and a specificity of 88.6% [13,14] for quantifying cfDNA, and has obtained a US global patent (patent number US 2012/0003625 A1). This technology platform is characterized by the use of modified Branched DNA (bDNA) molecules and new probe design to improve the amplification of marker chemical signals on the target DNA sequence without the need to amplify the target sequence itself (as shown in Figure 1). The working principle is as follows: each oligonucleotide probe group contains two types of synthetic probes, namely, capture extension probes (CEs) and labeled extension probes (LEs). Both CEs and LEs can bind to the target DNA sequence. First, MagPlex ™ Microspheres (magnetic beads) coupled capture probe captures the target DNA sequence through the common hybridization between CEs-capture probe and CEs-target DNA. Then, LES can combine with target DNA and preamplified probe at the same time. One preamplification probe contains 20 sites that bind to the amplification probe, and one amplification probe also contains 20 sites that bind to the labeled probe. Therefore, the target signal is finally amplified by 400 times. Finally, the biotin-labeled probe is combined with the phycoerythrin labeled streptavidin (SAPE), and the fluorescence intensity on the magnetic beads is measured by Luminex instrument such as MAGPIX. The fluorescence intensity is proportional to the number of DNA molecules present in the sample, and the level of cfDNA in the sample can be calculated. This method realizes the highly sensitive quantitative detection of cfDNA concentration in plasma samples, with the advantages of no extraction, no amplification, easy operation, short detection cycle, and suitable for clinical detection. By comparison, Canales and other scholars found that SuperbDNATM showed some advantages over PCR in detecting 244 common genes, such as smaller deviation; Eliminating the influence of errors caused by DNA extraction loss and amplification; Avoid cross contamination of samples; It is easy to realize automation and batch detection [15]. This technology provides necessary technical support for us to monitor the changes of cfDNA during tumor treatment.