Detection and clinical application of VAR2 synthetic peptide specific binding to circulating tumor cells

Abstract

Objective To investigate the detection and clinical application studies based on malaria protein VAR2CSA(VAR2) synthetic peptide specifically binding to circulating tumor cells (CTCs). Methods The peptide sequence of the functional structural domain of malaria protein VAR2CSA was selected to synthesize VAR2 that enriched CTCs based on nano-microfluidic technology, and used VAR2 synthetic peptide to detect enriched cells to establish a novel detection protocol for CTCs. Cellular immuno-fluorescence staining, flow cytometry and tumor cell doping recovery assays were used to analyze the specific binding and recovery efficiency of VAR2 synthetic peptide with tumor cells of different tissue sources and compare with immuno-staining-fluorescence in situ hybridization (imFISH) assay. Twenty-two colorectal cancer patients and twenty-two healthy individuals were selected, and the VAR2 synthetic peptide was used to detect peripheral blood CTCs in both. The VAR2 synthetic peptide was used to compare the positive detection rate of CTCs in patients with different TNM stages. Results The VAR2 synthetic peptide bound specifically to tumor cells collected from different tissue sources of human colon cancer cell line SW620, human breast cancer cell line MCF7 and human esophageal squamous carcinoma cell line KYSE180.The VAR2 synthetic peptide detected 100 SW620, MCF7 and KYSE180 tumor cells mixed into 3 mL of peripheral blood with recovery rates of 82.8%±8.41%, 56.2%±3.57%, 86.6%±8.19%, which were not significantly different from the imFISH assay. The VAR2 synthetic peptide assay recoveries of 50, 100, and 200 SW620 tumor cells were 80.7%, 82.8%, and 84.7%, respectively, which did not correlate significantly with the number of adulterated tumor cells. The VAR2 synthetic peptide detected 63.6% positive CTCs in peripheral blood samples from patients with clinical colorectal cancer, which was higher than the 0.0% positive CTCs rate in the group of healthy subjects, and also correlated with depth of invasion, lymph node metastasis, distant metastasis, and clinical stage (P＜0.05). Conclusions The VAR2-based synthetic peptide may be applied in specific and non-antibody dependent CTCs detection in different tissue samples and so has good clinical application value for clinical staging and severity evaluation of tumor patients.

Keywords

• circulating tumor cell|malaria protein var2csa synthetic peptide (var2)|non-antibody-dependent|colorectal cancer|clinical staging