Screening Of Human Single-chain Variable Fragment Antibodies Of Medullary Thyroid Carcinomaand Single Photon Emission Computed Tomography/Computed Tomography Imaging In Tumor-bearing Nude Mice

Objective:The aim of this study was to isolate single chain variable fragments(sc Fv) antibody against medullary thyroid carcinoma(MTC) from a large human phage display library and elucidate whether scFv antibody labeled with 131 I isotope is a potential imaging agent for diagnosing MTC.Methods:The large human phage display library was panned with thyroid epithelial cell(TEC) lines and MTC cell lines(TT). After that,western blotting and enzyme-linked immunosorbent assay(ELISA) were used to identify the biological characteristics of panned scFv. Methyl thiazolyl tetrazolium(MTT) assay was also used to exploring the optimal concentration of TT cell’s proliferation inhibition rate. They were divided into: TT cells group, SW 480 cells group and control group with PBS,absorbance of 450 nm was detected and inhibition rates were calculated.Later sc Fv was labeled with 131 I isotope and labeling rate was calculated.Finally, 131I-scFv was intravenously injected into nude mice-bearing TT cells xenograft. Biodistribution and imaging results in vivo were obtained.Result : After five repeating panning, positive MTC clones were completely enriched. The results of western blotting showed that the kDa value of scFv was about 28 kDa and the results of cell ELISA showed that the absorbance of TT cell group was significantly increased(P=0.000)compared with the other three groups. Results of MTT assay showed that the inhibition rate between the two cell lines was statistically significant different(P<0.05) when the concentration of sc Fv was 0.1, 1, 10 μmol/L.The inhibition rate of TT cells reached maximum(0.59±0.15)% when the concentration of scFv was 10μmol / L. Labeling rate of purified 131I-sc Fv was 78.6%. The tumor uptake of 131I-sc Fv was visible at 12 h and clear image was obtained at 48 h using the SPECT/CT.Conclusion:These results indicate that scFv rapidly and specifically target MTC cells, suggesting the potential of this antibody as an imaging agent for diagnosing MTC.