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Background Technetium-99m or 99mTc is widely used for labeling peptide in nuclear medicine.Somatostatin and its analog can inhibit tumor cell growth alter binding with its receptor.This research was to study the preclinical effect of a new 99mTc-6-hydrazinopyridine-3-carboxylic acid (HYNIC)-depreotide,indirect 99mTc labeling of depreotide using HYNIC as a bifunctional chelator.Methods The cyclopeptide,cyclo-[(N-Me) Phe-Tyr-D-Trp-Lys-VaI-Hcy],the linear peptide,and [CICH2-COββ-Dap-Lys-Cys-Lys.amide] were synthesized by Fmoc solid-phase synthesis.The cyclopeptide and the linear peptide were linked by liquid-phase synthesis.The product depreotide was isolated and purified by high performance liquid chromatography and was confirmed by mass spectrography.Depreotide was labeled with 99mTc through a direct labeling method,using HYNIC as a bifunctional chelator.Paper chromatography method was used to calculate the labeling rate,and through the comparative analysis selected the best mark conditions.The new 99mTc-HYNIC-depraotide was tested by high-performance liquid chromatography (HPLC).The internalization and externalization rates of the new 99mTc-HYNIC-depreotide were studied in A549 cells.Furthermore,biodistribution of the radiopeptide was studied in nude mice,bearing tumors from human lung carcinoma cells SPC-A1.Results The molecular of synthesize depreotide was 1358,and the purity of it was 95.29％.The labeling efficiency of 99mTc-HYNIC-depreotide was highest at pH 6.0 and 15°C,about (70.95±0.84)％.The labeling rate of the new 99mTc-HYNIC-depreotide rose to a peak of (20.75±0.48)％ at 60 minutes in A549 cells at 37°C and decreased slightly later,while it elevated gradually during the time course at 4°C and 25°C.The internalization rate of the new 99mTc-HYNIC-depreotide at 37°C increased gradually and reached the peak of 84.4％ in 120 minutes,while the externalization rate of the new 99mTc-HYNIC-depreotide was always less than 20％ In mice bearing the experimental SPC-A1 tumor,the new 99mTc-HYNIC-depreotide demonstrated a high tumor uptake of (4.05±0.04)％ ID/g at 1.5 hpi and remained high ((2.51±0.06)％ ID/g) at 4 hpi.The tumor-to-lung activity concentration ratio (T/Lu) was very high for the new 99mTc-HYNIC-depreotide at all time points.So did the tumor-to-muscle activity (T/Mu) and tumor-to-blood activity concentration ratios (T/BI).Conclusion The findings suggested that the new 99mTc-HYNIC-depreotide might be a promising candidate radiopharmaceutical for imaging somatostatin receptor positive lung cancer.