Abstract: Objective To develop a method for 99mTc radiolabeling of a small molecular peptide targeting lung carcinoma and
observe the biokinetics and biodistribution of the labeled peptide in normal mice and rabbits. Methods MAG3-peptide
(cNGQGEQc) was labeled with 99mTc and the labeling rate was determined with paper chromatography. In vitro stability test,
cysteine challenge test and serum incubation test were performed for radiochemical evaluation of the labeled peptide. Blood
99mTc-peptide clearance in rabbits was evaluated by determining blood radioactive concentrations at different time points after
injection of 37 MBq 99mTc-peptide, and its dynamic distribution was investigated by SPECT imaging. The percent injected dose
per gram of tissue was calculated for each organ of mice injected intravenously with 7.4 MBq 99mTc-peptide based on gamma
counter readings. Results The labeling rate of 99mTc-peptide exceeded 90%, and the radiochemical purity was 91% after placing
for 12 h at room temperature and 85% after incubation at 37 ℃ with human serum. The cysteine replacement rate was less than
7%, and the binding rate of 99mTc-peptide with serum proteins was below 5%. SPECT imaging showed that the labeled peptide
could be quickly cleared from the blood in normal animals primarily through the kidneys, and the radioactivity in other
tissues and organs remained low. Conclusion 99mTc-peptide can be easily prepared with a high labeling yield. With good
stability both in vitro and in vivo, 99mTc-peptide can be quickly cleared from the blood and excreted though the kidney with
ideal biodistribution and biokinetics in vivo.