Objective To establish a simple and reliable method of making ⁹⁹Tc^m-depreotide by direct labeling.Furthermore, to investigate ⁹⁹Tc^m-depreotide's specific receptor binding properties in vitro with human lung adenocarcinoma cell line A549, and to evaluate the potentiality of ⁹⁹Tc^m-depreotide as a somatostatin receptor imaging agent for lung cancer.

Methods ① Depreotide was labeled with ⁹⁹Tc^m through a direct labeling using SnCl₂as reductant.Compared the labeling efficiency in different pH and temperature, then searched the best labeling method.Assessed the radiochemical purity and stability in vitro.②Using radioreceptor assay, it was observed that ⁹⁹Tc^m-depreotide was incubated with A549 cell and uptake kinetics, then stagnation and half time were compared at different temperature and time points, and that ⁹⁹Tc^m-depreotide was incubated with A549 cell the internalization and surface-bound activity were compared at 37℃ and different time points.

Results ① At the same temperature, labeling rate of pH6.0 group was higher than that of pH5.0 and pH7.0 groups.At the same pH, the labeling rate of all of the three different pH experiment groups reduced with increasing temperature from 15℃ to 50℃ in this study.②The uptake rate increased with temperature at the same time point, and the peak time of maximum uptake was 60min at 37℃.The cleaning curves were similar at different temperature, and the half cleaning time at 37℃was 48 min.

Conclusions When depreotide was labeled with ⁹⁹Tc^m, the temperature could not be too high(< 15℃) and the pH would better be less than 6.0.⁹⁹Tc^m-depreotid was a potential somatostatin receptor imaging agent with its appropriate the peak time of maximum uptake and the half cleaning time at37℃.