The in vivo evaluation of biodistribution of methionine labeled with gallium-68, potential positron emission tomography agent

Positron emission tomography (PET) is one of the most reliable and highly sensitive method for tumor imaging. Over the past decades, PET with radiolabeled amino acids as radiotracers has become a widely used diagnostic tool. Gallium-68 (68Ga) is a promising radionuclide for PET due to its appropriate decay properties and the availability from the 68Ge/68Ga-generator system. For these reasons, we initiated the development of a new agent based on 68Ga-labeled amino acid methionine for cancer imaging. The aim of this study was the evaluation of biodistribution of 68Ga-methionine after intravenous administration in Wistar rats with cholangioma RS-1 xenografts and compare it with 68GaCl3. The samples of organs and tissues were taken at different time intervals after injection and counted in automatic gamma counter. The performed studies were shown that uptake of 68Ga-methionine in tumors increased from 0,28% of injected dose per gram (ID/g) at 5 min to 0,37% ID/g at 1 h, 0,77% ID/g at 3 h, and 0,85% ID/g at 5 h. At the same time the uptake of 68GaCl3 didn’t exceed 0,34% ID/g. High amount of radioactivity (1,56-3,98% ID/g) were observed in blood. Among the soft tissue organs, only liver, spleen and kidney had a relatively high uptake. The accumulation of radioactivity in other organs and tissues was less than 1% ID/g. The obtained results suggest that they can be used for development of radiotracer based on 68Ga and methionine for tumor imaging by PET.