Biological evaluation of histidine and tryptophan labeled with gallium-68 as potential tumor imaging agents

Abstract

Radiolabeled with gallium-68 amino acids can be interesting and promising probes for tumor imaging using positron emission tomography (PET). Radiolabeled amino acids target the increased amino acid transport in cancer cells compared with normal tissues. In this study we labeled two amino acids histidine and tryptophan with 68Ga, investigated its biodistribution in Wistar rats with subcutaneously transplanted cholangioma RS-1 by gamma counting and compared them with 68GaCl3. The accumulation of 68Ga-histidine in tumor tissue increased approximately 6 fold from 0.11±0.04 %ID/g at 5 min post injection (p.i.) to 0.67±0.07 %ID/g at 3 h p.i. The amount of 68Ga-tryptophan in tumor was also risen 2.4 fold from 0.34±0.18 %ID/g to 0.80±0.06 %ID/g at 5 min and 3 h p.i., respectively. In contrast, the uptake of 68GaCl3 decreased throughout the study from 0.34±0.07 %ID/g to 0.13±0.04 %ID/g. The uptake and retention of 68Ga-histidine and 68Ga-tryptophan in non-target organs, except kidney and femur, were higher than those of 68GaCl3. In conclusion, the obtained results suggest that 68Ga-histidine and 68Ga-tryptophan could serve as potential new PET tracers for tumor imaging.