Effect of structure on tumor specificity of alicyclic alpha-amino acids.

The selective affinity of [carboxyl-11C]-1-aminocyclopentanecarboxylic acid (ACPC) for tumor tissue has led us to study the tumor-localizing characteristics of a series of alicyclic alpha-amino acid analogs of ACPC. The tissue distributions of [14C]-1-aminocyclopropanecarboxylic acid, 1-aminocyclobutanecarboxylic acid (ACBC), 1-aminocyclohexanecarboxylic acid, 1-amino-2-methylcyclopentanecarboxylic acid were compared with that of ACPC in Buffalo rats bearing Morris 5123C hepatomas. ACPC and ACBC were found to have significantly higher tumor-to-nontumor concentration ratios than the other four amino acids. ACBC generally had higher tumor-to-nontumor ratios than did ACPC, significantly so for muscle, kidney, and testis and marginally so for blood. These results suggest that [carboxyl-11C]ACBC may be a better agent than [carboxyl-11C]ACPC for tumor imaging by positron tomography.