We studied the
tumor-localizing characteristics of alicyclic alpha-
amino acid analogs (a-j) without alpha-
hydrogen, because of the selective affinity of synthetic nonmetabolizing
amino acids such as
1-aminocyclopentanecarboxylic acid (ACPC) and
alpha-aminoisobutyric acid alpha-AIB) to
tumor tissues. Ten different alicyclic alpha-
amino acids (a-j) were labeled with 14C using a modified Bücherer synthesis for
amino acids. The tissue distributions and whole-body autoradiographic study of these 14C-labeled alicyclic alpha-
amino acid analogs (a-j) were investigated in mice bearing Ehrlich
tumor. These results showed that the
tumor uptakes and
tumor to tissue concentration ratios increased with decreasing ringsize in homologous series (8- through 4-membered ring systems) and alicyclic alpha-
amino acid analogs containing 3- or 4-methyl group had the higher
tumor to tissue concentration ratios. On the other hand, alicyclic alpha-
amino acid analogs containing 2-methyl group and 4-phenyl group showed the lower
tumor uptakes and the lower
tumor to tissue concentration ratios. These results suggest that the small ringsize alicyclic alpha-
amino acid analogs containing 3-methyl group such as 3-methyl-
1-aminocyclopentanecarboxylic acid (3-MeACPC) may be effective for the early detection of
tumors.