The studies on both structure-activity relationship study and identification of the target
enzyme of novel nonpeptide
aminopeptidase inhibitors with cyclic
imide skeleton are reviewed. Some
N-phenylphthalimide or N-
phenylhomophthalimide derivative showed potent
protease inhibitory activity in an assay system using human
acute lymphoblastic leukemia cells, Molt-4, with alanin-4-methylcoumaryl-7-amide (ala-AMC) as a substrate. Especially, 2-(2,6-diethylphenyl)-1,2,3,4-tetrahydroisoquinoline-1,3-dione (PIQ-22) (3) was found to be the most potent inhibitor and further it showed potent
tumor-cell invasion inhibitory activity that is more effective than potent
peptide aminopeptidase inhibitors such as
bestatin (1) or
actinonin (2). For the further investigation of this novel
protease inhibitory activity, we have carried out the structural development of
PIQ-22 (3) and it is assumed that tautomerism of imidobenzoylketone in cyclic
imide structure may be related to the inhibitory activity. The requirement for the activity of electron donating groups such as NH2 or
OH to the condensed phenyl ring in
phthalimide inhibitors also supports this possibility. The target
aminopeptidase of
PIQ-22 was identified as
puromycin-sensitive aminopeptidase (PSA), by N-terminal
amino acid sequencing, and by comparison with chromatographic behavior and substrate-selectivity, and so on. Lineweaver-Burk plot showed that PSA is inhibited by
PIQ-22 (3) in a noncompetitive manner while
puromycin (83) and
bestatin (1) inhibit PSA competitively.