Abstract: Iron is essential in cellular proliferation and survival based on its crucial roles in DNA and ATP synthesis. Tumor cells proliferate rapidly even in patients with low serum iron, although their actual mechanisms are not well known. To elucidate molecular mechanisms of efficient tumor progression under the hypoferric condition, we studied the roles of six-transmembrane epithelial antigen of the prostate family member 3 (STEAP3), which was reported to facilitate iron uptake. Using Raji cells with low STEAP3 mRNA expression, human STEAP3-overexpressing cells were established. The impact of STEAP3 expression was analyzed about the amount of iron storage, the survival under hypoferric conditions in vitro and the growth of tumor in vivo. STEAP3 overexpression increased ferritin, an indicator of iron storage, in STEAP3-overexpressing Raji cells. STEAP3 gave Raji cells the resistance to iron deprivation-induced apoptosis. These STEAP3-overexpressing Raji cells preserved efficient growth even in hypoferric mice, while parental Raji cells grew less rapidly. In addition, iron deficiency enhanced STEAP3 mRNA expression in tumor cells. Furthermore, human colorectal cancer tissues exhibited more STEAP3 mRNA expression and iron storage compared with normal colon mucosa. These findings indicate that STEAP3 maintains iron storage in human malignant cells and tumor proliferation under the hypoferric condition.
Abstract: tob is a member of antiproliferative family genes. Mice lacking tob are prone to spontaneous formation of tumors. The occurrence rate of diethylnitrosamine-induced liver tumors is higher in tob(-/-) mice than in wild-type mice. tob(-/-)p53(-/-) mice show accelerated tumor formation in comparison with single null mice. Expression of cyclin D1 mRNA is increased in the absence of Tob and is reduced by Tob. Tob acts as a transcriptional corepressor and suppresses the cyclin D1 promoter activity through an interaction with histone deacetylase. Levels of tob mRNA are often decreased in human cancers, implicating tob in cancer development.
Abstract: 2-(2,6-Diethylphenyl)-1,2,3,4-tetrahydroisoquinoline-1,3-dione (2: PIQ-22) was found to be a potent and specific inhibitor of puromycin-sensitive aminopeptidase (PSA). Lineweaver-Burk plot analysis showed that PSA is inhibited by PIQ-22 in a non-competitive manner. Structure -activity relationship studies indicated that tautomerism of the imidobenzoylketone group in the cyclic imide moiety of the PIQ-22 skeleton is important for the inhibitory activity.
Abstract: 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.
Abstract: Recently, we developed a series of novel and potent aminopeptidase inhibitors with a homophthalimide skeleton. Among them, N-(2,6-diethylphenyl)homophthalimide (PIQ-22) possesses a specific aminopeptidase-inhibiting activity more potent than that of bestatin or actinonin, as assayed in terms of hydrolysis of L-alanine 4-methylcoumaryl-7-amide (Ala-AMC) by human acute lymphoblastic leukemia MOLT-4 cells. We show here that PIQ-22 and its 2,6-dimethylphenyl derivative (PIQ-11) are more potent inhibitors of tumor cell invasion than bestatin and actinonin in a Matrigel assay using mouse melanoma B16F10/L5 cells.
Abstract: A novel series of small molecule nonpeptide aminopeptidase N (APN) inhibitors with a N-phenylphthalimide or N-phenylhomophthalimide skeleton were prepared. Evaluation of their protease inhibitory activities revealed that (i) some N-phenylphthalimide analogs are potent APN inhibitors, but they are also inhibitors of another protease, dipeptidylpeptidase IV (DPP-IV), and (ii) some N-phenylhomophthalimide analogs, including 2-(2,6-diethylphenyl)-1,2,3,4-tetrahydroisoquinoline-1,3-dione (PIQ-22), are potent and specific inhibitors of APN without DPP-IV-inhibitory activity. The structure-activity relationship studies of N-phenylphthalimides and N-phenylhomophthalimides are reviewed. PIQ-22 showed potent tumor-cell invasion-inhibitory activity.
