[Show abstract][Hide abstract] ABSTRACT: [*F.Z. and S.B. are joint first authors] Methionine aminopeptidases (MetAPs), which remove the initiator methionine from nascent peptides, are essential in all organisms. While MetAP2 has been demonstrated to be a therapeutic target for inhibiting angiogenesis in mammals, MetAP1 seems to be vital for cell proliferation. Our earlier efforts identified two structural classes of human MetAP1 (HsMetAP1)-selective inhibitors (1-4), but all of them failed to inhibit cellular HsMetAP1. Using Mn(II) or Zn(II) to activate HsMetAP1, we found that 1-4 could only effectively inhibit purified HsMetAP1 in the presence of physiologically unachievable concentrations of Co(II). In an effort to seek Co(II)-independent inhibitors, a novel structural class containing a 2-(pyridin-2-yl)quinazoline core has been discovered. Many compounds in this class potently and selectively inhibited HsMetAP1 without Co(II). Subsequently, we demonstrated that 11j, an auxiliary metal-dependent inhibitor, effectively inhibited HsMetAP1 in primary cells. This is the first report that an HsMetAP1-selective inhibitor is effective against its target in cells.
Journal of Medicinal Chemistry 05/2013; 56(10):3996-4016. · 5.61 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cellular protein synthesis is initiated with methionine in eukaryotes with few exceptions. Methionine aminopeptidases (MetAPs) which catalyze the process of N-terminal methionine excision are essential for all organisms. In mammals, type 2 MetAP (MetAP2) is known to be important for angiogenesis, while type 1 MetAP (MetAP1) has been shown to play a pivotal role in cell proliferation. Our previous high-throughput screening of a commercial compound library uncovered a novel class of inhibitors for both human MetAP1 (HsMetAP1) and human MetAP2 (HsMetAP2). This class of inhibitors contains a pyridinylpyrimidine core. To understand the structure-activity relationship (SAR) and to search for analogues of 2 with greater potency and higher HsMetAP1-selectivity, a total of 58 analogues were acquired through either commercial source or by in-house synthesis and their inhibitory activities against HsMetAP1 and HsMetAP2 were determined. Through this systematic medicinal chemistry analysis, we have identified (1) 5-chloro-6-methyl-2-pyridin-2-ylpyrimidine as the minimum element for the inhibition of HsMetAP1; (2) 5'-chloro as the favored substituent on the pyridine ring for the enhanced potency against HsMetAP1; and (3) long C4 side chains as the essentials for higher HsMetAP1-selectivity. At the end of our SAR campaign, 25b, 25c, 26d and 30a-30c are among the most selective and potent inhibitors of purified HsMetAP1 reported to date. In addition, we also performed crystallographic analysis of one representative inhibitor (26d) in complex with N-terminally truncated HsMetAP1.
[Show abstract][Hide abstract] ABSTRACT: Two substituted oxines, nitroxoline (5) and 5-chloroquinolin-8-yl phenylcarbamate (22), were identified as hits in a high-throughput screen aimed at finding new anti-angiogenic agents. In a previous study, we have elucidated the molecular mechanism of antiproliferative activity of nitroxoline in endothelial cells, which comprises of a dual inhibition of type 2 human methionine aminopeptidase (MetAP2) and sirtuin 1 (SIRT1). Structure-activity relationship study (SAR) of nitroxoline offered many surprises where minor modifications yielded oxine derivatives with increased potency against human umbilical vein endothelial cells (HUVEC), but with entirely different as yet unknown mechanisms. For example, 5-nitrosoquinolin-8-ol (33) inhibited HUVEC growth with sub-micromolar IC(50), but did not affect MetAP2 or MetAP1, and it only showed weak inhibition against SIRT1. Other sub-micromolar inhibitors were derivatives of 5-aminoquinolin-8-ol (34) and 8-sulfonamidoquinoline (32). A sulfamate derivative of nitroxoline (48) was found to be more potent than nitroxoline with the retention of activities against MetAP2 and SIRT1. The bioactivity of the second hit, micromolar HUVEC and MetAP2 inhibitor carbamate 22 was improved further with an SAR study culminating in carbamate 24 which is a nanomolar inhibitor of HUVEC and MetAP2.
[Show abstract][Hide abstract] ABSTRACT: Methionine aminopeptidase (MetAP) catalyzes the hydrolytic cleavage of the N-terminal methionine from newly synthesized polypeptides. The extent of removal of methionyl from a protein is dictated by its N-terminal peptide sequence. Earlier studies revealed that MetAPs require amino acids containing small side chains (e.g., Gly, Ala, Ser, Cys, Pro, Thr, and Val) as the P1' residue, but their specificity at positions P2' and beyond remains incompletely defined. In this work, the substrate specificities of Escherichia coli MetAP1, human MetAP1, and human MetAP2 were systematically profiled by screening against a combinatorial peptide library and kinetic analysis of individually synthesized peptide substrates. Our results show that although all three enzymes require small residues at the P1' position, they have differential tolerance for Val and Thr at this position. The catalytic activity of human MetAP2 toward Met-Val peptides is consistently 2 orders of magnitude higher than that of MetAP1, suggesting that MetAP2 is responsible for processing proteins containing N-terminal Met-Val and Met-Thr sequences in vivo. At positions P2'-P5', all three MetAPs have broad specificity but are poorly active toward peptides containing a proline at the P2' position. In addition, the human MetAPs disfavor acidic residues at the P2'-P5' positions. The specificity data have allowed us to formulate a simple set of rules that can reliably predict the N-terminal processing of E. coli and human proteins.
[Show abstract][Hide abstract] ABSTRACT: The synthesis and structure-activity relationships of zygosporamide, a known potent and selective cytotoxic natural product against SF-268 and RXF 393 cell lines, are described. The potencies of the synthetic zygosporamide are similar to those reported for the natural product toward all cancer cell lines examined with the exception of SF-268, the underlying cause of which remains to be elucidated.
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