A Novel Prodrug of a γ-Glutamylcyclotransferase Inhibitor Suppresses Cancer Cell Proliferation in vitro and Inhibits Tumor Growth in a Xenograft Mouse Model of Prostate Cancer

γ-Glutamylcyclotransferase (GGCT) depletion inhibits cancer cell proliferation. However, whether the enzymatic activity of GGCT is critical for the regulation of cancer cell growth remains unclear. In this study, a novel diester-type cell-permeable prodrug, pro-GA, was developed based on the structure of N-glutaryl-l-alanine (GA), by structure optimization using temporary fluorophore-tagged prodrug candidates. The antiproliferative activity of pro-GA was demonstrated using GGCT-overexpressing NIH-3T3 cells and human cancer cells including MCF7, HL-60, and PC3 cells. By contrast, normal cells were not significantly affected by pro-GA treatment. Moreover, pro-GA administration exhibited anticancer effects in a xenograft model using immunocompromised mice inoculated with PC3 cells. These results indicate that the enzymatic activity of GGCT accelerates tumor growth and that GGCT inhibition is a promising therapeutic strategy for the treatment of GGCT-overexpressing tumors.

Preparation of Peptide o-Aminoanilides Using a Modified Dawson's Linker for Microwave-Assisted Peptide Synthesis

Based on the structure of Dawson’s 3,4-diaminobenzoic acid (Dbz) linker designed for Fmoc solid-phase peptide-thioester synthesis, the 4-amino-3-nitrobenzoic acid [Dbz(NO2)] linker was developed for microwave-assisted synthesis. The Dbz(NO2) linker can be readily converted into the Dbz linker by on-resin reduction with SnCl2 after construction of the protected peptide resin. Although epimerization of C-terminal amino acid restricts the use of Dbz(NO2) linker to the synthesis of peptide-Gly-thioester, use of this linker can prevent side reactions that arise when Dbz or Dbz(Aloc) linkers are used in the microwave-assisted synthesis of Gly-rich peptides.

1,2,4-Triazole-aided native chemical ligation between peptide-N-acyl-N′-methyl-benzimidazolinone and cysteinyl peptide

Novel thiol-additive-free NCL using easy-to-prepare peptide-MeNbz and 1,2,4-triazole can be readily combined with one-pot desulfurization and Cys-modification.

N-Sulfanylethylaminooxybutyramide (SEAoxy): A Crypto-Thioester Compatible with Fmoc Solid-Phase Peptide Synthesis

An N-sulfanylethylaminooxybutyramide (SEAoxy) has been developed as a novel thioester equivalent for native chemical ligation. SEAoxy peptide was straightforwardly synthesized by conventional Fmoc solid-phase peptide synthesis without a problem. Moreover, SEAoxy peptide could be directly applied to native chemical ligation owing to the intramolecular N-to-S acyl shift that releases the peptide-thioester in situ. This methodology was successfully applied to the synthesis of two bioactive peptides.

Nicotianamine is a novel angiotensin-converting enzyme 2 inhibitor in soybean

Angiotensin-converting enzyme 2 (ACE2) is a carboxypeptidase which is highly homologous to angiotensin-converting enzyme (ACE). ACE2 produces vasodilator peptides angiotensin 1-7 from angiotensin II. In the present study, we synthesized various internally quenched fluorogenic (IQF) substrates (fluorophore-Xaa-Pro-quencher) based on the cleavage site of angiotensin II introducing N-terminal fluorophore N-methylanthranilic acid (Nma) and C-terminal quencher N(ε)-2,4- dinitrophenyl-lysine [Lys(Dnp)]. The synthesized mixed substrates "Nma-Xaa-Pro-Lys(Dnp)" were hydrolyzed by recombinant human (rh) ACE2. The amount of each product was determined by liquid chromatography mass spectrometry (LC-MS) with fluorescence detection and it was found that Nma-His-Pro-Lys(Dnp) is the most suitable substrate for rhACE2. The K(m), k(cat), and k(cat)/K(m) values of Nma-His-Pro-Lys(Dnp) on rhACE2 were determined to be 23.3 μM, 167 s(-1), and 7.17 μM(-1) s(-1), respectively. Using the rhACE2 and the newly developed IQF substrate, we found rhACE2 inhibitory activity in soybean and isolated the active compound soybean ACE2 inhibitor (ACE2iSB). The physicochemical data on the isolated ACE2iSB were identical to those of nicotianamine. ACE2iSB strongly inhibited rhACE2 activity with an IC50 value of 84 nM. This is the first demonstration of an ACE2 inhibitor from foodstuffs.

A GGCT fluorogenic probe: design, synthesis and application to cancer-related cells

Cancer-related γ-glutamyl cyclotransferase (GGCT) specifically decomposes γ-glutamyl amino acids. Here we report a novel GGCT fluorogenic probe “LISA-101”.

Non-pretreated O-acyl isopeptide of amyloid β peptide 1-42 is monomeric with a random coil structure but starts to aggregate in a concentration-dependent manner

An isopeptide of amyloid β peptide 1-42 (isoAβ42) was considered as a non-aggregative precursor molecule for the highly aggregative Aβ42. It has been applied to biological studies after several pretreatments. Here we report that isoAβ42 is monomeric with a random coil structure at 40 μM without any pretreatment. But we also found that isoAβ42 retains a slight aggregative nature, which is significantly weaker than that of the native Aβ42.

Click Peptide concept: o-acyl isopeptide of islet amyloid polypeptide as a nonaggregative precursor molecule

The O-acyl isopeptide (1) of islet amyloid polypeptide (IAPP), which contains an ester moiety at both Ala8-Thr9 and Ser19-Ser20, was prepared by sequential segment condensation based on the O-acyl isopeptide method. Isopeptide 1 possessed nonaggregative properties, retaining its random coil structure under the acidic conditions; this suggests that the insertion of the O-acyl isopeptide structures in IAPP suppressed aggregation of the molecule. As a result of the rapid O-to-N acyl shift of 1 under neutral pH, in situ-formed IAPP adopted a random-coil structure at the start of the experiment, and then underwent conformational change to α-helix/β-sheet mixed structures as well as aggregation. The click peptide strategy with the nonaggregative precursor molecule 1 could be a useful experimental tool to identify the functions of IAPP, by overcoming the handling difficulties that arise from IAPP's intense and uncontrollable self-assembling nature.

Epimerization-free synthesis of cyclic peptide by use of the O-acyl isopeptide method

A head-to-tail cyclization of a protected linear hexapeptide with a C-terminal O-acyl isopeptide proceeded to give a cyclic O-acyl isopeptide without epimerization. The cyclic O-acyl isopeptide possessed different secondary structures compared with the native cyclic peptide. The isopeptide was then efficiently converted to the desired cyclic peptide via an O-to-N acyl migration reaction using a silica gel-anchored base.

Synthesis and conformation of an analog of the helix-loop-helix domain of the Id1 protein containing the O-acyl iso-prolyl-seryl switch motif

Synthetic peptides reproducing the helix-loop-helix (HLH) domains of the Id proteins fold into highly stable helix bundles upon self-association. Recently, we have shown that the replacement of the dipeptide Val-Ser at the loop-helix-2 junction with the corresponding O-acyl iso-dipeptide leads to a completely unfolded state that only refolds after intramolecular O --> N acyl migration. Herein, we report on an Id HLH analog based on the substitution of the Pro-Ser motif at the helix-1-loop junction with the corresponding O-acyl iso-dipeptide. This analog has been successfully synthesized by solid-phase Fmoc chemistry upon suppression of DKP formation. No secondary structure could be detected for the O-acyl iso-peptide before its conversion into the native form by O --> N acyl shift. These results show that the loop-helix junctions are determinant for the folded/unfolded state of the Id HLH domain. Further, despite the high risk of DKP formation, peptides containing O-acyl iso-Pro-Ser/Thr units are synthetically accessible by Fmoc chemistry.