Advances in peptidyl Asx-specific ligases for the application of cyclic peptides / 药学学报

Asparaginyl endopeptidases (AEPs) in plants belong to the family of cysteine protease that undergo self-activation in the form of zymogen in acidic vacuole and play important physiological roles in maturation of seed storage proteins, protein degradation, programmed cell death and host defense. Bioprocessing enzymes (peptidyl Asx-specific ligases, PALs) that promote the maturation of cyclotides have recently been isolated and identified from several cyclotide-rich plants. PALs derived from AEPs can site-specifically catalyze the formation of asparagine or aspartate peptide bonds. Due to the advantages of relatively traceless peptide bonds and broad substrate spectrum and high catalytic efficiency, they have been playing important roles in the cyclization and modification of peptides and proteins, and are powerful tools for improving the stability of peptide drugs. This review describes the physiological functions of AEPs in plants and summarizes the discoveries, structural characteristics, catalytic mechanism and protein engineering of PALs, as well as the limitation of their applications and future trends. In addition, the applications of PALs in cyclotides biosynthesis and the development of macrocyclic peptides are highlighted, with the aim of providing a new idea for the biocatalytic synthesis of cyclic peptides.

Mass spectrometry-guided study on cyclic peptides from sponge Reniochalina sp / 药学实践杂志

Objective To study the cyclic peptides from sponge Reniochalina sp. under the guidance of mass spectrometry. Methods Mass spectrometry-guided procedural separation methods were used to track and isolate the cyclic peptides from the sponge genus Reniochalina. The structures of compounds were elucidated by the determination of physicochemical parameters and comparison of spectroscopic data. The preliminary cytotoxic activity of compounds was assessed by the Cell Counting Kit-8 (CCK-8) method. Results Three cyclic peptides were isolated from the sponge Reniochalina sp. and identified as stylopeptide 1 (1), hymenamide D (2) and axinastatin 2 (3). Compound 1 exhibited cytotoxicity against six human cancer cell lines with IC50 values ranging from 6.09 to 17.26 μmol/L. Conclusion Compound 1 - 3 were isolated from Reniochalina sp. for the first time, and compound 1 was a cytotoxic cyclic heptapeptide.

Research progress of cyclic peptide synthesis strategy and its application in new drug development / 药学学报

Protein-protein interaction (PPI) plays an important role in the regulation of life. Most of the PPI interfaces are large and discontinuous, and it is difficult for small molecules to specifically bind to them. Peptides are critical in PPI surface interactions due to their higher affinity and specificity. However, peptides have some defects such as easy hydrolysis by protease and poor membrane permeability. Due to good biocompatibility and chemical diversity, cyclic peptides play an important role in drug discovery. Therefore, the development of efficient cyclic peptide construction methods has become a frontier issue in peptide drug research. In recent years, a series of new progresses have been made in the synthesis strategy and the application of cyclic peptides, providing powerful technical tools for the research and development of cyclic peptide drugs. In this review, the synthesis strategies of cyclic peptides and their application will be reviewed from four aspects: synthesis strategies, property improvement, biological activity and prospect.

Chemical constituents of cyclic peptides from fibrous roots of Pseudostellaria heterophylla / 中国中药杂志

Four cyclic peptides were isolated from the 75% ethanol extract of the fibrous roots of Pseudostellaria heterophylla by silica gel, Sephadex LH-20 column chromatography, and semi-preparative HPLC. Through mass spectrometry, NMR and other methods, they were identified as pseudostellarin L(1), heterophyllin B(2), pseudostellarin B(3), and pseudostellarin C(4). Among them, compound 1 was a new cyclic peptide, and compounds 2-4 were isolated from the fibrous roots of P. heterophylla for the first time. None of these compounds displayed cytotoxic activities against MCF-7, A549, HCT-116, and SGC-7901 cells.

Research progress of cyclic peptides derived from phage display technology / 药学学报

Cyclic peptide drugs have gradually become an emerging research direction due to their some favorable properties such as high-efficiency binding affinity, high selectivity, lower toxicity, and stable metabolism. In recent years, the number of cyclic peptide drugs under clinical research has continued to increase. Unlike the previous cyclic peptide drugs, which were mostly derived from natural products and their derivatives, these cyclic peptide drugs are designed by genetically encoded display technologies which are based on rational design and in vitro evolution (such as BT1718, PTG-300, POL6326, etc). Among them, phage display technology has some advantages such as mature research system, low cost, and simpler operation that make it well recognized and praised by the majority of researchers in this field. Here, we reviewed the recent progress of applying phage display technology to explore diverse cyclic peptide libraries, which, we believe, will contribute more valuable candidate cyclic peptide drugs in clinical research.

Brucyclin, a novel antimicrobial peptide structurally designed from the antibacterial plant peptide, Brucin

A novel antimicrobial cyclic peptide, Brucyclin, was rationally designed from the original antibacterial plant peptide,Brucin. The chemically synthesized Brucyclin consists of amino acid sequence; (NH2- Gln-His-Thr-Leu-Cys-MetCys-Gly-Gly-Ala-Thr-Trp-COOH), with a molecular mass of m/z 1290. In the antimicrobial assay with 31 strainsof pathogenic microorganisms, the peptide exhibited the most antimicrobial activity with a minimum inhibitoryconcentration (MIC) values ranging from 50 to 100 μg/ml against two strains of Gram-negative bacteria (Vibriocholera non O1, non O139 and Klebsiella oxytoca), one strain of Gram-positive bacterium (Bacillus subtilis), andone strain of yeast (Candida albicans), respectively. Structural analysis of Brucyclin indicated that it has a neutralcharge with a hydrophobicity ratio of 50% and pI value of 6.72, respectively. The results from this study suggested thatthe Brucyclin is a new antibiotic peptide that might be an alternative potent drug for treatment of various infectiousdiseases caused by pathogenic microorganisms.

Effective strategies for improving the stability of peptides in vivo / 药学学报

Peptides have been extensively used in the fields of gene/drug delivery and disease targeting therapy. However, natural peptides are sensitive to protease digestion with short circulatory half-lives in vivo. Many studies on structural modifications of peptides have been reported to improve the delivery or therapeutic effect. In this review we focus on the recent literature on peptide stability in accordance with different structural modifications and summarize the methods and influential factors that are involved in the improvement of stability and half-life in vivo. This review will provide the scientific basis and theoretical references for further investigations and applications in vivo.

A novel cyclic peptide targeting LAG-3 for cancer immunotherapy by activating antigen-specific CD8 T cell responses

PD-1 and CTLA-4 antibodies offer great hope for cancer immunotherapy. However, many patients are incapable of responding to PD-1 and CTLA-4 blockade and show low response rates due to insufficient immune activation. The combination of checkpoint blockers has been proposed to increase the response rates. Besides, antibody drugs have disadvantages such as inclined to cause immune-related adverse events and infiltration problems. In this study, we developed a cyclic peptide C25 by using Ph.D.-C7C phage display technology targeting LAG-3. As a result, C25 showed a relative high affinity with human LAG-3 protein and could effectively interfere the binding between LAG-3 and HLA-DR (MHC-II). Additionally, C25 could significantly stimulate CD8 T cell activation in human PBMCs. The results also demonstrated that C25 could inhibit tumor growth of CT26, B16 and B16-OVA bearing mice, and the infiltration of CD8 T cells was significantly increased while FOXP3 Tregs significantly decreased in the tumor site. Furthermore, the secretion of IFN- by CD8 T cells in spleen, draining lymph nodes and especially in the tumors was promoted. Simultaneously, we exploited T cells depletion models to study the anti-tumor mechanisms for C25 peptide, and the results combined with MTT assay confirmed that C25 exerted anti-tumor effects CD8 T cells but not direct killing. In conclusion, cyclic peptide C25 provides a rationale for targeting the immune checkpoint, by blockade of LAG-3/HLA-DR interaction in order to enhance anti-tumor immunity, and C25 may provide an alternative for cancer immunotherapy besides antibody drugs.

Software-aided detection and structural characterization of cyclic peptide metabolites in biological matrix by high-resolution mass spectrometry / 药物分析学报

Compared to their linear counterparts, cyclic peptides show better biological activities, such as anti-bacterial, immunosuppressive, and anti-tumor activities, and pharmaceutical properties due to their conformational rigidity. However, cyclic peptides could form numerous putative metabolites from po-tential hydrolytic cleavages and their fragments are very difficult to interpret. These characteristics pose a great challenge when analyzing metabolites of cyclic peptides by mass spectrometry. This study was to assess and apply a software-aided analytical workflow for the detection and structural characterization of cyclic peptide metabolites. Insulin and atrial natriuretic peptide (ANP) as model cyclic peptides were incubated with trypsin/chymotrypsin and/or rat liver S9, followed by data acquisition using TripleTOF? 5600. Resultant full-scan MS and MS/MS datasets were automatically processed through a combination of targeted and untargeted peak finding strategies. MS/MS spectra of predicted metabolites were interrogated against putative metabolite sequences, in light of a, b, y and internal fragment series. The resulting fragment assignments led to the confirmation and ranking of the metabolite sequences and identification of metabolic modification. As a result, 29 metabolites with linear or cyclic structures were detected in the insulin incubation with the hydrolytic enzymes. Sequences of twenty insulin metabolites were further determined, which were consistent with the hydrolytic sites of these enzymes. In the same manner, multiple metabolites of insulin and ANP formed in rat liver S9 incubation were detected and structurally characterized, some of which have not been previously reported. The results demonstrated the utility of software-aided data processing tool in detection and identification of cyclic peptide metabolites.

Rational design of type-IA receptor-derived cyclic peptides to target human bone morphogenic protein 2

Human bone morphogenetic protein 2 (BMP2) is a bone-growth regulatory factor involved in the formation of bone andcartilage, and has been recognized as an attractive therapeutic target for a variety of bone diseases and defects. Here, wereport successful design of a head-to-tail cyclic peptide based on crystal structure to target BMP2. Computational alaninescanning identifies two hotspot regions at the crystal complex interface of BMP2 with its type-IA receptor; promising one isstripped from the interface to derive a linear self-inhibitory peptide RPS2[r78-94] that covers residues 78–94 of the receptorprotein. Dynamics simulation and energetics analysis reveal that the peptide is highly flexible in isolated state and cannotspontaneously bind to BMP2. The RPS2[r78-94] peptide is further extended from its N- and C-termini until reaching twospatially vicinal residues 74 and 98 in the crystal structure of intact BMP2–receptor complex system, consequently resultingin a longer peptide RPS2[r74-98], which is then cyclized in a head-to-tail manner to obtain its cyclic counterpartcycRPS2[r74-98]. Computational analysis suggests that the cyclic peptide can well maintain in a conformation similar withits active conformation in complex crystal structure, exhibiting a smaller disorder and a larger potency than its linearcounterpart. Further assays confirm that the two linear peptides RPS2[r78-94] and RPS2[r74-98] are nonbinders of BMP2,whereas, as designed, the cyclic peptide cycRPS2[r74-98] can bind to BMP2 with a moderate affinity. The cyclic peptide isexpected as a lead molecular entity to develop new and potent peptide-based drugs for BMP2-targeted therapy.

Total synthesis and structure-activity relationship of cyclic peptide antibiotic teixobactin:research advances / 国际药学研究杂志

Teixobactin, a cyclic-peptide antibiotic, destroys the cell walls of Gram-positive bacteria. It is therefore difficult for bacteria such as meticillin-resistant Staphylococcus aureus to develop resistance to it. Many scholars have studied the structure-activity relationship (SAR) of teixobactin. After reviewing the reports related to the discovery, structure, total synthesis and SAR of teixobactin, we found that the total synthesis of teixobactin was very difficult. The N-terminal methyl modification, ester bond and allo-End were unnecessary for the activity, the configuration of amino acids at the positions 1, 4, 5 and 8 could greatly influence the antibacterial activity, and the substitution of the amino acids at the 3, 4, 9 and 10 positions by Lys could retain the antibacterial activity.

Value of anti-cyclic peptide containing citrulline antibody for the early diagnosis of rheumatoid arthritis / 中国医师进修杂志

Objective To investigate the value of detection of anti-cyclic peptide containing citrulline (anti-CCP) antibody, rheumatoid factor (RF) and the combined detection of anti-CCP antibody and RF in rheumatoid arthritis (RA) patients. Methods From 2012 to 2014,1 961 patients were divided into three groups:diagnosed RA group(509 patients), not RA group(1 028 patients) and firstly was not diagnosed RA but later was diagnosed RA group (424 patients). The levels of RF and anti-CCP antibody were separately measured by rate nephelometry method and the electrochemical luminescence method. Results The sensitivity of detecting by anti-CCP antibody alone or anti-CCP antibody in combination with RF between RA group and not RA group was not significant difference ( P>0.05), but the specificity between two groups (88.6%vs. 60.4%) was significant difference ( P<0.05). There were significant differences in the sensitivity (81.7% vs. 74.3%) and specificity (88.6% vs. 66.0%) between by using anti-CCP antibody alone and RF alone.In firstly was not diagnosed RA but later was diagnosed RA group, there were significantly difference in sensitivity (98.3%vs. 82.1%) and specificity (91.6%vs. 81.5%) by using anti-CCP antibody alone and RF alone. Conclusion There is important clinical value by using anti-CCP antibody alone for the early diagnosis of RA.