Noncompetitive inhibition of hepatocyte growth factor-dependent Met signaling by a phage-derived peptide

Peptides as multifunctional players in cancer therapy

Peptides exhibit lower affinity and a shorter half-life in the body than antibodies. Conversely, peptides demonstrate higher efficiency in tissue penetration and cell internalization than antibodies. Regardless of the pros and cons of peptides, they have been used as tumor-homing ligands for delivering carriers (such as nanoparticles, extracellular vesicles, and cells) and cargoes (such as cytotoxic peptides and radioisotopes) to tumors. Additionally, tumor-homing peptides have been conjugated with cargoes such as small-molecule or chemotherapeutic drugs via linkers to synthesize peptide-drug conjugates. In addition, peptides selectively bind to cell surface receptors and proteins, such as immune checkpoints, receptor kinases, and hormone receptors, subsequently blocking their biological activity or serving as hormone analogs. Furthermore, peptides internalized into cells bind to intracellular proteins and interfere with protein-protein interactions. Thus, peptides demonstrate great application potential as multifunctional players in cancer therapy.

Targeting kinase signaling pathways with constrained peptide scaffolds

Kinases are amongst the largest families in the human proteome and serve as critical mediators of a myriad of cell signaling pathways. Since altered kinase activity is implicated in a variety of pathological diseases, kinases have become a prominent class of proteins for targeted inhibition. Although numerous small molecule and antibody-based inhibitors have already received clinical approval, several challenges may still exist with these strategies including resistance, target selection, inhibitor potency and in vivo activity profiles. Constrained peptide inhibitors have emerged as an alternative strategy for kinase inhibition. Distinct from small molecule inhibitors, peptides can provide a large binding surface area that allows them to bind shallow protein surfaces rather than defined pockets within the target protein structure. By including chemical constraints within the peptide sequence, additional benefits can be bestowed onto the peptide scaffold such as improved target affinity and target selectivity, cell permeability and proteolytic resistance. In this review, we highlight examples of diverse chemistries that are being employed to constrain kinase-targeting peptide scaffolds and highlight their application to modulate kinase signaling as well as their potential clinical implications.

Prognostic implication of serum hepatocyte growth factor in stage II/III breast cancer patients who received neoadjuvant chemotherapy

PURPOSE

In stage II/III breast cancer, neoadjuvant chemotherapy (NAC) is a standard treatment. Although several biomarkers are used to predict prognosis in breast cancer, there is no reliable predictive biomarker for NAC success. Recently, the hepatocyte growth factor (HGF) and cMet signaling pathway demonstrated to be involved in breast cancer tumor progression, and its potential as a biomarker is under active investigation. In this study, we assessed the potential of serum HGF as a prognostic biomarker for NAC efficacy.

METHODS

Venous blood samples were drawn from patients diagnosed with stage II/III breast cancer and treated with NAC in Seoul National University Hospital from August 2004 to November 2009. Serum HGF level was determined using an ELISA system. We reviewed the medical records of the patients and investigated the association of HGF level with patients' clinicopathologic characteristics.

RESULTS

A total of 121 female patients (median age = 45 years old) were included. Median level of HGF was 934 pg/ml (lower quartile: 772, upper quartile: 1145 pg/ml). Patients with higher HGF level than median value were significantly more likely to have clinically detectable regional node metastasis (p = 0.017, Fisher's exact test). Patients with complete and partial response according to the American Joint Committee on Cancer 7th Edition criteria tended to have higher HGF level (p = 0.105 by t test). Patients with an HGF level higher than the upper quartile value had longer relapse-free survival than the other patients (106 vs. 85 months, p = 0.008).

CONCLUSIONS

High serum HGF levels in breast cancer patients are associated with clinically detectable regional node metastasis and, paradoxically, with longer relapse-free survival in stage II/III breast cancer.

The HGF inhibitory peptide HGP-1 displays promising in vitro and in vivo efficacy for targeted cancer therapy

HGF/MET pathway mediates cancer initiation and development. Thus, inhibition on HGF-initiated MET signaling pathway would provide a new approach to cancer targeted therapeutics. In our study, we identified a targeting peptide candidate binding to HGF which was named HGF binding peptide-1 (HGP-1) via bacterial surface display methods coupled with fluorescence-activated cell sorting (FACS). HGP-1 showed the moderate affinity when determined with surface plasmon resonance (SPR) technique and high specificity in binding to HGF while assessed by fluorescence-based ELISA assay. The results from MTT and in vitro migration assay indicated that HGF-dependent cell proliferation and migration could be inhibited by HGP-1. In vivo administration of HGP-1 led to an effective inhibitory effect on tumor growth in A549 tumor xenograft models. Moreover, findings from Western Blots revealed that HGP-1 could down-regulated the phosphorylation levels of MET and ERK1/2 initiated by HGF, which suggested that HGP-1 could disrupt the activation of HGF/MET signaling to influence the cell activity. All the data highlighted the potential of HGP-1 to be a potent inhibitor for HGF/MET signaling.

Design of growth factor sequestering biomaterials

Growth factors (GFs) are major regulatory proteins that can govern cell fate, migration, and organization. Numerous aspects of the cell milieu can modulate cell responses to GFs, and GF regulation is often achieved by the native extracellular matrix (ECM). For example, the ECM can sequester GFs and thereby control GF bioavailability. In addition, GFs can exert distinct effects depending on whether they are sequestered in solution, at two-dimensional interfaces, or within three-dimensional matrices. Understanding how the context of GF sequestering impacts cell function in the native ECM can instruct the design of soluble or insoluble GF sequestering moieties, which can then be used in a variety of bioengineering applications. This Feature Article provides an overview of the natural mechanisms of GF sequestering in the cell milieu, and reviews the recent bioengineering approaches that have sequestered GFs to modulate cell function. Results to date demonstrate that the cell response to GF sequestering depends on the affinity of the sequestering interaction, the spatial proximity of sequestering in relation to cells, the source of the GF (supplemented or endogenous), and the phase of the sequestering moiety (soluble or insoluble). We highlight the importance of context for the future design of biomaterials that can leverage endogenous molecules in the cell milieu and mitigate the need for supplemented factors.

Pseudo-active sites of protease domains: HGF/Met and Sonic hedgehog signaling in cancer

Proteases represent a large class of enzymes with crucial biological functions. Although targeting various relevant proteases for therapeutic intervention has been widely investigated, structurally related proteins lacking proteolytic activity (pseudo-proteases) have received relatively little attention. Two distinct clinically relevant cancer pathways that contain signaling proteins with pseudo-protease domains include the Met and Hedgehog (Hh) pathways. The receptor tyrosine kinase Met pathway is driven by hepatocyte growth factor (HGF), a plasminogen-related ligand that binds Met and activates intracellular pathways resulting in cell proliferation, angiogenesis, motility and survival. HGF is a disulfide-linked α/β-heterodimer having a trypsin serine protease-like β-chain. The Hh pathway is driven by Sonic hedgehog (Shh), which has a Zn2+metalloprotease fold and binds Patched1 (Ptc1), which de-represses Smoothened and ultimately activates Gli-dependent transcription. Although HGF and Shh differ in structure and function, the pseudo-catalytic sites of both HGF and Shh are crucial for signal transduction. For HGF, this region binds the Met β-propeller domain, which leads to Met dimerization and signaling. For Hh, this region binds to the antagonist receptor Hedgehog-interacting protein (Hhip) and most probably to Ptc1 as well. Thus, for both HGF and Hh pathways, targeting ligand pseudo-active sites represents a new strategy for regulation.

Structural and interaction analysis of glycoprotein VI-binding peptide selected from a phage display library

Glycoprotein VI (GPVI) is a major collagen receptor on the platelet surface that recognizes the glycine-proline-hydroxyproline (GPO) sequence in the collagen molecule and plays a crucial role in thrombus formation. Inhibitors that block the interaction of GPVI with collagen have potential for use as antithrombotic drugs. For low molecular weight drug design for GPVI, it is essential to obtain precise structural and interaction information about GPVI-binding ligands. However, experimentally obtained structural and interaction information of small ligands, such as peptides, in the GPVI-bound state has not been reported. In this study, by screening a phage-displayed peptide library, we discovered a novel peptide ligand (pep-10L; YSDTDWLYFSTS) without any similarities to the sequence of collagen that inhibits GPVI-GPO binding. Systematic Ala scanning in surface plasmon resonance experiments and a saturation transfer difference NMR experiment revealed that Trp(6), Leu(7), Phe(9), and Ser(10) residues in the pep-10L peptide interacted with GPVI. Furthermore, the GPVI-bound conformation of the pep-10L peptide was determined using transferred nuclear Overhauser effect analysis. The obtained structure has revealed that the central part of pep-10L (Asp(5)-Phe(9)) has a helical conformation, the side chains of Trp(6), Leu(7), and Phe(9) form a hydrophobic side in the helix, and the Tyr(8) side chain faces the opposite direction from the hydrophobic side. Computational docking prediction has shown that the hydrophobic side of pep-10L sticks in the hydrophobic groove on the GPVI surface, which corresponds to the putative collagen-related peptide binding groove. These data could enable the structure-guided development of a small molecule GPVI antagonist.