Inhibitory effect of a dimerization-arm-mimetic peptide on EGF receptor activation

Synthesis and biological evaluation of EGFR binding peptides for near-infrared photoimmunotherapy

Near-infrared photoimmunotherapy (NIR-PIT) is a new cancer treatment that involves photoimmunotherapy drug injection and NIR light exposure. In NIR-PIT, antibodies are commonly used as target-directed molecules carrying IRDye700DX (IR700). However, antibodies have disadvantages, such as high cost, complex development strategies, and poor tumor penetration. In contrast, peptides have lower production costs, can be easy to chemically synthesize and modify, and can also be used for tumor-targeting like antibodies. In this study, we developed a novel PIT drug using a peptide as the target-directed molecule. Epidermal growth factor receptor (EGFR) was selected as the target, and monovalent and bivalent EGFR-binding peptides were synthesized. The bivalent peptide showed sufficient binding to EGFR-positive cells, and a bivalent peptide-IR700 conjugate with a long linker induced morphological changes in EGFR-positive cells. Additionally, the drug significantly reduced cell viability in vitro in an NIR light-dose- and drug-concentration-dependent manner. These results indicate the feasibility of NIR-PIT in treating cancer using peptide-based drugs.

The first structure-activity relationship study of oxytocin as a positive allosteric modulator for the µ opioid receptor

Positive allosteric modulators (PAMs) of G protein-coupled receptors (GPCRs) have drawn attention as novel drug candidates. PAMs can enhance the activities of endogenous agonists which are not only secreted at appropriate times and in parts of the body, but also are immediately metabolized. Therefore, they are expected to show fewer side effects than exogeneous orthosteric ligands. Recently, we have reported that oxytocin (OT) functioned as a PAM of the μ opioid receptor (MOR) which was one of the most potent targets for analgesics. OT is thus thought to be a useful compound for the development of novel analgesics. In this study, several OT analogs were synthesized and evaluated with an intact cell-based assay to investigate the crucial structures of OT for exerting the PAM activity. The assay results indicated that the cyclic structure formed by an intramolecular disulfide bond and the three C-terminal residues containing a small Gly residue of OT were essential for their function as a MOR-PAM. Intriguingly, two analogs having an amide or an ethylene tether instead of the intramolecular disulfide bridge did not have any PAM effects. The results suggested that the disulfide linkage of OT would be a key structure for exerting the PAM activity at the MOR.

Wandering beyond small molecules: peptides as allosteric protein modulators

Recent years have seen the rise of allosteric modulation as an innovative approach for drug design and discovery, efforts which culminated in the development of several clinical candidates. Allosteric modulation of many drug targets, including mainly membrane-embedded receptors, have been vastly explored through small molecule screening campaigns, but much less attention has been paid to peptide-based allosteric modulators. However, peptides have a significant impact on the pharmaceutical industry due to the typically higher potency and selectivity for their targets, as compared with small molecule therapeutics. Therefore, peptides represent one of the most promising classes of molecules that can modulate key biological pathways. Here, we report on the allosteric modulation of proteins (ranging from G protein-coupled receptors to specific protein-protein interactions) by peptides for applications in drug discovery.

EGFR-Binding Peptides: From Computational Design towards Tumor-Targeting of Adeno-Associated Virus Capsids

The epidermal growth factor receptor (EGFR) plays a central role in the progression of many solid tumors. We used this validated target to analyze the de novo design of EGFR-binding peptides and their application for the delivery of complex payloads via rational design of a viral vector. Peptides were computationally designed to interact with the EGFR dimerization interface. Two new peptides and a reference (EDA peptide) were chemically synthesized, and their binding ability characterized. Presentation of these peptides in each of the 60 capsid proteins of recombinant adeno-associated viruses (rAAV) via a genetic based loop insertion enabled targeting of EGFR overexpressing tumor cell lines. Furthermore, tissue distribution and tumor xenograft specificity were analyzed with systemic injection in chicken egg chorioallantoic membrane (CAM) assays. Complex correlations between the targeting of the synthetic peptides and the viral vectors to cells and in ovo were observed. Overall, these data demonstrate the potential of computational design in combination with rational capsid modification for viral vector targeting opening new avenues for viral vector delivery and specifically suicide gene therapy.

Effects of replacement and addition of an amino acid contained in a cyclic peptide corresponding to a β-hairpin loop sequence of human EGF receptor

Effects of replacement and addition of an amino acid in a cyclic decapeptide 1 (cyclic-CYNPTTYQMC) for inhibitory activity to dimerization of human epidermal growth factor receptor (EGFR) were examined. By alanine scanning of 1 corresponding to the arm structure (residues 246-254) of a β-hairpin loop sequence (residues 242-259) of EGFR, it was confirmed that replacement of any amino acid in the loop structure lowered the dimerization inhibitory activity of 1. Among the residues examined, Tyr at position 246 and Thr at 250 were found to be crucial for dimer formation. Addition of an amino acid to the N-terminus of 1 also affected the dimerization inhibitory activity. Addition of an amino acid containing a moderately hydrophilic side-chain increased the inhibitory activity. In contrast, an intramolecular hydrogen bond of 1 is not thought to be crucial for holding the dimer structure on the basis of the dimerization inhibitory activities of N-methylated analogues of 1. These results will be useful for the design and evaluation of a potent dimerization inhibitor as an anti-proliferation agent. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.

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.

Recent progress in protein-protein interaction study for EGFR-targeted therapeutics

INTRODUCTION

Epidermal growth factor receptor (EGFR) expression is upregulated in many tumors and its aberrant signaling drives progression of many cancer types. Consequently, EGFR has become a clinically validated target as extracellular tumor marker for antibodies as well as for tyrosine kinase inhibitors. Within the last years, new mechanistic insights were uncovered and, based on clinical experience as well as progress in protein engineering, novel bio-therapeutic approaches were developed and tested.

AREAS COVERED

The potential therapeutic targeting arsenal in the fight against cancer now encompasses bispecific or biparatopic antibodies, DARPins, Adnectins, Affibodies, peptides and combinations of these binding molecules with viral- and nano-particles. We review past and recent binding proteins from the literature and include a brief description of the various targeting approaches. Special attention is given to the binding modes with the EGFR. Expert commentary: Clinical data from the three approved anti EGFR antibodies indicate that there is room for improved therapeutic efficacy. Having choices in size, affinity, avidity and the mode of EGFR binding as well as the possibility to combine various effector functions opens the possibility to rationally design more effective therapeutics.

Functional evaluation of fluorescein-labeled derivatives of a peptide inhibitor of the EGF receptor dimerization

A cyclic decapeptide (1, ), which acts on the extracellular region of the EGF receptor, preventing it from dimerizing, has been developed. Peptide 2, which was labeled with fluorescein at the N-terminus of peptide 1, was synthesized based on structure-activity relationship studies. Peptide 2 essentially retained the inhibitory activity of peptide 1 against the receptor autophosphorylation. Confocal microscopy studies revealed that in carcinoma cells, the fluorescence of peptide 2 was localized inside some vesicles. Treatment of intact cells by peptide 1 in combination with peptide 2 decreased the fluorescence intensity significantly compared to treatment with only peptide 2. These results indicate that peptide 2 competes with peptide 1 for binding to the cellular surface. Six derivatives of peptide 2, in which constituent amino acids, with the exception of two cysteines and proline were randomized, were synthesized and used to treat the cells. Peptides 6 and 9 showed the highest fluorescence intensity in cells. From the results of the EGF receptor autophosphorylation assay, these two derivatives were proven to have higher inhibitory activity than peptide 2, which would therefore be a useful delivery peptide and fluorescent probe to find new inhibitors against the EGF receptor. Peptides 6 and 9 are promising leads for EGF receptor inhibitors.

Design of a selenylsulfide-bridged EGFR dimerization arm mimic

The epidermal growth factor receptor (EGFR) dimerization arm is a key feature that stabilizes dimerization of the extracellular receptor, thereby mediating activation of the tyrosine kinase domain. Peptides mimicking this β-loop feature can disrupt dimer formation and kinase activation, yet these peptides lack structural constraints or contain redox sensitive disulfide bonds which may limit their stability in physiological environments. Selenylsulfide bonds are a promising alternative to disulfide bonds as they maintain much of the same structural and chemical behavior, yet they are inherently less prone to reduction. Herein, we describe the synthesis, stability and activity of selenylsulfide-bridged dimerization arm mimics. The synthesis was accomplished using an Fmoc-based strategy along with C-terminal labeling for improved overall yield. This selenylsulfide-bridged peptide displayed both proteolytic stability and structural stability even under reducing conditions, demonstrating the potential application of the selenylsulfide bond to generate redox stable β-loop peptides for disruption of protein-protein interactions.

Inhibiting EGFR dimerization using triazolyl-bridged dimerization arm mimics

The epidermal growth factor receptor (EGFR) is overexpressed in multiple carcinomas and is the focus of a variety of targeted therapies. Here we report the design of peptide-based compounds that mimic the EGFR dimerization arm and inhibit allosteric activation of EGFR. These peptides are modified to contain a triazolyl bridge between the peptide strands to constrain the EGFR dimerization arm β-loop. In this study, we demonstrate that these peptides have significantly improved proteolytic stability over the non-modified peptide sequence, and their inhibitory effects are dependent on the number of the methylene units and orientation of the introduced triazolyl bridge. We identified a peptide, EDA2, which downregulates receptor phosphorylation and dimerization and reduces cell viability. This is the first example of a biologically active triazolyl-bridged peptide targeting the EGFR dimerization interface that effectively downregulates EGFR activation.

Evaluation of dimerization-inhibitory activities of cyclic peptides containing a β-hairpin loop sequence of the EGF receptor

Structure-activity relationships of cyclic peptides mimicking the β-hairpin structure of the 'dimerization arm' at residues 242-259 of the EGF receptor are examined. Cyclic peptides containing the arm head of the β-hairpin loop showed inhibitory activity toward the EGF receptor's dimerization. Cyclic peptides containing a Retro-Inverso sequence of the dimerization arm showed clear inhibitory effects on the dimerization in vitro and efficiently suppressed the proliferation of A431 cells, which abundantly express the EGF receptor on their surface. The effects at a specific hydrophobic site of the loop structure were expected to enhance the interactions with the receptor.

Intact-cell-based surface plasmon resonance measurements for ligand affinity evaluation of a membrane receptor

Toward future applications to the discovery of drugs against membrane receptors on pathological cells, an intact-cell-based surface plasmon resonance (SPR) methodology has been developed. The injection of a suspension of epidermal carcinoma A431 cells (5×10(7)cells/ml), as an analyte, generated clear SPR responses to epidermal growth factor (EGF) immobilized on the sensor chip. Because the responses were competitively reduced by the free ligand EGF, added to the analyte cell suspension, they certainly reflect the specific interaction of the immobilized EGF with the extracellular region of its receptor, which is highly expressed on the surface of the A431 cells.

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.