Discovery of a novel nonphosphorylated pentapeptide motif displaying high affinity for Grb2-SH2 domain by the utilization of 3'-substituted tyrosine derivatives

RNF173 suppresses RAF/MEK/ERK signaling to regulate invasion and metastasis via GRB2 ubiquitination in Hepatocellular Carcinoma

BACKGROUND

The role of the membrane-associated RING-CH (MARCH) family in carcinogenesis has been widely studied, but the member of this family, RNF173, has not yet been thoroughly explored in the context of hepatocellular carcinoma (HCC).

METHODS

With the use of an HCC tissue microarray and IHC staining, we aim to determine the differential expression of RNF173 in HCC patients and its clinical significance. The biological role of RNF173 is investigated through in vitro and in vivo experiments. RNA sequencing, mass spectrometry, and immunoprecipitation are performed to uncover the underlying mechanism of RNF173's impact on the development of HCC.

RESULTS

The mRNA and protein levels of RNF173 were significantly lower in HCC tissues than in normal tissues. HCC patients with low RNF173 expression had shorter overall survival and recurrence-free survival, and RNF173 was significantly correlated with tumor number, tumor capsule, tumor differentiation, and BCLC stage. In addition, in vitro and in vivo experiments showed that RNF173 downregulation exacerbated tumor progression, including migration, invasion, and proliferation. GRB2 is a key molecule in the RAF/MEK/ERK pathway. RNF173 inhibits the RAF/MEK/ERK signaling by ubiquitinating and degrading GRB2, thereby suppressing HCC cell proliferation, invasion and migration. Combining clinical samples, we found that HCC patients with high RNF173 and low GRB2 expression had the best prognosis.

CONCLUSION

RNF173 inhibits the invasion and metastasis of HCC by ubiquitinating and degrading GRB2, thereby suppressing the RAF/MEK/ERK signaling pathway. RNF173 is an independent risk factor for the survival and recurrence of HCC patients. RNF173 may serve as a novel prognostic molecule and potential therapeutic target for HCC. Video Abstract Graphical abstract Model of RNF173 on RAF/MEK/ERK signaling. RNF173 knockdown resulted in impaired ubiquitination and degradation of GRB2, leading to the activation of the RAF/MEK/ERK signaling pathway and promotion of invasion and metastasis in HCC cells.

Cyclic helix B peptide alleviates proinflammatory cell death and improves functional recovery after traumatic spinal cord injury

BACKGROUND

Necroptosis and pyroptosis, two types of proinflammatory programmed cell death, were recently found to play important roles in spinal cord injury (SCI). Moreover, cyclic helix B peptide (CHBP) was designed to maintain erythropoietin (EPO) activity and protect tissue against the adverse effects of EPO. However, the protective mechanism of CHBP following SCI is still unknown. This research explored the necroptosis- and pyroptosis-related mechanism underlying the neuroprotective effect of CHBP after SCI.

METHODS

Gene Expression Omnibus (GEO) datasets and RNA sequencing were used to identify the molecular mechanisms of CHBP for SCI. A mouse model of contusion SCI was constructed, and HE staining, Nissl staining, Masson staining, footprint analysis and the Basso Mouse Scale (BMS) were applied for histological and behavioural analyses. qPCR, Western blot analysis, immunoprecipitation and immunofluorescence were utilized to analyse the levels of necroptosis, pyroptosis, autophagy and molecules associated with the AMPK signalling pathway.

RESULTS

The results revealed that CHBP significantly improved functional restoration, elevated autophagy, suppressed pyroptosis, and mitigated necroptosis after SCI. 3-Methyladenine (3-MA), an autophagy inhibitor, attenuated these beneficial effects of CHBP. Furthermore, CHBP-triggered elevation of autophagy was mediated by the dephosphorylation and nuclear translocation of TFEB, and this effect was due to stimulation of the AMPK-FOXO3a-SPK2-CARM1 and AMPK-mTOR signalling pathways.

CONCLUSION

CHBP acts as a powerful regulator of autophagy that improves functional recovery by alleviating proinflammatory cell death after SCI and thus might be a prospective therapeutic agent for clinical application.

Discovery of novel danshensu derivatives bearing pyrazolone moiety as potential anti-ischemic stroke agents with antioxidant activity

Neuroprotective agents with attenuation of oxidative stress by directly scavenging ROS and indirectly through Keap1-Nrf2 signal pathway activation may be a promising cerebral ischemic stroke therapeutic strategy. In this study, a series of novel danshensu derivatives bearing pyrazolone moieties with dual antioxidant effects were synthesized for the treatment of ischemic stroke. Most compounds exhibited considerable DPPH free radical scavenging ability and neuroprotective activity against H₂O₂-induced oxidative injury in PC12 neuronal cells, without cytotoxicity. Among these target compounds, Del03 displayed the strongest dose-dependent neuroprotective activity in vitro, directly downregulated intracellular ROS levels, and improved the oxidative stress parameters MDA, SOD, and LDH. Del03 also promoted Nrf2 translocation to the nucleus, subsequently increasing the expression of the Nrf2 downstream target HO-1. Molecular docking analysis revealed that Del03 could anchor to the key site of Keap1. Del03 possessed the ability to penetrate blood-brain barrier and displayed good ability on pharmacokinetic properties in rats Del03 possessed good BBB penetration efficiency, suitable pharmacokinetic properties in vivo. Del03 reduced cerebral infarction volume and promoted neurological function in a middle cerebral artery occlusion (MCAO) mouse model at a dose of 20 mg/kg by intravenous injection. The characteristics of Del03 detailed in this study demonstrate its potential as a therapeutic agent in the treatment of ischemic stroke.

Computationally driven design of an artificial metalloenzyme using supramolecular anchoring strategies of iridium complexes to alcohol dehydrogenase

Artificial metalloenzymes (ArMs) confer non-biological reactivities to biomolecules, whilst taking advantage of the biomolecular architecture in terms of their selectivity and renewable origin. In particular, the design of ArMs by the supramolecular anchoring of metal catalysts to protein hosts provides flexible and easy to optimise systems. The use of cofactor dependent enzymes as hosts gives the advantage of both a (hydrophobic) binding site for the substrate and a cofactor pocket to accommodate the catalyst. Here, we present a computationally driven design approach of ArMs for the transfer hydrogenation reaction of cyclic imines, starting from the NADP⁺-dependent alcohol dehydrogenase from Thermoanaerobacter brockii (TbADH). We tested and developed a molecular docking workflow to define and optimize iridium catalysts with high affinity for the cofactor binding site of TbADH. The workflow uses high throughput docking of compound libraries to identify key structural motifs for high affinity, followed by higher accuracy docking methods on smaller, focused ligand and catalyst libraries. Iridium sulfonamide catalysts were selected and synthesised, containing either a triol, a furane, or a carboxylic acid to provide the interaction with the cofactor binding pocket. IC₅₀ values of the resulting complexes during TbADH-catalysed alcohol oxidation were determined by competition experiments and were between 4.410 mM and 0.052 mM, demonstrating the affinity of the iridium complexes for either the substrate or the cofactor binding pocket of TbADH. The catalytic activity of the free iridium complexes in solution showed a maximal turnover number (TON) of 90 for the reduction of salsolidine by the triol-functionalised iridium catalyst, whilst in the presence of TbADH, only the iridium catalyst with the triol anchoring functionality showed activity for the same reaction (TON of 36 after 24 h). The observation that the artificial metalloenzymes developed here lacked stereoselectivity demonstrates the need for the further investigation and optimisation of the ArM. Our results serve as a starting point for the design of robust artificial metalloenzymes, exploiting supramolecular anchoring to natural NAD(P)H binding pockets.

Efficient strategies to enhance plasmid stability for fermentation of recombinant Escherichia coli harboring tyrosine phenol lyase

OBJECTIVE

To solve the bottleneck of plasmid instability during microbial fermentation of L-DOPA with recombinant Escherichia coli expressing heterologous tyrosine phenol lyase.

RESULTS

The tyrosine phenol lyase from Fusobacterium nucleatum was constitutively expressed in E. coli and a fed-batch fermentation process with temperature down-shift cultivation was performed. Efficient strategies including replacing the original ampicillin resistance gene, as well as inserting cer site that is active for resolving plasmid multimers were applied. As a result, the plasmid stability was increased. The co-use of cer site on plasmid and kanamycin in culture medium resulted in proportion of plasmid containing cells maintained at 100% after fermentation for 35 h. The specific activity of tyrosine phenol lyase reached 1493 U/g dcw, while the volumetric activity increased from 2943 to 14,408 U/L for L-DOPA biosynthesis.

CONCLUSIONS

The established strategies for plasmid stability is not only promoted the applicability of the recombinant cells for L-DOPA production, but also provides important guidance for industrial fermentation with improved microbial productivity.

Protein Interaction Domains and Post-Translational Modifications: Structural Features and Drug Discovery Applications

Background:

Many pathways regarding healthy cells and/or linked to diseases onset and progression depend on large assemblies including multi-protein complexes. Protein-protein interactions may occur through a vast array of modules known as protein interaction domains (PIDs).

Objective:

This review concerns with PIDs recognizing post-translationally modified peptide sequences and intends to provide the scientific community with state of art knowledge on their 3D structures, binding topologies and potential applications in the drug discovery field.

Method:

Several databases, such as the Pfam (Protein family), the SMART (Simple Modular Architecture Research Tool) and the PDB (Protein Data Bank), were searched to look for different domain families and gain structural information on protein complexes in which particular PIDs are involved. Recent literature on PIDs and related drug discovery campaigns was retrieved through Pubmed and analyzed.

Results and Conclusion:

PIDs are rather versatile as concerning their binding preferences. Many of them recognize specifically only determined amino acid stretches with post-translational modifications, a few others are able to interact with several post-translationally modified sequences or with unmodified ones. Many PIDs can be linked to different diseases including cancer. The tremendous amount of available structural data led to the structure-based design of several molecules targeting protein-protein interactions mediated by PIDs, including peptides, peptidomimetics and small compounds. More studies are needed to fully role out, among different families, PIDs that can be considered reliable therapeutic targets, however, attacking PIDs rather than catalytic domains of a particular protein may represent a route to obtain selective inhibitors.

Phosphotyrosine isosteres: past, present and future

Tyrosine phosphorylation is a critical component of signal transduction for multicellular organisms, particularly for pathways that regulate cell proliferation and differentiation. While tyrosine kinase inhibitors have become FDA-approved drugs, inhibitors of the other important components of these signaling pathways have been harder to develop. Specifically, direct phosphotyrosine (pTyr) isosteres have been aggressively pursued as inhibitors of Src homology 2 (SH2) domains and protein tyrosine phosphatases (PTPs). Medicinal chemists have produced many classes of peptide and small molecule inhibitors that mimic pTyr. However, balancing affinity with selectivity and cell penetration has made this an extremely difficult space for developing successful clinical candidates. This review will provide a comprehensive picture of the field of pTyr isosteres, from early beginnings to the current state and trajectory. We will also highlight the major protein targets of these medicinal chemistry efforts, the major classes of peptide and small molecule inhibitors that have been developed, and the handful of compounds which have been tested in clinical trials.

Design of a Protein Motif Responsive to Tyrosine Nitration and an Encoded Turn-Off Sensor of Tyrosine Nitration

Tyrosine nitration is a protein post-translational modification that is predominantly non-enzymatic and is observed to be increased under conditions of nitrosative stress and in numerous disease states. A small protein motif (14-18 amino acids) responsive to tyrosine nitration has been developed. In this design, nitrotyrosine replaced the conserved Glu12 of an EF-hand metal-binding motif. Thus, the non-nitrated peptide bound terbium weakly. In contrast, tyrosine nitration resulted in a 45-fold increase in terbium affinity. Nuclear magnetic resonance spectroscopy indicated direct binding of nitrotyrosine to the metal and EF-hand-like metal contacts in this designed peptide. Nitrotyrosine is an efficient quencher of fluorescence. To develop a sensor of tyrosine nitration, the initial design was modified to incorporate Glu residues at EF-hand positions 9 and 16 as additional metal-binding residues, to increase the terbium affinity of the peptide with unmodified tyrosine. This peptide with a tyrosine at residue 12 bound terbium and effectively sensitized terbium luminescence. Tyrosine nitration resulted in a 180-fold increase in terbium affinity ( Kd = 1.6 μM) and quenching of terbium luminescence. This sequence was incorporated as an encoded protein tag and applied as a turn-off fluorescent protein sensor of tyrosine nitration. The sensor was responsive to nitration by peroxynitrite, with fluorescence quenched upon nitration. The greater terbium affinity upon tyrosine nitration resulted in a large dynamic range and sensitivity to substoichiometric nitration. An improved approach for the synthesis of peptides containing nitrotyrosine was also developed, via the in situ silyl protection of nitrotyrosine. This work represents the first designed, encodable protein motif that is responsive to tyrosine nitration.

Direct arene C-H fluorination with 18F- via organic photoredox catalysis

Positron emission tomography (PET) plays key roles in drug discovery and development, as well as medical imaging. However, there is a dearth of efficient and simple radiolabeling methods for aromatic C-H bonds, which limits advancements in PET radiotracer development. Here, we disclose a mild method for the fluorine-18 (18F)-fluorination of aromatic C-H bonds by an [18F]F- salt via organic photoredox catalysis under blue light illumination. This strategy was applied to the synthesis of a wide range of 18F-labeled arenes and heteroaromatics, including pharmaceutical compounds. These products can serve as diagnostic agents or provide key information about the in vivo fate of the labeled substrates, as showcased in preliminary tracer studies in mice.

Rapid acidolysis of benzyl group as a suitable approach for syntheses of peptides naturally produced by oxidative stress and containing 3-nitrotyrosine

3-Nitrotyrosine (Nit) belongs to products of oxidative stress and could probably influence conformation of neurodegenerative proteins. Syntheses of peptides require availability of suitable synthon for introduction of Nit residue. Common phenolic protection groups are more acid labile, when they are attached to Nit residue. We have found that Fmoc-Nit(Bn)-OH is a good building block for syntheses of Nit containing peptides by Fmoc/tBu strategy. Interestingly, the peptides containing multiple Nit residues can be available solely by use of Fmoc-Nit(Bn)-OH synthon. Bn is removed rapidly with ca 80 % trifluoroacetic acid in dark. The cleavage of Bn from Fmoc-Nit(Bn)-OH proceeds via pseudo-first order mechanism with activation barrier 32 kcal mol(-1) and rate k = 15.3 s(-1) at 20 °C. This rate is more than 2,000,000 times faster than that for cleavage of benzyl from Tyr(Bn).

A novel proteolysis-resistant cyclic helix B peptide ameliorates kidney ischemia reperfusion injury

Helix B surface peptide (HBSP), derived from erythropoietin, displays powerful tissue protection during kidney ischemia reperfusion (IR) injury without erythropoietic side effects. We employed cyclization strategy for the first time, and synthesized thioether-cyclized helix B peptide (CHBP) to improve metabolic stability and renoprotective effect. LC-MS/MS analysis was adopted to examine the stability of CHBP in vitro and in vivo. The renoprotective effect of CHBP in terms of renal function, apoptosis, inflammation, extracellular matrix deposition, and histological injury was also detected in vivo and in vitro. Antibody array and western blot were performed to analyze the signal pathway of involvement by CHBP in the IR model and renal tubular epithelial cells. In this study, thioether-cyclized peptide was significantly stable in vivo and in vitro. One dose of 8nmol/kg CHBP administered intraperitoneally at the onset of reperfusion improved renal protection compared with three doses of 8nmol/kg linear HBSP in a 48h murine IR model. In a one-week model, the one dose CHBP-treated group exhibited remarkably improved renal function over the IR group, and attenuated kidney injury, including reduced inflammation and apoptosis. Interestingly, we found that the phosphorylation of autophagy protein mTORC1 was dramatically reduced upon CHBP treatment. We also demonstrated that CHBP induced autophagy via inhibition of mTORC1 and activation of mTORC2, leading to renoprotective effects on IR. Our results indicate that the novel metabolically stable CHBP is a promising therapeutic medicine for kidney IR injury treatment.

Development and evaluation of novel phosphotyrosine mimetic inhibitors targeting the Src homology 2 domain of signaling lymphocytic activation molecule (SLAM) associated protein

Specific interactions between Src homology 2 (SH2) domain-containing proteins and the phosphotyrosine-containing counterparts play significant role in cellular protein tyrosine kinase (PTK) signaling pathways. The SH2 domain inhibitors could potentially serve as drug candidates in treating human diseases. Here we have incorporated a novel phosphotyrosine mimetic, which is an unusual amino acid carrying a cyclosaligenyl (cycloSal) phosphodiester moiety, into dipeptides to investigate the inhibitory effect on SH2 domain-containing proteins. A plate-based assay was also established to screen for inhibitors that disrupt the interaction between a phosphopeptide of SLAM (signaling lymphocytic activation molecule) and its interacting protein SAP (SLAM-associated protein). We identified a number of inhibitors with IC50 values in the range of 17-35 μM, implying that the cycloSal phosphodiester-carrying amino acid could mimic the phosphotyrosyl residue. Our results also raise the possibility of integrating the newly developed phosphotyrosine mimetic moiety into inhibitors designed for other SH2 domain-containing proteins.

Peptide bicycles that inhibit the Grb2 SH2 domain

Developing short peptides into useful probes and therapeutic leads remains a difficult challenge. Structural rigidification is a proven method for improving the properties of short peptides. In this work, we report a strategy for stabilizing peptide macrocycles by introducing side-chain-to-side-chain staples to produce peptide bicycles with higher affinity, selectivity, and resistance to degradation. We have applied this strategy to G1, an 11-residue peptide macrocycle that binds the Src homology 2 (SH2) domain of growth-factor-bound protein 2 (Grb2). Several homodetic peptide bicycles were synthesized entirely on-resin with high yields. Two rounds of iterative design produced peptide bicycle BC1, which is 60 times more potent than G1 and 200 times more selective. Moreover, BC1 is completely intact after 24 hours in buffered human serum, conditions under which G1 is completely degraded. Our peptide-bicycle approach holds promise for the development of selective inhibitors of SH2 domains and other phosophotyrosine (pTyr)-binding proteins, as well as inhibitors of many other protein-protein interactions.

Template-assisted and self-activating clicked peptide as a synthetic mimic of the SH2 domain

A new synthetic strategy for obtaining artificial receptors that selectively regulate and/or control specific protein/protein interactions was developed based on the template-assisted and the self-activating click reaction applied to a combinatorial library. Synthetic mimics of the Grb2-SH2 domain, examined as a model case, selectively bound to a target signaling protein to induce cytotoxicity and inhibit tumor growth in vivo.

A novel molecular mechanism of primary resistance to FLT3-kinase inhibitors in AML

Currently, FLT3 tyrosine kinase inhibitors (TKIs) are emerging as the most promising drug therapy to overcome the dismal prognosis of acute myelogenous leukemia (AML) patients harboring internal tandem duplications (ITDs) of FLT3. However, up-front drug resistance occurs in approximately 30% of patients, and molecular mechanisms of resistance are poorly understood. Here, we have uncovered a novel mechanism of primary resistance to FLT3 TKIs in AML: an FLT3 receptor harboring a nonjuxtamembrane ITD atypically integrating into the β-2 sheet of the first kinase domain (FLT3_ITD627E) induces dramatic up-regulation of the anti-apoptotic myeloid cell leukemia 1 protein (MCL-1). Using RNA interference technology, deregulated MCL-1 protein expression was shown to play a major role in conferring the resistance phenotype of 32D_ITD627E cells. Enhanced and sustained binding of the adaptor protein GRB-2 to the FLT3_ITD627E receptor is involved in MCL-1 up-regulation and is independent from TKI (PKC412)–induced inhibition of the receptor kinase. Thus, we describe a new mechanism of primary resistance to TKIs, which operates by reprogramming local and distant signal transduction events of the FLT3 tyrosine kinase. The data presented suggest that particular ITDs of FLT3 may be associated with rewired signaling and differential responsiveness to TKIs.

Proline isomerization preorganizes the Itk SH2 domain for binding to the Itk SH3 domain

We report here the NMR-derived structure of the binary complex formed by the interleukin-2 tyrosine kinase (Itk) Src homology 3 (SH3) and Src homology 2 (SH2) domains. The interaction is independent of both a phosphotyrosine motif and a proline-rich sequence, the classical targets of the SH2 and SH3 domains, respectively. The Itk SH3/SH2 structure reveals the molecular details of this nonclassical interaction and provides a clear picture for how the previously described prolyl cis/trans isomerization present in the Itk SH2 domain mediates SH3 binding. The higher-affinity cis SH2 conformer is preorganized to form a hydrophobic interface with the SH3 domain. The structure also provides insight into how autophosphorylation in the Itk SH3 domain might increase the affinity of the intermolecular SH3/SH2 interaction. Finally, we can compare this Itk complex with other examples of SH3 and SH2 domains engaging their ligands in a nonclassical manner. These small binding domains exhibit a surprising level of diversity in their binding repertoires.

Discovery of thioether-bridged cyclic pentapeptides binding to Grb2-SH2 domain with high affinity

Blocking the interaction between phosphotyrosine (pTyr)-containing activated receptors and the Src homology 2 (SH2) domain of the growth factor receptor-bound protein 2 (Grb 2) is considered to be an effective and non-cytotoxic strategy to develop new anti-proliferate agents due to its potential to shut down the Ras activation pathway. In this study, a series of phosphotyrosine containing cyclic pentapeptides were designed and synthesized based upon the phage library derived cyclopeptide, G1TE. A comprehensive SAR study was also carried out to develop potent Grb2-SH2 domain antagonists based upon this novel template. With both the peptidomimetic optimization of the amino acid side-chains and the constraint of the backbone conformation guided by molecular modeling, we developed several potent antagonists with low micromolar range binding affinity, such as cyclic peptide 15 with an K(d)=0.359microM, which is providing a novel template for the development of Grb2-SH2 domain antagonists as potential therapeutics for certain cancers.

Grb2 signaling in cell motility and cancer

BACKGROUND

Metastasis is the primary cause of death in most human cancers, and understanding the molecular mechanisms underpinning this multistep process is fundamental to identifying novel molecular targets and developing more effective therapies.

OBJECTIVE/METHODS

Here we review the role of growth factor receptor-bound protein 2 (Grb2) in cancer and specifically in metastasis-related processes, and summarize the development of anticancer therapeutics selectively targeting this adapter protein.

RESULTS/CONCLUSION

Grb2 is a key molecule in intracellular signal transduction, linking activated cell surface receptors to downstream targets by binding to specific phosphotyrosine-containing and proline-rich sequence motifs. Grb2 signaling is critical for cell cycle progression and actin-based cell motility, and, consequently, more complex processes such as epithelial morphogenesis, angiogenesis and vasculogenesis. These functions make Grb2 a therapeutic target for strategies designed to prevent the spread of solid tumors through local invasion and metastasis.

Calorimetric investigation of phosphorylated and non-phosphorylated peptide ligand binding to the human Grb7-SH2 domain

Grb7 is a member of the Grb7 family of proteins, which also includes Grb10 and Grb14. All three proteins have been found to be overexpressed in certain cancers and cancer cell lines. In particular, Grb7 (along with the receptor tyrosine kinase erbB2) is overexpressed in 20-30% of breast cancers. In general, growth factor receptor bound (Grb) proteins bind to activated membrane-bound receptor tyrosine kinases (RTKs; e.g., the epidermal growth factor receptor, EGFR) through their Src homology 2 (SH2) domains. In particular, Grb7 binds to erbB2 (a.k.a. EGFR2) and may be involved in cell signaling pathways that promote the formation of metastases and inflammatory responses. In previous studies, we reported the solution structure and the backbone relaxation behavior of the Grb7-SH2/erbB2 peptide complex. In this study, isothermal titration calorimetry studies have been completed by measuring the thermodynamic binding parameters of several phosphorylated and non-phosphorylated peptides representative of natural Grb7 receptor ligands as well as ligands developed through combinatorial peptide screening methods. The entirety of these calorimetric studies is interpreted in an effort to describe the specific ligand binding characteristics of the Grb7 protein.

Structure-based design of potent Grb2–SH2 domain antagonists not relying on phosphotyrosine mimics

Development of Grb2-SH2 domain antagonists is considered to be an effective and non-cytotoxic strategy to develop new antiproliferative agents because of their potential to shut down the Ras signaling pathway. We developed a concise route for the efficient synthesis of G1TE analogs on solid phase. Using this route, a series of cyclic peptides that do not rely on phosphotyrosine or its mimics were designed and synthesized based upon the phage library-derived cyclopeptide, G1TE. Considering that Gly7 plays prominent roles for G1TE binding to the Grb2-SH2 domain, we introduced different amino acids in the 7th position. The D-Ala7-containing peptide 3 demonstrates improved binding affinity by adopting favorable conformation for protein binding. This can be rationalized by molecular modeling. The optimization at the Leu2 position was also studied, and the resulting cyclopeptides exhibited remarkably improved binding affinity. Based upon these global modifications, a highly potent peptide ligand 9 was discovered with a Kd = 17 nM, evaluated by Biacore binding assay. This new analog is one of the most potent non-phosphorus-containing Grb2-SH2 antagonists reported to date. This potent peptidomimetic provides a new template for the development of non-pTyr containing Grb2-SH2 domain antagonists and acts as a chemotherapeutic lead for the treatment of erbB2-related cancer.