Synthesis of a C-terminally biotinylated macrocyclic peptide mimetic exhibiting high Grb2 SH2 domain-binding affinity

An active transport dual adaptive nanocarrier designed to overcome the corneal microenvironment for neovascularization therapy

The eyes have a complicated microenvironment with many clearance mechanisms, making it challenging for effective drug delivery to the targeted areas of the eyes. Substrate transport mediated by active transporters is an important way to change drug metabolism in the ocular microenvironment. We designed multifunctional, dual-adaptive nanomicelles (GSCQ@NTB) which could overcome multiple physiological barriers by acting on both the efflux transporter and influx transporter to achieve deep delivery of the P-gp substrate in the cornea. Specifically, an effective "triple" antiangiogenic agent, nintedanib (NTB), was loaded into the biocompatible micelles. The expression of the efflux transporter was reversed by grafting quercetin. The peptide (glycylsarcosine, GS) was modified to target the influx transporter "Peptide Transporter-1" (PepT-1). Quercetin (QRT) and nintedanib (NTB) were transported to the cornea cooperatively, achieving long retention on the ocular surface and high compatibility. In a New Zealand rabbit model, within 8 hours after local administration, GSCQ@NTB was enriched in corneal stromal neovascularization and effectively inhibited the progress of neovascularization. Its effectiveness is slightly better than that in the first-line clinical application of steroids. In this study, we introduce the preparation of a dual adaptive nano-micelle system, which may provide an effective non-invasive treatment for corneal neovascularization.

Highly Stereoselective Asymmetric Aldol Routes to tert-Butyl-2-(3,5-difluorophenyl)-1-oxiran-2-yl)ethyl)carbamates: Building Blocks for Novel Protease Inhibitors

Enantioselective syntheses of tert-butyl ((S)-2-(3,5-difluorophenyl)-1-((S)-oxiran-2-yl)ethyl)carbamate and ((S)-2-(3,5-difluorophenyl)-1-((R)-oxiran-2-yl)ethyl)carbamate are described. We utilized asymmetric syn- and anti-aldol reactions to set both stereogenic centers. We investigated ester-derived Ti-enolate aldol reactions as well as Evans' diastereoselective syn-aldol reaction for these syntheses. We have converted optically active ((S)-2-(3,5-difluorophenyl)-1-((S)-oxiran-2-yl)ethyl)carbamate to a potent β-secretase inhibitor.

Application of ring-closing metathesis to Grb2 SH3 domain-binding peptides

Molecular processes depending on protein–protein interactions can use consensus recognition sequences that possess defined secondary structures. Left-handed polyproline II (PPII) helices are a class of secondary structure commonly involved with cellular signal transduction. However, unlike -helices, for which a substantial body of work exists regarding applications of ring-closing metathesis (RCM), there are few reports on the stabilization of PPII helices by RCM methodologies. The current study examined the effects of RCM macrocyclization on left-handed PPII helices involved with the SH3 domain-mediated binding of Sos1–Grb2. Starting with the Sos1-derived peptide “Ac-V1-P2-P3-P4-V5-P6-P7-R8-R9-R10-amide,” RCM macrocyclizations were conducted using alkenyl chains of varying lengths originating from the pyrrolidine rings of the Pro4 and Pro7 residues. The resulting macrocyclic peptides showed increased helicity as indicated by circular dichroism and enhanced abilities to block Grb2–Sos1 interactions in cell lysate pull-down assays. The synthetic approach may be useful in RCM macrocyclizations, where maintenance of proline integrity at both ring junctures is desired.

Selectivity and mechanism of action of a growth factor receptor-bound protein 2 SRC homology 2 domain binding antagonist

We have shown previously that a potent synthetic antagonist of growth factor receptor-bound protein 2 (Grb2) Src homology 2 (SH2) domain binding (1) blocks growth factor stimulated motility, invasion, and angiogenesis in cultured cell models, as well as tumor metastasis in animals. To characterize the selectivity of 1 for the SH2 domain of Grb2 over other proteins containing similar structural binding motifs, we synthesized a biotinylated derivative (3) that retained high affinity Grb2 SH2 domain binding and potent biological activity. To investigate the selectivity of 1 and 3 for Grb2, the biotinylated antagonist 3 was used to immobilize target proteins from cell extracts for subsequent identification by mass spectrometry. Non-specific binding was identified in parallel using a biotinylated analogue that lacked a single critical binding determinant. The mechanism of action of the antagonist was further characterized by immunoprecipitation, immunoblotting, and light microscopy. This approach to defining protein binding antagonist selectivity and molecular basis of action should be widely applicable in drug development.

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.

Utilization of achiral alkenyl amines for the preparation of high affinity Grb2 SH2 domain-binding macrocycles by ring-closing metathesis

A family of previously reported ring-closing metathesis (RCM)-derived macrocycles that exhibit potent Grb2 SH2 domain-binding affinity is characterized by stereoselectively-introduced upper ring junctions that bear bicyclic aryl substituents. However, the synthetic complexity of these macrocycles presents a potential limit to their therapeutic application. Therefore, the current study was undertaken to simplify these macrocycles through the use of achiral 4-pentenylamides as ring-forming components. A series of macrocycles (5a-f) was prepared bearing both open and cyclic constructs at the upper ring junction. The Grb2 SH2 domain-binding affinities of these macrocycles varied, with higher affinities being obtained with cyclo-substituents. The most potent analogue (5d) contained a cyclohexyl group and exhibited Grb2 SH2 domain-binding affinity (K(D) = 1.3 nM) that was nearly equal to the parent macrocycle (2), which bore a stereoselectively-introduced naphthylmethyl substituent at the upper ring junction (K(D) = 0.9 nM). The results of this study advance design considerations that should facilitate the development of Grb2 SH2 domain-binding antagonists.

Development of Grb2 SH2 Domain Signaling Antagonists: A Potential New Class of Antiproliferative Agents

Aberrant signaling through protein-tyrosine kinase (PTK)-dependent pathways is associated with several proliferative diseases. Accordingly, PTK inhibitors are being developed as new approaches for the treatment of certain cancers. Growth factor receptor bound protein 2 (Grb2) is an important downstream mediator of PTK signaling that serves obligatory roles in many pathogenic processes. One of the primary functions of Grb2 is to bind to specific phosphotyrosyl (pTyr)-containing sequences through its Src homology 2 (SH2) domain. Agents that bind to the Grb2 SH2 domain and prevent its normal function could disrupt associated PTK signaling and serve as alternatives to kinase-directed inhibitors. Starting from the X-ray crystal structure of a lead peptide bound to the Grb2 SH2 domain, this review will summarize important contributions to these efforts. The presentation will be thematically arranged according to the region of peptide modified, proceeding from the N-terminus to the C-terminus, with a special section devoted to aspects of conformational constraint.

Molecular targeting of growth factor receptor-bound 2 (Grb2) as an anti-cancer strategy

Growth factor receptor-bound 2 (Grb2) is a ubiquitously expressed adapter protein that provides a critical link between cell surface growth factor receptors and the Ras signaling pathway. As such, it has been implicated in the oncogenesis of several important human malignancies. In addition to this function, research over the last decade has revealed other fundamental roles for Grb2 in cell motility and angiogenesis--processes that also contribute to tumor growth, invasiveness and metastasis. This functional profile makes Grb2 a high priority target for anti-cancer drug development. Knowledge of Grb2 protein structure, its component Src homology domains and their respective structure-function relationships has facilitated the rapid development of sophisticated drug candidates that can penetrate cells, bind Grb2 with high affinity and potently antagonize Grb2 signaling. These novel compounds offer considerable promise in our growing arsenal of rationally designed anti-cancer therapeutics.

Survey of the year 2005 commercial optical biosensor literature

We identified 1113 articles (103 reviews, 1010 primary research articles) published in 2005 that describe experiments performed using commercially available optical biosensors. While this number of publications is impressive, we find that the quality of the biosensor work in these articles is often pretty poor. It is a little disappointing that there appears to be only a small set of researchers who know how to properly perform, analyze, and present biosensor data. To help focus the field, we spotlight work published by 10 research groups that exemplify the quality of data one should expect to see from a biosensor experiment. Also, in an effort to raise awareness of the common problems in the biosensor field, we provide side-by-side examples of good and bad data sets from the 2005 literature.