Novel anti-cancer candidates from a combinatorial peptide library.

STAT3 is attractive target for development of anti-cancer therapeutics as it is implicated in nearly all forms of human tumors. To identify novel leads, we screened a combinatorial peptide library displayed on the surface of M13 bacteriophage. After three rounds of biopanning, a dodecapeptide with the YYVSWPPDMMHY sequence was found to be enriched by 36% while another with a short consensus motif was displayed in 20% of the phages.

Noncovalent structure of SENP1 in complex with SUMO2.

SUMOylation is a post-translational modification in which a small ubiquitin-like molecule (SUMO) is appended to substrate proteins and is known to influence myriads of biological processes. A delicate interplay between several families of SUMOylation proteins and their substrates ensures the proper level of SUMOylation required for normal cell function. Among the SUMO proteins, SUMO2 is known to form mono-SUMOylated proteins and engage in poly-SUMO chain formation, while sentrin-specific protease 1 (SENP1) is a key enzyme in regulating both events.

Identification of the first small-molecule inhibitor of the REV7 DNA repair protein interaction.

DNA interstrand crosslink (ICL) repair (ICLR) has been implicated in the resistance of cancer cells to ICL-inducing chemotherapeutic agents. Despite the clinical significance of ICL-inducing chemotherapy, few studies have focused on developing small-molecule inhibitors for ICLR. The mammalian DNA polymerase ζ, which comprises the catalytic subunit REV3L and the non-catalytic subunit REV7, is essential for ICLR.

Observation of an E2 (Ubc9)-homodimer by crystallography.

Post-translational modifications by the small ubiquitin-like modifiers (SUMO), in particular the formation of poly-SUMO-2 and -3 chains, regulates essential cellular functions and its aberration leads to life-threatening diseases (Geoffroy and Hay, 2009) [1]. It was shown previously that the non-covalent interaction between SUMO and the conjugating enzyme (E2) for SUMO, known as Ubc9, is required for poly-SUMO-2/3 chain formation (Knipscheer et al., 2007) [2].

Unexpected involvement of staple leads to redesign of selective bicyclic peptide inhibitor of Grb7.

The design of potent and specific peptide inhibitors to therapeutic targets is of enormous utility for both proof-of-concept studies and for the development of potential new therapeutics. Grb7 is a key signaling molecule in the progression of HER2 positive and triple negative breast cancers. Here we report the crystal structure of a stapled bicyclic peptide inhibitor G7-B1 in complex with the Grb7-SH2 domain.

Cyclic Peptides Incorporating Phosphotyrosine Mimetics as Potent and Specific Inhibitors of the Grb7 Breast Cancer Target.

The Grb7 adaptor protein is a therapeutic target for both TNBC and HER2+ breast cancer. A nonphosphorylated cyclic peptide 1 (known as G7-18NATE) inhibits Grb7 via targeting the Grb7-SH2 domain, but requires the presence of phosphate ions for both affinity and specificity. Here we report the discovery of malonate bound in the phosphotyrosine binding pocket of the apo-Grb7-SH2 structure.

Preparation of crystals for characterizing the Grb7 SH2 domain before and after complex formation with a bicyclic peptide antagonist.

Human growth factor receptor-bound protein 7 (Grb7) is an adapter protein involved in cell growth, migration and proliferation. It is now recognized that Grb7 is an emerging therapeutic target in specific cancer subtypes. Recently, the discovery of a bicyclic peptide inhibitor that targets the Grb7 SH2 domain, named G7-B1, was reported.

Design and testing of bicyclic inhibitors of Grb7--are two cycles better than one?

Grb7 is an adapter protein involved in the propagation of signals in cancer cell migration and proliferation, and is thus a target for the development of novel anti-cancer agents. An 11-residue thioether-cyclized peptide known as G7-18NATE has previously been developed, that inhibits Grb7 via specific interactions with its SH2 domain with micromolar affinity. Here we explore whether the peptide binding is enhanced by the addition of a second linkage designed to restrain the peptide in its bound conformation and thus reduce the entropic loss upon binding.

The discovery of phenylbenzamide derivatives as Grb7-based antitumor agents.

Grb7 is a non-catalytic protein, the overexpression of which has been associated with the proliferative and migratory potentials of cancer cells. Virtual screening strategies involving a shape-based similarity search, molecular docking, and 2D-similarity searches complemented by experimental binding studies (Thermofluor and isothermal titration calorimetry) resulted in the identification of nine novel phenylbenzamide-based antagonists of the Grb7 SH2 domain. Moderate binding affinities were observed, ranging from K(d)=32.

Interaction of the non-phosphorylated peptide G7-18NATE with Grb7-SH2 domain requires phosphate for enhanced affinity and specificity.

Src-homology (SH2) domains are an attractive target for the inhibition of specific signalling pathways but pose the challenge of developing a truly specific inhibitor. The G7-18NATE cyclic peptide is reported to specifically inhibit the growth factor receptor bound protein 7 (Grb7) adapter protein, implicated in the progression of several cancer types, via interactions with its SH2 domain. G7-18NATE effectively inhibits the interaction of Grb7 with ErbB3 and focal adhesion kinase in cell lysates and, with the addition of a cell permeability sequence, inhibits the growth and migration of a number of breast cancer cell lines.

Structural basis of binding by cyclic nonphosphorylated peptide antagonists of Grb7 implicated in breast cancer progression.

Growth-receptor-bound protein (Grb)7 is an adapter protein aberrantly overexpressed, along with the erbB-2 receptor in breast cancer and in other cancers. Normally recruited to focal adhesions with a role in cell migration, it is associated with erbB-2 in cancer cells and is found to exacerbate cancer progression via stimulation of cell migration and proliferation. The G7-18NATE peptide (sequence: WFEGYDNTFPC cyclized via a thioether bond) is a nonphosphorylated peptide that was developed for the specific inhibition of Grb7 by blocking its SH2 domain.

Benzopyrazine derivatives: A novel class of growth factor receptor bound protein 7 antagonists.

Growth factor receptor bound protein 7 (Grb7) is an adapter protein that functions as a downstream effector of growth factor mediated signal transduction. Over-expression of Grb7 has been implicated in a variety of cancers such as breast, blood, pancreatic, esophageal, and gastric carcinomas. Inhibition of Grb7 has been shown to reduce the migratory and proliferative potential of these cancers, making it an attractive therapeutic target.

Uptake of a cell permeable G7-18NATE contruct into cells and binding with the Grb-7-SH2 domain.

Grb7 is an adapter protein found to be overexpressed in several breast and other cancer cell types along with ErbB2. Grb7 is normally an interaction partner with focal adhesion kinase and in cancer cells also aberrantly interacts with ErbB2. It is thus implicated in the migratory and proliferative potential of cancer cells.