High affinity molecules disrupting GRB2 protein complexes as a therapeutic strategy for chronic myelogenous leukaemia

GRB2: A dynamic adaptor protein orchestrating cellular signaling in health and disease

GRB2, or Growth Factor Receptor-Bound Protein 2, is a pivotal adaptor protein in intracellular signal transduction pathways, particularly within receptor tyrosine kinase (RTK) signaling cascades. Its crystal structure reveals a modular architecture comprising a single Src homology 2 (SH2) domain flanked by two Src homology 3 (SH3) domains, facilitating dynamic interactions critical for cellular signaling. While SH2 domains recognize phosphorylated tyrosines, SH3 domains bind proline-rich sequences, enabling GRB2 to engage with various downstream effectors. Folding and binding studies of GRB2 in its full-length form and isolated domains highlight a complex interplay between its protein-protein interaction domains on the folding energy landscape and in driving its function. Being at the crosslink of many key molecular pathways in the cell, GRB2 possesses a role in cancer pathogenesis, particularly in mediating the Ras-mitogen activated protein kinase (MAPK) pathway. Thus, pharmacological targeting of GRB2 domains is a promising field in cancer therapy, with efforts focused on disrupting protein-protein interactions. However, the dynamic interplay driving GRB2 function suggests the presence of allosteric sites at the interface between domains that could be targeted to modulate the binding properties of its constituent domains. We propose that the analysis of GRB2 proteins from other species may provide additional insights to make the allosteric pharmacological targeting of GRB2 a more feasible strategy.

Potential pharmacological mechanisms of tanshinone IIA in the treatment of human neuroblastoma based on network pharmacological and molecular docking Technology

Tanshinone IIA (Tan-IIA) is the main bioactive component of Chinese herbal medicine salvia miltiorrhiza (Danshen). Sodium sulfonate of Tan-IIA is widely used in the treatment of cardiovascular and cerebrovascular diseases. Tan-IIA also has inhibitory effects on tumor cells such as gastric cancer, but its therapeutic effect and mechanism on human neuroblastoma have not been evaluated, so its pharmacological mechanism is systematically evaluated by the combined method of network pharmacology and molecular docking. PharmMapper and SwissTargetPrediction predicted 331 potential Tan-IIA-related targets, and 1,152 potential neuroblastoma-related targets were obtained from GeneCards, DisGeNET, DrugBank, OMIM and Therapeutic Target databases (TTD), 107 common targets for Tan-IIA and neuroblastoma. Through gene ontology (GO) functional annotation, Kyoto Encyclopedia of Genes and Genomesa (KEGG) pathway enrichment, protein-protein interaction (PPI) network and cytoHubba plug-in, 10 related signal pathways (Pathways in cancer, PI3K-Akt signaling pathway, Prostate cancer, etc.) and 10 hub genes were identified. The results of molecular docking showed that Tan-IIA could interact with 10 targets: GRB2, SRC, EGFR, PTPN1, ESR1, IGF1, MAPK1, PIK3R1, AKT1 and IGF1R. This study analyzed the related pathways and targets of Tan-IIA in the treatment of human neuroblastoma, as well as the potential anticancer and anti-tumor targets and related signaling pathways of Tan-IIA, which provides a reference for us to find and explore effective drugs for the treatment of human neuroblastoma.

Insights into the Shc Family of Adaptor Proteins

The Shc family of adaptor proteins is a group of proteins that lacks intrinsic enzymatic activity. Instead, Shc proteins possess various domains that allow them to recruit different signalling molecules. Shc proteins help to transduce an extracellular signal into an intracellular signal, which is then translated into a biological response. The Shc family of adaptor proteins share the same structural topography, CH2-PTB-CH1-SH2, which is more than an isoform of Shc family proteins; this structure, which includes multiple domains, allows for the posttranslational modification of Shc proteins and increases the functional diversity of Shc proteins. The deregulation of Shc proteins has been linked to different disease conditions, including cancer and Alzheimer’s, which indicates their key roles in cellular functions. Accordingly, a question might arise as to whether Shc proteins could be targeted therapeutically to correct their disturbance. To answer this question, thorough knowledge must be acquired; herein, we aim to shed light on the Shc family of adaptor proteins to understand their intracellular role in normal and disease states, which later might be applied to connote mechanisms to reverse the disease state.

Inhibition of Grb2 expression demonstrates an important role in BCR-ABL-mediated MAPK activation and transformation of primary human hematopoietic cells

Chronic myeloid leukemia (CML) results from the expression of the BCR/ABL oncogene in a primitive hematopoietic cell. However, BCR/ABL-activated signaling mechanisms are dependent on the cellular context in which it is expressed, and mechanisms underlying primitive human hematopoietic cell transformation by BCR-ABL are not well understood. Our previous studies have shown that BCR/ABL-Y177 has an essential role in Ras activation and human hematopoietic progenitor transformation in CML. The adapter protein growth factor receptor-binding protein-2 (Grb2) can bind phosphorylated BCR/ABL-Y177, induce Grb2-SoS complex formation and activate Ras signaling. We investigated the role of Grb2 in CML progenitor transformation by cotransducing human CD34+ cells with lentivirus vectors expressing short hairpin RNA to Grb2 and retrovirus vectors expressing BCR/ABL. We show that Grb2 knockdown significantly inhibits proliferation and survival of BCR-ABL-expressing CD34+ cells, but not control CD34+ cells. Grb2 knockdown reduced mitogen-activated protein kinase (MAPK) activity in BCR-ABL-expressing hematopoietic cells. We conclude that inhibition of Grb2 expression demonstrates an important role in BCR-ABL-mediated MAPK activation and transformation of primary human hematopoietic cells.These results support further investigation of downstream effectors of Grb2-mediated signals and targeting of Grb2 interactions in the treatment of CML.

Induction of the Ras activator Son of Sevenless 1 by environmental pollutants mediates their effects on cellular proliferation

TCDD (2,3,7,8-tetrachlorodibenzodioxin), a highly persistent environmental pollutant and a human carcinogen, is the ligand with the highest affinity for the Aryl Hydrocarbon Receptor (AhR) that induces via the AhR, xenobiotic metabolizing enzyme genes as well as several other genes. This pollutant elicits a variety of systemic toxic effects, which include cancer promotion and diverse cellular alterations that modify cell cycle progression and cell proliferation. Large-scale studies have shown that the expression of Son of Sevenless 1 (SOS1), the main mediator of Ras activation, is one of the targets of dioxin in human cultured cells. In this study, we investigated the regulation of the previously uncharacterized SOS1 gene promoter by the AhR and its ligands in the human hepatocarcinoma cell line, HepG2. We found that several environmental pollutants (AhR ligands) induce SOS1 gene expression by increasing its transcription. Chromatin immunoprecipitation experiments demonstrated that the AhR binds directly and activates the SOS1 gene promoter. We also showed that dioxin treatment leads to an activated Ras-GTP state, to ERK activation and to accelerated cellular proliferation. All these effects were mediated by SOS1 induction as shown by knock down experiments. Our data indicate that dioxin-induced cellular proliferation is mediated, at least partially, by SOS1 induction. Remarkably, our studies also suggest that SOS1 induction leads to functional effects similar to those elicited by the well-characterized oncogenic Ras mutations.

[Differential expression of MAPK-pathway genes during liver regeneration of mouse.]

To investigate the different expression profiles of MAPK pathway genes and their corresponding functions during liver regeneration, we used a CCl4 induced mouse liver regeneration model in this study. Mouse was injected with CCl4 in the abdominal cavity to cause damage in the liver and followed by liver histology examination and measurement of serum ALT levels in blood sample collected at 0, 0.5, 1.5, 4.5, and 7 d after CCl4 injection. Differentially expressed genes in the MAPK pathway during liver regeneration were analyzed using mouse cDNA microarray method (Affymetrix). The results obtained were further subjected to hierarchical clustering study and were validated with real-time PCR. Microarray hybridization identified 31 out of the 93 MAPK pathway component genes, which have significantly altered their expression levels during liver regeneration. Among them, both up- and down-regulated genes were classified into various groups according to clustering studies and functional analysis. At the initial stage of liver regeneration, the number of up-regulated genes was greater than the down-regulated genes, while at the late stage the situation was reversed. Our results suggest that MAPK pathway might play different regulatory roles in responding to different stages of liver regeneration.

Tnk1/Kos1 knockout mice develop spontaneous tumors

Tnk1/Kos1 is a non-receptor protein tyrosine kinase implicated in negatively regulating cell growth in a mechanism requiring its intrinsic catalytic activity. Tnk1/Kos1 null mice were created by homologous recombination by deleting the catalytic domain. Both Tnk1(+/-) and Tnk1(-/-) mice develop spontaneous tumors, including lymphomas and carcinomas, at high rates [27% (14 of 52) and 43% (12 of 28), respectively]. Tnk1/Kos1 expression is silenced in tumors that develop in Tnk1(+/-) mice but not in adjacent uninvolved tissue, and silencing occurs in association with Tnk1 promoter hypermethylation. Tissues and murine embryonic fibroblasts derived from Tnk1/Kos1-null mice exhibit proportionally higher levels of basal and epidermal growth factor-stimulated Ras activation that results from increased Ras-guanine exchange factor (GEF) activity. Mechanistically, Tnk1/Kos1 can directly tyrosine phosphorylate growth factor receptor binding protein 2 (Grb2), which promotes disruption of the Grb2-Sos1 complex that mediates growth factor-induced Ras activation, providing dynamic regulation of Ras GEF activity with suppression of Ras. Thus, Tnk1/Kos1 is a tumor suppressor that functions to down-regulate Ras activity.

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.

The cytotoxicity of a Grb2-SH3 inhibitor in Bcr-Abl positive K562 cells

Chronic myelogenous leukemia (CML) is characterized by the presence of Bcr-Abl oncoprotein. Gleevec has been designed to treat many CML patients by specifically targeting Bcr-Abl, but resistance to it is already apparent in many cases. In CML cells, Bcr-Abl activates several signaling pathways, including the Ras-dependent pathway, in which growth factor receptor binding 2 (Grb2) acts as an adaptor protein. A specific Grb2-SH3 inhibitor (denoted as peptidimer-c) that disrupts Grb2-Sos complex was designed and synthesized in our laboratory. In this study, we investigated the effect and the molecular mechanism of this inhibitor. Peptidimer-c was shown to bind to Grb2 in K562 cells, a cell line over-expressing Bcr-Abl oncoprotein. It caused cytotoxicity in the cells, and inhibited their ability of colony formation in the semi-solid medium. It was shown to induce apoptosis of K562 cells in a dose-dependent mode, the apoptotic effect of peptidimer-c being associated with caspase-3 activation. The effect of peptidimer-c on growth inhibition was also shown to be accompanied by S-phase arrest of cell cycle mediated by down-regulation of cyclin A and Cdk2, as well as phospho-Cdk2. The above results indicated that peptidimer-c may be another potential therapeutic agent for CML, which can induce S-phase arrest in the Bcr-Abl positive K562.

Molecular regulation of receptor tyrosine kinases in hematopoietic malignancies

Dysregulation of receptor tyrosine kinase (RTK) activity has been implicated in the progression of a variety of human leukemias. Most notably, mutations and chromosomal translocations affecting regulation of tyrosine kinase activity in the Kit receptor, the Flt3 receptor, and the PDGFbeta/FGF1 receptors have been demonstrated in mast cell leukemia, acute myeloid leukemia (AML), and chronic myelogenous leukemias (CML), respectively. In addition, critical but non-overlapping roles for the Ron and Kit receptor tyrosine kinases in the progression of animal models of erythroleukemia have been demonstrated [Persons, D., Paulson, R., Loyd, M., Herley, M., Bodner, S., Bernstein, A., Correll, P. and Ney, P., 1999. Fv2 encodes a truncated form of the Stk receptor tyrosine kinase. Nat. Gen. 23, 159-165.; Subramanian, A., Teal, H.E., Correll, P.H. and Paulson, R.F., 2005. Resistance to friend virus-induced erythroleukemia in W/Wv mice is caused by a spleen-specific defect which results in a severe reduction in target cells and a lack of Sf-Stk expression. J. Virol. 79 (23), 14586-14594.]. The various classes of RTKs implicated in the progression of leukemia have been recently reviewed [Reilly, J., 2003. Receptor tyrosine kinases in normal and malignant haematopoiesis. Blood Rev. 17 (4), 241-248.]. Here, we will discuss the mechanism by which alterations in these receptors result in transformation of hematopoietic cells, in the context of what is known about the molecular regulation of RTK activity, with a focus on our recent studies of the Ron receptor tyrosine kinase.

Facile synthesis and application of uniformly 13C, 15N-labeled phosphotyrosine for ligand binding studies

The first synthesis of [U-13C, 15N] labeled phosphotyrosine is described. Preliminary studies toward the binding of phosphotyrosine to an SH2 domain have been performed by means of heteronuclear NMR.

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

Although considerable effort has been devoted to developing Grb2 SH2 domain-binding antagonists, important questions related to ligand specificity, and identification of intracellular targets remain unanswered. In order to begin addressing these issues, the design, synthesis, and evaluation of a novel biotinylated macrocycle are reported that bears biotin functionality at a C-terminal rather than the traditional N-terminal position. With a Grb2 SH2 domain-binding K(eq) value of 3.4 nM, the title macrocycle (5) is among the most potent biotinylated SH2 domain-binding ligands yet disclosed. This should be a useful tool for elucidating physiological targets of certain Grb2 SH2 domain-binding antagonists.

Utilization of a nitrobenzoxadiazole (NBD) fluorophore in the design of a Grb2 SH2 domain-binding peptide mimetic

Fluorescence labeling has become a general technique for studying the intracellular accumulation and localization of exogenously administered materials. Reported herein is a low nanomolar affinity Grb2 SH2 domain-binding antagonist that utilizes the environmentally-sensitive nitrobenzoxadiazole (NBD) fluorophore as a naphthyl replacement. This novel agent should serve as a useful tool to visualize the actions of this class of Grb2 SH2 domain-binding antagonists in whole cell systems.

Examination of Phosphoryl-Mimicking Functionalities within a Macrocyclic Grb2 SH2 Domain-Binding Platform

Reported herein are the design, synthesis, and Grb2 SH2 domain-binding affinities of several phosphoryl-mimicking groups displayed within the context of a conformationally constrained macrocyclic platform. With use of surface plasmon resonance techniques, single-digit nanomolar affinities were exhibited by phosphonic acid and malonyl-containing diacidic phosphoryl mimetics (for 4h and 4g, K(D) = 1.47 and 3.62 nM, respectively). Analogues containing monoacidic phosphoryl mimetics provided affinities of K(D) = 16-67 nM. Neutral phosphoryl-mimicking groups did not show appreciable binding.

Animal models of chronic myelogenous leukemia

Of the current mouse chronic myelogenous leukemia (CML) models,the murine bone marrow (BM) transduction and transplantation model most efficiently mimics many of the central features of human CML. In this model, lethally irradiated mice are reconstituted with primary murine BM cells transduced with a P210BCR/ABL retrovirus. All recipient mice develop a fatal peripheral blood and BM granulocytosis and splenomegaly, a disease termed the murine CML-like myeloproliferative disorder. This model has been used to establish the causative role of Bcr/Abl in CML, identify those signaling pathways and regions of Bcr/Abl critical for leukemogenesis, and explore the limitations of targeted CML therapy. Future refinements in this CML mouse model will make it a more effective tool for studying imatinib-resistant CML, reproducing chronic- and blastic-phase human CML, and performing CML progenitor studies.

Development of l-3-aminotyrosine suitably protected for the synthesis of a novel nonphosphorylated hexapeptide with low-nanomolar Grb2-SH2 domain-binding affinity

Synthesis of orthogonally protected (2S)-2-amino-3-(3-amino-4-hydroxy-phenyl)-propionic acid (10) suitable for solid phase peptide synthesis and its first use for the preparation of nonphosphorylated Grb2-SH2 domain antagonists (4a-c) are reported. The 3-aminotyrosine containing sulfoxide-cyclized hexapeptide (4b) exhibited potent Grb2-SH2 domain binding affinity with IC50 = 50 nM, which represents the highest affinity yet reported for a peptide inhibitor against Grb2-SH2 domain with only 6 residues free of phosphotyrosine or phosphotyrosine mimics. This potent small peptidomimetic 4b may be representative of a new class of therapeutically relevant Grb2-SH2 domain-directed agents, and acts as a chemotherapeutic lead for the treatment of erbB2-related cancers.

A novel macrocyclic tetrapeptide mimetic that exhibits low-picomolar Grb2 SH2 domain-binding affinity

The growth factor receptor-bound protein 2 (Grb2) is an SH2 domain-containing docking module that participates in the signaling of numerous oncogenic growth factor receptor protein-tyrosine kinases (PTKs). Presented herein is a 5-methylindolyl-containing macrocyclic tetrapeptide mimetic (5) that binds to Grb2 SH2 domain protein with K(d)=75 pM. This represents the highest affinity yet reported for a synthetic inhibitor against any SH2 domain. In whole cell assays this novel analogue is able to effectively block the association of Grb2 to cognate cytoplasmic erbB-2 at IC(50)<10nM without prodrug derivatization or the addition of carrier peptide motifs. Anti-mitogenic effects against erbB-2-dependent breast cancers are achieved at non-cytotoxic concentrations (IC(50)=0.6 microM). Macrocycle 5 may be representative of a new class of therapeutically relevant Grb2 SH2 domain-directed agents.