Potent blockade of hepatocyte growth factor-stimulated cell motility, matrix invasion and branching morphogenesis by antagonists of Grb2 Src homology 2 domain interactions

Identification and Optimization of Protein Tyrosine Phosphatase Inhibitors Via Fragment Ligation

Phosphotyrosine biomimetics are starting points for potent inhibitors of protein tyrosine phosphatases (PTPs) and, thus, crucial for drug development. Their identification, however, has been heavily driven by rational design, limiting the discovery of diverse, novel, and improved mimetics. In this chapter, we describe two screening approaches utilizing fragment ligation methods: one to identify new mimetics and the other to optimize existing mimetics into more potent and selective inhibitors.

Synthesis and structural characterization of a monocarboxylic inhibitor for GRB2 SH2 domain

A monocarboxylic inhibitor was designed and synthesized to disrupt the protein-protein interaction (PPI) between GRB2 and phosphotyrosine-containing proteins. Biochemical characterizations show compound 7 binds with the Src homology 2 (SH2) domain of GRB2 and is more potent than EGFR₁₀₆₈ phosphopeptide 14-mer. X-ray crystallographic studies demonstrate compound 7 occupies the GRB2 binding site for phosphotyrosine-containing sequences and reveal key structural features for GRB2-inhibitor binding. This compound with a -1 formal charge offers a new direction for structural optimization to generate cell-permeable inhibitors for this key protein target of the aberrant Ras-MAPK signaling cascade.

Association between the HGF/c‑MET signaling pathway and tumorigenesis, progression and prognosis of hepatocellular carcinoma (Review)

Hepatocellular carcinoma (HCC) is one of the most aggressive and lethal malignancies with a rising incidence, and is characterized by rapid progression, frequent metastasis, late diagnosis, high postoperative recurrence and poor prognosis. Therefore, novel treatment strategies for HCC, particularly advanced HCC, are urgently required. The hepatocyte growth factor (HGF)/c‑mesenchymal‑epithelial transition receptor (c‑MET) axis is a key signaling pathway in HCC and is strongly associated with its highly malignant features. Available treatments based on HGF/c‑MET inhibition may prolong the lifespan of patients with HCC; however, they do not achieve the desired therapeutic effects. The aim of the present article was to review the basic knowledge regarding the role of the HGF/c‑MET signaling pathway in HCC, and examine the association between the HGF/c‑MET signaling pathway and the tumorigenesis, progression and prognosis of HCC.

In Silico Screening to Identify Inhibitors of Growth Factor Receptor 2-Focal Adhesion Kinase Interaction for Therapeutic Treatment of Pathological Cardiac Hypertrophy

The focal adhesion kinase-growth factor receptor 2 (FAK-Grb2) protein-protein interaction is implicated in pathogenesis of stress-induced cardiac hypertrophy. The focal adhesion targeting (FAT) domain of FAK unfolds to form a structural intermediate that interacts with a multibinding hot spot in the SH2 domain of Grb2. Disruption of the Grb2-FAT interaction is a therapeutic strategy for prevention of pathological cardiac hypertrophy. A pharmacophore was generated on the basis of structural and electrostatic properties of FAT bound to FAK using the Forge tool (Cresset). This pharmacophore was used as a query for Blaze server (Cresset) to screen a selectively enriched chemical library of 4,32,508 small molecules. The compounds selected were further filtered by hierarchical flexible docking approach using AutoDock v4. From the favorably docked compounds, five were selected on the basis of good adsorption, distribution, metabolism, excretion, and toxicity (ADMET) properties using SwissADME, MedChem Designer v.3, and MOLINSPIRATION. Stability of the binding mode of the inhibitors was further confirmed by molecular dynamic simulation study with AMBER v15 for a simulation time of 50 ns in aqueous environment. PM2307 was identified as the best inhibitor in terms of pharmacophoric features, dock score, and in silico ADMET analysis. The calculated binding affinity of PM2307 was better than that of the FAT-Grb2 complex as well as a previously reported small molecule inhibitor. PM2307 is also a quinolyl derivative sharing a similar scaffold with ofloxacin drugs, asserting its drug-like properties. Thus, it was proposed as a lead compound for development of drugs for pathological cardiac hypertrophy.

MET targeting: time for a rematch

MET, the receptor tyrosine kinase (RTK) for hepatocyte growth factor, is a proto-oncogene involved in embryonic development and throughout life in homeostasis and tissue regeneration. Deregulation of MET signaling has been reported in numerous malignancies, prompting great interest in MET targeting for cancer therapy. The present review offers a summary of the biology of MET and its known functions in normal physiology and carcinogenesis, followed by an overview of the most relevant MET-targeting strategies and corresponding clinical trials, highlighting both past setbacks and promising future prospects. By placing their efforts on a more precise stratification strategy through the genetic analysis of tumors, modern trials such as the NCI-MATCH trial could revive the past enthusiasm for MET-targeted therapy.

The Therapeutic Targeting of HGF/c-Met Signaling in Hepatocellular Carcinoma: Alternative Approaches

The poor prognosis of hepatocellular carcinoma (HCC), one of the most devastating cancers worldwide, is due to frequent recurrence and metastasis. Among the metastatic factors in the tumor microenvironment, hepatocyte growth factor (HGF) has been well known to play critical roles in tumor progression, including HCC. Therefore, c-Met is now regarded as the most promising therapeutic target for the treatment of HCC. However, there are still concerns about resistance and the side effects of using conventional inhibitors of c-Met, such as tyrosine kinase inhibitors. Recently, many alternative strategies of c-Met targeting have been emerging. These include targeting the downstream effectors of c-Met, such as hydrogen peroxide-inducible clone 5 (Hic-5), to block the reactive oxygen species (ROS)-mediated signaling for HCC progression. Also, inhibition of endosomal regulators, such as PKCε and GGA3, may perturb the c-Met endosomal signaling for HCC cell migration. On the other hand, many herbal antagonists of c-Met-dependent signaling, such as saponin, resveratrol, and LZ-8, were identified. Taken together, it can be anticipated that more effective and safer c-Met targeting strategies for preventing HCC progression can be established in the future.

A viral microRNA downregulates metastasis suppressor CD82 and induces cell invasion and angiogenesis by activating the c-Met signaling

Kaposi’s sarcoma (KS) is the most common AIDS-associated malignancy etiologically caused by Kaposi’s sarcoma-associated herpesvirus (KSHV). KS is a highly disseminated and vascularized tumor comprised of poorly differentiated spindle-shaped endothelial cells. KSHV encodes 12 pre-microRNAs (pre-miRNAs) that yield 25 mature miRNAs, but their roles in KSHV-induced tumor dissemination and angiogenesis remain largely unknown. KSHV-encoded miR-K12-6 (miR-K6) can produce two mature miRNAs, miR-K6-3p and miR-K6-5p. Recently, we have shown that miR-K6-3p promoted cell migration and angiogenesis by directly targeting SH3 domain binding glutamate-rich protein (SH3BGR) (PLoS Pathog. 2016;12(4):e1005605). Here, by using mass spectrometry, bioinformatics analysis and luciferase reporter assay, we showed that miR-K6-5p directly targeted the coding sequence (CDS) of CD82 molecule (CD82), a metastasis suppressor. Ectopic expression of miR-K6-5p specifically inhibited the expression of endogenous CD82 and strongly promoted endothelial cells invasion in vitro and angiogenesis in vivo. Overexpression of CD82 significantly inhibited cell invasion and angiogenesis induced by miR-K6-5p. Mechanistically, CD82 directly interacted with c-Met to inhibit its activation. MiR-K6-5p directly repressed CD82, relieving its inhibition on c-Met activation and inducing cell invasion and angiogenesis. Deletion of miR-K6 from KSHV genome abrogated KSHV suppression of CD82 resulting in compromised KSHV activation of c-Met pathway, and KSHV-induced invasion and angiogenesis. In conclusion, these results show that by inhibiting CD82, KSHV miR-K6-5p promotes cell invasion and angiogenesis by activating the c-Met pathway. Our findings illustrate that KSHV miRNAs may play an essential role in the dissemination and angiogenesis of KSHV-induced malignancies.

Targeting SH2 domains in breast cancer

Breast cancer is among the most commonly diagnosed cancer types in women worldwide and is the second leading cause of cancer-related disease in the USA. SH2 domains recruit signaling proteins to phosphotyrosine residues on aberrantly activated growth factor and cytokine receptors and contribute to cancer cell cycling, metastasis, angiogenesis and so on. Herein we review phosphopeptide mimetic and small-molecule approaches targeting the SH2 domains of Grb2, Grb7 and STAT3 that inhibit their targets and reduce proliferation in in vitro breast cancer models. Only STAT3 inhibitors have been evaluated in in vivo models and have led to tumor reduction. Taken together, these studies suggest that targeting SH2 domains is an important approach to the treatment of breast cancer.

Reciprocal activating crosstalk between c-Met and caveolin 1 promotes invasive phenotype in hepatocellular carcinoma

c-Met, the receptor for Hepatocyte Growth Factor (HGF), overexpressed and deregulated in Hepatocellular Carcinoma (HCC). Caveolin 1 (CAV1), a plasma membrane protein that modulates signal transduction molecules, is also overexpressed in HCC. The aim of this study was to investigate biological and clinical significance of co-expression and activation of c-Met and CAV1 in HCC. We showed that c-Met and CAV1 were co-localized in HCC cells and HGF treatment increased this association. HGF-triggered c-Met activation caused a concurrent rise in both phosphorylation and expression of CAV1. Ectopic expression of CAV1 accelerated c-Met signaling, resulted in enhanced migration, invasion, and branching-morphogenesis. Silencing of CAV1 downregulated c-Met signaling, and decreased migratory/invasive capability of cells and attenuated branching morphogenesis. In addition, activation and co-localization of c-Met and CAV1 were elevated during hepatocarcinogenesis. In conclusion reciprocal activating crosstalk between c-Met and CAV1 promoted oncogenic signaling of c-Met contributed to the initiation and progression of HCC.

Met degradation by SAIT301, a Met monoclonal antibody, reduces the invasion and migration of nasopharyngeal cancer cells via inhibition of EGR-1 expression

Nasopharyngeal carcinoma (NPC) is a common malignant tumor with high invasive and metastatic potential. The hepatocyte growth factor (HGF)-Met signaling pathway has a critical role in mediating the invasive growth of many different types of cancer, including head and neck squamous cell carcinoma. HGF also stimulates NPC cell growth and invasion in the cell line model. In this study, we determined the inhibitory effect of Met, using a Met-targeting monoclonal antibody (SAIT301), on the invasive and growth potential of NPC cell lines. Met inhibition by SAIT301 resulted in highly significant inhibition of cell migration and invasion in both the HONE1 and HNE1 cell lines. In addition, we also found that co-treatment of SAIT301 and HGF decreased the anchorage-independent growth induced by HGF in HNE1 cell lines. After SAIT301 treatment, Met, together with its downstream signaling proteins, showed downregulation of p-Met and p-ERK, but not p-AKT, in both HONE1 and HNE1 cell lines. Interestingly, we found that HGF treatment of NPC cell lines induced early growth response protein (EGR-1) expression, which is involved in cell migration and invasion. In addition, co-treatment with SAIT301 and HGF inhibited the HGF-induced expression of EGR-1. Next, knockdown of EGR-1 using small-interfering RNA inhibited HGF-induced cell invasion in NPC cell lines, suggesting that the expression level of EGR-1 is important in HGF-induced cell invasion of NPC cells. Therefore, the results support that SAIT301 inhibited Met activation as well as the downstream EGR-1 expression and could have therapeutic potential in NPC. Taken together, we suggest that Met is an anticancer therapeutic target for NPC that warrants further investigation and clinical trials and SAIT301 may be a promising tool for NPC therapy.

Met receptor-induced Grb2 or Shc signals both promote transformation of intestinal epithelial cells, albeit they are required for distinct oncogenic functions

Background

Deregulation of receptor tyrosine kinases (RTK) contributes to the initiation and progression of intestinal-derived epithelial cancers, including colorectal cancer (CRC). However, the roles of the proximal signaling molecules engaged by RTKs in different oncogenic functions of CRC remain unclear.

Methods

Herein, the functional impact of expressing variant forms of the oncogenic Met receptor (Tpr-Met) that selectively recruit the adaptor proteins Grb2 or Shc was investigated in a model derived from normal intestinal epithelial cells (IEC-6). An RNA interference (RNAi) approach was used to define the requirement of Grb2 or Shc in Tpr-Met-transformed IEC-6 cells. Since Grb2 and Shc couple RTKs to the activation of the Ras/MEK/Erk and PI3K/Akt pathways, Erk and Akt phosphorylation/activation states were monitored in transformed IEC-6 cells, and a pharmacological approach was employed to provide insights into the roles of these pathways in oncogenic processes evoked by activated Met, and downstream of Grb2 and Shc.

Results

We show, for the first time, that constitutive activation of either Grb2 or Shc signals in IEC-6 cells, promotes morphological transformation associated with down-regulation of E-cadherin, as well as increased cell growth, loss of growth contact inhibition, anchorage-independent growth, and resistance to serum deprivation and anoikis. Oncogenic activation of Met was revealed to induce morphological transformation, E-cadherin down-regulation, and protection against anoikis by mechanisms dependent on Grb2, while Shc was shown to be partly required for enhanced cell growth. The coupling of activated Met to the Ras/MEK/Erk and PI3K/Akt pathways, and the sustained engagement of Grb2 or Shc in IECs, was shown to trigger negative feedback, limiting the extent of activation of these pathways. Nonetheless, morphological alterations and E-cadherin down-regulation induced by the oncogenic Tpr-Met, and by Grb2 or Shc signals, were blocked by MEK, but not PI3K, inhibitors while the enhanced growth and resistance to anoikis induced by Tpr-Met were nearly abolished by co-treatment with both inhibitors.

Conclusion

Overall, these results identify Grb2 and Shc as central signaling effectors of Met-driven progression of intestinal epithelial-derived cancers. Notably, they suggest that Grb2 may represent a promising target for the design of novel CRC therapies.

MiR-376c down-regulation accelerates EGF-dependent migration by targeting GRB2 in the HuCCT1 human intrahepatic cholangiocarcinoma cell line

MicroRNA miR-376c was expressed in normal intrahepatic biliary epithelial cells (HIBEpiC), but was significantly suppressed in the HuCCT1 intrahepatic cholangiocarcinoma (ICC) cell line. The biological significance of the down-regulation of miR-376c in HuCCT1 cells is unknown. We hypothesized that miR-376c could function as a tumor suppressor in these cells. To test this hypothesis, we sought the targets of miR-376c, and characterized the effect of its down-regulation on HuCCT1 cells. We performed proteomic analysis of miR-376c-overexpressing HuCCT1 cells to identify candidate targets of miR-376c, and validated these targets by 3′-UTR reporter assay. Transwell migration assays were performed to study the migratory response of HuCCT1 cells to miR-376c overexpression. Furthermore, microarrays were used to identify the signaling that were potentially involved in the miR-376c-modulated migration of HuCCT1. Finally, we assessed epigenetic changes within the potential promoter region of the miR-376c gene in these cells. Proteomic analysis and subsequent validation assays showed that growth factor receptor-bound protein 2 (GRB2) was a direct target of miR-376c. The transwell migration assay revealed that miR-376c significantly reduced epidermal growth factor (EGF)-dependent cell migration in HuCCT1 cells. DNA microarray and subsequent pathway analysis showed that interleukin 1 beta and matrix metallopeptidase 9 were possible participants in EGF-dependent migration of HuCCT1 cells. Bisulfite sequencing showed higher methylation levels of CpG sites upstream of the miR-376c gene in HuCCT1 relative to HIBEpiC cells. Combined treatment with the DNA-demethylating agent 5-aza-2′-deoxycytidine and the histone deacetylase inhibitor trichostatin A significantly upregulated the expression of miR-376c in HuCCT1 cells. We revealed that epigenetic repression of miR-376c accelerated EGF-dependent cell migration through its target GRB2 in HuCCT1 cells. These findings suggest that miR-376c functions as a tumor suppressor. Since metastasis is the major cause of death in ICC, microRNA manipulation could lead to the development of novel anti-cancer therapy strategies for ICC.

Modulation of c-Met signaling and cellular sensitivity to radiation: potential implications for therapy

The c-Met/hepatocyte growth factor receptor and its family members are known to promote cancer cell migration and invasion. Signaling within and beyond this pathway contributes to the systemic spread of metastases through induction of the epithelial-mesenchymal transition, a process also implicated in mediating resistance to current anticancer therapies, including radiation. Induction of c-Met has also been observed after irradiation, suggesting that c-Met participates in radiation-induced disease progression through the epithelial-mesenchymal transition. Therefore, c-Met inhibition is an attractive target for potentially mitigating radiation resistance. This article summarizes key findings regarding crosstalk between radiotherapy and c-Met and discusses studies performed to date in which c-Met inhibition was used as a strategy to increase cellular radiosensitivity.

Targeting the HGF-cMET Axis in Hepatocellular Carcinoma

Under normal physiological conditions, the hepatocyte growth factor (HGF) and its receptor, the MET transmembrane tyrosine kinase (cMET), are involved in embryogenesis, morphogenesis, and wound healing. The HGF-cMET axis promotes cell survival, proliferation, migration, and invasion via modulation of epithelial-mesenchymal interactions. Hepatocellular cancer (HCC) is the third most common cause of worldwide cancer-related mortality; advanced disease is associated with a paucity of therapeutic options and a five-year survival rate of only 10%. Dysregulation of the HGF-cMET pathway is implicated in HCC carcinogenesis and progression through activation of multiple signaling pathways; therefore, cMET inhibition is a promising therapeutic strategy for HCC treatment. The authors review HGF-cMET structure and function in normal tissue and in HCC, cMET inhibition in HCC, and future strategies for biomarker identification.

Targeting c-Met as a promising strategy for the treatment of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a severe condition that is found worldwide. Liver transplantation, surgical resection, and local-regional therapy such as transarterial chemoembolization have made great progress and play a dominant role in HCC management. However, the high frequency of tumor recurrence and/or metastasis after those treatments acquires systematic drug intervention. The approval of sorafenib, an agent that targets receptor tyrosine kinases (RTKs), as the first effective drug for systemic treatment of HCC represents a milestone in treatment of this disease. As a typical member of the RTK family, c-Met represents an intriguing target for cancer therapy. However, the role of the c-Met signal transduction pathway is less unambiguous in HCC pathology, giving rise to concerns about the feasibility of utilizing c-Met targeting approaches for HCC treatment. Recently, studies on des-γ-carboxy prothrombin, an abnormal cytokine secreted by HCC cells, by the current authors and other researchers have highlighted the critical role of c-Met signaling in HCC progression. This review takes a second look at the c-Met signal transduction pathway and discusses the possibility of targeting c-Met as a therapeutic strategy for HCC treatment.

Systemic administration of naked plasmid encoding HGF attenuates puromycin aminonucleoside-induced damage of murine glomerular podocytes

Podocyte injury is considered to play important roles in the pathogenesis of human glomerular disease. There is accumulating evidence suggesting that hepatocyte growth factor (HGF) elicits preventive activity for glomerular cells in animal models of chronic renal diseases. In this study, we demonstrated that delivery of a naked plasmid vector encoding the human HGF gene into mice by a hydrodynamic-based in vivo gene transfection approach markedly reduced proteinuria and attenuated podocyte injury in a mouse model induced by puromycin aminonucleoside (PAN) injection. Systemic administration by rapid injection via the tail vein of a naked plasmid containing HGF cDNA driven under a cytomegalovirus promoter (pCMV-HGF) produced a remarkable level of human HGF protein in the circulation. Tissue distribution studies suggested that the kidney expressed a high level of the HGF transgene. Meanwhile, compared with tubules and interstitium, a higher level of exogenous HGF protein was detected in the glomeruli. Administration of pCMV-HGF dramatically abated the urine albumin excretion and podocyte injury in PAN nephropathy in mice. Exogenous expression of HGF produced evidently beneficial effects, leading to restoration of Wilms' tumor-1 (WT1) and α-actinin-4 expression and attenuation of ultrastructural damage of the podocytes. In vitro, HGF not only restored WT1 and α-actinin-4 expression but also inhibited albumin leakage of podocytes incubated with PAN in a Transwell culture chamber. These results suggest that HGF might provide a novel strategy for amelioration of podocyte injury.

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.

Targeting the Met signaling pathway in renal cancer

Renal cell carcinoma (RCC), the most common form of kidney cancer, accounts for 3% of all adult malignancies and its incidence has significantly increased over the last 20 years. RCC claims 13,000 lives annually in the USA and more than 100,000 worldwide. A better understanding of the molecular basis of RCC has facilitated the development of novel and more selective therapeutic approaches. An important role in RCC oncogenesis is played by the receptor for HGF, Met, which has attracted considerable attention, more recently as a molecular target for cancer therapy, and several drugs selectively targeting this pathway are now in clinical trials. This review will focus on efforts to understand the role of the Met signaling pathway in renal cancer and how this has contributed to the development of potent and selective drug candidates.

Targeting MET as a strategy to overcome crosstalk-related resistance to EGFR inhibitors

The hepatocyte growth factor (HGF)-mesenchymal-epithelial transition factor (MET) pathway has a key role in carcinogenesis; it is implicated in proliferation, inhibition of apoptosis, angiogenesis, migration, invasiveness, and metastasis. All of these molecular events are driven through membrane and intracellular coplayers and several downstream effector proteins. MET has been shown to cross react with epithelial growth factor receptor (EGFR) proteins and possibly substitutes their activity, thus conferring resistance to EGFR-targeting drugs. Therefore, identification of MET inhibitors might lead to new treatments for MET-triggered neoplasia and improve the sensitivity of molecularly targeted antineoplastic compounds that are currently in use. In this Review, we outline current data regarding the HGF-MET pathway during carcinogenesis and the strategies for therapeutic targeting of this pathway. We also discuss the rationale and future perspectives of the combinatorial blockade of HGF-MET and EGFR signalling cascades in cancer treatment.

Conformationally constrained peptidomimetic inhibitors of signal transducer and activator of transcription. 3: Evaluation and molecular modeling

Signal transducer and activator of transcription 3 (Stat3) is involved in aberrant growth and survival signals in malignant tumor cells and is a validated target for anticancer drug design. We are targeting its SH2 domain to prevent docking to cytokine and growth factor receptors and subsequent signaling. The amino acids of our lead phosphopeptide, Ac-pTyr-Leu-Pro-Gln-Thr-Val-NH(2), were replaced with conformationally constrained mimics. Structure-affinity studies led to the peptidomimetic, pCinn-Haic-Gln-NHBn (21), which had an IC(50) of 162 nM (fluorescence polarization), compared to 290 nM for the lead phosphopeptide (pCinn = 4-phosphoryloxycinnamate, Haic = (2S,5S)-5-amino-1,2,4,5,6,7-hexahydro-4-oxo-azepino[3,2,1-hi]indole-2-carboxylic acid). pCinn-Haic-Gln-OH was docked to the SH2 domain (AUTODOCK), and the two highest populated clusters were subjected to molecular dynamics simulations. Both converged to a common peptide conformation. The complex exhibits unique hydrogen bonding between Haic and Gln and Stat3 as well as hydrophobic interactions between the protein and pCinn and Haic.

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.

Rhein inhibits invasion and migration of human nasopharyngeal carcinoma cells in vitro by down-regulation of matrix metalloproteinases-9 and vascular endothelial growth factor

Progression of cancer invasion is believed to be dependent on the remodeling of extracellular matrix induced by tumor cells. Rhein has been shown to inhibit the growth and proliferation of human nasopharyngeal carcinoma (NPC) cells. However, the molecular mechanism underlying rhein-induced inhibition of cancer invasion has not been explored. Herein, we show that rhein could inhibit the invasion and migration of NPC cells in vitro. Rhein inhibits invasion by reducing the expression of matrix metalloproteinase-9 (MMP-9) and vascular endothelial growth factor (VEGF). Moreover, we demonstrate that the pathway involved in rhein-inhibited invasion is presumably through the growth factor receptor bound protein 2/son of sevenless-Ras-mitogen-activated protein kinase (GRB2/SOS-Ras-MAPK) pathway, as shown by an decrease in the expression levels of GRB2, SOS-1 and Ras as well as led to suppression of the phosphorylation of extracellular signal-regulated kinase (ERK) and p38 MAPK. Further study has shown that rhein also inhibited activation of transcription factor nuclear factor kappaB (NF-kappaB), which is known to implicate the regulation of MMP-9 and VEGF gene expression in cancer invasion. Our findings suggest that rhein inhibits the invasion of NPC cells may be mediated in part through the suppression of MMP-9 and VEGF expression via the modulation of NF-kappaB signaling pathway.

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.

Planar microfluidic chamber for generation of stable and steep chemoattractant gradients

The extracellular availability of growth factors, hormones, chemokines, and neurotransmitters under gradient conditions is required for directional cellular responses such as migration, axonal pathfinding, and tissue patterning. These responses are, in turn, important in disease and developmental processes. This article addresses critical barriers toward devising a chemotaxis assay that is broadly applicable for different kinds of cancer cells through the design of a microfluidic chamber that produces a steep gradient of chemoattractant. Photolithography was used to create microchannels for chemoattractant delivery, flow diversion barriers/conduits, and small outlets in the form of apertures. The 1-microm apertures were made at the active surface by uncapping a thin (1.5 microm) layer of AZ1518. This process also created a vertical conduit that diverted the flow such that it occurred perpendicularly to the active, experimental surface where the gradients were measured. The other side of the vertical conduit opened to underlying 20-microm deep channels that carried microfluidic flows of tracer dyes/growth factors. Modeled data using computational fluid dynamics produced gradients that were steep along the horizontal, active surface. This simulation mirrors empirically derived gradients obtained from the flow analyses of fluorescent compounds. The open chamber contains a large buffer volume, which prevents chemoattractant saturation and permits easy cell and compound manipulation. The technique obviates the use of membranes or laminar flow that may hinder imaging, rinsing steps, cell seeding, and treatment. The utility of the chamber in the study of cell protrusion, an early step during chemotaxis, was demonstrated by growing cancer cells in the chamber, inducing a chemoattractant gradient using compressed air at 0.7 bar, and performing time-lapse microscopy. Breast cancer cells responded to the rapidly developed and stable gradient of epidermal growth factor by directing centroid positions toward the gradient and by forming a leading edge at a speed of 0.45 microm/min.

Drug development of MET inhibitors: targeting oncogene addiction and expedience

The MET tyrosine kinase stimulates cell scattering, invasion, protection from apoptosis and angiogenesis, thereby acting as a powerful expedient for cancer dissemination. MET can also be genetically selected for the long-term maintenance of the primary transformed phenotype, and some tumours appear to be dependent on (or 'addicted' to) sustained MET activity for their growth and survival. Because of its dual role as an adjuvant, pro-metastatic gene for some tumour types and as a necessary oncogene for others, MET is a versatile candidate for targeted therapeutic intervention. Here we discuss recent progress in the development of molecules that inhibit MET function and consider their application in a subset of human tumours that are potentially responsive to MET-targeted therapies.

Mimp, a mitochondrial carrier homologue, inhibits Met-HGF/SF-induced scattering and tumorigenicity by altering Met-HGF/SF signaling pathways

We have recently shown that Mimp, a mitochondrial carrier protein homologue, is induced by Met-hepatocyte growth factor/scatter factor (HGF/SF) signaling and decreases the mitochondrial membrane potential in DA3 mammary adenocarcinoma cells. We show here that induction of Mimp leads to growth arrest in response to HGF/SF by arresting cells at the S phase of the cell cycle. Induction of Mimp or its transient expression does not lead to apoptosis. Mimp also attenuates HGF/SF-induced cellular scattering in vitro and tumor growth in vivo. The exogenous induction of Mimp at levels similar to its endogenous induction by HGF/SF increases the level of the Met protein and its phosphorylation by HGF/SF but reduces the levels of Shc and prevents the HGF/SF-induced tyrosine phosphorylation of Grb2 and Shc. In contrast, the level of phosphatidylinositol 3-kinase (PI3K) increases following Mimp induction and the level of phosphorylated PI3K in response to HGF/SF is unaffected by the exogenous induction of Mimp. Moreover, exogenous Mimp prevents the HGF/SF-induced transcription of the serum response element-luciferase reporter gene. Our results show that Mimp expression reduces Met-HGF/SF-induced proliferation and scattering by attenuating and altering the downstream signaling of Met. These data show a new link between a tyrosine kinase growth factor receptor and a mitochondrial carrier homologue that regulates cellular growth, motility, and tumorigenicity.

Caveolin-1 reduces osteosarcoma metastases by inhibiting c-Src activity and met signaling

Caveolin-1 (Cav-1) is highly expressed in normal osteoblasts. This article reports that Cav-1 down-regulation is part of osteoblast transformation and osteosarcoma progression and validates its role as oncosuppressor in human osteosarcoma. A survey of 6-year follow-up indicates a better overall survival for osteosarcoma expressing a level of Cav-1 similar to osteoblasts. However, the majority of primary osteosarcoma shows significantly lower levels of Cav-1 than normal osteoblasts. Accordingly, Met-induced osteoblast transformation is associated with Cav-1 down-regulation. In vitro, osteosarcoma cell lines forced to overexpress Cav-1 show reduced malignancy with inhibited anchorage-independent growth, migration, and invasion. In vivo, Cav-1 overexpression abrogates the metastatic ability of osteosarcoma cells. c-Src and c-Met tyrosine kinases, which are activated in osteosarcoma, colocalize with Cav-1 and are inhibited on Cav-1 overexpression. Thus, Cav-1 behaves as an oncosuppressor in osteosarcoma. Altogether, data suggest that Cav-1 down-modulation might function as a permissive mechanism, which, by unleashing c-Src and Met signaling, enables osteosarcoma cells to invade neighboring tissues. These data strengthen the rationale to target c-Src family kinases and/or Met receptor to improve the extremely poor prognosis of metastatic osteosarcoma.

Inhibition of tumor metastasis by a growth factor receptor bound protein 2 Src homology 2 domain-binding antagonist

Metastasis, the primary cause of death in most forms of cancer, is a multistep process whereby cells from the primary tumor spread systemically and colonize distant new sites. Blocking critical steps in this process could potentially inhibit tumor metastasis and dramatically improve cancer survival rates; however, our understanding of metastasis at the molecular level is still rudimentary. Growth factor receptor binding protein 2 (Grb2) is a widely expressed adapter protein with roles in epithelial cell growth and morphogenesis, as well as angiogenesis, making it a logical target for anticancer drug development. We have previously shown that a potent antagonist of Grb2 Src homology-2 domain-binding, C90, blocks growth factor-driven cell motility in vitro and angiogenesis in vivo. We now report that C90 inhibits metastasis in vivo in two aggressive tumor models, without affecting primary tumor growth rate. These results support the potential efficacy of this compound in reducing the metastatic spread of primary solid tumors and establish a critical role for Grb2 Src homology-2 domain-mediated interactions in this process.

Signaling pathways involved in cyclooxygenase-2 induction by hepatocyte growth factor in non small-cell lung cancer

Many studies have suggested a role for the hepatocyte growth factor (HGF)/c-Met pathway in tumorigenesis. Some actions of HGF are believed to be mediated by cyclooxygenase-2 (COX-2), resulting in the production of prostaglandin E2 (PGE(2)). We examined four c-Met-positive non-small-cell lung cancer (NSCLC) cell lines for effects of HGF on COX-2. HGF increased COX-2 protein expression 3-fold over basal levels. Induction of COX-2 occurred through both the extracellular signal-regulated kinase 1/2 and p38 pathways. HGF treatment caused activation of the activator protein-1, CCAAT/enhancer-binding protein, and cAMP response element-binding protein transcription factors, and COX-2 induction was blocked by actinomycin D. The half-life of COX-2 mRNA was also increased by HGF. HGF stimulation resulted in a 4-fold increase in PGE(2) secretion, and treatment of NSCLC cells with exogenous PGE(2) significantly increased cell proliferation. The addition of PGE(2) to NSCLC cells also led to rapid phosphorylation of c-Met in the absence of HGF, which was blocked by epidermal growth factor receptor (EGFR) inhibition. EGFR ligands were released in response to PGE(2). This suggests that secretion of PGE(2) induced by HGF/c-Met pathway activation can further activate the c-Met pathway via EGFR in a reinforcing loop that is independent of HGF. HGF and PGE(2) each significantly stimulated invasion in NSCLC cells. Cells transiently transfected with c-Met antisense plasmid showed a significant decrease in HGF- or PGE(2)-induced invasion. PGE(2)-induced invasion was EGFR-dependent, confirming a link between PGE(2), EGFR, and c-Met. Targeting of both the HGF/c-Met and PGE(2) pathways with a neutralizing antibody to HGF and celecoxib resulted in enhanced anti-invasion effects in response to HGF.

Treatment outcome for metastatic papillary renal cell carcinoma patients

BACKGROUND

Most clinical trial reports in metastatic renal cell carcinoma (RCC) do not distinguish between histologic subtypes, making it difficult to assess specific treatment efficacy. The current retrospective study sought to define clinical features and outcome data for metastatic papillary RCC.

METHODS

Clinical features, treatment outcome, and survival were evaluated in 38 patients with metastatic papillary RCC who underwent clinical evaluation at Memorial Sloan-Kettering Cancer Center (MSKCC) between 1985 and 2005. Twenty-three of 513 individuals were identified from a clinical trial database, 14 of 1895 from a surgery database, and 1 of 357 from a pathology database. A literature review of systemic therapy in metastatic papillary RCC was performed.

RESULTS

Among the 38 patients, 30 had been treated at MSKCC with various systemic therapies, including cytokines. Twelve therapies resulted in stable disease, 30 in initial progression of disease, and 1 in an unknown response. One patient had a partial response to sunitinib, a novel multitargeted tyrosine kinase inhibitor. The median overall survival time for the entire study group was 8 months (95% confidence interval, 5-12). A literature review on treatment of metastatic papillary RCC produced 4 reports, confirming a lack of efficacy for systemic therapy.

CONCLUSIONS

A resistance to systemic therapy characterizes patients with metastatic papillary RCC. Further understanding of the genetics and molecular biology and subtypes involved may provide the basis for more effective agents. Treatment with targeted therapies or other experimental agents is warranted.

The von Hippel-Lindau tumor suppressor gene product represses oncogenic beta-catenin signaling in renal carcinoma cells

Loss of von Hippel-Lindau (VHL) tumor suppressor gene function occurs in familial and most sporadic clear cell renal cell carcinoma (RCC), resulting in the aberrant expression of genes that control cell proliferation, invasion, and angiogenesis. The molecular mechanisms by which VHL loss leads to tumorigenesis are not yet fully defined. VHL loss has been shown to allow robust RCC cell motility, invasiveness, and morphogenesis in response to hepatocyte growth factor (HGF) stimulation, processes that are known to contribute to tumor invasiveness and metastatic potential. Among the most likely intracellular mediators of these HGF-driven activities is beta-catenin, a structural link between cadherens and the actin cytoskeleton, as well as a gene transactivator. We show that reconstitution of VHL expression in RCC cells repressed HGF-stimulated beta-catenin tyrosyl phosphorylation, adherens junction disruption, cytoplasmic beta-catenin accumulation, and reporter gene transactivation in RCC cells. Ectopic expression of a ubiquitination-resistant beta-catenin mutant specifically restored HGF-stimulated invasion and morphogenesis in VHL-transfected RCC cells. VHL gene silencing in non-RCC renal epithelial cells phenotypically mimicked VHL loss in RCC, and HGF-driven invasiveness was blocked by the expression of a dominant-negative mutant of Tcf. We conclude that, unlike many other cancers, where HGF pathway activation contributes to malignancy through the acquisition of autocrine signaling, receptor overexpression, or mutation, in RCC cells VHL loss enables HGF-driven oncogenic beta-catenin signaling. These findings identify beta-catenin as a potential target in biomarker and drug development for RCC.

Oncogenic Met receptor induces cell-cycle progression in Xenopus oocytes independent of direct Grb2 and Shc binding or Mos synthesis, but requires phosphatidylinositol 3-kinase and Raf signaling

Biological responses of hepatocyte growth factor (HGF) are mediated by the Met receptor tyrosine kinase. Although HGF is a potent mitogen for a variety of cells, the signals required for cell-cycle progression by the Met/HGF receptor are poorly defined. In this study, we have used the Xenopus oocyte system to define the role of various Met proximal-binding partners and downstream signaling pathways in cell-cycle regulation. We show that cell-cycle progression and activation of MAPK and JNK mediated by the oncogenic Met receptor, Tpr-Met, are dependent on its kinase activity and the presence of the twin phosphotyrosine (Y482 & Y489) residues in its C-terminus, but that the recruitment of Grb2 and Shc adaptor proteins is dispensable, implicating other signaling molecules. However, using Met receptor oncoproteins engineered to recruit specific signaling proteins, we demonstrate that recruitment of Grb2 or Shc adaptor proteins is sufficient to induce cell-cycle progression and activation of MAPK and JNK, while the binding of phospholipase-Cgamma or phosphatidylinositol 3-kinase alone fails to elicit these responses. Using various means to block phosphatidylinositol 3-kinase, phospholipase-Cgamma, MEK, JNK, Mos, and Raf1 activity, we show that unlike the fibroblast growth factor receptor, MEK-dependent and independent signaling contribute to Met receptor-mediated cell-cycle progression, but phospholipase-Cgamma or JNK activity and Mos synthesis are not critical. Notably, we demonstrate that Raf1 and phosphatidylinositol 3-kinase signaling are required for cell-cycle progression initiated by the Met receptor, a protein frequently deregulated in human tumors.

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.

Oncogenic Met receptor induces ectopic structures in Xenopus embryos

When aberrantly expressed or activated, the Met receptor tyrosine kinase is involved in tumor invasiveness and metastasis. In this study, we have used the Xenopus embryonic system to define the role of various Met proximal-binding partners and downstream signaling pathways in regulating an induced morphogenetic event. We show that expression of an oncogenic derivative of the Met receptor (Tpr-Met) induces ectopic morphogenetic structures during Xenopus embryogenesis. Using variant forms of Tpr-Met that are engineered to recruit a specific signaling molecule of choice, we demonstrate that the sole recruitment of either the Grb2 or the Shc adaptor protein is sufficient to induce ectopic structures and anterior reduction, while the recruitment of PI-3Kinase (PI-3K) is necessary but not sufficient for this effect. In contrast, the recruitment of PLCgamma can initiate the induction, but fails to maintain or elongate supernumerary structures. Finally, evidence indicates that the Ras/Raf/MAPK pathway is necessary, but not sufficient to induce these structures. This study also emphasizes the importance of examining signaling molecules in the regulatory context that is provided by receptor/effector interactions when assessing a role in cell growth and differentiation.

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.

Disruption of protein-protein interactions: towards new targets for chemotherapy

Protein-protein interactions play a key role in various mechanisms of cellular growth and differentiation, and in the replication of pathogen organisms in host cells. Thus, inhibition of these interactions is a promising novel approach for rational drug design against a wide number of cellular and microbial targets. In the past few years, attempts to inhibit protein-protein interactions using antibodies, peptides, and synthetic or natural small molecules have met with varying degrees of success, and these will be the focus of this review.

Cancer therapy: can the challenge be MET?

The deregulation of tyrosine kinase receptors (RTKs) is frequent in human tumors and is often associated with the acquisition of an aggressive phenotype. The Met oncogene, encoding the RTK for hepatocyte growth factor (HGF), controls genetic programs leading to cell growth, invasion and protection from apoptosis. The deregulated activation of Met is crucial not only for the acquisition of tumorigenic properties but also to achieve an invasive phenotype. The involvement of MET in human tumors has been definitively established and can be achieved through several mechanisms, including MET interaction with unrelated membrane receptors, such as integrins, plexins, CD44, FAS and other RTKs. Interfering with Met activation is thus a new and challenging approach to hamper tumorigenic and metastatic processes.

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.

Regulation of growth factor receptor bound 2 by electroconvulsive seizure

Electroconvulsive seizure (ECS) is a well-established non-chemical antidepressant that is effective in the treatment of severe depression and also in subjects resistant to chemical antidepressant treatment. Although the molecular mechanism governing the antidepressant efficacy of ECS is unknown, recent work suggests that an amplification of growth/neurotrophic signaling might play a role in mediating the therapeutic effects. In this context, we examined the regulation of growth factor receptor bound 2 (Grb2), an important adaptor molecule in several growth factor signaling cascades. In situ hybridization analysis revealed a more than 2-fold induction of Grb2 mRNA in the hippocampal dentate gyrus as well as superficial and deep layers of the cortex with both acute and chronic ECS. Grb2 also exhibited a time-dependent induction 4 and 8 h after acute ECS, returning to basal levels at 24 h. These results provide further evidence of increased growth factor signaling in response to ECS.

Enhanced growth of human met-expressing xenografts in a new strain of immunocompromised mice transgenic for human hepatocyte growth factor/scatter factor

Downstream signaling that results from the interaction of hepatocyte growth factor/scatter factor (HGF/SF) with the receptor tyrosine kinase Met plays critical roles in tumor development, progression, and metastasis. This ligand-receptor pair is an attractive target for new diagnostic and therapeutic agents, preclinical development of which requires suitable animal models. The growth of heterotopic and orthotopic Met-expressing human tumor xenografts in conventional strains of immunocompromised mice inadequately replicates the paracrine stimulation by human HGF/SF (hHGF/SF) that occurs in humans with cancer. We have therefore generated a mouse strain transgenic for hHGF/SF (designated hHGF-Tg) on a severe combined immunodeficiency (SCID) background. We report here that the presence of ectopically expressed hHGF/SF ligand significantly enhances growth of heterotopic subcutaneous xenografts derived from human Met-expressing cancer cells, including the lines SK-LMS-1 (human leiomyosarcoma), U118 (human glioblastoma), and DU145 (human prostate carcinoma), but not that of M14-Mel xenografts (human melanoma that expresses insignificant levels of Met). Our results indicate that ectopic hHGF/SF can specifically activate Met in human tumor xenografts. This new hHGF-Tg strain of mice should provide a powerful tool for evaluating drugs and diagnostic agents that target the various pathways influenced by Met activity.

Activation of the c-Met receptor complex in fibroblasts drives invasive cell behavior by signaling through transcription factor STAT3

c-Met is the receptor for hepatocyte growth factor/scatter factor (HGF/SF). It mediates multiple cellular responses in development and adult life, and c-Met hyperactivity is associated with malignant transformation of cells and the acquisition of metastatic properties. Signal transducer and activator of transcription 3 (STAT3) has been shown to contribute to c-Met-mediated cell motility and is, thus, potentially involved in the control of invasive cell behavior. We have functionally reconstituted c-Met-dependent signal transduction in fibroblasts with the aim of studying Met-driven cell invasiveness and the role of STAT3 in this phenomenon. Activation of the system was achieved by means of a hybrid receptor comprising the extracellular domain of the nerve growth factor (NGF) receptor TrkA, the cytoplasmic part of c-Met and a C-terminally fused blue fluorescent protein (BFP). In addition, a GFP-tagged derivative of adaptor protein Gab1 was expressed. NGF-stimulation of mouse fibroblasts expressing tagged versions of both Trk-Met and Gab1 with NGF resulted in anchorage-independent growth and enhanced invasiveness. By freeze-fracture cytochemistry and electron microscopy, we were able to visualize the ligand-induced formation of multivalent receptor complex assemblies within the cell membrane. NGF-stimulation of the heterologous receptor system evoked activation of STAT3 as evidenced by tyrosine phosphorylation and the formation of STAT3 clusters at the cell membrane. siRNA-mediated ablation of STAT3 expression resulted in a drastic reduction of c-Met-driven invasiveness, indicating an important role of STAT3 in the control of this particularly relevant property of transformed cells.

Novel Functional Biodegradable Polymer II: Fibroblast Growth Factor-2 Activities of Poly(γ-glutamic acid)-sulfonate

Basic fibroblast growth factor (FGF-2) mitogenic activities of sulfonated poly(gamma-glutamic acid) (gamma-PGA-S) were investigated with chlorate-treated L929 fibroblast culture tests. When 72% of the carboxyl groups in gamma-PGA were sulfonated (gamma-PGA-S72), cell numbers reached a maximum. The activity of gamma-PGA-S72 was higher than that of gamma-PGA and synthetic heparinoids and was almost comparable to that of heparin. Cytotoxicity of gamma-PGA-S72 was not observed, regardless of the degree of sulfonation. FGF-2-protective effects of gamma-PGA-S72 against acid and thermal inactivation were also evaluated, and gamma-PGA-S72 showed higher FGF-2-protective effects in comparison to nonsulfonated gamma-PGA. The steric structures of various sulfonated gamma-PGA-Ss were analyzed by molecular modeling (molecular orbital method (MOPAC)) and indicated that gamma-PGA-Ss are helical in vacuo. Results from MOPAC and the molecular mechanics method (MM2) demonstrated that electrostatic interactions can take place between sulfonic and carboxyl groups of gamma-PGA-S and basic amino acid residues in FGF-2. gamma-PGA-S72 can interact with FGF-2 strongly.