Identification of a nonpeptide ligand that releases bioactive insulin-like growth factor-I from its binding protein complex

The diverging roles of insulin-like growth factor binding proteins in pulmonary arterial hypertension

Pulmonary hypertension (PH) is a progressive, severe and to date not curable disease of the pulmonary vasculature. Alterations of the insulin-like growth factor 1 (IGF-1) system are known to play a role in vascular pathologies and IGF-binding proteins (IGFBPs) are important regulators of the bioavailability and function of IGFs. In this study, we show that circulating plasma levels of IGFBP-1, IGFBP-2 and IGFBP-3 are increased in idiopathic pulmonary arterial hypertension (IPAH) patients compared to healthy individuals. These binding proteins inhibit the IGF-1 induced IGF-1 receptor (IGF1R) phosphorylation and exhibit diverging effects on the IGF-1 induced signaling pathways in human pulmonary arterial cells (i.e. healthy as well as IPAH-hPASMCs, and healthy hPAECs). Furthermore, IGFBPs are differentially expressed in an experimental mouse model of PH. In hypoxic mouse lungs, IGFBP-1 mRNA expression is decreased whereas the mRNA for IGFBP-2 is increased. In contrast to IGFBP-1, IGFBP-2 shows vaso-constrictive properties in the murine pulmonary vasculature. Our analyses show that IGFBP-1 and IGFBP-2 exhibit diverging effects on IGF-1 signaling and display a unique IGF1R-independent kinase activation pattern in human pulmonary arterial smooth muscle cells (hPASMCs), which represent a major contributor of PAH pathobiology. Furthermore, we could show that IGFBP-2, in contrast to IGFBP-1, induces epidermal growth factor receptor (EGFR) signaling, Stat-3 activation and expression of Stat-3 target genes. Based on our results, we conclude that the IGFBP family, especially IGFBP-1, IGFBP-2 and IGFBP-3, are deregulated in PAH, that they affect IGF signaling and thereby regulate the cellular phenotype in PH.

Insulin-like growth factor binding protein 4 loaded electrospun membrane ameliorating tendon injury by promoting retention of IGF-1

Tendon injury is one of the most common musculoskeletal disorders that impair joint mobility and lower quality of life. The limited regenerative capacity of tendon remains a clinical challenge. Local delivery of bioactive protein is a viable therapeutic approach for tendon healing. Insulin-like growth factor binding protein 4 (IGFBP-4) is a secreted protein capable of binding and stabilizing insulin-like growth factor 1 (IGF-1). Here, we applied an aqueous-aqueous freezing-induced phase separation technology to obtain the IGFBP4-encapsulated dextran particles. Then, we added the particles into poly (L-lactic acid) (PLLA) solution to fabricate IGFBP4-PLLA electrospun membrane for efficient IGFBP-4 delivery. The scaffold showed excellent cytocompatibility and a sustained release of IGFBP-4 for nearly 30 days. In cellular experiments, IGFBP-4 promoted tendon-related and proliferative markers expression. In a rat Achilles tendon injury model, immunohistochemistry and quantitative real-time polymerase chain reaction confirmed better outcomes by using the IGFBP4-PLLA electrospun membrane at the molecular level. Furthermore, the scaffold effectively promoted tendon healing in functional performance, ultrastructure and biomechanical properties. We found addition of IGFBP-4 promoted IGF-1 retention in tendon postoperatively and then facilitated protein synthesis via IGF-1/AKT signaling pathway. Overall, our IGFBP4-PLLA electrospun membrane provides a promising therapeutic strategy for tendon injury.

IGFBPs mediate IGF-1's functions in retinal lamination and photoreceptor development during pluripotent stem cell differentiation to retinal organoids

Development of the retina is regulated by growth factors, such as insulin-like growth factors 1 and 2 (IGF-1/2), which coordinate proliferation, differentiation, and maturation of the neuroepithelial precursors cells. In the circulation, IGF-1/2 are transported by the insulin growth factor binding proteins (IGFBPs) family members. IGFBPs can impact positively and negatively on IGF-1, by making it available or sequestering IGF-1 to or from its receptor. In this study, we investigated the expression of IGFBPs and their role in the generation of human retinal organoids from human pluripotent stem cells, showing a dynamic expression pattern suggestive of different IGFBPs being used in a stage-specific manner to mediate IGF-1 functions. Our data show that IGF-1 addition to culture media facilitated the generation of retinal organoids displaying the typical laminated structure and photoreceptor maturation. The organoids cultured in the absence of IGF-1, lacked the typical laminated structure at the early stages of differentiation and contained significantly less photoreceptors and more retinal ganglion cells at the later stages of differentiation, confirming the positive effects of IGF-1 on retinal lamination and photoreceptor development. The organoids cultured with the IGFBP inhibitor (NBI-31772) and IGF-1 showed lack of retinal lamination at the early stages of differentiation, an increased propensity to generate horizontal cells at mid-stages of differentiation and reduced photoreceptor development at the later stages of differentiation. Together these data suggest that IGFBPs enable IGF-1's role in retinal lamination and photoreceptor development in a stage-specific manner.

IGFBP-2 acts as a tumour suppressor and plays a role in determining chemosensitivity in bladder cancer cells

There are mixed reports on the role that IGFBP-2 plays in cancer progression, with some indicating a tumour suppressive role and others showing that IGFBP-2 may act as an oncogene. These apparent contradictions may be context and tissue specific. In this study we determined the role that IGFBP-2 played on the phenotype and chemosensitivity of a selection of bladder cancer cell lines and investigated how the abundance of IGFBP-2 was regulated. We found that IGFBP-2 was more abundant in the epithelial bladder cancer cells, RT4 and UMUC3 and absent in the more mesenchymal T24 and TCCSUP cells. Silencing IGFBP-2 using siRNA in epithelial RT4 cells promoted cell proliferation, invasion, colony formation, resulted in a reduction in epithelial (E-cadherin) and an increase in mesenchymal (N-cadherin) markers and increased sensitivity to cisplatin-induced cell death. Conversely, we observed the opposite effects when adding exogenous IGFBP-2 to the mesenchymal T24 cells. We determined that IGFBP-2 was epigenetically silenced via DNA methylation as the cells adopted a mesenchymal phenotype. Collectively these data suggest that IGFBP-2 acts as a tumour suppressor and marker of chemosensitivity in epithelial bladder cancer cells and that IGFBP-2 is epigenetically silenced by methylation to promote bladder cancer progression.

Insulin-like growth factor binding proteins inhibit oocyte maturation of zebrafish

The function of insulin-like growth factor (Igf) system in ovary has attracted much attention, but the role of Igf binding proteins (Igfbps) in ovary is still largely unknown. In this study, the role of Igfbps in oocyte maturation was investigated in zebrafish. The expression of all eight identified Igfbps except Igfbp6b could be detected in the adult ovary and exhibited differential expression profiles during folliculogenesis. The expression of several Igfbps is dynamically changed during oocyte maturation induced by human chorionic gonadotropin (hCG). By treatment of an Igfbps inhibitor NBI-31772 in vitro, the oocyte maturation could be stimulated in a clear dose-, time- and stage-dependent manner. Such effects were also observed by administration of NBI-31772 in vivo. Igfbps are differentially expressed in both follicular cells and oocytes, but the effect of NBI-31772 could only be found in intact follicles and not in the denuded oocytes. Previous studies have demonstrated that Igf3 is the major Igf member in regulating oocyte maturation of zebrafish. Interestingly, NBI-31772 could increase the effect of Igf3 on oocyte maturation. Furthermore, we found the effect of NBI-31772 on oocyte maturation could be blocked by an Igf type 1 receptor inhibitor BMS-536924 in vitro, suggesting the Igfbps can inhibit the oocyte maturation via Igf/Igf1r pathway. Together, we provided the first evidence in fish that Igfbps inhibit oocyte maturation of zebrafish.

Microparticle-mediated sequestration of cell-secreted proteins to modulate chondrocytic differentiation

Protein delivery is often used in tissue engineering applications to control differentiation processes, but is limited by protein instability and cost. An alternative approach is to control the cellular microenvironment through biomaterial-mediated sequestration of cell-secreted proteins important to differentiation. Thus, we utilized heparin-based microparticles to modulate cellular differentiation via protein sequestration in an in vitro model system of endochondral ossification. Heparin and poly(ethylene-glycol) (PEG; a low-binding material control)-based microparticles were incorporated into ATDC5 cell spheroids or incubated with ATDC5 cells in transwell culture. Reduced differentiation was observed in the heparin microparticle group as compared to PEG and no microparticle-containing groups. To determine if observed changes were due to sequestration of cell-secreted protein, the proteins sequestered by heparin microparticles were analyzed using SDS-PAGE and mass spectrometry. It was found that heparin microparticles bound insulin-like growth factor binding proteins (IGFBP)-3 and 5. When incubated with a small-molecule inhibitor of IGFBPs, NBI 31772, a similar delay in differentiation of ATDC5 cells was observed. These results indicate that heparin microparticles modulated chondrocytic differentiation in this system via sequestration of cell-secreted protein, a technique that could be beneficial in the future as a means to control cellular differentiation processes.

STATEMENT OF SIGNIFICANCE

In this work, we present a proof-of-principle set of experiments in which heparin-based microparticles are shown to modulate cellular differentiation through binding of cell-secreted protein. Unlike existing systems that rely on expensive protein with limited half-lives to elicit changes in cellular behavior, this technique focuses on temporal modulation of cell-generated proteins. This technique also provides a biomaterials-based method that can be used to further identify sequestered proteins of interest. Thus, this work indicates that glycosaminoglycan-based biomaterial approaches could be used as substitutes or additions to traditional methods for modulating and identifying the cell-secreted proteins involved in directing cellular behavior.

IGFBPL1 Regulates Axon Growth through IGF-1-mediated Signaling Cascades

Activation of axonal growth program is a critical step in successful optic nerve regeneration following injury. Yet the molecular mechanisms that orchestrate this developmental transition are not fully understood. Here we identified a novel regulator, insulin-like growth factor binding protein-like 1 (IGFBPL1), for the growth of retinal ganglion cell (RGC) axons. Expression of IGFBPL1 correlates with RGC axon growth in development, and acute knockdown of IGFBPL1 with shRNA or IGFBPL1 knockout in vivo impaired RGC axon growth. In contrast, administration of IGFBPL1 promoted axon growth. Moreover, IGFBPL1 bound to insulin-like growth factor 1 (IGF-1) and subsequently induced calcium signaling and mammalian target of rapamycin (mTOR) phosphorylation to stimulate axon elongation. Blockage of IGF-1 signaling abolished IGFBPL1-mediated axon growth, and vice versa, IGF-1 required the presence of IGFBPL1 to promote RGC axon growth. These data reveal a novel element in the control of RGC axon growth and suggest an unknown signaling loop in the regulation of the pleiotropic functions of IGF-1. They suggest new therapeutic target for promoting optic nerve and axon regeneration and repair of the central nervous system.

Follicle-Stimulating Hormone Regulates igfbp Gene Expression Directly or via Downstream Effectors to Modulate Igf3 Effects on Zebrafish Spermatogenesis

Previous work showed that pharmacological inactivation of Igf-binding proteins (Igfbps), modulators of Igf activity, resulted in an excessive differentiation of type A undifferentiated (A_und) spermatogonia in zebrafish testis in tissue culture when Fsh was present in the incubation medium. Using this testis tissue culture system, we studied here the regulation of igfbp transcript levels by Fsh and two of its downstream effectors, Igf3 and 11-ketotestosterone (11-KT). We also explored how Fsh-modulated igfbp expression affected spermatogonial proliferation by adding or removing the Igfbp inhibitor NBI-31772 at different times. Fsh (100 ng/mL) decreased the transcript levels of igfbp1a, -3, and -6a after 1 or 3 days, while increasing igfbp2a and -5b expression, but only after 5 days of incubation. Igf3 down-regulated the same igfbp transcripts as Fsh but with a delay of at least 4 days. 11-KT increased the transcripts (igfbp2a and 5b) that were elevated by Fsh and decreased those of igfbp6a, as did Fsh, while 11-KT did not change igfbp1a or -3 transcript levels. To evaluate Igfbps effects on spermatogenesis, we quantified under different conditions the mitotic indices and relative section areas occupied by the different spermatogonial generations (type A_und, type A differentiating (A_diff), or type B (B) spermatogonia). Igf3 (100 ng/mL) increased the area occupied by A_diff and B while decreasing the one for A_und. Interestingly, a concentration of Igf3 that was inactive by itself (25 ng/mL) became active in the presence of the Igfbp inhibitor NBI-31772 and mimicked the effect of 100 ng/mL Igf3 on spermatogonia. Studies exploiting the different dynamics of igfbp expression in response to Fsh and adding or removing NBI-31772 at different times showed that the quick downregulation of three igfbp as well as the delayed upregulated of two igfbps all support Igf3 bioactivity, namely the stimulation of spermatogonial differentiation. We conclude that Fsh modulates, directly or via androgens and Igf3, igfbp gene expression, supporting Igf3 bioactivity either by decreasing igfbp1a, -3, -6a or by increasing igfbp2a and -5b gene expression.

Igf Binding Proteins Protect Undifferentiated Spermatogonia in the Zebrafish Testis Against Excessive Differentiation

IGF binding proteins (IGFBPs) modulate the availability of IGFs for their cognate receptors. In zebrafish testes, IGF3 promotes the proliferation and differentiation of type A undifferentiated (A_und) spermatogonia, and igf3 expression is strongly elevated by FSH but also responds to T₃. Here we report the effects of FSH and T₃ on igfbp transcript levels in adult zebrafish testis. We then examined T₃ and FSH effects on zebrafish spermatogenesis and explored the relevance of IGFBPs in modulating these T₃ or FSH effects, using a primary tissue culture system for adult zebrafish testis. T₃ up-regulated igfbp1a and igfbp3 expression, whereas FSH reduced igfbp1a transcript levels. To quantify effects on spermatogenesis, we determined the mitotic index and relative section areas occupied by A_und, type A differentiating, or type B spermatogonia. In general, T₃ and FSH stimulated spermatogonial proliferation and increased the areas occupied by spermatogonia, suggesting that both self-renewal and differentiating divisions were stimulated. Preventing IGF/IGFBP interaction by NBI-31772 further increased T₃- or FSH-induced spermatogonial proliferation. However, under these conditions the more differentiated type A differentiating and B spermatogonia occupied larger surface areas at the expense of the area held by A_und spermatogonia. Clearly decreased nanos2 transcript levels are in agreement with this finding, and reduced amh expression may have facilitated spermatogonial differentiation. We conclude that elevating IGF3 bioactivity by blocking IGFBPs shifted T₃- or FSH-induced signaling from stimulating spermatogonial self-renewal as well as differentiation toward predominantly stimulating spermatogonial differentiation, which leads to a depletion of type A_und spermatogonia.

Transplantation of Human Neural Progenitor Cells Expressing IGF-1 Enhances Retinal Ganglion Cell Survival

We have previously characterized human neuronal progenitor cells (hNP) that can adopt a retinal ganglion cell (RGC)-like morphology within the RGC and nerve fiber layers of the retina. In an effort to determine whether hNPs could be used a candidate cells for targeted delivery of neurotrophic factors (NTFs), we evaluated whether hNPs transfected with an vector that expresses IGF-1 in the form of a fusion protein with tdTomato (TD), would increase RGC survival in vitro and confer neuroprotective effects in a mouse model of glaucoma. RGCs co-cultured with hNP^IGF-TD cells displayed enhanced survival, and increased neurite extension and branching as compared to hNP^TD or untransfected hNP cells. Application of various IGF-1 signaling blockers or IGF-1 receptor antagonists abrogated these effects. In vivo, using a model of glaucoma we showed that IOP elevation led to reductions in retinal RGC count. In this model, evaluation of retinal flatmounts and optic nerve cross sections indicated that only hNP^IGF-TD cells effectively reduced RGC death and showed a trend to improve optic nerve axonal loss. RT-PCR analysis of retina lysates over time showed that the neurotrophic effects of IGF-1 were also attributed to down-regulation of inflammatory and to some extent, angiogenic pathways. This study shows that neuronal progenitor cells that hone into the RGC and nerve fiber layers may be used as vehicles for local production and delivery of a desired NTF. Transplantation of hNP^IGF-TD cells improves RGC survival in vitro and protects against RGC loss in a rodent model of glaucoma. Our findings have provided experimental evidence and form the basis for applying cell-based strategies for local delivery of NTFs into the retina. Application of cell-based delivery may be extended to other disease conditions beyond glaucoma.

Heart regeneration: opportunities and challenges for drug discovery with novel chemical and therapeutic methods or agents

Following a heart attack, more than a billion cardiac muscle cells (cardiomyocytes) can be killed, leading to heart failure and sudden death. Much research in this area is now focused on the regeneration of heart tissue through differentiation of stem cells, proliferation of existing cardiomyocytes and cardiac progenitor cells, and reprogramming of fibroblasts into cardiomyocytes. Different chemical modalities (i.e. methods or agents), ranging from small molecules and RNA approaches (including both microRNA and anti-microRNA) to modified peptides and proteins, are showing potential to meet this medical need. In this Review, we outline the recent advances in these areas and describe both the modality and progress, including novel screening strategies to identify hits, and the upcoming challenges and opportunities to develop these hits into pharmaceuticals, at which chemistry plays a key role.

In vivo monitoring of cardiomyocyte proliferation to identify chemical modifiers of heart regeneration

Adult mammalian cardiomyocytes have little capacity to proliferate in response to injury, a deficiency that underlies the poor regenerative ability of human hearts after myocardial infarction. By contrast, zebrafish regenerate heart muscle after trauma by inducing proliferation of spared cardiomyocytes, providing a model for identifying manipulations that block or enhance these events. Although direct genetic or chemical screens of heart regeneration in adult zebrafish present several challenges, zebrafish embryos are ideal for high-throughput screening. Here, to visualize cardiomyocyte proliferation events in live zebrafish embryos, we generated transgenic zebrafish lines that employ fluorescent ubiquitylation-based cell cycle indicator (FUCCI) technology. We then performed a chemical screen and identified several small molecules that increase or reduce cardiomyocyte proliferation during heart development. These compounds act via Hedgehog, Insulin-like growth factor or Transforming growth factor β signaling pathways. Direct examination of heart regeneration after mechanical or genetic ablation injuries indicated that these pathways are activated in regenerating cardiomyocytes and that they can be pharmacologically manipulated to inhibit or enhance cardiomyocyte proliferation during adult heart regeneration. Our findings describe a new screening system that identifies molecules and pathways with the potential to modify heart regeneration.

Controlled release of IGF-1 and HGF from a biodegradable polyurethane scaffold

PURPOSE

Biodegradable elastomers, which can possess favorable mechanical properties and degradation rates for soft tissue engineering applications, are more recently being explored as depots for biomolecule delivery. The objective of this study was to synthesize and process biodegradable, elastomeric poly(ester urethane)urea (PEUU) scaffolds and to characterize their ability to incorporate and release bioactive insulin-like growth factor-1 (IGF-1) and hepatocyte growth factor (HGF).

METHODS

Porous PEUU scaffolds made from either 5 or 8 wt% PEUU were prepared with direct growth-factor incorporation. Long-term in vitro IGF-1 release kinetics were investigated in saline or saline with 100 units/ml lipase to simulate in vivo degradation. Cellular assays were used to confirm released IGF-1 and HGF bioactivity.

RESULTS

IGF-1 release into saline occurred in a complex multi-phasic manner for up to 440 days. Scaffolds generated from 5 wt% PEUU delivered protein faster than 8 wt% scaffolds. Lipase-accelerated scaffold degradation led to delivery of >90% protein over 9 weeks for both polymer concentrations. IGF-1 and HGF bioactivity in the first 3 weeks was confirmed.

CONCLUSIONS

The capacity of a biodegradable elastomeric scaffold to provide long-term growth-factor delivery was demonstrated. Such a system might provide functional benefit in cardiovascular and other soft tissue engineering applications.

Antitumor vectorized oligonucleotides in a model of ewing sarcoma: unexpected role of nanoparticles

Oligonucleotides (ONs) such as antisense oligonucleotides (AS-ON) and siRNAs are used as experimental tools to study gene function and are currently being tested in clinical trials for use as therapeutic anticancer agents. However, their therapeutic use has been limited by their low physiological stability and their slow cellular uptake. The systemic delivery of sequence-specific AS-ON targeting the EWS/FLI1 gene product by a targeted, nonviral delivery system dramatically inhibits tumor growth in a murine model of Ewing's sarcoma. The nonviral delivery system uses a poly-iso-hexyl-cyanoacrylate (PIHCA)-containing polycation (chitosan) to bind and protect the AS-ON. No antitumor effect is observed using a control oligonucleotide sequence. We found here that injection of the free AS-ON stimulates tumor growth independently of its sequence and that this stimulation is abolished in the presence of nanosphere-chitosan, which exerts with the oligonucleotides a specific inhibitory effect on tumor growth. The stimulation of tumor growth is likely to be due to a polyanionic effect; indeed, a similar stimulatory response is observed upon treatment with dextran sulfate and heparin in vivo. These results suggest that ON loaded onto nanosphere-chitosan provides efficient and tumor-specific delivery, and provides protection against a polyanionic secondary effect.

The insulin-like growth factor family: molecular mechanisms, redox regulation, and clinical implications

Insulin-like growth factor (IGF)-induced signaling networks are vital in modulating multiple fundamental cellular processes, such as cell growth, survival, proliferation, and differentiation. Aberrations in the generation or action of IGF have been suggested to play an important role in several pathological conditions, including metabolic disorders, neurodegenerative diseases, and multiple types of cancer. Yet the exact mechanism involved in the pathogenesis of these diseases by IGFs remains obscure. Redox pathways involving reactive oxygen species (ROS) and reactive nitrogen species (RNS) contribute to the pathogenetic mechanism of various diseases by modifying key signaling pathways involved in cell growth, proliferation, survival, and apoptosis. Furthermore, ROS and RNS have been demonstrated to alter IGF production and/or action, and vice versa, and thereby have the ability to modulate cellular functions, leading to clinical manifestations of diseases. In this review, we provide an overview on the IGF system and discuss the potential role of IGF-1/IGF-1 receptor and redox pathways in the pathophysiology of several diseases.

Insulin-like growth factor system regulates oligodendroglial cell behavior: therapeutic potential in CNS

Amongst the many soluble extracellular factors stimulating intracellular signal transduction pathways and driving cellular processes such as proliferation, differentiation and survival, insulin-like growth factors (IGFs) stand out as indispensable factors for proper oligodendrocyte differentiation and accompanying myelin production. Owing to its potent myelinogenic capacity and its neuroprotective properties, IGFs hold therapeutic potential in demyelinating and neurodengenerative diseases. However, the IGF system is comprised of a complex molecular network involving regulatory binding proteins, proteases, cell surface and extracellular matrix components which orchestrate IGF-specific functions. Thus, the complexity by which these factors are tightly regulated makes a simplistic therapeutic approach towards treating demyelinating conditions unfeasible. In the present review, we address these issues and consider current therapeutic prospects of oligodendrocyte-targeted IGF-based therapies.

Increasing the levels of insulin-like growth factor-I by an IGF binding protein inhibitor produces anxiolytic and antidepressant-like effects

The present studies were conducted to determine if increasing central levels of the neurotrophic factor insulin-like growth factor-1 (IGF-I) either directly or indirectly produces anxiolytic and antidepressant-like effects in the mouse. Central levels of IGF-I can be increased directly, by administering IGF-I, or indirectly by blocking the insulin-like growth factor binding proteins (IGFBPs). The IGFBP family has the unique ability to regulate IGF-I levels by sequestering IGF-I into an inactive complex. Therefore, an IGFBP inhibitor increases the level of IGF-I available to bind to its receptor. Intracerebroventricular (icv) administration of the nonspecific IGFBP inhibitor NBI-31772 (10-30 microg) increases the number of punished crossings in the four-plate test and NBI-31772 (0.3-10 microg) increases time spent in the open quadrant of the elevated zero maze (EZM), indicative of anxiolytic-like effects. NBI-31772 (3-30 microg) also decreases immobility time in the tail suspension test, indicative of antidepressant-like effects. Similarly, icv administration of IGF-I (0.1 microg) produces anxiolytic-like effects in the four-plate test and IGF-1 (0.3-1 microg) produces anxiolytic-like effects in the EZM. IGF-I (10 microg) also produces antidepressant-like effects in the tail suspension test. Coadministration of the IGF-I receptor antagonist JB1 with NBI-31772 or IGF-I blocks the anxiolytic-like and antidepressant-like effects of these compounds. These results suggest that NBI-31772 produces behavioral effects by increasing levels of IGF-I that in turn activate the IGF-I receptor. The present studies demonstrate that an IGFBP inhibitor mimics the behavioral effects of IGF-I and that IGFBP inhibition may represent a novel mechanism by which to increase IGF-I to treat depression and anxiety.

Modifying IGF1 activity: an approach to treat endocrine disorders, atherosclerosis and cancer

Insulin-like growth factor 1 (IGF1) is a polypeptide hormone that has a high degree of structural similarity to human proinsulin. Owing to its ubiquitous nature and its role in promoting cell growth, strategies to inhibit IGF1 actions are being pursued as potential adjunctive measures for treating diseases such as short stature, atherosclerosis and diabetes. In addition, most tumour cell types possess IGF1 receptors and conditions in the tumour microenvironment, such as hypoxia, can lead to enhanced responsiveness to IGF1. Therefore, inhibiting IGF1 action has been proposed as a specific mechanism for potentiating the effects of existing anticancer therapies or for directly inhibiting tumour cell growth.

Modulation of insulin-like growth factor (IGF)-I and IGF-binding protein interactions enhances skeletal muscle regeneration and ameliorates the dystrophic pathology in mdx mice

Administration of recombinant human insulin-like growth factor-I (rhIGF-I) has beneficial effects in animal models of muscle injury and muscular dystrophy. However, the results of these studies may have been confounded by interactions of rhIGF-I with endogenous IGF-binding proteins (IGFBPs). To date, no study has examined whether inhibiting IGFBP interactions with endogenous IGF-I can improve muscle fiber regeneration or muscular pathologies. We tested the hypothesis that reducing IGFBP interactions with endogenous IGF-I would enhance muscle regeneration after myotoxic injury and improve the dystrophic pathology in mdx mice. We administered an IGF-I aptamer (NBI-31772; 6 mg/kg per day, continuous infusion) to C57BL/10 mice undergoing regeneration after myotoxic injury or to mdx dystrophic mice. NBI-31772 binds all six IGFBPs with high affinity and releases "free" endogenous IGF-I. NBI-31772 treatment increased the rate of functional repair in fast-twitch tibialis anterior muscles after notexin-induced injury as evidenced by an increase in maximum force producing capacity (P(o)) at 10 days after injury. In contrast, NBI-31772 administration for 28 days did not alter P(o) of extensor digitorum longus (EDL) and soleus muscles or normalized force of diaphragm muscle strips from mdx mice. Although IGFBP inhibition reduced the susceptibility of the fast-twitch EDL and the diaphragm muscle to contraction-mediated damage, it increased muscle fatigability during repeated maximal contractions. Although the results in the myotoxic injury model suggest IGF-I signaling is important in this model, the results in the mdx model are mixed.

IGF-II and IGFBP-2 differentially regulate PTEN in human breast cancer cells

The dual-function phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is the second most frequently mutated gene in human cancers. PTEN counteracts the functions of many growth factors, the most prevalent of which is insulin-like growth factor II (IGF-II). PTEN expression is stimulated by IGF-II forming a feedback loop. Investigating IGF-binding protein (IGFBP) modulation of IGF-II actions on MCF-7 breast cancer cells, we found that IGFBP-2 also regulates PTEN. The MCF-7 cells were not responsive to high doses of IGF-II due to induction of PTEN, which was not observed with an IGF-II-analog that does not bind to IGFBPs or in the presence of an inhibitor that prevents IGFs associating with IGFBPs. These cells predominantly produce IGFBP-2: blocking IGFBP-2 with a specific antibody, or preventing IGFBP-2 binding to integrins, restored the induction of PTEN and the cells were non-responsive to high doses of the IGF-II-analog. Our findings indicate that breast cancer cells do not respond to high doses of IGF-II due to induction of PTEN, but IGFBP-2, when free from IGF-II can suppress PTEN. Levels of IGFBP-2 are elevated frequently in human tumors: its ability to regulate PTEN could have important implications in relation to therapeutic strategies targeting growth factor pathways.

Development of a scintillation proximity assay for human insulin-like growth factor-binding protein 4 compatible with inhibitor high-throughput screening

The insulin-like growth factor-binding protein 4 (IGFBP-4), which exists in many different tissues and biological fluids, modulates insulin-like growth factor 1 (IGF-1) bioavailability in part by competitive sequestration and prevention of interaction with cell membrane IGF-1 receptors. Accordingly, small molecules that inhibit the ability of IGF-1 to associate with IGFBP-4 may have clinical utility as regulators of cellular proliferation, survival, and differentiation. Currently, a polyethylene glycol-based precipitation of [(125)I]IGF-1 bound to IGFBP-4 is used to quantify selective IGFBP-4 ligand interactions. We have developed a novel 96-well plate scintillation proximity assay (SPA) for measuring small molecule interactions at IGFBP-4 using a biotinylated form of IGFBP-4 coupled to streptavidin-coated polyvinyltoluene (PVT) SPA microbeads and using [(125)I]IGF-1 as the endogenous ligand. Dose-displacement curves with unlabeled IGF-1 exhibited a mean K(d) value of 0.46 nM. Parallel studies using the nonselective IGFBP inhibitor, NBI-31772, generated a K(i) value of 47 nM. Under optimized conditions, the IGFBP-4 SPA was stable for up to 24h at room temperature and was unaffected by dimethyl sulfoxide (DMSO,<0.5%). This homogeneous binding assay is simple, stable, sensitive, and amenable to automation. The good signal/noise ratio (10:1) and Z' factor (0.7-0.8) make it compatible with high-throughput screening platforms for the identification of IGFBP-4 inhibitors. The IGFBP-4 binding assay may be expanded to other IGFBP members, in biotinylated form, to provide a powerful tool amenable to drug screening and the design of therapeutics to treat a variety of IGF-responsive diseases.

The effects of the insulin-like growth factor-I aptamer, NBI-31772, on glucose homeostasis in the mouse

The majority of insulin-like growth factor-I (IGF-I) in the adult rodent circulation is bound to high affinity IGF binding proteins. We investigated the changes in IGF-I clearance, blood glucose and plasma insulin levels, and tissue 2-deoxyglucose uptake after intravenous administration of the IGF aptamer, NBI-31772, which selectively competes with IGF-I for binding to the IGFBPs, but has no effect at the IGF-I receptor. Clearance of 125I-IGF-I was significantly increased in NBI-31772-treated mice compared with vehicle-treated mice (t1/2 = 45.0 ± 1.9 vs. 56.3 ± 3.9 min, respectively; p = 0.021). However, NBI-31772 had no significant effect on glucose levels, and no insulin sparing effect was apparent neither under basal conditions nor during an intravenous glucose challenge. The decline in the specific activity after 3H-2-deoxyglucose administration was significantly less rapid in NBI-31772-treated mice compared with controls, suggesting that the IGF-I aptamer had an inhibitory effect on hepatic gluconeogenesis. In contrast, no insulin-like effect was apparent in other tissues examined. 3H-2-deoxyglucose accumulation was similar in all tissues analyzed, including skeletal muscle, which is thought to be particularly sensitive to IGF-I. These data suggest that the IGF-I aptamer affects clearance of radiolabeled IGF-I from the circulation, but has no marked effects on glucose nor insulin homeostasis. The search for hydrophilic IGF aptamers with longer duration of action that could be used in the treatment of diabetes may be rewarding. Key words: insulin resistance, gluconeogenesis, 2-deoxyglucose uptake, glucose clearance.

A methodology for distinguishing divergent cell fates within a common progenitor population: adenoma- and neuroendocrine-like cells are confounders of rat ileal epithelial cell (IEC-18) culture

Background

IEC-18 cells are a non-transformed, immortal cell line derived from juvenile rat ileal crypt cells. They may have experimental advantages over tumor-derived gastrointestinal lineages, including preservation of phenotype, normal endocrine responses and retention of differentiation potential. However, their proclivity for spontaneous differentiation / transformation may be stereotypical and could represent a more profound experimental confounder than previously realized. We hypothesized that IEC-18 cells spontaneously diverge towards a uniform mixture of epigenetic fates, with corresponding phenotypes, rather than persist as a single progenitor lineage.

Results

IEC-18 cells were cultured for 72 hours in serum free media (SFM), with and without various insulin-like growth factor agonists to differentially boost the basal rate of proliferation. A strategy was employed to identify constitutive genes as markers of divergent fates through gene array analysis by cross-referencing fold-change trends for individual genes against crypt cell abundance in each treatment. We then confirmed the cell-specific phenotype by immunolocalization of proteins corresponding to those genes. The majority of IEC-18 cells in SFM alone had a loss in expression of the adenomatous polyposis coli (APC) gene at the mRNA and protein levels, consistent with adenoma-like transformation. In addition, a small subset of cells expressed the serotonin receptor 2A gene and had neuroendocrine-like morphology.

Conclusions

IEC-18 cells commonly undergo a change in cell fate prior to reaching confluence. The most common fate switch that we were able to detect correlates with a down regulation of the APC gene and transformation into an adenoma-like phenotype.

Pharmacological disruption of insulin-like growth factor 1 binding to IGF-binding proteins restores anabolic responses in human osteoarthritic chondrocytes

Insulin-like growth factor 1 (IGF-1) has poor anabolic efficacy in cartilage in osteoarthritis (OA), partly because of its sequestration by abnormally high levels of extracellular IGF-binding proteins (IGFBPs). We studied the effect of NBI-31772, a small molecule that inhibits the binding of IGF-1 to IGFBPs, on the restoration of proteoglycan synthesis by human OA chondrocytes. IGFBPs secreted by human OA cartilage or cultured chondrocytes were analyzed by western ligand blot. The ability of NBI-31772 to displace IGF-1 from IGFBPs was measured by radiobinding assay. Anabolic responses in primary cultured chondrocytes were assessed by measuring the synthesis of proteoglycans in cetylpyridinium-chloride-precipitable fractions of cell-associated and secreted 35S-labeled macromolecules. The penetration of NBI-31772 into cartilage was measured by its ability to displace 125I-labeled IGF-1 from cartilage IGFBPs. We found that IGFBP-3 was the major IGFBP secreted by OA cartilage explants and cultured chondrocytes. NBI-31772 inhibited the binding of 125I-labeled IGF-1 to IGFBP-3 at nanomolar concentrations. It antagonized the inhibitory effect of IGFBP-3 on IGF-1-dependent proteoglycan synthesis by rabbit chondrocytes. The addition of NBI-31772 to human OA chondrocytes resulted in the restoration or potentiation of IGF-1-dependent proteoglycan synthesis, depending on the IGF-1 concentrations. However, NBI-31772 did not penetrate into cartilage explants. This study shows that a new pharmacological approach that uses a small molecule inhibiting IGF-1/IGFBP interaction could restore or potentiate proteoglycan synthesis in OA chondrocytes, thereby opening exciting possibilities for the treatment of OA and, potentially, of other joint-related diseases.

Neuroprotective effects of insulin-like growth factor-binding protein ligand inhibitors in vitro and in vivo

The role of brain insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs) in neuroprotection was further investigated using in vitro and in vivo models of cerebral ischemia by assessing the effects of IGF-I, IGF-II, and high affinity IGFBP ligand inhibitors (the peptide [Leu24, 59, 60, Ala31]hIGF-I (IGFBP-LI) and the small molecule NBI-31772 (1-(3,4-dihydroxybenzoyl)-3-hydroxycarbonyl-6, 7-dihydroxyisoquinoline), which pharmacologically displace and elevate endogenous, bioactive IGFs from IGFBPs. Treatment with IGF-I, IGF-II, or IGFBP-LI (2 microg/mL) significantly (P < 0.05) reduced CA1 damage in organotypic hippocampal cultures resulting from 35 minutes of oxygen and glucose deprivation by 71%, 60%, and 40%, respectively. In the subtemporal middle cerebral artery occlusion (MCAO) model of focal ischemia, intracerebroventricular (icv) administration of IGF-I and IGF-II at the time of artery occlusion reduced ischemic brain damage in a dose-dependent manner, with maximum reductions in total infarct size of 37% (P < 0.01) and 38% (P < 0.01), respectively. In this model of MCAO, i.c.v. administration of NBI-31772 at the time of ischemia onset also dose-dependently reduced infarct size, and the highest dose (100 microg) significantly reduced both total (by 40%, P < 0.01) and cortical (by 43%, P < 0.05) infarct volume. In the intraluminal suture MCAO model, administration of NBI-31772 (50 microg i.c.v.) at the time of artery occlusion reduced both cortical infarct volume (by 40%, P < 0.01) and brain swelling (by 24%, P < 0.05), and it was still effective when treatment was delayed up to 3 hours after the induction of ischemia. These results further define the neuroprotective properties of IGFs and IGFBP ligand inhibitors in experimental models of cerebral ischemia.

6,7-dihydroxyisoquinoline-3-carboxylic acids are potent inhibitors on the binding of insulin-like growth factor (IGF) to IGF-binding proteins: optimization of the 1-position benzoyl side chain

A series of 1-benzoyl isoquinolines, based on compound 1, was synthesized and evaluated for their ability to displace IGF-I from its complex with IGF-binding protein-3. Successful modifications of 1 included the replacement of the 3,4-dihydroxybenzoyl group with a substituted benzyl group. These alternations culminated in the discovery of compounds such as 7o which had excellent in vitro potency (K(i)=9.4 nM) but with one less of the labile catechol functionality of 1.

Quinoline-carboxylic acids are potent inhibitors that inhibit the binding of insulin-like growth factor (IGF) to IGF-binding proteins

4-benzylquinolines 5, based on a series of isoquinolines 1, were prepared and tested as inhibitors of the IGF/IGFBP-3 complex based on their ability to displace IGF-I from its binding to IGF-binding protein-3. SAR studies on the 6,7-dihydroxy moiety of the quinoline 5a showed that the catecol moiety could be replaced with other functional groups. Computational modeling of the 5a/mini-IGFBP-5 complex revealed the possible binding site of 5a on IGFBP-5.