Nonpeptide αvβ3 Antagonists. 8. In Vitro and in Vivo Evaluation of a Potent αvβ3 Antagonist for the Prevention and Treatment of Osteoporosis

Discovery and Development of Highly Potent and Orally Bioavailable Nonpeptidic αvβ6 Integrin Inhibitors

A series of 3-aryl((S)-3-fluoropyrrolidin-1-yl)butanoic acids were developed as potent orally bioavailable αvβ6 integrin inhibitors. Starting from a zwitterionic peptidomimetic series optimized for inhaled administration, the balancing of potency and passive permeability to achieve suitable oral agents through modification and exploration of aryl substituents and pKa of the central cyclic amine is described. (S)-4-((S)-3-Fluoro-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)-3-(3-(2-methoxyethoxy)phenyl)butanoic acid was found to have highly desirable oral pharmacokinetic profiles in rat, dog, and minipig, with low to moderate clearance (26%, 7%, and 18% liver blood flow, respectively), moderate volumes of distribution (3.6, 1.4, and 0.9 L/kg, respectively), high to complete oral bioavailabilities, high αvβ6 integrin potency of pIC50 of 8.0, and high solubility in physiological media (>2 mg/mL). Equating to the estimated human dose range of 10-75 mg b.i.d. to achieve 90% αvβ6 target engagement at Cmin, it was selected for further investigation as a potential therapeutic agent for the treatment of idiopathic pulmonary fibrosis.

Challenges and opportunities of developing small-molecule therapies for age-related macular degeneration

Age-related macular degeneration (AMD) is the leading cause of vision loss in senior adults. The disease can be categorized into two types: wet AMD and dry AMD. Wet AMD, also known as exudative or neovascular AMD, is less common but more severe than dry AMD and is responsible for 90% of the visual impairment caused by AMD and affects 20 million people worldwide. Current treatment options mainly involve biologics that inhibit the vascular endothelial growth factor or complement pathways. However, these treatments have limitations such as high cost, injection-related risks, and limited efficacy. Therefore, new therapeutic targets and strategies have been explored to improve the outcomes of patients with AMD. A promising approach is the use of small-molecule drugs that modulate different factors involved in AMD pathogenesis, such as tyrosine kinases and integrins. Small-molecule drugs offer advantages, such as oral administration, low cost, good penetration, and increased specificity for the treatment of wet and dry AMD. This review summarizes the current status and prospects of small-molecule drugs for the treatment of wet AMD. These advances are expected to support the development of effective and targeted treatments for patients with AMD.

Potential therapeutic medicines for renal fibrosis: Small-molecule compounds and natural products

Renal fibrosis is the pathological change process of chronic kidney disease deteriorating continuously. When the renal organ is stimulated by external stimuli, it will trigger the damage and phenotypic changes of some intrinsic cells in the kidney. When the body's autoimmune regulation or external treatment is not prompted enough to restore the organ, the pathological process is gradually aggravating, inducing a large amount of intracellular collagen deposition, which leads to the appearance of fibrosis and scarring. The renal parenchyma (including glomeruli and tubules) begins to harden, making it difficult to repair the kidney lesions. In the process of gradual changes in the kidney tissue, the kidney units are severely damaged and the kidney function shows a progressive decline, eventually resulting in the clinical manifestation of end-stage renal failure, namely uremia. This review provides a brief description of the diagnosis, pathogenesis, and potential therapeutic inhibitors of renal fibrosis. Since renal fibrosis has not yet had a clear therapeutic target and related drugs, some potential targets and relevant inhibitors are discussed, especially pharmacological effects and interactions with targets. Some existing natural products have potential efficacy for renal fibrosis, which is also roughly summarized, hoping that this article would have reference significance for the treatment of renal fibrosis.

Therapeutic targeting of anoikis resistance in cutaneous melanoma metastasis

The acquisition of resistance to anoikis, the cell death induced by loss of adhesion to the extracellular matrix, is an absolute requirement for the survival of disseminating and circulating tumour cells (CTCs), and for the seeding of metastatic lesions. In melanoma, a range of intracellular signalling cascades have been identified as potential drivers of anoikis resistance, however a full understanding of the process is yet to be attained. Mechanisms of anoikis resistance pose an attractive target for the therapeutic treatment of disseminating and circulating melanoma cells. This review explores the range of small molecule, peptide and antibody inhibitors targeting molecules involved in anoikis resistance in melanoma, and may be repurposed to prevent metastatic melanoma prior to its initiation, potentially improving the prognosis for patients.

Inhibition of angiogenesis and tumor progression of MK-0429, an integrin αvβ3 antagonist, on oral squamous cell carcinoma

Purpose

Integrin αvβ₃ is an essential molecule for tumor angiogenesis. This study aimed to investigate the anti-tumor effect of MK-0429, an integrin αvβ₃ antagonist, on oral squamous cell carcinoma (OSCC) through its inhibitory effect on angiogenesis.

Methods

In this study, we investigated the effect of MK-0429 on cellular function and angiogenesis in vitro with the use of an immortalized human umbilical vein endothelial cell, HUEhT-1, which is immortalized by the electroporatic transfection of hTERT. The effect of MK-0429 on the integrin αvβ₃ signaling pathway was examined by FAK, MEK1/2 and ERK 1/2 phosphorylation. The anti-angiogenic effect of MK-0429 was evaluated by in vitro tube formation assay. The anti-tumor effect on OSCC was assessed by administrating MK-0429 to mouse oral cancer xenografts.

Results

MK-0429 inhibited cell proliferation, migration, and adhesion of HUEhT-1 in a dose-dependent manner. FAK, MEK and ERK phosphorylation were significantly blocked by MK-0429 treatment. Tube formation was suppressed by MK-0429 in dose-dependent manner. Tumor progression was significantly suppressed by MK-0429 administration in mouse oral cancer xenografts. Histological study revealed that MK-0429 decreased tumor vascularization.

Conclusion

These results indicated integrin αvβ₃ as a therapeutic target for OSCC and suggested that MK-0429 might be clinically applicable as an anti-tumor agent with potent anti-angiogenic activity.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00432-022-04100-3.

Thermodynamic Understanding of an Aza-Michael Reaction Enables Five-Step Synthesis of the Potent Integrin Inhibitor MK-0429

We describe a general strategy for the aza-Michael addition of nucleophilic heterocycles into β-substituted acrylates using potassium tert-butoxide as catalyst. Demonstrating that the reaction is under thermodynamic control underpins optimization efforts and enables rapid exploration of the substrate scope, with yields ranging from 55% to 94%. We further leverage these lessons in a significantly shortened synthesis of MK-0429, a potent pan-integrin inhibitor previously taken into human clinical trials for the treatment of prostate cancer and osteoporosis.

RGD-Binding Integrins Revisited: How Recently Discovered Functions and Novel Synthetic Ligands (Re-)Shape an Ever-Evolving Field

Integrins have been extensively investigated as therapeutic targets over the last decades, which has been inspired by their multiple functions in cancer progression, metastasis, and angiogenesis as well as a continuously expanding number of other diseases, e.g., sepsis, fibrosis, and viral infections, possibly also Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV-2). Although integrin-targeted (cancer) therapy trials did not meet the high expectations yet, integrins are still valid and promising targets due to their elevated expression and surface accessibility on diseased cells. Thus, for the future successful clinical translation of integrin-targeted compounds, revisited and innovative treatment strategies have to be explored based on accumulated knowledge of integrin biology. For this, refined approaches are demanded aiming at alternative and improved preclinical models, optimized selectivity and pharmacological properties of integrin ligands, as well as more sophisticated treatment protocols considering dose fine-tuning of compounds. Moreover, integrin ligands exert high accuracy in disease monitoring as diagnostic molecular imaging tools, enabling patient selection for individualized integrin-targeted therapy. The present review comprehensively analyzes the state-of-the-art knowledge on the roles of RGD-binding integrin subtypes in cancer and non-cancerous diseases and outlines the latest achievements in the design and development of synthetic ligands and their application in biomedical, translational, and molecular imaging approaches. Indeed, substantial progress has already been made, including advanced ligand designs, numerous elaborated pre-clinical and first-in-human studies, while the discovery of novel applications for integrin ligands remains to be explored.

Discovery of a new class of integrin antibodies for fibrosis

Lung fibrosis, or the scarring of the lung, is a devastating disease with huge unmet medical need. There are limited treatment options and its prognosis is worse than most types of cancer. We previously discovered that MK-0429 is an equipotent pan-inhibitor of αv integrins that reduces proteinuria and kidney fibrosis in a preclinical model. In the present study, we further demonstrated that MK-0429 significantly inhibits fibrosis progression in a bleomycin-induced lung injury model. In search of newer integrin inhibitors for fibrosis, we characterized monoclonal antibodies discovered using Adimab's yeast display platform. We identified several potent neutralizing integrin antibodies with unique human and mouse cross-reactivity. Among these, Ab-31 blocked the binding of multiple αv integrins to their ligands with IC50s comparable to those of MK-0429. Furthermore, both MK-0429 and Ab-31 suppressed integrin-mediated cell adhesion and latent TGFβ activation. In IPF patient lung fibroblasts, TGFβ treatment induced profound αSMA expression in phenotypic imaging assays and Ab-31 demonstrated potent in vitro activity at inhibiting αSMA expression, suggesting that the integrin antibody is able to modulate TGFβ action though mechanisms beyond the inhibition of latent TGFβ activation. Together, our results highlight the potential to develop newer integrin therapeutics for the treatment of fibrotic lung diseases.

Facile synthesis of 7-alkyl-1,2,3,4-tetrahydro-1,8-naphthyridines as arginine mimetics using a Horner-Wadsworth-Emmons-based approach

Integrin inhibitors based on the tripeptide sequence Arg-Gly-Asp (RGD) are potential therapeutics for the treatment of idiopathic pulmonary fibrosis (IPF). Herein, we describe an expeditious three-step synthetic sequence of Horner-Wadsworth-Emmons olefination, diimide reduction, and global deprotection to synthesise cores for these compounds in high yields (63-83% over 3 steps) with no need for chromatography. Key to this transformation is the phosphoramidate protecting group, which is stable to metalation steps.

Iridium-catalysed C–H borylation of β-aryl-aminopropionic acids

Iridium-catalysed C–H borylation of β-aryl-aminopropionic acid derivatives gives 3,5-functionalised protected β-aryl-aminopropionic acid boronates. One-pot borylation–functionalisation provides diverse building blocks for medicinal chemistry.

Roles of integrin in tumor development and the target inhibitors

Integrin is a large family of cell adhesion molecules (CAMs) which involves in the interaction of cells/cells and cells/ extracellular matrix (ECM) to mediate cell proliferation, differentiation, adhesion, migration, etc. In recent years, aberrant expression of integrin has been clearly found in many tumor studies, indicating that integrin is closely related to tumor formation and development. Meanwhile, it has effects on tumor cell differentiation, cell migration, proliferation and tumor neovascularization. The study of drugs targeting integrins is of great significance for the clinical treatment of tumors. Because of its important role in tumorigenesis and development, integrin has become a promising target for the treatment of cancer. This review summarizes the role of integrin in tumor development and the current state of integrin inhibitors to provide a valuable reference for subsequent research.

Effect of αvβ3 Integrin Expression and Activity on Intraocular Pressure

Purpose

To determine the effects of αvβ3 integrin expression and activation on intraocular pressure (IOP).

Methods

Cre^+/−β3^flox/flox mice were treated with topical tamoxifen eye drops for 5 days to activate Cre and excise the β3 integrin gene from the anterior segment. IOP was measured weekly for 11 weeks using rebound tonometry. Mice were then killed and changes in expression of the β3 integrin subunit in Cre^+/− β3^flox/flox mice were determined using Western blotting analysis and immunofluorescence microscopy. To determine the effect of αvβ3 integrin activation on outflow facility, porcine organ culture anterior segments (POCAS) were perfused with the αvβ3 integrin-activating antibody AP5 or an isotype IgG control for 21 hours. The effect of αvβ3 integrin activation on IOP was measured over 7 days in C57BL/6J mice intracamerally infused with AP5, AP3, IgG, or PBS.

Results

Deletion of the β3 integrin subunit using the tamoxifen-inducible Cre-loxP system resulted in a decrease in expression of the β3 integrin subunit in the trabecular meshwork and ciliary muscle. Morphologically no gross changes in the anterior segment were detected. Deletion of the β3 integrin subunit resulted in a significantly (P < 0.05) lower IOP in mice within 2 weeks following the tamoxifen treatment and persisted for 11 weeks. Activating the αvβ3 integrin with the AP5 antibody resulted in a significant (P < 0.05) increase in IOP in C57BL/6J mice and a decrease in outflow facility in 42% of the POCAS.

Conclusions

These studies demonstrate a role for αvβ3 integrin signaling in the regulation of IOP.

Integrins as A New Target for Cancer Treatment

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Despite the great progress in the development of targeted therapies for different types of cancer utilizing monoclonal antibodies (e.g., cetuximab for colorectal cancer and head and neck cancer therapy), kinase inhibitors (e.g., sorafenib for kidney cancer and gastrointestinal stromal tumours therapy), and immunomodulatory treatments (e.g., nivolumab and pembrolizumab for melanoma therapy and lung cancer therapy), there is still a need to search for new, more effective treatments.

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Integrins are responsible for intercellular adhesion and interaction with the cellular matrix. The function of integrins is related to the transduction of intracellular signals associated with adhesion, migration, cell proliferation, differentiation, and apoptosis. Molecules targeting integrins that lead to cancer cell death have been developed. The most advanced molecules studied in clinical trials are abituzumab, intetumumab and cilengitide. There are different groups of anti-integrin drugs: monoclonal antibodies (e.g., abituzumab) and other such as cilengitide, E7820 and MK-0429. These drugs have been evaluated in various cancer types. However, they have shown modest efficacy, and none of them have yet been approved for cancer treatment. Studies have shown that patient selection using biomarkers might improve the efficacy of anti-integrin cancer treatment. Many preclinical models have demonstrated promising results using integrin visualization for cancer detection and treatment efficacy monitoring; however, these strategies require further evaluation in humans.

Discovery of ( S)-3-(3-(3,5-Dimethyl-1 H-pyrazol-1-yl)phenyl)-4-(( R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic Acid, a Nonpeptidic αvβ6 Integrin Inhibitor for the Inhaled Treatment of Idiopathic Pulmonary Fibrosis

A series of 3-aryl(pyrrolidin-1-yl)butanoic acids were synthesized using a diastereoselective route, via a rhodium catalyzed asymmetric 1,4-addition of arylboronic acids in the presence of ( R)-BINAP to a crotonate ester to provide the ( S) absolute configuration for the major product. A variety of aryl substituents including morpholine, pyrazole, triazole, imidazole, and cyclic ether were screened in cell adhesion assays for affinity against α_vβ₁, α_vβ₃, α_vβ₅, α_vβ₆, and α_vβ₈ integrins. Numerous analogs with high affinity and selectivity for the α_vβ₆ integrin were identified. The analog ( S)-3-(3-(3,5-dimethyl-1 H-pyrazol-1-yl)phenyl)-4-(( R)-3-(2-(5,6,7,8-tetrahydro-1,8-naphthyridin-2-yl)ethyl)pyrrolidin-1-yl)butanoic acid hydrochloride salt was found to have very high affinity for α_vβ₆ integrin in a radioligand binding assay (p K_i = 11), a long dissociation half-life (7 h), very high solubility in saline at pH 7 (>71 mg/mL), and pharmacokinetic properties commensurate with inhaled dosing by nebulization. It was selected for further clinical investigation as a potential therapeutic agent for the treatment of idiopathic pulmonary fibrosis.

An integrin antagonist (MK-0429) decreases proteinuria and renal fibrosis in the ZSF1 rat diabetic nephropathy model

Multiple integrins have been implicated in modulating renal function. Modulation of integrin function can lead to pathophysiological processes associated with diabetic nephropathy such as alterations in the glomerular filtration barrier and kidney fibrosis. The complexity of these pathophysiological changes implies that multiple integrin subtypes might need to be targeted to ameliorate the progression of renal disease. To address this hypothesis, we investigated the effects of MK‐0429, a compound that was originally developed as an αvβ3 inhibitor for the treatment of osteoporosis, on renal function and fibrosis. We demonstrated that MK‐0429 is an equipotent pan‐inhibitor of multiple av integrins. MK‐0429 dose‐dependently inhibited podocyte motility and also suppressed TGF‐β‐induced fibrosis marker gene expression in kidney fibroblasts. Moreover, in the obese ZSF1 rat model of diabetic nephropathy, chronic treatment with MK‐0429 resulted in significant reduction in proteinuria, kidney fibrosis, and collagen accumulation. In summary, our results suggest that inhibition of multiple integrin subtypes might lead to meaningful impact on proteinuria and renal fibrosis in diabetic nephropathy.

Transfer hydrogenative para-selective aminoalkylation of aniline derivatives with N-heteroarenes via ruthenium/acid dual catalysis

By ruthenium/acid dual catalysis, a novel transfer hydrogenative para-selective aminoalkylation of aniline derivatives with N-heteroarenes has been demonstrated.

Hydrogen-Transfer-Mediated α-Functionalization of 1,8-Naphthyridines by a Strategy Overcoming the Over-Hydrogenation Barrier

A general catalytic hydrogen transfer-mediated α-functionalization of 1,8-naphthyridines is reported for the first time that benefits from a hydrogen transfer-mediated activation mode for non-activated pyridyl cores. The pyridyl α-site selectively couples with the C8-site of various tetrahydroquinolines (THQs) to afford novel α-functionalized tetrahydro 1,8-naphthyridines, a class of synthetically useful building blocks and potential candidates for the discovery of therapeutic and bio-active products. The utilization of THQs as inactive hydrogen donors (HDs) appears to be a key strategy to overcome the over-hydrogenation barrier and address the chemoselectivity issue. The developed chemistry features operational simplicity, readily available catalyst and good functional group tolerance, and offers a significant basis for further development of new protocols to directly transform or functionalize inert N-heterocycles.

Passing on the medicinal chemistry baton: training undergraduates to be industry-ready through research projects between the University of Nottingham and GlaxoSmithKline

In this article we describe a radically different industry-academia collaboration between the School of Chemistry, University of Nottingham, and GlaxoSmithKline (GSK), aiming to train students in research and give them an insight into medicinal chemistry as practiced in industry. The project concerns the discovery of potent and selective αvβ6 integrin antagonists to treat idiopathic pulmonary fibrosis; the synthetic chemistry is performed by a group of ten final-year undergraduates and the biological and physicochemical screening data are generated by GSK. The project planning, organisation and operation are discussed, together with some of the challenges and rewards of working with undergraduates.

Serum C-Telopeptide Collagen Crosslinks and Plasma Soluble VEGFR2 as Pharmacodynamic Biomarkers in a Trial of Sequentially Administered Sunitinib and Cilengitide

PURPOSE

Fit-for-purpose pharmacodynamic biomarkers could expedite development of combination antiangiogenic regimens. Plasma sVEGFR2 concentrations ([sVEGFR2]) mark sunitinib effects on the systemic vasculature. We hypothesized that cilengitide would impair microvasculature recovery during sunitinib withdrawal and could be detected through changes in [sVEGFR2].

EXPERIMENTAL DESIGN

Advanced solid tumor patients received 50 mg sunitinib daily for 14 days. For the next 14 days, patients were randomized to arm A (cilengitide 2,000 mg administered intravenously twice weekly) or arm B (no treatment). The primary endpoint was change in [sVEGFR2] between days 14 and 28. A candidate pharmacodynamic biomarker of cilengitide inhibition of integrin αvβ3, serum c-telopeptide collagen crosslinks (CTx), was also measured.

RESULTS

Of 21 patients, 14 (7 per arm) received all treatments without interruption and had all blood samples available for analysis. The mean change and SD of [sVEGFR2] for all sunitinib-treated patients was consistent with previous data. There was no significant difference in the mean change in [sVEGFR2] from days 14 to 28 between the arms [arm A: 2.8 ng/mL; 95% confidence interval (CI), 2.1-3.6 vs. arm B: 2.0 ng/mL; 95% CI, 0.72-3.4; P = 0.22, 2-sample t test]. Additional analyses suggested (i) prior bevacizumab therapy to be associated with unusually low baseline [sVEGFR2] and (ii) sunitinib causes measurable changes in CTx.

CONCLUSIONS

Cilengitide had no measurable effects on any circulating biomarkers. Sunitinib caused measurable declines in serum CTx. The properties of [sVEGFR2] and CTx observed in this study inform the design of future combination antiangiogenic therapy trials.

Orally active αvβ3 integrin inhibitor MK-0429 reduces melanoma metastasis

Melanoma remains one of the most aggressive types of cancer with a historically low survival rate. The αvβ3 integrin is involved in the progression of malignant melanoma. In the present study, the efficacy of MK-0429, a selective inhibitor of the αvβ3 integrin, was evaluated for its potential in the prevention of melanoma metastasis. Female B6D2F1 mice injected via the tail vein with murine B16F10 melanoma developed lung metastases within ~10 days. In the first experiment, the prevention of lung metastasis was assessed in the model treated with either vehicle, MK-0429 at 100 and 300 mg/kg orally twice daily or cyclophosphamide at 300 mg/kg, i.p. once daily. Study endpoints included determination of the study time period to achieve metastasis in lungs in this model, evaluation of the health effects on the study animals, the total number of lung colonies identified and lung tumor area. Unlike cyclophosphamide, the MK-0429 treatment did not lead to a significant weight reduction in mice. MK-0429 at 100 and 300 mg/kg reduced the number of metastatic tumor colonies by 64 and 57%, respectively, and the high dose also reduced the tumor area by 60% as compared to the vehicle. The second experiment employed B16F10 luciferase-expressing cells to examine the de novo progression of melanoma metastasis over 15 days with bioluminescent imaging of mice treated with MK-0429 at 300 mg/kg as compared to the vehicle. Tumor burden progressively advanced in the lungs of the B16F10-treated animals. However, MK-0429 reduced the progression of ventral and dorsal lung metastases by 22 and 38%, respectively, as compared to the vehicle, by study completion. Quantification of ex vivo tumor burden showed a 30-40% reduction in lung colonies by MK-0429. The two studies collectively demonstrated that MK-0429 was safe and efficacious in significantly decreasing melanoma metastasis in the lungs. The results emphasized the potential of MK-0429 as a novel, therapeutic agent for the prevention of metastatic melanoma.

Novel strategies for the treatment of chondrosarcomas: targeting integrins

Chondrosarcomas are a heterogeneous group of malignant bone tumors that are characterized by the production of cartilaginous extracellular matrix. They are the second most frequently occurring type of bone malignancy. Surgical resection remains the primary mode of treatment for chondrosarcomas, since conventional chemotherapy and radiotherapy are largely ineffective. Treatment of patients with high-grade chondrosarcomas is particularly challenging, owing to the lack of effective adjuvant therapies. Integrins are cell surface adhesion molecules that regulate a variety of cellular functions. They have been implicated in the initiation, progression, and metastasis of solid tumors. Deregulation of integrin expression and/or signaling has been identified in many chondrosarcomas. Therefore, the development of new drugs that can selectively target regulators of integrin gene expression and ligand-integrin signaling might hold great promise for the treatment of these cancers. In this review, we provide an overview of the current understanding of how growth factors, chemokines/cytokines, and other inflammation-related molecules can control the expression of specific integrins to promote cell migration. We also review the roles of specific subtypes of integrins and their signaling mechanisms, and discuss how these might be involved in tumor growth and metastasis. Finally, novel therapeutic strategies for targeting these molecules will be discussed.

Dexamethasone increases αvβ3 integrin expression and affinity through a calcineurin/NFAT pathway

The purpose of this study was to determine how dexamethasone (DEX) regulates the expression and activity of αvβ3 integrin. FACS analysis showed that DEX treatment induced expression of an activated αvβ3 integrin. Its expression remained high as long as DEX was present and continued following DEX removal. FACS analysis showed that the upregulation of αvβ3 integrin was the result of an increase in the expression of the β3 integrin subunit. By real time qPCR, DEX treatment induced a 6.2-fold increase (p<0.04) in β3 integrin mRNA by day 2 compared to control and remained elevated for 6days of treatment and then an additional 10days once the DEX was removed. The increase in β3 integrin mRNA levels required only 1day of DEX treatment to increase levels for 4days in the absence of DEX. In contrast, DEX did not alter β1 integrin mRNA or protein levels. The DEX-induced upregulation of β3 integrin mRNA was partly due to an increase in its half-life to 60.7h from 22.5h in control cultures (p<0.05) and could be inhibited by RU486 and cycloheximide, suggesting that DEX-induced de novo protein synthesis of an activation factor was needed. The calcineurin inhibitors cyclosporin A (CsA) and FK506 inhibited the DEX induced increase in β3 integrin mRNA. In summary, the DEX-induced increase in β3 integrin is a secondary glucocorticoid response that results in prolonged expression of αvβ3 integrin and the upregulation of the β3 integrin subunit through the calcineurin/NFAT pathway.

Integrin targeted therapeutics

Integrins are heterodimeric, transmembrane receptors that function as mechanosensors, adhesion molecules and signal transduction platforms in a multitude of biological processes. As such, integrins are central to the etiology and pathology of many disease states. Therefore, pharmacological inhibition of integrins is of great interest for the treatment and prevention of disease. In the last two decades several integrin-targeted drugs have made their way into clinical use, many others are in clinical trials and still more are showing promise as they advance through preclinical development. Herein, this review examines and evaluates the various drugs and compounds targeting integrins and the disease states in which they are implicated.

Integrin αvβ3-targeted gold nanoshells augment tumor vasculature-specific imaging and therapy

PURPOSE

Gold nanoshells (NSs) have already shown great promise as photothermal actuators for cancer therapy. Integrin αvβ3 is a marker that is specifically and preferentially overexpressed on multiple tumor types and on angiogenic tumor neovasculature. Active targeting of NSs to integrin αvβ3 offers the potential to increase accumulation preferentially in tumors and thereby enhance therapy efficacy.

METHODS

Enzyme-linked immunosorbent assay (ELISA) and cell binding assay were used to study the in vitro binding affinities of the targeted nanoconjugate NS-RGDfK. In vivo biodistribution and tumor specificity were analyzed using 64Cu-radiolabeled untargeted and targeted NSs in live nude rats bearing head and neck squamous cell carcinoma (HNSCC) xenografts. The potential thermal therapy applications of NS-RGDfK were evaluated by subablative thermal therapy of tumor xenografts using untargeted and targeted NSs.

RESULTS

ELISA and cell binding assay confirmed the binding affinity of NS-RGDfK to integrin αvβ3. Positron emission tomography/computed tomography imaging suggested that tumor targeting is improved by conjugation of NSs to cyclo(RGDfK) and peaks at ~20 hours postinjection. In the subablative thermal therapy study, greater biological effectiveness of targeted NSs was implied by the greater degree of tumor necrosis.

CONCLUSION

The results presented in this paper set the stage for the advancement of integrin αvβ3-targeted NSs as therapeutic nanoconstructs for effective cancer therapy.

Small molecules for bone diseases

IMPORTANCE OF THE FIELD

Bones play many roles in the body, providing structure, protecting organs, anchoring muscles and storing calcium. Over 100 million people worldwide suffer from bone diseases, mainly osteoporosis, cancer-related bone loss, osteoarthritis and inflammatory arthritis. Osteoporosis itself has no specific symptoms, and the main consequence is the increased risk of bone fractures. Therefore, the prevention of bone diseases is important to maintain the quality of life in the human society. However, treatment options are still insufficient.

AREAS COVERED IN THIS REVIEW

This review article gives a summary of the low molecular mass modulators of bone diseases targets disclosed in patent applications and articles, mainly during the last 5 years.

WHAT THE READER WILL GAIN

Readers will rapidly gain an overview of these modulators not only for historical targets, but also of emerging and re-visited targets. Readers will also be able to see the current research trend and the main players in this field.

TAKE HOME MESSAGE

Drug discovery for bone diseases has made progress in the last years. The research area has dynamically shifted from historical targets (bisphosphonate, parathyroid hormone and calcitonin) to newly confirmed targets or targets re-visited which were biologically validated in the past. Cathepsin K inhibitors should be very close to launching in the market.

5-lipoxygenase-activating protein inhibitors: development of 3-[3-tert-butylsulfanyl-1-[4-(6-methoxy-pyridin-3-yl)-benzyl]-5-(pyridin-2-ylmethoxy)-1H-indol-2-yl]-2,2-dimethyl-propionic acid (AM103)

The potent and selective 5-lipoxygenase-activating protein leukotriene synthesis inhibitor 3-[3-tert-butylsulfanyl-1-[4-(6-methoxy-pyridin-3-yl)-benzyl]-5-(pyridin-2-ylmethoxy)-1H-indol-2-yl]-2,2-dimethyl-propionic acid (11j) is described. Lead optimization was designed to afford compounds with superior in vitro and in vivo inhibition of leukotriene synthesis in addition to having excellent pharmacokinetics and safety in rats and dogs. The key structural features of these new compounds are incorporation of heterocycles on the indole N-benzyl substituent and replacement of the quinoline group resulting in compounds with excellent in vitro and in vivo activities, superior pharmacokinetics, and improved physical properties. The methoxypyridine derivative 11j has an IC(50) of 4.2 nM in a 5-lipoxygenase-activating protein (FLAP) binding assay, an IC(50) of 349 nM in the human blood LTB(4) inhibition assay, and is efficacious in a murine ovalbumin model of allergen-induced asthma. Compound 11j was selected for clinical development and has successfully completed phase 1 trials in healthy volunteers.

Synthesis and biological activity of GnRH antagonists modified at position 3 with 3-(2-methoxy-5-pyridyl)-alanine*

Degarelix is a potent very long-acting GnRH antagonist after subcutaneous administration. In this paper, we describe the synthesis of two analogs of degarelix incorporating racemic 3-(2-methoxy-5-pyridyl)-alanine (2-OMe-5Pal, 5) at position 3. The two diastereomers were separated by reverse-phase high-performance liquid chromatography (RP-HPLC) and the absolute stereochemistry at position 3 in the peptides was determined by enzymatic digestion with proteinase K. These analogs were tested in vitro for their ability to antagonize the GnRH receptor and in vivo for duration of action in a castrated male rat assay. Analog 7 with D2-OMe-5Pal was potent in vitro (IC50 = 5.22 nM); however, analog 8 with L2-OMe-5Pal at position 3 in degarelix lost potency as an antagonist of the human GnRH receptor (IC50 = 36.95 nM). Both the analogs were found to be short-acting in vivo.

The effect of integrin-specific bioactive coatings on tissue healing and implant osseointegration

Implant osseointegration, defined as bone apposition and functional fixation, is a requisite for clinical success in orthopaedic and dental applications, many of which are restricted by implant loosening. Modification of implants to present bioactive motifs such as the RGD cell-adhesive sequence from fibronectin (FN) represents a promising approach in regenerative medicine. However, these biomimetic strategies have yielded only marginal enhancements in tissue healing in vivo. In this study, clinical-grade titanium implants were grafted with a non-fouling oligo(ethylene glycol)-substituted polymer coating functionalized with controlled densities of ligands of varying specificity for target integrin receptors. Biomaterials presenting the alpha5beta1-integrin-specific FN fragment FNIII 7-10 enhanced osteoblastic differentiation in bone marrow stromal cells compared to unmodified titanium and RGD-presenting surfaces. Importantly, FNIII 7-10-functionalized titanium significantly improved functional implant osseointegration compared to RGD-functionalized and unmodified titanium in vivo. This study demonstrates that bioactive coatings that promote integrin binding specificity regulate marrow-derived progenitor osteoblastic differentiation and enhance healing responses and functional integration of biomedical implants. This work identifies an innovative strategy for the rational design of biomaterials for regenerative medicine.

Antiresorptive agents and osteoclast apoptosis

Antiresorptive agents have proven to be effective therapies for the treatment of bone diseases associated with excessive osteoclast activity. Decreased osteoclast formation, inhibition of osteoclast actions, and reduced osteoclast survival represent mechanisms by which antiresorptive agents could act. The goals of this article are to present the evidence that antiresorptive agents can decrease osteoclast survival through apoptosis, to review the mechanisms by which they are thought to activate the apoptotic process, and to consider whether the actions on apoptosis fully account for the antiresorptive effects. As background, the apoptotic process will be briefly summarized together with the evidence that factors that promote osteoclast survival affect steps in the process. Following this, therapeutic agents that are both antiresorptive and can stimulate osteoclast apoptosis will be discussed. Other bone therapeutic agents that are either antiresorptive or apoptotic, but not both, will be described. Finally, newer antiresorptive compounds that elicit apoptosis and could represent potential therapeutic agents will be noted.