Design, synthesis and biological evaluation of nonpeptide integrin antagonists

The challenges and opportunities of αvβ3-based therapeutics in cancer: From bench to clinical trials

Integrins are main cell adhesion receptors serving as linker attaching cells to extracellular matrix (ECM) and bidirectional hubs transmitting biochemical and mechanical signals between cells and their environment. Integrin αvβ3 is a critical family member of integrins and interacts with ECM proteins containing RGD tripeptide sequence. Accumulating evidence indicated that the abnormal expression of integrin αvβ3 was associated with various tumor progressions, including tumor initiation, sustained tumor growth, distant metastasis, drug resistance development, maintenance of stemness in cancer cells. Therefore, αvβ3 has been explored as a therapeutic target in various types of cancers, but there is no αvβ3 antagonist approved for human therapy. Targeting-integrin αvβ3 therapeutics has been a challenge, but lessons from the past are valuable to the development of innovative targeting approaches. This review systematically summarized the structure, signal transduction, regulatory role in cancer, and drug development history of integrin αvβ3, and also provided new insights into αvβ3-based therapeutics in cancer from bench to clinical trials, which would contribute to developing effective targeting αvβ3 agents for cancer treatment.

A novel method of screening combinations of angiostatics identifies bevacizumab and temsirolimus as synergistic inhibitors of glioma-induced angiogenesis

Tumor angiogenesis is critical for the growth and progression of cancer. As such, angiostasis is a treatment modality for cancer with potential utility for multiple types of cancer and fewer side effects. However, clinical success of angiostatic monotherapies has been moderate, at best, causing angiostatic treatments to lose their early luster. Previous studies demonstrated compensatory mechanisms that drive tumor vascularization despite the use of angiostatic monotherapies, as well as the potential for combination angiostatic therapies to overcome these compensatory mechanisms. We screened clinically approved angiostatics to identify specific combinations that confer potent inhibition of tumor-induced angiogenesis. We used a novel modification of the ex ovo chick chorioallantoic membrane (CAM) model that combined confocal and automated analyses to quantify tumor angiogenesis induced by glioblastoma tumor onplants. This model is advantageous due to its low cost and moderate throughput capabilities, while maintaining complex in vivo cellular interactions that are difficult to replicate in vitro. After screening multiple combinations, we determined that glioblastoma-induced angiogenesis was significantly reduced using a combination of bevacizumab (Avastin®) and temsirolimus (Torisel®) at doses below those where neither monotherapy demonstrated activity. These preliminary results were verified extensively, with this combination therapy effective even at concentrations further reduced 10-fold with a CI value of 2.42E-5, demonstrating high levels of synergy. Thus, combining bevacizumab and temsirolimus has great potential to increase the efficacy of angiostatic therapy and lower required dosing for improved clinical success and reduced side effects in glioblastoma patients.

Proteins, peptides and peptidomimetics as active agents in implant surface functionalization

The recent impact of implants on improving the human life quality has been enormous. During the past two decades we witnessed major advancements in both material and structural development of implants. They were driven mainly by the increasing patients' demand and the need to address the major issues that come along with the initially underestimated complexity of the bone-implant interface. While both, the materials and design of implants reached a certain, balanced state, recent years brought a shift in focus towards the bone-implant interface as the weakest link in the increasing implant long-term usability. As a result, several approaches were developed. They aimed at influencing and enhancing the implant osseointegration and its proper behavior when under load and stress. With this review, we would like to discuss the recent advancements in the field of implant surface modifications, emphasizing the importance of chemical methods, focusing on proteins, peptides and peptidomimetics as promising agents for titanium surface coatings.

Endogenous ribosomal protein L29 (RPL29): a newly identified regulator of angiogenesis in mice

Cellular ribosomal protein L29 (RPL29) is known to be important in protein synthesis, but its function during angiogenesis has never been described before. We have shown previously that mice lacking β3-integrins support enhanced tumour angiogenesis and, therefore, deletion of endothelial αvβ3 can provide a method for discovery of novel regulators of tumour angiogenesis. Here, we describe significant upregulation of RPL29 in β3-null endothelial cells at both the mRNA and protein level. Ex vivo, we show that VEGF-stimulated microvessel sprouting was reduced significantly in Rpl29-heterozygous and Rpl29-null aortic ring assays compared with wild-type controls. Moreover, we provide in vivo evidence that RPL29 can regulate tumour angiogenesis. Tumour blood vessel density in subcutaneously grown Lewis lung carcinomas was reduced significantly in Rpl29-mutant mice. Additionally, depletion of Rpl29 using RNA interference inhibited VEGF-induced aortic ring sprouting, suggesting that anti-RPL29 strategies might have anti-angiogenic potential. Overall, our results identify that loss or depletion of RPL29 can reduce angiogenesis in vivo and ex vivo.

Acurhagin-C, an ECD disintegrin, inhibits integrin alphavbeta3-mediated human endothelial cell functions by inducing apoptosis via caspase-3 activation

BACKGROUND AND PURPOSE

Acurhagin, a member of versatile metalloproteinase disintegrins from Agkistrodon acutus venom, has been identified as a platelet aggregation inhibitor, previously. Here, acurhagin-C, the C-terminal Glu-Cys-Asp (ECD)-containing fragment of acurhagin, was evaluated for its biological activities and potential applications in anti-angiogenic therapy.

EXPERIMENTAL APPROACH

Human umbilical vein endothelial cells (HUVECs) were treated with acurhagin-C to assay effects on viability, apoptosis, adhesion, migration, invasion, proliferation and angiogenesis. The recognition site and signalling involved for the interactions of acurhagin-C with HUVEC were determined using flow cytometric, electrophoresis and immunoblotting analyses.

KEY RESULTS

Acurhagin-C decreased viability and induced apoptosis in HUVEC. It also dose-dependently inhibited HUVEC adhesion to immobilized extracellular matrices fibronectin, collagen I and vitronectin with respective IC(50) values of approximately 0.6, 0.3 and 0.1 microM. Acurhagin-C prevented migration and invasion of HUVEC through vitronectin- and Matrigel-coated barriers respectively. Furthermore, acurhagin-C attenuated fibroblast growth factor-2-primed angiogenesis both in vitro and in vivo, and specifically blocked the binding of anti-alphavbeta3 monoclonal antibody 23C6 to HUVEC in an ECD-dependent manner. However, purified alphavbeta3 also dose-dependently bound to immobilized acurhagin and acurhagin-C with a saturable pattern. Interference with integrin alphavbeta3-mediated functions and promotion of caspase-3 activation by acurhagin-C affected morphology of HUVEC and induced apoptosis.

CONCLUSIONS AND IMPLICATIONS

Acurhagin-C elicited endothelial anoikis via disruption of alphavbeta3/focal adhesion kinase/phosphatidylinositol 3-kinase/Akt survival cascade and subsequent initiation of the procaspase-3 apoptotic signalling pathway.

1-Isopropyl-4-nitro-6-meth-oxy-1H-benzimidazole

There are two independent mol­ecules in the asymmetric unit of the title compound, C₁₁H₁₃N₃O₃. The inter­planar angles for the two rings of the benzimidazole ring system is 2.21 (12)° in one mol­ecule and 0.72 (12)° in the other. The nitro group is twisted in the same direction relative to the least-squares plane through its attached benzene ring in both mol­ecules, with inter­planar angles of 15.22 (9) and 18.02 (8)°. In the crystal structure, mol­ecules are stacked along the a axis through π–π inter­actions (centroid–centroid distance 4.1954 Å). C—H⋯O hydrogen bonds are also present.

Synthesis and biological evaluation of non-peptide αvβ3/α5β1 integrin dual antagonists containing 5,6-dihydropyridin-2-one scaffolds

Small constrained non-peptidic molecules consisting of a polyfunctionalized rigid core, carrying appendages corresponding to arginine and aspartic acid side chains, have been recently reported to be promising for drug development. In this work, the 5,6-dihydropyridin-2-one was envisaged as a scaffold to turn into potential integrin ligands, introducing a carboxylic acid and a basic appendage. The synthesis and the antiadhesion activity of a small library of peptidomimetics capable to recognize alpha(v)beta(3) and alpha(5)beta(1) integrins has been herein reported.

Tricyclic pharmacophore-based molecules as novel integrin αvβ3 antagonists. Part 1: Design and synthesis of a lead compound exhibiting αvβ3/αIIbβ3 dual antagonistic activity

In order to generate novel compounds with integrin alpha(v)beta3-antagonistic activity together with antiplatelet activity, tricyclic pharmacophore-based molecules were designed and synthesized. Although piperazine-containing compounds initially prepared were selective alpha(IIb)beta3 antagonists, replacement of piperazine with piperidine furnished a potent alpha(v)beta3/alpha(IIb)beta3 dual antagonist. Structure-activity relationship (SAR) studies provided clues for further development of tricyclic pharmacophore-based integrin antagonists.

Use of RNA interference to inhibit integrin subunit alphaV-mediated angiogenesis

One of the central molecules in capillary formation during angiogenesis is the integrin alphaVbeta3. The aim of this study was to inhibit alphaV-mediated angiogenesis in vitro using RNAs (siRNA) as well as antisense oligodeoxyribonucleotides (asON). Five siRNAs, against the alphaV chain of alphaVbeta3, and three asON, which had the respective sequence of the antisense sequence of three of the siRNAs molecules, were examined. Two of the siRNAs and their respective asON were designed on the basis of computer-predicted secondary structure analysis of alphaV mRNA. The different molecules were transfected into human umbilical vein endothelials cells (HUVEC) using lipofection. Following stimulation by PMA, two siRNAs showed a dose-dependent inhibition of PMA-induced alphaV mRNA and protein upregulation, as assessed by real-time RT-PCR and flow cytometry. At a concentration of 25 nM a complete inhibition of protein upregulation was found using siRNAs while transfection of the respective asON sequences reduced the protein upregulation only by 44%. To evaluate the anti-angiogenic potential a cell culture model of human angiogenesis based on the co-cultivation of endothelial cells and dermal fibroblasts was used. Transfection of the siRNA sequence (50 nM) resulted in an inhibition of the total length of capillary-like tubules by 40.6% in comparison to 21.1% using the respective asON sequence. In conclusion, siRNA-based downregulation of alphaV expression showed a stronger inhibition of capillary tube formation in an angiogenesis in vitro assay, than asON having the same sequence as the antisense strand of the siRNAs. Therefore, siRNAs are useful tools for functional alphaV knock-down experiments and might be a therapeutic alternative for antagonists which bind directly to the integrins alphaVbeta3 or alphaVbeta5.

Synthetic RGD-containing α-helical coiled coil peptides promote integrin-dependent cell adhesion

Integrin receptors are the main mediators of cell adhesion to the extracellular matrix. They bind to their ligands by interacting with short amino acid sequences, such as the RGD sequence. Soluble, small RGD-based peptides have been used to block integrin-binding to ligands, thereby interfering with cell adhesion, migration and survival, while substrate-immobilized RGD sequences have been used to enhance cell binding to artificial surfaces. This approach has several important medical applications, e.g. in suppression of tumor angiogenesis or stimulation of bone formation around implants. However, the relatively weak affinity of short RGD-containing peptides often results in incomplete integrin inhibition or ineffective ligation. In this work, we designed and synthesized several new multivalent RGD-containing molecules and tested their ability to inhibit or to promote integrin-dependent cell adhesion when used in solution or immobilized on substrates, respectively. These molecules consist of an oligomeric structure formed by alpha-helical coiled coil peptides fused at their amino-terminal ends with an RGD-containing fragment. When immobilized on a substrate, these peptides specifically promoted integrin alphaVbeta3-dependent cell adhesion, but when used in solution, they blocked alphaVbeta3-dependent cell adhesion to the natural substrates fibronectin and vitronectin. One of the peptides was nearly 10-fold more efficient than fibronectin or vitronectin in promoting cell adhesion, and almost 100-fold more efficient than a linear RGD tripeptide in blocking adhesion. These results indicate that alpha-helical coiled coil peptides carrying an amino-terminal RGD motif can be used as soluble antagonists or surface-immobilized agonists to efficiently inhibit or promote integrin alphaVbeta3-mediated cell adhesion, respectively.

Synthesis of a 6(V)-sulfated mannopentasaccharide analogue related to PI-88

An efficient and convergent synthesis of a regioselectively 6(V)-sulfated mannopentasaccharide derivative 1c, octyl 6-O-sulfo-alpha-D-mannopyranosyl-(1-->3)-alpha-D-mannopyranosyl-(1-->3)-alpha-d-mannopyranosyl-(1-->3)-alpha-D-mannopyranosyl-(1-->2)-alpha-D-mannopyranoside, was achieved by a '3 + 2' strategy. The target was designed to mimic the promising anticancer agent PI-88 and was obtained from the building blocks, octyl 3,4,6-tri-O-benzoyl-alpha-D-mannopyranoside, allyl 2,4,6-tri-O-benzoyl-3-O-(4-methoxybenzyl)-alpha-D-mannopyranoside, and 6-O-acetyl-2,3,4-tri-O-benzoyl-alpha-D-mannopyranosyl trichloroacetimidate (11), under TMSOTf-catalyzed glycosylation conditions. Compound 1c displays a mild anti-angiogenic activity based on a chorioallantoic membrane (CAM) model study.

Novel RGD-like molecules based on the tyrosine template: design, synthesis, and biological evaluation on isolated integrins αVβ3/αIIbβ3 and in cellular adhesion tests

RGD (Arg-Gly-Asp) peptidomimetics have been designed for covalent anchorage on biomaterials. The tyrosine template was thus equipped with (i) a basic side chain of various flexibility, (ii) an acidic side chain, which incorporated the XPS fluorine tag, and (iii) a spacer-arm terminated by a primary amine for surface grafting. The most active compounds showed IC50 values in the nanomolar range versus isolated human integrins alphaVbeta3 and alphaIIbbeta3. Preincubation of CaCo2 cells with soluble peptidomimetics (2 and 19a) prevented cellular adhesion on culture plates coated with vitronectin. On the other hand, peptidomimetics (19a and 19b) immobilized on a poly(ethylene)terephthalate membrane (PET) promoted CaCo2 cells adhesion. A modeling study at the ab initio level in MINI-1' basis allowed to compare the various synthetic ligands of integrins and to propose novel pharmacophore structures.

Meta-iodobenzylguanidine derivatives containing a second guanidine moiety

Radioiodinated meta-iodobenzylguanidine (MIBG) is used in the diagnosis and therapy of various neuroendocrine tumors. To investigate whether an additional guanidine function in the structure of MIBG will yield analogues that may potentially enhance tumor-to-target ratios, two derivatives-one with a guanidine moiety and another with a guanidinomethyl group at the 4-position of MIBG-were prepared. In the absence of any uptake-1 inhibiting conditions, the uptake of 4-guanidinomethyl-3-[(131)I]iodobenzylguanidine ([(131)I]GMIBG) by SK-N-SH cells in vitro was 1.7+/-0.1% of input counts, compared to a value of 40.3+/-1.4% for [(125)I[MIBG suggesting that guanidinomethyl group at the 4-position negated the biological properties of MIBG. On the other hand, 4-guanidino-3-[(131)I]iodobenzylguanidine ([(131)I]GIBG) had an uptake (5.6+/-0.3%) that was 12-13% that of [(125)I]MIBG (46.1+/-2.7%), and the ratio of uptake by control over DMI-treated (nonspecific) cultures was higher for [(131)I]GIBG (20.9+/-0.3) than [(125)I]MIBG itself (15.0+/-2.7). The exocytosis of [(131)I]GIBG and [(125)I]MIBG from SK-N-SH cells was similar. The uptake of [(131)I]GIBG in the mouse target tissues, heart and adrenals, as well as in a number of other tissues was about half that of [(125)I]MIBG. These results suggest that substitution of guanidine functions, especially a guanidinomethyl group, in MIBG structure may not be advantageous.

Docking studies on alphavbeta3 integrin ligands: pharmacophore refinement and implications for drug design

Starting from the first crystal structure of the extracellular segment of the alpha(v)beta(3) integrin receptor with a cyclic RGD ligand bound to the active site, structural models for the interactions of known ligands with the alpha(v)beta(3) integrin receptor were generated by automated computational docking. The obtained complexes were evaluated for their consistency with structure-activity relationships and site-directed mutagenesis data. A comparison between the calculated interaction free energies and the experimental biological activities was also made. All the possible interactions of the investigated compounds at the active site and the probable ligand binding conformations provide an improved basis for structure-based rational ligand design. Additionally, our docking results allow a further validation and refinement of the pharmacophore model previously postulated by us.

Design and synthesis of 1,5- and 2,5-substituted tetrahydrobenzazepinones as novel potent and selective integrin alphaVbeta3 antagonists

The design and synthesis of novel integrin alpha(V)beta(3) antagonists based on a 1,5- or 2,5-substituted tetrahydrobenzaezpinone core is described. In vitro activity of respective compounds was determined via alpha(V)beta(3) binding assay, and selected derivatives were submitted to further characterization in functional cellular assays. SAR was obtained by modification of the benzazepinone core, variation of the spacer linking guanidine moiety and core, and modification of the guanidine mimetic. These efforts led to the identification of novel alpha(V)beta(3) inhibitors displaying potency in the subnanomolar range, selectivity versus alpha(IIb)beta(3) and functional efficacy in relevant cellular assays. A method for the preparation of enantiomerically pure derivatives was developed, and respective enantiomers evaluated in vitro. Compounds 31 and 37 were assessed for metabolic stability, resorption in the Caco-2 assay and pharmacokinetics.

Rapid insulin-like growth factor (IGF)-independent effects of IGF binding protein-3 on endothelial cell survival

Angiogenic factors, such as vascular endothelial-derived growth factor (VEGF) and IGF-I, play pivotal roles in endothelial proliferation and migration. IGF binding protein-3 (IGFBP-3) is emerging as a key regulator of cell growth and apoptosis, both as an IGF antagonist and as an independent molecule. We investigated the role of IGFBP-3 in VEGFmediated survival of human macrovascular umbilical vein endothelial cells (HUVEC). Specific commercial ELISAs quantified cell proliferation and apoptosis, and Akt phosphorylation was assessed by immunoblots and confocal microscopy. IGF-I and VEGF significantly stimulated HUVEC proliferation and survival. Addition of IGFBP-3 reversed both IGF- and VEGF-induced proliferation and prevented the survival induced by these factors. The antiproliferative and proapoptotic effects of exogenous IGFBP-3 upon VEGF-induced HUVEC survival were not inhibited by blockade of the type 1 IGF receptor with alpha IR-3 immunoglobulin, which fully prevented IGF actions. An IGFBP-3 mutant, which binds IGFs normally but has a substituted mid-region domain, lost the ability to inhibit VEGF actions. VEGF-induced phosphorylation of Akt, as evident by both specific immunoblots and confocal microscopy, was significantly and rapidly reduced in the presence of IGFBP-3, as well as wortmannin.

Inhibition of angiogenesis in vitro by alphav integrin-directed antisense oligonucleotides

The integrin alpha v beta 3 plays a central role in angiogenesis. In this study, we used antisense oligodeoxyribonucleotides (ONs) directed against the alpha v subunit of alpha v beta 3 to inhibit integrin expression. Ten ON sequences, which were selected by systematic alignment of computer-predicted secondary structures of alpha v mRNA, were transfected into human umbilical vein endothelial cells (HUVECs). Following stimulation by PMA, five antisense ONs significantly inhibited alpha v mRNA and protein expression in activated HUVEC at a concentration of 0.05 mciroM with complete prevention of PMA-induced alpha v up-regulation by the most potent antisense ON. Inhibition of alpha v expression was associated with significant inhibition of migration of HUVEC by 28% and had no effect on proliferation and apoptosis. Moreover, transfection of antisense ON inhibited the formation of tube-like structures of HUVEC in Matrigel by 44%. In a cell culture model of angiogenesis consisting of a co-culture of endothelial cells with fibroblasts, transfection of antisense ONs resulted in an inhibition of tube formation of 61%. In conclusion, alpha v antisense ONs are potent inhibitors of angiogenesis in vitro. They might, therefore, be a therapeutic alternative to antagonists, which directly bind to alpha v integrins, and might be useful for the treatment of malignant tumors and hematological malignancies.

Induction of angiogenesis by a fragment of human tyrosyl-tRNA synthetase

The first step of protein synthesis is catalyzed by aminoacyl-tRNA synthetases. In addition, certain mammalian tRNA synthetases link protein synthesis to cytokine signaling pathways. In particular, human tyrosyl-tRNA synthetase (TyrRS) can be split by proteolysis into two fragments having distinct cytokine activities. One of the TyrRS fragments (mini TyrRS) contains features identical to those in CXC chemokines (like interleukin-8) that also act as angiogenic factors. Here mini TyrRS (but not full-length TyrRS) is shown to stimulate chemotaxis of endothelial cells in vitro and stimulate angiogenesis in each of two in vivo animal models. The angiogenic activity of mini TyrRS can be opposed by anti-angiogenic chemokines like IP-10. Thus, a biological fragment of human tyrosyl-tRNA synthetase links protein synthesis to regulation of angiogenesis.

Nanomolar small molecule inhibitors for alphav(beta)6, alphav(beta)5, and alphav(beta)3 integrins

Integrin adhesion receptors frequently recognize a core amino acid sequence, Arg-Gly-Asp, in their target ligands. Inhibitors with the ability to inhibit one or a small subset of such RGD-dependent integrins have been invaluable in defining their biological function. Here, we have characterized low molecular weight inhibitors for their ability to specifically inhibit alphav(beta)6 integrin, a fibronectin/tenascin receptor. As of yet, no nonpeptidic inhibitor of alphav(beta)6 was known. New peptidomimetic and nonpeptidic compounds were examined in isolated integrin binding assays and in cell adhesion assays for their ability to block alphav(beta)6, alphav(beta)3, alphav(beta)5, and alphalIb(beta)3 integrins. The compounds are based on an aromatically substituted beta amino acid or glutaric acid derivative as an acidic center and an aminopyridyl or guanidyl residue as a basic mimetic. We found several classes of inhibitors with different selectivities, especially mono- or biselectivity on the alpha(v)-integrins alphav(beta)6 and alphav(beta)3, and nanomolar activity. Furthermore, nearly all compounds are inactive on alphaIIb(beta)3. Compound 11 is the first specific, peptidomimetic inhibitor of the alphav(beta)6 integrin receptor.

Solid-phase synthesis of c(RGDfK) derivatives: on-resin cyclisation and lysine functionalisation

The cyclic pentapeptide c(RGDfK), a selective ligand for the alpha(v)beta3 integrin, was synthesised on solid phase. All synthetic operations including the cyclisation step and the appendage of the Bolton-Hunter reagent was conducted on-resin.

Synthesis and SAR of N-substituted dibenzazepinone derivatives as novel potent and selective alpha(V)beta(3) antagonists

Synthesis and SARs of new integrin alpha(V)beta(3) antagonists based on an N-substituted dibenzazepinone scaffold are described. Variation of spacer and guanidine mimetic led to potent compounds exhibiting an IC(50) towards alpha(V)beta(3) in the nanomolar range, high selectivity versus integrin alpha(IIb)beta(3) and efficacy in functional cellular assays.

A human aminoacyl-tRNA synthetase as a regulator of angiogenesis

Aminoacyl-tRNA synthetases catalyze the first step of protein synthesis. It was shown recently that human tyrosyl-tRNA synthetase (TyrRS) can be split into two fragments having distinct cytokine activities, thereby linking protein synthesis to cytokine signaling pathways. Tryptophanyl-tRNA synthetase (TrpRS) is a close homologue of TyrRS. A natural fragment, herein designated as mini TrpRS, was shown by others to be produced by alternative splicing. Production of this fragment is reported to be stimulated by IFN-gamma, a cytokine that also stimulates production of angiostatic factors. Mini TrpRS is shown here to be angiostatic in a mammalian cell culture system, the chicken embryo, and two independent angiogenesis assays in the mouse. The full-length enzyme is inactive in the same assays. Thus, protein synthesis may be linked to the regulation of angiogenesis by a natural fragment of TrpRS.

Solid-phase synthesis of a nonpeptide RGD mimetic library: new selective alphavbeta3 integrin antagonists

The solid-phase synthesis of a low molecular weight RGD mimetic library is described. Activities of the compounds in inhibiting the interaction of ligands, vitronectin and fibrinogen, with isolated immobilized integrins alphavbeta3 and alphaIIbbeta3 were determined in a screening assay. Highly active and selective nonpeptide alphavbeta3 integrin antagonists with regard to orally bioavailability were developed, based on the aza-glycine containing lead compound 1. An important variation is the substitution of the aspartic amide of 1 by an aromatic residue. Furthermore, different guanidine mimetics have been incorporated to improve the pharmacokinetic profile. Exchange of the beta-amino acid NH by a methylene moiety in one set of RGD mimetics leads to the azacarba analogue compounds representing a novel peptidomimetic approach, which should increase the metabolic stability.

Design, synthesis and preliminary biological evaluation of a focused combinatorial library of stereodiverse carbohydrate-scaffold-based peptidomimetics

A focused combinatorial library of 126 mimetics of the RGD sequence based on sugar scaffolds have been rationally constructed using molecular modeling, with a particular emphasis on the stereodiversity of the library. A liquid phase, mix and divide synthesis was used, active compounds being identified by using orthogonal libraries and recursive deconvolution strategies.

Angiogenesis-dependent diseases and angiogenesis therapy

The discovery of the molecular mechanisms of physiological vasculogenesis and pathological angiogenesis helped to recognize two classes of diseases: one where the therapeutic angiogenesis can repair the tissue damages (arteriosclerosis, myocardial infarction, limb ischemia) and the other one where inhibition of pathological angiogenesis can cure the disease or delay its progression (retinopathies, benign and malignant angiogenic tumors, progression of malignant tumors). Although there are an exponentially growing number of new synthetic molecules characterized mainly by antiangiogenic properties, the discovery of a large battery of natural pro- and anti-angiogenic factors suggests that this may provide a more physiological approach to treat both class of angiogenesis-dependent diseases in the near future.

Expression of antisense to integrin subunit beta 3 inhibits microvascular endothelial cell capillary tube formation in fibrin

alpha(v)beta(3) antagonists are potent angiogenesis inhibitors, and several different classes of inhibitors have been developed, including monoclonal antibodies, synthetic peptides, and small organic molecules. However, each class of inhibitor works by the same principal, by blocking the binding of ligands to alpha(v)beta(3). In an effort to develop an alpha(v)beta(3) inhibitor that down-regulates the actual level of alpha(v)beta(3), we developed an antisense strategy to inhibit alpha(v)beta(3) expression in vitro. beta(3) antisense expressed in endothelial cells specifically down-regulated alpha(v)beta(3) and inhibited capillary tube formation, with the extent of down-regulation correlating with the extent of tube formation inhibition. This inhibition was matrix-specific, since tube formation was not inhibited in Matrigel. These findings support the notion that alpha(v)beta(3) is required for an essential step of angiogenesis in fibrin, namely capillary tube formation. These results suggest that pseudogenetic inhibition of beta(3) integrins using antisense techniques may ultimately provide a therapeutic means to inhibit angiogenesis in vivo.

Nonpeptide alpha(v)beta(3) antagonists. 1. Transformation of a potent, integrin-selective alpha(IIb)beta(3) antagonist into a potent alpha(v)beta(3) antagonist

Modification of the potent fibrinogen receptor (alpha(IIb)beta(3)) antagonist 1 generated compounds with high affinity for the vitronectin receptor alpha(v)beta(3). Sequential modification of the basic N-terminus of 1 led to the identification of the 5,6,7, 8-tetrahydro[1,8]naphthyridine moiety (THN) as a lipophilic, moderately basic N-terminus that provides molecules with excellent potency and selectivity for the integrin receptor alpha(v)beta(3). The THN-containing analogue 5 is a potent inhibitor of bone resorption in vitro and in vivo. In addition, the identification of a novel, nonpeptide radioligand with high affinity to alpha(v)beta(3) is also reported.

Identification and in vivo efficacy of small-molecule antagonists of integrin alphavbeta3 (the vitronectin receptor)

The integrin alphavbeta3 is thought to play a key role in the initiation and/or progression of several human diseases, including osteoporosis, restenosis following percutaneous transluminal coronary angioplasty (PTCA), rheumatoid arthritis, cancer and ocular diseases. Antagonism of integrin alphavbeta3 is therefore expected to provide an approach for the treatment and/or prevention of these diseases. A variety of potent, small-molecule alphavbeta3 antagonists have been identified, several of which are active in disease models, thereby demonstrating the therapeutic potential of alphavbeta3 antagonism. This review will focus on recent advances in the identification of small-molecule alphavbeta3 antagonists, with an emphasis on those studies where small-molecule alphavbeta3 antagonists have been used in proof-of-concept studies in vivo.