Isoxazolines as potent antagonists of the integrin alpha(v)beta(3)

Starting with lead compound 2, we sought to increase the selectivity for alpha(v)beta(3)-mediated cell adhesion by examining the effects of structural changes in both the guanidine mimetic and the substituent alpha to the carboxylate. To prepare some of the desired aminoimidazoles, a novel reductive amination utilizing a trityl-protected aminoimidazole was developed. It was found that guanidine mimetics with a wide range of pK(a)'s were potent antagonists of alpha(v)beta(3). In general, it appeared that an acylated 2-aminoimidazole guanidine mimetic imparted excellent selectivity for alpha(v)beta(3)-mediated adhesion versus alpha(IIb)beta(3)-mediated platelet aggregation, with selectivity of approximately 3 orders of magnitude observed for compounds 3g and 3h. It was also found in this series that the alpha-substituent was required for potent activity and that 2,6-disubstituted arylsulfonamides were optimal. In addition, the selective alpha(v)beta(3) antagonist 3h was found to be a potent inhibitor of alpha(v)beta(3)-mediated cell migration.     

Binding model for nonpeptide antagonists of alpha(v)beta(3) integrin

A binding model for nonpeptide antagonists of integrin alpha(v)beta(3) has been developed through docking analyses utilizing the MMFFs force field and the recently published crystal structure, 1JV2. Results of this docking study have led to the identification of a novel binding model for selective antagonists of alpha(v)beta(3) over alpha(IIb)beta(3) integrins. Four different chemical classes are shown to bind in a similar fashion providing a measure of confidence in the proposed model. All alpha(v)beta(3) and alpha(IIb)beta(3) antagonists have a basic nitrogen separated some distance from a carboxylic acid to mimic RGD. For the alpha(v)beta(3) antagonists under present consideration, these charged ends are separated by twelve bonds. The basic nitrogen of the active alpha(v)beta(3) ligands are shown to interact with D150 of alpha(v) and the ligands' carboxylic acid interact with R214 of beta(3) while adopting an extended conformation with minimal protein induced internal strain. In addition, an energetically favorable interaction is found with all of the active alpha(v)beta(3) molecules with Y178 of alpha(v) when docked to the crystallographically determined structure. This novel interaction may be characterized as pi-pi stacking for the most active of the alpha(v)beta(3) selective antagonists. The proposed model is consistent with observed activity as well as mutagenicity and photoaffinity cross-linking studies of the alpha(v)beta(3) integrin.     

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.     

alpha(v)beta(3) Integrin antagonists as inhibitors of bone resorption

The alpha(v)beta(3) integrin is a non-covalent, heterodimeric, cell-surface protein that is expressed with varying density on numerous cell types, including osteoclasts, vascular smooth muscle cells, endothelial cells and a variety of tumour cells. Functionally, alpha(v)beta(3) mediates a diverse range of biological events including the adhesion of osteoclasts to bone matrix, smooth muscle cell migration and angiogenesis. Specifically, there has been significant attention focused on the preparation of inhibitors of alpha(v)beta(3) for use as inhibitors of bone resorption, in recognition of the medical need for improved prevention and treatment of osteoporosis. Herein, we summarise the pertinent chemistry and biological advances in the medicinal design and biological evaluation of peptide and small molecule alpha(v)beta(3) antagonists as inhibitors of bone resorption.     

Radiolabeled RGD peptides as integrin alpha(v)beta3-targeted PET tracers

Imaging techniques targeting tumor angiogenesis have been investigated for past decade. Of these, the radiolabeled Arg-Gly- Asp (RGD) peptide has been focused because it has high affinity and selectivity for integrin alpha(v)beta3. Integrin alpha(v)beta3 is expressed on the plasma membrane in an active status in which it binds its ligands and transduce signals when exposed activating external stimuli of tumor angiogenesis such as vascular endothelial growth factor (VEGF). Many linear or cyclic RGD peptides were developed for positron emission tomography (PET). In this review, we focused on currently developed RGD peptides as PET probes for non-invasive detection of integrin alpha(v)beta3 expression.     

Design and synthesis of potent and selective alpha(4)beta(7) integrin antagonists

Interactions of the integrins alpha(4)beta(7) with its cognate ligand mucosal addressin cell adhesion molecule-1 (MAdCAM-1) play a crucial role in the development of mucosa-associated lymphoid organs, in the generation of mucosal immune responses, and in diverse pathological processes such as chronic inflammatory bowel disease and type I diabetes. Using a previously developed spatial screening technique we describe the development of potent and selective alpha(4)beta(7) integrin antagonists based on the domain 1 Leu-Asp-Thr (LDT) sequence of MAdCAM-1 that is essential for alpha(4)beta(7) integrin binding. A library of homodetic cyclic penta- and hexapeptides was synthesized presenting the pharmacophoric LDT-sequence in different conformations. The cyclic hexapeptide P10 cyclo(Leu-Asp-Thr-Ala-D-Pro-Ala) inhibits alpha(4)beta(7) integrin mediated cell adhesion to MAdCAM-1 effectively. Further optimization of the lead structure P10 resulted in cyclic hexapeptides with enhanced activity. The compounds P25 cyclo(Leu-Asp-Thr-Ala-D-Pro-Phe), P28 cyclo(Leu-Asp-Thr-Asp-D-Pro-Phe), P29 cyclo(Leu-Asp-Thr-Asp-D-Pro-His), and P30 cyclo(Leu-Asp-Thr-Asp-D-Pro-Tyr) strongly inhibited alpha(4)beta(7) integrin mediated cell adhesion to MAdCAM-1, but they did not affect binding of the closely related alpha(4)beta(1) integrin to VCAM-1.     

N-Methylated cyclic RGD peptides as highly active and selective alpha(V)beta(3) integrin antagonists.

The alpha(V)beta(3) integrin receptor plays an important role in human tumor metastasis and tumor-induced angiogenesis. The in vivo inhibition of this receptor by antibodies or by cyclic peptides containing the RGD sequence may in the future be used to selectively suppress these diseases. Here we investigate the influence of N-methylation of the active and selective alpha(V)beta(3) antagonist cyclo(RGDfV) (L1) on biological activity. Cyclo(RGDf-N(Me)V-) (P5) was found to be even more active than L1 and is one of the most active and selective compounds in inhibiting vitronectin binding to the alpha(V)beta(3) integrin. Its high-resolution, three-dimensional structure in water was determined by NMR techniques, distance geometry calculations, and molecular dynamics calculations, providing more insight into the structure-activity relationship.     

The alpha v integrin antagonists as novel anticancer agents: an update

Integrins are involved in many cellular processes, including some pathological ones associated with various cancers, both solid tumours and metastases. Since integrins are involved in such critical processes as gene expression, which lead to cellular proliferation, migration, survival and angiogenesis, they represent potential targets for therapeutic intervention. The alpha(v)beta(3) integrin is one of the most widely studied integrins because it is one of the most promiscuous. Published studies provide compelling evidence that small molecule antagonists have the potential to treat both solid tumours and metastases, serve as diagnostic imaging agents and be used for site-directed delivery of drugs to solid tumours. The alpha(v)beta(3) integrin antagonists also inhibit blood vessel formation associated with tumour growth. Therapeutic candidates have included antibodies, cyclic peptides, peptidomimetics and small molecules. A number of potent small-molecule antagonists of the alpha(v)beta(3) integrin have now been identified and are progressing in the clinic. This review focuses on the role of alpha(v)beta(3) in cancer. The rationale for the development of the therapeutic and diagnostic candidates based on the key role of alpha(v)beta(3) is discussed.     

Integrin alpha v beta 3 antagonists for anti-angiogenic cancer treatment

Direct contact between cellular and extracellular matrix (ECM) proteins is necessary for a diverse array of physiologic processes including cellular activation, migration, proliferation, and differentiation. These direct interactions are modulated by cell adhesion molecules (CAMs) such as integrins, selectins, cadherins, and immunoglobulins. Integrin signaling also plays a key role in tumor growth, angiogenesis, and metastasis. Recent advances in the discovery and characterization of CAMs and their receptors, most notably integrin alpha(v)beta(3), and the clarification of their roles in disease states have laid the groundwork for the development and clinical implementation of novel anti-cancer treatments. Integrin alpha (v)beta(3) is a glycoprotein membrane receptor which recognizes ECM proteins expressing an arginine-glycine-aspartic acid (RGD) peptide sequence. The receptor is highly expressed on activated tumor endothelial cells, but not resting endothelial cells and normal organ systems, thus making alpha(v)beta(3) an appropriate target for anti-angiogenic therapeutics. In addition, alpha(v)beta(3) is also expressed on tumor cells, allowing for both tumor cell and tumor vasculature targeting of anti-integrin therapy. Throughout the past decade, numerous patents have been published and issued using alpha(v)beta(3) antagonists for the prevention and/or treatment of cancer, with many antagonists demonstrating positive pre-clinical anti-angiogenic and anti-tumor results. This review will focus on the key points and distinguishing factors for patents which use antibodies, RGD peptides, non-RGD peptides, peptidomimetics, and amine salts as alpha(v)beta(3) antagonists.     

Molecular model of the alpha(IIb)beta(3) integrin

A molecular model of the alpha(IIb)beta(3) integrin has been developed utilizing (i). the crystal structure of alpha(v)beta(3), (ii). homology model of the alpha(IIb) subdomain, and (iii). the docking of alpha(IIb)beta(3)/alpha(v)beta(3) dual and selective inhibitors into the putative binding sites of alpha(IIb)beta(3) and alpha(v)beta(3). Since the binding sites of these integrins are located at the interface between the two heads of the individual subunits, only the alpha(IIb)beta(3) head region is modeled. The 3D conformations of two loops in alpha(IIb), whose residues have been implicated in non-peptide ligand binding, could not be determined from homology with alpha(v) alone. Mutagenesis data and the modeling of small ligand binding contributed to the rational design of these loop conformations. The final energy minimized loop conformations exhibit permissible phi/psi angles and contribute to a binding site model of alpha(IIb)beta(3) that is consistent with both the known mutagenesis studies and in-house structure-activity relationships. The charged residues alpha(IIb):E117 and beta(3):R214 are found to dominate the ligand-protein binding interaction. The previously identified "exosite" is also identified as a hydrogen bond, hydrophobic or pi-pi interaction with Y190, similar to the recently proposed binding model of alpha(v)beta(3).     

Alpha(v)beta(3) integrin in angiogenesis and restenosis

Various integrins are thought to be intimately involved in several pathological processes, including cancers (solid tumors and metastasis), cardiovascular diseases (stroke and heart failure), inflammatory diseases (rheumatoid arthritis) and ocular pathologies. The mechanism of the involvement of integrins in these acute and chronic disease states is slowly being elucidated. Recently, various therapeutic candidates, including antibodies, cyclic peptides and peptidomimetics, have been clinically evaluated and have been shown to successfully modulate certain disease processes. This review focuses on the key role of the alpha(v) integrin (alpha(v)beta(3)) in the angiogenic processes in diseases such as cancer, restenosis following percutaneous transluminal coronary angioplasty, stroke, ocular disease and rheumatoid arthritis.     

Targeting cell surface alpha(v)beta(3) integrin increases therapeutic efficacies of a legumain protease-activated auristatin prodrug

Novel monomethylauristatin E (MMAE) prodrug 8 was designed and prepared that bound cell surface glycoprotein integrin αvβ3, and was activated using legumain protease as a catalyst. Upon activation, prodrug 8 strongly induced the death of MDA-MB-435 cells that express integrin αvβ3 on cell surface. Efficacies of prodrug 8 were also determined in vivo using animal models of 4T1 murine breast cancer, D121 Lewis lung carcinoma, and MDA-MB-435 human breast cancer. The results demonstrated that prodrug 8 decreased tumor growth and metastasis effectively. In comparison to the parent cytotoxin, MMAE, and prodrug 3, prodrug 8 was less toxic to mouse white blood cells. The latter caused no loss in weight gain of mice at a dose 3 mg/kg, which is over 30 times in excess to MMAE (0.1 mg/kg). We hypothesize that overexpression and colocalization of integrin αvβ3 and legumain protease on tumor cells, tumor vasculature, and/or tumor microenvironments can be exploited to enhance the efficacy and selectivity of potent cytotoxins, such as MMAE, which is otherwise too toxic to use for therapy.     

Vitronectin receptor alpha(V)beta(3) integrin antagonists: chemical and structural requirements for activity and selectivity

Alpha(V)beta(3) integrin, a cell surface protein, has been targeted by a variety of natural and synthetic antagonists in the search for potential cancer and osteoporosis drug candidates. This review discusses chemical and structural requirements for activity and selectivity deduced from SAR studies and draws a tentative picture of the pharmacophore.     

Selective alpha4beta7 integrin antagonists and their potential as antiinflammatory agents

The accumulation of leukocytes in various tissues contributes to the pathogenesis of numerous human autoimmune diseases. The integrin alpha4beta7, expressed on the surface of B and T lymphocytes, plays an essential role in lymphocyte trafficking throughout the gastrointestinal (GI) tract via interaction with its primary ligand, mucosal addressin cell adhesion molecule (MAdCAM). Elevated MAdCAM expression in the intestines and liver has been linked to GI-associated autoimmune disorders, including Crohn's disease, ulcerative colitis, and hepatitis C. Monoclonal antibodies that block the interaction of alpha4beta7 with MAdCAM inhibit lymphocyte homing to murine intestines without effecting migration to peripheral organs; this suggests that alpha4beta7-selective antagonists might be useful as GI specific antiinflammatory agents. Here, we report the discovery of highly potent and selective alpha4beta7 antagonists affinity selected from a random peptide-phage library. Subsequent optimization of initial peptide leads afforded alpha4beta7-selective heptapeptide inhibitors that competitively inhibit binding to MAdCAM in vitro and inhibit lymphocyte homing to murine intestines in vivo. Substitution of a single carboxylate moiety alters selectivity for alpha4beta7 by more than 500-fold to afford a potent and selective alpha4beta1 antagonist. The antagonists described here are the first peptides to demonstrate potency and selectivity for alpha4beta7 compared to other integrins.     

Phenylpiperazinylalkylamino substituted pyridazinones as potent alpha(1) adrenoceptor antagonists.

QSAR models have been used for designing a series of compounds characterized by a N-phenylpiperazinylalkylamino moiety linked to substituted pyridazinones, which have been synthesized. Measurements of the binding affinities of the new compounds toward the alpha(1a)-, alpha(1b)-, and alpha(1d)-AR cloned subtypes as well as the 5-HT(1A) receptor have been done validating, at least in part, the estimations of the theoretical models. This study provides insight into the structure activity relationships of the alpha(1)-ARs ligands and their alpha(1)-AR/5-HT(1A) selectivity.     

Disposition of a novel and potent alpha(v)beta3 antagonist in animals, and extrapolation to man

1. The disposition of 3-[2-oxo-3-[3-(5,6,7,8-tetrahydro-[1,8]naphthyridin-2-yl) propyl]-imidazolidin-1-yl]-3(S)-(6-methoxy-pyridin-3-yl)propionic acid (compound A), a potent and selective alpha(v)beta(3) antagonist, was characterized in several animal species in support of its selection for preclinical safety studies and potential clinical development. 2. Compound A exhibited marked species differences in pharmacokinetics; the plasma clearances and bioavailabilities ranged from 33-47 ml min(-1) kg(-1) in rats and mice to 4-9 ml min(-1) kg(-1) in dogs and monkeys, and about 20% in rats to 70-80% in dogs and monkeys, respectively. Both the intravenous (i.v.) and oral kinetics of compound A were linear over the dose range studied in dogs (0.1-5 mg kg(-1) i.v. and 0.25-20 mg kg(-1) orally [p.o.]) and rats (1-30 mg kg(-1) i.v. and 4-160 mg kg(-1) p.o.). 3. Compound A was eliminated substantially by urinary excretion; the urinary recovery of the unchanged drug was 67% in rhesus, 48% in dogs and about 30% in rats. In these animal species, biotransformation was modest. 4. Following i.v. administration of [(14)C]-compound A to rats, the radioactivity rapidly distributed to all tissues investigated, with high levels of the radioactivity detected in liver, kidney and intestine soon after the drug administration. The radioactivity declined rapidly, with less than 1% of the i.v. dose remaining at 30-h post-dose. 5. Compound A was moderately bound to plasma proteins, with unbound fractions of 26, 20, 14 and 5% for rats, dogs, monkeys and humans, respectively. It was bound primarily to human alpha(1)-acid glycoprotein (about 85% binding at 0.1% concentration), as compared with human albumin (< 50% binding at 4% concentration). 6. Using simple allometry, compound A was predicted to exhibit relatively low clearance (1-3 ml min(-1) kg(-1)) and low volume of distribution (0.1-0.3 l kg(-1)) in humans. Based on the predicted values, compound A was projected to exhibit a favourable oral pharmacokinetic profile in humans, with good bioavailability (50-80%). These predicted values provided a basis for compound selection for further development.     

Ligand binding analysis for human alpha5beta1 integrin: strategies for designing new alpha5beta1 integrin antagonists

We report a three-dimensional model of the alpha5beta1 integrin headgroup bound to the most potent and selective ligand (SJ749) known to date. The model was built using the comparative protein modeling method, and it is consistent with experimental data. From this study, we identified two potentially important regions in the alpha5beta1 receptor that are peculiar to this integrin and might be worth considering for drug targeting.     

整合素αvβ3拮抗剂的研究进展

肿瘤生长初期没有新血管生成（无血管期）,其生长到一定程度时依赖新生血管的维持.肿瘤血管生成是肿瘤生长和转移的形态学基础,它不仅向肿瘤提供营养,也向宿主输出大量的肿瘤细胞导致肿瘤的生长和转移.因此对以抑制肿瘤血管生成为目的的抗肿瘤药物的研究方兴未艾,有很多具有抑制肿瘤血管生成作用的化合物如大黄素与青蒿琥酯等被发现.整合素αvβ3介导血管内皮细胞和肿瘤细胞的黏附,参与血管生成和肿瘤转移,在肿瘤生长中起重要作用.当其功能受到抑制时,血管内皮细胞出现凋亡,肿瘤生长受到抑制,甚至肿瘤消退.整合素αvβ3受体拮抗剂作为抗新生血管肿瘤药物的同时,对骨质流失、血栓、风湿性关节炎的治疗也起了重要作用.