Alphavbeta3 integrin binding affinity and specificity of SM256 in various species

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.

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.

Acting via a cell surface receptor, thyroid hormone is a growth factor for glioma cells

Recent evidence suggests that the thyroid hormone L-thyroxine (T4) stimulates growth of cancer cells via a plasma membrane receptor on integrin alphaVbeta3. The contribution of this recently described receptor for thyroid hormone and receptor-based stimulation of cellular mitogen-activated protein kinase [MAPK; extracellular signal-regulated kinase 1/2 (ERK1/2)] activity, to enhancement of cell proliferation by thyroid hormone was quantitated functionally and by immunologic means in three glioma cell lines exposed to T4. At concentrations of 1 to 100 nmol/L, T4 caused proliferation of C6, F98, and GL261 cells, measured by accumulation of proliferating cell nuclear antigen (PCNA) and radiolabeled thymidine incorporation. This effect was inhibited by the T4 analogue, tetraiodothyroacetic acid, and by an alphaVbeta3 RGD recognition site peptide, both of which block T4 binding to integrin alphaVbeta3 but are not agonists. Activation of MAPK by T4 was similarly inhibited by tetraiodothyroacetic acid and the RGD peptide. The thyroid hormone 3,5,3'-triiodo-L-thyronine (T3) and T4 were equipotent stimulators of PCNA accumulation in C6, F98, and GL261 cells, but physiologic concentrations of T3 are 50-fold lower than those of T4. In conclusion, our studies suggest that glioblastoma cells are thyroid hormone dependent and provide a molecular basis for recent clinical observations that induction of mild hypothyroidism may improve duration of survival in glioblastoma patients. The present experiments infer a novel cell membrane receptor-mediated basis for the growth-promoting activity of thyroid hormone in such tumors and suggest new therapeutic approaches to the treatment of patients with glioblastoma.

Membrane receptors mediating thyroid hormone action

A recently identified thyroid hormone cell surface receptor on the extracellular domain of integrin alphaVbeta3 leads in human cell lines to activation of the mitogen-activated protein kinase (MAPK) signal transduction cascade. Examples of MAPK-dependent thyroid hormone actions are plasma membrane ion pump stimulation and specific nuclear events. These events include serine phosphorylation of the nuclear thyroid hormone receptor, leading to coactivator protein recruitment and complex tissue responses, such as thyroid hormone-induced angiogenesis or tumor cell growth. The existence of this cell surface receptor means that the activity of administered hormone could be limited through structural modification of the molecule to reproduce or inhibit only those hormone actions initiated at the cell surface. Examples of such modifications are provided.

Human alphavbeta3 integrin potency and specificity of TA138 and its DOTA conjugated form (89)Y-TA138

The present study was undertaken to define the alphavbeta3-binding potency and specificity of TA138, a nonpeptide integrin antagonist, and its conjugated form, 89Y-TA138. Various integrin-specific binding and functional assays as well as cell-adhesion assays were used to determine the potency and integrin specificity for TA138 and 89Y-TA138. Both TA138 and 89Y-TA138 inhibited alphavbeta3-mediated [125I]echistatin binding to 293-beta3-transfected cells, with IC50 values of 0.046 and 0.059 microM, respectively, and IC50 values of 0.012 and 0.018 microM, respectively, in inhibiting an alphavbeta3 integrin-mediated 293-beta3-transfected cell adhesion to fibrinogen. TA138 inhibited human umbilical vein endothelial cell adhesion to fibrinogen, with an IC50 value of 0.052 +/- 0.006 microM. Both TA138 and 89Y-TA138 demonstrated a relatively high degree of specificity for human alphavbeta3 integrin as compared with other human integrins, including alphavbeta5, alphaIIbbeta3, and alpha5beta1 (IC50 > 10 microM). Both 89Y-TA138 and TA138 demonstrated comparable alphavbeta3 affinity and specificity as compared with other closely related human integrins such as alphavbeta5, alphaIIbbeta3, or alpha5beta1.

αv Integrin Affinity/Specificity and Antiangiogenesis Effect of a Novel Tetraaza Cyclic Peptide Derivative, SU015, in Various Species

The present study was undertaken to define the alpha v beta3 and alpha v beta5 binding potency and specificity of SU015, an integrin antagonist. SU015 inhibited alpha v beta3-mediated human umbilical vein endothelial cell or 293/beta3-transfected CHO cell adhesion to fibrinogen, with IC50 values of 0.21 +/- 0.11 muM and 0.32 +/- 0.02 microM. SU015 demonstrated comparable affinity to alpha v beta5 as compared with alpha v beta3 affinity, as well as a relatively high degree of specificity for human alpha v beta3- and alpha v beta5-mediated functions, as compared with other human integrins, including alphaIIbbeta3 (IC50 >100 microM), alpha5/beta1 (IC50 >100 microM), and alpha4/beta1 (IC50 >100 microM). SU015 demonstrated different degrees of species specificity in blocking alpha v beta3-mediated cellular adhesion, with relatively higher affinity to monkey (IC50 = 0.10 microM) and dog (IC50 = 1.30 microM) endothelial or smooth muscle cell alpha v beta3-mediated adhesion. Additionally, SU015 demonstrated a high degree of alpha v beta3 and alpha v beta5 specificity as compared with alpha4beta1-, alpha5beta1-, or alpha IIb beta3-mediated binding in the above species. In conclusion, SU015 is an alpha v beta3 and alpha v beta5 antagonist with relatively higher potency and specificity as compared with alpha IIb beta3, alpha5beta1, or alpha4beta1 integrins. Additionally, comparable alpha v beta3 and alpha v beta5 affinity for SU015 was demonstrated with human and monkey endothelial cells. These data also suggest that this bicyclic RGD analogue linked to a linker at the bottom leaves the RGD at the top available for binding and allows for conjugation with radioisotope for imaging and radiotherapy.

Bovine aortic endothelial cells are susceptible to hantavirus infection; a new aspect in hantavirus ecology

Hantaviruses are enveloped RNA viruses that belong to the family Bunyaviridae. They are the causative agents of hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS). Hantaviruses show a worldwide distribution with specific rodent species as natural hosts. It is known that rodents can transmit the virus via feces, urine, saliva, or bites to humans. Additionally, antibodies against different hantaviruses were also found in domestic animals, For example, Danes et al. documented hantavirus-specific IgG titers in 2% of examined cattle [Ceskoslov. Epidemiol. Mikrobiol. Imunol. 41 (1992) 15]. In order to clarify the possibility of a nonrodent and nonhuman hantavirus infection, the susceptibility of bovine aortic endothelial cells (BAEC) to Hantavirus serotype Puumala infection was investigated. The hantaviral nucleocapsid protein was detected in 95% of infected BAEC at the fourth cell culture passage 12 weeks after initial infection by immunofluorescence assay (IFA). The presence of Puumala virus (PUU) nucleocapsid protein and the viral glycoproteins G1 and G2 in infected cells were additionally confirmed by Western blot analysis. The viral RNA genome was identified in infected BAEC cultures and in cell-free culture medium at the fourth passage by reverse transcription polymerase chain reaction (RT-PCR), verified by cDNA nucleotide sequence analysis, showing a 98-100% homology to the input virus. The infected BAEC cultures were shown to express alpha(V)beta(3)-integrin surface receptors that are known to mediate virus entry in human cells and revealed no major cytopathic effects (CPEs) as assayed by immunofluorescence staining of the cytoskeletal components actin and microtubules. In the present study, we documented for the first time that a nonrodent and nonhuman aortic endothelial cell culture of bovine origin (BAEC) can be efficiently infected with a hantavirus. This finding is of particular importance because it adds new aspects to questions dealing with host species barrier, viral reservoir, virus transmission, and ecology of hantaviruses.

Synthesis and biological evaluation of nonpeptide integrin antagonists containing spirocyclic scaffolds

Analogues of isoxazoline alpha(v)beta(3) antagonist 1 designed to further restrict the four carbon alkyl tether were prepared by incorporating two spirocyclic scaffolds, 1-oxa-2-azaspiro[4,5]dec-2-ene and 1-oxa-2,7-diazaspiro[4,4]non-2-ene. Additional optimization provided potent antagonists of both alpha(v)beta(3) and alpha(5)beta(1) which are selective over GPIIb/IIIa.

Anti-integrin as novel drug-discovery targets: potential therapeutic and diagnostic implications

The role of integrin and extracellular matrix proteins in various pathological processes (including angiogenesis, thrombosis, apoptosis and cell migration and proliferation), leading to both acute and chronic disease states (e.g. ocular diseases, metastasis, unstable angina, myocardial infarction, stroke, osteoporosis, a wide range of inflammatory diseases, vascular remodeling and neurodegenerative disorders) has been recently documented. A key success in this field is evident from the potential role of the platelet GPIIb/IIIa (alphaIIbbeta3) integrin in the prevention, treatment and perhaps diagnosis of various thromboembolic disorders. Additionally, progress has been shown in the development of leukocyte alpha4beta1 antagonists for various inflammatory indications and alphav integrin antagonists for angiogenesis and vascular-related disorders. However, the exact modes of action of certain integrin antagonists are still not fully clear. Integrin antagonists in clinical or pre-clinical development are expected to be used as a stand-alone therapy or, better, as an adjunct to other pharmacotherapy, radiotherapy or interventional procedures.

Synthesis of highly potent and selective hetaryl ureas as integrin alpha(V)beta3-receptor antagonists

Solid-phase synthesis and SAR of integrin alpha(V)beta3-receptor antagonists containing a urea moiety as non-basic guanidine mimetic are described. The most potent compounds exhibited IC(50) values towards alpha(V)beta3 in the nanomolar range and high selectivity versus related integrins like alpha(IIb)beta3. For selected examples efficacy in functional cellular assays is demonstrated.

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.

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.

Members of the Jagged/Notch gene families are expressed in injured arteries and regulate cell phenotype via alterations in cell matrix and cell-cell interaction

The Jagged/Notch signaling pathways control cell fate determination and differentiation, and their dysfunction is associated with human pathologies involving cardiovascular abnormalities. To determine the presence of these genes during vascular response to injury, we analyzed expression of Jagged1, Jagged2, and Notch1 through 4 after balloon catheter denudation of the rat carotid artery. Although low levels of Jagged1, Jagged2, and constitutive expression of Notch1 were seen in uninjured endothelium, expression of all was significantly increased in injured vascular cells. High Jagged1 expression was restricted to the regenerating endothelial wound edge, whereas Notch transcripts were abundant in endothelial and smooth muscle cells. To understand the basis for Jagged/Notch control of cellular phenotype, we studied an in vitro model of NIH3T3 cells transfected with a secreted form of the extracellular domain of Jagged1. We report that the soluble Jagged1 protein caused decreased cell-matrix adhesion and cell migration defects. Cadherin-mediated intercellular junctions as well as focal adhesions were modified in soluble Jagged1 transfectants, demonstrating that cell-cell contacts and adhesion plaques may be targets of Jagged/Notch activity. We suggest that Jagged regulation of cell-cell and cell-matrix interactions may contribute to the control of cell migration in situations of tissue remodeling in vivo.

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.

Selective alpha(v)beta(3)-receptor blockade reduces macrophage infiltration and restenosis after balloon angioplasty in the atherosclerotic rabbit

BACKGROUND

alpha(v)beta(3)-Integrin receptors are upregulated in atherosclerotic arteries and play a key role in smooth muscle cell and possibly inflammatory cell migration. We hypothesized that after balloon angioplasty (BA) of atherosclerotic arteries, selective inhibition of the alpha(v)beta(3)-receptor by XT199, a small-molecule, non-peptide-selective alpha(v)beta(3)-receptor antagonist, would reduce restenosis.

METHODS AND RESULTS

After induction of focal atherosclerosis, rabbits underwent femoral BA and received XT199 (2.5 mg/kg IV bolus plus 2.5 mg. kg(-1). d(-1) IV; n=19) or vehicle (n=20) for 14 days. At 28 days after BA, the XT199 group had a larger lumen (0.75+/-0.26 versus 0.57+/-0.20 mm(2), P=0.03) and a smaller neointimal area (0.49+/-0.18 versus 0.68+/-0.25 mm(2), P=0.01) than the vehicle group. Angiographic analysis confirmed a 30% to 40% reduction in restenosis. Arteries harvested at 28 days after BA did not show a reduction in intima plus media smooth muscle cell content but did show a 50% reduction in macrophage cell density in the XT199 group (716+/-452 versus 1458+/-989 cells/mm(2), P<0.006). Neovessel density at 28 days was also reduced (23+/-42 versus 58+/-46 vessel cross sections/mm(2), P<0.02). Early after BA (ie, 3 to 7 days), there was a decrease in intracellular adhesion molecule-1 and vascular cell adhesion molecule-1 expression, indicative of a reduction in vascular cell activation.

CONCLUSIONS

Selective alpha(v)beta(3)-receptor blockade for 14 days after BA in the focally atherosclerotic rabbit significantly reduced restenosis and limited macrophage infiltration and neovascularization in the vessel wall.

Human platelet alphaIIbeta3 integrin binding affinity and specificity of SJ874: antiplatelet efficacy versus aspirin

OBJECTIVE

To define the affinity and specificity of SJ874, a nonpeptide antiplatelet agent for platelet glycoprotein Ilb/IIIa integrin, and to determine the antiplatelet efficacy of SJ874 relative to those of glycoprotein IIbIIIa antagonists and aspirin.

METHODS

Binding affinity and specificity of SJ874 for platelet glycoprotein IIb/IIIa integrin were determined using integrin-mediated binding and adhesion assays with human cells. Additionally, the antiplatelet efficacy of SJ874 was determined and compared with those of other glycoprotein IIb/IIIa antagonists and aspirin using light-transmittance and laser-scattering aggregometry.

RESULTS

SJ874 inhibited aggregation of human platelets induced by 10 micromol/l adenosine diphosphate (ADP) with a concentration for half-maximal effect of 0.046 +/- 0.005 micromol/l using light-transmittance aggregometry. Using laser-scattering aggregometry, SJ874 was found to totally inhibit formation both of micro-aggregates and of macro-aggregates induced either by ADP or by epinephrine. In contrast, administration of 325 mg aspirin to normal healthy volunteers attenuated formation of macro-aggregates but not micro-aggregates. SJ874 inhibited binding of [125I]-fibrinogen to activated (by ADP, epinephrine, and arachidonic acid at concentrations of 100 micromol/l each) gel-filtered human platelets with a concentration for half-maximal effect of 0.0012 +/- 0.0005 micromol/l. SJ874 was demonstrated to associate more tightly with resting human platelets than did DMP754 [1] and slightly less tightly than did DMP802 [2]. SJ874 was demonstrated to exhibit a high degree of specificity for platelet glycoprotein IIb/IIIa (alphaIIb/beta3) integrin compared with other known integrins, including alphavbeta3, alphavbeta5, and alpha5beta1 (concentration for half-maximal effect > 100 micromol/l).

CONCLUSION

SJ874 is a potent and specific platelet glycoprotein IIb/IIIa antagonist with high affinity for and tight association with human platelets. These data suggest that SJ874 might have good antiplatelet utility for inhibiting formation both of platelet micro-aggregates and of macro-aggregates of platelets and a long duration of action in humans due to its slow dissociation from human platelets.

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.

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

A new series of indazole-containing alpha(v)beta(3) integrin antagonists is described. Starting with lead compound 18a, variations in a number of structural features were explored with respect to inhibition of the binding of beta(3)-transfected 293 cells to fibrinogen and to selectivity for alpha(v)beta(3) over GPIIbIIIa, another RGD-binding integrin. Indazoles attached to a 2-aminopyridine or 2-aminoimidazole by a propylene linker at the indazole 1-position and to a diaminopropionate derivative via a 5-carboxylate amide provided the best potency with moderate selectivity. Several differences in the SAR of the diaminopropionate moiety were observed between this series and a series of isoxazoline-based selective GPIIbIIIa antagonists. Compound 34a (SM256) was a potent antagonist of alpha(v)beta(3) (IC(50) 2.3 nM) with 9-fold selectivity over GPIIbIIIa.