RGD Mimetics Research Articles

Blockade of αvβ3 and αvβ5 integrins by RGD mimetics induces anoikis and not integrin-mediated death in human endothelial cells

Abstractαv integrins are thought to play an important role in tumor angiogenesis. However, discrepancies between findings with Arg-Gly-Asp (RGD) mimetics, which block angiogenesis in animal models, and knockout mice, in which loss of some αv integrins enhances tumor angiogenesis, raise questions concerning the function of these integrins and the precise role of αv substrate mimetics in antiangiogenic therapies. We have examined the effects of a novel non–peptide RGD mimetic, S 36578-2, on human endothelial cells to elucidate its antagonist activity and to identify possible agonist functions. S 36578-2 is highly selective for αvβ3 and αvβ5 integrins and induces detachment, caspase-8 activation, and apoptosis in human umbilical endothelial cells (HUVECs) plated on vitronectin. Importantly, the compound has no effect on the morphology or survival of cells plated on interstitial matrix components such as fibronectin, and it does not potentiate the apoptotic process in suspended cells. Identical results were obtained with a cyclic RGD peptide with similar target specificity. In microvascular endothelial cells, S 36578-2–induced death was also linked to its antiadhesive effect, with established lines markedly more resistant than primary cultures to the antiadhesive and proapoptotic effects. Altogether, these findings have important implications for the development of this class of antiangiogenics.

The synthesis of alternative diketopiperazines as potential RGD mimetics

Alternative RGD mimetics-with the exception of glycine-c(Arg-Asp) 1, c(Arg-Glu) 2 and c[Arg-Asp(Phe-OH)] 3 were synthesized. The DKPs were prepared on solid phase with orthogonal protection allowing further derivatization in solution. During solution phase cyclization in NH(3)/methanol, the side chain benzyl ester group of H-Arg(Tos)-Asp(OBzl)-OMe and H-Arg(Tos)-Glu(OBzl)-OMe suffer transesterification, while beta-t-butyl or beta-cyclohexyl esters are stable under the same conditions. In spite of the simple structure, all compounds bind selectively to the alpha(v)beta(3) integrin receptor, 3 showing the highest affinity with an IC(50) value of 0.74 microM value. On the other hand only 3 binds with measurable activity to the alpha(IIb)beta(3) receptor (IC(50) 159 microM). The binding affinities seem to be in accordance with the distances between the arginine guanidino and the aspartic acid carboxyl group in extended conformation determined by semiempirical geometry optimization.

Nonpeptide αvβ3 Antagonists: Identification of Potent, Chain‐Shortened 7‐Oxo RGD Mimetics.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Enhanced Intracellular Uptake of Sterically Stabilized Liposomal Doxorubicin in Vitro Resulting in Improved Antitumor Activity in Vivo

To investigate the correlation between the in vitro intracellular uptake and the in vivo antitumor activity of anticancer drugs delivered by sterically stabilized liposomes (SSL). Arginine-glycine-aspartic acid (RGD) peptide or RGD mimetic (RGDm) was coupled onto the surface of SSL to obtain the cell-binding carrier to facilitate the intracellular delivery of the encapsulated drugs. DOX-loaded SSL (SSL-DOX), DOX-loaded RGD-modified SSL (RGD-SSL-DOX) and DOX-loaded RGDm-modified SSL (RGDm-SSL-DOX) were prepared by lipid film dispersion followed by remote loading of DOX. The intracellular uptake of DOX from the various liposomal formulations was evaluated in vitro with melanoma B16 cells, and the pharmacokinetics, biodistribution, and antitumor activity were compared in C57BL/6 mice carrying melanoma B16 tumors. In vitro intracellular uptake of DOX by B16 cells and in vivo antitumor activity in terms of tumor growth inhibition and mice survival time prolongation for various liposomal DOX were in the following order: RGD-SSL-DOX > RGDm-SSL-DOX > SSL-DOX. The mean survival time of the mice treated with RGD-SSL-DOX, RGDm-SSL-DOX, and SSL-DOX was 55, 49, and 44 days, respectively. The three liposomal DOX formulations produced very close DOX accumulation in tumor, which is significantly higher than that of free DOX. RGD- or RGDm-SSL-DOX demonstrated prolonged circulation time similar to that of SSL-DOX, whereas they showed significantly lower DOX level in blood and remarkably higher uptake by spleen than SSL-DOX. Enhanced intracellular uptake of DOX encapsulated in SSL could produce an improved therapeutic effect for the melanoma B16 tumors. Enhancing intracellular delivery of the anticancer drugs encapsulated in SSL may be a promising strategy to improve their therapeutic efficacy for solid tumors.

Non-peptidic αvβ3 antagonists containing indol-1-yl propionic acids

We describe the synthesis and structure/activity relationship of RGD mimetics that are potent inhibitors of the integrin αvβ3. Indol-1-yl propionic acids containing a variety of basic moieties at the 5-position, as well as substitutions alpha and beta to the carboxy terminus were synthesized and evaluated. Novel compounds with improved potency have been identified.

Nonpeptide α vβ 3 antagonists: identification of potent, chain-shortened 7-oxo RGD mimetics

Potent, novel 7-oxo α vβ 3 antagonists have been prepared. These antagonists offer decreased plasma protein binding and excellent pharmacokinetic profiles.

Aspartate and glutamate mimetic structures in biologically active compounds.

Glutamate and aspartate are frequently recognized as key structural elements for the biological activity of natural peptides and synthetic compounds. The acidic side-chain functionality of both the amino acids provides the basis for the ionic interaction and subsequent molecular recognition by specific receptor sites that results in the regulation of physiological or pathophysiological processes in the organism. In the development of new biologically active compounds that possess the ability to modulate these processes, compounds offering the same type of interactions are being designed. Thus, using a peptidomimetic design approach, glutamate and aspartate mimetics are incorporated into the structure of final biologically active compounds. This review covers different bioisosteric replacements of carboxylic acid alone, as well as mimetics of the whole amino acid structure. Amino acid analogs presented include those with different distances between anionic moieties, and analogs with additional functional groups that result in conformational restriction or alternative interaction sites. The article also provides an overview of different cyclic structures, including various cycloalkane, bicyclic and heterocyclic analogs, that lead to conformational restriction. Higher di- and tripeptide mimetics in which carboxylic acid functionality is incorporated into larger molecules are also reviewed. In addition to the mimetic structures presented, emphasis in this article is placed on their steric and electronic properties. These mimetics constitute a useful pool of fragments in the design of new biologically active compounds, particularly in the field of RGD mimetics and excitatory amino acid agonists and antagonists.

Conformationally tailored N-[(2-methyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazin-2-yl)carbonyl]proline templates as molecular tools for the design of peptidomimetics. Design and synthesis of fibrinogen receptor antagonists.

The proline peptide bond was shown by 2D proton NMR studies to exist exclusively in the trans conformation in benzyl (2S)-1-[[(2S)-2-methyl-6-nitro-3-oxo-3,4-dihydro-2H-1,4-benzoxazin-2-yl]carbonyl]-2-pyrrolidinecarboxylate [(S,S)-11], benzyl (2S)-1-[[(2S)-2-methyl-7-nitro-3-oxo-3,4-dihydro-2H-1,4-benzoxazin-2-yl]carbonyl]-2-pyrrolidinecarboxylate [(S,S)-9], and in the corresponding 6-amino and 7-amino carboxylic acids (S,S)-3 and (S,S)-4. On the other hand, the diastereomers (R,S)-11 and (R,S)-9 containing an (R)[2-methyl-6/7-nitro-3-oxo-3,4-dihydro-2H-1,4-benzoxazin-2-yl]carbonyl moiety, and the diastereoisomers (R,S)-3 and (R,S)-4 incorporating an (R)[6/7-amino-2-methyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazin-2-yl]carbonyl moiety were found to exist as equilibria of trans(63-83%) and cis(17-37%) isomers. These conformationally defined templates were applied in the construction of RGD mimetics possessing antagonistic activity at the platelet fibrinogen receptor.

Non-peptide αvβ3 antagonists: Identification of potent, chain-shortened RGD mimetics that incorporate a central pyrrolidinone constraint

Antagonists of the integrin receptor αvβ3 are expected to have utility in the treatment of osteoporosis through inhibition of bone resorption. A series of potent, chain-shortened, pyrrolidinone-containing αvβ3 receptor antagonists is described. Two sets of diasteromeric pairs of high-affinity antagonists demonstrated marked differences in log P values, which translated into differing dog pharmacokinetic properties. One member of this set was demonstrated to be effective in reducing bone resorption in rats.

Non-Peptide α vβ 3 antagonists. Part 6: Design and synthesis of α vβ 3 antagonists containing a pyridone or pyrazinone central scaffold

Two novel series of small-molecule RGD mimetics containing either a substituted pyridone or pyrazinone central constraint were prepared. Modification of the β-alanine 3-substituent produced compounds that are potent and selective α vβ 3 antagonists and exhibit a range of physicochemical properties.

Non‐Peptide αvβ3 Antagonists. Part 5. Identification of Potent RGD Mimetics Incorporating 2‐Aryl β‐Amino Acids as Aspartic Acid Replacements.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Non-peptide α vβ 3 antagonists. Part 5: identification of potent RGD mimetics incorporating 2-aryl β-amino acids as aspartic acid replacements

A series of novel, highly potent α vβ 3 receptor antagonists with favorable pharmacokinetic profiles has been identified. In this series of antagonists, 2-aryl β-amino acids function as potent aspartic acid replacements.

Non-Peptide α vβ 3 Antagonists. Part 4: Potent and Orally Bioavailable Chain-Shortened RGD Mimetics

Potent non-peptidic α vβ 3 antagonists have been prepared where deletion of an amide bond from an earlier series of linear RGD-mimetics provides a novel series of chain-shortened α vβ 3 antagonists with significantly improved oral pharmacokinetics. These chain-shortened α vβ 3 antagonists represent structurally novel integrin inhibitors.

Incorporation of (2 S,3 S) and (2 S,3 R) β-Methyl aspartic acid into RGD-Containing peptides

We report the synthesis and biological activity of a series of side-chain-constrained RGD peptides containing the (2 S,3 R) or (2 S,3 S) β-methyl aspartic acid within the RGD sequence. These compounds have been assayed for binding to the integrin receptors α IIbβ 3 and α vβ 3 and the results demonstrate the importance of the side-chain orientation of this particular residue within the RGD sequence. Based on our findings, the (2 S,3 S) β-methylated analogues of our RGD sequences maintain their binding potency to the integrin receptors while the (2 S,3 R) β-methylated analogues exhibit a drastically reduced binding affinity. Our studies demonstrate that the three-dimensional orientation of the aspartyl side chain is a very important parameter for integrin binding and that small changes that affect the side-chain orientations give rise to drastic changes in binding affinity. These results provide important information for the design of more potent RGD mimetics.

The first synthetic receptor for the RGD sequence.

[structure: see text] The combination of an optimized arginine receptor unit with a semirigid linker carrying a strategically placed primary ammonium group leads to the first synthetic RGD receptor. It binds to the free RGD peptide as well as to cyclo(RGDfV) in water with association constants around 1000 M(-1). RGD mimetics such as benzamidine 6 are not recognized, rendering the new host a prototype of a new class of receptors selective for the true RGD sequence in peptides.

ChemInform Abstract: Non‐Peptide αvβ3 Antagonists. Part 3. Identification of Potent RGD Mimetics Incorporating Novel β‐Amino Acids as Aspartic Acid Replacements.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Photochemical Rearrangement of Oxaziridines and Nitrones in the Hexahydroindole Series: A Convenient Synthetic Route to 1‐Azabicyclo[5.2.0]nonan‐2‐ones as Novel RGD Mimetics.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Non-Peptide α vβ 3 antagonists. Part 3: Identification of potent RGD mimetics incorporating novel β-Amino acids as aspartic acid replacements

Potent non-peptidic α vβ 3 antagonists have been prepared incorporating various β-amino acids as aspartic acid mimetics. Modification of the β-alanine 3-substituents alters the potency and physicochemical properties of these receptor antagonists and in some cases provides orally bioavailable α vβ 3 inhibitors.

Photochemical rearrangement of oxaziridines and nitrones in the hexahydroindole series: a convenient synthetic route to 1-azabicyclo[5.2.0]nonan-2-ones as novel RGD mimetics.

[reaction: see text] Photolysis of oxaziridines a or nitrones b provides a convenient synthetic route to fused bicyclic lactams c adequately substituted on both cycles A and B as scaffolds for mimicking conformationally constrained beta-turn peptides as in the tripeptide RGD signaling motif of fibronectin.

Solid-phase syntheses of constrained RGD scaffolds and their binding to the α vβ 3 integrin receptor

We report the solid-phase synthesis of two different families, containing either diketopiperazine or hydantoin structures, of rigidified RGD mimetics and their binding affinity to the α vβ 3 receptor.