Antiangiogenic effect of dual/selective alpha(5)beta(1)/alpha(v)beta(3) integrin antagonists designed on partially modified retro-inverso cyclotetrapeptide mimetics.

Recent evidence highlighted the role of alpha(5)beta(1) integrin in angiogenesis and in regulating alpha(v)beta(3) integrin function. As a consequence, selective alpha(5)beta(1) integrin inhibitors or dual alpha(5)beta(1)/alpha(v)beta(3) integrin inhibitors are considered promising candidates for the development of cancer therapeutic agents. In this paper, we describe the synthesis and pharmacological characterization of a minilibrary of cyclotetrapeptide mimetics containing a PMRI Arg-Gly-Asp sequence. In particular, c[(R)-betaPhepsi(NHCO)Asppsi(NHCO)Gly-Arg] (3) displayed a good activity in inhibiting the alpha(v)beta(3) integrin-mediated cell adhesion of fibronectin or vitronectin, as well as the adhesion of fibronectin to the alpha(5)beta(1) integrin. Interestingly, the diastereomeric compound c[(S)-betaPhepsi(NHCO)Asppsi(NHCO)Gly-Arg] (2) maintained a good efficacy in inhibiting alpha(5)beta(1) integrin while gaining a certain selectivity over alpha(v)beta(3) integrin. These two integrin antagonists significantly inhibited bFGF-induced human endothelial cell tube formation at submicromolar concentrations. Conformational analysis and Molecular Docking calculations suggest that the different alpha(5)beta(1) versus alpha(v)beta(3) selectivity of 2 and 3 can be rationalized on the basis of the alternative display of the aromatic side chain adjacent to Asp.

Cyclopeptide analogs for generating new molecular and 3D diversity.

Cyclic peptides have been often utilized as metabolically stable, conformationally restricted mimics of different kinds of biologically active peptides, including peptide antibiotics, endogenous opioid peptides, integrin inhibitors, peptide hormones, anticancer peptides, and so on. And in particular, cyclic compounds which can mimic important secondary structure elements such as beta-turns are of outstanding importance. Since greater chemical and structural diversity are primary features to pursue for finding novel leads for pharmacological and biotechnological applications, we explored the potential utility of the retro-inverso modification. We introduced this modification into the sequence of 13-membered cyclotetrapeptides, which can be regarded as easily available, conformationally stable analogs of cyclotetrapeptides composed of all alpha-residues. In this paper we describe the synthesis of a selected mini-library of partially modified retro-inverso cyclic peptides as conformationally homogeneous scaffolds for medicinal chemistry applications. The different compounds have been obtained by simple scramble of the same residues. Finally, we discuss the conformational features of such molecules as turn mimics. The comparison suggests that the retro-inverso modification allows a higher degree of three-dimensional diversity than normal peptides.

Investigation of the interaction between the atypical agonist c[YpwFG] and MOR.

Endogenous and exogenous opiates are currently considered the drugs of choice for treating different kinds of pain. However, their prolonged use produces several adverse symptoms, and in addition, many forms of pain are resistant to any kind of therapy. Therefore, the discovery of compounds active towards mu-opioid receptors (MORs) by alternative pharmacological mechanisms could be of value for developing novel classes of analgesics. There is evidence that some unusual molecules can bind opioid receptors, albeit lacking some of the typical opioid pharmacophoric features. In particular, the recent discovery of a few compounds that showed agonist behavior even in the absence of the primary pharmacophore, namely a protonable amine, led to a rediscussion of the importance of ionic interactions in stabilizing the ligand-receptor complex and in activating signal transduction. Very recently, we synthesized a library of cyclic analogs of the endogenous, MOR-selective agonist endomorphin-1 (YPWF-NH(2)), containing a Gly5 bridge between Tyr1 and Phe4. The cyclopeptide c[YpwFG] showed good affinity and agonist behavior. This atypical MOR agonist does not have the protonable Tyr amine. In order to gain more information about plausible mechanisms of interaction between c[YpwFG] and the opioid receptor, we synthesized a selected set of derivatives containing different bridges between Tyr1 and Phe4, and tested their affinities towards mu-opioid receptors. We performed conformational analysis of the cyclopeptides by NMR spectroscopy and molecular dynamics, and investigated plausible, unprecedented modes of interaction with the MOR by molecular docking. The successive quantum mechanics/molecular mechanics investigation of the complexes obtained by the molecular docking procedure furnished a more detailed description of the binding mode and the electronic properties of the ligands. The comparison with the binding mode of the potent agonist JOM-6 seems to indicate that the cyclic endomorphin-1 analogs interact with the receptor by way of an alternative mechanism, still maintaining the ability to activate the receptor.

Inhibition of cancer cell adhesion by heterochiral Pro-containing RGD mimetics.

In this paper, we describe the synthesis of a selected library of heterochiral d-Pro-containing RGD-peptidomimetics (RpD) and we investigate the biological activity as inhibitors of fibronectin adhesion to SK-MEL-24 tumor cells. In particular, peptides 4 and 8 showed an IC(50) in the 10(-8)M range. Despite the linear structure, the peptides tend to adopt a folded conformation in a polar environment.

Re-discussion of the importance of ionic interactions in stabilizing ligand-opioid receptor complex and in activating signal transduction.

Among the many receptor classes of the GPCR family, ORs constitute a privileged drug target for their involvement in pain modulation and in a number of physiological functions and behavioural effects. Endogenous and exogenous opioid agonists have been the subject of intense investigations aiming to develop safe and potent analgesics for clinical practice; however, despite the large number of highly selective opioid agonists so far discovered, there is no convincing alternative to the use of morphine, fentanyls, and their derivatives. Alternative compounds could be very useful for treating pain forms "resistant" to the usual therapeutic agents. The recent discovery of a small number of atypical opioid agonists can furnish promising candidates for the development of alternative analgesic. In particular, a few molecules exist that can bind and activate ORs even deprived of the "minimal pharmacological requisites" generally considered to be necessary. In these cases it appears that receptor activation must be based on different ligand-receptor interaction mechanisms. Taken together, the data discussed in the review suggest that the prevailing assumptions about OR binding need revision. In particular, they strengthen the evidence that ORs can bind ligands via diverse binding modes, and in some cases an electrostatic interaction is not an absolute requirement.

Topological exploration of cyclic endomorphin-1 analogues, structurally defined models for investigating the bioactive conformation of MOR agonists.

Although there have been several reports on the conformational analysis of endomorphin-1 (YPWF-NH(2)) and related MOR (mu-opioid receptor) agonists, a definitive, convincing model of the biologically active structure is not yet available. We recently reported the synthesis and pharmacological characterization of the atypical endomorphin-analogue agonist c[YpwFG]. In this paper we discuss the conformational analysis of c[YpwFG] in comparison to its epimers, for investigating the topological features responsible for ligand recognition and receptor activation, and the role of the different pharmacophores.

Peptides and peptidomimetics in medicine, surgery and biotechnology.

Despite the fact that they have been used for a century to treat several kinds of diseases, peptides and short proteins are now considered the new generation of biologically active tools. Indeed, recent findings suggest a wide range of novel applications in medicine, biotechnology, and surgery. The efficacy of native peptides has been greatly enhanced by introducing structural modifications in the original sequences, giving rise to the class of peptidomimetics. This review gives an overview of both classical applications and promising new categories of biologically active peptides and analogs. Besides the new entries in well known peptide families, such as antibiotic macrocyclic peptides, integrin inhibitors, as well as immunoactive, anticancer, neuromodulator, opioid, and hormone peptides, a number of novel applications have been recently reported. Outstanding examples include peptide-derived semi-synthetic vaccines, drug delivery systems, radiolabeled peptides, self-assembling peptides, which can serve as biomaterials in tissue engineering for creating cartilage, blood vessels, and other tissues, or as substrates for neurite outgrowth and synapse formation, immobilized peptides, and proteins. Finally, peptide-based biomaterials can find applications in bio-nanotechnology for bio-microchips, peptide nanorods and nanotubes, bio-sensors, bio-electronic devices, and peptide-metal wires.

A novel family of minimal PMRI cyclic peptides as versatile scaffolds for generating new molecular topology.

The surface loops of proteins and active peptides are implicated in the activation of biological responses upon recognition by enzymes and receptors. Obviously, it is of interest to investigate these loops as potential leads for drug discovery. Currently, there is an urgent need for novel, general, and conformationally definite cyclic peptidomimetic scaffolds capable to mimic small portions of the protein surface. In this respect, 13-membered ring peptidomimetics can be considered privileged structures, since they represent the smallest possible systems that can retain all of the features of organized protein structures, such as single H-bonded alfa-helix loops and different kind of turns. In the present work, we report a novel family of 13-membered ring cyclic peptidomimetics based on a minimal PMRI (partially modified retro-inverse) peptide strategy; in particular, we describe the synthesis and the conformational analysis of a representative member of the family. These scaffolds have been designed to permit easy introduction in a combinatorial fashion of a range of pharmacophores that possess a diversity of structure, function, and 3D disposition.