Conformational studies of vasopressin analogues modified with N-methylphenylalanine enantiomers in dimethyl sulfoxide solution

Development and therapeutic potential of vasopressin synthetic analog [V4Q5]dDAVP as a novel anticancer agent

Since its discovery, arginine vasopressin (AVP) was subjected to several modifications with the aim of obtaining novel derivatives with increased potency and selectivity for biomedical use. Desmopressin (dDAVP) is a first generation synthetic analog of AVP with hemostatic and antimetastatic activity. dDAVP acts as a selective agonist of the arginine vasopressin type 2 receptor (AVPR2) present in microvascular endothelium and cancer cells. Considering its selective effects on AVPR2-expressing malignant and vascular tissue, and interesting antitumor profile, dDAVP was used as a lead compound for the development of novel peptide analogs with enhanced anticancer efficacy. After conducting different structure-activity relationship studies to determine key aminoacidic positions for its antitumor activity against AVPR2-expressing malignant cells, dDAVP was rationally modified and a wide panel of synthetic analogs with different sequence and structural modifications was assessed. As a result of this structure-based drug derivatization novel AVP analog [V⁴Q⁵]dDAVP (1-deamino-4-valine-5-glutamine-8-d-arginine vasopressin) was selected as the most active candidate and further developed. [V⁴Q⁵]dDAVP was evaluated in highly aggressive and metastatic cancer preclinical models deploying enhanced cytostatic, antimetastatic and angiostatic effects in comparison to parental peptide dDAVP. In addition, novel compound demonstrated good tolerability as evaluated in several toxicological studies, and cooperative therapeutic effects after combination with standard-of-care chemotherapy. In summary, due to its ability to inhibit growth and tumor-associated angiogenesis, as well as impairing progression of metastatic disease, AVP analogs such as novel [V⁴Q⁵]dDAVP are promising compounds for further development as coadjuvant agents for the management of advance or recurrent cancers.

Integrin Ligands with α/β-Hybrid Peptide Structure: Design, Bioactivity, and Conformational Aspects

Integrins are cell surface receptors for proteins of the extracellular matrix and plasma-borne adhesive proteins. Their involvement in diverse pathologies prompted medicinal chemists to develop small-molecule antagonists, and very often such molecules are peptidomimetics designed on the basis of the short native ligand-integrin recognition motifs. This review deals with peptidomimetic integrin ligands composed of α- and β-amino acids. The roles exerted by the β-amino acid components are discussed in terms of biological activity, bioavailability, and selectivity. Special attention is paid to the synthetic accessibility and efficiency of conformationally constrained heterocyclic scaffolds incorporating α/β-amino acid span.

Aspartate buffer and divalent metal ions affect oxytocin in aqueous solution and protect it from degradation

Oxytocin is a peptide drug used to induce labor and prevent bleeding after childbirth. Due to its instability, transport and storage of oxytocin formulations under tropical conditions is problematic. In a previous study, we have found that the stability of oxytocin in aspartate buffered formulation is improved by the addition of divalent metal ions (unpublished results). The stabilizing effect of Zn(2+) was by far superior compared to that of Mg(2+). In addition, it was found that stabilization correlated well with the ability of the divalent metal ions to interact with oxytocin in aspartate buffer. Furthermore, LC-MS (MS) measurements indicated that the combination of aspartate buffer and Zn(2+) in particular suppressed intermolecular degradation reactions near the Cys(1,6) disulfide bridge. These results lead to the hypothesis that in aspartate buffer, Zn(2+) changes the conformation of oxytocin in such a way that the Cys(1,6) disulfide bridge is shielded from its environment thereby suppressing intermolecular reactions involving this region of the molecule. To verify this hypothesis, we investigate here the conformation of oxytocin in aspartate buffer in the presence of Mg(2+) or Zn(2+), using 2D NOESY, TOCSY, (1)H-(13)C HSQC and (1)H-(15)N HSQC NMR spectroscopy. Almost all (1)H, (13)C and (15)N resonances of oxytocin could be assigned using HSQC spectroscopy, without the need for (13)C or (15)N enrichment. (1)H-(13)C and (1)H-(15)N HSQC spectra showed that aspartate buffer alone induces minor changes in oxytocin in D2O, with the largest chemical shift changes observed for Cys(1). Zn(2+) causes more extensive changes in oxytocin in aqueous solution than Mg(2+). Our findings suggest that the carboxylate group of aspartate neutralizes the positive charge of the N-terminus of Cys(1), allowing the interactions with Zn(2+) to become more favorable. These interactions may explain the protection of the disulfide bridge against intermolecular reactions that lead to dimerization.

NMR studies of new arginine vasopressin analogs modified with alpha-2-indanylglycine enantiomers at position 2 bound to sodium dodecyl sulfate micelles

In this paper, we use NMR spectroscopy and molecular modeling to examine four new vasopressin analogs modified with alpha-2-indanylglycine (Igl) at position 2, [L-Igl(2)]AVP (I), [D-Igl(2)]AVP (II), [Mpa(1),L-Igl(2)]AVP (III) and [Mpa(1),D-Igl(2)]AVP (IV), embedded in a sodium dodecyl sulfate (SDS) micelle. All the analogs display antiuterotonic activity. In addition, the analogs with D-Igl reveal antipressor properties. Each analog exhibits the tendency to adopt beta-turns at positions 2, 3 and/or 3, 4, which is characteristic of oxytocin-like peptides. Mutual arrangement of aromatic residues at positions 2 and 3 has been found to be crucial for binding antagonists with the OT and V(1a) receptors. The orientation of the Gln(4) side chain seems to be important for the V(1a) receptor affinity. In each of the peptides studied, the Gln(4) side chain is folded back over the ring moiety. However, it lies on the opposite face of the tocin moiety in analogs with L and D enantiomers of Igl.

Modeling the human oxytocin receptor for drug discovery efforts

The oxytocin receptor belongs to class A receptors within the great family of G protein-coupled receptors. The endogenous ligand oxytocin is a nonapeptide hormone that induces the uterine contractions at parturition and is used to induce the labor. The peptide oxytocin and, even more, its non-peptide antagonist, could be valuable tools in tocolysis. The knowledge of the three-dimensional structure of the oxytocin receptor and the determination of the main interaction points between the receptor and the ligands may help to develop selective oxytocin agonists and antagonist. This review summarizes the knowledge about the mapping of the binding domain of the oxytocin receptor and the efforts in the field of molecular modeling studies related to oxytocin receptor-ligand interactions.