Peptide and protein mimetics by retro and retroinverso analogs

Retroinverso analog of a natural polypeptide can sometimes mimic the structure and function of the natural peptide. The additional advantage of using retroinverso analog is that it is resistant to proteolysis. The retroinverso analogs have peptide sequence in reverse direction with respect to natural peptide and also have chirality of amino acid inverted from L to D. The D amino acids cannot be recognized by common proteases of the body; therefore, these peptides will not be degraded easily and have a longer-lasting effect as vaccine and inhibitor drugs. There have been many contested propositions about the geometric relationship between a peptide and its retro, inverso, or retroinverso analog. A retroinverso analog sometimes fails to adopt the structure that can mimic the function of the natural peptide. In such cases, partial retroinverso analog and other modifications can help in achieving the desired structure and function. Here, we review the theory, major experimental attempts, prediction methods, and alternative strategies related to retroinverso peptidomimetics.

Comparative Functional Alanine Positional Scanning of the α-Melanocyte Stimulating Hormone and NDP-Melanocyte Stimulating Hormone Demonstrates Differential Structure-Activity Relationships at the Mouse Melanocortin Receptors

The melanocortin system has been implicated in the regulation of various physiological functions including melanogenesis, steroidogenesis, energy homeostasis, and feeding behavior. Five melanocortin receptors have been identified to date and belong to the family of G protein-coupled receptors (GPCR). Post-translational modification of the proopiomelanocortin (POMC) prohormone leads to the biosynthesis of the endogenous melanocortin agonists, including α-melanocyte stimulating hormone (α-MSH), β-MSH, γ-MSH, and adrenocorticotropic hormone (ACTH). All the melanocortin agonists derived from the POMC prohormone contain a His-Phe-Arg-Trp tetrapeptide sequence that has been implicated in eliciting the pharmacological responses at the melanocortin receptors. Herein, an alanine (Ala) positional scan is reported for the endogenous α-MSH ligand and the synthetic, more potent, NDP-MSH peptide (Ac-Ser(1)-Tyr(2)-Ser(3)-Nle(4)-Glu(5)-His(6)-DPhe(7)-Arg(8)-Trp(9)-Gly(10)-Lys(11)-Pro(12)-Val(13)-NH2) at the cloned mouse melanocortin receptors to test the assumption that the structure-activity relationships of one ligand would apply to the other. Several residues outside of the postulated pharmacophore altered potency at the melanocortin receptors, most notably the 1560-, 37-, and 15-fold potency loss when the Glu(5) position of α-MSH was substituted with Ala at the mMC1R, mMC3R, and mMC4R, respectively. Importantly, the altered potencies due to Ala substitutions in α-MSH did not necessarily correlate with equivalent Ala substitutions in NDP-MSH, indicating that structural modifications and corresponding biological activities in one of these melanocortin ligands may not be predictive for the other agonist.

Retroinverso analogs of spadin display increased antidepressant effects

RATIONALE

Although depression is the most common mood disorder, only one third of patients are treated with success. Finding new targets, new drugs, and also new drug intake way are the main challenges in the depression field. Several years ago, we identified a new target with the TWIK-related potassium channel-1 (TREK-1) potassium channel, and more recently, we have discovered a peptide of 17 amino acids with antidepressant properties. This peptide, that we called spadin, can be considered as a new concept in antidepressant drug design. Spadin derives from a larger peptide resulting to a posttranslational maturation of sortilin; consequently, spadin can be considered as a natural molecule. Moreover, spadin acts more rapidly than classical antidepressants and does not induce side effects.

OBJECTIVES

In this work, we sought analogs of spadin displaying a better affinity on TREK-1 channels and an increased action duration.

METHODS

Analogs were characterized by electrophysiology measurements, by behavioral tests, and by their ability to induce neurogenesis.

RESULTS

We identified two retro-inverso peptides that have kept the antidepressant properties of spadin; particularly, they increased the hippocampal neurogenesis after a 4-day treatment. As spadin, these analogs did not induce side effects on either pain, epilepsy processes, or at the cardiac level.

CONCLUSIONS

Together, our results indicated that spadin retro-inverso peptides could represent new potent antidepressant drugs. As exemplified by spadin in the field of depression, retro-inverso strategies could represent a useful technique for developing new classes of drugs in a number of pathologies.

Malignant melanoma and melanocortin 1 receptor

The conventional chemotherapeutic treatment of malignant melanoma still remains poorly efficient in most cases. Thus the use of specific features of these tumors for development of new therapeutic modalities is highly needed. Melanocortin 1 receptor (MC1R) overexpression on the cell surface of the vast majority of human melanomas, making MC1R a valuable marker of these tumors, is one of these features. Naturally, MC1R plays a key role in skin protection against damaging ultraviolet radiation by regulating eumelanin production. MC1R activation is involved in regulation of melanocyte cell division. This article reviews the peculiarities of regulation and expression of MC1R, melanocytes, and melanoma cells, along with the possible connection of MC1R with signaling pathways regulating proliferation of tumor cells. MC1R is a cell surface endocytic receptor, thus considered perspective for diagnostics and targeted drug delivery. A number of new therapeutic approaches that utilize MC1R, including endoradiotherapy with Auger electron and α- and β-particle emitters, photodynamic therapy, and gene therapy are now being developed.

Immunosuppressive activity of a novel peptide analog of α-melanocyte stimulating hormone (α-MSH) in experimental autoimmune uveitis

Autoimmune uveitis is an inflammatory disorder of the eye that can lead to pain and vision loss. Steroids and immunosuppressive drugs are currently the only therapeutics for uveitis and have serious ocular and systemic toxicities. Therefore, safer alternative therapeutics are desired. Alpha-melanocyte stimulating hormone (α-MSH) is a neuropeptide that suppresses effector T cell functions, induces regulatory T cells and has beneficial effects in certain autoimmune and transplant models. A novel d-amino acid peptide analog of native α-MSH (dRI-α-MSH) was produced that was protected from protease digestion and had increased selectivity for the melanocortin-1 receptor. Systemic delivery of the dRI-α-MSH analog dramatically suppressed disease progression and retained retinal architecture in the experimental autoimmune uveitis (EAU) model. Local delivery by periorbital injection was equally effective. Importantly, treatment with the novel dRI-α-MSH analog suppressed uveitis with a similar magnitude to the corticosteroid, dexamethasone. Data indicate that the novel dRI-α-MSH analogs show anti-inflammatory activities and have potential therapeutic use in uveitis and other autoimmune diseases.