Serum stability of selected decapeptide agonists of KISS1R using pseudopeptides

Influence of Aza-Glycine Substitution on the Internalization of Penetratin

The cell-penetrating peptide (CPP) penetratin has gained much attention over many years due to its potential role as a transporter for a broad range of cargo into cells. The modification of penetratin has been extensively investigated too. Aza-peptides are peptide analogs in which one or more of the amino residues are replaced by a semicarbazide. This substitution results in conformational restrictions and modifications in hydrogen bonding properties, which affect the structure and may lead to enhanced activity and selectivity of the modified peptide. In this work, the Trp residues of penetratin were substituted by aza-glycine or glycine residues to examine the effect of these modifications on the cellular uptake and the internalization mechanism. The substitution of Trp48 or Trp48,56 dramatically reduced the internalization, showing the importance of Trp48 in cellular uptake. Interestingly, while aza-glycine in the position of Trp56 increased the cellular uptake, Gly reduced it. The two Trp-modified derivatives showed altered internalization pathways, too. Based on our knowledge, this is the first study about the effect of aza-amino acid substitution on the cell entry of CPPs. Our results suggest that aza-amino acid insertion is a useful modification to change the internalization of a CPP.

Kisspeptin-10 binding to Gpr54 in osteoclasts prevents bone loss by activating Dusp18-mediated dephosphorylation of Src

Osteoclasts are over-activated as we age, which results in bone loss. Src deficiency in mice leads to severe osteopetrosis due to a functional defect in osteoclasts, indicating that Src function is essential in osteoclasts. G-protein-coupled receptors (GPCRs) are the targets for ∼35% of approved drugs but it is still unclear how GPCRs regulate Src kinase activity. Here, we reveal that GPR54 activation by its natural ligand Kisspeptin-10 (Kp-10) causes Dusp18 to dephosphorylate Src at Tyr 416. Mechanistically, Gpr54 recruits both active Src and the Dusp18 phosphatase at its proline/arginine-rich motif in its C terminus. We show that Kp-10 binding to Gpr54 leads to the up-regulation of Dusp18. Kiss1, Gpr54 and Dusp18 knockout mice all exhibit osteoclast hyperactivation and bone loss, and Kp-10 abrogated bone loss by suppressing osteoclast activity in vivo. Therefore, Kp-10/Gpr54 is a promising therapeutic target to abrogate bone resorption by Dusp18-mediated Src dephosphorylation.

Invited review: Translating kisspeptin and neurokinin B biology into new therapies for reproductive health

The reproductive neuropeptide kisspeptin has emerged as the master regulator of mammalian reproduction due to its key roles in the initiation of puberty and the control of fertility. Alongside the tachykinin neurokinin B and the endogenous opioid dynorphin, these peptides are central to the hormonal control of reproduction. Building on the expanding body of experimental animal models, interest has flourished with human studies revealing that kisspeptin administration stimulates physiological reproductive hormone secretion in both healthy men and women, as well as patients with common reproductive disorders. In addition, emerging therapeutic roles based on neurokinin B for the management of menopausal flushing, endometriosis and uterine fibroids are increasingly recognised. In this review, we focus on kisspeptin and neurokinin B and their potential application as novel clinical strategies for the management of reproductive disorders.

Advances in clinical applications of kisspeptin-GnRH pathway in female reproduction

BACKGROUND

Kisspeptin is the leading upstream regulator of pulsatile and surge Gonadotrophin-Releasing Hormone secretion (GnRH) in the hypothalamus, which acts as the key governor of the hypothalamic-pituitary-ovary axis.

MAIN TEXT

Exogenous kisspeptin or its receptor agonist can stimulate GnRH release and subsequent physiological gonadotropin secretion in humans. Based on the role of kisspeptin in the hypothalamus, a broad application of kisspeptin and its receptor agonist has been recently uncovered in humans, including central control of ovulation, oocyte maturation (particularly in women at a high risk of ovarian hyperstimulation syndrome), test for GnRH neuronal function, and gatekeepers of puberty onset. In addition, the kisspeptin analogs, such as TAK-448, showed promising agonistic activity in healthy women as well as in women with hypothalamic amenorrhoea or polycystic ovary syndrome.

CONCLUSION

More clinical trials should focus on the therapeutic effect of kisspeptin, its receptor agonist and antagonist in women with reproductive disorders, such as hypothalamic amenorrhoea, polycystic ovary syndrome, and endometriosis.

Synthesis and Antitumor Application of Antiangiogenetic Gold Nanoclusters

Conventional antiangiogenetic inhibitors suffered from poor delivery problems that result in unsatisfactory antitumor treatment efficacy. Although the liposomes or nanomaterial-based delivery systems can improve the therapeutic efficacy of antiangiogenic molecules, the assembly process is far too complex. Herein, a nanomaterial or a new nanodrug that could work without the help of a carrier and could be easily synthesized is needed. Au nanoclusters (AuNCs) are a kind of ideal nanostructures that could spontaneously enter into the cell and could be synthesized by a relatively easy one-pot method. Here, changing the traditional ligand glutathione (GSH) into an anti-Flt1 peptide (AF) has enriched the newly synthesized AF@AuNCs with targeted antiangiogenic properties. Based on the specific binding between AF and vascular endothelial growth factor receptor 1 (VEGFR1), the interaction between VEGFR1 and its ligands could be blocked. Furthermore, the expression of VEGFR2 could be downregulated. Compared with pure AF peptide- and GSH-participated AuNCs (GSH@AuNCs), AF@AuNCs were more effective in inhibiting both tube formation and migration of the endothelial cells in vitro. Furthermore, the in vivo chick embryo chorioallantoic membrane (CAM) experiment and antitumor experiment were conducted to further verify the enhanced antiangiogenesis and tumor inhibition effect of AF@AuNCs. Our findings provide promising evidence of a carrier-free nanodrug for tumors and other vascular hyperproliferative diseases.

Kisspeptin-8 Induces Anxiety-Like Behavior and Hypolocomotion by Activating the HPA Axis and Increasing GABA Release in the Nucleus Accumbens in Rats

Kisspeptins (Kp) are RF-amide neuropeptide regulators of the reproductive axis that also influence anxiety, locomotion, and metabolism. We aimed to investigate the effects of intracerebroventricular Kp-8 (an N-terminally truncated octapeptide) treatment in Wistar rats. Elevated plus maze (EPM), computerized open field (OF), and marble burying (MB) tests were performed for the assessment of behavior. Serum LH and corticosterone levels were determined to assess kisspeptin1 receptor (Kiss1r) activation and hypothalamic-pituitary-adrenal axis (HPA) stimulation, respectively. GABA release from the nucleus accumbens (NAc) and dopamine release from the ventral tegmental area (VTA) and NAc were measured via ex vivo superfusion. Kp-8 decreased open arm time and entries in EPM, and also raised corticosterone concentration, pointing to an anxiogenic effect. Moreover, the decrease in arm entries in EPM, the delayed increase in immobility accompanied by reduced ambulatory activity in OF, and the reduction in interactions with marbles show that Kp-8 suppressed exploratory and spontaneous locomotion. The increase in GABA release from the NAc might be in the background of hypolocomotion by inhibiting the VTA-NAc dopaminergic circuitry. As Kp-8 raised LH concentration, it could activate Kiss1r and stimulate the reproductive axis. As Kiss1r is associated with hyperlocomotion, it is more likely that neuropeptide FF receptor activation is involved in the suppression of locomotor activity.

Kiss1R Identification and Biodistribution Analysis Employing a Western Ligand Blot and Ligand-Derivative Stain with a FITC-Kisspeptin Derivative

It is not always easy to establish specific antibodies against receptors. Most receptors are hydrophobic and have complicated three-dimensional structures, making them difficult to use as immunogens. Thus, we developed receptor detection methods with a fluorescein-labeled ligand as an antibody alternative, which we referred to as a western ligand blot (WLB) and ligand derivative stain (LDS). Kisspeptin receptor (Kiss1R) was detected by its ligand. Kiss1R expression was confirmed in eight human cell lines by the WLB and in four pathological tissues by the LDS. Next, Kiss1R was stained by LDS in organs, revealing Kiss1R expression by [⁶⁷ Ga]Ga-DOTA-kisspeptin 10 accumulation. As a result, Kiss1R-expressing cells in each organ could be stained with fluorescein-labeled kisspeptin 14 instead of an antibody and observed by light microscopy. The combination of the WLB and LDS allows identification of receptors in tissues, which can be readily applied to target receptor detection by a synthetic ligand derivative.

Functional examination of novel kisspeptin phosphinic peptides

Kisspeptins acting on their cognate G protein-coupled receptor, kisspeptin receptor, play important roles in the suppression of cancer cell metastasis and regulation of the reproductive system, and therefore are important for therapeutic intervention. All native functional human kisspeptins (kisspeptin-54, kisspsptin-14 and kisspeptin-13) share the 10 amino acids of kisspeptin-10 at their C-terminus (45–54). However, they are inactivated rapidly by matrix metalloproteinases (MMPs) through the cleavage of the peptide bond between glycine⁵¹ and leucine⁵², which limits their clinical applications. Development of MMP-resistant analogues of kisspeptins may provide better therapeutic outputs. In the present study, two kisspeptin phosphinic peptides were designed and synthesized, and their ability to induce phosphorylation of ERK1/2 through kisspeptin receptor and their inhibition on MMP-2 and MMP-9 whose activity correlates with cancer metastasis were assessed. The results showed that one analogue, phosphinic kisspeptin R isomer (PKPR), exhibited kisspeptin receptor-agonistic activity and also inhibitory activity on MMP-2, indicating that PKPR may serve as a lead for the further development of kisspeptin analogues for therapeutic purpose.

Kisspeptin Receptor GPR54 Promotes Adipocyte Differentiation and Fat Accumulation in Mice

GPR54, Kisspeptin-1 receptor (KISS1R), a member of rhodopsin family, plays a critical role in puberty development and has been proposed to be involved in regulation of energy metabolism. This study aims to explore the function of GPR54 in adipogenesis, lipid metabolism, and obesity in addition to its effect through hormones. Results showed that when fed a high-fat diet, the weight growth of castrated or ovariectomized Gpr54^−/− mice was significantly slower than that of WT control, together with a lower triglyceride concentration. The ratio of white adipose tissue was lower, and average size of adipocytes was smaller in Gpr54^−/− mice. Meanwhile, there were less adipose tissue macrophages (ATMs), especially pro-inflammatory macrophages. Expression of inflammatory related genes also indicated that inflammatory response caused by obesity was not as drastic in Gpr54^−/− mice as in WT mice. Liver triglyceride in Gpr54^−/− mice was reduced, especially in female mice. On the other hand, oil drop formation was accelerated when hepatocytes were stimulated by kisspeptin-10 (Kp-10). Primary mesenchymal stem cells (MSCs) of Gpr54^−/− mice were less likely to differentiate into adipocytes. When stimulated by Kp-10, 3T3-L1 cell differentiation into adipocytes was accelerated and triglyceride synthesis was significantly promoted. These data indicated that GPR54 could affect obesity development by promoting adipocyte differentiation and triglyceride accumulation. To further elucidate the mechanism, genes related to lipid metabolism were analyzed. The expression of genes involved in lipid synthesis including PPARγ, ACC1, ADIPO, and FAS was significantly changed in Gpr54^−/− mice. Among them PPARγ which also participate in adipocyte differentiation displayed a marked reduction. Moreover, phosphorylation of ERK, which involved in GPR54 signaling, was significantly decreased in Gpr54^−/− mice, suggesting that GPR54 may promote lipid synthesis and obesity development by activating MAP kinase pathway. Therefore, in addition to the involvement in hormone regulation, our study demonstrated that GPR54 directly participates in obesity development by promoting adipocyte differentiation and fat accumulation. This provided evidence of involvement of GPR54 in lipid metabolism, and revealed new potentials for the identification and development of novel drug targets for metabolic diseases.

Towards new strategies to manage livestock reproduction using kisspeptin analogs

The discovery of the hypothalamic neuropeptide kisspeptin and its receptor (KISS1R) have dramatically improved our knowledge about the central mechanisms controlling reproduction. Kisspeptin neurons could be considered the hub where internal and external information controlling reproduction converge. The information is here elaborated and the command dispatched to GnRH neurons, the final output of the brain system controlling reproduction. Several studies have shown that in mammals administration of kisspeptin could finely modulate many aspects of reproduction from puberty to ovulation. For example in ewes kisspeptin infusion triggered ovulation during the non-breeding season and in prepubertal rat repeated injections advanced puberty onset. However, especially in livestock, the suboptimal pharmacological properties of endogenous kisspeptin, notably it short half-life and consequently its poor pharmacodynamics, fetters its use to experimental setting. To overcome this issue synthetic KISS1R agonists, mainly based on kisspeptin backbone, were created. Their more favorable pharmacological profile, longer half-life and duration of action, allowed to perform promising initial experiments for controlling ovulation and puberty. Additional experiments and further refinement of analogs would still be necessary to exploit fully the potential of targeting the kisspeptin system. Nevertheless, it is already clear that this new strategy may represent a breakthrough in the field of reproduction control.

Potent and selective oxytocin receptor agonists without disulfide bridges

Oxytocin (OT) is a neuropeptide involved in a wide variety of physiological actions, both peripherally and centrally. Many human studies have revealed the potential of OT to treat autism spectrum disorders and schizophrenia. OT interacts with the OT receptor (OTR) as well as vasopressin 1a and 1b receptors (V_1aR, V_1bR) as an agonist, and agonistic activity for V_1aR and V_1bR may have a negative impact on the therapeutic effects of OTR agonism in the CNS. An OTR-selective agonistic peptide, FE 202767, in which the structural differences from OT are a sulfide bond instead of a disulfide bond, and N-alkylglycine replacement for Pro at position 7, was reported. However, the effects of amino acid substitutions in OT have not been comprehensively investigated to compare OTR, V_1aR, and V_1bR activities. This led us to obtain a new OTR-selective analog by comprehensive amino acid substitutions of OT and replacement of the disulfide bond. A systematic amino acid scanning (Ala, Leu, Phe, Ser, Glu, or Arg) of desamino OT (dOT) at positions 2, 3, 4, 5, 7, and 8 revealed the tolerability for the substitution at positions 7 and 8. Further detailed study showed that trans-4-hydroxyproline (trans-Hyp) at position 7 and γ-methylleucine [Leu(Me)] at position 8 were markedly effective for improving receptor selectivity without decreasing the potency at the OTR. Subsequently, a combination of these amino acid substitutions with the replacement of the disulfide bond of dOT analogs with a sulfide bond (carba analog) or an amide bond (lactam analog) yielded several promising analogs, including carba-1-[trans-Hyp⁷,Leu(Me)⁸]dOT (14) with a higher potency (7.2pM) at OTR than that of OT and marked selectivity (>10,000-fold) over V_1aR and V_1bR. Hence, we investigated comprehensive modification of OT and obtained new OT analogs that exhibited high potency at OTR with marked selectivity. These OTR-selective agonists could be useful to investigate OTR-mediated effects on psychiatric disorders.

Beta amino acid-modified and fluorescently labelled kisspeptin analogues with potent KISS1R activity

Kisspeptin analogues with improved metabolic stability may represent important ligands in the study of the kisspeptin/KISS1R system and have therapeutic potential. In this paper we assess the activity of known and novel kisspeptin analogues utilising a dual luciferase reporter assay in KISS1R-transfected HEK293T cells. In general terms the results reflect the outcomes of other assay formats and a number of potent agonists were identified among the analogues, including β(2) -hTyr-modified and fluorescently labelled forms. We also showed, by assaying kisspeptin in the presence of protease inhibitors, that proteolysis of kisspeptin activity within the reporter assay itself may diminish the agonist outputs. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.

Neuropeptide derivatives to regulate the reproductive axis: Kisspeptin receptor (KISS1R) ligands and neurokinin-3 receptor (NK3R) ligands

Recent research has indicated pivotal roles for neuropeptides and their cognate receptors in reproductive physiology. Kisspeptins are RF-amide neuropeptides that stimulate gonadotropin-releasing hormone (GnRH) neurons in the hypothalamus. Neurokinin B (NKB) is a member of the tachykinin family of neuropeptides and positively regulates pulsatile GnRH secretion. These peptides are coexpressed in kisspeptin/NKB/Dyn (KNDy) neurons of the arcuate nucleus, where they contribute to the regulation of puberty onset and other reproductive functions. In this review, the design of peptide ligands for the kisspeptin (KISS1R) and neurokinin-3 (NK3R) receptors are described. © 2016 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 106: 588-597, 2016.

RF-amide neuropeptides and their receptors in Mammals: Pharmacological properties, drug development and main physiological functions

RF-amide neuropeptides, with their typical Arg-Phe-NH2 signature at their carboxyl C-termini, belong to a lineage of peptides that spans almost the entire life tree. Throughout evolution, RF-amide peptides and their receptors preserved fundamental roles in reproduction and feeding, both in Vertebrates and Invertebrates. The scope of this review is to summarize the current knowledge on the RF-amide systems in Mammals from historical aspects to therapeutic opportunities. Taking advantage of the most recent findings in the field, special focus will be given on molecular and pharmacological properties of RF-amide peptides and their receptors as well as on their implication in the control of different physiological functions including feeding, reproduction and pain. Recent progress on the development of drugs that target RF-amide receptors will also be addressed.

Rational design of triazololipopeptides analogs of kisspeptin inducing a long-lasting increase of gonadotropins

New potent and selective KISS1R agonists were designed using a combination of rational chemical modifications of the endogenous neuropeptide kisspeptin 10 (KP10). Improved resistance to degradation and presumably reduced renal clearance were obtained by introducing a 1,4-disubstituted 1,2,3-triazole as a proteolysis-resistant amide mimic and a serum albumin-binding motif, respectively. These triazololipopeptides are highly potent full agonists of KISS1R and are >100 selective over the closely related NPFF1R. When injected in ewes with a quiescent reproductive system, the best compound of our series induced a much prolonged increase of luteinizing hormone release compared to KP10 and increased follicle-stimulating hormone plasma concentration. Hence, this KISS1R agonist is a new valuable pharmacological tool to explore the potential of KP system in reproduction control. Furthermore, it represents the first step to develop drugs treating reproductive system disorders due to a reduced activity of the hypothalamo-pituitary-gonadal axis such as delayed puberty, hypothalamic amenorrhea, and hypogonadotropic hypogonadism.

Sustained exposure to the investigational Kisspeptin analog, TAK-448, down-regulates testosterone into the castration range in healthy males and in patients with prostate cancer: results from two phase 1 studies

BACKGROUND/OBJECTIVE

Kisspeptin-54, an endogenous naturally occurring ligand of the G protein-coupled receptor-54, stimulates GnRH-gonadotropin secretion and suppresses metastases in animal models of cancer but is subject to rapid degradation and inactivation. TAK-448 is an investigational oligopeptide analog of the fully active 10-amino acid C terminus of kisspeptin-54. This phase 1 study evaluated the safety, pharmacokinetics, and pharmacodynamics of TAK-448 in healthy subjects and patients with prostate cancer (PC).

DESIGN

Healthy subjects aged 50 years or older received TAK-448 sc as a single-bolus or 2-hour infusion (0.01-6 mg/d; part A) and as a 14-day sc administration (0.01-1 mg/d; part B). In a subsequent, open-label, phase 1 study in PC patients aged 40-78 years, TAK-448 was given as a 1-month depot formulation.

RESULTS

Eighty-two healthy subjects received TAK-448; 30 received placebo. Grades 1-2 adverse events were reported in 26% of subjects during TAK-448 treatment. All dosing regimens resulted in dose-proportional exposures. The maximum observed plasma concentration occurred after 0.25-0.5 hours, and median terminal elimination half-life was 1.4-5.3 hours. T increased approximately 1.3- to 2-fold by 48 hours after a single bolus or 2 hour injections, whereas during the 14-day infusion, at doses above 0.1 mg/d, T dropped to below-baseline values by 60 hours and reached a subsequently sustained below-castration level by day 8. In PC patients, T decreased to less than 20 ng/dL in four of five patients dosed with 12 or 24 mg TAK-448 sc-depot injections. The prostate-specific antigen decreased greater than 50% in all patients dosed with 24 mg.

CONCLUSIONS

Continuous TAK-448 infusion was well tolerated by healthy males and resulted in sustained T suppression. Depot injection in patients with PC similarly reduced T and resulted in prostate-specific antigen responses.

Molecular evolution of GPCRs: Kisspeptin/kisspeptin receptors

Following the discovery of kisspeptin (Kiss) and its receptor (GPR54 or KissR) in mammals, phylogenetic studies revealed up to three Kiss and four KissR paralogous genes in other vertebrates. The multiplicity of Kiss and KissR types in vertebrates probably originated from the two rounds of whole-genome duplication (1R and 2R) that occurred in early vertebrates. This review examines compelling recent advances on molecular diversity and phylogenetic evolution of vertebrate Kiss and KissR. It also addresses, from an evolutionary point of view, the issues of the structure-activity relationships and interaction of Kiss with KissR and of their signaling pathways. Independent gene losses, during vertebrate evolution, have shaped the repertoire of Kiss and KissR in the extant vertebrate species. In particular, there is no conserved combination of a given Kiss type with a KissR type, across vertebrate evolution. The striking conservation of the biologically active ten-amino-acid C-terminal sequence of all vertebrate kisspeptins, probably allowed this evolutionary flexibility of Kiss/KissR pairs. KissR mutations, responsible for hypogonadotropic hypogonadism in humans, mostly occurred at highly conserved amino acid positions among vertebrate KissR. This further highlights the key role of these amino acids in KissR function. In contrast, less conserved KissR regions, notably in the intracellular C-terminal domain, may account for differential intracellular signaling pathways between vertebrate KissR. Cross talk between evolutionary and biomedical studies should contribute to further understanding of the Kiss/KissR structure-activity relationships and biological functions.

Design and synthesis of fluorescent probes for GPR54

Kisspeptins are neuropeptides that induce the secretion of gonadotropin-releasing hormone via the activation of the cognate receptor, G-protein coupled receptor 54 (GPR54). The kisspeptin-GPR54 axis is associated with the onset of puberty and the maintenance of the reproductive system. In this study, several fluorescent probes have been designed and synthesized for rat GPR54 through the modification of the N-terminus of rat kisspeptins to allow for the visualization of the expression and localization of kisspeptin receptor(s) in living cells and native tissues. The tetramethylrhodamine (TMR) and rhodamine green (RG)-labeled kisspeptins exhibited good binding and agonistic activities towards GPR54, and the results of the application studies demonstrated that these fluorescent probes could be used effectively for the detection of GPR54 receptors in flow cytometry and confocal microscopy experiments.

Effects and therapeutic potentials of kisspeptin analogs: regulation of the hypothalamic-pituitary-gonadal axis

The hypothalamic peptide kisspeptin (metastin), the endogenous ligand of the G protein-coupled receptor KISS1R, plays a critical role in controlling GnRH release from hypothalamic GnRH neurons and thereby regulates hypothalamic-pituitary-gonadal functions. Although the therapeutic potential of kisspeptin is attractive, its susceptibility to proteolytic degradation limits its utility. To overcome this, KISS1R agonists or antagonists as peptide analogs or small molecules have been investigated. Kisspeptin analogs have been most extensively studied by reducing the length of the peptide from the original 54 amino acids to 10 amino acids or less and by substituting key amino acid residues. Also, 2 investigational kisspeptin agonist analogs have been evaluated in clinical studies in men; in agreement with animal studies, abrupt elevations in gonadotropin and testosterone levels were observed as an acute effect, followed by rapid reductions in these hormones as a chronic effect. Some studies of small-molecule KISS1R antagonists have also been published. In this review, we present a brief overview on kisspeptin/KISS1R physiology in reproductive functions and summarize the available knowledge of both agonists and antagonists. We also focus on the kisspeptin agonist analogs by summarizing key pharmacological findings from both clinical and preclinical studies, and discuss their potential therapeutic utility.

Design, synthesis, and biological evaluation of novel investigational nonapeptide KISS1R agonists with testosterone-suppressive activity

Metastin/kisspeptin is a 54 amino acid peptide ligand of the KISS1R receptor and is a critical regulator of GnRH secretion. The N-terminally truncated peptide, metastin(45-54), possesses a 10-fold higher receptor-binding affinity than full-length metastin and agonistic KISS1R activity but is rapidly inactivated in rodent plasma. We have developed a decapeptide analog [D-Tyr(45),D-Trp(47),azaGly(51),Arg(Me)(53)]metastin(45-54) with improved serum stability compared with metastin(45-54) but with decreased KISS1R agonistic activity. Amino acid replacements at positions 45-47 led to an enhancement of KISS1R agonistic activity and metabolic stability. N-terminal truncation resulted in a stable nonapeptide, [D-Tyr(46),D-Pya(4)(47),azaGly(51),Arg(Me)(53)]metastin(46-54), compound 26, which displayed KISS1R binding affinities comparable to metastin(45-54) and had improved serum stability. Compound 26 reduced plasma testosterone in male rats and is the first short-length metastin analog to possess testosterone suppressive activities. Compound 26 has led to the elucidation of investigational analogs TAK-683 and TAK-448, both of which have undergone clinical evaluation for hormone-dependent diseases such as prostate cancer.

Characterization of the receptor binding residues of kisspeptins by positional scanning using peptide photoaffinity probes

Kisspeptins, endogenous peptide ligands for GPR54, play an important role in GnRH secretion. Since in vivo administration of kisspeptins induces increased plasma LH levels, GPR54 agonists hold promise as therapeutic agents for the treatment of hormonal secretion diseases. To facilitate the design of novel potent GPR54 ligands, residues in kisspeptins that involve in the interaction with GPR54 were investigated by kisspeptin-based photoaffinity probes. Herein, we report the design and synthesis of novel kisspeptin-based photoaffinity probes, and the application to crosslinking experiments for GPR54-expressing cells.