Target 2035 - an update on private sector contributions.

Target 2035, an international federation of biomedical scientists from the public and private sectors, is leveraging 'open' principles to develop a pharmacological tool for every human protein. These tools are important reagents for scientists studying human health and disease and will facilitate the development of new medicines. It is therefore not surprising that pharmaceutical companies are joining Target 2035, contributing both knowledge and reagents to study novel proteins. Here, we present a brief progress update on Target 2035 and highlight some of industry's contributions.

Target 2035 - update on the quest for a probe for every protein.

Twenty years after the publication of the first draft of the human genome, our knowledge of the human proteome is still fragmented. The challenge of translating the wealth of new knowledge from genomics into new medicines is that proteins, and not genes, are the primary executers of biological function. Therefore, much of how biology works in health and disease must be understood through the lens of protein function. Accordingly, a subset of human proteins has been at the heart of research interests of scientists over the centuries, and we have accumulated varying degrees of knowledge about approximately 65% of the human proteome. Nevertheless, a large proportion of proteins in the human proteome (∼35%) remains uncharacterized, and less than 5% of the human proteome has been successfully targeted for drug discovery. This highlights the profound disconnect between our abilities to obtain genetic information and subsequent development of effective medicines. Target 2035 is an international federation of biomedical scientists from the public and private sectors, which aims to address this gap by developing and applying new technologies to create by year 2035 chemogenomic libraries, chemical probes, and/or biological probes for the entire human proteome.

Pharmacokinetic and pharmacodynamic modeling of the metastin/kisspeptin analog, TAK-448, for its anti-tumor efficacy in a rat xenograft model.

TAK-448 is the investigational metastin/kisspeptin analog, which is known to have an anti-tumor effect through suppression of androgen hormones (luteinizing hormone and testosterone) levels. This study developed pharmacokinetic-pharmacodynamic (PK/PD) models of TAK-448 and leuprorelin acetate (TAP-144) in a rat vertebral-cancer of the prostate (VCaP) androgen-sensitive prostate cancer xenograft model to quantitatively assess and compare the anti-tumor effects of both drugs. A potential contribution of the hormone-independent direct effects of TAK-448 to the tumor growth inhibition was also investigated in the in vivo rat xenograft model, because our in vitro experiments revealed that TAK-448 may also directly suppress VCaP cellular proliferation. The PK/PD model successfully described the time course of tumor growth inhibition after drug treatment as well as the development of resistance to the inhibition of androgen hormones, following drug treatment or castration. The EC50 of the hormone-dependent inhibitory effect of TAK-448 was much lower than that of TAP-144, and TAK-448 also has a faster onset of anti-tumor effect than TAP-144, demonstrating that TAK-448 has a stronger overall anti-tumor effect than TAP-144. In addition, model inference, by incorporating a hormone-independent inhibition pathway of TAK-448 into the PK-PD model, suggested that such a direct inhibition pathway for TAK-448 cannot be excluded, as also indicated by in vitro studies, but its EC50 would be approximately three orders of magnitude higher than that of the hormone-dependent pathway. This study helps to understand the potential and mechanism of TAK-448 as a prostate cancer treatment.

A new class of pentapeptide KISS1 receptor agonists with hypothalamic-pituitary-gonadal axis activation.

The kisspeptin (Kp, Kp-54, metastin)/KISS1R system plays crucial roles in regulating the secretion of gonadotropin-releasing hormone. Continuous administration of nonapeptide Kp analogs caused plasma testosterone depletion, whereas bolus administration caused strong plasma testosterone elevation in male rats. To develop a new class of small peptide drugs, we focused on stepwise N-terminal truncation of Kp analogs and discovered potent pentapeptide analogs. Benzoyl-Phe-azaGly-Leu-Arg(Me)-Trp-NH2 (16) exhibited high agonist activity for KISS1R and excellent metabolic stability in rat serum. A single injection of a 4-pyridyl analog (19) at the N-terminus of 16 into male Sprague Dawley rats caused a robust increase in plasma luteinizing hormone levels, but unlike continuous administration of nonapeptide Kp analogs, continuous administration of 19 maintained moderate testosterone levels in rats. These results indicated that small peptide drugs can be successfully developed for treating sex hormone deficiency.

Reduction of Kiss1 expression in the anteroventral periventricular nucleus is associated with atrazine-induced attenuation of the luteinizing hormone surge in female rats.

Atrazine, a commonly used herbicide, suppresses the luteinizing hormone (LH) surge in female rats, although the underlying mechanism remains unclear. Kisspeptin, encoded by the Kiss1 gene, is a hypothalamic peptide that controls gonadotropin-releasing hormone (GnRH) release from the GnRH neurons. Kisspeptin neurons in the anteroventral periventricular nucleus (AVPV) are involved in regulating pre-ovulatory GnRH and LH surge. To clarify the effect of atrazine on the LH surge in female rats, we investigated its effects on hypothalamic GnRH and kisspeptin. Ovariectomized female rats in a high-dose estradiol supplementation model were orally administered vehicle or 100 mg/kg of atrazine once daily for 5 days. This attenuated the LH surge but did not affect baseline LH levels, with no difference in hypothalamic GnRH levels between the vehicle-treated and atrazine-treated animals. After the fifth treatment, subcutaneous administration of kisspeptin (at 0, 0.1, 1, and 10 nmol/kg) induced a dose-dependent LH release almost equivalent in the vehicle- and atrazine-treated animals, suggesting that GnRH neurons maintain normal responsiveness to kisspeptin. However, Kiss1 mRNA expression levels in the AVPV were significantly reduced in the atrazine-treated animals. Given the normal response of GnRH neurons to exogenously administered kisspeptin, the suppressive effect of atrazine may be explained by suppression of Kiss1 expression in the AVPV leading to the attenuation of kisspeptin release from kisspeptin neurons in the AVPV. Further studies are warranted to elucidate more precisely the mechanism of atrazine's involvement in the suppression of Kiss1 mRNA expression in the AVPV.

Donated chemical probes for open science.

Potent, selective and broadly characterized small molecule modulators of protein function (chemical probes) are powerful research reagents. The pharmaceutical industry has generated many high-quality chemical probes and several of these have been made available to academia. However, probe-associated data and control compounds, such as inactive structurally related molecules and their associated data, are generally not accessible. The lack of data and guidance makes it difficult for researchers to decide which chemical tools to choose. Several pharmaceutical companies (AbbVie, Bayer, Boehringer Ingelheim, Janssen, MSD, Pfizer, and Takeda) have therefore entered into a pre-competitive collaboration to make available a large number of innovative high-quality probes, including all probe-associated data, control compounds and recommendations on use (https://openscienceprobes.sgc-frankfurt.de/). Here we describe the chemical tools and target-related knowledge that have been made available, and encourage others to join the project.

Usefulness of pharmacokinetic/efficacy analysis of an investigational kisspeptin analog, TAK-448, in quantitatively evaluating anti-tumor growth effect in the rat VCaP androgen-sensitive prostate cancer model.

TAK-448 is a kisspeptin analog with improved in vivo potency. In our previous studies in the rat JDCaP prostate cancer model, TAK-448 showed more rapid and profound reductions in plasma testosterone (T) and prostate-specific antigen (PSA, a biomarker of prostate tumor growth) levels than the gonadotropin releasing hormone (GnRH) analog leuprolide (TAP-144); however, its effects on tumor volume and subsequent tumor recurrence have not been elucidated fully. To overcome these challenges, we established the rat VCaP subcutaneous xenograft model replicating both the androgen-sensitive and castration-resistant phases of prostate cancer, and we performed pharmacokinetic/efficacy (PK/E) correlation analyses to compare the overall anti-tumor growth effects of TAK-448 to those of TAP-144. Our approach demonstrated TAK-448 had greater anti-tumor growth potential, including in the castration-resistant phase, than TAP-144 in this rat VCaP model. TAK-448 treatment was associated with a reduction in intra-tumoral dihydrotestosterone levels, which might explain its superior anti-tumor activity. Thus, our PK/E analysis was effective at providing new insights into the therapeutic efficacy of TAK-448 as a novel ADT agent in our rat VCaP model.

Evaluation of pharmacokinetics/pharmacodynamics and efficacy of one-month depots of TAK-448 and TAK-683, investigational kisspeptin analogs, in male rats and an androgen-dependent prostate cancer model.

TAK-448 and TAK-683 are kisspeptin agonist analogs with improved in vivo stability and activity. Previous studies showed that continuous subcutaneous administration of TAK-448 or TAK-683 caused rapid and profound reductions in plasma testosterone levels in various species, including male healthy volunteers, suggesting their therapeutic potential as anti-prostate cancer agents. For clinical drug development, one-month sustained-release depots of TAK-448 and TAK-683, TAK-448-SR(1M) and TAK-683-SR(1M), were designed to improve usability in clinical practice. In this study, the pharmacokinetics/pharmacodynamics (PK/PD) profiles of TAK-448-SR(1M) and TAK-683-SR(1M) were initially tested in male rats to ensure their eligibility as one-month depots. The therapeutic advantages of TAK-448-SR(1M) and TAK-683-SR(1M) over TAP-144-SR(1M) were then investigated in a JDCaP xenograft rat model. TAK-448-SR(1M) and TAK-683-SR(1M) maintained certain levels of plasma TAK-448 free form (TAK-448F) and plasma TAK-683 free form (TAK-683F) for at least 4 weeks, before clearance from the circulation. Accompanying their desirable PK profiles, TAK-448-SR(1M) and TAK-683-SR(1M) showed favorable PD responses as one-month depots and demonstrated better testosterone control than TAP-144-SR(1M). Both depots exerted rapid and profound suppression of plasma testosterone levels in male rats. These profound suppressive effects were maintained in dose-dependent manners, before recovery toward normal levels. In the JDCaP xenograft model, TAK-448-SR(1M) and TAK-683-SR(1M) both showed better prostate-specific antigen (PSA) control than TAP-144-SR(1M), although all treatment groups eventually experienced PSA recurrence and tumor regrowth. In conclusion, this study demonstrates that both TAK-448-SR(1M) and TAK-683-SR(1M) have desirable and better PK/PD profiles than TAP-144-SR(1M) in rats, which could potentially provide better clinical outcomes in androgen-dependent prostate cancer.

An administration of TAK-683 at a minimally effective dose for luteinizing hormone stimulation under the absence of the ovary induces luteinizing hormone surge in ovary-intact goats.

The present study aimed to evaluate hormonal responses and their association with the TAK-683 blood concentrations in goats administered TAK-683 at a low dose, which had been previously determined as the minimally effective dose for luteinizing hormone (LH) stimulation in ovariectomized goats. In Experiment 1, 5 µg of TAK-683 treatment had no significant stimulatory effect on LH secretion in ovariectomized Shiba goats (n = 4). In Experiment 2, cycling goats received the treatment of prostaglandin F2α and progesterone-releasing controlled internal drug releasing (CIDR) to induce the follicular phase, then they were treated with 5 µg of TAK-683 (hour 0) intravenously (n = 4, IV) or subcutaneously (n = 3, SC) or with vehicle intravenously (n = 4, control) at 12 h after CIDR removal. Blood samples were collected at 10-min (-2-6 h), 2-h (6-24 h), or 6-h (24-48 h) intervals. Ovarian ultrasonographic images were assessed daily to confirm ovulation after the treatment. A surge-like release of LH was immediately observed after injection in all animals in the IV (peak time: 4.2 ± 0.6 h, peak concentration: 73.3 ± 27.5 ng/ml) and SC (peak time: 4.6 ± 0.4 h, peak concentration: 62.6 ± 23.2 ng/ml) groups, but not in the control group. Ovulation was detected within 3 days after TAK-683 injection in all animals in the IV and SC groups, and the interval period from TAK-683 administration to ovulation in the IV group was significantly (P < 0.05) shorter than that of the control group. No significant changes were observed between the IV and SC groups in terms of luteal diameter and blood progesterone levels after ovulation. The present findings suggest that the involvement of one or more ovarian factor(s) is indispensable for a TAK-683-induced LH surge leading to ovulation in goats.

Design and Synthesis of an Investigational Nonapeptide KISS1 Receptor (KISS1R) Agonist, Ac-d-Tyr-Hydroxyproline (Hyp)-Asn-Thr-Phe-azaGly-Leu-Arg(Me)-Trp-NH2 (TAK-448), with Highly Potent Testosterone-Suppressive Activity and Excellent Water Solubility.

Metastin/kisspeptin is an endogenous ligand of KISS1 Receptor (KISS1R). Metastin and KISS1R are suggested to play crucial roles in regulating the secretion of gonadotropin-releasing hormone (GnRH), and continuous administration of metastin derivatives attenuated the plasma testosterone levels in male rats. Our optimization studies of metastin derivatives led to the discovery of 1 (Ac-d-Tyr-d-Trp-Asn-Thr-Phe-azaGly-Leu-Arg(Me)-Trp-NH2, TAK-683), which suppressed plasma testosterone in rats at lower doses than those of leuprolide. Although 1 possessed extremely potent pharmacological activity, 20 mg/mL aqueous solution of 1 has a gel formation property. In order to improve this physicochemical property, we substituted d-Trp at position 47 with a variety of amino acids; we identified that substitution with cyclic amino acids, which could change peptide conformation, retained its potency. Especially, analogue 24 (TAK-448) with trans-4-hydroxyproline (Hyp) at position 47 showed not only superior pharmacological activity to 1 but also excellent water solubility. Furthermore, 20 mg/mL aqueous solution of 24 did not show gel formation up to 5 days.

Anti-inflammatory and cytoprotective effects of a squalene synthase inhibitor, TAK-475 active metabolite-I, in immune cells simulating mevalonate kinase deficiency (MKD)-like condition.

TAK-475 (lapaquistat acetate) and its active metabolite-I (TAK-475 M-I) inhibit squalene synthase, which catalyzes the conversion of farnesyl diphosphate (FPP) to squalene. FPP is a substrate for synthesis of other mevalonate-derived isoprenoids (MDIs) such as farnesol (FOH), geranlygeranyl diphosphate (GGPP), and geranylgeraniol. In patients with MKD, a rare autosomal recessive disorder, defective activity of mevalonate kinase leads to a shortage of MDIs. MDIs especially GGPP are required for prenylation of proteins, which is a posttranslation modification necessary for proper functioning of proteins like small guanosine triphosphatases. Malfunction of prenylation of proteins results in upregulation of the inflammatory cascade, leading to increased production of proinflammatory cytokines like interleukin-1ß (IL-1ß), eventually leading to episodic febrile attacks. In vitro, TAK-475 M-I incubation in a concentration dependent manner increased levels of FPP, GGPP, and FOH in human monocytic THP-1 cells. In subsequent experiments, THP-1 cells or human peripheral blood mononuclear cells (PBMCs) were incubated with simvastatin, which inhibits hydroxymethylglutaryl-coenzyme A reductase and thereby decreases levels of the precursors of MDIs, leading to the depletion of MDIs as expected in MKD patients. Increased levels of GGPP and FPP attenuated lipopolysaccharide (LPS)-induced IL-1ß production in THP-1 cells and human PBMCs in statin-treated conditions. The MDIs also significantly reduced the damaged cell ratio in this active MKD-like condition. Moreover, TAK-475 M-I directly inhibited LPS-induced IL-1ß production from statin-treated THP-1 cells. These results show anti-inflammatory and cytoprotective effects of MDIs via TAK-475 M-I treatment in statin-treated immune cells, suggesting that possible therapeutic effects of TAK-475 treatment in MKD patients.

Differential changes in luteinizing hormone secretion after administration of the investigational metastin/kisspeptin analog TAK-683 in goats.

This study aimed to evaluate the hormonal and ovarian responses to the administration of a metastin/kisspeptin analog (TAK-683) under the endocrine environments of luteal and follicular phases in goats. Five estrous cycling goats received a prostaglandin F2α injection followed by 10 days of progesterone treatment by CIDR. The TAK-683 (35nmol) was intravenously administered (Hour 0) on 3 days after CIDR insertion (luteal phase condition; LC) and at 12h after CIDR removal (follicular phase condition; FC). Blood samples were collected at 10min (-2 to 6h), 2h (6-24h) or 6h intervals (24-48h). In the LC, small increases in the basal concentrations of LH were observed after TAK-683 administration from 0 to 6h, which were associated with an increase in estradiol concentration, followed by a surge-like release of LH with a peak at 12.5±1.0h (n=4) after TAK-683 administration. In the FC, a surge-like release of LH occurred immediately after TAK-683 administration with a peak at 6.0±3.5h (n=5), which was earlier than that in the LC (P<0.01). The peak concentration of estradiol did not differ between the two conditions, whereas the time interval from TAK-683 treatment to estradiol peak in the LC was longer than that in the FC (12.0±0.0 compared with 6.0±4.2h, P<0.05). These findings suggest that the timing of surge-like release of LH after TAK-683 administration is associated with blood estradiol concentration at the time of treatment.

The effects of chronic subcutaneous administration of an investigational kisspeptin analog, TAK-683, on gonadotropin-releasing hormone pulse generator activity in goats.

The continuous activation of the kisspeptin receptor by its agonists causes the abrogation of kisspeptin signaling, leading to decreased pulsatile luteinizing hormone (LH) secretion. Employing this phenomenon as a tool for probing kisspeptin action, this study aimed to clarify the role of kisspeptin in gonadotropin-releasing hormone (GnRH) pulse generation in goats. We examined the effects of chronic administration of TAK-683, an investigational kisspeptin analog, on LH secretion, GnRH immunostaining, pituitary responses to exogenous GnRH, and GnRH pulse generator activity, reflected by a characteristic increase in multiple-unit activity (MUA volley). An osmotic pump containing TAK-683 was subcutaneously implanted on day 0. TAK-683 treatment dose-dependently suppressed pulsatile LH secretion on day 1. Higher doses of chronic TAK-683 profoundly suppressed pulsatile LH secretion but had little effect on GnRH immunostaining patterns and pituitary responses to GnRH on day 5. In ovariectomized goats, MUA volleys occurred at approximately every 30 min on day -1. On day 5 of chronic TAK-683 administration, pulsatile LH secretion was markedly suppressed, whereas MUA volleys were similar to those observed on day -1. Male pheromones and senktide (neurokinin B receptor agonist) induced an MUA volley but had no effect on LH secretion during chronic TAK-683 administration. The results indicate that the chronic administration of a kisspeptin analog profoundly suppresses pulsatile LH secretion without affecting GnRH content, pituitary function or GnRH pulse generator activity, and they suggest an indispensable role for kisspeptin signaling in the cascade driving GnRH/LH pulses by the GnRH pulse generator.

Physicochemically and pharmacokinetically stable nonapeptide KISS1 receptor agonists with highly potent testosterone-suppressive activity.

Modifications of metastin(45-54) produced peptide analogues with higher metabolic stability than metastin(45-54). N-terminally truncated nonapeptide 4 ([D-Tyr46,D-Pya(4)47,azaGly51,Arg(Me)53]metastin(46-54)) is a representative compound with both potent agonistic activity and metabolic stability. Although 4 had more potent testosterone-suppressant activity than metastin, it possessed physicochemical instability at pH 7 and insufficient in vivo activity. Instability at pH 7 was dependent upon Asn48 and Ser49; substitution of Ser49 with Thr49 reduced this instability and maintained KISS1 receptor agonistic activity. Furthermore, [D-Tyr46,D-Trp47,Thr49,azaGly51,Arg(Me)53,Trp54]metastin(46-54) (14) showed 2-fold greater [Ca2+]i-mobilizing activity than metastin(45-54) and an apparent increase in physicochemical stability. N-terminal acetylation of 14 resulted in the most potent analogue, 22 (Ac-[D-Tyr46,D-Trp47,Thr49,azaGly51,Arg(Me)53,Trp54]metastin(46-54)). With continuous administration, 22 possessed 10-50-fold more potent testosterone-suppressive activity in rats than 4. These results suggested that a controlled release of short-length KISS1 receptor agonists can suppress the hypothalamic-pituitary-gonadal axis and reduce testosterone levels. Compound 22 was selected for further preclinical evaluation for hormone-dependent diseases.

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.

Pharmacologic profiles of investigational kisspeptin/metastin analogues, TAK-448 and TAK-683, in adult male rats in comparison to the GnRH analogue leuprolide.

Kisspeptin/metastin, a hypothalamic peptide, plays a pivotal role in controlling gonadotropin-releasing hormone (GnRH) neurons, and we have shown that continuous subcutaneous administration of kisspeptin analogues suppresses plasma testosterone in male rats. This study examined pharmacologic profiles of investigational kisspeptin analogues, TAK-448 and TAK-683, in male rats. Both analogues showed high receptor-binding affinity and potent and full agonistic activity for rat KISS1R, which were comparable to natural peptide Kp-10. A daily subcutaneous injection of TAK-448 and TAK-683 (0.008-8µmol/kg) for consecutive 7 days initially induced an increase in plasma luteinizing hormone and testosterone levels; however, after day 7, plasma hormone levels and genital organ weights were reduced. Continuous subcutaneous administrations of TAK-448 (≥10pmol/h, ca. 0.7nmol/kg/day) and TAK-683 (≥30pmol/h, ca. 2.1nmol/kg/day) induced a transient increase in plasma testosterone, followed by abrupt reduction of plasma testosterone to castrate levels within 3-7 days. This profound testosterone-lowering effect was sustained throughout 4-week dosing periods. At those dose levels, the weights of the prostate and seminal vesicles were reduced to castrate levels. These suppressive effects of kisspeptin analogues were more rapid and profound than those induced by the GnRH agonist analogue leuprolide treatment. In addition, TAK-683 reduced plasma prostate specific antigen (PSA) in the JDCaP androgen-dependent prostate cancer rat model. Thus, chronic administration of kisspeptin analogues may hold promise as a novel therapeutic approach for suppressing reproductive functions and hormone-related diseases such as prostate cancer. Further studies are warranted to elucidate clinical significance of TAK-448 and TAK-683.

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.