St. John's wort extract with a high hyperforin content does not induce P-glycoprotein activity at the human blood-brain barrier.

St. John's wort (SJW) extract, a herbal medicine with antidepressant effects, is a potent inducer of intestinal and/or hepatic cytochrome P450 (CYP) enzymes and P-glycoprotein (P-gp), which can cause clinically relevant drug interactions. It is currently not known whether SJW can also induce P-gp activity at the human blood-brain barrier (BBB), which may potentially lead to decreased brain exposure and efficacy of certain central nervous system (CNS)-targeted P-gp substrate drugs. In this study, we used a combination of positron emission tomography (PET) imaging and cocktail phenotyping to gain a comprehensive picture on the effect of SJW on central and peripheral P-gp and CYP activities. Before and after treatment of healthy volunteers (n = 10) with SJW extract with a high hyperforin content (3-6%) for 12-19 days (1800 mg/day), the activity of P-gp at the BBB was assessed by means of PET imaging with the P-gp substrate [11C]metoclopramide and the activity of peripheral P-gp and CYPs was assessed by administering a low-dose phenotyping cocktail (caffeine, omeprazole, dextromethorphan, and midazolam or fexofenadine). SJW significantly increased peripheral P-gp, CYP3A, and CYP2C19 activity. Conversely, no significant changes in the peripheral metabolism, brain distribution, and P-gp-mediated efflux of [11C]metoclopramide across the BBB were observed following the treatment with SJW extract. Our data suggest that SJW does not lead to significant P-gp induction at the human BBB despite its ability to induce peripheral P-gp and CYPs. Simultaneous intake of SJW with CNS-targeted P-gp substrate drugs is not expected to lead to P-gp-mediated drug interactions at the BBB.

Pharmacokinetics and Bioequivalence of Mirogabalin Orally Disintegrating Tablets and Conventional Tablets in Healthy Japanese Participants.

This single-center, randomized, open-label, single-dose, 2-group, 2-stage crossover trial evaluated the bioequivalence of 15 mg of mirogabalin as orally disintegrating tablets (ODTs) with conventional mirogabalin tablets in healthy Japanese men. The trial involved two studies: in Study 1, the ODT formulation was taken without water, and in Study 2, the ODT formulation was taken with water. The conventional tablet was taken with water in both studies. We investigated the pharmacokinetic parameters and bioequivalence of the 2 formulations, including the maximum plasma concentration and the area under the plasma concentration-time curve up to the last quantifiable time. The plasma concentrations of mirogabalin were determined by a validated liquid chromatography with tandem mass spectrometry method. A total of 72 participants were enrolled and completed the trial. The geometric least-squares mean ratios of maximum plasma concentration of the ODT formulation to the conventional formulation were within the prespecified bioequivalence range of 0.80-1.25 (Study 1, 0.995; Study 2, 1.009), as was the area under the plasma concentration-time curve up to the last quantifiable time (Study 1, 1.023; Study 2, 1.035). No serious adverse events were observed. In conclusion, mirogabalin 15-mg ODTs, either with or without water, were bioequivalent to conventional 15-mg tablets.

Safety, Tolerability and Pharmacokinetics of Single and Multiple Doses of Mirogabalin in Healthy Chinese Participants: A Randomized, Double-Blind, Placebo-Controlled Study.

INTRODUCTION: Mirogabalin is a treatment option for patients with neuropathic pain; however, safety, tolerability, and pharmacokinetics (PK) data specifically for Chinese individuals are limited to a single-dose study. We aimed to assess these for both single- and multiple-dose mirogabalin in healthy Chinese participants. METHODS: In this randomized, double-blind, placebo-controlled, phase I study, 54 healthy Chinese men and women aged 18-45 years were randomly allocated to receive single- (5, 10, or 15 mg, daily) or multiple-dose (5 mg titrated to 15 mg, twice-daily, over 22 days) oral mirogabalin or placebo. In each of three single-dose groups, 10 participants received mirogabalin and 2 received placebo; in the multiple-dose group, 14 participants received mirogabalin and 4 received placebo. The primary endpoints were PK, safety, and tolerability variables, including treatment-emergent adverse events (TEAEs), laboratory tests, and vital signs. PK data were collected for both single- and multiple-dose cohorts and evaluated by non-compartmental analysis. RESULTS: Single- and multiple-dose mirogabalin was generally well tolerated with no deaths, serious TEAEs, or TEAEs leading to treatment discontinuation. Frequently reported TEAEs included dizziness, nystagmus, increased blood triglycerides, headache, and increased blood uric acid and creatine phosphokinase. Single-dose mirogabalin was rapidly absorbed (median time to maximum plasma concentration, 1.00 h) and eliminated (mean terminal elimination half-life, 2.57-3.08 h). The exposure was approximately dose-proportional. In the multiple-dose cohort, the trough plasma concentration increased dose-proportionally, and exposure and clearance were comparable to that following a single 15-mg dose. The mean cumulative amount excreted into urine up to 48 h post-dose increased in a dose-proportional manner, the mean cumulative percentage excreted into urine was 61.9%-74.3%, and renal clearance remained relatively constant. CONCLUSION: Consistent with previous phase I studies in other populations, mirogabalin was safe and well tolerated in healthy Chinese participants at single and multiple doses of up to 15 mg twice-daily.

Design and in Vivo Characterization of A1 Adenosine Receptor Agonists in the Native Ribose and Conformationally Constrained (N)-Methanocarba Series.

(N)-Methanocarba ([3.1.0]bicyclohexyl) adenosines and corresponding ribosides were synthesized to identify novel A1 adenosine receptor (A1AR) agonists for CNS or peripheral applications. Human and mouse AR binding was determined to assess the constrained ring system's A1AR compatibility. N6-Dicyclobutylmethyl ribose agonist (9, MRS7469, >2000-fold selective for A1AR) and known truncated N6-dicyclopropylmethyl methanocarba 7 (MRS5474) were drug-like. The pure diastereoisomer of known riboside 4 displayed high hA1AR selectivity. Methanocarba modification reduced A1AR selectivity of N6-dicyclopropylmethyl and endo-norbornyladenosines but increased ribavirin selectivity. Most analogues tested (ip) were inactive or weak in inducing mouse hypothermia, despite mA1AR full agonism and variable mA3AR efficacy, but strong hypothermia by 9 depended on A1AR, which reflects CNS activity (determined using A1AR or A3AR null mice). Conserved hA1AR interactions were preserved in modeling of 9 and methanocarba equivalent 24 (∼400-fold A1AR-selective). Thus, we identified, and characterized in vivo, ribose and methanocarba nucleosides, including with A1AR-enhancing N6-dicyclobutylmethyl-adenine and 1,2,4-triazole-3-carboxamide (40, MRS7451) nucleobases.

Open-Label Single-Dose Study to Assess the Effect of Mild and Moderate Hepatic Impairment on the Pharmacokinetics of Mirogabalin.

BACKGROUND AND OBJECTIVES: Mirogabalin is an α2δ ligand being developed to treat neuropathic pain. A small fraction of mirogabalin is metabolized by the liver, where hepatic impairment may affect exposure. The objective of this phase I, open-label single-dose study was to determine if mild or moderate hepatic impairment alters the pharmacokinetics of mirogabalin. METHODS: Serial blood samples were collected for determination of maximum observed concentration, time to maximum concentration, and area under the concentration-time curve until the last quantifiable concentration of the active free form (A200-700) and inactive lactam metabolite (A204-4455) of mirogabalin. RESULTS: The A200-700 maximum observed concentration was similar in subjects with mild hepatic impairment but lower in subjects with moderate hepatic impairment vs. control subjects. The A204-4455 maximum observed concentration was lower in subjects with mild and moderate hepatic impairment vs. control groups. The A200-700 area under the concentration-time curve until the last quantifiable concentration was slightly lower in subjects with mild hepatic impairment and slightly higher in subjects with moderate hepatic impairment vs. control subjects. Peak A204-4455 levels were approximately 22% and 31% lower for subjects with mild and moderate hepatic impairment vs. control individuals, respectively. Exposure to A204-4455 was approximately 37% lower in subjects with mild hepatic impairment but unaffected in subjects with moderate hepatic impairment vs. control groups. Two subjects in the mild hepatic impairment group reported a treatment-emergent adverse event of mild somnolence. No serious or severe treatment-emergent adverse events, discontinuations as a result of treatment-emergent adverse events, or deaths were reported. CONCLUSIONS: Mild hepatic impairment resulted in lower A200-700 and A204-4455 exposure, while moderate hepatic impairment did not affect A200-700 exposure. Overall, mild-to-moderate hepatic impairment did not have a significant effect on mirogabalin exposure. A single 15-mg dose of mirogabalin was well tolerated by subjects with mild or moderate hepatic impairment.

Effect of coadministration of metformin with mirogabalin: Results from a phase 1, randomized, open-label, drug-drug interaction study
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Mirogabalin, a selective voltage-dependent calcium channel α2δ ligand under development for treatment of neuropathic pain, may be coadministered with metformin in patients with type 2 diabetes mellitus who have diabetic peripheral neuropathic pain. A randomized, open-label, single-dose, 3-treatment, 3-period crossover study evaluated the pharmacokinetics (PK) and safety of mirogabalin and metformin upon coadministration. Eligible subjects received 3 treatments separated by a 7-day washout period: 1 oral dose of mirogabalin 15 mg; 1 oral dose of metformin 850 mg; and coadministration of mirogabalin 15 mg with metformin 850 mg. PK assessments included maximum observed plasma concentration (Cmax); time of maximum plasma concentration; area under the concentration-time curve from time 0 to the last quantifiable concentration, and from 0 to infinity (AUClast and AUC0-inf, respectively). Safety assessments included adverse event (AE) monitoring and physical and clinical laboratory evaluations. 21 healthy men with a mean age of 30.4 years were enrolled and completed the study. Geometric least square means ratios (coadministration vs. alone; 90% confidence interval) for metformin Cmax, AUClast, and AUC0-inf were 1.00 (0.95 - 1.05), 1.04 (1.00 - 1.07), and 1.03 (1.00 - 1.07), respectively; ratios for mirogabalin were 0.94 (0.87 - 1.02), 0.99 (0.95 - 1.04), and 1.00 (0.96 - 1.04), respectively. Three subjects reported treatment-emergent AEs: dyspepsia, headache, and increased hepatic enzymes (resolved upon follow-up without sequelae). There were no deaths, serious AEs, or discontinuations due to AEs. Coadministration of mirogabalin and metformin is well tolerated in healthy subjects with no evidence of a drug-drug interaction.
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Coadministration of probenecid and cimetidine with mirogabalin in healthy subjects: A phase 1, randomized, open-label, drug-drug interaction study.

AIMS: The primary aim of this study was to assess the individual effects of probenecid and cimetidine on mirogabalin exposure. METHODS: This phase 1, open-label, crossover study randomized healthy adults to receive three treatment regimens, each separated by ≥5-day washout: a single oral dose of mirogabalin 15 mg on day 2, mirogabalin 15 mg on day 2 plus probenecid 500 mg every 6 h from days 1 to 4, and mirogabalin 15 mg on day 2 plus cimetidine 400 mg every 6 h from days 1 to 4. RESULTS: Coadministration of mirogabalin with probenecid or cimetidine increased the maximum and total mirogabalin exposure. The geometric mean ratios of Cmax and AUC(0-t) (90% CI) with and without coadministration of probenecid were 128.7% (121.9-135.7%) and 176.1% (171.9-180.3%), respectively. The geometric mean ratios of Cmax and AUC(0-t) (90% CI) with and without coadministration of cimetidine were 117.1% (111.0-123.6%) and 143.7% (140.3-147.2%), respectively. Mean (standard deviation) renal clearance of mirogabalin (l h-1 ) was substantially slower after probenecid [6.67 (1.53)] or cimetidine [7.17 (1.68)] coadministration, compared with mirogabalin alone [11.3 (2.39)]. Coadministration of probenecid or cimetidine decreased mirogabalin mean (standard deviation) apparent total body clearance [10.5 (2.33) and 12.8 (2.67) l h-1 , respectively, vs. 18.4 (3.93) for mirogabalin alone]. CONCLUSIONS: A greater magnitude of change in mirogabalin exposure was observed when coadministered with a drug that inhibits both renal and metabolic clearance (probenecid) vs. a drug that only affects renal clearance (cimetidine). However, as the increase in exposure is not clinically significant (>2-fold), no a priori dose adjustment is recommended.

A Randomized, Placebo-Controlled, Double-Blind Study of the Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of Single and Repeated Doses of Mirogabalin in Healthy Asian Volunteers.

Mirogabalin is a novel, preferentially selective α2 δ-1 ligand under investigation to treat neuropathic pain. The purpose of this study was to evaluate the safety, tolerability, and pharmacokinetics of various doses of mirogabalin in healthy subjects of different ethnicities. This randomized, placebo-controlled, double-blind, sequential, ascending-dose study evaluated single (10-40 mg) and repeated (10, 15 mg twice a day) doses of mirogabalin in Japanese subjects, and a single dose of mirogabalin in Korean, Chinese, and white subjects. Mirogabalin was rapidly absorbed, with a median time to maximum plasma concentration of 1 hour, and rapidly eliminated, with a mean elimination half-life of 2 to 3 hours. Single-dose mirogabalin pharmacokinetic parameters were comparable between Asian and white subjects. Exposure increased proportionally as mirogabalin dose increased in Japanese subjects. Mean mirogabalin steady-state clearance and volume of distribution values were comparable across dose levels. No accumulation of mirogabalin was observed on repeated dosing in Japanese subjects. Mirogabalin had an acceptable safety and tolerability profile in Asian and white subjects at doses up to 15 mg twice a day for 7 days. The most common treatment-emergent adverse events (somnolence, headache, and dizziness) were consistent with the known mechanism of action and safety profile of mirogabalin.

Synthesis and Pharmacological Characterization of C4ß-Amide-Substituted 2-Aminobicyclo[3.1.0]hexane-2,6-dicarboxylates. Identification of (1 S,2 S,4 S,5 R,6 S)-2-Amino-4-[(3-methoxybenzoyl)amino]bicyclo[3.1.0]hexane-2,6-dicarboxylic Acid (LY2794193), a Highly Potent and Selective mGlu3 Receptor Agonist.

Multiple therapeutic opportunities have been suggested for compounds capable of selective activation of metabotropic glutamate 3 (mGlu3) receptors, but small molecule tools are lacking. As part of our ongoing efforts to identify potent, selective, and systemically bioavailable agonists for mGlu2 and mGlu3 receptor subtypes, a series of C4ß-N-linked variants of (1 S,2 S,5 R,6 S)-2-amino-bicyclo[3.1.0]hexane-2,6-dicarboxylic acid 1 (LY354740) were prepared and evaluated for both mGlu2 and mGlu3 receptor binding affinity and functional cellular responses. From this investigation we identified (1 S,2 S,4 S,5 R,6 S)-2-amino-4-[(3-methoxybenzoyl)amino]bicyclo[3.1.0]hexane-2,6-dicarboxylic acid 8p (LY2794193), a molecule that demonstrates remarkable mGlu3 receptor selectivity. Crystallization of 8p with the amino terminal domain of hmGlu3 revealed critical binding interactions for this ligand with residues adjacent to the glutamate binding site, while pharmacokinetic assessment of 8p combined with its effect in an mGlu2 receptor-dependent behavioral model provides estimates for doses of this compound that would be expected to selectively engage and activate central mGlu3 receptors in vivo.

Pharmacokinetics and Safety of a Single Oral Dose of Mirogabalin in Japanese Subjects With Varying Degrees of Renal Impairment.

Mirogabalin (DS-5565) is a novel preferentially selective α2 δ-1 ligand being developed for the treatment of diabetic peripheral neuropathic pain and postherpetic neuralgia. The current multicenter open-label study determined the effect of varying degrees of renal impairment on the pharmacokinetics and safety of a single dose of mirogabalin 5 mg in Japanese subjects. A total of 30 subjects (6 subjects per renal function category [normal, mild, moderate, or severe impairment; and end-stage renal disease (ESRD)]) were enrolled and completed the study. The AUClast increased with severity of renal impairment; the geometric least-squares mean ratios of AUClast compared with subjects with normal renal function were 1.3, 1.9, 3.6, and 5.3 for patients with mild, moderate, and severe impairment and ESRD, respectively. In accordance with this AUClast increase, apparent total body clearance (CL/F), renal clearance (CLr), and the cumulative percentage of mirogabalin dose excreted into urine all decreased with severity of renal impairment. There were no deaths and no severe treatment-related adverse events (TEAEs), serious TEAEs, or TEAEs resulting in study discontinuation. Mirogabalin was well tolerated in Japanese subjects with normal renal function and those with mild to severe renal impairment. It was also tolerated in subjects with ESRD but with a higher incidence of TEAEs. The most frequently reported TEAEs were dizziness (ESRD, n = 3), somnolence (ESRD, n = 2), and vomiting (ESRD, n = 2). Based on these data, a mirogabalin dose adjustment will be considered in Japanese subjects with moderate to severe renal impairment and those with ESRD.

Development and validation of a high-performance liquid chromatography-tandem mass spectrometry method to quantify LY-354,740 in rat and marmoset plasma.

LY-354,740 (eglumegad) is a selective and potent agonist of the metabotropic glutamate group II receptors (mGluR2,3) that has already entered clinical trials as a potential anti-psychotic agent and therefore has well-documented pharmacokinetic (PK), safety and tolerability profiles in human. Whereas its development as an anti-psychotic agent has not been pursued, LY-354,740 may have potential in other neuroscience-related fields, notably anxiety and neuro-protection. The common marmoset is a small primate that has long been used in neuroscience. However, given its small size and small circulating blood volume, conducting PK studies to determine the therapeutic effectiveness of LY-354,740 at clinically-relevant doses is challenging. Here, we have developed and validated a simple, sensitive and selective analytical method that enables quantification of LY-354,740 using a small volume of plasma. The analytical method consisted of protein precipitation followed by high-performance liquid chromatography with heat assisted electrospray ionisation mass spectrometry (UHPLC-HESI-MS/MS). The chromatographic separation was achieved using gradient elution with a mobile phase consisting of acetonitrile and 10mM ammonium formate (pH 3) on a Thermo Scientific Acclaim Trinity P1 analytical column (100x3.0mm I.D., 3µm) operating at 45°C and at a flow rate of 900µl/min. The method displays a linear relationship ranging from 20.0 to 5000ng/ml. Intra- and inter-day relative standard deviations are less than 5.7% and 7.0%, respectively and the accuracy ranged from 91.0 to 106.0%. The UHPLC-HESI-MS/MS analytical method we describe here is simple, sensitive, specific and capable of quantifying LY-354,740 in both rat and marmoset plasma, and is suitable to conduct PK studies after a single sub-cutaneous dose of 1.0mg/kg or lower in both species.

Discovery of 4-((3'R,4'S,5'R)-6″-Chloro-4'-(3-chloro-2-fluorophenyl)-1'-ethyl-2″-oxodispiro[cyclohexane-1,2'-pyrrolidine-3',3″-indoline]-5'-carboxamido)bicyclo[2.2.2]octane-1-carboxylic Acid (AA-115/APG-115): A Potent and Orally Active Murine Double Minute 2 (MDM2) Inhibitor in Clinical Development.

We previously reported the design of spirooxindoles with two identical substituents at the carbon-2 of the pyrrolidine core as potent MDM2 inhibitors. In this paper we describe an extensive structure-activity relationship study of this class of MDM2 inhibitors, which led to the discovery of 60 (AA-115/APG-115). Compound 60 has a very high affinity to MDM2 (Ki < 1 nM), potent cellular activity, and an excellent oral pharmacokinetic profile. Compound 60 is capable of achieving complete and long-lasting tumor regression in vivo and is currently in phase I clinical trials for cancer treatment.

[2.2.1]-Bicyclic sultams as potent androgen receptor antagonists.

This letter describes the discovery, synthesis, SAR, and biological activity of [2.2.1]-bicyclic sultams as potent antagonists of the androgen receptor. Optimization of the series led to the identification of compound 25, which displayed robust pharmacodynamic effects in rats after oral dosing.

Novel bicyclo[3.1.0]hexane analogs as antagonists of metabotropic glutamate 2/3 receptors for the treatment of depression.

Negative modulators of metabotropic glutamate 2 & 3 receptors demonstrate antidepressant-like activity in animal models and hold promise as novel therapeutic agents for the treatment of major depressive disorder. Herein we describe our efforts to prepare and optimize a series of conformationally constrained 3,4-disubstituted bicyclo[3.1.0]hexane glutamic acid analogs as orthosteric (glutamate site) mGlu2/3 receptor antagonists. This work led to the discovery of a highly potent and efficacious tool compound 18 (hmGlu2 IC50 46±14.2nM, hmGlu3 IC50=46.1±36.2nM). Compound 18 showed activity in the mouse forced swim test with a minimal effective dose (MED) of 1mg/kg ip. While in rat EEG studies it exhibited wake promoting effects at 3 and 10mg/kg ip without any significant effects on locomotor activity. Compound 18 thus represents a novel tool molecule for studying the impact of blocking mGlu2/3 receptors both in vitro and in vivo.

Pharmacokinetics in Mouse and Comparative Effects of Frondosides in Pancreatic Cancer.

The frondosides are triterpenoid glycosides from the Atlantic sea cucumber Cucumaria frondosa. Frondoside A inhibits growth, invasion, metastases and angiogenesis and induces apoptosis in diverse cancer types, including pancreatic cancer. We compared the growth inhibitory effects of three frondosides and their aglycone and related this to the pharmocokinetics and route of administration. Frondoside A potently inhibited growth of pancreatic cancer cells with an EC50 of ~1 µM. Frondoside B was less potent (EC50 ~2.5 µM). Frondoside C and the aglycone had no effect. At 100 µg/kg, frondoside A administered to CD2F1 mice as an i.v. bolus, the Cpmax was 129 nM, Cltb was 6.35 mL/min/m², and half-life was 510 min. With i.p. administration the Cpmax was 18.3 nM, Cltb was 127 mL/min/m² and half-life was 840 min. Oral dosing was ineffective. Frondoside A (100 µg/kg/day i.p.) markedly inhibited growth cancer xenografts in nude mice. The same dose delivered by oral gavage had no effect. No evidence of acute toxicity was seen with frondoside A. Frondoside A is more potent inhibitor of cancer growth than other frondosides. The glycoside component is essential for bioactivity. Frondoside A is only effective when administered systemically. Based on the current and previous studies, frondoside A appears safe and may be valuable in the treatment of cancer.

Population pharmacokinetic modeling and simulation for assessing renal impairment effect on the pharmacokinetics of mirogabalin.

A population pharmacokinetic model was developed to describe plasma concentrations of mirogabalin and lactam metabolite, obtained following a single oral dose of 5 mg mirogabalin to subjects with varying degrees of renal function.A 2-compartment model was used for both mirogabalin and lactam metabolite. Body weight was a significant covariate on volume of distribution of mirogabalin and lactam metabolite, whereas creatinine clearance significantly affected both renal and nonrenal clearance of mirogabalin. The total clearance of mirogabalin was decreased by 25%, 54%, and 76% in subjects with mild, moderate, and severe renal impairment, respectively, relative to normal controls. Simulation results showed that in comparison with the normal renal function group receiving mirogabalin 15 mg once or twice daily, dose reduction by 50% or 75% in subjects with moderate or severe renal impairment would produce similar AUCss values, but 37%-43% or 28%-32% lower Cmax,ss of mirogabalin. Predicted mirogabalin AUCss was 26% higher, whereas Cmax,ss was similar in subjects with mild renal impairment compared with those having normal renal function taking the same dose. Results support a dose reduction by 50% or 75% in subjects with moderate or severe renal impairment. No dose adjustment seemed necessary for subjects with mild renal impairment.

Synthesis and evaluation of novel 2,4-diaminopyrimidines bearing bicyclic aminobenzazepines for anaplastic lymphoma kinase (ALK) inhibitor.

A series of novel 2,4-diaminopyrimidine compounds bearing bicyclic aminobenzazepine were synthesized and evaluated for their anti-ALK activities. The activities of these compounds were confirmed in both enzyme- and cell-based ALK assays. Amongst compounds synthesized, KRCA-0445 showed very promising results in pharmacokinetic study and in vivo efficacy study with H3122 xenograft mouse model.

Synthesis and Pharmacological Characterization of C4-(Thiotriazolyl)-substituted-2-aminobicyclo[3.1.0]hexane-2,6-dicarboxylates. Identification of (1R,2S,4R,5R,6R)-2-Amino-4-(1H-1,2,4-triazol-3-ylsulfanyl)bicyclo[3.1.0]hexane-2,6-dicarboxylic Acid (LY2812223), a Highly Potent, Functionally Selective mGlu2 Receptor Agonist.

Identification of orthosteric mGlu(2/3) receptor agonists capable of discriminating between individual mGlu2 and mGlu3 subtypes has been highly challenging owing to the glutamate-site sequence homology between these proteins. Herein we detail the preparation and characterization of a series of molecules related to (1S,2S,5R,6S)-2-aminobicyclo[3.1.0]hexane-2,6-dicarboxylate 1 (LY354740) bearing C4-thiotriazole substituents. On the basis of second messenger responses in cells expressing other recombinant human mGlu2/3 subtypes, a number of high potency and efficacy mGlu2 receptor agonists exhibiting low potency mGlu3 partial agonist/antagonist activity were identified. From this, (1R,2S,4R,5R,6R)-2-amino-4-(1H-1,2,4-triazol-3-ylsulfanyl)bicyclo[3.1.0]hexane-2,6-dicarboxylic acid 14a (LY2812223) was further characterized. Cocrystallization of 14a with the amino terminal domains of hmGlu2 and hmGlu3 combined with site-directed mutation studies has clarified the underlying molecular basis of this unique pharmacology. Evaluation of 14a in a rat model responsive to mGlu2 receptor activation coupled with a measure of central drug disposition provides evidence that this molecule engages and activates central mGlu2 receptors in vivo.

Retinal ganglion cell neuroprotection induced by activation of alpha7 nicotinic acetylcholine receptors.

The α7nAChR agonist, PNU-282987, has previously been shown to have a neuroprotective effect against loss of retinal ganglion cells (RGCs) in an in vivo glaucoma model when the agent was injected into the vitreous chamber of adult Long Evans rat eyes. Here, we characterized the neuroprotective effect of PNU-282987 at the nerve fiber and retinal ganglion cell layer, determined that neuroprotection occurred when the agonist was applied as eye drops and verified detection of the agonist in the retina, using LC/MS/MS. To induce glaucoma-like conditions in adult Long Evans rats, hypertonic saline was injected into the episcleral veins to induce scar tissue and increase intraocular pressure. Within one month, this procedure produced significant loss of RGCs compared to untreated conditions. RGCs were quantified after immunostaining with an antibody against Thy 1.1 and imaged using a confocal microscope. In dose-response studies, concentrations of PNU-282987 were applied to the animal's right eye two times each day, while the left eye acted as an internal control. Eye drops of PNU-282987 resulted in neuroprotection against RGC loss in a dose-dependent manner using concentrations between 100 µM and 2 mM PNU-282987. LC/MS/MS results demonstrated that PNU-282987 was detected in the retina when applied as eye drops, relatively small amounts of PNU-282987 were measured in blood plasma and no PNU-282987 was detected in cardiac tissue. These results support the hypothesis that eye drop application of PNU-282987 can prevent loss of RGCs associated with glaucoma, which can lead to neuroprotective treatments for diseases that involve α7nAChRs.