Discovery Of Highly Potent And Selective α4β2-Nicotinic Acetylcholine Receptor (Nachr) Partial Agonists Containing An Isoxazolylpyridine Ether Scaffold That Demonstrate Antidepressant-Like Activity. Part II

In our continued efforts to develop α4β2-nicotinic acetylcholine receptor (nAChR) partial agonists as novel antidepressants having a unique mechanism of action, structure-activity relationship (SAR) exploration of certain isoxazolylpyridine ethers is presented. In particular, modifications to both the azetidine ring present in the starting structure 4 and its metabolically liable hydroxyl side chain substituent have been explored to improve compound druggability. The pharmacological characterization of all new compounds has been carried out using [ 3 H]epibatidine binding studies together with functional assays based on 86 Rb + ion flux measurements. We found that the deletion of the metabolically liable hydroxyl group or its replacement by a fluoromethyl group not only maintained potency and selectivity but also resulted in compounds showing antidepressant-like properties in the mouse forced swim test. These isoxazolylpyridine ethers appear to represent promising lead candidates in the design of innovative chemical tools containing reporter groups for imaging purposes and of possible therapeutics. © 2012 American Chemical Society

Identification Of Novel α4β2-Nicotinic Acetylcholine Receptor (Nachr) Agonists Based On An Isoxazole Ether Scaffold That Demonstrate Antidepressant-Like Activity

There is considerable evidence to support the hypothesis that the blockade of nAChR is responsible for the antidepressant action of nicotinic ligands. The nicotinic acetylcholine receptor (nAChR) antagonist, mecamylamine, has been shown to be an effective add-on in patients that do not respond to selective serotonin reuptake inhibitors. This suggests that nAChR ligands may address an unmet clinical need by providing relief from depressive symptoms in refractory patients. In this study, a new series of nAChR ligands based on an isoxazole-ether scaffold have been designed and synthesized for binding and functional assays. Preliminary structure-activity relationship (SAR) efforts identified a lead compound 43, which possesses potent antidepressant-like activity (1 mg/kg, IP; 5 mg/kg, PO) in the classical mouse forced swim test. Early stage absorption, distribution, metabolism, excretion, and toxicity (ADME-Tox) studies also suggested favorable drug-like properties, and broad screening toward other common neurotransmitter receptors indicated that compound 43 is highly selective for nAChRs over the other 45 neurotransmitter receptors and transporters tested. © 2011 American Chemical Society

Chemistry Pharmacology And Behavioral Studies Identify Chiral Cyclopropanes As Selective α4β2-Nicotinic Acetylcholine Receptor Partial Agonists Exhibiting An Antidepressant Profile. Part II

A 3-pyridyl ether scaffold bearing a cyclopropane-containing side chain was recently identified in our efforts to create novel antidepressants that act as partial agonists at α4β2-nicotinic acetylcholine receptors. In this study, a systematic structure-activity relationship investigation was carried out on both the azetidine moiety present in compound 3 and its right-hand side chain, thereby discovering a variety of novel nicotinic ligands that retain bioactivity and feature improved chemical stability. The most promising compounds, 24, 26, and 30, demonstrated comparable or enhanced pharmacological profiles compared to the parent compound 4, and the N-methylpyrrolidine analogue 26 also exhibited robust antidepressant-like efficacy in the mouse forced swim test. The favorable ADMET profile and chemical stability of 26 further indicate this compound to be a promising lead as a drug candidate warranting further advancement down the drug discovery pipeline. © 2013 American Chemical Society

SAHA Enhances Synaptic Function and Plasticity In Vitro but Has Limited Brain Availability In Vivo and Does Not Impact Cognition

Suberoylanilide hydroxamic acid (SAHA) is an inhibitor of histone deacetylases (HDACs) used for the treatment of cutaneous T cell lymphoma (CTCL) and under consideration for other indications. In vivo studies suggest reducing HDAC function can enhance synaptic function and memory, raising the possibility that SAHA treatment could have neurological benefits. We first examined the impacts of SAHA on synaptic function in vitro using rat organotypic hippocampal brain slices. Following several days of SAHA treatment, basal excitatory but not inhibitory synaptic function was enhanced. Presynaptic release probability and intrinsic neuronal excitability were unaffected suggesting SAHA treatment selectively enhanced postsynaptic excitatory function. In addition, long-term potentiation (LTP) of excitatory synapses was augmented, while long-term depression (LTD) was impaired in SAHA treated slices. Despite the in vitro synaptic enhancements, in vivo SAHA treatment did not rescue memory deficits in the Tg2576 mouse model of Alzheimer’s disease (AD). Along with the lack of behavioral impact, pharmacokinetic analysis indicated poor brain availability of SAHA. Broader assessment of in vivo SAHA treatment using high-content phenotypic characterization of C57Bl6 mice failed to demonstrate significant behavioral effects of up to 150 mg/kg SAHA following either acute or chronic injections. Potentially explaining the low brain exposure and lack of behavioral impacts, SAHA was found to be a substrate of the blood brain barrier (BBB) efflux transporters Pgp and Bcrp1. Thus while our in vitro data show that HDAC inhibition can enhance excitatory synaptic strength and potentiation, our in vivo data suggests limited brain availability may contribute to the lack of behavioral impact of SAHA following peripheral delivery. These results do not predict CNS effects of SAHA during clinical use and also emphasize the importance of analyzing brain drug levels when interpreting preclinical behavioral pharmacology

The Potent And Selective α4β2*/α6*-Nicotinic Acetylcholine Receptor Partial Agonist 2-[5-[5-((S)Azetidin-2-Ylmethoxy)-3-Pyridinyl]-3-Isoxazolyl]Ethanol Demonstrates Antidepressive-Like Behavior In Animal Models And A Favorable Adme-Tox Profile

Preclinical and clinical studies demonstrated that the inhibition of cholinergic supersensitivity through nicotinic antagonists and partial agonists can be used successfully to treat depressed patients, especially those who are poor responders to selective serotonin reuptake inhibitors (SSRIs). In our effort to develop novel antidepressant drugs, LF-3-88 was identified as a potent nicotinic acetylcholine receptor (nAChR) partial agonist with subnanomolar to nanomolar affinities for β2-containing nAChRs (α2β2, α3β2, α4β2, and α4β2*) and superior selectivity away from α3β4 − (K i  \u3e 10 4  nmol/L) and α7-nAChRs (K i  \u3e 10 4  nmol/L) as well as 51 other central nervous system (CNS)-related neurotransmitter receptors and transporters. Functional activities at different nAChR subtypes were characterized utilizing 86 Rb + ion efflux assays, two-electrode voltage-clamp (TEVC) recording in oocytes, and whole-cell current recording measurements. In mouse models, administration of LF-3-88 resulted in antidepressive-like behavioral signatures 15 min post injection in the SmartCube ® test (5 and 10 mg/kg, i.p.; about 45-min session), decreased immobility in the forced swim test (1–3 mg/kg, i.p.; 1–10 mg/kg, p.o.; 30 min pretreatment, 6-min trial), and decreased latency to approach food in the novelty-suppressed feeding test after 29 days chronic administration once daily (5 mg/kg but not 10 mg/kg, p.o.; 15-min trial). In addition, LF-3-88 exhibited a favorable profile in pharmacokinetic/ADME-Tox (absorption, distribution, metabolism, excretion, and toxicity) assays. This compound was also shown to cause no mortality in wild-type Balb/CJ mice when tested at 300 mg/kg. These results further support the potential of potent and selective nicotinic partial agonists for use in the treatment of depression

Biomarker Analysis of Orally Dosed, Dual Active, Matrix Metalloproteinase (MMP)-2 and MMP-9 Inhibitor, AQU-118, in the Spinal Nerve Ligation (SNL) Rat Model of Neuropathic Pain

There is an unmet medical need for the development of non-addicting pain therapeutics with enhanced efficacy and tolerability. The current study examined the effects of AQU-118, an orally active inhibitor of metalloproteinase-2 (MMP-2) and MMP-9, in the spinal nerve ligation (SNL) rat model of neuropathic pain. Mechanical allodynia and the levels of various biomarkers were examined within the dorsal root ganglion (DRG) before and after oral dosing with AQU-118. The rats that received the SNL surgery exhibited significant mechanical allodynia as compared to sham controls. Animals received either vehicle, positive control (gabapentin), or AQU-118. After SNL surgery, the dorsal root ganglion (DRG) of those rats dosed with vehicle had elevated messenger RNA (mRNA) expression levels for MMP-2, IL1-β & IL-6 and elevated protein levels for caspase-3 while exhibiting decreased protein levels for myelin basic protein (MBP) & active IL-β as compared to sham controls. Rats orally dosed with AQU-118 exhibited significantly reduced mechanical allodynia and decreased levels of caspase-3 in the DRG as compared to vehicle controls. Results demonstrate that oral dosing with the dual active, MMP-2/-9 inhibitor, AQU-118, attenuated mechanical allodynia while at the same time significantly reduced the levels of caspase-3 in the DRG