Publications by authors named "J Guy Breitenbucher"

46 Publications

Azetidine-based selective glycine transporter-1 (GlyT1) inhibitors with memory enhancing properties.

Bioorg Med Chem Lett 2020 07 25;30(14):127214. Epub 2020 Apr 25.

Dart Neuroscience, 12278 Scripps Summit Dr, San Diego, CA 92131, United States.

A strategy to conformationally restrain a series of GlyT1 inhibitors identified potent analogs that exhibited slowly interconverting rotational isomers. Further studies to address this concern led to a series of azetidine-based inhibitors. Compound 26 was able to elevate CSF glycine levels in vivo and demonstrated potency comparable to Bitopertin in an in vivo rat receptor occupancy study. Compound 26 was subsequently shown to enhance memory in a Novel Object Recognition (NOR) behavioral study after a single dose of 0.03 mg/kg, and in a contextual fear conditioning (cFC) study after four QD doses of 0.01-0.03 mg/kg.
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http://dx.doi.org/10.1016/j.bmcl.2020.127214DOI Listing
July 2020

Rapid identification of a novel phosphodiesterase 7B tracer for receptor occupancy studies using LC─MS/MS.

Neurochem Int 2020 07 1;137:104735. Epub 2020 Apr 1.

Dart NeuroScience LLC, 12278 Scripps Summit Drive, San Diego, CA, 92131, United States.

Phosphodiesterase 7B (PDE7B) inhibition has been considered as a therapeutic target for the treatment of several neurological disorders. Currently, there are no radio-labeled tracers available to determine receptor occupancy (RO) of this target. Developing such a tracer could greatly facilitate the identification of viable PDE7B inhibitors. In the current study, a liquid chromatography tandem mass spectrometry (LC─MS/MS) method was utilized to evaluate the brain distribution of unlabeled tracer candidates following intravenous micro-dosing. This novel approach resulted in an accelerated identification of a potential novel RO tracer for PDE7B. The identified molecule, Compound 30, showed reasonable target-tissue specificity (striatum/cerebellum ratio of 2.2) and suitable uptake (0.25% of the injected dose/g brain tissue) as demonstrated in rats dosed with the unlabeled compound. Compound 30 was subsequently labeled with tritium (H). In vitro characterization of H-Compound 30 demonstrated that this compound possessed a high target affinity with a subnanomolar K (0.8 nM) and a B of 58 fmol/mg of protein using rat brain homogenate. Intravenous microdosing of H-Compound 30 showed preferential binding in the rat striatum, consistent with the mRNA distribution of PDE7B. In vitro displacement study with other structurally distinct PDE7B target-specific inhibitors using rat brain homogenate indicated that H-Compound 30 is an ideal tracer for K analysis. This is the first report of a preclinical tracer for PDE7B. With further characterization, Compound 30 may ultimately show the appropriate properties required to be further developed as a PDE7B PET ligand for clinical studies.
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http://dx.doi.org/10.1016/j.neuint.2020.104735DOI Listing
July 2020

Target Engagement of a Phosphodiesterase 2A Inhibitor Affecting Long-Term Memory in the Rat.

J Pharmacol Exp Ther 2019 09 28;370(3):399-407. Epub 2019 Jun 28.

Departments of Preclinical Research (G.G., T.S., N.W., A.T., A.M., Y.-W.L., J.V., A.D.), Chemistry Manufacturing and Control (A.Z.), Biology (Y.Y., E.M.), Structural Biology (H.X., K.A.), and Medicinal Chemistry (L.G., J.G.B.), Dart NeuroScience, LLC, San Diego, California.

Inhibition of phosphodiesterase 2A (PDE2A) has been proposed as a potential approach to enhance cognitive functioning and memory through boosting intracellular cGMP/cAMP and enhancing neuroplasticity in memory-related neural circuitry. Previous preclinical studies demonstrated that PDE2A inhibitors could reverse -methyl-D-aspartate receptor antagonist (5S,10R)-(+)-5-methyl-10,11-dihydro-5-dibenzo[,]cyclohepten-5,10-imine or ketamine-induced memory deficit. Here, we report that the potent and selective PDE2A inhibitor 4-(1-azetidinyl)-7-methyl-5-[1-methyl-5-[5-(trifluoromethyl)-2-pyridinyl]-1-pyrazol-4-yl]-imidazo[5,1-][1,2,4]triazine (PF-05180999) enhances long-term memory in a contextual fear conditioning model in the rat at the oral dose of 0.3 mg/kg. Target engagement at this efficacious dose was explored using in vivo autoradiography. Converse to the results of a decrease of PDE2A binding (target occupancy) by the PDE2A inhibitor, a paradoxical increase (up to 40%) in PDE2A binding was detected. However, a typical target occupancy curve could be generated by PF-05180999 at much higher doses. In vitro experiments using recombinant PDE2A protein or rat brain homogenate that contains native PDE2A protein demonstrated that increased cGMP after initial PDE2A inhibition could be responsible for the activation of PDE2A enzyme via allosteric binding to the GAF-B domain, leading to positive cooperativity of the dormant PDE2A enzymes. Our results suggest that when evaluating target engagement of PDE2A inhibitors for memory disorder in clinical setting with occupancy assays, the efficacious dose may not fall on the typical receptor/target curve. On the contrary, an increase in PDE2A tracer binding is likely seen. Our results also suggest that when evaluating target occupancy of enzymes, potential regulation of enzyme activities should be considered.
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http://dx.doi.org/10.1124/jpet.118.255851DOI Listing
September 2019

Mathematical and Structural Characterization of Strong Nonadditive Structure-Activity Relationship Caused by Protein Conformational Changes.

J Med Chem 2018 09 20;61(17):7754-7766. Epub 2018 Aug 20.

Dart Neuroscience LLC , 12278 Scripps Summit Drive , San Diego , California 92131 , United States.

In medicinal chemistry, accurate prediction of additivity-based structure-activity relationship (SAR) analysis rests on three assumptions: (1) a consistent binding pose of the central scaffold, (2) no interaction between the R group substituents, and (3) a relatively rigid binding pocket in which the R group substituents act independently. Previously, examples of nonadditive SAR have been documented in systems that deviate from the first two assumptions. Local protein structural change upon ligand binding, through induced fit or conformational selection, although a well-known phenomenon that invalidates the third assumption, has not been linked to nonadditive SAR conclusively. Here, for the first time, we present clear structural evidence that the formation of a hydrophobic pocket upon ligand binding in PDE2 catalytic site reduces the size of another distinct subpocket and contributes to strong nonadditive SAR between two otherwise distant R groups.
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http://dx.doi.org/10.1021/acs.jmedchem.8b00713DOI Listing
September 2018

Design and Synthesis of Novel and Selective Glycine Transporter-1 (GlyT1) Inhibitors with Memory Enhancing Properties.

J Med Chem 2018 07 11;61(14):6018-6033. Epub 2018 Jul 11.

Dart NeuroScience LLC , 12278 Scripps Summit Drive , San Diego , California 92121 , United States.

We report here the identification and optimization of a novel series of potent GlyT1 inhibitors. A ligand design campaign that utilized known GlyT1 inhibitors as starting points led to the identification of a novel series of pyrrolo[3,4- c]pyrazoles amides (21-50) with good in vitro potency. Subsequent optimization of physicochemical and in vitro ADME properties produced several compounds with promising pharmacokinetic profiles. In vivo inhibition of GlyT1 was demonstrated for select compounds within this series by measuring the elevation of glycine in the cerebrospinal fluid (CSF) of rats after a single oral dose of 10 mg/kg. Ultimately, an optimized lead, compound 46, demonstrated in vivo efficacy in a rat novel object recognition (NOR) assay after oral dosing at 0.1, 1, and 3 mg/kg.
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http://dx.doi.org/10.1021/acs.jmedchem.8b00372DOI Listing
July 2018