Design and optimization of selective azaindole amide M1 positive allosteric modulators.

Selective activation of the M1 receptor via a positive allosteric modulator (PAM) is a new approach for the treatment of the cognitive impairments associated with schizophrenia and Alzheimer's disease. A novel series of azaindole amides and their key pharmacophore elements are described. The nitrogen of the azaindole core is a key design element as it forms an intramolecular hydrogen bond with the amide N-H thus reinforcing the bioactive conformation predicted by published SAR and our homology model. Representative compound 25 is a potent and selective M1 PAM that has well aligned physicochemical properties, adequate brain penetration and pharmacokinetic (PK) properties, and is active in vivo. These favorable properties indicate that this series possesses suitable qualities for further development and studies.

Design of Next-Generation DGAT2 Inhibitor PF-07202954 with Longer Predicted Half-Life.

Diacylglycerol O-acyltransferase 2 (DGAT2) inhibitors have been shown to lower liver triglyceride content and are being explored clinically as a treatment for non-alcoholic steatohepatitis (NASH). This work details efforts to find an extended-half-life DGAT2 inhibitor. A basic moiety was added to a known inhibitor template, and the basicity and lipophilicity were fine-tuned by the addition of electrophilic fluorines. A weakly basic profile was required to find an appropriate balance of potency, clearance, and permeability. This work culminated in the discovery of PF-07202954 (12), a weakly basic DGAT2 inhibitor that has advanced to clinical studies. This molecule displays a higher volume of distribution and longer half-life in preclinical species, in keeping with its physicochemical profile, and lowers liver triglyceride content in a Western-diet-fed rat model.

Target occupancy study and whole-body dosimetry with a MAGL PET ligand [11C]PF-06809247 in non-human primates.

BACKGROUND: Monoacylglycerol lipase (MAGL) is a key serine hydrolase which terminates endocannabinoid signaling and regulates arachidonic acid driven inflammatory responses within the central nervous system. To develop [11C]PF-06809247 into a clinically usable MAGL positron emission tomography (PET) radioligand, we assessed the occupancy of MAGL by an inhibitor in the non-human primate (NHP) brain. Additionally, we measured the whole-body distribution of [11C]PF-06809247 in NHP and estimated human effective radiation doses. METHODS: Seven cynomolgus monkeys were enrolled for brain PET measurements. Two PET measurements along with arterial blood sampling were performed in each NHP: one baseline and one pretreatment condition with intravenous administration of PF-06818883, a pro-drug of a selective MAGL inhibitor (total of seven doses between 0.01 and 1.27 mg/kg). Kinetic parameters K1, k2 and k3 were estimated by a two tissue compartment (2TC) model using metabolite corrected plasma radioactivity as the input function. k4 was set as 0 according to the irreversible binding of [11C]PF-06809247. Ki by 2TC and Patlak analysis were calculated as the influx constant. The target occupancy was calculated using Ki at baseline and pretreatment conditions. Two cynomolgus monkeys were enrolled for whole-body PET measurements. Estimates of the absorbed radiation dose in humans were calculated with OLINDA/EXM 1.1 using the adult male reference model. RESULTS: Radioactivity retention was decreased in all brain regions following pretreatment with PF-06818883. Occupancy was measured as 25.4-100.5% in a dose dependent manner. Whole-body PET showed high radioactivity uptake values in the liver, small intestine, kidney, and brain. The effective dose of [11C]PF-06809247 was calculated as 4.3 µSv/MBq. CONCLUSIONS: [11C]PF-06809247 is a promising PET ligand for further studies of MAGL in the human brain.

Global Portrait of Protein Targets of Metabolites of the Neurotoxic Compound BIA 10-2474.

Clinical investigation of the fatty acid amide hydrolase (FAAH) inhibitor BIA 10-2474 resulted in serious adverse neurological events. Structurally unrelated FAAH inhibitors tested in humans have not presented safety concerns, suggesting that BIA 10-2474 has off-target activities. A recent activity-based protein profiling (ABPP) study revealed that BIA 10-2474 and one of its major metabolites inhibit multiple members of the serine hydrolase class to which FAAH belongs. Here, we extend these studies by performing a proteome-wide analysis of covalent targets of BIA 10-2474 metabolites. Using alkynylated probes for click chemistry-ABPP in human cells, we show that des-methylated metabolites of BIA 10-2474 covalently modify the conserved catalytic cysteine in aldehyde dehydrogenases, including ALDH2, which has been implicated in protecting the brain from oxidative stress-related damage. These findings indicate that BIA 10-2474 and its metabolites have the potential to inhibit multiple mechanistically distinct enzyme classes involved in nervous system function.

Identification and Development of an Irreversible Monoacylglycerol Lipase (MAGL) Positron Emission Tomography (PET) Radioligand with High Specificity.

Monoacylglycerol lipase (MAGL), a serine hydrolase extensively expressed throughout the brain, serves as a key gatekeeper regulating the tone of endocannabinoid signaling. Preclinically, inhibition of MAGL is known to provide therapeutic benefits for a number of neurological disorders. The availability of a MAGL-specific positron emission tomography (PET) ligand would considerably facilitate the development and clinical characterization of MAGL inhibitors via noninvasive and quantitative PET imaging. Herein, we report the identification of the potent and selective irreversible MAGL inhibitor 7 (PF-06809247) as a suitable radioligand lead, which upon radiolabeling was found to exhibit a high level of MAGL specificity; this enabled cross-species measurement of MAGL brain expression (Bmax), assessment of in vivo binding in the rat, and nonhuman primate PET imaging.

Discovery and Lead Optimization of Atropisomer D1 Agonists with Reduced Desensitization.

The discovery of D1 subtype-selective agonists with drug-like properties has been an enduring challenge for the greater part of 40 years. All known D1-selective agonists are catecholamines that bring about receptor desensitization and undergo rapid metabolism, thus limiting their utility as a therapeutic for chronic illness such as schizophrenia and Parkinson's disease. Our high-throughput screening efforts on D1 yielded a single non-catecholamine hit PF-4211 (6) that was developed into a series of potent D1 receptor agonist leads with high oral bioavailability and CNS penetration. An important structural feature of this series is the locked biaryl ring system resulting in atropisomerism. Disclosed herein is a summary of our hit-to-lead efforts on this series of D1 activators culminating in the discovery of atropisomer 31 (PF-06256142), a potent and selective orthosteric agonist of the D1 receptor that has reduced receptor desensitization relative to dopamine and other catechol-containing agonists.

Discovery of Trifluoromethyl Glycol Carbamates as Potent and Selective Covalent Monoacylglycerol Lipase (MAGL) Inhibitors for Treatment of Neuroinflammation.

Monoacylglycerol lipase (MAGL) inhibition provides a potential treatment approach to neuroinflammation through modulation of both the endocannabinoid pathway and arachidonoyl signaling in the central nervous system (CNS). Herein we report the discovery of compound 15 (PF-06795071), a potent and selective covalent MAGL inhibitor, featuring a novel trifluoromethyl glycol leaving group that confers significant physicochemical property improvements as compared with earlier inhibitor series with more lipophilic leaving groups. The design strategy focused on identifying an optimized leaving group that delivers MAGL potency, serine hydrolase selectivity, and CNS exposure while simultaneously reducing log  D, improving solubility, and minimizing chemical lability. Compound 15 achieves excellent CNS exposure, extended 2-AG elevation effect in vivo, and decreased brain inflammatory markers in response to an inflammatory challenge.

Discovery of the Potent and Selective M1 PAM-Agonist N-[(3R,4S)-3-Hydroxytetrahydro-2H-pyran-4-yl]-5-methyl-4-[4-(1,3-thiazol-4-yl)benzyl]pyridine-2-carboxamide (PF-06767832): Evaluation of Efficacy and Cholinergic Side Effects.

It is hypothesized that selective muscarinic M1 subtype activation could be a strategy to provide cognitive benefits to schizophrenia and Alzheimer's disease patients while minimizing the cholinergic side effects observed with nonselective muscarinic orthosteric agonists. Selective activation of M1 with a positive allosteric modulator (PAM) has emerged as a new approach to achieve selective M1 activation. This manuscript describes the development of a series of M1-selective pyridone and pyridine amides and their key pharmacophores. Compound 38 (PF-06767832) is a high quality M1 selective PAM that has well-aligned physicochemical properties, good brain penetration and pharmacokinetic properties. Extensive safety profiling suggested that despite being devoid of mAChR M2/M3 subtype activity, compound 38 still carries gastrointestinal and cardiovascular side effects. These data provide strong evidence that M1 activation contributes to the cholinergic liabilities that were previously attributed to activation of the M2 and M3 receptors.

Structure-activity relationships of potent, selective inhibitors of neuronal nitric oxide synthase based on the 6-phenyl-2-aminopyridine structure.

The synthesis and structure-activity relationships of a series of 6-phenyl-2-aminopyridines that potently and selectively inhibit the neuronal isoform of nitric oxide synthase (nNOS) are described. Compound 14bi from this series exhibits potent in vivo activity in harmaline-induced cGMP formation in rat cerebellum, a functional model of nNOS inhibition, and in the PCP-induced hypermotility model in the rat. These results suggest that 14bi may be a useful reagent for evaluating potential therapeutic applications of nNOS inhibitors in the central nervous system.

Pharmacology of selective acetylcholinesterase inhibitors: implications for use in Alzheimer's disease.

Cholinesterase inhibitors vary in their selectivity for acetylcholinesterase versus butyrylcholinesterase. We examined several cholinesterase inhibitors and assessed the relative role of acetylcholinesterase versus butyrylcholinesterase inhibition in central and peripheral responses to these medications. Donepezil and icopezil are highly selective for acetylcholinesterase, whereas tacrine and heptylphysostigmine demonstrated greater potency for butyrylcholinesterase over acetylcholinesterase. All four compounds increased acetylcholine levels in mouse brains. Dose-response curves for tremor (central effect) and salivation (peripheral effect) showed that donepezil and icopezil possess a more favourable therapeutic index than the nonselective inhibitors, tacrine and heptylphysostigmine. Co-administration of the selective butyrylcholinesterase inhibitor tetraisopropylpyrophosphoramide (iso-OMPA) potentiated peripheral, but not central, effects of the selective acetylcholinesterase inhibitor icopezil. The improved therapeutic index observed in mice with icopezil is due to a high degree of selectivity for acetylcholinesterase versus butyrylcholinesterase, suggesting that high selectivity for acetylcholinesterase may contribute to the clinically favourable tolerability profile of agents such as donepezil in Alzheimer's disease patients.

Measurement of atropisomer racemization kinetics using segmented flow technology.

When stable atropisomers are encountered by drug discovery teams, they can have important implications due to potential differences in their biological activity, pharmacokinetics, and toxicity. Knowledge of an atropisomer's activation parameters for interconversion is required to facilitate informed decisions on how to proceed. Herein, we communicate the development of a new method for the rapid measurement of atropisomer racemization kinetics utilizing segmented flow technology. This method leverages the speed, accuracy, low sample requirement, safety, and semiautomated nature of flow instrumentation to facilitate the acquisition of kinetics data required for experimentally probing atropisomer activation parameters. Measured kinetics data obtained for the atropo isomerization of AMPA antagonist CP-465021 using segmented flow and traditional thermal methods were compared to validate the method.

Substituted 6-phenyl-pyridin-2-ylamines: selective and potent inhibitors of neuronal nitric oxide synthase.

The synthesis and nNOS and eNOS activity of 6-(4-(dimethylaminoalkyl)-/6-(4-(dimethylaminoalkoxy)-5-ethyl-2-methoxyphenyl)-pyridin-2-ylamines and 6-(4-(dimethylaminoalkyl)-/6-(4-(dimethylaminoalkoxy)-2,5-dimethoxyphenyl)-pyridin-2-ylamines 1-8 are described. These compounds are potent inhibitors of the human nNOS isoform.