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.

Characterization of PF-6142, a Novel, Non-Catecholamine Dopamine Receptor D1 Agonist, in Murine and Nonhuman Primate Models of Dopaminergic Activation.

Selective activation of dopamine D1 receptors remains a promising pro-cognitive therapeutic strategy awaiting robust clinical investigation. PF-6142 is a key example from a recently disclosed novel series of non-catechol agonists and partial agonists of the dopamine D1/5 receptors (D1R) that exhibit pharmacokinetic (PK) properties suitable for oral delivery. Given their reported potential for functionally biased signaling compared to known catechol-based selective agonists, and the promising rodent PK profile of PF-6142, we utilized relevant in vivo assays in male rodents and male and female non-human primates (NHP) to evaluate the pharmacology of this new series. Studies in rodents showed that PF-6142 increased locomotor activity and prefrontal cortex acetylcholine release, increased time spent in wakefulness, and desynchronized the EEG, like known D1R agonists. D1R selectivity of PF-6142 was supported by lack of effect in D1R knock-out mice and blocked response in the presence of the D1R antagonist SCH-23390. Further, PF-6142 improved performance in rodent models of NMDA receptor antagonist-induced cognitive dysfunction, such as MK-801-disrupted paired-pulse facilitation, and ketamine-disrupted working memory performance in the radial arm maze. Similarly, PF-6142 reversed ketamine-induced deficits in NHP performing the spatial delayed recognition task. Of importance, PF-6142 did not alter the efficacy of risperidone in assays predictive of antipsychotic-like effect in rodents including pre-pulse inhibition and conditioned avoidance responding. These data support the continued development of non-catechol based D1R agonists for the treatment of cognitive impairment associated with brain disorders including schizophrenia.

α5 nAChR modulation of the prefrontal cortex makes attention resilient.

A loss-of-function polymorphism in the α5 nicotinic acetylcholine receptor (nAChR) subunit gene has been linked to both drug abuse and schizophrenia. The α5 nAChR subunit is strategically positioned in the prefrontal cortex (PFC), where a loss-of-function in this subunit may contribute to cognitive disruptions in both disorders. However, the specific contribution of α5 to PFC-dependent cognitive functions has yet to be illustrated. In the present studies, we used RNA interference to knockdown the α5 nAChR subunit in the PFC of adult rats. We provide evidence that through its contribution to cholinergic modulation of cholinergic modulation of neurons in the PFC, the α5 nAChR plays a specific role in the recovery of attention task performance following distraction. Our combined data reveal the potent ability of this subunit to modulate the PFC and cognitive functions controlled by this brain region that are impaired in disease.

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.

Dopamine D3/D2 Receptor Antagonist PF-4363467 Attenuates Opioid Drug-Seeking Behavior without Concomitant D2 Side Effects.

Dopamine receptor antagonism is a compelling molecular target for the treatment of a range of psychiatric disorders, including substance use disorders. From our corporate compound file, we identified a structurally unique D3 receptor (D3R) antagonist scaffold, 1. Through a hybrid approach, we merged key pharmacophore elements from 1 and D3 agonist 2 to yield the novel D3R/D2R antagonist PF-4363467 (3). Compound 3 was designed to possess CNS drug-like properties as defined by its CNS MPO desirability score (≥4/6). In addition to good physicochemical properties, 3 exhibited low nanomolar affinity for the D3R (D3 Ki = 3.1 nM), good subtype selectivity over D2R (D2 Ki = 692 nM), and high selectivity for D3R versus other biogenic amine receptors. In vivo, 3 dose-dependently attenuated opioid self-administration and opioid drug-seeking behavior in a rat operant reinstatement model using animals trained to self-administer fentanyl. Further, traditional extrapyramidal symptoms (EPS), adverse side effects arising from D2R antagonism, were not observed despite high D2 receptor occupancy (RO) in rodents, suggesting that compound 3 has a unique in vivo profile. Collectively, our data support further investigation of dual D3R and D2R antagonists for the treatment of drug addiction.

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.

Pharmacological disruption of mouse social approach behavior: relevance to negative symptoms of schizophrenia.

Social withdrawal is one of several negative symptoms of schizophrenia, all of which are poorly treated by current therapies. One challenge in developing agents with efficacy against negative symptoms is the lack of suitable preclinical models. The social approach test was used as the basis for developing an assay to test emerging therapies for negative symptoms. NMDA antagonists and dopamine agonists have been used extensively to produce or disrupt behaviors thought to be rodent correlates of positive and cognitive symptoms of schizophrenia. The aim of these studies was to determine whether sociability of mice in the 3-chamber social approach test could be disrupted and whether this paradigm could have utility in predicting efficacy against negative symptoms. The criteria for such a model were: a lack of response to antipsychotics and attenuation by agents such as the glycine agonist, d-cycloserine, which has been shown to possess clinical efficacy against negative symptoms. Administration of the NMDA antagonists MK-801, PCP, or ketamine did not disrupt sociability. In contrast, Grin1 hypomorph mice displayed a social deficit which was not reversed by atypical antipsychotics or d-serine. d-Amphetamine disrupted sociability without stimulating locomotor activity and its effect was not reversed by antipsychotics. The GABAA inverse agonist, FG-7142, reduced sociability and this was reversed by the GABAA antagonist, flumazenil and dcycloserine, but not by clozapine, or the GABAA benzodiazepine anxiolytic, alprazolam. Based on our criteria, the GABAA model warrants further evaluation to confirm that this paradigm has utility as a preclinical model for predicting efficacy against negative symptoms of schizophrenia.