Keith J. Miller

Functional Selectivity and Classical Concepts of Quantitative Pharmacology

The concept of intrinsic efficacy has been enshrined in pharmacology for half of a century, yet recent data have revealed that many ligands can differentially activate signaling pathways mediated via a single G protein-coupled receptor in a manner that challenges the traditional definition of intrinsic efficacy. Some terms for this phenomenon include functional selectivity, agonist-directed trafficking, and biased agonism. At the extreme, functionally selective ligands may be both agonists and antagonists at different functions mediated by the same receptor. Data illustrating this phenomenon are presented from serotonin, opioid, dopamine, vasopressin, and adrenergic receptor systems. A variety of mechanisms may influence this apparently ubiquitous phenomenon. It may be initiated by differences in ligand-induced intermediate conformational states, as shown for the β2-adrenergic receptor. Subsequent mechanisms that may play a role include diversity of G proteins, scaffolding and signaling partners, and receptor oligomers. Clearly, expanded research is needed to elucidate the proximal (e.g., how functionally selective ligands cause conformational changes that initiate differential signaling), intermediate (mechanisms that translate conformation changes into differential signaling), and distal mechanisms (differential effects on target tissue or organism). Besides the heuristically interesting nature of functional selectivity, there is a clear impact on drug discovery, because this mechanism raises the possibility of selecting or designing novel ligands that differentially activate only a subset of functions of a single receptor, thereby optimizing therapeutic action. It also may be timely to revise classic concepts in quantitative pharmacology and relevant pharmacological conventions to incorporate these new concepts.

Novel, highly potent, selective 5-HT2A/D2 receptor antagonists as potential atypical antipsychotics.

The discovery of N-substituted-pyridoindolines and their binding affinities at the 5-HT(2A), 5-HT(2C) and D(2) receptors, and in vivo efficacy as 5-HT(2A) antagonists is described. The structure-activity relationship of a series of core tetracyclic derivatives with varying butyrophenone sidechains is also discussed. This study has led to the identification of potent, orally bioavailable 5-HT(2A)/D(2) receptor dual antagonists as potential atypical antipsychotics.

Discovery of 5-chloro-4-((1-(5-chloropyrimidin-2-yl)piperidin-4-yl)oxy)-1-(2-fluoro-4-(methylsulfonyl)phenyl)pyridin-2(1H)-one (BMS-903452), an antidiabetic clinical candidate targeting GPR119.

G-protein-coupled receptor 119 (GPR119) is expressed predominantly in pancreatic β-cells and in enteroendocrine cells in the gastrointestinal tract. GPR119 agonists have been shown to stimulate glucose-dependent insulin release by direct action in the pancreas and to promote secretion of the incretin GLP-1 by action in the gastrointestinal tract. This dual mechanism of action has generated significant interest in the discovery of small molecule GPR119 agonists as a potential new treatment for type 2 diabetes. Herein, we describe the discovery and optimization of a new class of pyridone containing GPR119 agonists. The potent and selective BMS-903452 (42) was efficacious in both acute and chronic in vivo rodent models of diabetes. Dosing of 42 in a single ascending dose study in normal healthy humans showed a dose dependent increase in exposure and a trend toward increased total GLP-1 plasma levels.

Tricyclic dihydroquinazolinones as novel 5-HT2C selective and orally efficacious anti-obesity agents.

Agonists of the 5-HT(2C) receptor have been shown to suppress appetite and reduce body weight in animal models as well as in humans. However, agonism of the related 5-HT(2B) receptor has been associated with valvular heart disease. Synthesis and biological evaluation of a series of novel and highly selective dihydroquinazolinone-derived 5-HT(2C) agonists with no detectable agonism of the 5-HT(2B) receptor is described. Among these, compounds (+)-2a and (+)-3c were identified as potent and highly selective agonists which exhibited weight loss in a rat model upon oral dosing.

Central G-Protein Coupled Receptors (GPCR)s as molecular targets for the treatment of obesity: assets, liabilities and development status.

In the last decade, the G-Protein-Coupled Receptor (GPCR) superfamily has emerged as a very promising and enriched source of therapeutic targets for the treatment of obesity. GPCRs represent the largest family of mammalian proteins, with approximately 1000 members. It is estimated that the GPCR family may comprise greater than 1% of the human genome and is the molecular target for approximately 30% of currently marketed drugs. Human GPCRs are modulated by a large variety of ligands, including peptides, lipids, neurotransmitters, nucleotides, ions and external sensory signals such as pheromones, tastes or odors. Many of the above ligands have been implicated in the physiological control of energy balance. This article will examine the biological rationale, assets, identified liabilities and current drug development status of these receptors as anti-obesity drug targets.

Synthesis and structure–activity relationship of dihydrobenzofuran derivatives as novel human GPR119 agonists

Through appropriate medicinal chemistry design tactics and computer-assisted conformational modeling, the initial lead A was evolved into a series of dihydrobenzofuran derivatives 3 as potent GPR119 agonists. This Letter describes the optimization of general structure 3, including the substituent(s) on dihydrobenzofuran, the R(1) attachment on right-hand piperidine nitrogen, and the left-hand piperidine/piperazine and its attachment R(2). The efforts led to the identification of compounds 13c and 24 as potent human GPR119 modulators with favorable metabolic stability, ion channel activity, and PXR profiles.

Synthesis and SAR of 2,3,3a,4-tetrahydro-1H-pyrrolo[3,4-c]isoquinolin-5(9bH)-ones as 5-HT2C receptor agonists.

A series of 2,3,3a,4-tetrahydro-1H-pyrrolo[3,4-c]isoquinolin-5(9bH)-ones is described, several examples of which exhibit potent 5-HT(2C) agonism with excellent selectivity over the closely related 5-HT(2A) and 5-HT(2B) receptors. Compounds such as 38 and 44 were shown to be effective in reducing food intake in an acute rat feeding model.

Position 5.46 of the Serotonin 5-HT2A Receptor Contributes to a Species-Dependent Variation for the 5-HT2C Agonist (R)-9-Ethyl-1,3,4,10b-tetrahydro-7-trifluoromethylpyrazino[2,1-a]isoindol-6(2H)-one: Impact on Selectivity and Toxicological Evaluation

Successful development of 5-HT2C agonists requires selectivity versus the highly homologous 5-HT2A receptor, because agonism at this receptor can result in significant adverse events. (R)-9-Ethyl-1,3,4,10b-tetrahydro-7-trifluoromethylpyrazino[2,1-a]isoindol-6(2H)-one (compound 1) is a potent 5-HT2C agonist exhibiting selectivity over the human 5-HT2A receptor. Evaluation of the compound at the rat 5-HT2A receptor, however, revealed potent binding and agonist functional activity. The physiological consequence of this higher potency was the observation of a significant increase in blood pressure in conscious telemeterized rats that could be prevented by ketanserin. Docking of compound 1 in a homology model of the 5-HT2A receptor indicated a possible binding mode in which the ethyl group at the 9-position of the molecule was oriented toward position 5.46 of the 5-HT2A receptor. Within the human 5-HT2A receptor, position 5.46 is Ser242; however, in the rat 5-HT2A receptor, it is Ala242, suggesting that the potent functional activity in this species resulted from the absence of the steric bulk provided by the -OH moiety of the Ser in the human isoform. We confirmed this hypothesis using site-directed mutagenesis through the mutation of both the human receptor Ser242 to Ala and the rat receptor Ala242 to Ser, followed by radioligand binding and second messenger studies. In addition, we attempted to define the space allowed by the alanine by evaluating compounds with larger substitutions at the 9-position. The data indicate that position 5.46 contributed to the species difference in 5-HT2A receptor potency observed for a pyrazinoisoindolone compound, resulting in the observation of a significant cardiovascular safety signal.

Characterization of a novel and selective CB1 antagonist as a radioligand for receptor occupancy studies

Obesity remains a significant public health issue leading to Type II diabetes and cardiovascular disease. CB1 antagonists have been shown to suppress appetite and reduce body weight in animal models as well as in humans. Evaluation of pre-clinical CB1 antagonists to establish relationships between in vitro affinity and in vivo efficacy parameters are enhanced by ex vivo receptor occupancy data. Synthesis and biological evaluation of a novel and highly selective radiolabeled CB1 antagonist is described. The radioligand was used to conduct ex vivo receptor occupancy studies.

Synthesis and SAR of potent and selective tetrahydropyrazinoisoquinolinone 5-HT 2C receptor agonists

The 5-HT2C receptor has been implicated as a critical regulator of appetite. Small molecule activation of the 5-HT2C receptor has been shown to affect food intake and regulate body weight gain in rodent models and more recently in human clinical trials. Therefore, 5-HT2C is a well validated target for anti-obesity therapy. The synthesis and structure-activity relationships of a series of novel tetrahydropyrazinoisoquinolinone 5-HT2C receptor agonists are presented. Several members of this series were identified as potent 5-HT2C receptor agonists with high functional selectivity against the 5-HT2A and 5-HT2B receptors and reduced food intake in an acute rat feeding model upon oral dosing.