Identification of Novel Adenosine A_2A Receptor Antagonists by Virtual Screening

Virtual screening was performed against experimentally enabled homology models of the adenosine A_2A receptor, identifying a diverse range of ligand efficient antagonists (hit rate 9%). By use of ligand docking and Biophysical Mapping (BPM), hits <b>1</b> and <b>5</b> were optimized to potent and selective lead molecules (<b>11</b>–<b>13</b> from <b>5</b>, p<i>K</i>_I = 7.5–8.5, 13- to >100-fold selective versus adenosine A₁; <b>14</b>–<b>16</b> from <b>1</b>, p<i>K</i>_I = 7.9–9.0, 19- to 59-fold selective)

Controlling the Dissociation of Ligands from the Adenosine A_2A Receptor through Modulation of Salt Bridge Strength

The association and dissociation kinetics of ligands binding to proteins vary considerably, but the mechanisms behind this variability are poorly understood, limiting their utilization for drug discovery. This is particularly so for G protein-coupled receptors (GPCRs) where high resolution structural information is only beginning to emerge. Engineering the human A_2A adenosine receptor has allowed structures to be solved in complex with the reference compound ZM241385 and four related ligands at high resolution. Differences between the structures are limited, with the most pronounced being the interaction of each ligand with a salt bridge on the extracellular side of the receptor. Mutagenesis experiments confirm the role of this salt bridge in controlling the dissociation kinetics of the ligands from the receptor, while molecular dynamics simulations demonstrate the ability of ligands to modulate salt bridge stability. These results shed light on a structural determinant of ligand dissociation kinetics and identify a means by which this property may be optimized

Biophysical Fragment Screening of the β₁‑Adrenergic Receptor: Identification of High Affinity Arylpiperazine Leads Using Structure-Based Drug Design

Biophysical fragment screening of a thermostabilized β₁-adrenergic receptor (β₁AR) using surface plasmon resonance (SPR) enabled the identification of moderate affinity, high ligand efficiency (LE) arylpiperazine hits <b>7</b> and <b>8</b>. Subsequent hit to lead follow-up confirmed the activity of the chemotype, and a structure-based design approach using protein–ligand crystal structures of the β₁AR resulted in the identification of several fragments that bound with higher affinity, including indole <b>19</b> and quinoline <b>20</b>. In the first example of GPCR crystallography with ligands derived from fragment screening, structures of the stabilized β₁AR complexed with <b>19</b> and <b>20</b> were determined at resolutions of 2.8 and 2.7 Å, respectively

Structure-Based Optimization Strategies for G Protein-Coupled Receptor (GPCR) Allosteric Modulators: A Case Study from Analyses of New Metabotropic Glutamate Receptor 5 (mGlu₅) X‑ray Structures

Two interesting new X-ray structures of negative allosteric modulator (NAM) ligands for the mGlu₅ receptor, M-MPEP (<b>3</b>) and fenobam (<b>4</b>), are reported. The new structures show how the binding of the ligands induces different receptor water channel conformations to previously published structures. The structure of fenobam, where a urea replaces the acetylenic linker in M-MPEP and mavoglurant, reveals a binding mode where the ligand is rotated by 180° compared to a previously proposed docking model. The need for multiple ligand structures for accurate GPCR structure-based drug design is demonstrated by the different growing vectors identified for the head groups of M-MPEP and mavoglurant and by the unexpected water-mediated receptor interactions of a new chemotype represented by fenobam. The implications of the new structures for ligand design are discussed, with extensive analysis of the energetics of the water networks of both pseudoapo and bound structures providing a new design strategy for allosteric modulators

Structure-Based Optimization Strategies for G Protein-Coupled Receptor (GPCR) Allosteric Modulators: A Case Study from Analyses of New Metabotropic Glutamate Receptor 5 (mGlu₅) X‑ray Structures

Two interesting new X-ray structures of negative allosteric modulator (NAM) ligands for the mGlu₅ receptor, M-MPEP (<b>3</b>) and fenobam (<b>4</b>), are reported. The new structures show how the binding of the ligands induces different receptor water channel conformations to previously published structures. The structure of fenobam, where a urea replaces the acetylenic linker in M-MPEP and mavoglurant, reveals a binding mode where the ligand is rotated by 180° compared to a previously proposed docking model. The need for multiple ligand structures for accurate GPCR structure-based drug design is demonstrated by the different growing vectors identified for the head groups of M-MPEP and mavoglurant and by the unexpected water-mediated receptor interactions of a new chemotype represented by fenobam. The implications of the new structures for ligand design are discussed, with extensive analysis of the energetics of the water networks of both pseudoapo and bound structures providing a new design strategy for allosteric modulators

Fragment and Structure-Based Drug Discovery for a Class C GPCR: Discovery of the mGlu₅ Negative Allosteric Modulator HTL14242 (3-Chloro-5-[6-(5-fluoropyridin-2-yl)pyrimidin-4-yl]benzonitrile)

Fragment screening of a thermostabilized mGlu₅ receptor using a high-concentration radioligand binding assay enabled the identification of moderate affinity, high ligand efficiency (LE) pyrimidine hit <b>5</b>. Subsequent optimization using structure-based drug discovery methods led to the selection of <b>25</b>, HTL14242, as an advanced lead compound for further development. Structures of the stabilized mGlu₅ receptor complexed with <b>25</b> and another molecule in the series, <b>14</b>, were determined at resolutions of 2.6 and 3.1 Å, respectively

Fragment and Structure-Based Drug Discovery for a Class C GPCR: Discovery of the mGlu₅ Negative Allosteric Modulator HTL14242 (3-Chloro-5-[6-(5-fluoropyridin-2-yl)pyrimidin-4-yl]benzonitrile)

Fragment screening of a thermostabilized mGlu₅ receptor using a high-concentration radioligand binding assay enabled the identification of moderate affinity, high ligand efficiency (LE) pyrimidine hit <b>5</b>. Subsequent optimization using structure-based drug discovery methods led to the selection of <b>25</b>, HTL14242, as an advanced lead compound for further development. Structures of the stabilized mGlu₅ receptor complexed with <b>25</b> and another molecule in the series, <b>14</b>, were determined at resolutions of 2.6 and 3.1 Å, respectively