Use of molecular modeling aided design to dial out hERG liability in adenosine A(2A) receptor antagonists.

Molecular modeling was performed on a triazolo quinazoline lead compound to help develop a series of adenosine A2A receptor antagonists with improved hERG profile. Superposition of the lead compound onto MK-499, a benchmark hERG inhibitor, combined with pKa calculations and measurement, identified terminal fluorobenzene to be responsible for hERG activity. Docking of the lead compound into an A2A crystal structure suggested that this group is located at a flexible, spacious, and solvent-exposed opening of the binding pocket, making it possible to tolerate various functional groups. Transformation analysis (MMP, matched molecular pair) of in-house available experimental data on hERG provided suggestions for modifications in order to mitigate this liability. This led to the synthesis of a series of compounds with significantly reduced hERG activity. The strategy used in the modeling work can be applied to other medicinal chemistry programs to help improve hERG profile.

3-Aryl-5-phenoxymethyl-1,3-oxazolidin-2-ones as positive allosteric modulators of mGluR2 for the treatment of schizophrenia: Hit-to-lead efforts.

Hit to lead optimization of (5R)-5-hexyl-3-phenyl-1,3-oxazolidin-2-one as a positive allosteric modulator of mGluR2 is described. Improvements in potency and metabolic stability were achieved through SAR on both ends of the oxazolidinone. An optimized lead compound was found to be brain penetrant and active in a rat ketamine-induced hyperlocomotion model for antipsychotic activity.

Dihydroxypyridopyrazine-1,6-dione HIV-1 integrase inhibitors.

A series of potent novel dihydroxypyridopyrazine-1,6-dione HIV-1 integrase inhibitors was identified. These compounds inhibited the strand transfer process of HIV-1 integrase and viral replication in cells. Compound 6 is active against replication of HIV with a CIC(95) of 0.31 microM and exhibits no shift in potency in the presence of 50% normal human serum. It displays a good pharmacokinetic profile when dosed in rats and no covalent binding with microsomal proteins in both in vitro and in vivo models.

Molecular determinants of KCNQ1 channel block by a benzodiazepine.

KCNQ1 channels underlie the slow delayed rectifier K+ current, mediate repolarization of cardiac action potentials, and are a potential therapeutic target for treatment of arrhythmia. (E)-(+)-N-[(3R)-2,3-dihydro-1-methyl-2-oxo-5-phenyl-1H-1,4-benzodiazepin-3-yl]-3-(2,4-dichlorophenyl)-2-propenamide [L-735821 (L-7)] is a potent blocker of KCNQ1 channels. Here we describe the structural determinants of KCNQ1 that are critical for high-affinity block by L-7 using site-directed mutagenesis to alter specific residues and voltage clamp to record channel currents in Xenopus laevis oocytes. Chimeric channels were constructed by combination of regions from L-7-sensitive KCNQ1 and L-7-insensitive KCNQ2 channel subunits. This approach localized the drug interaction site to the pore and S6 domains of KCNQ1. Substitution of single amino acids identified Thr-312 of the pore domain and Ile-337, Phe-339, Phe-340, and Ala-344 of the S6 domain as the most important molecular determinants of channel block. Some mutations also altered the inactivation properties of KCNQ1, but there was no correlation between extent of inactivation and sensitivity to block by L-7. Modeling was used to simulate the docking of L-7 to the KCNQ1 channel pore. The docking was consistent with our experimental data and predicts that L-7 blocks K+ conductance by physically precluding the occupancy of a K+ ion to a pore helix-coordinated site within the central hydrated cavity, a crucial step in ion permeation.

Molecular determinants of voltage-dependent human ether-a-go-go related gene (HERG) K+ channel block.

The structural determinants for the voltage-dependent block of ion channels are poorly understood. Here we investigate the voltage-dependent block of wild-type and mutant human ether-a-go-go related gene (HERG) K(+) channels by the antimalarial compound chloroquine. The block of wild-type HERG channels expressed in Xenopus oocytes was enhanced as the membrane potential was progressively depolarized. The IC(50) was 8.4 +/- 0.9 microm when assessed during 4-s voltage clamp pulses to 0 mV. Chloroquine also slowed the apparent rate of HERG deactivation, reflecting the inability of drug-bound channels to close. Mutation to alanine of aromatic residues (Tyr-652 or Phe-656) located in the S6 domain of HERG greatly reduced the potency of channel block by chloroquine (IC(50) > 1 mm at 0 mV). However, mutation of Tyr-652 also altered the voltage dependence of the block. In contrast to wild-type HERG, block of Y652A HERG channels was diminished by progressive membrane depolarization, and complete relief from block was observed at +40 mV. HERG channel block was voltage-independent when the hydroxyl group of Tyr-652 was removed by mutating the residue to Phe. Together these findings indicate a critical role for Tyr-652 in voltage-dependent block of HERG channels. Molecular modeling was used to define energy-minimized dockings of chloroquine to the central cavity of HERG. Our experimental findings and modeling suggest that chloroquine preferentially blocks open HERG channels by cation-pi and pi-stacking interactions with Tyr-652 and Phe-656 of multiple subunits.

Identification of metabotropic glutamate receptor antagonists using an automated high-throughput screening system.

Antagonists to the human metabotropic glutamate receptor subtype 5a(mGluR(5a)) have been implicated as potential therapeutics for the treatment of a variety of nervous system disorders, including pain, anxiety, and Parkinson's disease. To discover novel antagonists to the mGluR(5a), a functional assay measuring agonist-induced intracellular calcium release was developed. The assay was used for the high-throughput screening of a large collection of compounds in single wells using a fully automated robotic platform. Primary high-throughput screening hits were subjected to a combination of data analysis and counterscreening assays to identify several compounds with both efficacy and selectivity for the metabotropic glutamate receptor target.