Characterization of a ligand binding site in the human transient receptor potential ankyrin 1 pore.

The pharmacology and regulation of Transient Receptor Potential Ankyrin 1 (TRPA1) ion channel activity is intricate due to the physiological function as an integrator of multiple chemical, mechanical, and temperature stimuli as well as differences in species pharmacology. In this study, we describe and compare the current inhibition efficacy of human TRPA1 on three different TRPA1 antagonists. We used a homology model of TRPA1 based on Kv1.2 to select pore vestibule residues available for interaction with ligands entering the vestibule. Site-directed mutation constructs were expressed in Xenopus oocytes and their functionality and pharmacology assessed to support and improve our homology model. Based on the functional pharmacology results we propose an antagonist-binding site in the vestibule of the TRPA1 ion channel. We use the results to describe the proposed intravestibular ligand-binding site in TRPA1 in detail. Based on the single site substitutions, we designed a human TRPA1 receptor by substituting several residues in the vestibule and adjacent regions from the rat receptor to address and explain observed species pharmacology differences. In parallel, the lack of effect on HC-030031 inhibition by the vestibule substitutions suggests that this molecule interacts with TRPA1 via a binding site not situated in the vestibule.

In vitro pharmacological characterization of a novel TRPA1 antagonist and proof of mechanism in a human dental pulp model.

AZ465 is a novel selective transient receptor potential cation channel, member A1 (TRPA1) antagonist identified during a focused drug discovery effort. In vitro, AZ465 fully inhibits activation by zinc, O-chlorobenzylidene malononitrile (CS), or cinnamaldehyde of the human TRPA1 channel heterologously expressed in human embryonic kidney cells. Our data using patch-clamp recordings and mouse/human TRPA1 chimeras suggest that AZ465 binds reversibly in the pore region of the human TRPA1 channel. Finally, in an ex vivo model measuring TRPA1 agonist-stimulated release of neuropeptides from human dental pulp biopsies, AZD465 was able to block 50%-60% of CS-induced calcitonin gene-related peptide release, confirming that AZ465 inhibits the native human TRPA1 channel in neuronal tissue.

N-1-Alkyl-2-oxo-2-aryl amides as novel antagonists of the TRPA1 receptor.

A series of potent antagonists of the ion channel transient receptor potential A1 (TRPA1) was developed by modifying lead structure 16 that was discovered by high-throughput screening. Based on lead compound 16, a SAR was established, showing a narrow region at the nitro-aromatic R(1) moiety and at the warhead, while the R(2) side had a much wider scope including ureas and carbamates. Compound 16 inhibits Ca(2+)-activated TRPA1 currents reversibly in whole cell patch clamp experiments, indicating that under in vivo conditions, it does not react covalently, despite its potentially electrophilic ketone.

ProSAR: a new methodology for combinatorial library design.

A method is introduced for performing reagent selection for chemical library design based on topological (2D) pharmacophore fingerprints. Optimal reagent selection is achieved by optimizing the Shannon entropy of the 2D pharmacophore distribution for the reagent set. The method, termed ProSAR, is therefore expected to enumerate compounds that could serve as a good starting point for deriving a structure activity relationship (SAR) in combinatorial library design. This methodology is exemplified by library design examples where the active compounds were already known. The results show that most of the pharmacophores on the substituents for the active compounds are covered by the designed library. This strategy is further expanded to include product property profiles for aqueous solubility, hERG risk assessment, etc. in the optimization process so that the reagent pharmacophore diversity and the product property profile are optimized simultaneously via a genetic algorithm. This strategy is applied to a two-dimensional library design example and compared with libraries designed by a diversity based strategy which minimizes the average ensemble Tanimoto similarity. Our results show that by using the PSAR methodology, libraries can be designed with simultaneously good pharmacophore coverage and product property profile.