ABSTRACT
In this study, we show that compound 3 (osanetant) binds with a pseudoirreversible, apparent noncompetitive mode of antagonism at the guinea pig NK(3), while it behaves competitively at the human NK(3). This difference is caused by a slower dissociation rate of compound 3 at the guinea pig NK(3) compared to human NK(3). The only amino acid difference between the human and guinea pig NK(3) in the binding site (Thr139(2.58) in human, corresponding to Ala114(2.58) in guinea pig) has been shown to be responsible for the different behavior. Compound 1 (talnetant), however, behaves competitively at both receptors. Using these data, 3D homology modeling, and site-directed mutagenesis, a model has been developed to predict the mode of antagonism of NK(3) antagonists based on their binding mode. This model was successfully used to predict the mode of antagonism of compounds of another chemical series including piperidine-based structures at human and guinea pig NK(3).
Subject(s)
Cell Membrane , Piperidines/chemistry , Piperidines/pharmacology , Receptors, Neurokinin-3/antagonists & inhibitors , Receptors, Neurokinin-3/chemistry , Amino Acid Sequence , Animals , Cattle , Cell Line , Dogs , Guinea Pigs , Humans , Inositol Phosphates/metabolism , Isotope Labeling , Kinetics , Models, Molecular , Molecular Conformation , Molecular Sequence Data , Mutagenesis, Site-Directed , Mutation , Piperidines/metabolism , Protein Structure, Tertiary , Rats , Receptors, Neurokinin-3/genetics , Receptors, Neurokinin-3/metabolism , Reproducibility of Results , Tritium/chemistryABSTRACT
We reported earlier the refinement of our initial five-point pharmacophore model for the Histamine 3 receptor (H(3)R), with a new acceptor feature important for binding and selectivity against the other histamine receptor subtypes 1, 2 and 4. This approach was validated with a new series of H(3)R inverse agonists: the naphthalene series. In this Letter, we describe our efforts to overcome the phospholipidosis flag identified with our initial lead compound (1a). During the optimization process, we monitored the potency of our molecules toward the H(3) receptor, their selectivity against H(1)R, H(2)R and H(4)R, as well as some key molecular properties that may influence phospholipidosis. Encouraged by the promising profile of the naphthalene series, we used our deeper understanding of the H(3)R pharmacophore model to lead us towards the quinoline series. This series is perceived to have intrinsic advantages with respect to its amphiphilic vector.