Optimization of the previously reported 2-phenyl-4-quinolinecarboxamide NK-3 receptor antagonist 14, with regard to potential metabolic instability of the ester moiety and affinity and selectivity for the human neurokinin-3 (hNK-3) receptor, is described. The ester functionality could be successfully replaced by the ketone (31) or by lower alkyl groups (Et, 21, or n-Pr, 24). Investigation of the substitution pattern of the quinoline ring resulted in the identification of position 3 as a key position to enhance hNK-3 binding affinity and selectivity for the hNK-3 versus the hNK-2 receptor. All of the chemical groups introduced at this position, with the exception of halogens, increased the hNK-3 binding affinity, and compounds 53 (3-OH, SB 223412, hNK-3-CHO binding Ki = 1.4 nM) and 55 (3-NH2, hNK-3-CHO binding Ki = 1.2 nM) were the most potent compounds of this series. Selectivity studies versus the other neurokinin receptors (hNK-2-CHO and hNK-1-CHO) revealed that 53 is about 100-fold selective for the hNK-3 versus hNK-2 receptor, with no affinity for the hNK-1 at concentrations up to 100 microM. In vitro studies demonstrated that 53 is a potent functional antagonist of the hNK-3 receptor (reversal of senktide-induced contractions in rabbit isolated iris sphincter muscles and reversal of NKB-induced Ca2+ mobilization in CHO cells stably expressing the hNK-3 receptor), while in vivo this compound showed oral and intravenous activity in NK-3 receptor-driven models (senktide-induced behavioral responses in mice and senktide-induced miosis in rabbits). Overall, the biological data indicate that (S)-N-(1-phenylpropyl)-3-hydroxy-2-phenylquinoline-4-carboxamide (53, SB 223412) may serve as a pharmacological tool in animal models of disease to assess the functional and pathophysiological role of the NK-3 receptor and to establish therapeutic indications for non-peptide NK-3 receptor antagonists.

No abstract

No abstract

The homology modeling of GPCRs has benefitted vastly from the availability of some resolved structures, which allow the generation of many reliable GPCR models. However, the dynamic behavior of such receptors has been only minimally examined in silico, although several pieces of evidence have highlighted some conformational switches that can orchestrate the activation mechanism. Among such switches, Pro-containing helices play a key role in determining bending in TM helices and thereby the width of the TM bundle. The approach proposed herein involves the generation of a set of possible models (conformational chimeras) by exhaustively combining the two main conformations (straight and bent) that a Pro-containing helix can assume. This approach was validated by generating conformational chimeras for the Cys-LTR1 receptor, which is involved in contractile and inflammatory processes. The generated chimeras were then used for docking a small set of representative ligands. The results revealed the flexibility mechanisms of Cys-LTR1, showing how the docked agonists vary their stabilizing interactions, shifting from the open to closed state, and how the examined antagonists are able to block the receptor in an open and inactive conformation, thus behaving as inverse agonists. This study emphasizes the promising potential of chimera modeling, confirms the key role of proline residues in receptor activation, and suggests that docking results can be improved by considering the often-overlooked flexibility of receptors.

No abstract