Perhydrothiopyranopyrroles derivatives : A novel series of potent and selective nonpeptide NK1 antagonists

The design and synthesis of novel NK1/NK2 dual antagonists

Functional probing of the backbone of the Sanofi NK2 antagonist SR 48968 has resulted in the discovery of two new classes of NK1/NK2 dual antagonists: the diamine class and the oxime class. The addition of the amino or the oxime functional group results in the reversal of the stereochemical preference of the NK2 receptor.

Derivation of a three-dimensional pharmacophore model of substance P antagonists bound to the neurokinin-1 receptor

Constrained systematic search was used in an exhaustive conformational analysis of a structurally diverse set of substance P (SP) antagonists to identify a unique hypothesis for their bound conformation at the neurokinin-1 receptor. In this conformation, two aromatic groups essential for high affinity adopt a perpendicular or edge-on arrangement. This pharmacophore hypothesis for the receptor-bound conformation was used in a comparative molecular field analysis (CoMFA) of an expanded set of SP antagonists, and the predictive ability of the resulting three-dimensional quantitative structure-activity relationship (3D-QSAR) was evaluated against a test set of SP antagonists different from those in the training set. This CoMFA model based on the Constrained Search alignment yielded significant cross-validated, conventional, and predictive r2 values equal to 0.70, 0.93, and 0.82, respectively. For comparison, the SP antagonists were forced into an alternative poorer alignment in which the two aromatic rings were parallel and then subjected to a CoMFA analysis. Both the parallel and perpendicular arrangements of the aromatic rings are seen in X-ray structures of SP antagonists and have been proposed as candidates for the receptor-bound conformation. The parallel (or stacked) conformation yielded a poorer correlation with a cross-validated r2 = 0.57, a conventional r2 = 0.90, and a predictive r2 = 0.78. Our results indicate that although both alignments could generate a reasonable CoMFA correlation, the stacked conformation is unlikely to be the receptor-bound conformation, as the covalent structure of the antagonists precludes a common geometry in which the aromatic rings are stacked.

The nonpeptide NK-1 receptor antagonists LY303870 and LY306740 block the responses of spinal dorsal horn neurons to substance P and to peripheral noxious stimuli

The effects of novel substance P (NK-1) receptor antagonists LY303870 and LY306740, as well as LY306155, the enantiomer of LY303870, were tested on the responses of nociceptive spinal dorsal horn neurons to iontophoretically applied substance P and to peripheral noxious stimuli. The peripheral stimuli included noxious thermal and pinch stimuli applied to the cutaneous receptive field in the hind paw and stimulation of the superficial peroneal nerve with a train of high-intensity electrical stimuli. Extracellular recordings were obtained using multi-barrel electrodes from L4-L7 segments of the spinal cord in cats anaesthetized with alpha-chloralose and spinalized at the L1 level. The antagonists were given i.v. (0.5-4.0 mg/kg). Responses to substance P were inhibited by LY303870 and by LY306740 in a dose-related manner, but were not affected by LY306155. Responses to peripheral noxious thermal stimulation were inhibited in a dose-related manner by LY303870 and LY306740, and only at higher doses (2 mg/kg or more) by LY306155. Responses to pinch stimuli were inhibited by LY303870 and LY306740. LY306155 lacked consistent effects on pinch responses. LY303870 selectively inhibited the late component of the response to electrical stimulation of the superficial peroneal nerve. When these three drugs were tested against the responses of dorsal horn neurons to the excitatory amino acid, N-methyl-D-aspartate, the responses were unaffected. These data suggest that LY303870 and LY306740 pass from the circulation into the spinal cord where they antagonize dorsal horn neuronal responses to substance P and nociceptive inputs.

Cyclosporin A is a substance P (tachykinin NK1) receptor antagonist

The immunosuppressive cyclic undecapeptide, cyclosporin A, inhibited the binding of [125I]substance P to tachykinin NK1 receptors expressed by human IM-9 lymphoblastoid cells, U-373 MG human astrocytoma cells and guinea pig lung parenchyma with IC50 values of 425 +/- 58, 783 +/- 180, and 784 +/- 163 nM respectively. The dihydro derivative of cyclosporin A (dihydro-cyclosporin A) was an equally effective inhibitor, but the O-acetylated derivative (cyclosporin A-OAc) was 3-4 fold less potent. The cyclosporin compounds also inhibited [125I]neurokinin A binding to human NK2 receptors with potencies slightly less than at NK1 sites. In contrast, they were 8-20-fold less effective inhibitors of [125I]MePhe7-neurokinin B binding to guinea pig NK3 receptors (p < 0.001). Thus, the cyclosporin A compounds showed selectivity for NK1 and NK2 receptors. The structure-activity pattern for the effects of cyclosporin A compounds at tachykinin receptors differs from the pattern previously described for their immunosuppressive activity. All three compounds inhibited substance P induced interleukin-6 (IL-6) secretion from U-373 MG astrocytoma cells with potencies similar to their NK1 receptor binding affinities. In addition, cyclosporin A blocked substance P induced phosphatidylinositol (PI) turnover in U-373 MG cells without blocking the corresponding response to histamine. This novel pharmacological profile of the cyclosporin A compounds as NK1 receptor antagonists does not appear to correlate with other known in vitro cyclosporin A functions.