Csj. Walpole et al., COMPARATIVE, GENERAL PHARMACOLOGY OF SDZ NKT 343, A NOVEL, SELECTIVE NK1 RECEPTOR ANTAGONIST, British Journal of Pharmacology, 124(1), 1998, pp. 83-92
1 The in vitro and in vivo pharmacology of SDZ NKT 343 l-(S)-3-(2-naph
thyl)alanyl-N-benzyl-N-methylamide) a novel tachykinin NK1 receptor an
tagonist was investigated. 2 SDZ NKT 343 inhibited [H-3]-substance P b
inding to the human NK1 receptor in transfected Cos-7 cell membranes (
IC50 = 0.62 +/- 0.11 nM). In comparison, in the same assay K-i values
for FK888, CP 99,994, SR 140,333 and RPR 100,893 were 2.13 +/- 0.04 nM
, 0.96 +/- 0.20 nM, 0.15 +/- 0.06 nM and 1.77 +/- 0.41 nM, respectivel
y. SBZ NKT 343 showed a markedly lower affinity at rat NK1 receptors i
n whole forebrain membranes (IC50 = 451 +/- 139 nM). 3 SDZ NKT 343 cau
sed an increase in EC50 as well as reduction in the number of binding
sites (B-max) determined for [H-3]-substance P, suggesting a non-compe
titive interaction at the human NK1 receptor. SDZ NKT 343 also caused
a reduction in the maximum elevation of [C2+](i) evoked by substance P
(SP) in human U373MG cells and depressed the maximum [Sar(9)]SP sulph
one-induced contraction of the guinea-pig isolated ileum. The antagoni
sm of SP effects on U373MG cells by SDZ NKT 343 was reversible. 4 SDZ
NKT 343 showed weak affinity to human NK2 and NK3 receptors in transfe
cted Cos-7 cells (K-i of 0.52 +/- 0.04 mu M and 3.4 +/- 1.2 mu M, resp
ectively). SDZ NKT 343 was inactive in a broad array of binding assays
including the bradykinin B-2 receptor the histamine H-1 receptor, opi
ate receptors and adrenoceptors. SDZ NKT 343 only weakly inhibited the
voltage-activated Ca2+ and Na+ currents in guinea-pig dorsal root gan
glion neurones. The enantiomer of SDZ NKT 343, (R,R)-SDZ NKT 343 was a
bout 1000 times less active at human NK1 receptors expressed in Cos-7
cell membranes. 5 Contractions of the guinea-pig ileum by [Sar(9)]SP s
ulphone were inhibited by SDZ NKT 343 in a concentration-dependent man
ner, with an IC50 = 1.60 +/- 0.94 nM, while the enantiomer (R,R)-SDZ N
KT 343 was 100 times less active (IC50 = 162 +/- 26 nM). In comparison
, in the same assay IC50 values for other NK1 receptor antagonists CP
99,994, SR 140,333, RPR 100,893 and FK 858 were 2.90 +/- 07 nM, 0.14 /- 0.02 nM, 11.4 +/- 2.9 nM and 2.4 +/- 0.83 nM, respectively. 6 In an
aesthetized guinea-pigs i.v. administered SDZ NKT 343 antagonized [Sar
(9)]SP sulphone-evoked bronchoconstriction (70% reduction at 0.4 mg kg
(-1), i.v.). Basal airway resistance, mean arterial blood pressure and
heart rate were not affected. 7 In conclusion, SDZ NKT 343 is a highl
y selective NK1 receptor antagonist with high potency at the human and
guinea-pig receptors. SDZ NKT 343 may be used as a potential novel th
erapeutic agent inhuman diseases where NK1 receptor hyperfunction is i
nvolved.