Characterization of the binding of a potent, selective, radioiodinated antagonist to the human neurokinin-1 receptor.
We have synthesized a potent, selective, radioiodinated antagonist of the human neurokinin-1 (NK1) receptor and have characterized its binding to the cloned receptor expressed in Chinese hamster ovary cells. (cis)-2-(Diphenylmethyl)-N-[(2-iodophenyl)-methyl]-1- azabicyclo[2.2.2]octan-3-amine (L-703606) inhibits binding of 125I-Tyr8-substance P to the human NK1 receptor with an IC50 of 2 nM. This compound is a competitive antagonist of substance P-induced inositol phosphate generation, with a Kb of 29 nM. [125I]L-703606 binds to a single class of high affinity binding sites in human NK1/Chinese hamster ovary cell membranes (Kd = 0.3 nM). Substance P inhibits the binding of [125I]L-703606 to 65% of the NK1 receptor sites with a Kd of 0.04 +/- 0.03 nM and to the remaining 35% of the sites with a Kd of 1.5 +/- 0.7 nM. Addition of the nonhydrolyzable GTP analog guanylyl-5'-(beta, gamma-imido)diphosphate [Gpp(NH)p] shifts greater than 90% of the binding sites to the lower affinity state. In addition, Gpp(NH)p markedly alters the dissociation of substance P from the NK1 receptor by increasing the number of sites in the low affinity, rapidly dissociating state. However, Gpp(NH)p does not affect the rate of dissociation of [125I]L-703606. These data suggest that the pharmacological properties of [125I]L-703606 binding to the human NK1 receptor are similar to those of antagonists of nonpeptide guanine nucleotide-binding protein-coupled receptors and that this ligand will be useful for the biochemical and pharmacological characterization of the human NK1 receptor.
Cascieri
M A
MA
Merck Research Laboratories, Rahway, New Jersey 07065.
Ber
E
E
Fong
T M
TM
Sadowski
S
S
Bansal
A
A
Swain
C
C
Seward
E
E
Frances
B
B
Burns
D
D
Strader
C D
CD
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D016466:CHO Cells / Q000502:physiology; D006224:Cricetinae; D019204:GTP-Binding Proteins / Q000378:metabolism; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D006801:Humans; D007457:Iodine Radioisotopes; D007700:Kinetics; D008969:Molecular Sequence Data; D011812:Quinuclidines / Q000138:chemical synthesis / Q000378:metabolism* / Q000494:pharmacology; D017981:Receptors, Neurotransmitter / Q000037:antagonists & inhibitors* / Q000378:metabolism; D018039:Receptors, Tachykinin; D013373:Substance P / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology
D007457:Iodine Radioisotopes; D011812:Quinuclidines; D017981:Receptors, Neurotransmitter; D018039:Receptors, Tachykinin; C076851:L 703606; D013373:Substance P; D006165:Guanylyl Imidodiphosphate; C055640:substance P, Tyr(8)-; D019204:GTP-Binding Proteins