Biochemical characterization of desloratadine, a potent antagonist of the human histamine H(1) receptor.
We have characterized desloratadine (5H-benzo[5,6]cyclohepta[1,2-b]pyridine, 8-chloro-6,11-dihydro-11-(4-piperidinylidene), CAS 100643-71-8) as a potent antagonist of the human histamine H(1) receptor. [3H]Desloratadine bound to membranes expressing the recombinant human histamine H(1) receptor in Chinese hamster ovary cells (CHO-H(1)) in a specific and saturable manner with a K(d) of 1.1+/-0.2 nM, a B(max) of 7.9+/-2.0 pmol/mg protein, and an association rate constant of 0.011 nM(-1) x min(-1). The K(d) calculated from the kinetic measurements was 1.5 nM. Dissociation of [3H]desloratadine from the human histamine H(1) receptor was slow, with only 37% of the binding reversed at 6 h in the presence of 5 microM unlabeled desloratadine. Seventeen histamine H(1)-receptor antagonists were evaluated in competition-binding studies. Desloratadine had a K(i) of 0.9+/-0.1 nM in these competition studies. In CHO-H(1) cells, histamine stimulation resulted in a concentration-dependent increase in [Ca(2+)](i) with an EC(50) of 170+/-30 nM. After a 90-min preincubation with desloratadine, the histamine-stimulated increase in [Ca(2+)](i) was shifted to the right, with a depression of the maximal response at higher concentrations of antagonist. The apparent K(b) value was 0.2+/-0.14 nM with a slope of 1.6+/-0.1. The slow dissociation from the receptor and noncompetitive antagonism suggests that desloratadine may be a pseudoirreversible antagonist of the human histamine H(1) receptor. The mechanism of desloratadine antagonism of the human histamine H(1) receptor may help to explain the high potency and 24-h duration of action observed in clinical studies.
Anthes
John C
JC
Schering-Plough Research Institute, K15-1-1600, 2015 Galloping Hill Rd., Kenilworth, NJ 07033, USA. john.anthes@spcorp.com
Gilchrest
Helen
H
Richard
Christian
C
Eckel
Stephen
S
Hesk
Dave
D
West
Robert E
RE
Williams
Shirley M
SM
Greenfeder
Scott
S
Billah
Motasim
M
Kreutner
William
W
Egan
Robert E
RE
D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D016466:CHO Cells; D002118:Calcium / Q000378:metabolism; D003001:Cloning, Molecular; D006224:Cricetinae; D017931:DNA Primers / Q000494:pharmacology; D005260:Female; D006634:Histamine H1 Antagonists / Q000378:metabolism / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D017336:Loratadine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology*; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D011738:Pyrilamine / Q000378:metabolism; D011969:Receptors, Histamine H1 / Q000187:drug effects* / Q000378:metabolism
D017931:DNA Primers; D006634:Histamine H1 Antagonists; D016376:Oligonucleotides, Antisense; D011969:Receptors, Histamine H1; D017336:Loratadine; C121345:desloratadine; D011738:Pyrilamine; D002118:Calcium