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Dimethindene Occupancy of Central H1 Receptors: Applying Drug Receptor Occupancy to Dissociation Rate
Author(s) -
Malany Siobhan,
Hoare Sam,
Hernandez Lisa,
Smith William,
Crowe Paul
Publication year - 2007
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.21.6.a785-c
Subject(s) - radioligand , chemistry , ex vivo , kinetics , receptor , dissociation (chemistry) , binding potential , in vivo , receptor–ligand kinetics , antagonist , biophysics , pharmacology , biochemistry , in vitro , biology , physics , microbiology and biotechnology , quantum mechanics
We introduce a novel method to determine receptor occupancy of administered drug and calculate its dissociation rate (k off ) from the receptor. Furthermore, we derive a kinetic rate equation to simulate fractional occupancy of an antagonist based on its k off as determined by the method of kinetics of competitive radioligand binding in an effort to relate dissociation rate and receptor occupancy. To validate our model, we performed in vitro kinetics and ex vivo occupancy experiments in rat frontal cortex with varying concentrations of dimethindene, a sedating antihistamine. Tissue was removed 2hrs post oral administration. Amount of [ 3 H]‐Doxepin binding to homogenates from drug‐treated or vehicle‐treated rats was measured at multiple time points over 80 mins (25°C). Fractional receptor occupancy and dissociation rate of dimethindene to H 1 receptors was calculated by data fitted to proposed model. Results show 35, 60 and 70% occupancy of central H 1 receptors dosed at 10, 30 and 60 mg/kg, respectively with corresponding dimethindine brain levels of 10, 50, and 100 ng/g. Drug k off rate calculated by our ex vivo method is an equivalent measure of k off determined by kinetics of competitive radioligand binding (t 1/2 ~ 12 min). We further show a simulation of dimethindene fractional occupancy based on its kinetic parameters. This method can be used to assess, by simulation and experiment, occupancy for compounds based on dissociation rates and contributes to current efforts in drug optimization to profile antagonist efficacy in terms of its drug‐target binding parameters.