title: Use of LC/MS to assess brain tracer distribution in preclinical, in vivo receptor occupancy studies: dopamine D2, serotonin 2A and NK-1 receptors as examples.
abstract: High performance liquid chromatography combined with either single quad or triple quad mass spectral detectors (LC/MS) was used to measure the brain distribution of receptor occupancy tracers targeting dopamine D2, serotonin 5-HT2A and neurokinin NK-1 receptors using the ligands raclopride, MDL-100907 and GR205171, respectively. All three non-radiolabeled tracer molecules were easily detectable in discrete rat brain areas after intravenous doses of 3, 3 and 30 microg/kg, respectively. These levels showed a differential brain distribution caused by differences in receptor density, as demonstrated by the observation that pretreatment with compounds that occupy these receptors reduced this differential distribution in a dose-dependent manner. Intravenous, subcutaneous and oral dose-occupancy curves were generated for haloperidol at the dopamine D2 receptor as were oral curves for the antipsychotic drugs olanzapine and clozapine. In vivo dose-occupancy curves were also generated for orally administered clozapine, olanzapine and haloperidol at the cortical 5-HT2A binding site. In vivo occupancy at the striatal neurokinin NK-1 binding site by various doses of orally administered MK-869 was also measured. Our results demonstrate the utility of LC/MS to quantify tracer distribution in preclinical brain receptor occupancy studies.
authors.affiliation: Lilly Research Laboratories, Lilly Corporate Center, Indianapolis, Indiana 46285, USA.
authors.forename: Eyassu
authors.initials: E
authors.lastname: Chernet
authors.forename: Laura J
authors.initials: LJ
authors.lastname: Martin
authors.forename: Dominic
authors.initials: D
authors.lastname: Li
authors.forename: Anne B
authors.initials: AB
authors.lastname: Need
authors.forename: Vanessa N
authors.initials: VN
authors.lastname: Barth
authors.forename: Karen S
authors.initials: KS
authors.lastname: Rash
authors.forename: Lee A
authors.initials: LA
authors.lastname: Phebus
mesh_terms: D000818:Animals; D014150:Antipsychotic Agents / Q000494:pharmacology; D000077608:Aprepitant; D001569:Benzodiazepines / Q000494:pharmacology; D001921:Brain / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D003024:Clozapine / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000493:pharmacokinetics; D065127:Dopamine D2 Receptor Antagonists; D004305:Dose-Response Relationship, Drug; D004333:Drug Administration Routes; D004353:Drug Evaluation, Preclinical; D005464:Fluorobenzenes / Q000493:pharmacokinetics; D005849:Gerbillinae; D006220:Haloperidol / Q000494:pharmacology; D008297:Male; D013058:Mass Spectrometry / Q000379:methods*; D009025:Morpholines / Q000494:pharmacology; D064729:Neurokinin-1 Receptor Antagonists; D000077152:Olanzapine; D010880:Piperidines / Q000493:pharmacokinetics; D020891:Raclopride / Q000493:pharmacokinetics; D051381:Rats; D044402:Receptor, Serotonin, 5-HT2A / Q000378:metabolism*; D017448:Receptors, Dopamine D2 / Q000378:metabolism*; D018040:Receptors, Neurokinin-1 / Q000378:metabolism*; D058830:Serotonin 5-HT2 Receptor Antagonists; D012702:Serotonin Antagonists / Q000493:pharmacokinetics; D013777:Tetrazoles / Q000493:pharmacokinetics
chemical_list: D014150:Antipsychotic Agents; D018492:Dopamine Antagonists; D065127:Dopamine D2 Receptor Antagonists; D005464:Fluorobenzenes; D009025:Morpholines; D064729:Neurokinin-1 Receptor Antagonists; D010880:Piperidines; D044402:Receptor, Serotonin, 5-HT2A; D017448:Receptors, Dopamine D2; D018040:Receptors, Neurokinin-1; D058830:Serotonin 5-HT2 Receptor Antagonists; D012702:Serotonin Antagonists; D013777:Tetrazoles; D001569:Benzodiazepines; D000077608:Aprepitant; D020891:Raclopride; C079049:volinanserin; D003024:Clozapine; D006220:Haloperidol; C103207:vofopitant; D000077152:Olanzapine