PT  - JOURNAL ARTICLE
AU  - Elin Boger
AU  - Pär Ewing
AU  - Ulf G. Eriksson
AU  - Britt-Marie Fihn
AU  - Michael Chappell
AU  - Neil Evans
AU  - Markus Fridén
TI  - A Novel In Vivo Receptor Occupancy Methodology for the Glucocorticoid Receptor: Toward An Improved Understanding of Lung Pharmacokinetic/Pharmacodynamic Relationships
AID  - 10.1124/jpet.114.221226
DP  - 2015 May 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 279--287
VI  - 353
IP  - 2
4099  - http://jpet.aspetjournals.org/content/353/2/279.short
4100  - http://jpet.aspetjournals.org/content/353/2/279.full
SO  - J Pharmacol Exp Ther2015 May 01; 353
AB  - Investigation of pharmacokinetic/pharmacodynamic (PK/PD) relationships for inhaled drugs is challenging because of the limited possibilities of measuring tissue exposure and target engagement in the lung. The aim of this study was to develop a methodology for measuring receptor occupancy in vivo in the rat for the glucocorticoid receptor (GR) to allow more informative inhalation PK/PD studies. From AstraZeneca’s chemical library of GR binders, compound 1 [N-(2-amino-2-oxo-ethyl)-3-[5-[(1R,2S)-2-(2,2-difluoropropanoylamino)-1-(2,3-dihydro-1,4-benzodioxin-6-yl)propoxy]indazol-1-yl]-N-methyl-benzamide] was identified to have properties that are useful as a tracer for GR in vitro. When given at an appropriate dose (30 nmol/kg) to rats, compound 1 functioned as a tracer in the lung and spleen in vivo using liquid chromatography–tandem mass spectrometry bioanalysis. The methodology was successfully used to show the dose-receptor occupancy relationship measured at 1.5 hours after intravenous administration of fluticasone propionate (20, 150, and 750 nmol/kg) as well as to characterize the time profile for receptor occupancy after a dose of 90 nmol/kg i.v. The dose giving 50% occupancy was estimated as 47 nmol/kg. The methodology is novel in terms of measuring occupancy strictly in vivo and by using an unlabeled tracer. This feature confers key advantages, including occupancy estimation not being influenced by drug particle dissolution or binding/dissociation taking place postmortem. In addition, the tracer may be labeled for use in positron emission tomography imaging, thus enabling occupancy estimation in humans as a translatable biomarker of target engagement.