Understanding the clinical pharmacokinetics of a GABA_Apartial agonist by application ofin vitrotools

Abstract

1. 4-Oxo-4,5,6,7-tetrahydro-1H-indole-3-carboxylic acid (4-methylaminomethyl-phenyl)-amide (1), developed for general anxiety disorder, was discontinued from clinical development due to unsuitable oral pharmacokinetics. 2. In humans, (1) demonstrated an unacceptable high apparent oral clearance (Cl(p)/F) that also demonstrated a supraproportional dose-exposure relationship. Secondary peaks in the plasma concentration-time profile suggested possible enterohepatic recirculation of (1). A combination of in vitro mechanistic tools was applied to better understand the processes underlying these complex clinical pharmacokinetic profiles of (1). 3. In metabolism experiments, (1) was shown to be a substrate of monoamine oxidase A (MAO-A) as well as being metabolized by cytochrome P450. The former appeared to be a high K(M) process with a high capacity, while the latter showed saturation between 1 and 10 microM, consistent with the supraproportional dose-exposure relationship. 4. In a sandwich-cultured hepatocyte model, (1) was shown to be a substrate for both uptake and efflux into the canicular space, which is consistent with the observation of pharmacokinetics suggestive of enterohepatic recirculation. Finally, in human epithelial colon adenocarcinoma cell line (Caco-2) and Madin-Darby canine kidney cells transwell flux experiments, (1) was shown to have relatively low permeability and a basolateral-to-apical flux ratio consistent with the activity of P-glycoprotein. 5. In combination, a compounding of the contributions of MAO-A, hepatic uptake and efflux transporters, and P-glycoprotein to the disposition of (1) may underlie the low oral exposure, saturable clearance, and aberrant concentration versus time profiles observed for this compound in humans.

A Perspective on the Prediction of Drug Pharmacokinetics and Disposition in Drug Research and Development

“…Prediction of human clearance for compounds that are glucuronidated has been accomplished using alamethicintreated liver microsomes (Kilford et al, 2009). Examples of the use of in vitro approaches to predict human clearance for compounds metabolized by sulfotransferase, aldehyde oxidase, and monoamine oxidase have also been reported (Sawant et al, 2010;Zientek et al, 2010;Cubitt et al, 2011;Akabane et al, 2012). These new approaches are now being applied to drug discovery, as the instance merits.…”

Double or multiple/secondary peaks in pharmacokinetics: considerations and challenges from a bio‐analytical perspective

“…In another separate report that described the development and application of a sensitive tandem mass spectrometric method for bupropion and hydroxybupropion, double or secondary peaks were observed to manifest for the major metabolite hydroxybupropion, although such peaks were not observed for bupropion, the parent compound (Parekha et al, 2011). The occurrence of such double or secondary peaks in plasma profiles are not a recent phenomenonit has been reported for a number of compounds both in preclinical and clinical studies (Chi et al, 2011;Guo et al, 2011;Xiao et al, 2010;Sawant et al, 2010;Hendrickson et al, 2010;Lehr et al, 2009;Sidharta et al, 2009;Metsugi et al, 2008;Fujita et al, 2008;Huang et al, 2007;Alousi et al, 2007;Okusanya et al, 2007;Ma et al, 2006;Piyapolrungroj et al, 2000;Ogiso et al, 2001;Wang et al, 1999;Plusquellec et al, 1998;Lipka et al, 1995). The intention of this communication is to provide some considerations and perspectives on the double or multiple/secondary peak phenomenon with applicable bioanalytical strategy.…”