The synthesis and structure-activity relationship of a novel series of compounds with combined effects on 5-HT(3A) and 5-HT(1A) receptors and on the serotonin (5-HT) transporter (SERT) are described. Compound 5m (Lu AA21004) was the lead compound, displaying high affinity for recombinant human 5-HT(1A) (K(i) = 15 nM), 5-HT(1B) (K(i) = 33 nM), 5-HT(3A) (K(i) = 3.7 nM), 5-HT(7) (K(i) = 19 nM), and noradrenergic β(1) (K(i) = 46 nM) receptors, and SERT (K(i) = 1.6 nM). Compound 5m displayed antagonistic properties at 5-HT(3A) and 5-HT(7) receptors, partial agonist properties at 5-HT(1B) receptors, agonistic properties at 5-HT(1A) receptors, and potent inhibition of SERT. In conscious rats, 5m significantly increased extracellular 5-HT levels in the brain after acute and 3 days of treatment. Following the 3-day treatment (5 or 10 (mg/kg)/day) SERT occupancies were only 43% and 57%, respectively. These characteristics indicate that 5m is a novel multimodal serotonergic compound, and 5m is currently in clinical development for major depressive disorder.

Drug-induced liver injury (DILI) is a patient-specific, temporal, multifactorial pathophysiological process that cannot yet be recapitulated in a single in vitro model. Current pre-clinical testing regimes for the detection of human DILI thus remain inadequate. A systematic and concerted research effort is required to address the deficiencies in current models and to present a defined approach towards the development of new or adapted model systems for DILI prediction. This Perspective defines the current status of available models and mechanistic understanding of DILI, and proposes our vision of a roadmap for the development of predictive preclinical models of human DILI.

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ABSTRACT:We identify here for the first time the low-affinity cytochrome P450 (P450) isoforms that metabolize paroxetine, using cDNA-expressed human P450s measuring substrate depletion and paroxetine-catechol (product) formation by liquid chromatography-tandem mass spectrometry. CYP1A2, CYP2C19, CYP2D6, CYP3A4, and CYP3A5 were identified as paroxetine-catechol-forming P450 isoforms, and CYP2C19 and CYP2D6 were identified as metabolizing P450 isoforms by substrate depletion. Michaelis-Menten constants K m and V max were determined by product formation and substrate depletion. Using selective inhibitory studies and a relative activity factor approach for pooled and single-donor human liver microsomes, we confirmed involvement of the identified P450 isoforms for paroxetine-catechol formation at 1 and 20 M paroxetine. In addition, we used the population-based simulator Simcyp to estimate the importance of the identified paroxetine-metabolizing P450 isoforms for human metabolism, taking mechanismbased inhibition into account. The amount of active hepatic CYP2D6 and CYP3A4 (not inactivated by mechanism-based inhibition) was also estimated by Simcyp. For extensive and poor metabolizers of CYP2D6, Simcyp-estimated pharmacokinetic profiles were in good agreement with those reported in published in vivo studies. Considering the kinetic parameters, inhibition results, relative activity factor calculations, and Simcyp simulations, CYP2D6 (high affinity) and CYP3A4 (low affinity) are most likely to be the major contributors to paroxetine metabolism in humans. For some individuals CYP1A2 could be of importance for paroxetine metabolism, whereas the importance of CYP2C19 and CYP3A5 is probably limited.Paroxetine is a selective serotonin reuptake inhibitor used for the treatment of depression, generalized anxiety disorder, obsessive-compulsive disorder, panic disorder, post-traumatic stress disorder, and social anxiety disorder. It is extensively metabolized in humans and exhibits nonlinear kinetics Kaye et al., 1989).After administration of a single dose of paroxetine, poor metabolizers (PMs) and extensive metabolizers (EMs) of CYP2D6 display a 7-fold difference in the median total clearance. Under steady-state (SS) conditions, this difference falls dramatically to 2-fold. Nonlinear paroxetine kinetics is more prominent in EMs of CYP2D6 than in PMs of CYP2D6 (Sindrup et al., 1992a,b). Figure 1 shows the major reported P450 metabolic pathways. CYP2D6 catalyzes demethylation of the methylenedioxy group, presumably yielding paroxetine-catechol and formate (Bloomer et al., 1992). The paroxetine-catechol metabolite is described as an unstable intermediate (Kaye et al., 1989). Catechol-O-methyltransferase enzymes methylate paroxetine-catechol (Maurer et al., 2000), yielding metabolites I and II. In humans, metabolites I and II are found as the conjugated glucuronide or sulfate conjugates in urine, with metabolite I as the main metabolite . CYP2D6 has been identified as a high-affinity paroxetine-metabolizing enzyme, and because PMs...

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