Bitopertin R enantiomer (RG1678 R enantiomer; RO4917838 R enantiomer) is the R-enantiomer of Bitopertin. Bitopertin is a potent, noncompetitive glycine reuptake inhibitor, inhibits glycine uptake at human GlyT1 with a concentration exhibiting IC50 of 25 nM. IC50: 25 nM (GlyT1)[1]
Bitopertin (RG1678) competitively blocks [3H]ORG24598 binding sites at human GlyT1b in membranes from Chinese hamster ovary cells. Bitopertin potently inhibits [3H]glycine uptake in cells stably expressing hGlyT1b and mGlyT1b, with IC50 values of 25±2 nM and 22±5 nM, respectively (n=6). Conversely, Bitopertin has no effect on hGlyT2-mediated glycine uptake up to 30 μM concentration. Bitopertin has high affinity for the recombinant hGlyT1b transporter. Under equilibrium conditions (1 h at room temperature), Bitopertin displaces [3H]ORG24598 binding with a Ki of 8.1 nM. In hippocampal CA1 pyramidal cells, Bitopertin enhances NMDA-dependent long-term potentiation at 100 nM but not at 300 nM[1]. Additional profiling revealed that Bitopertin (RG1678) has an excellent selectivity profile against the GlyT2 isoform (IC50>30 μM) and toward a panel of 86 targets including transmembrane and soluble receptors, enzymes, ion channels, and monoamine transporters (<41% inhibition at 10 μM is measured for all targets)[2].
Bitopertin (RG1678) dose-dependently increases cerebrospinal fluid and striatal levels of glycine measured bymicrodialysis in rats. Additionally Bitopertin attenuates hyperlocomotion induced by the psychostimulant D-amphetamine or the NMDA receptor glycine site antagonist L-687,414 in mice. Bitopertin also prevents the hyper-response to D-amphetamine challenge in rats treated chronically with phencyclidine, an NMDA receptor open-channel blocker. Administration of vehicle has no effect on extracellular levels of striatal glycine, which remained constant throughout the experiment. In contrast, p.o. administration of Bitopertin (1-30 mg/kg) produced a dose-dependent increase in extracellular glycine levels. Bitopertin 30 mg/kg produces glycine levels 2.5 times higher than pretreatment levels. A similar dose-dependent increase in glycine concentration is observed in the CSF of rats treated p.o. with Bitopertin (1-10 mg/kg) compared with vehicle-treated animals, 3 h after drug administration. Interestingly, the level of CSF glycine increase 3 h after Bitopertin dosing is very similar to the increase in the microdialysis experiment at the same time point[1]. In vivo pharmacokinetic studies in rat and monkey reveals that Bitopertin (RG1678) has, in both species, a low plasma clearance, an intermediate volume of distribution, a good oral bioavailability (78% for rat, 56% for monkey), and a favorable terminal half-life (5.8 h for rat, 6.4 h for monkey). The plasma protein binding is high in the two preclinical species (97%) and in human (98%). The CNS penetration of Bitopertin in rat (brain/plasma=0.7) is better than that in mouse (brain/plasma=0.5)[2].
[1]. Alberati D, et al. Glycine reuptake inhibitor RG1678: A pharmacologic characterization of an investigational agent for the treatment of schizophrenia. Neuropharmacology. 2012 Feb;62(2):1152-61. [2]. Pinard E, et al. Selective GlyT1 Inhibitors: Discovery of [4-(3-Fluoro-5-trifluoromethylpyridin-2-yl)piperazin-1-yl][5-methanesulfonyl-2-((S)-2,2,2-trifluoro-1-methylethoxy)phenyl]methanone (RG1678), a Promising Novel Medicine To Treat Schizophrenia. J Me [3]. Alberati, Daniela; Moreau, Jean-Luc; Lengyel, Judith et al. Glycine reuptake inhibitor RG1678: A pharmacologic characterization of an investigational agent for the treatment of schizophrenia. Neuropharmacology (2012), 62(2), 1152-1161. [4]. Hofmann C, Banken L, Hahn M et al. Evaluation of the Effects of Bitopertin (RG1678) on Cardiac Repolarization: A Thorough Corrected QT Study in Healthy Male Volunteers. Clin Ther. 2012 Oct;34(10):2061-71. [5]. Martin-Facklam M, Pizzagalli F, Zhou Y et al. Glycine Transporter Type 1 Occupancy by Bitopertin: a Positron Emission Tomography Study in Healthy Volunteers. Neuropsychopharmacology. 2012 Nov 7. doi: 10.1038/npp.2012.212. [Epub ahead of print]