Cariprazine (RGH-188), a potent D3/D2 dopamine receptor partial agonist, binds to dopamine D3 receptors in vivo and shows antipsychotic-like and procognitive effects in rodents
Graphical abstract
Highlights
► Cariprazine, a D3/D2 partial agonist potently bound rat D3 and D2 receptors in vivo. ► Cariprazine had high potency and efficacy in preclinical antipsychotic screening tests. ► Cariprazine lacked cataleptogenic activity in rats. ► Cariprazine showed procognitive effects in scopolamine-impaired rats.
Introduction
During the 50-year history of antipsychotic medications, the dopamine (DA) D2 receptor has been the crucial and indispensable main target of drug action. Typical antipsychotics, the so-called neuroleptics, dominated the first 25 years of antipsychotic treatment but were succeeded by atypical antipsychotics. These agents retain D2 receptor antagonism as the basic mode of action but have better side effect profiles and somewhat better efficacy on negative symptoms. Whether the superior side-effect profile of atypical antipsychotic agents is due to their serotonin 5-HT2A receptor antagonist activity (Meltzer et al., 2003) or to their higher dissociation rate constant (koff) at the D2 receptor (Kapur and Seeman, 2001) is still a matter of debate.
A recently developed atypical antipsychotic agent, aripiprazole, while preserving the predominant D2 action, introduced a new pharmacological approach: D2 receptor partial agonism (Lawler et al., 1999). A compound with an appropriate degree of partial agonism can both inhibit overstimulated DA receptors to function as an antagonist, and stimulate these same receptors when the endogenous dopaminergic tone is low. This balancing feature presumably results in effective blockade of overstimulated D2 receptors and improvement in psychotic symptoms in schizophrenic patients. Concurrently, it potentially prevents the induction of extrapyramidal symptoms (EPS) or secondary negative symptoms by avoiding complete silencing of dopaminergic transmission (DeLeon et al., 2004). Interestingly, aripiprazole also has considerable binding affinity to the D3 receptor (Lawler et al., 1999) with variable and assay-dependent intrinsic activity (Bruins Slot et al., 2007).
Originally, the high density of the D3 receptor in areas of the ventral striatum gave rise to the expectation that selective D3 antagonists would exert antipsychotic activity without causing motor side effects related to the dorsal striatum (Schwartz et al., 2000). Although highly selective D3 receptor antagonists such as SB-277011 and S33084 were found to be devoid of cataleptogenic actions, they demonstrated poor efficacy in animal models of schizophrenia (Millan et al., 2000, Reavill et al., 2000). However, preclinical studies of D3 receptor antagonists did demonstrate pharmacological properties that are potentially advantageous in the treatment of schizophrenia.
D3 receptor antagonists demonstrated increased locomotor activity in rodents habituated to their environment (Gyertyan and Saghy, 2004, Millan et al., 2004), procognitive effects in experimental learning paradigms (Laszy et al., 2005, Millan et al., 2007), and inhibited haloperidol-induced catalepsy (Gyertyan and Saghy, 2007, Millan et al., 1997). These findings suggested that D3 receptor antagonists may have some potential against negative symptoms and reduced EPS potential. We hypothesized that a mixed D3/D2 receptor antagonist with high affinity and preference for the D3 receptor that retained considerable D2 affinity could be an effective antipsychotic that would be free of EPS and have beneficial effects on cognition and negative symptoms.
Experimental confirmation of this hypothesis is demonstrated in putative antipsychotic compounds like S33138 (Millan et al., 2008a, Millan et al., 2008b) and RG-15 (Kiss et al., 2008). Both drugs showed, in addition to standard antipsychotic-like activity attributed to D2 receptor antagonism, cognitive enhancing effects (Gyertyan et al., 2008, Millan et al., 2008a), while RG-15 also displayed anticataleptogenic and motor activating effects (Gyertyan et al., 2008).
Our search for novel antipsychotics focused on the strategic goal of combining D2 receptor partial agonism and D3 receptor preference in one molecule. Our synthesis and screening efforts identified cariprazine (formerly RGH-188, Fig. 1), a compound with D3/D2 partial agonism and preference to the D3 receptor (Kiss et al., 2010). Based on theoretical considerations as well as experimental findings (Richtand et al., 2001, Schotte et al., 1992), the D3 receptor is assumed to be tonically occupied by endogenous DA. Therefore, cariprazine, as a D3 receptor partial agonist, presumably exerts antagonist-like actions in vivo by inhibiting the binding of the full agonist dopamine, and it behaves as a D2 receptor antagonist in the basal ganglia of schizophrenic patients where dopaminergic transmission is increased (Abi-Dargham et al., 2000). To elucidate the antipsychotic-like profile of cariprazine, the compound was evaluated in a series of animal behavioral models including antipsychotic, cognitive, and motor performance tests, and pharmacokinetic and in vivo D3 receptor binding assays.
Section snippets
Animals
Experimental rats and mice (strains and weights given with specific method) were housed in a thermostatically controlled room at 22 ± 2 °C and 50 ± 10% relative humidity on 12-h light/dark cycle (lights off from 18.00 to 6.00 h). The animals were kept in polycarbonate cages (Lignifer Ltd., Isaszeg, Hungary) in groups of 5 (rats) or 10 (mice); they received unlimited access to commercial pellet rat-mouse feed (ssniff R/M + H produced by Spezialdiäten GmbH, Soest, Germany), autoclaved at 105 °C, and tap
In vivo pharmacokinetics of cariprazine in rats
Following i.v. administration of cariprazine to rats, bi-exponential disposition was exhibited (Fig. 2). Systemic plasma clearance was moderate and the relatively high volume of distribution indicated extensive tissue distribution (Table 1). The apparent terminal half-life (t1/2) of cariprazine was approximately 2 h following i.v. or p.o. administration (Fig. 2, Table 1). Oral absorption of the drug was rapid, with Tmax values in the range of 0.5–1 h. The absolute oral bioavailability of
Discussion
Cariprazine is a novel antipsychotic candidate compound characterized by subnanomolar affinity for dopamine D3 receptors with about 10-fold selectivity over D2 receptors (Kiss et al., 2010). It showed partial agonist functional profiles at both receptors in cellular systems. In in vivo turnover and biosynthesis experiments, the compound demonstrated D2-related partial agonist properties. Cariprazine also displayed high affinity binding at human serotonin 5-HT2B receptors with pure antagonism.
Conflict of interest
All of the authors are employees of Gedeon Richter Plc., who provided financial support for this study. Employees of Gedeon Richter were responsible for study design and conduct, and for data collection, analysis, and interpretation; the decision to submit the paper for publication was made by Gedeon Richter employees.
Acknowledgements
We thank A. Bakos Scheff, K. Domján, T. Féth Janik, G. Adorjányi Perjés, Cs. Nagy, Zs. Szarka and A. Vasadi for their technical assistance. We are grateful to Dr. Nika Adham and Dr. Peter Werner of Forest Research Institute for the critical reading and comments on this manuscript, and to Carol Dyer and Dr. Adam Ruth of Prescott Medical Communications Group for editorial support. Special thanks to Dr. A. Wilson (PET Centre, Centre for Addiction and Mental Health, 250 College St. Toronto M5T 1R8)
References (59)
- et al.
The behavioral effects of MK-801 injected into nucleus accumbens and caudate-putamen of rats
Pharmacol. Biochem. Behav.
(1995) - et al.
Mouse behavioral endophenotypes for schizophrenia
Brain Res. Bull.
(2010) - et al.
Action of novel antipsychotics at human dopamine D3 receptors coupled to G protein and ERK1/2 activation
Neuropharmacology
(2007) Effects of mecamylamine, nicotine, atropine and physostigmine on the phencyclidine-induced behavioral toxicity
Pharmacol. Biochem. Behav.
(1984)- et al.
Aripiprazole: a comprehensive review of its pharmacology, clinical efficacy, and tolerability
Clin. Ther.
(2004) - et al.
The selective dopamine D3 receptor antagonists, SB 277011-A and S 33084 block haloperidol-induced catalepsy in rats
Eur. J. Pharmacol.
(2007) - et al.
Striatal and extrastriatal dopamine D2/D3 receptors in schizophrenia evaluated with [18 F]fallypride positron emission tomography
Biol. Psychiatry
(2010) - et al.
Effects of risperidone on phencyclidine-induced behaviors: comparison with haloperidol and ritanserin
Jpn. J. Pharmacol.
(1994) - et al.
Novel antipsychotic agents with 5-HT(1A) agonist properties: role of 5-HT(1A) receptor activation in attenuation of catalepsy induction in rats
Neuropharmacology
(2005) - et al.
Interactions of the novel antipsychotic aripiprazole (OPC-14597) with dopamine and serotonin receptor subtypes
Neuropsychopharmacology
(1999)
The dopamine D3 receptor mediates locomotor hyperactivity induced by NMDA receptor blockade
Neuropharmacology
Differential distribution of D3 dopamine receptors in the brains of several mammalian species
Brain Res.
Serotonin receptors: their key role in drugs to treat schizophrenia
Prog. Neuropsychopharmacol. Biol. Psychiatry
Enhanced cognitive performance of dopamine D3 receptor “knock-out” mice in the step-through passive-avoidance test: assessing the role of the endocannabinoid/endovanilloid systems
Pharmacol Res.
Effects of aripiprazole/OPC-14597 on motor activity, pharmacological models of psychosis, and brain activity in rats
Neuropharmacology
5-HT2 receptor antagonism reduces hyperactivity induced by amphetamine, cocaine, and MK-801 but not D1 agonist C-APB
Pharmacol. Biochem. Behav.
D3 dopamine receptor, behavioral sensitization, and psychosis
Neurosci. Biobehav. Rev.
Autoradiographic evidence for the occlusion of rat brain dopamine D3 receptors in vivo
Eur. J. Pharmacol.
Possible implications of the dopamine D(3) receptor in schizophrenia and in antipsychotic drug actions
Brain Res. Brain Res. Rev.
Risperidone attenuates MK-801-induced hyperlocomotion in mice via the blockade of serotonin 5-HT 2A/2C receptors
Eur. J. Pharmacol.
Dopamine D(2) receptor occupancy is a common mechanism underlying animal models of antipsychotics and their clinical effects
Neuropsychopharmacology
Aripiprazole and its human metabolite are partial agonists at the human dopamine D2 receptor, but the rodent metabolite displays antagonist properties
Eur. J. Pharmacol.
Increased baseline occupancy of D2 receptors by dopamine in schizophrenia
Proc. Natl. Acad. Sci. USA
A targeted mutation of the D3 dopamine receptor gene is associated with hyperactivity in mice
Proc. Natl. Acad. Sci. USA
Antipsychotic-like vs cataleptogenic actions in mice of novel antipsychotics having D2 antagonist and 5-HT1A agonist properties
Neuropsychopharmacology
Cholinesterase inhibitors ameliorate behavioral deficits induced by MK-801 in mice
Neuropsychopharmacology
Current state of agonist radioligands for imaging of brain dopamine D2/D3 receptors in vivo with positron emission tomography
Curr. Top Med. Chem.
Cited by (121)
Volumetric absorptive microsampling for the therapeutic drug monitoring of psychiatric patients treated with cariprazine
2023, Journal of Pharmaceutical and Biomedical AnalysisUse of cariprazine in bipolar disorder: A systematic review and practical considerations
2022, Psiquiatria Biologica