In vitro activity: Cariprazine hydrochloride is a novel and potent antipsychotic drug candidate that is in late-stage clinical development for the treatment of schizophrenia, as well as for bipolar disorder (manic/mixed and depressive episodes), and as an adjunctive agent for the treatment of major depressive disorder. Cariprazine is a dopamine D3-preferring D3/D2 receptor partial agonist that exhibits high affinity for the D3 receptor with Ki of 0.085 nM and D2 receptor with Ki of 0.49 nM, and moderate affinity for the 5-HT1A receptor with Ki of 2.6 nM. Cariprazine stimulates inositol phosphate (IP) formation with a high potency (pEC50 8.5) with relatively low efficacy (Emax 30%). Cariprazine stimulates inositol phosphate (IP) formation with a high potency (pEC50 8.5) with relatively low efficacy (Emax 30%.Cariprazine, a novel candidate antipsychotic, demonstrated approximately 10-fold higher affinity for human D3 versus human D2L and human D2S receptors (pKi 10.07, 9.16, and 9.31, respectively). Cariprazine displays high affinity at human serotonin (5-HT) type 2B receptors (pKi 9.24) with pure antagonism. Cariprazine has lower affinity at human and rat hippocampal 5-HT1A receptors (pKi 8.59 and 8.34, respectively) and demonstrates low intrinsic efficacy. Cariprazine displays low affinity at human 5-HT2A receptors (pKi 7.73). Moderate or low affinity for histamine H1 and 5-HT2C receptors (pKi 7.63 and 6.87, respectively) suggest Cariprazine's reduced propensity for adverse events related to these receptors.Cariprazine is over sixfold more potent (EC50=1.4 nM) than Aripiprazole (EC50=9.2 nM) in inhibiting isoproterenol-induced cAMP production in HEK-293 cells

Kinase Assay: These assays are done in 50 mM Tris (pH 7.4), 100 mM NaCl, 7 mM MgCl2, 1 mM EDTA, and 1 mM DTT. Assay tubes (final volume 250 μL) contain 50 μM (striatum and hippocampus) or 1 μM (D2 and D3 cell membrane) GDP, the ligand to be examined, and membrane suspension (250 μg tissue/tube for the striatum and hippocampus and 20 μg protein/tube for hD2 and hD3 membranes). Samples are preincubated for 10 min at 30°C. After the addition of 50 pM [35S]GTPγS, membranes are incubated for an additional 60 min at 30°C. Nonspecific binding is determined in the presence of 10 μM GTPγS; basal binding is determined in the presence of buffer only. The assay is terminated by rapid filtration through UniFilter GF/B using a harvester, and the membranes washed four times with 1 mL of ice-cold buffer. After drying (40°C for 1 h), 40 μL of Microscint is added to the filters, and the bound radioactivity is determined by a TopCount NXT counter

Cell Assay: Cells are seeded on a 24-well tissue culture plate in 500 μL of medium. Fifty microliters of medium containing 0.55 μCi myo-[3H]inositol is added (final concentration 1 μCi/mL) and incubated for 18-20 h. Cells are then washed three times with buffer containing 140 mM NaCl, 5 mM KCl, 2 mM CaCl2, 5 mM HEPES, 5 mM Na-HEPES, 20 mM glucose, and 10 mM LiCl (pH 7.4). Cells are then incubated for an additional 60 min (37°C) in medium with test compounds alone (agonist test) or alongside 1000 nM (±)-Quinpirole (antagonist test). Medium is then aspirated off, cells are lysed by adding 400 μL of 0.1 M HCl/2 mM CaCl2, and supernatants are frozen at –72°C. After thawing and centrifugation at 1000g for 10 min, 200 μL of each supernatant is loaded on 250 μL of AG1-X8 (formate form) anion exchange column. Effluent is discarded, and columns are washed twice in 1.5 mL of distilled water. IPs are eluted with 2.5 mL of 1 M ammonium formate/0.1 M formic acid directly into scintillation vials, 10 mL of Optiphase HiSafe 3 is added, and the radioactivity is determined in a TriCarb 4900 scintillation counter.