The dissociation behaviours of aripiprazole and cariprazine at the human D₂and D₃receptor are evaluated. A potential correlation between kinetics andin vivoprofiles, especially cariprazine’s action on negative symptoms in schizophrenia, is investigated. The binding kinetics of four ligands were indirectly evaluated. After the receptor preparations were pre-incubated with the unlabelled ligands, the dissociation was initiated with an excess of [³H]spiperone. Slow dissociation kinetics characterizes aripiprazole and cariprazine at the D₂receptor. At the D₃receptor, aripiprazole exhibits a slow monophasic dissociation, while cariprazine displays a rapid biphasic behaviour. Functional ß-arrestin assays and molecular dynamics simulations at the D₃receptor confirm a biphasic binding behaviour of cariprazine. This may influence itsin vivoaction, as the partial agonist could react rapidly to variations in the dopamine levels of schizophrenic patients and the ligand will not quantitatively dissociate from the receptor in one single step. With these findings novel agents may be developed that display rapid, biphasic dissociation from the D₃R to further investigate this effect onin vivoprofiles.

Autism spectrum disorder (ASD) is a complex heterogeneous neurodevelopmental disorder characterized by social and communicative impairments, as well as repetitive and restricted behaviors (RRBs). With the limited effectiveness of current pharmacotherapies in treating repetitive behaviors, the present study determined the effects of acute systemic treatment of the novel multi-targeting ligand ST-2223, with incorporated histamine H₃ receptor (H₃R) and dopamine D₂/D₃ receptor affinity properties, on ASD-related RRBs in a male Black and Tan BRachyury (BTBR) mouse model of ASD. ST-2223 (2.5, 5, and 10 mg/kg, i.p.) significantly mitigated the increase in marble burying and self-grooming, and improved reduced spontaneous alternation in BTBR mice (all p < 0.05). Similarly, reference drugs memantine (MEM, 5 mg/kg, i.p.) and aripiprazole (ARP, 1 mg/kg, i.p.), reversed abnormally high levels of several RRBs in BTBR (p < 0.05). Moreover, ST-2223 palliated the disturbed anxiety levels observed in an open field test (all p < 0.05), but did not restore the hyperactivity parameters, whereas MEM failed to restore mouse anxiety and hyperactivity. In addition, ST-2223 (5 mg/kg, i.p.) mitigated oxidative stress status by decreasing the elevated levels of malondialdehyde (MDA), and increasing the levels of decreased glutathione (GSH), superoxide dismutase (SOD), and catalase (CAT) in different brain parts of treated BTBR mice (all p < 0.05). These preliminary in vivo findings demonstrate the ameliorative effects of ST-2223 on RRBs in a mouse model of ASD, suggesting its pharmacological prospective to rescue core ASD-related behaviors. Further confirmatory investigations on its effects on various brain neurotransmitters, e.g., dopamine and histamine, in different brain regions are still warranted to corroborate and expand these initial data.

A newly developed series of non-imidazole histamine H3 receptor (H3R) antagonists (1–16) was evaluated in vivo for anticonvulsant effects in three different seizure models in Wistar rats. Among the novel H3R antagonists examined, H3R antagonist 4 shortened the duration of tonic hind limb extension (THLE) in a dose-dependent fashion in the maximal electroshock (MES)-induced seizure and offered full protection against pentylenetetrazole (PTZ)-induced generalized tonic-clonic seizure (GTCS), following acute systemic administration (2.5, 5, 10, and 15 mg/kg, i.p.). However, only H3R antagonist 13, without appreciable protective effects in MES- and PTZ-induced seizure, fully protected animals in the strychnine (STR)-induced GTCS following acute systemic pretreatment (10 mg/kg, i.p.). Moreover, the protective effect observed with H3R antagonist 4 in MES-induced seizure was completely abolished when animals were co-administered with the H3R agonist (R)-α-methylhistamine (RAMH, 10 mg/kg, i.p.). However, RAMH failed to abolish the full protection provided by the H3R antagonist 4 in PTZ-induced seizure and H3R antagonist 13 in STR-induced seizure. Furthermore, in vitro antiproliferative effects or possible metabolic interactions could not be observed for compound 4. Additionally, the predictive in silico, as well as in vitro, metabolic stability for the most promising H3R antagonist 4 was assessed. The obtained results show prospective effects of non-imidazole H3R antagonists as innovative antiepileptic drugs (AEDs) for potential single use against epilepsy.

Dual target ligands are a promising concept for the treatment of Parkinson’s disease (PD). A combination of monoamine oxidase B (MAO B) inhibition with histamine H₃ receptor (H₃R) antagonism could have positive effects on dopamine regulation. Thus, a series of twenty-seven 4-tert-butylphenoxyalkoxyamines were designed as potential dual-target ligands for PD based on the structure of 1-(3-(4-tert-butylphenoxy)propyl)piperidine (DL76). Probed modifications included the introduction of different cyclic amines and elongation of the alkyl chain. Synthesized compounds were investigated for human H₃R (hH₃R) affinity and human MAO B (hMAO B) inhibitory activity. Most compounds showed good hH₃R affinities with K_i values below 400 nM, and some of them showed potent inhibitory activity for hMAO B with IC₅₀ values below 50 nM. However, the most balanced activity against both biological targets showed DL76 (hH₃R: K_i = 38 nM and hMAO B: IC₅₀ = 48 nM). Thus, DL76 was chosen for further studies, revealing the nontoxic nature of DL76 in HEK293 and neuroblastoma SH-SY5Ycells. However, no neuroprotective effect was observed for DL76 in hydrogen peroxide-treated neuroblastoma SH-SY5Y cells. Furthermore, in vivo studies showed antiparkinsonian activity of DL76 in haloperidol-induced catalepsy (Cross Leg Position Test) at a dose of 50 mg/kg body weight.

Dopamine is an important neurotransmitter in the human brain and its altered concentrations can lead to various neurological diseases. We studied the binding of novel compounds at the dopamine D₂ (D₂R) and D₃ (D₃R) receptor subtypes, which belong to the D₂‐like receptor family. The synthesis, in silico, and in vitro characterization of 10 dopamine receptor ligands were performed. Novel ligands were docked into the D₂R and D₃R crystal structures to examine the precise binding mode. A quantum mechanics/molecular mechanics study was performed to gain insights into the nature of the intermolecular interactions between the newly introduced pentafluorosulfanyl (SF₅) moiety and D₂R and D₃R. A radioligand displacement assay determined that all of the ligands showed moderate‐to‐low nanomolar affinities at D₂R and D₃R, with a slight preference for D₃R, which was confirmed in the in silico studies. N‐{4‐[4‐(2‐Methoxyphenyl)piperazin‐1‐yl]butyl}‐4‐(pentafluoro‐λ6‐sulfanyl)benzamide (7i) showed the highest D₃R affinity and selectivity (pK_i values of 7.14 [D₂R] and 8.42 [D₃R]).