Gerd Bartoszyk

Low doses of sarizotan reduce dyskinesias and maintain antiparkinsonian efficacy of L-Dopa in parkinsonian monkeys

Dyskinesia is an important complication of treatment in Parkinsons disease (PD). Sarizotan, a 5-HT(1A) agonist with high affinity for D3 and D4 receptors was investigated on L-Dopa-induced dyskinesia (LID) in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) animal model of PD. Five MPTP female cynomolgus monkeys (Macaca fascicularis) with a moderate to severe parkinsonian syndrome and LID were used. Sarizotan 0.2, 1, and 2 mg/kg administered alone did not worsen parkinsonian symptoms; there were no effect on locomotor counts or on normal behavior of the monkeys. Sarizotan 0.2, 1, and 2 mg/kg administered 30 min before a fixed dose of L-Dopa (25-30 mg/kg s.c.) + benserazide (50 mg) did not affect the antiparkinsonian response to L-Dopa. However, mean dyskinetic scores were significantly reduced with sarizotan 1 and 2 mg/kg but not at 0.2 mg/kg. Higher doses of sarizotan (4 and 8 mg/kg, administered immediately before L-Dopa) reduced L-Dopa-induced locomotor response in all monkeys. A pharmacokinetic investigation in these monkeys showed a dose-dependent increase in mean plasma sarizotan concentrations with similar mean plasma concentrations for sarizotan 1 mg/kg alone or with L-Dopa, indicating a lack of sarizotan/L-Dopa interaction. The time course of plasma sarizotan concentrations was associated with time of maximal reduction of dyskinesias. When administered daily for two weeks in combination with L-Dopa in the same MPTP monkeys, sarizotan 1 mg/kg had a sustained antidyskinetic effect while maintaining the antiparkinsonian and locomotor effect of L-Dopa. This detailed sarizotan investigation in MPTP monkeys supports the antidyskinetic activity of this drug and for 5-HT(1A) agonists.

EMD 68843, a serotonin reuptake inhibitor with selective presynaptic 5-HT1A receptor agonistic properties

The 5-HT1A receptor agonist 8-hydroxy-(di-n-propylamino)tetralin (8-OH-DPAT; 0.55 mg/kg s.c.) and the 5-HT (5-hydroxytryptamine, serotonin) reuptake inhibitor/5-HT1A receptor ligand 5-[4-[4-(5-cyano-3-indolyl)-butyl]-1-piperazinyl]-benzofuran-2-carbox ami de (EMD 68843; 55 mg/kg p.o.) inhibited ultrasonic vocalization in rats, an effect which was antagonized by the 5-HT1A receptor antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]-ethyl]-N-(2-pyridyl)- cyclohexancarboxamide (WAY 100635; 1.0 mg/kg s.c.). 8-OH-DPAT decreased body temperature in rats, an effect which was also antagonized by WAY 100635, whereas EMD 68843 neither affected body temperature by itself nor interacted with 8-OH-DPAT or WAY 100635. The selective 5-HT reuptake inhibitor fluoxetine (100 mg/kg p.o.) had no effect on ultrasonic vocalization or body temperature. Therefore EMD 68843 is suggested to be a 5-HT1A receptor agonist selective for presynaptic 5-HT1A receptors.

Sarizotan, a serotonin 5-HT1A receptor agonist and dopamine receptor ligand. 1. Neurochemical profile.

Summary.Sarizotan exhibited high affinities only to serotonin 5-HT1A receptors and dopamine DA D4>D3>D2 receptors with the profile of a 5-HT1A agonist and DA antagonist demonstrated by the inhibition of cAMP-stimulation and guinea pig ileum contraction, decreased accumulation of the 5-HT precursor 5-hydroxytryptophan and increased levels of 5-HT metabolites, increased accumulation of DA precursor dihydroxyphenylalanine (DOPA) and the reduced levels of DA metabolites in intact rats. However, sarizotan at higher doses decreased DA precursor accumulation in reserpinized rats and induced contralateral rotational behavior in unilaterally substantia nigra lesioned rats, indicating some intrinsic dopaminergic activity; at D2 receptors sarizotan may act as a partial agonist, depending on the dopaminergic impulse flow. Sarizotan represents a new approach for the treatment of extrapyramidal motor complications such as l-DOPA-induced dyskinesia in Parkinson’s disease.

Anxiolytic effects of dopamine receptor ligands: I. involvement of dopamine autoreceptors

The anxiolytic-like properties of dopamine agonists and antagonists with different receptor profiles were investigated in the ultrasonic vocalization test in rats after subcutaneous administration. Only dopamine D2 receptor agonists inhibited ultrasonic vocalization with the following ED50 values: apomorphine (0.07 mg/kg), quinelorane (0.01 mg/kg), quinpirole (0.04 mg/kg), pramipexole (0.09 mg/kg), roxindole (0.04 mg/kg), talipexole (0.04 mg/kg), (+/-)-7-OH-DPAT (0.05 mg/kg), (+/-)-PPHT (0.03 mg/kg), (-)-TNPA (0.06 mg/kg), PD128907 (0.13 mg/kg). The D2 antagonists haloperidol, mazapertine, raclopride, remoxipride, L745870, U99194A, U101958 and S(-)-DS121, the partial agonists PD143188 and preclamol, the selective D1 agonist R(+)-SKF38393 and the D1 antagonist SCH23390, and the uptake inhibitors GBR12909, GBR12935 and indatraline lacked significant inhibitory effects on ultrasonic vocalization. Because at least some of the D2 receptor agonists investigated have selectivity for dopamine autoreceptors, it is speculated that the dopamine autoreceptor may be a target for the development of new antianxiety drugs.

Selective serotonin 5-HT2A receptor antagonist EMD 281014 improves delayed matching performance in young and aged rhesus monkeys

RationaleThe superior cognitive effects of atypical neuroleptics over typical agents reported in the schizophrenia literature are often attributed to the more prominent antagonist activity of the atypical drugs at serotonin 5HT2A receptors. However, atypical neuroleptics also have activity at many additional neurotransmitter receptors and few studies have specifically (and prospectively) tested the hypothesis that 5HT2A antagonism alone results in enhanced cognitive function.ObjectivesThe purpose of this study was to evaluate the selective 5-HT2A antagonist, 7-{4-[2-(4-fluoro-phenyl)-ethyl]-piperazine-1-carbonyl}-1H-indole-3-carbonitrile HCl (EMD 281014) in young and aged monkeys in a test designed to assess working memory function.MethodsFour oral doses (0.1, 1.0, 3.0, and 10.0 mg/kg) of EMD 281014 were evaluated in six young adult (mean age=9.2 years) and eight aged rhesus macaques (mean age=24.9 years) trained to perform a computer-assisted delayed matching-to-sample (DMTS) task.ResultsDepending on dose, EMD 281014 improved DMTS accuracy in young and aged monkeys primarily at either the medium or long retention intervals. While the latencies associated with incorrect color selections (choices latencies) tended to be longer than those associated with correct selections (particularly in the aged subjects) under baseline conditions, there were no significant effects of EMD 281014 on either sample or choice latencies in either age group. In addition, no adverse effects were observed across the range of doses evaluated in either cohort of animals.ConclusionThese experiments, conducted in a non-human primate model, suggest that selective 5HT2A antagonists such as EMD 281014 could offer therapeutic benefit to younger and older psychiatric patients by improving working memory function.

5-HT1A receptors are not involved in clozapine's lack of cataleptogenic potential

Clozapine and 8-OH-DPAT antagonized haloperidol-induced catalepsy in rats (ED50 10 and 0.1 mg/kg s.c., respectively). Whereas the selective 5-HT1A receptor antagonist WAY 100635 (0.1 mg/kg s.c.) completely antagonized the inhibitory effect of 8-OH-DPAT, clozapines effect was not affected. On the other hand, clozapine and 8-OH-DPAT inhibited ultrasonic vocalization in rats (ED50 0.7 and 0.03 mg/kg s.c., respectively), which effects were antagonized by WAY 100635. The lack of catalepsy of clozapine, therefore, cannot be addressed primarily to clozapines agonistic activity at 5-HT1A receptors.

The novel antidyskinetic drug sarizotan elicits different functional responses at human D2-like dopamine receptors.

Sarizotan (EMD 128130) is a chromane derivative that exhibits affinity at serotonin and dopamine receptors. Sarizotan effectively suppresses levodopa-induced dyskinesia in primate and rodent models of Parkinsons disease, and tardive dyskinesia in a rodent model. Results from clinical trials suggest that sarizotan significantly alleviates levodopa-induced dyskinesia. The functional effects of sarizotan on individual dopamine receptor subtypes are not known. Here we report the functional effects of sarizotan on human D2-like dopamine receptors (D2S, D2L, D3, D4.2 and D4.4) individually expressed in the AtT-20 neuroendocrine cell line. Using the coupling of D2-like dopamine receptors to G-protein coupled inward rectifier potassium channels we determined that sarizotan is a full agonist at D3 and D4.4 receptors (EC50=5.6 and 5.4 nM, respectively) but a partial agonist at D2S, D2L and D4.2 receptors (EC50=29, 23 and 4.5 nM, respectively). Consistent with its partial agonist property, sarizotan is an antagonist at D2S and D2L receptors (IC50=52 and 121 nM, respectively). Using the coupling of D2-like dopamine receptors to adenylyl cyclase we determined that sarizotan is a full agonist at D2L, D3, D4.2 and D4.4 receptors (EC50=0.51, 0.47, 0.48 and 0.23 nM, respectively) but a partial agonist at D2S receptors (EC50=0.6 nM).

Systemic EMD 68843 injections reduce anxiety in the shock-probe, but not the plus-maze test

Selective serotonin (5-hydroxytryptamine; 5-HT) reuptake inhibitors and 5-HT(1A) receptor agonists are believed to reduce anxiety. In the present study we examined the effects of injections of 5-(4-[4-(5-cyano-3-indolyl)-butyl]-1-piperazinyl)-benzofuran-2-carboxamide hydrochloride salt (EMD 68843), a 5-HT(1A) receptor agonist and selective 5-HT reuptake inhibitor, in two animal models of anxiety, plus-maze and shock-probe. Rats received intraperitoneal injections of vehicle, diazepam (2.5 mg/kg), or EMD 68843 (10, 20, or 40 mg/kg) 1 h prior to testing. Diazepam at the single dose tested and EMD 68843 dose-dependently (significantly at 20 and 40 mg/kg) reduced burying in shock-probe. However, only diazepam significantly increased open arm exploration in the plus-maze. Therefore, EMD 68843 has task specific anxiolytic properties.

Sar of novel biarylmethylamine dopamine D4 receptor ligands

SAR for a novel series of dopamine D4 receptor ligands is shown. Very selective, highly potent compounds like 1-(2-pyrimidinyl)-4-(3-(3-thienyl)-benzyl)-piperazine (5f) and 2-(4-(1-fluorenylmethyl)-1-piperazinyl)-pyrimidine (8c) were obtained.

Contribution of the serotonin 5-HT1A receptor agonism of 8-OH-DPAT and EMD 128130 to the regulation of haloperidol-induced muscle rigidity in rats

The aim of the present study was to find out whether (+/-)-8-hydroxy-2(di-n-propylamino)tetralin (8-OH-DPAT), a prototypical 5-HT1A agonist, and (R)-(-)-2-[5-(4-fluorophenyl)-3-pyridylmethylaminomethyl]-chromane HCl (EMD 128130), a compound with serotonin 5-HT1A-agonist and dopamine D2-like antagonist properties, are able to attenuate the haloperidol-induced (1 mg/kg) muscle rigidity in rats. Muscle tone was examined using a combined mechano- and electromyographic (EMG) method that simultaneously measured the mechanical muscle resistance (MMG) of the rats hind foot to passive movements in the ankle joint, and the EMG activity of two antagonist muscles. Both 8-OH-DPAT (0.125-0.5 mg/kg i.p.) and EMD 128130 (1-10 mg/kg i.p.) dose-dependently decreased the haloperidol-enhanced MMG to passive movements, as well as the tonic and the long-latency reflex EMG activities. Provided these results can be extrapolated to humans, the efficacy of EMD 128130 in relieving the haloperidol-induced muscle rigidity supports the concept that novel antipsychotics with 5-HT1A agonist and dopamine D2 antagonist activities should have a favourable extrapyramidal side-effect profile.