Henrik Ponten

In vivo pharmacology of the dopaminergic stabilizer pridopidine

Pridopidine (ACR16) belongs to a new pharmacological class of agents affecting the central nervous system called dopaminergic stabilizers. Dopaminergic stabilizers act primarily at dopamine type 2 (D(2)) receptors and display state-dependent behavioural effects. This article aims to give an overview of the preclinical neurochemical and behavioural in vivo pharmacological properties of pridopidine. Pridopidine was given s.c. to male Sprague-Dawley rats (locomotor, microdialysis and tissue neurochemistry) and i.p. to Swiss male mice (tail suspension test). Pridopidine dose-dependently increased striatal tissue levels of the dopamine metabolite 3,4-dihydroxyphenylalanin (ED(50)=81 micromol/kg), and prefrontal cortex dialysate levels of dopamine and noradrenaline as measured by high performance liquid chromatography. The agent reduced hyperlocomotion (d-amphetamine: ED(50)=54 micromol/kg; MK-801: ED(50)=40 micromol/kg), but preserved spontaneous locomotor activity, confirming state-dependent behavioural effects. In addition, pridopidine significantly reduced immobility time in the tail suspension test. We conclude that pridopidine state-dependently stabilizes psychomotor activity by the dual actions of functional dopamine D(2) receptor antagonism and strengthening of cortical glutamate functions in various settings of perturbed neurotransmission. The putative restoration of function in cortico-subcortical circuitry by pridopidine is likely to make it useful for ameliorating several neurological and psychiatric disorders, including Huntingtons disease.

Coadministration of (-)-OSU6162 with l-DOPA normalizes preproenkephalin mRNA expression in the sensorimotor striatum of primates with unilateral 6-OHDA lesions.

The substituted phenylpiperidine (-)-OSU6162 is a novel modulator of the dopaminergic systems with low affinity for dopamine D(2) receptors and potent normalizing effects on l-DOPA-induced dyskinesias. We studied the effects of coadministration of (-)-OSU6162 with l-DOPA on the regulation of striatal preproenkephalin (PPE) and prodynorphin (PDyn) mRNA expression in the primate brain by in situ hybridization histochemistry. Common marmoset monkeys sustaining unilateral 6-hydroxydopamine lesions of the nigrostriatal pathway received l-DOPA/carbidopa, l-DOPA/carbidopa plus (-)-OSU6162, or vehicle over 14 days. In vehicle-treated animals, PPE mRNA levels were markedly increased in the sensorimotor territory of the lesioned striatum. By contrast, a rather uniform lesion-induced reduction of PDyn mRNA levels was found in the vehicle group. Subchronic l-DOPA treatment induced a further increase in PPE mRNA expression in a number of sensorimotor and associative subregions of the denervated striatum. Coadministration of (-)-OSU6162 with l-DOPA partially reversed the lesion- and l-DOPA-induced elevation of PPE expression and, by affecting PPE mRNA expression differentially on the intact and lesioned striatum, markedly reduced the side-to-side difference in PPE mRNA expression. The effects on PPE mRNA expression were apparent throughout the rostrocaudal extent of the putamen and the dorsal portions of the caudate nucleus. l-DOPA treatment resulted in an enhancement in PDyn mRNA expression in all functional compartments of the striatum. Coadministration of (-)-OSU6162 had no apparent influence on these l-DOPA-induced changes in PDyn mRNA expression. The present results suggest that (-)-OSU6162 acts primarily by modifying striatal output via the indirect pathway.

The dopaminergic stabilizer pridopidine decreases expression of l-DOPA-induced locomotor sensitisation in the rat unilateral 6-OHDA model

Treatment-limiting motor complications occur in patients with Parkinsons disease after chronic levodopa (L-DOPA) treatment, and represent an unmet medical need. We examined the motor and neurochemical effects of the dopaminergic stabilizer pridopidine (NeuroSearch A/S, Ballerup, Denmark) in the unilateral rodent 6-OHDA lesion model, which is often used to evaluate the potential of experimental compounds for such dopamine-related motor complications. In total, 72 rats were hemi-lesioned and allocated to receive twice-daily injections of either vehicle; 6.5mg/kg L-DOPA; L-DOPA + 25 μmol/kg pridopidine; or L-DOPA + 25 μmol/kg (-)-OSU6162-a prototype dopaminergic stabilizer used previously in 6-OHDA hemi-lesion models. Animals were treated for 7, 14 or 21 days, and locomotor activity and ex vivo brain tissue neurochemistry analysed. In agreement with previous studies, L-DOPA sensitised the motor response, producing significantly more contralateral rotations than vehicle (P<0.05). Concomitant administration of pridopidine and L-DOPA significantly decreased the number of L-DOPA-induced contralateral rotations on day 7, 14 and 21 (P<0.05 versus L-DOPA alone), while still allowing a beneficial locomotor stimulant effect of L-DOPA. Concomitant pridopidine also reduced L-DOPA-induced rotation asymmetry (P<0.05 versus L-DOPA alone) and had no adverse effects on distance travelled. Brain neurochemistry was generally unaffected in all treatments groups. In conclusion, pridopidine shows potential for reducing motor complications of L-DOPA in Parkinsons disease and further testing is warranted.

Co-administration of the Dopaminergic Stabilizer Pridopidine and Tetrabenazine in Rats.

BACKGROUND The efficacy of the dopaminergic stabilizer, pridopidine, in reducing the voluntary and involuntary motor symptoms of Huntingtons disease (HD) is under clinical evaluation. Tetrabenazine is currently the only approved treatment for chorea, an involuntary motor symptom of HD; both compounds influence monoaminergic neurotransmission. OBJECTIVE To investigate pharmacological interactions between pridopidine and tetrabenazine. METHODS Drug-interaction experiments, supplemented by dose-response data, examined the effects of these compounds on locomotor activity, on striatal levels of dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC), and on levels of activity-regulated cytoskeleton-associated (Arc) gene expression in the striatum and frontal cortex of male Sprague-Dawley rats. Haloperidol, a classical dopamine D2 receptor antagonist, was also tested for comparison. RESULTS Monitoring for 1 hour after co-administration of tetrabenazine 0.64 mg/kg and pridopidine 32 mg/kg revealed a reduction in locomotor activity, measured as distance travelled, in the tetrabenazine treated group, down to 61% vs. vehicle controls (p < 0.001). This was significantly alleviated by pridopidine (distance travelled reached 137% vs. tetrabenazine controls, p < 0.01). In contrast, co-administration of haloperidol 0.12 mg/kg and tetrabenazine produced increased inhibition of locomotor activity over the same period (p < 0.01, 41% vs. tetrabenazine). Co-administration of pridopidine, 10.5 mg/kg or 32 mg/kg, with tetrabenazine counteracted significantly (p < 0.05) and dose-dependently the decrease in frontal cortex Arc levels induced by tetrabenazine 0.64 mg/kg (Arc mRNA reached 193% vs. tetrabenazine mean at 32 mg/kg); this counteraction was not seen with haloperidol. Tetrabenazine retained its characteristic neurochemical effects of increased striatal DOPAC and reduced striatal dopamine when co-administered with pridopidine. CONCLUSIONS Pridopidine alleviates tetrabenazine-induced behavioural inhibition in rats. This effect may be associated with pridopidine-induced changes in cortical activity and may justify clinical evaluation of pridopidine/tetrabenazine combination therapy.

In Vivo Systems Response Profiling and Multivariate Classification of CNS Active Compounds: A Structured Tool for CNS Drug Discovery

This paper describes the application of in vivo systems response profiling in CNS drug discovery by a process referred to as the Integrative Screening Process. The biological response profile, treated as an array, is used as major outcome for selection of candidate drugs. Dose-response data, including ex vivo brain monoaminergic biomarkers and behavioral descriptors, are systematically collected and analyzed by principal component analysis (PCA) and partial least-squares (PLS) regression, yielding multivariate characterization across compounds. The approach is exemplified by assessing a new class of CNS active compounds, the dopidines, compared to other monoamine modulating compounds including antipsychotics, antidepressants, and procognitive agents. Dopidines display a distinct phenotypic profile which has prompted extensive further preclinical and clinical investigations. In summary, in vivo profiles of CNS compounds are mapped, based on dose response studies in the rat. Applying a systematic and standardized work-flow, a database of in vivo systems response profiles is compiled, enabling comparisons and classification. This creates a framework for translational mapping, a crucial component in CNS drug discovery.