Pridopidine (ACR16)

Pridopidine Promotes Synaptogenesis and Reduces Spatial Memory Deficits in the Alzheimer's Disease APP/PS1 Mouse Model

Sigma-1 receptor agonists have recently gained a great deal of interest due to their anti-amnesic, neuroprotective, and neurorestorative properties. Compounds such as PRE-084 or pridopidine (ACR16) are being studied as a potential treatment against cognitive decline associated with neurodegenerative disease, also to include Alzheimer's disease. Here, we performed in vitro experiments using primary neuronal cell cultures from rats to evaluate the abilities of ACR16 and PRE-084 to induce new synapses and spines formation, analyzing the expression of the possible genes and proteins involved. We additionally examined their neuroprotective properties against neuronal death mediated by oxidative stress and excitotoxicity. Both ACR16 and PRE-084 exhibited a concentration-dependent neuroprotective effect against NMDA- and H2O2-related toxicity, in addition to promoting the formation of new synapses and dendritic spines. However, only ACR16 generated dendritic spines involved in new synapse establishment, maintaining a more expanded activation of MAPK/ERK and PI3K/Akt signaling cascades. Consequently, ACR16 was also evaluated in vivo, and a dose of 1.5 mg/kg/day was administered intraperitoneally in APP/PS1 mice before performing the Morris water maze. ACR16 diminished the spatial learning and memory deficits observed in APP/PS1 transgenic mice via PI3K/Akt pathway activation. These data point to ACR16 as a pharmacological tool to prevent synapse loss and memory deficits associated with Alzheimer's disease, due to its neuroprotective properties against oxidative stress and excitotoxicity, as well as the promotion of new synapses and spines through a mechanism that involves AKT and ERK signaling pathways.

Pridopidine in the treatment of Huntington's disease

Huntington's disease (HD) is a highly common inherited monogenic neurodegenerative disease, and the gene responsible for its development is located in the 4p16.3 chromosome. The product of that gene mutation is an abnormal huntingtin (Htt) protein that disrupts the neural conduction, thus leading to motor and cognitive disorders. The disease progresses to irreversible changes in the central nervous system (CNS). Although only a few drugs are available to symptomatic treatment, 'dopamine stabilizers' (as represented by the pridopidine) may be the new treatment options. The underlying causes of HD are dopaminergic conduction disorders. Initially, the disease is hyperkinetic (chorea) until it eventually reaches the hypokinetic phase. Studies confirmed a correlation between the amount of dopamine in the CNS and the stage of the disease. Pridopidine has the capacity to be a dopamine buffer, which could increase or decrease the dopamine content depending on the disease phase. A research carried out on animal models demonstrated the protective effect of pridopidine on nerve cells thanks to its ability to alter the cortical glutamatergic signaling through the N-methyl-D-aspartate (NMDA) receptors. Studies on dopamine stabilizers also reported that pridopidine has a 100-fold greater affinity for the sigma-1 receptor than for the D2 receptor. Disturbances in the activity of sigma-1 receptors occur in neurodegenerative diseases, including HD. Their interaction with pridopidine results in the neuroprotective effect, which is manifested as an increase in the plasticity of synaptic neurons and prevention of their atrophy within the striatum. To determine the effectiveness of pridopidine in the treatment of HD, large multicenter randomized studies such as HART, MermaiHD, and PRIDE-HD were carried out.

Pridopidine selectively occupies sigma-1 rather than dopamine D2 receptors at behaviorally active doses

Rationale: Dopamine stabilizers have stimulatory actions under low dopamine tone and inhibitory actions under high dopamine tone without eliciting catalepsy. These compounds are dopamine D2 receptor (D2R) antagonists or weak partial agonists and may have pro-mnemonic and neuroprotective effects. The mechanism underlying their stimulatory and neuroprotective actions is unknown but could involve sigma-1R binding.
Objectives: The present study examined sigma-1R and D2R occupancy by the dopamine stabilizer pridopidine (ACR16) at behaviorally relevant doses in living rats.
Methods: Rats were administered 3 or 15 mg/kg pridopidine, or saline, before injection of the radiotracer (11)C-SA4503 (sigma-1R) or (11)C-raclopride (D2R). Some animals received 60 mg/kg pridopidine and were only scanned with (11)C-raclopride. Cerebral (11)C-SA4503 binding was quantified using metabolite-corrected plasma input data and distribution volume (V T) calculated by Logan graphical analysis. (11)C-raclopride binding was quantified using striatum-to-cerebellum ratios and binding potentials calculated with a simplified reference tissue model.
Results: Cunningham-Lassen plots indicated sigma-1R occupancies of 57 ± 2 and 85 ± 2% after pretreatment of animals with 3 and 15 mg/kg pridopidine. A significant (44-66%) reduction of (11)C-raclopride binding was only observed at 60 mg/kg pridopidine.
Conclusions: At doses shown to elicit neurochemical and behavioral effects, pridopidine occupied a large fraction of sigma-1Rs and a negligible fraction of D2Rs. Significant D2R occupancy was only observed at a dose 20-fold higher than was required for sigma-1R occupancy. The characteristics of dopamine stabilizers may result from the combination of high sigma-1R and low D2R affinity.

Regional cerebral glucose metabolism after pridopidine (ACR16) treatment in patients with Huntington disease

Objectives: Huntington disease is a hereditary neurodegenerative disorder resulting in loss of motor, cognitive, and behavioral functions and is characterized by a distinctive pattern of cerebral metabolic abnormalities. Pridopidine (ACR16) belongs to a novel class of central nervous system compounds in development for the treatment of Huntington disease. The objective of the study was to investigate the metabolic changes in patients with Huntington disease before and after pridopidine treatment.
Methods: [(18)F]Fluorodeoxyglucose positron emission tomographic imaging was used to measure the regional cerebral metabolic rate of glucose at baseline and after 14 days of open-label pridopidine treatment in 8 patients with Huntington disease. Clinical assessments were performed using the Unified Huntington's Disease Rating Scale.
Results: Statistical parametric mapping analysis showed increased metabolic activity in several brain regions such as the precuneus and the mediodorsal thalamic nucleus after treatment. In addition, after pridopidine treatment, the correlation between the clinical status and the cerebral metabolic activity was strengthened.
Conclusions: Our findings suggest that pridopidine induces metabolic changes in brain regions implicated as important for mediating compensatory mechanisms in Huntington disease. In addition, the finding of a strong relationship between clinical severity and metabolic activity after treatment also suggests that pridopidine treatment targets a Huntington disease-related metabolic activity pattern.

Profile of pridopidine and its potential in the treatment of Huntington disease: the evidence to date

Huntington disease (HD) is a chronic, genetic, neurodegenerative disease for which there is no cure. The main symptoms of HD are abnormal involuntary movements (chorea and dystonia), impaired voluntary movements (ie, incoordination and gait balance), progressive cognitive decline, and psychiatric disturbances. HD is caused by a CAG-repeat expanded mutation in the HTT gene, which encodes the huntingtin protein. The inherited mutation results in the production of an elongated polyQ mutant huntingtin protein (mHtt). The cellular functions of the Htt protein are not yet fully understood, but the functions of its mutant variant are thought to include alteration of gene transcription and energy production, and dysregulation of neurotransmitter metabolism, receptors, and growth factors. The phenylpiperidines pridopidine (4-[3-methanesulfonyl-phenyl]-1-propyl-piperidine; formerly known as ACR16) and OSU6162 ([S]-[-]-3-[3-methane [sulfonyl-phenyl]-1-propyl-piperidine) are members of a new class of pharmacologic agents known as "dopamine stabilizers". Recent clinical trials have highlighted the potential of pridopidine for symptomatic treatment of patients with HD. More recently, the analysis of HD models (ie, in vitro and in mice) highlighted previously unknown effects of pridopidine (increase in brain-derived neurotrophic factor, reduction in mHtt levels, and σ-1 receptor binding and modulation). These additional functions of pridopidine suggest it might be a neuroprotective and disease-modifying drug. Data from ongoing clinical trials of pridopidine will help define its place in the treatment of HD. This commentary examines the available preclinical and clinical evidence regarding the use of pridopidine in HD.