Deutetrabenazine (trade name Austedo) is a vesicular monoamine transporter 2 (VMAT2) inhibitor indicated for the treatment of chorea associated with Huntington’s disease. The drug was developed by Auspex Pharmaceuticals and is being commercialized by Teva Pharmaceuticals. Deutetrabenazine is a deuterated derivative of tetrabenazine. The incorporation of deuterium in place of hydrogen at the sites of primary metabolism results in metabolic clearance being slowed, allowing less frequent dosing and better tolerability.

Tetrabenazine (trade name Xenazine) is a monoamine depleter and used as the symptomatic treatment of chorea associated with Huntington's disease. Tetrabenazine is a reversible human vesicular monoamine transporter type 2 inhibitor (Ki = 100 nM). It acts within the basal ganglia and promotes depletion of monoamine neurotransmitters serotonin, norepinephrine, and dopamine from stores. It also decreases uptake into synaptic vesicles. Dopamine is required for fine motor movement, so the inhibition of its transmission is efficacious for hyperkinetic movement. Tetrabenazine exhibits weak in vitro binding affinity at the dopamine D2 receptor. The most common adverse reactions, which have occurred in at least 10% of subjects in studies and at least 5% greater than in subjects who received placebo, have been: sedation or somnolence, fatigue, insomnia, depression, suicidal thoughts, akathisia, anxiety, and nausea.

Selisistat (EX 527) was discovered by Elixir scientists as a selective human SIRT1 inhibitor and exhibits >200-fold selectivity against SIRT2 and SIRT3. Human SIRT1 is an enzyme that deacetylates the p53 tumor suppressor protein and has been suggested to modulate p53-dependent functions including DNA damage-induced cell death. It was shown that drug was highly safe in toxicology studies. Selisistat passed Phase II clinical trials to treat Huntington’s disease, but that study was discontinued.

Mavoglurant (AFQ056) was developed as a new metabotropic glutamate receptor 5 (mGluR5) antagonist. The efficacy of mavoglurant in humans has been assessed in L-dopa induced dyskinesia in Parkinson's disease and Fragile X syndrome in proof of principle clinical studies. However, Novartis had announced that the company would be discontinuing its development program in Fragile X following negative results in a large international clinical trial in adults, and more recently in a trial in adolescents. In both placebo-controlled trials, patients taking mavoglurant did not show improvement over placebo in any outcome measures. In patients with L-Dopa-induced dyskinesias studies failed to meet the primary objective of demonstrating improvement of dyskinesia. Mavoglurant was also investigated in phase II clinical trials to reduce chorea in Huntington's disease, but the target result was not achieved. Currently Novartis is conducting a phase II clinical trial to demonstrate whether or not this drug can benificially reduce cocaine use in Cocaine Use Disorder.

Pridopidine is an experimental drug candidate belonging to a class of agents known as dopidines, which act as dopaminergic stabilizers in the central nervous system. As a dopamine stabilizer, pridopidine is thought to reduce the effects of dopamine when there’s too much and increase its effects when there’s too little. Pridopidine, therefore, plays two opposing roles in the brain, which stabilize dopamine levels. In this way, pridopidine is thought to help the brain reestablish a normal balance of neurotransmitters, and thus regain control over motion. Pridopidine intended to treat Huntington’s disease movement symptoms. Pridopidine was well tolerated and had an adverse event profile similar to a placebo.

PF-2545920 is an orally-active phosphodiesterase 10A (PDE10A) inhibitor originated by Pfizer, for the treatment of Huntington's disease. PF-2545920 was originally developed by Pfizer for the treatment of schizophrenia. But later clinical studies for Schizophrenia were discontinued. PF-2545920 is a potent and selective PDE10A inhibitor with IC50 of 0.37 nM, with >1000-fold selectivity over the PDE. PF-2545920 is active in a range of antipsychotic models, antagonizing apomorphine-induced climbing in mice, inhibiting conditioned avoidance responding in both rats and mice, and blocking N-methyl-D-aspartate antagonist-induced deficits in prepulse inhibition of acoustic startle response in rats, while improving baseline sensory gating in mice.

LM11A-31 is a small, nonpeptide, monomeric ligand of p75 neutrophin receptor (p75NTR). The compound promotes neuron survival in vitro. PharmatrophiX is developing a modified version of LM11A-31 (LM11A 31 BHS) for the oral treatment of Alzheimer's disease.

C16 (PKRi) is a selective inhibitor of the enzyme double-stranded RNA-dependent protein kinase (PKR). PKRi prevents striatal neurodegeneration and improves behavioral outcomes in a chemically induced mouse model of Huntington's disease, the efffect mediated by off-target inhibition of CDKs. PKRi restored memory deficit in a mouse model of Alzheimer's disease. In a mouse model of colon-26 adenocarcinoma, treatment with C16 lead to a significantly higher level of blood glucose and lower level of serum triglyceride compared with placebo group, which indicates potential use for alleviation of cachexia.

AK-7 is a brain penetrant selective SIRT2 inhibitor. AK-7 exerts neuroprotective properties in vitro and in vivo models of neurodegenerative diseases (Huntington’s, Parkinson’s and Alzheimer’s disease).

SCH-23390 is a potent and selective antagonist of the D1A and D1B dopamine receptors having Ki of 0.2 and 0.3 nM respectively. The C11 radiolabeled version has proven to be useful as a PET imaging probe in humans for the investigation of a number of neurological conditions including Schizophrenia, Parkinson's Disease, and Huntington's Disease. It should be noted that the non-radiolabeled compound did receive preclinical interest as a potential therapeutic (annotated separately), although such efforts have been discontinued due to side-effects and a lack of therapeutic efficacy.