small molecules

2026-02-17 | Alpha-methyl-para-tyrosine and amphetamine ameliorate hyperactivity in a novel mouse model of dopamine transporter deficiency syndrome.

The dopamine transporter is essential for dopamine homeostasis maintenance. Therefore, single amino acid changes in its gene can be sufficient to induce disease, such as dopamine transporter deficiency syndrome (DTDS). DTDS-associated variants may lead to DAT protein misfolding, retention in the endoplasmic reticulum, and reduced DAT surface expression. In turn, proper dopaminergic regulation is lost. Current treatments for DTDS are largely ineffective, necessitating better options. We developed a novel mouse model of DTDS harboring the A313V knock-in DAT variant, a proxy for the human A314V variant. The A313V mice are hyperactive, have decreased striatal tissue content of dopamine and increases in its metabolite HVA, and impaired dopamine uptake. FDA approved compounds alpha-methyl-para-tyrosine and amphetamine ameliorate the observed hyperactivity. Moreover, alpha-methyl-para-tyrosine may be a disease-modifying treatment by addressing the hyperdopaminergic tone underlying this hyperactivity. Noribogaine, a pharmacological chaperone for DAT, is unable to rescue DAT expression. These findings demonstrate that the A313V knock-in DAT variant mice recapitulate several defining phenotypes seen in patients with DTDS, and provide evidence for two novel treatments for the disease.

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2026-01-27 | Mouse model of atypical DAT deficiency syndrome uncovers dopamine dysfunction associated with parkinsonism and ADHD.

Atypical dopamine transporter (DAT) deficiency syndrome (DTDS) arises from genetic disruption of DAT function and is characterized by early-onset parkinsonism alongside comorbid psychiatric symptoms. However, the underlying pathobiological processes are largely unknown. Here, we present a mouse model of atypical DTDS based on the patient-derived compound heterozygote genotype, DAT-I312F/D421N+/+. DAT-I312F/D421N+/+ mice exhibited markedly impaired DAT function, leading to widespread changes in dopamine homeostasis, including elevated extracellular dopamine levels, reduced tyrosine hydroxylase and dopamine D1/D2 receptor expression, and decreased evoked dopamine release, mechanistically linked to enhanced tonic D2 autoreceptor inhibition. Fiber photometry measurements revealed disrupted fast striatal dopamine release dynamics, while confocal imaging showed reduced striatal dopaminergic axon fiber density. These neurochemical changes were accompanied by a psychomotor phenotype characterized by hyperlocomotion, enhanced exploration, and pronounced clasping. Both amphetamine and anticholinergic treatment ameliorated the aberrant hyperactivity. Notably, amphetamine-induced dopamine release was profoundly blunted in ventral striatum but largely preserved in dorsal striatum, implicating region-specific dopamine release dynamics as a determinant of divergent behavioral and pharmacological responses. Summarized, our findings uncover multiscale dopamine dysfunction that links presynaptic DAT impairment to synaptic and circuit-level disruptions, offering insight into atypical DTDS and the co-occurrence of movement and psychiatric features.

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2025-07-14 | A Needle in a Haystack: Leveraging Machine Learning for Drug-Mechanism of Action Identification across Existing Therapeutics, with Specific Applications for Drug Repurposing for Rare Diseases

Rare diseases are a prevalent problem within the healthcare sector, primarily due to the multitude of conditions and the limited profiling available for each. Consequently, developing novel therapeutics for rare diseases through traditional pipelines is fraught with risk and cost. The integration of machine learning into bioinformatics has facilitated the growth of in silico drug repurposing, where existing compounds are repositioned based on newly identified molecular targets. This study proposes a multi-class predictive model capable of accurately determining the mechanisms of action for existing compounds. By leveraging even limited rare disease profiles, the model aims to identify candidates for drug repurposing. Four supervised learning algorithms were trained using a combination of Clue and PubChem datasets. The results indicate that the random forest model boasts the best performance with an accuracy of 72.4% – comparable to existing literature. As all the top-performing models in this study were black-box, interpretability features of LIME and OpenAI API were integrated to ensure transparency in the recommendation of drug candidates, preparing the model for clinical integration. This model was then applied to a case study of Infantile Dystonia-Parkinson (IDP), where 105,552 compounds were screened for association with the condition. This study proposes pramipexole, bromocriptine, and ropinirole as candidate compounds for further investigation for IDP treatment. Due to the accuracy of both mechanism prediction and candidate generation, this computational model stands as a suitable approach for rare disease drug repurposing.

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2025-03-25 | Characterization of a novel mouse model of Dopamine Transporter Deficiency Syndrome and pharmacological therapeutic strategies

Abstract The dopamine transporter (DAT) is an essential protein in the maintenance of dopamine homeostasis in the brain. Thus, single amino acid changes in the gene that encodes for DAT can be sufficient to induce disease, such as Dopamine Transporter Deficiency Syndrome (DTDS). DTDS-associated variants are posited to cause DAT protein misfolding, retention in the endoplasmic reticulum, and a consequent depletion or loss of DAT at the cell surface. In turn, proper dopaminergic regulation is lost. Current treatments for DTDS are largely ineffective, and improved therapeutic options are greatly needed. To this end, we have created a novel mouse model of DTDS harboring the A313V knock-in DAT variant, a proxy for the DTDS-causing A314V variant in humans. We show that the A313V knock-in DAT mice are hyperactive, have increased striatal tissue content of dopamine and its metabolites homovanillic acid (HVA) and DOPAC, and impaired dopamine uptake. We demonstrate that FDA approved compounds alpha-methyl-para-tyrosine (ɑMPT) and amphetamine (AMPH) ameliorate hyperactivity in this mouse model. Moreover, ɑMPT may be a disease-modifying treatment by addressing the hyperdopaminergic tone underlying this hyperactivity. In contrast, noribogaine, a pharmacological chaperone for DAT, is unable to rescue DAT expression. Taken together, these findings show that the A313V knock-in DAT variant mice recapitulate several defining phenotypes seen in patients with DTDS, and provide evidence for two novel treatments for the disease.

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2024-07-10 | Characterization of Dnajc12 knockout mice, a model of hypodopaminergia

Abstract Homozygous DNAJC12 c.79-2A>G (p. V27Wfs*14) loss-of-function mutations were first reported as a cause of young-onset Parkinson’s disease. However, bi-allelic autosomal recessive pathogenic variants in DNAJC12 may lead to an alternative constellation of neurological features, including infantile dystonia, developmental delay, intellectual disability and neuropsychiatric disorders. DNAJC12 is understood to co-chaperone aromatic amino acid hydroxylases to foster the synthesis of biogenic amines. In vitro , we discover overexpressed DNAJC12 forms a complex with guanine triphosphate cyclohydrolase 1 (GCH1), the rate-limiting enzyme in the synthesis of tetrahydrobiopterin, a cofactor paramount for biogenic amines synthesis. We also confirm DNAJC12’s interaction with tyrosine (TH) and tryptophan hydroxylase (TPH), which are rate-limiting enzymes for synthesis of biogenic amines dopamine (DA) and serotonin (5-HT). In-vitro knock-down of DNAJC12 with a siRNA destabilizes the DNAJC12-TH-GCH1 complex, reducing GCH1 levels, whereas reciprocal overexpression of both TH and GCH1 increases endogenous DNAJC12, alluding to the significance of modulating the DNAJC12-TH-GCH1 complex as a therapy for DNAJC12 and other biogenic amine disorders. We extend these investigations to a Cre-conditional knock-out mice (cDKO) in which loxP sites flanking Dnajc12 exon 2 enable its excision by cre-recombinase. With germline Cre expression, we have created a constitutive Dnajc12 knock-out (DKO). DKO mice exhibit reduced locomotion/ exploratory behavior at 3 months in automated open-field testing, accompanied by increased plasma phenylalanine which is a cardinal feature of patients with pathogenic DNAJC12 variants. In striatal tissue, total DA and 5-HT, their metabolites, and electrically-evoked DA release are all reduced. Biochemical alterations in synaptic proteins are also apparent, with enhanced phosphorylation of Th pSer31 and pSer40 reflecting biological compensation. Most immediately, cDKO and DKO mice present models to develop and refine therapeutic approaches for biogenic amines disorders, including dystonia and parkinsonism. They will also enable the pleiotropic functions of biogenic amines (including DA), usually synthesized in the brain or periphery, to be separated.

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