Zebrafish in Neurological Drug Discovery: Marketed Compounds and Translational Insights

Zebrafish in neurological drug discovery have emerged as a powerful model, offering unique advantages such as genetic similarity to humans, transparent embryos, and rapid development. These features make them ideal for in vivo neuropharmacological screening and studying neurological disease mechanisms. In this article, we explore how zebrafish models of neurological diseases have been used to test several marketed compounds, many of which have advanced to clinical trials for conditions like epilepsy, ALS, and lysosomal storage disorders. These studies highlight the value of zebrafish as a preclinical model for CNS drug development.

Zebrafish in Neurological Drug Discovery: Case Studies

Clemizole and Epilepsy [1]

Investigations into potential treatments for Dravet syndrome, a severe form of epilepsy, have highlighted clemizole as a promising candidate. Originally an antihistamine, clemizole was evaluated by Baraban et al. (2013) using zebrafish models to test its efficacy in reducing seizure activity. 

Zebrafish larvae with a mutation in the Scn1a gene, which mimics Dravet syndrome, were utilized. The study found that clemizole significantly reduced seizure-like behaviors, as evidenced by both behavioral observations and electrophysiological recordings, which showed a reduction in abnormal brain activity. The researchers proposed that clemizole’s anticonvulsant effects might be mediated through its interaction with serotonin receptors, suggesting a new potential therapeutic pathway for epilepsy. 

Currently, there is an active randomized double-blind placebo-control study (NCT04462770) to evaluate the safety and efficacy of clemizole as adjunctive therapy for Dravet Syndrome. This research underscores the utility of zebrafish in screening for antiepileptic drugs and exploring their mechanisms of action, paving the way for innovative treatments for refractory epilepsy.

Fenfluramine in Dravet Syndrome [2]

Fenfluramine, a drug historically used for weight loss, has recently been explored for its potential to treat Dravet syndrome. The initial screening for its antiepileptic properties was conducted using zebrafish models by Dinday and Baraban (2015). These models were the same employed for clemizole assessment (zebrafish larvae with mutations in the Scn1a gene), which closely mimic the human condition of Dravet syndrome, characterized by spontaneous seizure activity.

In their study, Dinday and Baraban screened approximately 1,000 compounds using a high-throughput phenotype-based approach. Fenfluramine emerged as one of the promising candidates, showing significant antiepileptic activity. The epileptic zebrafish treated with fenfluramine exhibited a marked reduction in seizure behavior. Behavioral assays indicated that fenfluramine significantly reduced swim velocity and seizure-like activity in the larvae. Further electrophysiological analysis confirmed that fenfluramine suppressed abnormal electrographic discharges associated with seizures, providing a strong preclinical rationale for its use in treating Dravet syndrome.

Following these promising results from zebrafish models, fenfluramine's efficacy and safety were tested in a clinical trial. This phase 3, randomized, double-blind, placebo-controlled trial involved 119 patients with Dravet syndrome. The primary aim was to assess whether fenfluramine could effectively reduce the frequency of convulsive seizures in children and young adults with this condition. The clinical trial results were significant. Patients treated with fenfluramine experienced a substantial reduction in the frequency of convulsive seizures. Specifically, the median reduction in monthly seizure frequency was 62.3% in the fenfluramine group compared to 32.4% in the placebo group. Additionally, a clinically meaningful reduction (defined as a 50% or greater decrease from baseline) was observed in 70% of patients treated with fenfluramine. The safety profile was also carefully monitored, and while some adverse effects were noted, they were generally manageable and did not outweigh the benefits in seizure reduction.

Trazodone and Lorcaserin's Role in Treating Seizures [3]

Trazodone and lorcaserin have shown potential in treating seizures, particularly in the context of Dravet syndrome. Griffin et al. (2017) utilized zebrafish models to investigate the efficacy of these compounds. The zebrafish larvae were genetically modified to carry mutations in the Scn1a gene, which closely mimics the convulsive behaviors observed in Dravet syndrome. The study employed a high-throughput screening of drug libraries, identifying trazodone and lorcaserin as promising candidates due to their significant antiepileptic activity. Zebrafish treated with these drugs exhibited a marked reduction in seizure-like behaviors, as demonstrated by decreased swim velocity and suppressed electrographic seizures. This provided strong preclinical evidence supporting the use of trazodone and lorcaserin for seizure management.

Trazodone, traditionally used as an antidepressant, showed effective seizure suppression in zebrafish models. The study demonstrated that trazodone reduced seizure activity by 89.0 ± 9.1% during a 2-hour treatment period. The drug's ability to modulate serotonin receptors, particularly 5-HT2A and 5-HT2C, is believed to underpin its antiepileptic effects.

Lorcaserin, a serotonin receptor agonist prescribed for weight management, also showed promise in reducing seizure activity. The zebrafish models revealed that lorcaserin treatment resulted in a 27.2 ± 15.7% suppression of seizure activity during the 2-hour treatment window. The drug's selective activation of the 5-HT2C receptor plays an essential role in its anticonvulsant properties. Following the success in zebrafish models, lorcaserin was tested in children with Dravet syndrome under a compassionate use program at the Children’s Hospital Colorado. This program involved five children who had not responded to at least five other antiepileptic drugs. The clinical data indicated that lorcaserin was well tolerated and led to a reduction in seizure frequency in all treated patients. Notably, one patient experienced a 90% reduction in generalized tonic-clonic seizures without the need for rescue medications. The study showed that lorcaserin could provide seizure control in patients resistant to other treatments, highlighting its potential as a valuable therapeutic option for Dravet syndrome.

Pimozide for Amyotrophic Lateral Sclerosis (ALS) [4]

Pimozide, traditionally known for its antipsychotic properties, has garnered interest for its potential therapeutic effects in treating ALS, a devastating neurodegenerative disorder. In a study by Patten et al. (2017), zebrafish models were employed to evaluate the efficacy of pimozide in ALS. The zebrafish used in this study carried mutations in the Sod1 gene, which is commonly associated with familial ALS. These mutant zebrafish exhibited hallmark ALS symptoms, such as motor neuron degeneration and impaired swimming abilities.

The research demonstrated that pimozide treatment led to a significant improvement in motor function and an increase in the survival of motor neurons. Specifically, pimozide was shown to stabilize neuromuscular junctions (NMJs), which are critical for motor function. Treated zebrafish exhibited more robust NMJs compared to untreated controls, as evidenced by improved synaptic transmission and reduced muscle denervation. Additionally, the study explored the mechanism behind pimozide’s neuroprotective effects. It was suggested that pimozide acts by modulating calcium channels, thereby maintaining calcium homeostasis within neurons. This action helps to protect against the excitotoxicity that is often implicated in the progression of ALS.

These findings are significant because they suggest that pimozide could potentially slow down or even halt the progression of ALS in humans. A phase II study (NCT03272503) was registered to assess the efficacy of pimozide to slow the progression of ALS.

Miglustat in Lysosomal Storage Disorders [5]

Miglustat, primarily used for treating Gaucher’s disease, has shown promise in addressing the neurological symptoms of GM2 gangliosidosis, a severe lysosomal storage disorder. Boutry et al. (2018) conducted a comprehensive study using zebrafish models to evaluate the drug’s efficacy in this context. The zebrafish were genetically modified to mimic the pathological conditions of GM2 gangliosidosis, allowing for an accurate assessment of miglustat’s therapeutic potential.

The research demonstrated that miglustat treatment led to a significant reduction in the accumulation of GM2 gangliosides in the brains of the zebrafish. This reduction correlated with notable improvements in motor function and increased survival rates. Behavioral assays revealed that treated zebrafish exhibited enhanced swimming abilities and reduced neurological deficits compared to their untreated counterparts, indicating the drug’s effectiveness in mitigating the symptoms of the disease.

A key finding of the study was that miglustat inhibits the synthesis of glycosphingolipids, the substrates that accumulate due to lysosomal dysfunction in GM2 gangliosidosis. By reducing the production of these harmful substrates, miglustat alleviated cellular stress and neuroinflammation, common features of the disorder. Histological analysis confirmed that treated zebrafish had less neuronal degeneration and fewer inflammatory markers in their brains, further supporting the drug’s neuroprotective effects.

The study also explored the molecular mechanisms underlying miglustat’s action. The researchers suggested that the drug’s ability to modulate glycosphingolipid synthesis pathways helps stabilize lysosomal function, thereby preventing the neurodegenerative processes associated with GM2 gangliosidosis. This stabilization was evident from the preservation of neuronal architecture and the maintenance of normal cellular functions in treated zebrafish.

These findings underscore the potential of miglustat as a therapeutic agent for the neurological manifestations of GM2 gangliosidosis. A small phase II study testing the safety of miglustat in patients with Spastic Paraplegia 11 was completed (NCT04768166).

Summary Table of Marketed Compounds Tested in Zebrafish Models of Human Neurological Diseases

ZeClinics’ Contribution to Drug Development

ZeClinics stands at the forefront of utilizing zebrafish models to advance drug development. With a focus on high-throughput screening and detailed phenotypic analysis, ZeClinics offers a comprehensive platform for evaluating the safety and efficacy of new compounds. Our zebrafish models enable rapid and cost-effective testing, providing critical data on drug behavior, toxicity, and therapeutic potential. This approach accelerates the early stages of drug discovery, allowing for the identification of promising candidates and the elucidation of their mechanisms of action. By leveraging the unique advantages of zebrafish, ZeClinics bridges the gap between preclinical research and clinical applications, facilitating the development of innovative treatments for neurological disorders and beyond.

Conclusions

Zebrafish have proven to be an indispensable tool in neurological drug discovery, enabling rapid and cost-effective screening of candidate compounds for a wide range of central nervous system disorders. From antiepileptic drug screening in Dravet syndrome models to evaluating neuroprotective therapies for ALS and lysosomal storage diseases, zebrafish offer both phenotypic depth and translational value. As the demand for more predictive and scalable preclinical models for CNS drugs grows, zebrafish will continue to bridge the gap between early research and clinical success, advancing the future of neuropharmacology.

REFERENCES

[1] Baraban SC, Dinday MT, Hortopan GA. Drug screening in Scn1a zebrafish mutant identifies clemizole as a potential Dravet syndrome treatment. Nat Commun. 2013;4:2410. doi: 10.1038/ncomms3410. 

[2] Dinday MT, Baraban SC. Large-Scale Phenotype-Based Antiepileptic Drug Screening in a Zebrafish Model of Dravet Syndrome. eNeuro. 2015 Aug 31;2(4):ENEURO.0068-15.2015. doi: 10.1523/ENEURO.0068-15.2015

[3] Griffin A, Hamling KR, Knupp K, Hong S, Lee LP, Baraban SC. Clemizole and modulators of serotonin signalling suppress seizures in Dravet syndrome. Brain. 2017 Mar 1;140(3):669-683. doi: 10.1093/brain/aww342

[4] Patten SA, Aggad D, Martínez K et al. Neuroleptics as therapeutic compounds stabilizing neuromuscular transmission in amyotrophic lateral sclerosis. JCI Insight. 2017 Nov 16; 2(22): e97152. doi: 10.1172/jci.insight.97152

[5] Boutry M, Branchu J, Lustremant C, Pujol C, Pernelle J, Matusiak R, Seyer A, Poirel M, Chu-Van E, Pierga A, Dobrenis K, Puech JP, Caillaud C, Durr A, Brice A, Colsch B, Mochel F, El Hachimi KH, Stevanin G, Darios F. Inhibition of Lysosome Membrane Recycling Causes Accumulation of Gangliosides that Contribute to Neurodegeneration. Cell Rep. 2018 Jun 26;23(13):3813-3826. doi: 10.1016/j.celrep.2018.05.098. 

By Miriam Martínez

Miriam is a Human Biologist with a strong background in neuropharmacology and a passion for bridging science and innovation. After earning a master’s degree in the Pharmaceutical and Biotech Industry, she completed her PhD in Biomedicine at Pompeu Fabra University (Barcelona), where her research focused on the behavioral analysis of animal models for neurophenotypical characterization. Following her doctoral studies, Miriam transitioned into the healthcare marketing and communication sector, where she played a key role in developing impactful marketing strategies and educational campaigns for leading pharmaceutical brands. She now leverages her scientific expertise, strategic thinking, and creative communication skills in her current role at ZeClinics.