Authors :
Presenting Author: Karishma Randhave, BS – Vanderbilt University Medical center
Marshall Biven, BS – Vanderbilt University Medical Center
Kirill Zavalin, PhD – Vanderbilt University Medical center
Krista Paffenroth, BS – Vanderbilt University
John Allison, PhD – Vanderbilt University
Wangzhen Shen, PhD – Vanderbilt University Medical center
Muhammad Khan, PhD – Vanderbilt University Medical center
Fiona Harrison, MD – Vanderbilt University
Jingqiong Kang, MD, PhD – Vanderbilt University Medical center
Rationale:
We have previously identified that loss of GABA uptake is a major pathophysiology for neurodevelopmental disorders mediated S295L mutation in SLC6A1 for GABA transporter 1 (GAT-1). Patients with this mutation suffer from epilepsy plus complex neurodevelopmental comorbidities, including autism and learning disabilities. Developmental and Epileptic Encephalopathy (DEEs) are characterized by epilepsy and developmental delay, with poorly understood pathophysiology and limited treatment options. In this study, we have shown that the chemical chaperone 4-phenylbutyrate (4-PBA) is capable of rescuing seizures as well as several neurobehavioral comorbidities in genetic epilepsy (GE) mouse models, including Slc6a1+/S295L. This work has led to a clinical trial (NCT04937062) with promising results, where participants either became seizure-free or experienced a substantial reduction in seizures, with the drug being well tolerated.Methods:
In this study, we investigated the behavioral deficits underlying SLC6A1-associated DEE in the Slc6a1+/S295L mouse model and assessed the therapeutic potential of 4-PBA. We conducted a comprehensive battery of behavioral for mice at 1, 4 and 10 months old of both sexes. we designed a battery of neurobehavioral assays, including grip strength, marble burying, nest building, elevated zero maze, three-chamber test, open field test, Barnes maze, light-dark cycle, and home cage scan (HCS). Mice were subjected to chronic 4-PBA treatment for 28 days, as well as acute treatment for 7 days, followed by evaluation of the effects on neurobehavioral phenotypes.
Results:
The battery of behavioral tests showed subtle neurobehavioral phenotypes; however, home cage scan identified a robust phenotype in this mouse model. Our preliminary experiments suggested that behavioral abnormalities in these mice become more apparent with age, so we focused our behavioral study on seven months old mice. Slc6a1+/S295L exhibited reduced travel distance and hanging at 7 months of age. Acute 4-PBA treatment for 7 days showed reduced locomotion deficits, while chronic treatment for 28 days resulted in significant improvement, normalizing both locomotion and hanging behavior. Slc6a1+/S295L also exhibited increased sleep during daytime. With both chronic and acute 4-PBA treatment, we could see partial rescue of sleep phenotype. Our findings provide the first evidence that 4-PBA is disease-modifying and can mitigate comorbidities in addition to seizures.
Conclusions:
Our study indicates 4-phenylbutyrate may be an effective treatment option to rescue significant behavioral abnormalities including locomotion, exploration, repetitive behaviors and sleep. The promising results from the ongoing clinical trial, coupled with the findings from this preclinical mouse model, will likely expedite the clinical application of 4-PBA for treating DEEs, offering a potential breakthrough for this challenging condition.
Funding:
The work was supported by research grants from SLC6A1 Connect, and NIH R01 NS121718 to KJQ.