Chemical enhancement of torsinA function in cell and animal models of torsion dystonia

Abstract

SUMMARYMovement disorders represent a significant societal burden for which therapeutic options are limited and focused on treating disease symptomality. Early-onset torsion dystonia (EOTD) is one such disorder characterized by sustained and involuntary muscle contractions that frequently cause repetitive movements or abnormal postures. Transmitted in an autosomal dominant manner with reduced penetrance, EOTD is caused in most cases by the deletion of a glutamic acid (DE) in the DYT1 (also known as TOR1A) gene product, torsinA. Although some patients respond well to anticholingerics, therapy is primarily limited to either neurosurgery or chemodenervation. As mutant torsinA (DE) expression results in decreased torsinA function, therapeutic strategies directed toward enhancement of wild-type (WT) torsinA activity in patients who are heterozygous for mutant DYT1 may restore normal cellular functionality. Here, we report results from the first-ever screen for candidate small molecule therapeutics for EOTD, using multiple activity-based readouts for torsinA function in Caenorhabditis elegans, subsequent validation in human DYT1 patient fibroblasts, and behavioral rescue in a mouse model of DYT1 dystonia. We exploited the nematode to rapidly discern chemical effectors of torsinA and identified two classes of antibiotics, quinolones and aminopenicillins, which enhance WT torsinA activity in two separate in vivo assays. Representative molecules were assayed in EOTD patient fibroblasts for improvements in torsinA-dependent secretory function, which was improved significantly by ampicillin. Furthermore, a behavioral defect associated with an EOTD mouse knock-in model was also rescued following administration of ampicillin. These combined data indicate that specific small molecules that enhance torsinA activity represent a promising new approach toward therapeutic development for EOTD, and potentially for other diseases involving the processing of mutant proteins.

Designing Clinical Trials for Dystonia

“…Another strategy for identifying novel drugs for dystonia involves screening drugs in animal models of dystonia. A high-throughput screen conducted in a Caenorhabditis elegans model of DYT1 dystonia has revealed potential agents for further study, such as ampicillin [23]. Other promising agents have been identified through pharmacological studies of rodent models of dystonia, including the dystonic dt sz hamster and tottering mouse models [6,24].…”

Invertebrate Models of Dystonia

“…In this regard, overexpression of C. elegans TOR-2 or human torsinA can reduce protein aggregation resulting from polyglutamine repeats (Fig. 3A-C) or α-synuclein in vivo [65,79,80]. Overexpression of human torsinA in H4 neuroglioma cells expressing α-synuclein also display significantly reduced protein aggregation [81].…”

A Predictable Worm: Application of Caenorhabditis elegans for Mechanistic Investigation of Movement Disorders

“…A survey of a few worm-to-cell culture translational studies reveals wide ranging fold Ethosuximide 2 mg/ml 30 μg/ml 66X [52] differences between these experimental systems, wherein 0.5× to 160× chemical was used in the C. elegans studies (Table 3). It should be noted, however, that in most of these studies, only a single concentration of chemical was examined in either the worm or cell culture experiments [26,45,54]. Thus, it is likely that the minimum fold difference required for a biological response is not accurately represented in these studies, nor was it the goal for the cited literature.…”

“…This advantage of C. elegans research can also facilitate systematic drug discovery efforts in distinct genetic backgrounds. Cao et al [54] reported results of a C. elegans-based small molecule screen to identify compounds that modulate the chaperone-like activity of torsinA. Using multiple transgenic lines and thousands of animals, molecules that selectively altered the activity of WT versus ΔE torsinA with statistically substantial effect could be delineated; this facilitated prioritization for downstream experimentation in mammalian models.…”

“…Strikingly, one compound, ampicillin, was shown to restore functional capacity of torsinA to human DYT1 dystonia patient fibroblasts defective in protein processing. Administration of this drug also reversed behavioral abnormalities in a DYT1 knock-in mouse model of EOTD [54,75]. Although an antibiotic is not ideal for chronic dosing regimens in dystonia, the identification of a compound that selectively modifies torsinA activity across multiple cellular and organismal models represents a significant molecular lead toward novel treatment alternatives.…”