Therapeutic efficacy of small molecules to treat channelopathies

UoM administered thesis: Phd

  • Authors:
  • Jingshu Liu

Abstract

Bestrophinopathies, including autosomal dominant Best vitelliform macular dystrophy (BVMD) and autosomal recessive bestrophinopathy (ARB), are inherited retinal disorders caused by variants in BEST1 gene that encoding bestrophin-1 protein, a Clchannel expressed in the retinal pigment epithelium. The aim of this study was to investigate the effect of small molecules on the expression and function of mutant proteins, using bestrophin-1 as an exemplar. Of nine test compounds, an FDA-approved drug sodium phenylbutyrate (4PBA) and its analogue 2- naphthoxyacetic acid sodium salt (2-NOAA) were able to increase the global and membrane expression of mutant bestrophin-1 associated with both BVMD and ARB either by enhancing protein stability or increasing protein synthesis respectively. Additionally, 4PBA and 2-NOAA restored the impaired channel function of mutant bestrophin-1 in both HEK293T cells and retinal pigment epithelium (RPE) generated from induced pluripotent stem cells (iPSC-RPEs) derived from patients with a dominant or recessive bestrophinopathy to a level comparable to wildtype bestrophin-1. The therapeutic potential of 4PBA and 2-NOAA was then supported by their effect on another protein, CLC5, a 2Cl-/H+ exchanger that is mutated in type 1 Dent disease. 4PBA and 2-NOAA rescued the function of non-Class I CLC5 mutants that could exit from the endoplasmic reticulum, but had no effect on the ER-retained Class I mutants, suggesting that the rescue effect depended on the degree of disruption of the protein structure. After demonstrating the feasibility of small molecules to rescue the function of two channelopathies, it is of value to identify more potent molecules. Therefore, a fluorescence-based assay was developed, which was able to detect the impaired channel function of mutant bestrophin-1 and recognise the rescue effect of 4PBA, making it a useful tool for further high-throughput compound screening. Given the time, cost and limited applicability associated with gene therapy, this study strengthens the notion that identifying novel small molecules (or analogues of existing drugs) to treat diseases caused by mutant protein misfolding/instability is a worthwhile alternative therapeutic strategy.

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Original languageEnglish
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Award date31 Dec 2020