Developing Bivalent Ligands to Target CUG Triplet Repeats, the Causative Agent of Myotonic Dystrophy Type 1

Abstract

An expanded CUG repeat transcript (CUGexp) is the causative agent of myotonic dystrophy type 1 (DM1) by sequestering muscleblind-like 1 protein (MBNL1), a regulator of alternative splicing. Based on a ligand (1) that was previously reported to be active in an in vitro assay, we present the synthesis of a small library containing ten dimeric ligands (4-13) that differ in length, composition and attachment point of the linking chain. The oligoamino linkers gave a greater gain in affinity for CUG RNA and were more effective when compared to oligoether linkers. The most potent in vitro ligand (9) was shown to be aqueous-soluble and both cell- and nucleus-permeable displaying almost complete dispersion of MBNL1 ribonuclear foci in a DM1 cell model. Direct evidence for the bioactivity of 9 was observed in its ability to disperse ribonuclear foci in individual live DM1 model cells using time-lapse confocal fluorescence microscopy.

Modeling ALS and FTD with iPSC-derived neurons

“…Another challenge for ASO-based approach is to develop highly efficient delivery of ASO into brain and spinal cord. Considering these obstacles, small molecule inhibitors that aim at disrupting specific RNA-protein interactions might circumvent the technical challenges confronting ASO-based therapy and be more effective in releasing endogenous proteins from the gain-of-function properties of RNA repeats (Arambula et al, 2009; Jahromi et al, 2013; Warf et al, 2009). In this context, C9ORF72 iPSC-derived neurons should serve as effective tools to screen for small molecule inhibitors.…”

RNA Structures as Mediators of Neurological Diseases and as Drug Targets

“…Several key advances have pushed the RNA-targeting field forward including those in RNA structural biology, structure-based approaches including modeling of dynamic ensembles, and identification of RNA-binding modules (Batey et al, 2004; Childs-Disney et al, 2014; Davidson et al, 2009; Disney, 2013; Disney et al, 2014; Gallego and Varani, 2001; Jahromi et al, 2013a; Lee et al, 2010; Montange and Batey, 2006; Ofori et al, 2012; Palde et al, 2010; Parkesh et al, 2011; Shortridge and Varani, 2015; Stelzer et al, 2011; Trausch et al, 2011; Yildirim et al, 2013). High-resolution structures of ribosomes and other RNA-protein complexes combined with modeling of RNA dynamics have enabled structure-based approaches to develop new antibiotics and antivirals.…”

“…Finally, phase I and II clinical trials of a gapmer targeting mutant DMPK mRNA has been recently initiated (Isis Pharmaceuticals, 2014). A number of small molecule probes have also been developed for targeting r(CUG) exp that displace MBNL1 and improve downstream defects (Arambula et al, 2009; Childs-Disney et al, 2012a, 2012b, 2013; Hoskins et al, 2014; Jahromi et al, 2013a, 2013b; Parkesh et al, 2012). These compounds were either identified from screening, designed from the structure of r(CUG) repeats, or designed from privileged RNA motif-small molecule interactions including modularly assembled compounds thereof.…”

RNA–protein interactions in unstable microsatellite diseases

“…However, effective gene delivery and expression in multiple tissues poses a major technical challenge. Another therapeutic strategy is to deploy small molecule inhibitors of specific protein-RNA interactions to release endogenous RNA binding proteins from toxic repeat RNAs (Arambula et al, 2009; Jahromi et al, 2013; Warf et al, 2009). However, a potential problem with this approach is the possibility that altering these protein-RNA interactions may result in more deleterious effects, possibly due to enhanced RAN translation (Childs-Disney et al, 2013).…”