# Development of small molecule chemical probes to study r(G4C2)exp pathomechanisms

> **NIH NIH P01** · SCRIPPS FLORIDA · 2020 · $259,425

## Abstract

PROJECT SUMMARY 
 Frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) are linked by clinical, 
neuropathological and genetic overlap1. It was recently discovered that a G4C2 repeat expansion in 
C9ORF72 is the most common genetic cause of FTD and ALS (“c9FTD/ALS”)2, 3. A growing body of 
evidence suggesting that repeat-containing RNA [r(G4C2)exp or r(G2C4)exp], which is bidirectionally 
transcribed from the C9ORF72 expansion, is a key player in c9FTD/ALS pathogenesis14. Currently, 
there are no effective treatments for FTD or ALS, in part because of an incomplete understanding of 
the causative pathological mechanisms. Herein we propose to develop small molecule chemical 
probes of r(G4C2)exp and r(G2C4)exp (dys)function to study repeat biology, thereby identifying the most 
therapeutically relevant targets and pathways to treat c9FTD/ALS. Indeed, this grant application 
brings forward novel and innovative chemical approaches to develop highly selective chemical probes 
that target RNA, to validate the RNA targets of small molecules (with Core B), to study cellular 
selectivity (with Core B), and to image RNA in cellular systems. Not only will our findings benefit 
c9FTD/ALS patients, they will have broad implications for many microsatellite expansion diseases. 
 Our proposed studies are enabled by our recently reported studies in which we discovered three 
compounds that bind r(G4C2)exp in cells and significantly inhibit two modes of RNA toxicity (generation 
of toxic proteins via repeat-associated non-ATG (RAN) translation and formation of foci) in 
c9FTD/ALS in cells over-expressing r(G4C2)66 and induced neurons (iNeurons) directly converted 
from fibroblasts of C9ORF72 repeat expansion carriers12. In particular, we will: (i) lead optimize our 
previously identified compounds in collaboration with Core B; (ii) define features in small molecules 
that provide an ideal chemical probe of repeat (dys)function; and (iii) use our chemical probes to 
uncover the underlying pathophysiology of the c9FTD/ALS repeat expansion, including the 
mechanism of RAN translation, identification of all proteins sequestered in foci, and studying defects 
in nucleocytoplasmic transport of C9ORF72 by imaging the RNA in its natural context with small 
molecule probes (Core B). 
 Our studies are highly synergistic with Project 2 (development of biomarkers against c9RAN 
proteins and studying pathophysiology in a recently developed mouse model of c9ALS/FTD13) and 
Project 3 (abnormalities in nuclear pores and transport caused by the c9FTD/ALS repeat expansion). 
Indeed, our optimal chemical probes will be provided to Profs. Petrucelli, Gendron, & Rothstein to 
augment their studies.

## Key facts

- **NIH application ID:** 9962905
- **Project number:** 5P01NS099114-04
- **Recipient organization:** SCRIPPS FLORIDA
- **Principal Investigator:** Matthew D Disney
- **Activity code:** P01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $259,425
- **Award type:** 5
- **Project period:** — → —

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9962905

## Citation

> US National Institutes of Health, RePORTER application 9962905, Development of small molecule chemical probes to study r(G4C2)exp pathomechanisms (5P01NS099114-04). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9962905. Licensed CC0.

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