Scientists at UF Scripps Biomedical Research have developed a potential drug for ALS and a leading cause of dementia that works by eliminating disease-causing segments of RNA. The compound restored the health of neurons in the lab and protected mice from disease.
The potential drug is described this week in the scientific journal Proceedings of the National Academy of Sciences. It’s designed to be taken as a pill or injection, said lead inventor, Professor Matthew Disney, PhD, chair of the UF Scripps Department of Chemistry. Importantly, the experiments showed that the compound is small enough to cross the blood-brain barrier, a barrier other approaches have failed to clear, he said.
Amyotrophic lateral sclerosis, or ALS, progressively destroys the neurons that control muscles, leading to muscle loss and eventually death. The mutation, a major cause of inherited ALS, is known as “C9 open reading frame 72,” or C9orf72. This mutation also leads to a form of frontotemporal dementia, a brain disease that causes the frontal and temporal lobes of the brain to shrink, resulting in changes in personality, behavior, and speech, eventually resulting in death.
The C9orf72 mutation has an expanded repeat of the six “letters” of the genetic code, GGGGCC, on chromosome 9, which can be repeated between 65 and tens of thousands of times. When this mutated stretch of RNA is present, it results in the production of toxic proteins that sicken and eventually kill affected neurons. The compound developed by Disney’s lab targets the RNA carrying those genetic instructions, thus preventing toxic proteins from assembling in cells.
“The compound works by binding to natural cellular processes and alerting the cell’s degradation machinery to eliminate disease-causing RNA to dispose of it as waste,” Disney said.
He said this approach could work for other untreatable neurological diseases in which toxic RNAs play a role.
The paper’s first author is Jessica Bush, a graduate student in the Skaggs Graduate School of Chemical and Biological Sciences at UF Scripps who works in Disney’s lab. Other co-authors include Leonard Petrucelli, PhD, of the Mayo Clinic in Jacksonville, and Raphael Benhamou, a former Disney Lab postdoctoral researcher on the faculty of the Hebrew University of Jerusalem.
“It was identified from a large screen of compounds from the Caliber library at Scripps Research, which includes 11,000 drug-like molecules,” Bush said.
From that initial screen, they identified 69 compounds that inhibited translation of the toxic C9 mutation. They then refined the compounds based on size, weight, structure and other factors, eliminating compounds that could not cross the blood-brain barrier. This resulted in 16 candidate compounds, one of which was selected for further refinement based on its potency and structural simplicity.
“A battery of tests in neurons derived from ALS patients and in vivo models showed that compound 1 binds selectively and toxically to RNA, allowing it to be degraded by the body’s own natural processes,” said Bush. “
Patients being treated for ALS donated skin samples for research purposes at the Johns Hopkins University School of Medicine’s Laboratory for Neurodegenerative Research. These skin cells were genetically modified into stem cells, after which Disney’s team treated the cells for several months to develop them into neurons.
“Cells from four different patients were used for the evaluation, all of which showed a dose-dependent reduction in known ALS markers, while there were no off-target effects,” Bush said.
They tested the compound in mice bred for the C9orf72 mutation and showing behavioral and blood markers typical of ALS. The mice were treated daily for two weeks, after which the mice displayed significantly reduced markers of disease and improved health.
Disney said the next steps will be to study the compound’s effects on cellular health and rodent models of C9 ALS. The evidence so far suggests that this approach represents a remarkable advance in the field of RNA drug discovery, he said.
“We show for the first time that you can make brain-penetrating molecules that can eliminate toxic gene products,” Disney said. “The fact that we have highlighted this in ALS indicates that this may be a general approach for other neurological diseases, including Huntington’s, forms of muscular dystrophy and others.”
The study, “A blood-brain penetrant RNA-targeted small molecule nuclear RNA triggers elimination of r(G4C2) exp in c9ALS/FTD via exosomes,” appears in the week of November 21 in Proceedings of the National Academy of Sciences Is. 2022. In addition to Disney, Bush, Petrucelli and Benhamou, authors include Samantha M. Mayer, Rita Fuerst, Yuquan Tong, Yu Li, Haruo Aikawa, Patrick RA Zanon, Quentin MR Gibout, Alicia Angelabello, Tania Gendron, Yong-Ji Zhang, Torben Hick Jensen and Jessica Childs-Disney.
This study was funded by the National Institutes of Health, (NIH P01 NS099114 to MDD and LP; DP1 NS096898 and R35 NS116846 to MDD; and R35 NS097273 to LP); target ALS (to MDD); Nelson Family Fund (to MDD); First Family Fund (to MDD); and the Scheler Graduate Student Fellowship (to SMM). Competitive Interest Description: MDD is the founder of Expansion Therapeutics.