Scientists at UF Scripps Biomedical Research have developed a potential drug for a leading cause of ALS and dementia that works by eliminating disease-causing segments of RNA. The compound restored the health of neurons in the lab and saved mice with the disease.
The potential drug is described this week in the scientific journal Proceedings of the National Academy of Sciences. It is designed to be taken as a pill or injection, said lead inventor Professor Matthew Disney, Ph.D., 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 hurdle that other approaches have failed to overcome, he said.
Amyotrophic lateral sclerosis, or ALS, progressively destroys the neurons that control muscles, leading to worsening muscle wasting and eventually death. The mutation leading to hereditary ALS is called “C9 open reading frame 72” or C9orf72. This mutation also leads to one form of frontotemporal dementia, a brain disease that causes the frontal and temporal lobes of the brain to shrink, leading to changes in personality, behavior and speech that eventually lead to death.
The C9orf72 mutation involves an expanded repeat of six “letters” of the genetic code, GGGGCC, on chromosome 9, which can be duplicated between 65 and tens of thousands of times. When this mutated stretch of RNA is present, it leads to the production of toxic proteins that sicken and eventually kill the affected neurons. The compound developed by Disney’s lab targets the RNA carrying these genetic instructions, thereby preventing the toxic proteins from assembling in cells.
“The compound works by binding to and using natural cellular processes to eliminate this disease-causing RNA by alerting the cell’s degrading machinery to discard it as waste,” Disney said.
This approach could work for other incurable neurological diseases where toxic RNA plays a role, he added.
The paper’s first author is Jessica Bush, a graduate student at the Skaggs Graduate School of Chemical and Biological Sciences at UF Scripps who works in the Disney lab. Other co-authors include Leonard Petrucelli, Ph.D., of the Mayo Clinic in Jacksonville, and Raphael Benamu, a former postdoctoral researcher in the Disney lab who is now on the faculty of the Hebrew University of Jerusalem.
“This was identified from a large screen of compounds from the Calibr library at Scripps Research, which consists of 11,000 drug-like molecules,” Bush said.
From this initial screen, they identified 69 compounds that inhibited translation of the toxic C9 mutation. They then further refined the compounds by eliminating those that could not cross the blood-brain barrier based on size, weight, structure and other factors. This resulted in 16 candidate compounds, one of which was selected for further refinement based on its efficacy and structural simplicity.
“A battery of tests in neurons obtained from ALS patients and in vivo models showed that compound 1 binds selectively and avidly to the toxic RNA, forcing it to be degraded by the body’s own natural processes,” Bush said.
Patients treated for ALS at the Johns Hopkins University Laboratory for Neurodegenerative Research donated skin samples for research purposes. These skin cells were genetically engineered into stem cells, then the Disney team treated the cells for several months to develop into neurons.
“Four different patient cells were used for the evaluation, all of which showed a dose-dependent reduction in known ALS markers while having no adverse effects,” Bush said.
They also tested the compound in mice bred to have the C9orf72 mutation and show behavior and blood markers typical of ALS. The mice were treated daily for two weeks, after which the mice showed significantly reduced disease markers and improved health.
The next steps will be to further study the compound’s effects on cellular health and rodent models of C9 ALS, Disney said. The evidence so far shows 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 create brain-penetrating molecules that eliminate toxic gene products,” Disney said. “The fact that we 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-penetrating RNA-targeted small molecule induces elimination of r(G4C2)exp in c9ALS/FTD via the nuclear RNA exosome,” appears in this week’s Proceedings of the National Academy of Sciences. 21, 2022. Authors include Samantha M. Meyer, Rita Furst, Yuquan Tong, Yue Li, Haruo Aikawa, Patrick R.A. Zanon, Quentin M.R. Gibeau, Alicia Angelbello, Tanya Gendron, Yong-Jie Zhang, Torben Heik 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); the Nelson Family Fund (of MDD); The First Family Fund (of MDD); and a Scheller Graduate Student Fellowship (to SMM). Statement of Competing Interest: MDD is the founder of Expansion Therapeutics.