Synthetic molecules were able to increase frataxin protein levels in cells taken from Friedreich’s ataxia patients to levels near those found in cells of healthy people, results of an early study, reported at IARC 2017, showed.
The presentation, by David Corey at the University of Texas Southwestern, was titled “Activation of Frataxin expression by duplex RNAs and antisense oligonucleotides,” and was part of Session 4: Therapeutics and Clinical Trials on Friday at IARC. The International Ataxia Research Conference continues in Pisa, Italy, through Saturday.
Friedreich’s ataxia is caused by a mutation in the gene coding for a mitochondrial protein called frataxin. This genetic mutation is an expansion of a GAA trinucleotide repeat that causes a severe reduction in frataxin protein levels. Increasing the levels of this protein is a goal of investigational efforts at treating the disease.
Previous studies suggest that the expanded GAA repeats interfere with the transcription step, i.e., with the formation of the RNA messenger molecule based on the DNA information encoded in the frataxin gene, information that serves as a template for producing the frataxin protein. This problem in transcription is thought to occur because a structure called R-loop forms between the RNA molecule and its complementary DNA molecule.
Researchers came up with a plan to synthesize molecules that can recognize the expanded GAA trinucleotide repeats, and activate the transcription of the frataxin gene.
They investigated two types of synthetic nucleic acid molecules: anti-GAA duplex RNAs, and antisense oligonucleotides that are called single-stranded locked nucleic acid (LNAs) antisense oligonucleotides.
According to Corey, duplex RNAs and antisense oligonucleotides targeting expanded repeats have been used successfully in other medical conditions, including Huntington’s disease, Machado-Joseph disease, and amyotrophic lateral sclerosis (ALS).
Now, researchers showed that both — duplex RNAs and antisense oligonucleotides — were capable of blocking R-loop formation in Friedreich’s ataxia patient-derived cells, allowing for transcription and restoring the levels of frataxin protein.
“Blocking R-loop formation can increase FXN [frataxin] expression,” Corey said in the presentation.
The researcher also emphasized that both antisense oligonucleotides and duplex RNAs were shown to activate FXN expression in multiple patient-derived cells.
Studies are underway to investigate if it is possible to make these synthetic molecules and activation more potent.
“Current studies are focusing on exploring how chemical modifications affect the potency of activation. We are also examining the potency of activation in patient-derived cell lines that contain diverse numbers of mutant repeats,” the researchers wrote.
Their goal is to identify the best compounds that might be put to early testing in further preclinical studies.
The team also plans to evaluate the “biodistribution, efficacy, and toxicity data” of their synthethic molecules in animals.
Priority tasks, said Corey, are to “evaluate toxicity in animals (if toxic no/go)” and to “evaluate efficacy in ex vivo human models.” If the molecules are well-tolerated and preclinical studies successful, then clinical trials can be considered.