First molecular therapeutic for Angelman syndrome to advance into clinical trials

The scientists from Texas A&M have developed GTX-102, a novel therapeutic candidate to target Angelman syndrome by reactivating expression of deficient protein.

Karyotype of Angelman syndrome, labelled 3D illustration. A genetic disorder caused by a lack of function of part of chromosome 15 inherited from a person's mother

Researchers from Texas A&M School of Veterinary Medicine and Biomedical Sciences’ (VMBS), US, have published an article where they share the process in which they developed a novel therapeutic candidate, also known as 4.4.PS.L, or GTX-102 to target Angelman syndrome (AS). The ground-breaking study was recently published in Science Translational Medicine.

AS is a devastating, rare neurogenetic disorder that triggered by a loss of function of the maternal UBE3A gene in the brain, causing developmental delay, absent speech, movement or balance disorder, and seizures. There are no approved therapies for AS, and the current standard of care is focused on behavioural therapy and controlling specific symptoms, specifically the seizures that often affect patients with AS.

In healthy individuals, the copy of the UBE3A maternal gene is expressed in the brain and the copy of the UBE3A paternal gene is turned off by another gene, called the UBE3A antisense (UBE3A-AS) transcript. Individuals living with AS have mutations that affect the expression or function of the maternal copy of UBE3A and, as a result, they lack the UBE3A protein in their brain. The team, therefore, began their research looking for a way to prevent the silencing of the paternal UBE3A gene and reactivate expression of the deficient protein.

In their research, the researchers used different genomic approaches to understand how the UBE3A-AS transcript is regulated in the brain. Their work uncovered a previously unknown region in UBE3A-AS that they believe represents the ancestral origin of the gene in mammals. They also believe this region plays a key role in regulating the expression of UBE3A-AS.

“Parts of this region have remained unchanged for over 30 million years,” Dr Scott Dindot reported. “The UBE3A-AS transcript is an incredibly complex gene. What it is and how it is regulated has been debated for years.”

The team then developed antisense oligonucleotides (ASOs) — small synthetic molecules comprising DNA and RNA — to target the conserved region in the UBE3A-AS transcript. ASO drugs work by binding to a target RNA and cutting it, causing the gene to stop making the RNA.

The team found that ASOs targeting the conserved region effectively turned off UBE3A-AS, which, in turn, reactivated the expression of the paternal UBE3A allele. The studies show that the ASOs reactivated the expression of the paternal UBE3A allele and increased UBE3A protein in cultured neurons from individuals with AS.

As a result of this research, Dindot developed the lead compound referred to as GTX-102, which is now in clinical development.

“We used a novel approach to designing the ASOs, targeting a very specific part of a gene rather than just giving a drug to treat a symptom,” Dindot said. “In theory, this treatment goes after the heart of the condition.”

Interim data from a Phase I/II clinical trial of GTX-102 in the US, UK and Canada have previously indicated that the compound has demonstrated “meaningful improvement” in paediatric patients afflicted with AS.

“Moving forward, our research and findings not only offer promise for AS but also provide a path forward for developing ASO therapies for other genetic disorders,” Dindot concluded.

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