Deferoxamine, a medication normally used to remove excess iron and aluminum from the body, can counteract the effects of a disease-causing genetic variant often found in people with late-onset Pompe disease (LOPD).
These findings highlight the potential of drug repurposing for the development of new therapies for LOPD, scientists said.
The study, titled “Deferoxamine mesylate improves splicing and GAA activity of the common c.-32-13T>G allele in late-onset PD patient fibroblasts” and conducted by a team of Italian researchers, was published in the journal Molecular Therapy Methods & Clinical Development.
Pompe disease is caused by mutations in the GAA gene, which provides instructions for making an enzyme called acid alpha-glucosidase (GAA) that is responsible for the breakdown of a sugar molecule called glycogen. Without GAA, glycogen starts accumulating inside cells until it reaches toxic levels, impairing certain organs and systems.
Enzyme replacement therapy (ERT), a form of treatment in which patients are provided with a man-made form of the enzyme they are missing, is the only therapy currently approved for Pompe.
“Although most of the studies on ERT support its efficacy in improving survival of PD [Pompe disease] patients, long-term follow-up studies have shown that ERT does not completely prevent disease progression,” the researchers wrote.
In addition, it’s been found that not all patients respond well to ERT and that skeletal muscles — one of the tissues most affected by the disease — often fail to respond to the therapy, as compared with other tissues in the body. These findings suggest that new approaches are needed for treating Pompe, the scientists said.
To date, nearly 600 genetic variants have been identified in the GAA gene. One disease-causing variant, known as c.-32-13T>G, has been found to be particularly prevalent among patients with LOPD, in which symptoms begin later in life, during childhood or adulthood.
Because this disease-causing variant is known to affect the splicing of the GAA messenger RNA (mRNA), therapies that are able to restore this process may possibly be explored as alternative treatments to ERT in people carrying these variants.
Notably, mRNA is the molecule created from a gene that cells use as a template to produce the protein encoded by that gene. Splicing, meanwhile, is the process by which certain non-coding genetic sequences, called introns, are removed from the final mRNA sequence that will be used for protein production.
Now, investigators in Italy sought to identify new treatment candidates that could restore mRNA splicing from GAA. The team performed a screening of 1,280 compounds approved by the U.S Food and Drug Administration. More specifically, they were looking for compounds that would prevent the gene’s second exon from being wrongly discarded. Of note, exons are portions of gene sequences that contain instructions to make a protein.
To identify which compounds might prevent the loss of this second exon, the investigators used a splicing assay in which cells would emit a green fluorescent signal every time the exon was discarded in the final mRNA molecule. No fluorescence would be emitted when this portion of the gene was included in that final molecule.
Using this method, the researchers identified several compounds that were able to restore splicing. The three most promising candidates were then tested in fibroblasts or connective tissue cells derived from people with LOPD who carried the c.-32-13T>G variant.
Of all three compounds, deferoxamine was the only one with a significant effect on patients’ cells.
After treating patient-derived fibroblasts with deferoxamine, the investigators found that the compound increased the inclusion of the gene’s second exon by twofold, and GAA’s enzymatic activity by nearly 40%.
According to the team, and based on preliminary experiments, deferoxamine’s effects on GAA splicing were mediated, at least partially, by its effects on iron availability.
“This work provides the bases for drug repurposing and development of new chemically modified molecules aimed at improving the clinical outcome in LO-PD patients,” the researchers wrote.
However, the use of deferoxamine in a clinical setting should be carefully considered, the team noted, as the effects of the medication in patients who do not have excessively high iron levels might not be recommended.
“Nevertheless, our work provides the basis for the development of more potent chemically modified molecules, which either alone or in combination with ERT could improve the clinical outcome in LO-PD patients carrying the c.-32-13T>G variant,” they wrote.
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