Optimized versions of Gal A enzyme may pave way to better treatments
Modified enzymes last longer in bloodstream, show better activity in tissues
Scientists have engineered versions of the alpha-galactosidase A (Gal A) enzyme that could eventually be used to produce a more stable and effective enzyme replacement therapy (ERT) for Fabry disease.
In animal models, the modified enzymes lasted longer in the bloodstream and showed better activity in target tissues like the heart and kidneys. In cell cultures, they demonstrated they may be less likely to evoke an immune response against Gal A that can reduce a person’s responsiveness to treatment.
Although more long-term research is still needed, scientists say the enzymes could possibly “address the therapeutic shortcomings of [Gal A] for the treatment of Fabry disease,” with the potential ability to “reduce the dosing frequency or increase the efficacy for an enzyme replacement therapy.”
The study, “Optimizing human α-galactosidase for treatment of Fabry disease,” was published in the journal Scientific Reports.
Two ERTs currently approved for Fabry
In Fabry disease, mutations in the GLAÂ gene result in little or no production of functional Gal A, which is responsible for breaking down certain fatty molecules inside cells.
Consequently, these molecules, namely globotriaosylceramide (Gb3) and lyso-Gb3, build to toxic levels and cause organ damage.
ERT is a mainstay treatment that works by providing patients with a lab-made version of the Gal A enzyme they lack. There are currently two approved ERTs — Sanofi’s Fabrazyme and Takeda’s Replagal — both of which have shown to slow disease progression.
However, existing ERTs are cleared rapidly from the bloodstream, meaning patients require frequent into-the-vein infusions, and even still may experience significant symptoms. This rapid clearance may mean that the treatments don’t get to key target tissues like the heart and kidneys, researchers suggested.
Moreover, for patients who lack their own GLA enzyme, their immune system may launch an attack against the therapy, rendering it less effective.
In the study, the scientists looked for ways of modifying the Gal A protein sequence to improve its performance. Essentially, they introduced different mutations to the GLA gene that would produce various working versions of the protein.
After screening more than 12,000 of them in yeast and cell cultures, the team identified two in particular that might be able to increase Gal A’s stability and lessen the risk of immune responses.
One version, GLAv05, housed 11 mutations that differed from the typical enzyme, and the other, GLAv09, had 17 mutations. Both were found to be more stable than standard Gal A.
In human blood samples, each modified enzyme retained more than 90% of its activity after 24 hours, whereas standard Gal A retained less than 10% activity in the same window.
GLAv09 also exhibited significantly higher enzyme activity in cells from Fabry patients, with a 19-fold higher activity than Gal A after a week that corresponded to a 10-fold greater reduction in Gb3 buildup.
The benefits of GLAv05 weren’t as robust, suggesting its cellular uptake may be impaired relative to GLAv09, the researchers suggested.
Overall, the increased stability and cellular uptake of the modified enzymes translated to sustained enzyme activity in animals.
Findings support future development of GLAv05 and GLAv09
A single into-the-vein-infusion of either modified version of the enzyme in mice or non-human primates led to measurable enzyme in the bloodstream for 6-8 hours, compared with Gal A, which rapidly decreased in concentration over 1-2 hours.
Both GLAv05 and GLAv09 showed increased activity in the heart and liver of a Fabry mouse model relative to Fabrazyme a week after dosing, which corresponded to a reduction in Gb3 for GLAv09. In the kidneys, all three versions of the enzyme showed similar profiles.
Using human immune cell cultures, the researchers found that GLAv05 and GLAv09 may be able to reduce or at least lead to similar anti-GLA immune responses relative to the standard enzyme.
Together, the findings “suggest favorable properties for GLAv05 and GLAv09 as compared to [Gal A] and support their development as next-generation therapies for the treatment of Fabry disease,” the researchers wrote.
The stability of GLAv05 and GLAv09 compare favorably with PRX-102 (pegunigalsidase alfa), an experimental ERT, although PRX-102 lasts longer in the bloodstream, according to the researchers.
PRX-102 is currently under regulatory review in the U.S. and Europe.
“Future studies directly comparing these enzymes would be helpful toward understanding how these parameters may impact tissue distribution and efficacy,” the researchers added.
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