From genetically engineered rice cells, scientists have produced human beta-glucocerebrosidase (GCase) — the enzyme deficient in Gaucher disease — with some of the therapeutic properties of the treatment Cerezyme, a study reports.
The report, “Production of recombinant human acid β-glucosidase with high mannose-type N-glycans in rice gnt1 mutant for potential treatment of Gaucher disease,” was published in the journal Protein Expression and Purification.
Delivering healthy copies of the GCase enzyme — an approach called enzyme replacement therapy — is an effective treatment for Gaucher patients, helping to relieve symptoms and allowing most to live normal lives.
Currently, three approved ERTs exist for Gaucher disease, Sanofi’s Cerezyme, which is made from Chinese hamster ovary (CHO) cells, Pfizer’s Elelyso, which is made using carrot cells, and Vpriv by Shire (now Takeda), which is produced in a human fibroblast cell line.
In an approach known as molecular farming, plants are used as production systems or “factories” to create proteins in large quantities, including medicinal ones. Producing a target protein in plant cells growing in the lab can be cheaper and safer compared with using animal cells.
Plant cells and proteins can also be engineered to allow the desired proteins to be secreted to the outside of cells, making them easier to recover and purify.
There have been several attempts to express GCase in different plant species, including rice cells. However, normal rice cells are not the best for producing GCase with therapeutic properties, as they cannot guarantee that small sugar molecules, called mannoses, are exposed at the surface of the enzyme.
Mannose sugars are necessary for GCase to be processed by macrophages, the white blood cells most affected in Gaucher disease.
For instance, making Cerezyme involves the production of recombinant human GCase in CHO cells, followed by a process of sugar engineering called deglycosylation. In this particular case, deglycosylation consists of sequentially stripping out certain sugars from GCase to expose the mannose molecules. The introduction of this step was key to enhance the delivery of Cerezyme to macrophages.
In this study, researchers attempted to improve the production of a therapeutically suitable GCase in rice.
For that, they introduced the gene coding for a recombinant human GCase in rice cells that were genetically modified (gnt1 rice) to enhance the exposure of mannose sugars at the surface of proteins.
The strategy proved successful. A solution of genetically engineered gnt1 rice cells was able to produce and secrete the recombinant GCase enzyme, and the enzyme showed activity levels as high as the GCase produced in animal CHO cells, the same type of cells used to produce Cerezyme.
Noticeably, the results also confirm that the gnt1 rice-derived GCase presented a favorable pattern of sugars, with a high content of mannoses similar to that of Cerezyme, which “can help (in) targeting macrophages,” the researchers wrote.
Thus, rice-derived GCase “could be an alternative therapeutic for ERT Gaucher disease,” they concluded.