Idursulfase is considered as a purified form of human iduronate-2-sulfatase, a lysosomal enzyme. This is an enzyme that hydrolyzes the 2-sulfate esters of iduronate sulfate. It has a molecular weight of approximately 76 kilodaltons and is a 525-amino acid glycoprotein. There are eight asparagine-linked glycosylation sites in complex oligosaccharide structures.
This drug is a product of recombinant DNA technology in a human cell line. Idursulfase activity is dependent on the post-translational change of cysteine to formylglycine. Idursulfase is designated to replace the natural enzyme that increases the catabolism of glycosaminoglycans that accumulates in the tissues of patients with mucopolysaccharidosis II (MPS-II, or Hunter syndrome). Hunter syndrome is an X-linked recessive disease that is caused by insufficient levels of the lysosomal enzyme iduronate-2-sulfatase. This enzyme changes the terminal 2-O-sulfate moieties of the glycosaminoglycans dermatan sulfate and heparan sulfate. The glucosaminoglycans progressively accumulate in the lysosomes of various cells, leading to cellular engorgement, organomegaly, tissue damage, and organ system malfunction. All these changes are due to the defective iduronate-2-sulfatase enzyme in patients with Hunter’s syndrome, and idursulfase serves as an exogenous enzyme for the uptake of glycosaminoglycans into cellular lysosomes.