The global EPO drugs market is likely to reach US $11.9 Billion by 2020. Rising cases of cancer, renal disease and HIV have increased the demand for these drugs, with EPO continuing to be one of the best-selling biopharmaceutical products worldwide. A number of EPO biosimilars are already on the market with more in development.
Darbepoetin (DPO) is a modified form of EPO containing a number of amino acid changes and two additional N-linked glycosylation sites. DPO has a 3-fold longer serum half-life compared to EPO and stimulates erythropoiesis (increases red blood cell levels) by the same mechanism.
Biosimilar Characterization Considerations
The guidelines state that characterization of Erythropoietin products should include determination of physicochemical and structural properties, purity, impurities and quantity in line with ICH Topic Q6B:
- Primary (de novo) Amino Acid Sequence
- Amino Acid Composition
- Terminal Amino Acid Sequence
- Peptide Map
- Disulfide Bridges
- Carbohydrate Structure
- Secondary and Tertiary Structure
Product Specific Technical Considerations
The analysis of glycosylation is important when analyzing EPO and DPO. As requested in the ICH guidelines (Topic Q6B), the carbohydrate content (neutral sugars, amino sugars and sialic acids) should be determined. In addition, the structure of the carbohydrate chains, the oligosaccharide pattern (antennary profile), the glycosylation site(s) and occupancy should be analyzed.
EPO has three N-glycosylation sites at Asn24, Asn38 and Asn83 and one O-linked site at Ser126. DPO has an additional two N-linked glycosylation sites at Asn residues 30 and 86.
Glycan structures should be characterized and particular attention should be paid to their degree of sialylation, the glycans present at each of the sites and the degree of glycosylation at each site (glycosylation site occupancy).