Purpose: Filgrastim, a recombinant human granulocyte colony-stimulating factor (rhG-CSF) produced
in Escherichia coli, is indicated for treatment of neutropenia-related conditions in cancer patients. It has been
marketed as Neupogen since 1991. In 2006, biosimilar rhG-CSF products have been approved in the European
Union (EU). The aim of this study was to compare quality attributes of the originator filgrastim with its three
biosimilars which came from the EU market in 2014 to verify whether their similarity is maintained since their
Materials/Methods: Spectrophotometric analysis was used to determine protein content in analyzed products.
Chromatographic and electrophoretic analyses were applied to verify the presence of high and low-molecular
weight impurities. Secondary and tertiary structure of the drugs were investigated with circular dichroism and
intrinsic fluorescence. Finally, biological activity of the drugs was assessed using cell proliferation assay.
Results: All products displayed protein content close to the label concentration with a ±6% variation. Two oxidized
forms and a deamidated form were present at <0.5%. Levels of dimers and other high molecular-weight
impurities were similar except for one product, which contained higher amount of the dimer. Profiles and levels
of process-related impurities were comparable. The three-dimensional conformation of the molecules with respect
to exposed tryptophan residues was similar. The relative potencies of the products were comparable to the reference
standard with a ±2% variation.
Conclusion: This study shows that a high level of similarity is maintained among originator and three biosimilar
filgrastims up to 5 years from their first registration in the EU.