Purpose: Following two cases of neutralizing antibodies to epoetin alfa in an investigational clinical study, a small number of individual syringes of two drug product batches were found to contain unusually high levels of aggregation at the end of the clinical trial.
Methods: We undertook an extensive analytical approach to determine the root-cause of the increased aggregation in the affected batches.
Results: Soluble tungsten was found in the syringes, most likely derived from the pins used to manufacture the syringes. Spiking of epoetin alfa with sodium polytungstate or an extract of tungsten pins used to manufacture the syringes induced the formation of aggregates, both dimers that appeared to be covalently linked by disulphide bonds as well as higher-order aggregates. Sodium polytungstate had also a strong denaturing effect on the protein.
Conclusions: We propose tungsten-mediated unfolding and aggregation of epoetin alfa in pre-filled syringes as a potential root cause for increased immunogenicity. This finding may be more broadly applicable to this and other classes of therapeutic proteins.