Studies on Stable Formulations for a Hydrophobic Cytokine

The goal of the thesis was to analyze the impact of the formulation
conditions on the stabilization of a hydrophobic cytokine. A
standard way to formulate the cytokine at physiological pH is using
Human Serum Albumin (HSA) as excipient. Based on a lyophilized
formulation with mannitol as bulking agent and HSA as stabilizer
analogous to commercially available systems, the impact of
HSA-stabilizers, NaCl and pH on particle formation and stability of
the cytokine in the liquid state was elucidated. As NaCl can impact
the freezing and lyophilization behavior, the impact of NaCl on the
behavior of mannitol-HSA placebo mixtures based on the cytokine-HSA
formulations was studied. The goal was to understand how freezing,
lyophilization and a subsequent storage of the formulations are
influenced by NaCl and the HSA-stabilizers. The use of HSA as
excipient is related to the risk of blood born pathogens, enhanced
immunogenicity, as well as to analytical difficulties. Therefore,
approaches to replace HSA in the cytokine formulation and to
achieve stable HSA-free formulations were developed. For the
lyophilized formulations HSA was replaced by sucrose as amorphous
stabilizer and the physico-chemical properties of the system
mannitol–sucrose during freezing and lyophilization were analyzed.
To achieve a stable HSA-free formulation, cytokine adsorption and
its low solubility were the major issues that had to be overcome.
Overall, it was feasible to stabilize the cytokine without the use
of HSA at low pH as liquid and lyophilized formulation. By using
glass type I+ vials, respectively adding polysorbate 20 it was
possible to minimize protein adsorption. Thus, the studies provided
an extensive characterization of the hydrophobic cytokine, its
stabilization with HSA and the pH dependent instability of
HSA-containing systems. As an alternative a stable HSA-free
formulation for the cytokine could be presented. Especially for the
lyophilized formulations it could be shown that subtle changes of
excipients e.g. in the NaCl content can have a detrimental impact.