Stabilisierung von rekombinantem Mistellektin durch Gefriertrocknung
The aim of this thesis was to develop a lyophilized aviscumine formulation (recombinant mistletoe lectin from Viscum album L.) with adequate shelf life stability. To gain insight into the stabilizing mechanism during the freezing and drying step of the lyophilization process a variety of excipients in different concentrations, crystallinity and water content of the dried product were investigated. At first, the behavior of variable bulk solutions during freezing was characterized. Rapid freezing and the use of “biological” buffer substances like TRIS, HEPES, and Tricin resulted in a pH shift into the alkaline region. Buffer solutions containing the amorphous solidifying excipients dextran, hydroxypropyl-beta-cyclodextrin (HP-beta-CD) or hydroxyethystarch maintained the adjusted pH value down to a temperature of –10 °C. The freeze drying of aviscumine required a combination of different excipients such as surfactants in low concentrations (by preference Polysorbate 80) and a buffer system. The most important excipient in the bulk solution was one of the lyoprotectants dextran, HES or HP-beta-CD showing a stabilizing effect depending on the concentration. The failure of dextrans in stabilizing proteins as reported in literature is attributed to utilizing a high molecular weight dextran as a lyoprotector. In contrast to these earlier findings, our results showed a successful stabilization of aviscumine with low molecular weight dextran. Finally, a shelf life stability of 52 weeks could be obtained with a formulation containing TRIS/HCl, Polysorbate 80 and dextran, HES or HP-beta-CD when stored at temperatures between 2 and 8 °C.