Abstract

Protein powder suspensions in non-aqueous vehicles provide an interesting alternative to conventional formulations such as aqueous solutions and lyophilizates and potentially feature a variety of advantages for different applications. Besides powder manufacturing, vehicle selection is key for such preparations. Powders for the use in such formulations can be prepared in several ways including milling of lyophilizates and spray-drying. Chapter III aimed to get a deeper understanding on how milling of model monoclonal antibody (mAb) lyophilizates can be used as a technique to generate protein powders for suspensions in non-aqueous vehicles. It was of interest, if wet media milling can yield protein powder suspensions without damage to the protein. An alternative is dry milling in absence of a suspension vehicle. The chapter aimed to identify critical process parameters and to optimize the milling process. Studied process parameters included the milling ball size, milling frequency, ball to powder mass ratio, milling duration as well as application of cooling. Furthermore, it was tested whether excipients or the protein to stabilizer ratio influence protein stability during milling. With the obtained powder, suspensions were prepared and their viscosities and glide forces were tested. Highly concentrated protein formulations currently play an important role in the pharmaceutical industry, but face different challenges such as decreased protein stability and increased glide forces needed for injection. Protein powder suspensions in non-aqueous vehicles may represent a beneficial alternative and can yield low viscosity formulations depending on the selected suspension vehicle. Traditionally used non-aqueous liquids for injection, such as vegetable oils, are not suitable for high concentration suspension formulations due to their high inherent viscosity. Consequently, low viscosity alternatives are of particular interest. Thus, the goal of Chapter IV was to test various potential vehicles regarding their ability to yield high concentration low viscosity formulations. Promising candidates included semifluorinated alkanes (SFAs), due to their low viscosity, good biocompatibility and inertness towards biopharmaceuticals. In contrary to the previous chapter, spray-drying was used to prepare the protein powder. It was of interest how SFA based suspensions perform with regard to rheology and injection characteristics compared to aqueous solutions. In order to select a suitable syringe design, prediction of glide forces using mathematical models and equations was evaluated. Finally, with commercial manufacturability in mind, the feasibility of the vial filling process of the developed suspensions, using a peristaltic pump, was tested and evaluated. Chapter V provides more detailed insight into long term physical suspension stability of lysozyme, mAb and bevacizumab powder suspensions in different suspension vehicles including SFAs, medium chain triglycerides (MCT) and ethyl oleate (EO). Physical suspension stability includes resuspendability, particle size constancy and injectability. Both excipients and the protein to stabilizer ratio might influence the stability. Furthermore, the application of an additional drying step was tested to improve the physical suspension stability. Suspensions were stored in vials, as well as in prefillable syringes, which provide easier administration. Not only suspension physical stability, but also protein stability has to be maintained over storage time. In the case of protein powder suspensions in non-aqueous vehicles, protein instabilities can have two different causes. First the inherent stability of the powder has to be considered. Secondly, the influence of the suspension vehicle on protein stability might play a role. The focus of Chapter VI lied on the influence of different potential vehicles and powder compositions on protein stability in non-aqueous powder suspensions. For this purpose, stability of a mAb and bevacizumab in SFAs, MCT and EO were studied. Combined with investigations on suspension physical stability this chapter should give valuable information on the applicability of the non-aqueous powder suspension approach for protein formulations. Besides subcutaneous injection, topical ocular protein delivery to the cornea is of interest, especially after the recent approval of a protein drug for the treatment of neurotrophic keratitis. This application route faces poor drug penetration and short residence time as important challenges. In Chapter VII formulations for improved corneal protein delivery based on protein powder suspensions in non-aqueous vehicles, considering the addition of penetration enhancers, were investigated. A main focus lied on the performance of protein powder suspension in SFAs, as previous investigations on topical ocular delivery of small molecule drugs in SFAs showed promising results. The overall goal of the thesis was to study the various opportunities of powder suspensions in non-aqueous vehicles for protein formulation with a focus on SFAs. The various chapters present pathways for successfully developing, characterizing and manufacturing such preparations, which may provide superior suspension and protein stability also at high protein concentration.