Impact of crystalline and amorphous matrices on successful spray drying of siRNA polyplexes for inhalation of nano-in-microparticles

To develop stable and inhalable dry powder formulations with long shelf life, we spray dried polyplexes consisting of siRNA and a polyethylenimine based block copolymer in presence of mannitol or trehalose. We investigated the effect of inlet (T-In) and outlet (T-Out) temperature on the recovery of siRNA as well as adsorption effects within the tubing material. Choosing a low abrasion silicon tubing prevented siRNA loss due to adsorption. Mannitol and trehalose formulations preserved siRNA integrity regardless of excipient concentration and temperature at T-Out below the siRNA melting temperature. Trehalose formulations allowed full siRNA recovery whereas mannitol formulations resulted in spray drying induced losses of ~20 % siRNA and of 50-60 % polymer. Mannitol formulations showed optimal aerodynamic characteristics as confirmed by next generation impaction analysis based upon siRNA content. All spray dried formulations resulted in GFP silencing comparable or better than freshly prepared polyplexes. To test if the observed results could be transferred, formulations of siRNA and transferrin-PEI conjugates were spray dried, characterized and used to transfect primary human T cells ex vivo. Results confirmed successful silencing of the Th2 transcription factor GATA3 in primary CD4+ T cells with spray dried formulations as a potential treatment for severe asthma.

Freeze-drying of nanoparticles: How to overcome colloidal instability by formulation and process optimization

Lyophilization of nanoparticle (NP) suspensions is a promising technology to improve stability, especially during long-term storage, and offers new routes of administration in solid state. Although considered as a gentle drying process, freeze-drying is also known to cause several stresses leading to physical instability, e.g. aggregation, fusion, or content leakage. NPs are heterogeneous regarding their physico-chemical properties which renders them different in their sensitivity to lyophilization stress and upon storage. But still basic concepts can be deducted. We summarize basic colloidal stabilization mechanisms of NPs in the liquid and the dried state. Furthermore, we give information about stresses occurring during the freezing and the drying step of lyophilization. Subsequently, we review the most commonly investigated NP types including lipophilic, polymeric, or vesicular NPs regarding their particle properties, stabilization mechanisms in the liquid state, and important freeze-drying process, formulation and storage strategies. Finally, practical advice is provided to facilitate purposeful formulation and process development to achieve NP lyophilizates with high colloidal stability.

Powder suspensions in non-aqueous vehicles for delivery of therapeutic proteins

Formulating biopharmaceuticals is a challenging task due to their complex and sensitive nature. Protein drugs are typically marketed either as an aqueous solution or as a lyophilizate. Usually aqueous solutions are preferred as neither drying nor reconstitution are required. But it may be unfeasible if the protein features low stability. An interesting alternative to avoid at least reconstitution are protein powder suspensions in non-aqueous vehicles. Such formulations combine the ready-to-use approach with the high protein stability in the solid state. Additionally, protein powder suspensions offer a potentially lower viscosity compared to aqueous solutions at high protein concentrations. Besides injection, other application routes might also benefit from the protein powder approach such as topical or inhalational delivery. Protein powders, which can be dispersed in the non-aqueous suspension vehicle, are usually prepared by spray-drying or freeze-drying with an additional milling step, but other techniques have also been described in literature. An ideal powder preparation technique results in minimum protein damage and yields particle sizes in the lower micrometre range and homogeneous particle size distribution enabling subcutaneous or intramuscular injection through hypodermic needles. As suspension vehicles traditional non-aqueous injectable liquids, such as plant oils, may be selected. But they show an inherent high viscosity, which can lead to unacceptable glide forces during injection. Furthermore, the vehicle should provide high product stability with respect to protein integrity and suspension resuspendability. This review will describe how proteins can be formulated as protein powder suspensions in non-aqueous vehicles for subcutaneous injection including potential vehicles, protein powder preparation techniques, protein and suspension physical stability, as well as the use in the field of high concentration protein formulations.

Identification of monoclonal antibody variants involved in aggregate formation - Part 2: Hydrophobicity variants

Monoclonal antibodies (mAbs) are valuable tools both in therapy and in diagnostic. Their tendency to aggregate is a serious concern. Since a mAb drug substance (DS) is composed of different variants, it is important for manufacturers to know the behavior and stability not only of the mAb as a whole, but also of the variants contained in the product. We present a method to separate hydrophobicity variants of a mAb and subsequently analyzed these variants for stability and aggregation propensity. We identified a potentially aggregation prone hydrophilic variant which is interrelated with another previously identified aggregation prone acidic charge variant. Additionally, we assessed the risk posed by the aggregation prone variant to the DS by spiking hydrophobicity variants into DS and did not observe an enhanced aggregation propensity. Thus we present an approach to separate, characterize and analyze the criticality of aggregation prone variants in protein DS which is a step forward to further assure drug safety.

Process optimization and transfer of freeze-drying in nested vial systems

Scale-up and transfer of freeze-drying processes is a crucial challenge in biopharma industry. With the success of small batch processing lines utilizing rack vial holding systems, further detailed knowledge about freeze-drying cycles and their scale-up for vials in a rack is required. Therefore, product temperature (T_P) profiles as well as Kv values of vials nested in a Polyetheretherketon (PEEK) rack were compared to those of vials placed in a commonly used stainless steel tray. Additionally, both setups were challenged with varying fill volume and partially versus fully loaded rack. Additionally, a process developed for rack was compared to a tray freeze-drying cycle. Freeze-drying in vials placed in the rack is markedly faster for center vials and more homogeneous compared to vials in bulk tray setting, as indicated by T_P and Kv values. Due to the more homogeneous drying the rack is more flexible regarding variation of the fill volume. The key point for the transfer of a freeze-drying cycle from rack to tray is to consider the higher sublimation rates in the rack by adapting chamber pressure or shelf temperature for the tray. Furthermore, transfer from one rack per shelf in a laboratory freeze-dryer to pilot scale with four racks per shelf was successful. Thus, understanding of the process in rack and tray setup was enhanced to ensure efficient scale-up and transfer of freeze-drying processes.

Impact of chamber wall temperature on energy transfer during freeze-drying

Minimization of radiation coming from the chamber wall during lyophilization has the potential to reduce the edge-vial-effect. The edge-vial-effect is a phenomenon in which vials positioned at the shelf edges and corners tend to run warmer compared to center vials. A higher product temperature may result in product collapse in these vials. Consequently, more conservative and time-consuming freeze-drying cycles with lower shelf temperatures and pressures are chosen to ensure a product temperature below the collapse temperature in all vials. The edge-vial-effect is of even higher impact in small batches, where the ratio of corner and edge to center vials is higher compared to large scale manufacturing. The chamber wall is often discussed as the primary source of radiation impacting corner and edge vials. A radiation cage was set at different low temperatures to determine the impact of chamber wall temperatures below 0 °C on product temperature. At the end of primary drying, product temperature of corner vials could be reduced by 6 °C through the radiation cage but primary drying was elongated. Compared to vials in a tray, the chamber wall temperature had less impact on vials nested in a rack system due to a shielding effect of the rack itself. Corner and center vials ran more homogeneous with radiation cage since the edge and corner vials were slowed down. The difference in primary drying time between corner and center vials in the tray could be significantly reduced by 18% by means of 7 h when the radiation cage was controlled at product temperature and combined with a higher shelf temperature. In summary, the radiation cage is a useful tool for a more homogeneous batch with the potential to reduce primary drying time. Nevertheless, the drying difference between corner and center vials could only be reduced and was not completely eliminated.

The Influence of Arginine and Counter-Ions: Antibody Stability during Freeze-Drying

Amino acids, for example L-arginine, are used in lyophilisation as crystalline bulking, buffering, viscosity reducing or stabilising excipients. In this study, arginine was formulated with different counter ions (hydrochloride, citrate, lactobionate, phosphate, and succinate). A monoclonal antibody was investigated in sugar-free arginine formulations and mixtures with sucrose regarding cake appearance and protein aggregation and fragmentation. Arginine hydrochloride formulations collapsed during lyophilisation due to its low Tg' and partially crystallised during storage, but provided the best protein stability at low antibody concentration, followed by arginine succinate. Arginine citrate/phosphate/lactobionate formulations resulted in amorphous elegant cakes, but inferior protein stability. Addition of sucrose improved cake appearance and protein stability. Arginine phosphate with sucrose resulted in similar protein stability as the sucrose reference. Mixtures of sucrose with arginine hydrochloride/lactobionate/succinate provided better stability than sucrose alone. While 50 mg/mL antibody improved the cake appearance, only arginine lactobionate provided sufficient protein stability next to sucrose. Overall, sugar-free arginine hydrochloride and lactobionate lyophilisates stabilised the antibody comparably or better than sucrose depending on antibody concentration. The best protein stability was found for mixtures of arginine hydrochloride/lactobionate/succinate with sucrose.

Finding the Needle in the Haystack: High-Resolution Techniques for Characterization of Mixed Protein Particles Containing Shed Silicone Rubber Particles Generated During Pumping

During the manufacturing process of biopharmaceuticals, peristaltic pumps are employed at different stages for transferring and dosing of the final product. Commonly used silicone tubings are known for particle shedding from the inner tubing surface due to friction in the pump head. These nanometer sized silicone rubber particles could interfere with proteins. Until now, only mixed protein particles containing micrometer-sized contaminations such as silicone oil have been characterized, detected, and quantified. To overcome the detection limits in particle sizes of contaminants, this study aimed for the definite identification of protein particles containing nanometer sized silicone particles in qualitative and quantitative manner. The mixed particles consisted of silicone rubber particles either coated with a protein monolayer or embedded into protein aggregates. Confocal Raman microscopy allows label free chemical identification of components and 3D particle imaging. Labeling the tubing enables high-resolution imaging via confocal laser scanning microscopy and counting of mixed particles via Imaging Flow Cytometry. Overall, these methods allow the detection and identification of particles of unknown origin and composition and could be a forensic tool for solving problems with contaminations during processing of biopharmaceuticals.

Freeze concentration during freezing: How does the maximally freeze concentrated solution influence protein stability?

During freeze drying of biologics, a highly viscous freeze concentrate (FC) is formed upon the initial freezing due to the crystallisation of ice. Protein stability in this freeze concentrated phase is not yet well understood, but can decide upon the success of the lyophilisation itself. Protein stability may be high below the T_g' as it is typically the case during primary drying but decreases above T_g', e.g. during annealing or during aggressive freeze drying above T_g' in presence of a crystalline bulking agent or, beyond freeze drying, during storage of frozen bulk. Different FCs containing monoclonal antibody, sucrose, histidine or phosphate buffer and sodium chloride were prepared via partial freeze drying and analysed for protein aggregation. No solute crystallisation is visible and the systems are vitrifying during cooling. Increasing sugar or buffer concentration showed positive effects on either melting and aggregation temperature or on protein self-interaction as indicated by A₂ values. Protein integrity in the FC was not affected by 1 month storage at temperatures above T_g'. Thus, upconcentration of solutes during freezing does not negatively impact protein stability. Exceeding T_g' during freeze drying e.g. upon annealing or, intentionally or unintentionally, during primary drying does not lead to protein aggregation.

Trouble With the Neighbor During Freeze-Drying: Rivalry About Energy

Batch homogeneity during lyophilization is crucial to ensure products with high quality. Known as edge-vial-effect, vials at the corners and edges tend to run warmer than center vials during primary drying. This is associated with risk of collapse or increased costs due to use of more conservative, longer drying conditions resulting in lower product temperature. The edge-vial-effect has been attributed to radiation coming from the chamber wall. We could show that the neighbor vial has a dominant impact on product temperature during lyophilization. Depending on the number of neighbors as well as the distance to a neighbor vial, the neighbor vial exerts a remarkable cooling effect. Energy transfer by gas conduction enables the cooling effect of a neighboring vial over a distance up to 10 mm. This not only leads to prolonged primary drying but also impacts cake appearance. Thus, to avoid trouble during lyophilization you have to watch out for the neighborhood.

Method development and analysis of the water content of the maximally freeze concentrated solution suitable for protein lyophilisation

During freeze-drying of a liquid formulation, a freeze-concentrate is formed in the first phase, the freezing step. Understanding the composition of the maximally freeze concentrated solution can help to judge the process stability of biopharmaceuticals during lyophilisation. Our objective was to develop a suitable method to determine the water content of the maximally freeze concentrated solution using differential scanning calorimetry (DSC). Three different methods were compared: (i) the intercept of the glass transition temperature of the maximally freeze concentrated solution T_g' and the melting temperature T_m for a concentration series, (ii) the linear regression of the melting enthalpy starting from the onset of T_g' until the end of the melting event for a concentration series, and (iii) a one-point determination of the amount of unfrozen water. While Method 1 is accurate but requires the analysis of a high number of samples, Method 3 requires only one single sample, with a loss of accuracy. Method 2 works best taking sample preparation and accuracy into account. Various systems containing sugar (sucrose, trehalose) and other excipients (histidine buffer, phosphate buffer, sodium chloride, arginine hydrochloride, arginine citrate) were evaluated with different antibody concentrations to evaluate the composition of the maximally freeze concentrated solution. The freeze concentrates exhibited a water content of 20-30%, slightly dependent on the excipients, but independent of the antibody concentration. The methodology we developed is broadly applicable for the analysis of the composition of maximally freeze concentrated solutions and can help to elucidate protein stability during lyophilisation.

Excipients for Room Temperature Stable Freeze-Dried Monoclonal Antibody Formulations

Sucrose is a common cryoprotectant and lyoprotectant to stabilize labile biopharmaceuticals during freeze-drying and storage. Sucrose-based formulations require low primary drying temperatures to avoid collapse and monoclonal antibody (mAb) containing products need to be stored refrigerated. The objective of this study is to investigate different excipients enabling storage at room temperature and aggressive, shorter lyophilization cycles. We studied combinations of 2-hydroxypropyl-beta-cyclodextrin (CD), recombinant human albumin, polyvinylpyrroldione (PVP), dextran 40 kDa (Dex), and sucrose (Suc) using 2 mAbs. Samples were characterized for collapse temperature (Tc), glass transition temperature of the liquid (Tg') and freeze-dried formulation (Tg), cake appearance, residual moisture, and reconstitution time. Freeze-dried formulations were stored at 5°C, 25°C, and 40°C for up to 9 months and mAb stability was analyzed for color, turbidity, visible and sub-visible particles, and monomer content. Formulations with CD/Suc or CD/PVP/Suc were superior to pure Suc formulations for long-term storage at 40°C. When using aggressive freeze-drying cycles, these formulations were characterized by pharmaceutically elegant cakes, short reconstitution times, higher Tg', Tc, and Tg. We conclude that the addition of CD allows for shorter freeze-drying cycles with improved cake appearance and enables storage at room temperature, which might reduce costs of goods substantially.

Be Aggressive! Amorphous Excipients Enabling Single-Step Freeze-Drying of Monoclonal Antibody Formulations

Short freeze-drying cycles for biopharmaceuticals are desirable. Formulations containing an amorphous disaccharide, such as sucrose, are prone to collapse upon aggressive primary drying at higher shelf temperature. We used 2-hydroxypropyl-betacyclodextrin (HPBCD) in combination with sucrose and polyvinylpyrrolidone (PVP) to develop an aggressive lyophilization cycle for low concentration monoclonal antibody (mAb) formulations. Glass transition temperature and collapse temperature of the formulations were determined, and increasingly aggressive cycle parameters were applied. Using a shelf temperature of +30 °C during primary drying, the concept of combining sublimation and desorption of water in a single drying step was investigated. Cake appearance was evaluated visually and by micro-computed tomography. Lyophilisates were further analyzed for reconstitution time, specific surface area, residual moisture, and glass transition temperature. We demonstrated the applicability of single-step freeze-drying, shortening the total cycle time by 50% and providing elegant lyophilisates for pure HPBCD and HPBCD/sucrose formulations. HPBCD/PVP/sucrose showed minor dents, while good mAb stability at 10 mg/mL was obtained for HPBCD/sucrose and HPBCD/PVP/sucrose when stored at 40 °C for 3 months. We conclude that HPBCD-based formulations in combination with sucrose are highly attractive, enabling aggressive, single-step freeze-drying of low concentration mAb formulations, while maintaining elegant lyophilisates and ensuring protein stability at the same time.

Lyophilization of Synthetic Gene Carriers

Lyophilization, also known as freeze drying, is a widely used method for stabilization, improvement of long-term storage stability, and simplification of handling of drugs and/or carrier systems. Lyophilization is time-consuming and energy-consuming, and hence optimized processes are required to avoid time loss and higher costs without compromising product stability. Beginning from the last decade, nonviral, synthetic carriers for gene delivery have been of increasing interest. However, these systems suffer from poor physical stability in aqueous solution or suspension. Hence, to ensure long-term storage stability lyophilization of the gene carrier systems is favored. This chapter gives an overview of the basic steps and troubleshooting for successful lyophilization of synthetic gene carriers. Furthermore, the required excipients and their mechanism of action are summarized.

Comparison of ice fog methods and monitoring of controlled nucleation success after freeze-drying

Improving freeze-drying processes regarding drying time and batch homogeneity is subject of ongoing research work. In this context, controlled nucleation raised great expectations. However, practically we face some challenges, e.g. how to non-destructively monitor successfully performed controlled nucleation. The question if different controlled nucleation methods lead to comparable products, as not every method can easily be implemented in lab and production scale equipment, is also of high interest. Additionally, the optimal nucleation temperature for controlled nucleation is an open question. In our study, we addressed these challenges. We successfully evaluated frequency modulated spectroscopy as a fast and non-destructive method to monitor controlled nucleation success and batch homogeneity. We found that the better homogeneity generated by controlled nucleation during the freezing step did not sustain in the dried product. Lyophilizates produced by three different ice fog methods for controlled nucleation were characterized by comparable specific surface areas but differed in residual moisture content. To investigate the impact of the ice nucleation temperature (T_N) on the resulting specific surface area, we performed controlled nucleation at -3 °C and -10 °C. We concluded that T_N is not the only specific surface area determining factor and a high T_N does not necessarily lead to larger pores but poses a higher risk of not-nucleating vials.