Thin-Film Freeze-Drying Is a Viable Method to Convert Vaccines Containing Aluminum Salts from Liquid to Dry Powder

Feasibility of intranasal delivery of thin-film freeze-dried, mucoadhesive vaccine powders

Intranasal vaccination by directly applying a vaccine dry powder is appealing. However, a method that can be used to transform a vaccine from a liquid to a dry powder and a device that can be used to administer the powder to the desired region(s) of the nasal cavity are critical for successful intranasal vaccination. In the present study, using a model vaccine that contains liposomal monophosphoryl lipid A and QS-21 adjuvant (AdjLMQ) and ovalbumin (OVA) as a model antigen, it was shown that thin-film freeze-drying can be applied to convert the liquid vaccine containing sucrose at a sucrose to lipid ratio of 15:1 (w/w) into dry powders, in the presence or absence of carboxymethyl cellulose sodium salt (CMC) as a mucoadhesive agent. Ultimately, the thin-film freeze-dried AdjLMQ/OVA vaccine powder containing 1.9% (w/w) of CMC (i.e., TFF AdjLMQ/OVA/CMC_1.9% powder) was selected for additional evaluation because the TFF AdjLMQ/OVA/CMC_1.9% powder was mucoadhesive and maintained the integrity of the antigen and the physical properties of the vaccine. Compared to the TFF AdjLMQ/OVA powder that did not contain CMC, the TFF AdjLMQ/OVA/CMC_1.9% powder had a lower moisture content and a higher glass transition temperature. In addition, the TFF AdjLMQ/OVA/CMC_1.9% thin films were relatively thicker than the TFF AdjLMQ/OVA thin films without CMC. When sprayed with Aptar Pharma's Unidose Powder Nasal Spray System (UDSP), the TFF AdjLMQ/OVA powder and the TFF AdjLMQ/OVA/CMC_1.9% powder generated similar particle size distribution curves, spray patterns, and plume geometries. Importantly, after the TFF AdjLMQ/OVA/CMC_1.9% powder was sprayed with the UDSP nasal device, the integrity of the OVA antigen and the AdjLMQ liposomes did not change. Finally, a Taguchi L4 orthogonal array was applied to identify the optimal parameters for using the UDSP device to deliver the TFF AdjLMQ/OVA/CMC_1.9% vaccine powder to the middle and lower turbinate and the nasopharynx regions in both adult and child nasal replica casts. Results from this study showed that it is feasible to apply the TFF technology to transform a nasal vaccine candidate from liquid to a dry powder and then use the UDSP nasal device to deliver the TFF vaccine powder to the desired regions in the nasal cavity for intranasal vaccination.

Aerosolizable Plasmid DNA Dry Powders Engineered by Thin-film Freezing

PURPOSE

This study was designed to test the feasibility of using thin-film freezing (TFF) to prepare aerosolizable dry powders of plasmid DNA (pDNA) for pulmonary delivery.

METHODS

Dry powders of pDNA formulated with mannitol/leucine (70/30, w/w) with various drug loadings, solid contents, and solvents were prepared using TFF, their aerosol properties (i.e., mass median aerodynamic diameter (MMAD) and fine particle fraction (FPF)) were determined, and selected powders were used for further characterization.

RESULTS

Of the nine dry powders prepared, their MMAD values were about 1-2 µm, with FPF values (delivered) of 40-80%. The aerosol properties of the powders were inversely correlated with the pDNA loading and the solid content in the pDNA solution before TFF. Powders prepared with Tris-EDTA buffer or cosolvents (i.e., 1,4-dioxane or tert-butanol in water), instead of water, showed slightly reduced aerosol properties. Ultimately, powders prepared with pDNA loading at 5% (w/w), 0.25% of solid content, with or without Tris-EDTA were selected for further characterization due to their overall good aerosol performance. The pDNA powders exhibited a porous matrix structure, with a moisture content of < 2% (w/w). Agarose gel electrophoresis confirmed the chemical integrity of the pDNA after it was subjected to TFF and after the TFF powder was actuated. A cell transfection study confirmed that the activity of the pDNA did not change after it was subjected to TFF.

CONCLUSION

It is feasible to use TFF to produce aerosolizable pDNA dry powder for pulmonary delivery, while preserving the integrity and activity of the pDNA.

Aggregation of Lactoferrin Caused by Droplet Atomization Process via a Two-Fluid Nozzle: The Detrimental Effect of Air-Water Interfaces

Biological macromolecules, especially therapeutic proteins, are delicate and highly sensitive to denaturation from stresses encountered during the manufacture of dosage forms. Thin-film freeze-drying (TFFD) and spray freeze-drying (SFD) are two processes used to convert liquid forms of protein into dry powders. In the production of inhalable dry powders that contain proteins, these potential stressors fall into three categories based on their occurrence during the primary steps of the process: (1) droplet formation (e.g., the mechanism of droplet formation, including spray atomization), (2) freezing, and (3) frozen water removal (e.g., sublimation). This study compares the droplet formation mechanism used in TFFD and SFD by investigating the effects of spraying on the stability of proteins, using lactoferrin as a model. This study considers various perspectives on the denaturation (e.g., conformation) of lactoferrin after subjecting the protein solution to the atomization process using a pneumatic two-fluid nozzle (employed in SFD) or a low-shear drop application through the nozzle. The surface activity of lactoferrin was examined to explore the interfacial adsorption tendency, diffusion, and denaturation process. Subsequently, this study also investigates the secondary and tertiary structure of lactoferrin and the quantification of monomers, oligomers, and, ultimately, aggregates. The spraying process affected the tertiary structure more negatively than the tightly woven secondary structure, resulting in the peak position corresponding to the tryptophan (Trp) residues red-shifting by 1.5 nm. This conformational change can either (a) be reversed at low concentrations via relaxation or (b) proceed to form irreversible aggregates at higher concentrations. Interestingly, when the sample was allowed to progress into micrometer-sized aggregates, such a dramatic change was not detected using methods such as size-exclusion chromatography, polyacrylamide gel electrophoresis, and dynamic light scattering at 173°. A more complete understanding of the heterogeneous protein sample was achieved only through a combination of 173 and 13° backward and forward scattering, a combination of derived count rate measurements, and microflow imaging (MFI). After studying the impact of droplet formation mechanisms on aggregation tendency of lactoferrin, we further investigated two additional model proteins with different surface activity: bovine IgG (serving as a non surface-active negative reference), and β-galactosidase (another surface-active protein). The results corroborated the lactoferrin findings that spray-atomization-related stress-induced protein aggregation was much more pronounced for proteins that are surface active (lactoferrin and β-galactosidase), but it was minimal for non-surface-active protein (bovine IgG). Finally, compared to the low-shear dripping used in the TFFD process, lactoferrin underwent a relatively fast conformational change upon exposure to the high air-water interface of the two-fluid atomization nozzle used in the SFD process as compared to the low shear dripping used in the TFFD process. The interfacial-induced denaturation that occurred during spraying was governed primarily by the size of the atomized droplets, regardless of the duration of exposure to air. The percentage of denatured protein population and associated activity loss, in the case of β-galactosidase, was determined to range from 2 to 10% depending on the air-flow rate of the spraying process.

Development of (Inhalable) Dry Powder Formulations of AS01B-Containing Vaccines Using Thin-Film Freeze-Drying

AS01_B is a liposomal formulation of two immunostimulants namely 3-O-desacyl-4́-monophosphoryl lipid A (MPL) and QS-21. The liposomal formulation of AS01_B reduces the endotoxicity of MPL and the lytic activity of QS-21. The AS01_B-adjuvanted Shingrix vaccine is marketed in a two-vial presentation, with the liquid AS01_B liposomes in one vial and the antigen as a dry powder in another vial. In the present study, we tested the feasibility of applying thin-film freeze-drying (TFFD) to engineer dry powders of the AS01_B liposomal adjuvant alone or vaccines containing AS01_B as an adjuvant. Initially, we showed that after the AS01_B liposomal adjuvant was subjected to TFFD using sucrose as a stabilizer at 4% w/v, the particle size distribution of AS01_B liposomes reconstituted from the dry powder was identical to the liquid adjuvant before drying. We then showed using ovalbumin (OVA) as a model antigen adjuvanted with AS01_B (AS01_B/OVA) that subjecting the AS01_B/OVA vaccine to TFFD and subsequent reconstitution did not negatively affect the AS01_B liposome particle size, nor the immunogenicity of the vaccine. Importantly, the thin-film freeze-dried AS01_B/OVA vaccine, unlike its liquid counterpart, was not sensitive to repeated freezing-and-thawing. The developed AS01_B/OVA dry powder also showed the desirable aerosol properties (i.e., fine particle fraction of 66.3 ± 4.9% and mass median aerodynamic diameter of 2.4 ± 0.1 µm) for potential pulmonary administration. Finally, the feasibility of using TFFD to prepare dry powders of AS01_B-adjuvanted vaccines was further confirmed using AS01_B-adjuvanted Fluzone Quadrivalent and Shingrix, which contains AS01_B. It is concluded that the TFFD technology can enable the formulation of AS01_B-adjuvanted vaccines as freezing-insensitive, inhalable dry powders in a single-vial presentation.

Development of thermostable vaccine adjuvants

INTRODUCTION

The importance of vaccine thermostability has been discussed in the literature. Nevertheless, the challenge of developing thermostable vaccine adjuvants has sometimes not received appropriate emphasis. Adjuvants comprise an expansive range of particulate and molecular compositions, requiring innovative thermostable formulation and process development approaches.

AREAS COVERED

Reports on efforts to develop thermostable adjuvant-containing vaccines have increased in recent years, and substantial progress has been made in enhancing the stability of the major classes of adjuvants. This narrative review summarizes the current status of thermostable vaccine adjuvant development and looks forward to the next potential developments in the field.

EXPERT OPINION

As adjuvant-containing vaccines become more widely used, the unique challenges associated with developing thermostable adjuvant formulations merit increased attention. In particular, more focused efforts are needed to translate promising proof-of-concept technologies and formulations into clinical products.

Next-Generation COVID-19 Vaccines Should Take Efficiency of Distribution into Consideration

The dire need for safe and effective coronavirus disease (COVID-19) vaccines is met with many vaccine candidates being evaluated in pre-clinical and clinical studies. The COVID-19 vaccine candidates currently in phase 3 or phase 2/3 clinical trials as well as those that recently received emergency use authorization (EUA) from the United States Food and Drug Administration (FDA) and/or other regulatory agencies worldwide require either cold (i.e., 2–8°C) or even freezing temperatures as low as −70°C for storage and distribution. Thus, existing cold chain will struggle to support both the standard national immunization programs and COVID-19 vaccination. The requirement for cold chain is now a major challenge towards worldwide rapid mass vaccination against COVID-19. In this commentary, we stress that thermostabilizing technologies are available to enable cold chain-free vaccine storage and distribution, as well as potential needle-free vaccination. Significant efforts on thermostabilizing technologies must now be applied on next-generation COVID-19 vaccines for more cost-effective worldwide mass vaccination and COVID-19 eradication.