Li Lily Qu

Background: Protein‑based therapeutics represent a substantial fraction of FDA‑approved biologics, and the continued expansion of protein modalities has increased the demand for effective stabilization strategies. Although solid‑state protein formulations generally offer superior storage stability compared to liquid formulations, drying processes such as lyophilization, spray drying, and spray freeze‑drying can introduce significant physical and chemical stresses that compromise protein stability. Area covered: This review focuses on the role of high‑molecular‑weight polymeric excipients in the solid‑state stabilization of protein‑based injectable formulations. It discusses common sources of instability introduced during drying and long‑term storage, while summarizing and highlighting the growing interest in polymeric excipients as stabilizers. Mechanisms by which polymeric excipients enhance protein stability including amorphous matrix formation, reduced molecular mobility, and surface‑active protection against interfacial stresses are discussed. The regulatory status of polymeric excipients currently used in FDA‑approved injectables versus investigational materials is also considered. Expert opinion: Polymeric excipients offer unique advantages for solid-state protein stabilization and may complement or surpass traditional low-molecular-weight stabilizers when rationally selected. However, broader adoption will require improved mechanistic understanding, careful consideration of excipient–protein interactions, and alignment with regulatory expectations. Continued development and systematic evaluation of polymeric excipients are expected to expand formulation design options and improve the stability and performance of next-generation protein therapeutics.

Spray-freeze drying (SFD) is a promising drying technique for stabilizing RNA lipid nanoparticles (RNA-LNPs) by converting them into solid-state formulatio

Subcutaneous administration has become an increasingly important route for delivering protein therapeutics, driven by patient convenience and the growing use of self-administration devices. However, conventional subcutaneous injection systems are typically limited to injection volumes of approximately 1–2 mL, posing significant formulation challenges for protein drugs requiring high therapeutic doses. Monoclonal antibodies (mAbs), for example, often require concentrations exceeding 100 mg/mL to enable subcutaneous delivery, which introduces challenges related to limited solubility, elevated viscosity, and an increased risk of physical and chemical instability. Therefore, high-concentration protein suspensions have emerged as a promising formulation strategy to overcome these limitations and enable subcutaneous administration of high-dose proteins. In such systems, therapeutic protein solid particles are suspended in vehicles in which they are insoluble, giving rise to unique considerations related to particle properties, protein stability, and suspension behaviors such as viscosity, injectability, and sedimentation. Accordingly, multiple particle production approaches have been explored to enable the development of ultra-high-concentration protein suspensions (>200 mg/mL). This review article aims to provide a comprehensive overview of particle formation techniques and the relationships between key particle properties and suspension performance attributes relevant to the development of high-concentration protein suspensions for injectable applications, as well as future directions in this field.

Purpose: Drying is widely used to enhance the storage stability of biologic drug products which are susceptible to degradation in aqueous solutions. Compared to conventional freeze-drying, spray drying offers continuous, high-throughput manufacturing. Stabilizing excipients are critical for protecting proteins from stresses during drying and storage. This study evaluated the potential of polysaccharide- and protein-lysate–based polymeric excipients as alternatives to commonly used stabilizers such as trehalose and mannitol, using bovine serum albumin (BSA) as a model protein. Methods: Spray-dried BSA formulations were prepared with (2-hydroxypropyl)-β-cyclodextrin (HPβCD), hydrolyzed gelatin, dextran 20 kDa, or sodium carboxymethyl cellulose (NaCMC) polymers, either alone or in combination with trehalose or mannitol. Protein stability was assessed by monitoring monomer loss under stressed storage (40°C, 3 months). Crystallinity and changes in the secondary structure were analyzed using powder X-ray diffraction (PXRD) and solid-state Fourier transform infrared spectroscopy (ssFTIR), respectively. Particle size and size distribution, surface morphology and reconstitution time were also evaluated. Results: Spray-dried BSA formulations containing HPβCD or hydrolyzed gelatin, either alone or with sugars, exhibited lower monomer loss than the trehalose- or mannitol-only formulations. In contrast, formulations with Dextran 20 kDa and NaCMC showed poor stability. PXRD revealed progressive sodium chloride crystallization during storage. ssFTIR detected secondary structure changes in the BSA over 3 months. The spray-dried powders with polysaccharides generally showed longer reconstitution times than those with polymers. Conclusion: HPβCD and hydrolyzed gelatin improved the physical stability of spray-dried BSA compared to sugar excipients, which highlights their potential use as stabilizing additives.

The development of dry powder inhalers (DPIs) is challenging due to the need for micronized particles to achieve lung delivery. The high specific surface area of micronized particles renders them cohesive and adhesive. Addition of certain excipients like magnesium stearate has been reported to coat the particles and improve the aerosolization in the carrier-based DPI. Therefore, application of particle coating in DPI developments has been investigated and expanded over the years, along with the growing need of high-dose carrier-free DPIs. In addition to modifying inter-particulate forces, particle coating has also been demonstrated to effectively provide moisture resistance, modify particle morphology, improve the stability of biologics, alter dissolution behaviors for DPI developments. These different coating functions have been discussed in the current work. Moreover, various coating techniques including solvent-based coating, dry coating, and vapor coating, as well as coating characterization have been summarized in the present review. The extent of particle coating is critical to DPI performance; however, there is a demand for advanced characterization techniques to quantify and understand the coating quality. Further advancements in coating materials, methods, characterization techniques are needed to better relate coating properties to performance, especially for complex drug modalities.

Background: Pseudomonas aeruginosa is one of the major pathogens that cause respiratory infections. The rise of antimicrobial resistance has prompted a need for alternatives to conventional antibiotics. Bacteriophages (phages), natural predators of bacteria, are gaining interest as an alternative therapeutic option against drug-resistant infections. However, phage viability can be lost during manufacturing and delivery. Recent studies show that phages can be taken up by lung epithelial cells, which makes fewer phages available for antibacterial action against extracellular bacteria P. aeruginosa in the airways. Methods: In this study, we encapsulated phages in liposomes using thin film hydration. The effect of processing conditions and phage loading titer on the phage encapsulation and viability was studied. The impact of nebulization on phage viability was tested using an air-jet nebulizer (PARI-LC Plus). Phage cellular uptake was evaluated using an in vitro H441 lung epithelial cell model, grown at the air–liquid interface. Results: Our results demonstrate favorable encapsulation (58 ± 6.02%) can be achieved with minimum loss in phage titer (0.64 ± 0.21 log) by using a low phage titer for hydration. The liposomal formulations exhibited controlled release of phages over 10 h. The formulation also reduced the loss of phage viability during nebulization from 1.55 ± 0.04 log (for phage suspension) to 1.08 ± 0.05 log (for phage liposomes). Encapsulation of phages in liposomes enabled a two-fold reduction in phage cellular uptake and longer extracellular phage retention in the human lung epithelial cell monolayer. Conclusions: Our results indicate that liposomal encapsulation favors phage protection and improves phage availability for antibacterial activity. These findings highlight the potential of liposomes for inhaled phage delivery.

Background/Objective: Surface enrichment of hydrophobic excipients via spray drying has been demonstrated as an efficient way to protect the dry powder inhaler formulations against moisture-induced deterioration in aerosol performance. However, the impact of such surface enrichment on dissolution and cellular uptake is less investigated, which can affect the safety and efficacy of dry powder inhalers (DPIs). Methods: In the present work, hygroscopic colistin was coated with leucine or trileucine, at different weight ratios during spray drying. All the powders were exposed to 75% relative humidity for one week. The aerosol performance was compared before and after the moisture exposure. Various solid-state characterizations, including particle size, particle morphology, crystallinity, water sorption/desorption, and surface composition, were conducted to evaluate the properties of spray-dried colistin with/without leucine or trileucine. Results: The results indicated that leucine or trileucine could protect the aerosol performance of spray-dried colistin against moisture deterioration. Leucine crystallized after spray drying with colistin, and such crystal leucine could further hinder water uptake when leucine was at a 20% or higher weight ratio. Trileucine did not crystallize after spray drying with colistin nor reduce the water uptake. Interestingly, trileucine showed a superior moisture protective effect to that of leucine, which could be attributed to its better surface enrichment efficiency than that of leucine due to its lower water solubility. Conclusions: Importantly, our results showed that the surface enrichment with leucine and trileucine did not significantly affect in vitro dissolution of colistin in the Franz cell test and cellular uptake of colistin in the H441 lung epithelium cell model, which could be attributed to small particle size and incomplete surface coverage by leucine or trileucine.