Inhalable bacteriophage powders: Glass transition temperature and bioactivity stabilization

Area of Science:

• Biotechnology
• Pharmaceutical Sciences
• Microbiology

Background:

• Inhaled bacteriophage (phage) therapy is gaining traction for treating pulmonary infections resistant to antibiotics.
• Phage powder formulations are being developed for inhalable delivery, but their stabilization mechanisms remain unclear.
• Proteins and biologics can be preserved in a dry, glassy matrix if storage temperatures are sufficiently below the glass transition temperature (Tg).

Purpose of the Study:

• To investigate the stabilization mechanism of bacteriophages in dry powder formulations for inhalation.
• To determine the critical temperature difference (Tg - Ts) required for phage stabilization in spray-dried powders.
• To validate the vitrification hypothesis for phage stabilization in pharmaceutical powders.

Main Methods:

• Spray-dried powders of Pseudomonas phage PEV20 with lactose and leucine were prepared.
• Powders were stored at various temperatures (5, 25, 50°C) and relative humidities (15%, 33%).
• Phage bioactivity (titer) and physical properties, including glass transition temperature (Tg), were assessed over time.

Main Results:

• Phage PEV20 remained stable at 5°C/15% RH for 250 days.
• Higher RH (33%) plasticized the matrix, lowering Tg and leading to significant phage titer loss at 5°C and 25°C.
• Optimal phage stability was observed when the difference between glass transition temperature and storage temperature (Tg - Ts) exceeded 46°C.

Conclusions:

• Phage stabilization in dry powders is achievable by maintaining a (Tg - Ts) value above 46°C, supporting the vitrification hypothesis.
• Phages are immobilized and protected within a rigid glassy sugar matrix, preventing inactivation.
• These findings offer guidance for manufacturing and storage of inhaled phage powder therapeutics.