Developing resistance among bacteria towards all the available antibiotics makes the clinical treatment of infections more serious and difficult. Alternative therapy is required to control the dissemination of antibiotic-resistant bacterial infections. Bacteriophage use has potential as alternative therapy to antibiotic treatment, hence the renewed scientific interest in its clinical applications. There is a wide range of animal studies and clinical trials that could prove and support phage therapy as a good alternative to antibiotics. However, despite evidence of therapeutic efficacy, potential pharmaceutical formulations for long-term storage and treatment are lacking.
Bacteriophages are viruses made of proteins and nucleic acids, which can lose their viability during long-term storage especially in suspension. Phages are primarily protein particles therefore, phage formulations can reasonably have similarities to other protein formulations. Majority of the proteins are more stable in the dry state than in solutions.
Lyophilization of proteins can provide more stability through reducing the molecular mobility, hydrolysis and contamination but physical and chemical instabilities are not clear. During protein lyophilization it is important to consider their conformation (protein structure), and chemical and physical stability as well as their ability to completely dissolve upon reconstitution. Many therapeutically important proteins and vaccines are lyophilized to obtain therapeutic pharmaceutical formulations. Phages can undergo physical stresses in aqueous solution (suspensions) such as pH/temperature changes, agitation and exposure to denaturants, which can lead to aggregation and phage loss.
To maintain stability during long-term storage of phages, preparation of lyophilization powders is one of the effective mechanisms that need more exploration. Studies show that the lyophilized phages are stable at −80 °C for up to 10 years.
Additionally, excipients used for lyophilization are one of the important criteria for effective phage lyophilization and also for their viability. The use of skimmed milk, gelatin, peptone, sodium glutamate, polyethylene glycol, glycerol and other sugars (mannitol, sucrose, and trehalose) as effective excipients for phage lyophilization. Sugars are considered as good excipients for phage lyophilization because they can stabilize phages during lyophilization process and also help in shelf storage of phage products.
When phages are lyophilized for therapeutic purpose, the morphology of these phages should be retained in order to achieve the viability. Therefore, the choice of excipients used for lyophilization of different families of tailed phages should be taken into consideration.
The most common used excipients are sugars because sugars can act as good cryoprotectants which have an ability to undergo vitrification during freezing, eventually forming glass matrix that can prevent phages from aggregation.
The studies on bacteriophage lyophilization are important for the development of novel phage formulations, for example, dry powders for inhalation and also for storage of phages at non-refrigerated conditions, during transport. More research on bacteriophage lyophilization could move phage therapy a step forward as an alternative to antibiotics.
Original article: "Improved lyophilization conditions for long-term storage of bacteriophages"