Formulation, stabilisation and encapsulation of bacteriophage for phage therapy

Abstract

Against a backdrop of global antibiotic resistance and increasing awareness of the importance of the human microbiota, there has been resurgent interest in the potential use of bacteriophages for therapeutic purposes, known as phage therapy. A number of phage therapy phase I and II clinical trials have concluded, and shown phages don't present significant adverse safety concerns. These clinical trials used simple phage suspensions without any formulation and phage stability was of secondary concern. Phages have a limited stability in solution, and undergo a significant drop in phage titre during processing and storage which is unacceptable if phages are to become regulated pharmaceuticals, where stable dosage and well defined pharmacokinetics and pharmacodynamics are de rigueur. Animal studies have shown that the efficacy of phage therapy outcomes depend on the phage concentration (i.e. the dose) delivered at the site of infection, and their ability to target and kill bacteria, arresting bacterial growth and clearing the infection. In addition, in vitro and animal studies have shown the importance of using phage cocktails rather than single phage preparations to achieve better therapy outcomes. The in vivo reduction of phage concentration due to interactions with host antibodies or other clearance mechanisms may necessitate repeated dosing of phages, or sustained release approaches. Modelling of phage-bacterium population dynamics reinforces these points. Surprisingly little attention has been devoted to the effect of formulation on phage therapy outcomes, given the need for phage cocktails, where each phage within a cocktail may require significantly different formulation to retain a high enough infective dose. This review firstly looks at the clinical needs and challenges (informed through a review of key animal studies evaluating phage therapy) associated with treatment of acute and chronic infections and the drivers for phage encapsulation. An important driver for formulation and encapsulation is shelf life and storage of phage to ensure reproducible dosages. Other drivers include formulation of phage for encapsulation in micro- and nanoparticles for effective delivery, encapsulation in stimuli responsive systems for triggered controlled or sustained release at the targeted site of infection. Encapsulation of phage (e.g. in liposomes) may also be used to increase the circulation time of phage for treating systemic infections, for prophylactic treatment or to treat intracellular infections. We then proceed to document approaches used in the published literature on the formulation and stabilisation of phage for storage and encapsulation of bacteriophage in micro- and nanostructured materials using freeze drying (lyophilization), spray drying, in emulsions e.g. ointments, polymeric microparticles, nanoparticles and liposomes. As phage therapy moves forward towards Phase III clinical trials, the review concludes by looking at promising new approaches for micro- and nanoencapsulation of phages and how these may ad...

Microencapsulation of Clostridium difficile specific bacteriophages using microfluidic glass capillary devices for colon delivery using pH triggered release

“…Most phages only infect a small number of prevalent strains, thereby necessitating the use of phage cocktails to provide adequate therapeutic coverage. Phages incorporated in the cocktail may require tailored formulations to ensure adequate stability [96]. …”

Phage therapy: What factors shape phage pharmacokinetics and bioavailability? Systematic and critical review

“…Notably, sensitivity of phages to extreme pHs is typically investigated in vitro, thus excluding the potential impact of ionic composition and variety of organic (potentially protective) macromolecules present in the stomach. Therapeutic phage can be protected by encapsulation for example in polymeric microparticles, liposomes, or others . In vitro exposition of encapsulated phages to low pH clearly demonstrated that they were more resistant to acidic environment than free bacteriophages, some data indicate that encapsulation improve phage antibacterial activity in vivo .…”

“…Therapeutic phage can be protected by encapsulation for example in polymeric microparticles, liposomes, or others . In vitro exposition of encapsulated phages to low pH clearly demonstrated that they were more resistant to acidic environment than free bacteriophages, some data indicate that encapsulation improve phage antibacterial activity in vivo . Thus, at least in phage strains that are highly sensitive to acidic environment, encapsulation may protect them during gut transit.…”

“…Phage pharmacokinetics can be markedly changed by encapsulation of bacteriophages. Most of available data indicate prolonged release of phage, close to constant release and different to bolus administrations . In addition to delivering control release systems, encapsulation protects bacteriophages and allows for longer circulation in human or animal body.…”

The antibacterial effect of chitosan‐based edible coating incorporated with a lytic bacteriophage against Escherichia coli O157:H7 on the surface of tomatoes

“…The lysis from without is the most likely route of biocontrol of foodborne pathogens, mostly at usual cold storage temperatures (Sillankorva et al, ; Ferguson et al, ). However, under experimental conditions used in this study, it is unlikely that the reduction of E. coli on tomato surfaces could be caused by lysis from without, which this phenomenon usually occurs when the phage concentration is higher than the concentration of host bacteria (Malik et al, ).…”