Scale-Independent Microfluidic Production of Cationic Liposomal Adjuvants and Development of Enhanced Lymphatic Targeting Strategies.

Cationic liposomes prepared from dimethyldioctadecylammonium bromide (DDAB) and trehalose 6,6'-dibehenate (TDB) are strong liposomal adjuvants. As with many liposome formulations, within the laboratory DDAB:TDB is commonly prepared by the thin-film method, which is difficult to scale-up and gives high batch-to-batch variability. In contrast, controllable technologies such as microfluidics offer robust, continuous, and scale-independent production. Therefore, within this study, we have developed a microfluidic production method for cationic liposomal adjuvants that is scale-independent and produces liposomal adjuvants with analogous biodistribution and immunogenicity compared to those produced by the small-scale lipid hydration method. Subsequently, we further developed the DDAB:TDB adjuvant system to include a lymphatic targeting strategy using microfluidics. By exploiting a biotin-avidin complexation strategy, we were able to manipulate the pharmacokinetic profile and enhance targeting and retention of DDAB:TDB and antigen within the lymph nodes. Interestingly, redirecting these cationic liposomal adjuvants did not translate into notably improved vaccine efficacy.

Scalable solvent-free production of liposomes.

OBJECTIVES: A major challenge faced with the manufacture of liposomes is the high volumes of organic solvents used during manufacturing. Therefore, we have implemented an organic solvent-free production method for drug-loaded liposomes and demonstrated its applicability with both aqueous core-loaded and bilayer-loaded drugs. METHODS: Liposomes were produced by high shear mixing dry powder lipids with an aqueous buffer, followed by down-sizing using a Microfluidizer processor. Liposomes were purified via tangential flow filtration and characterised in terms of size, polydispersity index, zeta potential and drug loading. KEY FINDINGS: Doxorubicin-loaded PEGylated liposomes can be manufactured using this solvent-free method with particle sizes of 100-110 nm, low polydispersity index (PDI) (<0.2) and high drug loading (97-98%). If required, liposomes can be further down-sized via microfluidic processing without impacting drug loading. Similar results were achieved with non-PEGylated liposomes. With bilayer-loaded amphotericin B liposomes, again liposomes can be prepared within a clinically appropriate size range (100-110 nm in size, low PDI) with high drug loading (98-100%). CONCLUSIONS: We apply a simple and scalable solvent-free method for the production of both aqueous core or bilayer drug-loaded liposomes.

Formulation and manufacturing of lymphatic targeting liposomes using microfluidics.

The lymphatics are a target for a range of therapeutic purposes, including cancer therapy and vaccination, and both vesicle size and charge have been considered as factors controlling lymphatic targeting. Within this work, a range of liposomal formulations were investigated to develop a liposomal lymphatic targeting system. Initial screening of formulations considered the effect of charge, with neutral, cationic and anionic liposomes being investigated. Biodistribution studies demonstrated that after intramuscular injection, anionic liposomes offered the most rapid clearance to the draining lymphatics with cationic liposomes forming a depot at the injection site. Anionic liposomes containing phosphatidylserine showed higher clearance to the lymphatics and this may result form preferential uptake by macrophages. In terms of vesicle size, smaller unilamellar vesicles gave high lymphatic targeting and a 10-fold increase in concentration was achieved in dose escalation studies. Given that effective trafficking to the lymphatics was achieved, the next step was to enhance retention of the liposomes within the lymphatics, therefore the liposome formulation was combined with an avidin/biotin complex mechanism. The affinity of avidin for biotin allows biotinylated liposomes to complex in the presence of avidin. By pre-dosing with avidin, the biotin-avidin complex can be exploited to promote longer retention of the liposomes at the draining lymphatics. To load these small, biotinylated liposomes with protein, microfluidics manufacturing was used. Using microfluidics, protein could easily be incorporated in these small (~90nm) biotinylated liposomes. Both liposome and protein retention at the local draining lymph nodes was demonstrated with the liposome-biotin-avidin system. These results demonstrate that microfluidics can be used to prepare protein-loaded liposomes that offer enhanced lymphatic targeting and retention of both the liposomes and entrapped antigen.

Point of use production of liposomal solubilised products.

With the progression towards personalised and age-appropriate medicines, the production of drug loaded liposomes at the point of care would be highly desirable. In particular, liposomal solubilisation agents that can be produced rapidly and easily would provide a new option in personalised medicines. Such a process could also be used as a rapid tool for the formulation and pre-clinical screening of low soluble drugs. Within this paper, we outline a novel easy-to-use production method for point of use production of liposome solubilised drugs. Our results demonstrate that pre-formed multilamellar liposomes, stored in a fresh or frozen format, can be bilayer loaded with low solubility drugs using a simple bath sonication process. Sonication is undertaken in a sealed vial allowing the contents to remain sterile. Liposomes around 100 nm were prepared and these liposomes were able to increase the amount of drug dissolved by up to 10 fold. These liposomal solubilisation agents were stable in terms of size and drug solubilisation for up to 8 days when stored in the fridge making them an easy to use and robust small-scale tool for drug solubilisation.

Manufacturing Methods for Liposome Adjuvants.

A wide range of studies have shown that liposomes can act as suitable adjuvants for a range of vaccine antigens. Properties such as their amphiphilic character and biphasic nature allow them to incorporate antigens within the lipid bilayer, on the surface, or encapsulated within the inner core. However, appropriate methods for the manufacture of liposomes are limited and this has resulted in issues with cost, supply, and wider scale application of these systems. Within this chapter we explore manufacturing processes that can be used for the production of liposomal adjuvants, and we outline new manufacturing methods can that offer fast, scalable, and cost-effective production of liposomal adjuvants.