Liposomal nanotherapy for treatment of atherosclerosis : passive versus active targeting

• Main Author: Darwitan, Anastasia
• Other Authors: Subbu S. Venkatraman
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Nanotechnology
• Online Access: https://hdl.handle.net/10356/137197
• Institution: Nanyang Technological University

In spite of the success of current therapies and preventive strategies in reducing cardiovascular risk, cardiovascular diseases (CVD) continue to be the leading cause of death globally. Inflammation is the underlying pathological process of atherosclerosis, the major cause of most CVD, but has not been adequately addressed. Additionally, the increasing age trend of general population will present increasing incidence with individual’s unique and complex coronary anatomy with high-risk comorbidities. Thus, there is a need for novel therapies that are effective. Anti-inflammatory agents, such as glucocorticoids (GC), when administered systemically for long duration, are associated with systemic adverse effect. One strategy to circumvent this is by utilizing a nanocarrier to encapsulate the active agents, thereby preventing off-target interaction and enabling targeted and sustained delivery of the active compounds at the diseased site; hence, enhancement of benefit/risk ratio of the therapeutic agents. In this report, both passive and active targeting strategies were explored using nanoliposomes as the nanocarrier. In passive strategy, nanoliposomes circulate in the bloodstream and preferentially accumulate at the sites of inflammation, which are characterized by dysfunctional endothelium and enhanced vascular leakiness, through ‘Enhanced Permeability and Retention’ (EPR) effect. Passive liposomes encapsulating fluocinolone acetonide (FA) were developed and reported in this thesis. Encapsulation efficiency of around 90% was achieved with final drug/lipid molar ratio of around 0.11. Release was sustained up to 30 days in vitro and the formulation was stable for at least 3 months. In active strategy, active ligands were decorated on nanoliposomal surface for enhancement of cell internalization. In this report, it was demonstrated that foam cells expressed high number of targetable cell surface folate receptors. Optimum cell uptake enhancement was achieved with 0.5 mol% folate (FOL) with polyethylene glycol (PEG) 2000 spacer. Subsequently, ligand-free PEG was incorporated on active liposomes with PEG 2000 (0.5% FOL) and cell uptake was evaluated after pre-incubation of liposomes in 80% serum in order to mimic the presence of high level of serum in vivo. It was demonstrated that the active targeting effect of active targeting nanoliposomes progressively decreased and eventually be lost as PEG-to-ligand ratio is increased. However, the value of PEG-to-ligand ratio at which the targeting effect was lost depended on PEG length (>2 for PEG 750; >0.5 for PEG 2000; <0.5 for PEG 5000). The novel anti-inflammatory therapy developed in this PhD work could be envisioned for treatment after an acute clinical event or as adjunct therapy for prevention of in-stent restenosis in patients receiving bare metal stents. Individually, the passive liposomal formulation developed represents novel anti-inflammatory therapeutic option for atherosclerosis. It can also be considered for other inflammatory conditions, such as diabetic macular edema. The active liposome formulation developed could potentially enhance therapeutic efficacy of liposomal anti-inflammatory nanotherapy. The knowledge from active liposome studies could contribute in development of other active nanocarriers utilizing PEG and ligand-PEG.