Biodegradable lipid bilayer-assisted indocyanine green J- aggregates for photothermal therapy: Formulation, in vitro toxicity and in vivo clearance

Indocyanine green (ICG) J-aggregates (IJA) are a unique form of aggregation that exhibits superior properties to monomeric ICG. Despite their higher photoacoustic (PA) signals for imaging and heating stability during photothermal therapy (PTT), they exhibit low stability under a biological milieu. Our group previously proposed a simple procedure for in-situ preparation of IJA into liposomes, accelerating their formation and optical properties. To comprehend their potential applications, we systematically investigated the effect of the lipid bilayer composition on ICG J-aggregation and stability. Moreover, their in vitro compatibility and photothermal toxicity in monolayers and cancer spheroids, besides their in vivo biodistribution and clearance were evaluated. Our findings revealed the importance of high cholesterol and PEG-lipid content and low charged lipids (∼ 5 mol %) in liposomes to promote a high IJA/ICG ratio and, thus, high heating stability. More importantly, IJA-liposomes revealed high biocompatibility in monolayer and cancer spheroids with efficient photothermal toxicity. Finally, IJA-liposomes were cleared from the body without toxicity. Interestingly, IJA-liposomes mainly showed lower affinity to the liver than monomeric ICG, resulting in higher renal clearance. Overall, our biodegradable IJA-liposomes could be an excellent alternative to gold-based agents suitable for PA imaging and cancer PTT.