Mechanistic investigation of thermosensitive liposome immunogenicity and understanding the drivers for circulation half-life: A polyethylene glycol versus 1,2-dipalmitoyl-sn-glycero-3-phosphodiglycerol study

Abstract

Various thermosensitive liposome (TSL) formulations have been described to date and it is currently unclear which are optimal for solid tumor treatment. Sufficient circulation half-life is important and most liposomes obtain this by polyethylene glycol (PEG) surface modification. 1,2-dipalmitoyl-sn-glycero-3-phosphodiglycerol (DPPG₂) has been described as a promising alternative which increases TSL circulation half-life and facilitates rapid drug release under mild hyperthermia at 20-30 mol%. The present work describes an investigation of the DPPG₂-TSL protein corona, blood cell interactions, complement activation in human plasma/blood and hypersensitivity reactions in rats. Furthermore, accelerated blood clearance (ABC) was investigated to obtain a complete assessment of DPPG₂-TSL interactions with components of the blood and identify drivers for circulation half-life. A higher mol% DPPG₂ increased Apolipoprotein E (ApoE) adsorption and decreased complement activation and granulocyte interaction in vitro. In contrast to PEG-TSL, DPPG₂-TSL showed no ABC effect. In vivo hypersensitivity assessment by eicosanoid measurements, platelet and lymphocyte counting resembled the results of in vitro complement activation assays although here all DPPG₂-TSL formulations induced hypersensitive responses upon i.v. administration. Prolonged circulation half-life of DPPG₂-TSL may be ApoE-induced and the absent ABC effect demonstrates an advantage over PEG-TSL. Low complement activation in human plasma and blood for 20-30 mol% DPPG₂-TSL presents a unique formulation attribute with the potential to strengthen clinical evaluation.

Keywords: ABC effect; Hypersensitivity reactions; Pharmacokinetics; Protein corona; Thermosensitive liposome.