Masking and Triggered Unmasking of Targeting Ligands on Liposomal Chemotherapy Selectively Suppress Tumor Growth in Vivo

Abstract

We investigated the feasibility and efficacy of a drug delivery strategy to vascularized cancer that combines targeting selectivity with high uptake by targeted cells and high bioexposure of cells to delivered chemotherapeutics. Targeted lipid vesicles composed of pH responsive membranes were designed to reversibly form phase-separated lipid domains, which are utilized to tune the vesicle's apparent functionality and permeability. During circulation, vesicles mask functional ligands and stably retain their contents. Upon extravasation in the tumor interstitium, ligand-labeled lipids become unmasked and segregated within lipid domains triggering targeting to cancer cells followed by internalization. In the acidic endosome, vesicles burst release the encapsulated therapeutics through leaky boundaries around the phase-separated lipid domains. The pH tunable vesicles contain doxorubicin and are labeled with an anti-HER2 peptide. In vitro, anti-HER2 pH tunable vesicles release doxorubicin in a pH dependent manner, and exhibit 233% increase in binding to HER2-overexpressing BT474 breast cancer cells with lowering pH from 7.4 to 6.5 followed by significant (50%) internalization. In subcutaneous BT474 xenografts in nude mice, targeted pH tunable vesicles decrease tumor volumes by 159% relative to nontargeted vesicles, and they also exhibit better tumor control by 11% relative to targeted vesicles without an unmasking property. These results suggest the potential of pH tunable vesicles to ultimately control tumor growth at relatively lower administered doses.

Liposomes derivatized with multimeric copies of KCCYSL peptide as targeting agents for HER-2-overexpressing tumor cells

“…[10][11][12][13] Single-positron emission computed tomography/computed tomography studies showed that radioconjugated peptides were able to accumulate specifically at the tumor site, with K d ranging from 30 to 45 nM, with minimal nonspecific retention in other organs. This peptide sequence has also been proposed for the selective delivery of supramolecular carriers such as copolymeric micelles 14 or pH-tunable liposomes 15 for diagnostic or therapeutic applications.…”

Fliposomes: stimuli-triggered conformational flip of novel amphiphiles causes an instant cargo release from liposomes

“…During the last three decades, this idea developed into many strategies for construction of pH-sensitive liposomes. One of the major approaches employs an acid-triggered change of interactions between molecules in a mixture of non-polar and anionic lipids that results in phase transition (5) and/ or formation of domains with 'leaky' interfaces (32,33). Variation of the pKa of anionic lipids and their molar ratio can slightly modify the pH sensitivity.…”

Minimizing antibody surface density on liposomes while sustaining cytokine-activated EC targeting

“…A plateau is reached, between 5 and 10 mol%, where increasing the surface density no longer achieves greater binding [12]. In addition, vehicles need to balance cell targeting with immune recognition [17,18]. High antibody densities lead to a faster rate of liposome clearance from circulation (above 70e80 mg antibody/mmol phospholipid [19,20]) whereas low densities lack specificity.…”