Paclitaxel-Loaded Cationic Fluid Lipid Nanodiscs and Liposomes with Brush-Conformation PEG Chains Penetrate Breast Tumors and Trigger Caspase-3 Activation

Abstract

Novel approaches are required to address the urgent need to develop lipid-based carriers of paclitaxel (PTX) and other hydrophobic drugs for cancer chemotherapy. Carriers based on cationic liposomes (CLs) with fluid (i.e., chain-melted) membranes (e.g., EndoTAG-1) have shown promise in preclinical and late-stage clinical studies. Recent work found that the addition of a cone-shaped poly(ethylene glycol)-lipid (PEG-lipid) to PTX-loaded CLs (CLsPTX) promotes a transition to sterically stabilized, higher-curvature (smaller) nanoparticles consisting of a mixture of PEGylated CLsPTX and PTX-containing fluid lipid nanodiscs (nanodiscsPTX). These CLsPTX and nanodiscsPTX show significantly improved uptake and cytotoxicity in cultured human cancer cells at PEG coverage in the brush regime (10 mol % PEG-lipid). Here, we studied the PTX loading, in vivo circulation half-life, and biodistribution of systemically administered CLsPTX and nanodiscsPTX and assessed their ability to induce apoptosis in triple-negative breast-cancer-bearing immunocompetent mice. We focused on fluid rather than solid lipid nanodiscs because of the significantly higher solubility of PTX in fluid membranes. At 5 and 10 mol % of a PEG-lipid (PEG5K-lipid, molecular weight of PEG 5000 g/mol), the mixture of PEGylated CLsPTX and nanodiscsPTX was able to incorporate up to 2.5 mol % PTX without crystallization for at least 20 h. Remarkably, compared to preparations containing 2 and 5 mol % PEG5K-lipid (with the PEG chains in the mushroom regime), the particles at 10 mol % (with PEG chains in the brush regime) showed significantly higher blood half-life, tumor penetration, and proapoptotic activity. Our study suggests that increasing the PEG coverage of CL-based drug nanoformulations can improve their pharmacokinetics and therapeutic efficacy.

Cryo-TEM Reveals the Influence of Multivalent Charge and PEGylation on Shape Transitions in Fluid Lipid Assemblies: From Vesicles to Discs, Rods, and Spheres

“…For example, recent cell-based studies have shown that the small size and shape anisotropy of micellar discs enhance cell uptake of these vectors − , because distinct additional endocytic pathways are available to them: nanodiscs were found to use macropinocytosis and microtubule-mediated endocytosis in addition to the typical clathrin- and caveolae-mediated endocytic pathways used by larger spherical lipid vectors . Consistent with these in vitro results, formulations of PTX-loaded coexisting nanometer-scale fluid lipid discs and vesicles showed tumor penetration and proapoptotic activity in vivo in a model of triple-negative breast cancer in immunocompetent mice …”

“…39 Consistent with these in vitro results, formulations of PTX-loaded coexisting nanometer-scale fluid lipid discs and vesicles showed tumor penetration and proapoptotic activity in vivo in a model of triple-negative breast cancer in immunocompetent mice. 38 It is important to point out that all lipid assemblies studied in the present work have membranes that were in the fluid state. This contrasts with previous studies that have characterized the structure and properties of solid lipid nanodiscs, 35,36,39,64 where the (charge-neutral or slightly anionic) assemblies of lipids with saturated tails form the chain-ordered "gel" phase 69 with very low chain mobility.…”

“…However, the a priori prediction of assembly structure from lipid structure remains elusive, especially for lipid mixtures and less abundant assembly structures, such as disc micelles. Therefore, elucidation of key physical and chemical properties of lipids that enable formation of stable disc micelles, whether kinetically or due to thermal equilibrium, is of high importance for hydrophobic drug delivery in vitro and in vivo. − …”

Brain Targeting Nanomedicines: Pitfalls and Promise

“…30,63,64 By counteracting the nonspecific adhesion due to van der Waals interactions, PEGylation opens the opportunity for targeting of NPs with targeting moieties such as antibodies and homing peptides. 65,66 These ligands either engage with the endocytosis or transcytosis receptors expressed on the BMEC surface (eg, transferrin, insulin, lactoferrin, and lipoprotein receptors), penetrate directly through cellular membranes (cell-penetrating peptides (CPP)), 65,67,68 or used mixed pathways for BBB penetration. NP-CPP conjugates were the first BBB-crossing NPs that did not compromise the integrity of the BBB.…”

Personalized Cancer Nanomedicine: Overcoming Biological Barriers for Intracellular Delivery of Biopharmaceuticals

“…The authors concluded that augmented tumor penetration was contingent upon both the degree of PEGylation and concomitant particle size, as particles with 10 mol% PEG exhibited favorable results. [130] There are other works that have Addressing the challenge of efficient NP diffusion within the tumor stroma has been pursued through three strategies. First, the physicochemical properties of the NPs, comprising particle size and rigidity, have demonstrated improved access to intratumoral regions.…”