Solid Magnetoliposomes as Multi-Stimuli-Responsive Systems for Controlled Release of Doxorubicin: Assessment of Lipid Formulations

Abstract

Stimuli-responsive liposomes are a class of nanocarriers whose drug release occurs, preferentially, when exposed to a specific biological environment, to an external stimulus, or both. This work is focused on the design of solid magnetoliposomes (SMLs) as lipid-based nanosystems aiming to obtain multi-stimuli-responsive vesicles for doxorubicin (DOX) controlled release in pathological areas under the action of thermal, magnetic, and pH stimuli. The effect of lipid combinations on structural, colloidal stability, and thermodynamic parameters were evaluated. The results confirmed the reproducibility for SMLs synthesis based on nine lipid formulations (combining DPPC, DSPC, CHEMS, DOPE and/or DSPE-PEG), with structural and colloidal properties suitable for biological applications. A loss of stability and thermosensitivity was observed for formulations containing dioleoylphosphatidylethanolamine (DOPE) lipid. SMLs PEGylation is an essential step to enhance both their long-term storage stability and stealth properties. DOX encapsulation (encapsulation efficiency ranging between 87% and 96%) in the bilayers lowered its pK_a, which favors the displacement of DOX from the acyl chains to the surface when changing from alkaline to acidic pH. The release profiles demonstrated a preferential release at acidic pH, more pronounced under mimetic mild-hyperthermia conditions (42 °C). Release kinetics varied with the lipid formulation, generally demonstrating hyperthermia temperatures and acidic pH as determining factors in DOX release; PEGylation was shown to act as a diffusion barrier on the SMLs surface. The integrated assessment and characterization of SMLs allows tuning lipid formulations that best respond to the needs for specific controlled release profiles of stimuli-responsive nanosystems as a multi-functional approach to cancer targeting and therapy.

Keywords: controlled release; doxorubicin; drug delivery; magnetoliposomes; stimuli-responsive.

Figure 1

Schematic representation of the lipid combinations used to prepare DOX-loaded SMLs.

Figure 2

DSC heating thermograms of DOX-loaded SMLs based on different lipid formulations.

Figure 3

ζ-potential-pH profiles of DOX-loaded SMLs based on Group A, Group B and Group C lipid formulations.

Figure 4

HSA fluorescence quenching (%) as a function of increasing free DOX concentration (as a reference in Group A) and loaded in Group A, Group B and Group C lipid formulations. All experiments were performed at pH 7.4 and room temperature. A non-linear fit according to Equation (3) is presented (corresponding lines).

Figure 5

Stability data of DOX-loaded SMLs aqueous suspensions, based on Group A, Group B and Group C lipid formulations, upon storage at 4 °C. The stability of the formulations is expressed as the mean size and PDI variations compared to the original values (measured at day 1).

Figure 6

(a) Fluorescence intensity and steady-state fluorescence anisotropy (r) variation with pH (from 2 to 11) of DOX-loaded SMLs based on different lipid formulations. Total lipid concentration: 1 mM; DOX: 2 µM. (b) Schematic representation of DOX molecules localization in the lipid bilayer at different pH (predictive for formulations with DPPC as the base lipid).

Figure 7

In vitro kinetic release profile of DOX encapsulated in SMLs based on (a) Group A, (b) Group B, and (c) Group C lipid formulations at different conditions of temperature and pH. Triplicate mean fitted to the Weibull kinetic model.