New insights on the release and self-healing model of stimuli-sensitive liposomes.

The mixing of conventional and pH-sensitive lipids was exploited to design novel stimuli-responsive liposomes (fliposomes) that could be used for smart drug delivery. We deeply investigated the structural properties of the fliposomes and revealed the mechanisms that are involved in a membrane transformation during a pH change. From ITC experiments we observed the existence of a slow process that was attributed to lipid layers arrangement with changing pH. Moreover, we determined for the first time the pKa value of the trigger-lipid in an aqueous milieu that is drastically different from the methanol-based values reported previously in the literature. Furthermore, we studied the release kinetics of encapsulated NaCl and proposed a novel model of release that involves the physical fitting parameters that could be extracted from the release curves fitting. We have obtained for the first time, the values of pores self-healing times and were able to trace their evolution with changing pH, temperature, the amount of lipid-trigger.

Stimulus-sensitive liposomal delivery system based on new 3,7-diazabicyclo[3.3.1]nonane derivatives.

3,7-Diazabicyclo[3.3.1]nonane scaffold can serve as a basis for the design of molecular switches stimulating the fast release of water soluble compounds under the influence of external factors from the liposomal containers having those switches incorporated into the lipid bilayer. It was demonstrated that liposomes having 3,7-dihexadecyl-1,5-diphenyl-3,7-diazabicyclo[3.3.1]nonan-9-one (3) incorporated into the liposomal membrane sharply increase the permeability upon pH decrease from 7.4 to 6.5, and compound 3 can serve as a pH-sensitive agent in the bilayer of liposomal nanocontainers. Similar but less pronounced effect was shown for liposomes modified with 3,7-bis(methyldodecylaminoacetyl)-1,5-dimethyl-3,7-diazabicyclo[3.3.1]nonane (5) and 3,7-didodecylsulfonyl-1,5-dimethyl-3,7-diazabicyclo[3.3.1]nonan-9-one (4). The structure (morphology) and size of modified liposomes were studied with scanned transmission electron microscopy.

Molecular Mechanisms of the Interactions of N-(2-Hydroxypropyl)methacrylamide Copolymers Designed for Cancer Therapy with Blood Plasma Proteins.

The binding of plasma proteins to a drug carrier alters the circulation of nanoparticles (NPs) in the bloodstream, and, as a consequence, the anticancer efficiency of the entire nanoparticle drug delivery system. We investigate the possible interaction and the interaction mechanism of a polymeric drug delivery system based on N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers (pHPMA) with the most abundant proteins in human blood plasma-namely, human serum albumin (HSA), immunoglobulin G (IgG), fibrinogen (Fbg), and apolipoprotein (Apo) E4 and A1-using a combination of small-angle X-ray scattering (SAXS), analytical ultracentrifugation (AUC), and nuclear magnetic resonance (NMR). Through rigorous investigation, we present evidence of weak interactions between proteins and polymeric nanomedicine. Such interactions do not result in the formation of the protein corona and do not affect the efficiency of the drug delivery.

Modification of fliposomes with a polycation can enhance the control of pH-induced release.

PURPOSE: Nowadays, the development of stimuli-sensitive nanocontainers for targeted drug delivery is of great value. Encapsulation of a drug in a pH-sensitive liposomal container not only provides protective and transport functions, but also helps to create a system with a controlled release mechanism. METHODS: In this study, we investigated the influence of a cationic polypeptide on the pH-induced release of anticancer drug doxorubicin (DXR) from the anionic fliposomes - liposomes consisting of a neutral lipid, an anionic lipid (prone to interact with a polycation), and a lipid trigger (imparting the pH-sensitivity). RESULTS: First, we showed the possibility to control the pH-induced release by the simple modification of the anionic fliposomes with linear polylysine. Second, we optimized the fliposomal composition such that the obtained fliposomes responded to the pH changes only when complexed with the polycation ("turning on" the release). Finally, pH-induced release from the polylysine-modified anionic fliposomes was tested on an anticancer drug DXR. CONCLUSION: We have succeeded in developing "smart" stimuli-sensitive nanocontainers capable of tunable controlled release of a drug. Moreover, based on the data on release of a low molecular salt, one can predict the release profile of DXR.

Capacious and programmable multi-liposomal carriers.

Spherical polycationic brushes (SPBs) were synthesized by grafting polycationic chains onto 100 nm polystyrene particles. These particles were exposed to unilamellar egg-lecithin (EL) liposomes with a mean diameter of 40 nm that had been rendered anionic via the presence of 10 molar% of phosphatidylserine (PS(1-)). The liposomes also contained 30 mole% of a morpholinocyclohexanol-based lipid (MOCH) that undergoes a conformational flip when the pH is decreased from 7.0 to 5.0. Mixtures of SPBs and liposomes at pH 7 gave an electrostatically-driven complex possessing, on average, about 40 liposomes for each SPB particle. It was found that the bound liposomes rapidly release much of their contents when the pH is reduced from 7.0 to 5.0 owing mostly to a MOCH conformational change that creates defects in the bilayer membrane. The drop in pH does not, however, induce a separation of the liposomes from the SPBs. Around 50-60% of the liposome contents escape before, it is reasoned, lateral and transmembrane motion of the membrane components heals the defects and prevents further release. Remarkably, the liposomes complexed with SPB release their cargo much faster than the identical but non-complexed liposomes.

Electrostatically driven complexation of liposomes with a star-shaped polyelectrolyte to low-toxicity multi-liposomal assemblies.

Anionic liposomes are electrostatically complexed to a star-shaped cationic polyelectrolyte. Upon complexation, the liposomes retain their integrity and the resulting liposome-star complexes do not dissociate in a physiological solution with 0.15 M NaCl. This provides a multi-liposomal container for possible use as a high-capacity carrier.

Lipid Segregation in Membranes of Anionic Liposomes Adsorbed onto Polycationic Brushes.

Two-phased: Complexation of liposomes to spherical polycationic brushes induces lipid segregation in the liposomal membrane. The greater the initial anionic lipid content in the membrane, the more the electroneutral lipid dilutes the induced anionic clusters.

Composition and properties of complexes between spherical polycationic brushes and anionic liposomes.

A spherical polycationic brush (SPB) is made by graft-polymerizing a cationic monomer onto the surface of a 100 nm polystyrene bead. It is possible to adsorb anionic liposomes (40-60 nm diameter) onto the SPBs while maintaining the liposome integrity. The liposomes were constructed with phosphatidyl choline (PC) admixed with 0.05-0.4 mol fraction of an dianionic lipid, cardiolipin (CL(2-)). As shown by electrophoretic mobility measurements, SPB-to-liposome complexation leads to a conversion from the initial positive charge of the copolymer to a negative charge. The higher the CL(2-) content of the liposomes, the lower the concentration needed for charge neutralization. Dynamic light scattering (DLS) revealed that multicomplex aggregates are formed with a maximum size at the SPB/liposome charge-equivalence point. Experiments with fluorescent-labeled liposomes show that at low CL(2-) content about 80 liposomes are adsorbed per SPB. As the mole fraction of CL(2-) increases from 0.05 to 0.4, fewer liposomes adsorb owing to electrostatic repulsion among neighboring liposomes. The effect of added NaCl also depends upon the CL(2-) content. With 0.05 mol fraction CL(2-), the SPB/liposome complex dissociates into its components at 0.15 M NaCl. With a mole fraction of >0.1, complexes fail to dissociate even at 1.2 M NaCl. Additional information about the SPB/liposome morphology was obtained from cryo-TEM. For example, cryo-TEM data confirm liposome integrity upon complexation, a behavior that contrasts with the liposome destruction as found with adsorption to many other types of surfaces.