Investigations on the transfer of porphyrin from o/w emulsion droplets to liposomes with two different methods

Cubic nanoparticles as potential carriers for a natural anticancer drug: development, in vitro and in vivo characterization

Natural compounds that elicit anticancer properties are of great interest for cancer therapy. However, the low solubility and bioavailability of these compounds limit their use as efficient anticancer drugs. To avoid these drawbacks, incorporation of these compounds into cubic nanoparticles (cubosomes) was carried out. Cubosomes containing bergapten which is a natural anticancer compound isolated from Ficus carica were prepared by the homogenization technique using monoolein and poloxamer. These cubosomes were characterized for size, zeta potential, entrapment efficiency, small angle X-ray diffraction, in vitro release, in vitro cytotoxicity, cellular uptake, and antitumor activity. Particle size of cubosomes was 220 ± 3.6 nm with almost neutral zeta potential - 5 ± 1.2 mV and X-ray measurements confirmed the existence of the cubic structure. Additionally, more than 90% of the natural anticancer drug was entrapped within the cubosomes. A sustained release over 30 h was obtained for these cubosomes. Finally, these cubosomes illustrated higher in vitro cytotoxicity and in vivo tumor inhibition compared with the free natural anticancer compound. Thus, cubosomes could be promising carriers for enhancement of antitumor efficiency of this natural compound.

Comparative study on the performance of monoolein cubic nanoparticles and trimyristin solid lipid nanoparticles as carriers for docetaxel

Nowadays the application of lipid nanoparticles as carriers for the delivery of anticancer drugs gained great attention in cancer therapy. Solid lipid nanoparticles (SLN_s) and cubic nanoparticles (cubosomes) are considered as promising carriers in cancer therapy. The comparison of these two lipid nanoparticles as efficient carriers for the anticancer drug docetaxel was our main goal in this study. Both nanoparticles were prepared by the hot melt homogenization technique followed by measurement of particle size, zeta potential, entrapment efficiency and in vitro release of docetaxel. An advanced technique has been applied to measure the release of docetaxel from these nanoparticles using small unilamellar vesicles (SUV_s) as acceptor particles which resemble many compartments in our body. All prepared nanoparticles revealed a neutral zeta potential with particle sizes of about 200 nm. While SUV_s showed a negative surface charge with a zeta potential of -55 mV, cubosomes showed higher entrapment efficiency and a slower docetaxel release compared to SLN_s. Additionally, cubosomes improved in vitro cytotoxicity as well as the in vivo antitumor inhibition of docetaxel compared to SLN_s and docetaxel solution. Overall, our results showed that incorporation of docetaxel into cubosomes could enhance its in vitro and in vivo performance compared to docetaxel incorporated into SLN_s.

Ion exchange column technique as a novel method for evaluating the release of docetaxel from different lipid nanoparticles

Lipid nanoparticles with their unique characters showed many advantages as carriers for anticancer drugs. To compare between these nanoparticles as carriers for anticancer drugs, it was important to evaluate and characterize their drug retention and release properties. In this study, ion exchange column is used as a new evaluation technique. Solid lipid nanoparticles (SLN), nanostructured lipid carrier (NLC), and cubic nanoparticles were prepared using the homogenization technique. Characterization of these nanoparticles was carried out by measuring particle size, zeta potential, and entrapment efficiency. The ion exchange column was used to evaluate docetaxel release from the different nanoparticles as donors to acceptor liposomes that mimic the cell membranes. Both populations were mixed and at different time points, separated using the columns. The amounts of docetaxel in the eluted nanoparticles and retained liposomes were calculated. The particle size of all donors was in the nanometer range with almost neutral zeta potential. The particle size of the acceptor liposomes was 135 nm with a high negative zeta potential -55 mV. Ion exchange columns showed excellent retention of the negative acceptor liposomes while less than 1% of the different donors were retained on the columns. Cubic nanoparticles showed the highest entrapment efficiency (95%) and the slowest drug transfer in comparison with SLN and NLC. In conclusion, the ion exchange column technique can be applied successfully to evaluate the release of docetaxel from the different lipid nanoparticles to acceptor liposomes. Cubic nanoparticles showed advantageous docetaxel incorporation and transfer over SLN and NLC.

Mechanism and kinetics of the loss of poorly soluble drugs from liposomal carriers studied by a novel flow field-flow fractionation-based drug release-/transfer-assay

Liposomes represent a versatile drug formulation approach e.g. for improving the water-solubility of poorly soluble drugs but also to achieve drug targeting and controlled release. For the latter applications it is essential that the drug remains associated with the liposomal carrier during transit in the vascular bed. A range of in vitro test methods has been suggested over the years for prediction of the release of drug from liposomal carriers. The majority of these fail to give a realistic prediction for poorly water-soluble drugs due to the intrinsic tendency of such compounds to remain associated with liposome bilayers even upon extensive dilution. Upon i.v. injection, in contrast, rapid drug loss often occurs due to drug transfer from the liposomal carriers to endogenous lipophilic sinks such as lipoproteins, plasma proteins or membranes of red blood cells and endothelial cells. Here we report on the application of a recently introduced in vitro predictive drug transfer assay based on incubation of the liposomal drug carrier with large multilamellar liposomes, the latter serving as a biomimetic model sink, using flow field-flow fractionation as a tool to separate the two types of liposomes. By quantifying the amount of drug remaining associated with the liposomal drug carrier as well as that transferred to the acceptor liposomes at distinct times of incubation, both the kinetics of drug transfer and release to the water phase could be established for the model drug p-THPP (5,10,15,20-tetrakis(4-hydroxyphenyl)21H,23H-porphine). p-THPP is structurally similar to temoporfin, a photosensitizer which is under clinical evaluation in a liposomal formulation. Mechanistic insights were gained by varying the donor-to-acceptor lipid mass ratio, size and lamellarity of the liposomes. Drug transfer kinetics from one liposome to another was found rate determining as compared to redistribution from the outermost to the inner concentric bilayers, such that the overall process could be adequately described by a single 1st order kinetic model. By varying the donor-to-acceptor lipid mass ratio in the range 1:1 to 1:10, a correlation was established between donor-to-acceptor-lipid mass ratio and transfer kinetics, which is regarded essential for scaling to physiological lipid mass ratios. By applying the assay to a series of structurally related model compounds of different bilayer affinity, transfer and release kinetics were established over the whole expected range of liposome bilayer associated drugs in terms of water solubility and lipophilicity. A very rapid transfer and considerable release from liposomes to the water phase was observed for the more water-soluble compounds Sudan II (clogP 5.45) and Sudan III (clogP 6.83). For the more lipophilic compounds, the rate of transfer from the donor liposomes followed the rank order Sudan IV (fastest)>Oil Red O>Sudan Black>p-THPP (slowest). For an equimolar donor-to-acceptor lipid mass ratio, half-lifes of transfer in the range of 12min (Sudan IV) up to 1.5h (p-THPP) were determined. In essence, the results presented here allow for both, mechanistic insights and predictions of drug loss from liposomal carriers upon exposure to biological sinks, which appear more realistic than the commonly employed in vitro release tests.

Comparison of drug release from liquid crystalline monoolein dispersions and solid lipid nanoparticles using a flow cytometric technique

Colloidal lipid particles such as solid lipid nanoparticles and liquid crystalline nanoparticles have great opportunities as drug carriers especially for lipophilic drugs intended for intravenous administration. In order to evaluate drug release from these nanoparticles and determine their behavior after administration, emulsion droplets were used as a lipophilic compartment to which the transfer of a model drug was measured. The detection of the model drug transferred from monoolein cubic particles and trimyristin solid lipid nanoparticles into emulsion droplets was performed using a flow cytometric technique. A higher rate and amount of porphyrin transfer from the solid lipid nanoparticles compared to the monoolein cubic particles was observed. This difference might be attributed to the formation of a highly ordered particle which leads to the expulsion of drug to the surface of the crystalline particle. Furthermore, the sponge-like structure of the monoolein cubic particles decreases the rate and amount of drug transferred. In conclusion, the flow cytometric technique is a suitable technique to study drug transfer from these carriers to large lipophilic acceptors. Monoolein cubic particles with their unique structure can be used successfully as a drug carrier with slow drug release compared with trimyristin nanoparticles.

Comparative study on the suitability of two techniques for measuring the transfer of lipophilic drug models from lipid nanoparticles to lipophilic acceptors

Due to their particle size in the submicrometer range, lipid nanoparticles are suitable for parenteral administration. In order to obtain information on their potential in vivo performance, a simple and effective in vitro assay to evaluate the drug release behavior of such particles is required. This study compares the use of different experimental setups for this purpose. Lipid nanoparticles from trimyristin which were loaded with fluorescent lipophilic drug models (a temoporfin and Nile red) were used as donor particles. The transfer of the two drug models to multilamellar vesicles (MLV) and emulsion droplets as lipophilic acceptor compartments was examined. The determination of the transferred substance was performed either after separation by centrifugation or by an in situ flow cytometric technique. The transfer of temoporfin was slow to the acceptor MLV and very rapid to the acceptor emulsion. With both acceptors, the transfer of temoporfin stopped at a concentration much lower than the theoretical equilibrium values. The transfer of the less lipophilic drug Nile red was very rapid to both acceptors with equilibrium concentrations close to the expected values. The transfer results of temoporfin especially to the acceptor MLV obtained with the two detection techniques were comparable while the centrifugation technique indicated an apparently higher Nile red transfer rate than the flow cytometric technique. Both techniques are equally suitable to study the transfer of temoporfin, while the flow cytometric technique is advantageous to measure the very rapid transfer of Nile red.