Development of a new approach to investigating the drug transfer from colloidal carrier systems applying lipid nanosuspension-containing alginate microbeads as acceptor

Nanosuspension encapsulated chitosan-pectin microbeads as a novel delivery platform for enhancing oral bioavailability

The current study aimed to overcome the poor solubility and colon-specific delivery of curcumin (CUR) by formulating a curcumin nanosuspension (CUR-NS) using the antisolvent precipitation method. Freeze-dried CUR-NS was encapsulated into microbeads (CUR-NS-MB) by the ionotropic gelation method using zinc chloride (as a cross-linking agent) with the help of rate-controlling polymers, pectin, and chitosan. Furthermore, cellulose acetate phthalate (CAP) is incorporated as an enteric polymer to protect against acidic medium degradation. Particle size, surface morphology, interaction studies, and entrapment studies were performed to optimize CUR-NSs. Nanosuspensions stabilized with hydroxypropyl methylcellulose (HPMC E-15; 1 % w/v) showed an average particle size of 193.5 ± 4.31 nm and a polydispersity index (PDI) of 0.261 ± 0.020. The optimized microbeads (CUR-NS-MB) showed 89.45 ± 3.11 % entrapment efficiency with a drug loading of 14.54 ± 1.02 %. The optimized formulation (CUR-NS-MB) showed colon-specific in vitro drug release bypassing acid pH degradation. In animal studies, a 2.5-fold increase in Cmax and a 4.4-fold increase in AUC048h were observed with CUR-NS-MB, which was more significant than that of plain CUR. Therefore, the developed CUR-NS-MB has the potential to be used as a colon-specific delivery system.

Development of an In Vitro Release Assay for Low-Density Cannabidiol Nanoparticles Prepared by Flash NanoPrecipitation

Nanoparticle encapsulation is an attractive approach to improve the oral bioavailability of hydrophobic therapeutics. The high specific surface area of nanoparticle formulations, combined with the thermodynamically driven increased solubility of an amorphous drug core, promotes rapid drug dissolution. However, the physicochemical properties of the hydrophobic therapeutic can present obstacles to in vitro characterization of nanoparticle formulations. Namely, drugs with low density and high membrane binding affinity frustrate traditional analytical methods to monitor release kinetics from nanoparticles. In this work, cannabidiol (CBD) was encapsulated into nanoparticles with low polydispersity and high drug loading via Flash NanoPrecipitation (FNP), a scalable self-assembly process. Hydroxypropyl methylcellulose acetate succinate (HPMCAS) and lecithin were employed as amphiphilic particle stabilizers during the FNP process. However, the low density and high membrane binding affinity of the amorphous CBD nanoparticle core prevented the characterization of in vitro release kinetics by conventional methods. Released CBD could not be separated from intact nanoparticles by filtration or centrifugation. To address this challenge, an alternative approach is described to coencapsulate 6 nm hydrophobic Fe₃O₄ colloids with CBD during FNP. The Fe₃O₄ colloids were added at 33% by mass (approximately 20% by volume) to increase the density of the nanoparticles, resulting in particles with an average diameter of 160 nm (CBD-lecithin-Fe₃O₄) or 280 nm (CBD-HPMCAS-Fe₃O₄). This densification enabled the centrifugal separation of dissolved (released) CBD from unreleased CBD during the in vitro assay while avoiding the losses associated with a filtration step. The resulting nanoparticle formulations provided more rapid and complete in vitro dissolution kinetics than bulk CBD, representing a 6-fold improvement in dissolution compared to crystalline CBD. The coencapsulation of high-density Fe₃O₄ colloids to enable the separation of nanoparticles from release media is a novel approach to measuring in vitro release kinetics of nanoencapsulated low-density, hydrophobic drug molecules.

Application of Asymmetrical Flow Field-Flow Fractionation for Characterizing the Size and Drug Release Kinetics of Theranostic Lipid Nanovesicles

Liposome size and in vitro release of the active substance belong to critical quality attributes of liposomal carriers. Here, we apply asymmetric flow field-flow fractionation (AF4) to characterize theranostic liposomes prepared by thin lipid film hydration/extrusion or microfluidics. The vesicles' size was derived from multi-angle laser light scattering following fractionation (AF4) and compared to sizes derived from dynamic light scattering measurements. Additionally, we adapted a previously developed AF4 method to study zinc phthalocyanine (ZnPc) release/transfer from theranostic liposomes. To this end, theranostic liposomes were incubated with large acceptor liposomes serving as a sink (mimicking biological sinks) and were subsequently separated by AF4. During incubation, ZnPc was transferred from donor to acceptor fraction until reaching equilibrium. The process followed first-order kinetics with half-lives between 119.5-277.3 min, depending on the formulation. The release mechanism was postulated to represent a combination of Fickian diffusion and liposome relaxation. The rate constant of the transfer was proportional to the liposome size and inversely proportional to the ZnPc/POPC molar ratio. Our results confirm the usefulness of AF4 based method to study in vitro release/transfer of lipophilic payload, which may be useful to estimate the unwanted loss of drug from the liposomal carrier in vivo.

Transfer Investigations of Lipophilic Drugs from Lipid Nanoemulsions to Lipophilic Acceptors: Contributing Effects of Cholesteryl Esters and Albumin as Acceptor Structures

When studying the release of poorly water-soluble drugs from colloidal drug delivery systems designed for intravenous administration, the release media should preferentially contain lipophilic components that represent the physiological acceptors present in vivo. In this study, the effect of different acceptor structures was investigated by comparing the transfer of fenofibrate, retinyl acetate, and orlistat from trimyristin nanoemulsion droplets into lipid-containing hydrogel particles, as well as to bovine serum albumin (BSA). A nanodispersion based on trimyristin and cholesteryl nonanoate was incorporated into the hydrogel particles (mean diameter ~40 µm) in order to mimic the composition of lipoproteins. The course of transfer observed utilizing the lipid-containing hydrogel particles as an acceptor was in relation to the lipophilicity of the drugs: the higher the logP value, the slower the transfer. There was no detectable amount of the drugs transferred to BSA in liquid solution, demonstrating clearly that albumin alone does not contribute substantially as acceptor for the lipophilic drugs under investigation in this study. In contrast, cholesteryl nonanoate contributes to a much greater extent. However, in all cases, the partition equilibrium of the drugs under investigation was in favor of the trimyristin emulsion droplets.

Transfer of Lipophilic Drugs from Nanoemulsions into Lipid-Containing Alginate Microspheres

Knowledge about the release behavior and drug retention properties of colloidal carriers is of essential importance for quality control as well as to predict in vivo performance. When conducting release studies from such systems, the release media should preferentially contain lipophilic acceptor components in order to mimic physiological conditions. In this study, transfer from a trimyristin nanoemulsion into lipid-containing hydrogel beads was investigated for fenofibrate, cannabidiol, retinyl acetate, orlistat, and lumefantrine. To generate the acceptor system, a trimyristin nanoemulsion was incorporated into Ca-alginate microspheres (mean diameter ~40 µm) with a spraying method. Using this approach, the advantages of small lipophilic acceptor particles with a large interfacial area were combined with a single separation process from the donor via a filtration step. The method was applicable to distinguish between fast (fenofibrate) and slow drug transfer (lumefantrine) with good time resolution. Lipophilicity, estimated according to the calculated logP value of the respective drug, was a major factor influencing the transfer performance: the higher the logP value, the slower the transfer. This experimental setup is a promising technique to investigate the release of poorly water-soluble drugs from various types of nanocarriers under closer to physiological conditions than with many other methods currently applied.

Self-Assembly of pH-Labile Polymer Nanoparticles for Paclitaxel Prodrug Delivery: Formulation, Characterization, and Evaluation

The efficacy of paclitaxel (PTX) is limited due to its poor solubility, poor bioavailability, and acquired drug resistance mechanisms. Designing paclitaxel prodrugs can improve its anticancer activity and enable formulation of nanoparticles. Overall, the aim of this work is to improve the potency of paclitaxel with prodrug synthesis, nanoparticle formation, and synergistic formulation with lapatinib. Specifically, we improve potency of paclitaxel by conjugating it to α-tocopherol (vitamin E) to produce a hydrophobic prodrug (Pro); this increase in potency is indicated by the 8-fold decrease in half maximal inhibitory concentration (IC50) concentration in ovarian cancer cell line, OVCA-432, used as a model system. The efficacy of the paclitaxel prodrug was further enhanced by encapsulation into pH-labile nanoparticles using Flash NanoPrecipitation (FNP), a rapid, polymer directed self-assembly method. There was an 1100-fold decrease in IC50 concentration upon formulating the prodrug into nanoparticles. Notably, the prodrug formulations were 5-fold more potent than paclitaxel nanoparticles. Finally, the cytotoxic effects were further enhanced by co-encapsulating the prodrug with lapatinib (LAP). Formulating the drug combination resulted in synergistic interactions as indicated by the combination index (CI) of 0.51. Overall, these results demonstrate this prodrug combined with nanoparticle formulation and combination therapy is a promising approach for enhancing paclitaxel potency.

Separation of no-carrier-added 203Pb, a surrogate radioisotope, from proton irradiated natTl2CO3 target using calcium alginate hydrogel beads

203Pb is a promising radioisotope in the field of medical science as an imaging surrogate of 212Pb. In the present investigation 203Pb was produced by proton irradiation of natural Tl2CO3 target and was separated from the bulk Tl target using calcium alginate (CA) hydrogel beads with a high separation factor (3.8×104 at 10−3 M HNO3). During the separation process 203Pb was encapsulated in CA beads and desorption of the radioisotope could only be achieved in 1M HNO3. Possibility of Tl uptake was also checked in Fe doped CA (Fe-CA) beads after oxidation of Tl(I) to Tl(III) by sodium bismuthate. No significant uptake of Tl(III) was noticed in the Fe-CA beads. The matrix is therefore suitable for isolation of 203Pb from the target as well as its storage in the bead for therapeutic as well as diagnostic purpose.

Determining drug release rates of hydrophobic compounds from nanocarriers

Obtaining meaningful drug release profiles for drug formulations is essential prior to in vivo testing and for ensuring consistent quality. The release kinetics of hydrophobic drugs from nanocarriers (NCs) are not well understood because the standard protocols for maintaining sink conditions and sampling are not valid owing to mass transfer and solubility limitations. In this work, a new in vitroassay protocol based on 'lipid sinks' and magnetic separation produces release conditions that mimic the concentrations of lipid membranes and lipoproteins in vivo, facilitates separation, and thus allows determination of intrinsic release rates of drugs from NCs. The assay protocol is validated by (i) determining the magnetic separation efficiency, (ii) demonstrating that sink condition requirements are met, and (iii) accounting for drug by completing a mass balance. NCs of itraconazole and cyclosporine A (CsA) were prepared and the drug release profiles were determined. This release protocol has been used to compare the drug release from a polymer stabilized NC of CsA to a solid drug NP of CsA alone. These data have led to the finding that stabilizing block copolymer layers have a retarding effect on drug release from NCs, reducing the rate of CsA release fourfold compared with the nanoparticle without a polymer coating.This article is part of the themed issue 'Soft interfacial materials: from fundamentals to formulation'.

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.