Liposomal Copermeation Assay Reveals Unexpected Membrane Interactions of Commonly Prescribed Drugs.

The permeation of small molecules across biological membranes is a crucial process that lies at the heart of life. Permeation is involved not only in the maintenance of homeostasis at the cell level but also in the absorption and biodistribution of pharmacologically active substances throughout the human body. Membranes are formed by phospholipid bilayers that represent an energy barrier for permeating molecules. Crossing this energy barrier is assumed to be a singular event, and permeation has traditionally been described as a first-order kinetic process, proportional only to the concentration gradient of the permeating substance. For a given membrane composition, permeability was believed to be a unique property dependent only on the permeating molecule itself. We provide experimental evidence that this long-held view might not be entirely correct. Liposomes were used in copermeation experiments with a fluorescent probe, where simultaneous permeation of two substances occurred over a single phospholipid bilayer. Using an assay of six commonly prescribed drugs, we have found that the presence of a copermeant can either enhance or suppress the permeation rate of the probe molecule, often more than 2-fold in each direction. This can have significant consequences for the pharmacokinetics and bioavailability of commonly prescribed drugs when used in combination and provide new insight into so-far unexplained drug-drug interactions as well as changing the perspective on how new drug candidates are evaluated and tested.

Computational Prodrug Design Methodology for Liposome Formulability Enhancement of Small-Molecule APIs.

Encapsulation into liposomes is a formulation strategy that can improve efficacy and reduce side effects of active pharmaceutical ingredients (APIs) that exhibit poor biodistribution or pharmacokinetics when administered alone. However, many APIs are unsuitable for liposomal formulations intended for parenteral administration due to their inherent physicochemical properties─lipid bilayer permeability and water-lipid equilibrium partitioning coefficient. Too high permeability results in premature leakage from liposomes, while too low permeability means the API is not able to pass across biological barriers. There are several options for solving this issue: (i) change of the lipid bilayer composition, (ii) addition of a permeability enhancer, or (iii) modification of the chemical structure of the API to design a prodrug. The latter approach was taken in the present work, and the effect of small changes in the molecular structure of the API on its permeation rate across a lipidic bilayer was systematically explored utilizing computer simulations. An in silico methodology for prodrug design based on the COSMOperm approach has been proposed and applied to four APIs (abiraterone, cytarabine, 5-fluorouracil, and paliperidone). It is shown that the addition of aliphatic hydrocarbon chains via ester or amide bonds can render the molecule more lipophilic and increase its permeability by approximately 1 order of magnitude for each 2 carbon atoms added, while the formation of fructose adducts can provide a more hydrophilic character to the molecule and reduce its lipid partitioning. While partitioning was found to depend only on the size and type of the added group, permeability was found to depend also on the added group location. Overall, it has been shown that both permeability and lipid partitioning coefficient can be systematically shifted into the desired liposome formulability window by appropriate group contributions to the parental drug. This can significantly increase the portfolio of APIs for which liposome or lipid nanoparticle formulations become feasible.

The effect of deoxyfluorination and O-acylation on the cytotoxicity of N-acetyl-D-gluco- and D-galactosamine hemiacetals.

Fully acetylated deoxyfluorinated hexosamine analogues and non-fluorinated 3,4,6-tri-O-acylated N-acetyl-hexosamine hemiacetals have previously been shown to display moderate anti-proliferative activity. We prepared a set of deoxyfluorinated GlcNAc and GalNAc hemiacetals that comprised both features: O-acylation at the non-anomeric positions with an acetyl, propionyl and butanoyl group, and deoxyfluorination at selected positions. Determination of the in vitro cytotoxicity towards the MDA-MB-231 breast cancer and HEK-293 cell lines showed that deoxyfluorination enhanced cytotoxicity in most analogues. Increasing the ester alkyl chain length had a variable effect on the cytotoxicity of fluoro analogues, which contrasted with non-fluorinated hemiacetals where butanoyl derivatives had always higher cytotoxicity than acetates. Reaction with 2-phenylethanethiol indicated that the recently described S-glyco-modification is an unlikely cause of cytotoxicity.

Nanoformulations for dermal delivery of imiquimod: The race of "soft" against "hard".

Imiquimod (IMQ) is an immunostimulating agent used in the treatment of basal cell carcinoma and actinic keratosis. Due to its low solubility and poor skin bioavailability, the dermal formulation of IMQ remains challenging. In analogy to tyre compounds used in Formula 1 racing, we compare four types of nanosystems belonging to three groups: (i) "hard" nanoparticles in the form of IMQ nanocrystals, (ii) "intermediate" nanoparticles in the form of liposomes and lipid nanocapsules, and (iii) "soft" nanoparticles in the form of a nanoemulsion based on oleic acid. The nanoemulsion and nanocrystals were able to incorporate the highest amount of IMQ (at least 2 wt%) compared to liposomes (0.03 wt%) and lipid nanocapsules (0.08 wt%). Regarding size, liposomes, and lipid nanocapsules were rather small (around 40 nm) whereas nanocrystals and nanoemulsion were larger (around 200 nm). All developed nanoformulations showed high efficiency to deliver IMQ into the skin tissue without undesirable subsequent permeation through the skin to acceptor. Especially, the 2 wt% IMQ nanoemulsion accumulated 129 µg/g IMQ in the skin, compared to 34 µg/g of a 5 wt% commercial cream. The effects of the respective nanoparticulate systems were discussed with respect to their possible diffusion kinetics (Brownian motion vs. settling) in the aqueous phase.

Ceramide liposomes for skin barrier recovery: A novel formulation based on natural skin lipids.

Diseases related to a disrupted skin barrier are accompanied by lower levels of ceramides in the stratum corneum (SC) lipid matrix. Delivering ceramides directly into damaged skin is a viable alternative to conventional corticosteroids, but is hindered by their low skin bioavailability and limited nanoformulation ability. Here, we developed stable liposomal systems containing ceramides and other SC lipids, and tested their effectiveness in skin barrier repair. Lipid film hydration and high-pressure homogenization were used to prepare different types of liposomes. To determine the stability, the particle size and polydispersity index were measured. The optimal systems were found to include ceramide 3 and 6, cholesterol and stearic acid, with 10% urea in phosphate-buffered saline as the aqueous phase. The ability of the system to repair chemically-damaged porcine skin was tested. While treatment by a standard lipid suspension reduced the passage of a model permeant only to a limited extent, drug flux through the liposomally-treated skin was much closer to permeation through intact skin. The non-homogenized liposomes were more effective than their homogenized version. These findings were also confirmed by FTIR measurements. This suggests that our approach to liposomal development has considerable potential for the repair of a disrupted skin barrier.

Multilobed Magnetic Liposomes Enable Remotely Controlled Collection, Transport, and Delivery of Membrane-Soluble Cargos to Vesicles and Cells.

Lipid bilayers are the basic structural components of all living systems, forming the membranes of cells, sub-cellular organelles, and extracellular vesicles. A class of man-made lipidic vesicles called multilobed magnetic liposomes (MMLs) is reported in this work; these MMLs possess a previously unattained combination of features owing to their unique multilobe structure and composition. MMLs consist of a central cluster of lipid-coated magnetic iron oxide nanoparticles that lend them a magnetophoretic velocity comparable to the most efficient living microswimmers. Multiple liposome-like lobes protrude from the central region; these can incorporate both water-soluble and lipid-soluble molecular payloads at high carrying capacity and exchange the incorporated substances with the membranes of both artificial and live cells by the contact diffusion mechanism. The size of MMLs is controllable in the range of 200-800 nm. Their functionality is demonstrated by completing a model mission where MMLs are remotely controlled to collect, transport, and deliver a cargo to live cells.

Evaluation of ß-glucan particles as dual-function carriers for poorly soluble drugs.

Yeast glucan particles are porous polysaccharide cell walls extracted from Saccharomyces cerevisiae. Being mildly immunogenic, they are efficiently phagocytosed and have therefore been proposed as possible vehicles for drug delivery. Using curcumin as a model poorly water-soluble drug, a systematic comparison of three different physical loading methods - incipient wetness impregnation, slurry evaporation, and spray drying - was carried out and their influence on the particle morphology, encapsulation efficiency, amorphous drug content and release kinetics was evaluated. It was found that yeast glucan particles can contain up to 30% wt. of curcumin in the amorphous form when prepared by slurry evaporation. The dissolution of curcumin from glucan particles lead to a supersaturated solution in asimilar way as amorphous solid dispersions do, despite the fact that glucan particles themselves do not dissolve. Bi-phasic dissolution tests revealed up to 4-fold acceleration of curcumin dissolution rate from amorphous glucan particles compared to its crystalline form. Crucially, glucan particles were shown to retain the ability to be recognised and phagocytosed even after drug encapsulation.

Drug loading to mesoporous silica carriers by solvent evaporation: A comparative study of amorphization capacity and release kinetics.

The sorption of poorly aqueous soluble active pharmaceutical ingredients (API) to mesoporous silica carriers is an increasingly common formulation strategy for dissolution rate enhancement for this challenging group of substances. However, the success of this approach for a particular API depends on an array of factors including the properties of the porous carrier, the loading method, or the attempted mass fraction of the API. At present, there is no established methodology for the rational selection of these parameters. In the present work, we report a systematic comparison of four well-characterised silica carriers and seven APIs loaded by the same solvent evaporation method. In each case, we find the maximum amorphization capacity by x-ray powder diffraction analysis and measure the in vitro drug release kinetics. For a selected case, we also demonstrate the potential for bioavailability enhancement by a permeation essay.