Screening for Optimal Liposome Preparation Conditions by Using Dual Centrifugation and Time-Resolved Fluorescence Measurements

Dual centrifugation as fast and novel screening approach for optimal RNA loaded lipid-based nanoparticles

The last decade has shown increased benefits for non-viral gene delivery. To overcome the challenges of nucleic acid administration, appropriate drug delivery systems (DDS) are required. The recently approved RNA formulations have demonstrated that lipid nanoparticles (LNPs) are suitable DDS for delivering RNAs. LNPs are commonly composed of cationic and/or ionizable lipids, helper lipids and PEGylated lipids. Conventional manufacturing procedures for LNPs are mixing systems, such as microfluidics, with drawbacks in terms of time and resource consumption. The LNPs produced also pose problems with storage stability. Based on a microRNA (miRNA) model, we present dual centrifugation (DC) as a novel and reproducible way for preparing RNA loaded LNP formulations via in-vial homogenization. Our formulations show promising results in size characteristics, as well as in their cell performance. Depending on the lipid composition of the LNPs, a remarkable knockdown efficiency is achieved. With a net formulation time of 7 min, an enormously fast approach can be presented. DC offers the capability for fast LNP screenings, with a loading capacity of up to 40 vials per run. The simplicity of the method could take advantage of bedside preparation, overcoming the hurdles of storage stability for LNP formulations.

Novel thermosensitive small multilamellar lipid nanoparticles with promising release characteristics made by dual centrifugation

Thermosensitive liposomes (TSLs) have great potential for the selective delivery of cytostatic drugs to the tumor site with greatly reduced side effects. Here we report the discovery and characterization of new thermosensitive small multilamellar lipid nanoparticles (tSMLPs) with unusually high temperature selectivity. Furthermore, the temperature-dependent release of the fluorescent marker calcein from tSMLPs is enhanced by human serum albumin. tSMLPs can easily be prepared through dual centrifugation (DC) at very high lipid concentrations using dipalmitoyl and distearoyl phosphatidylcholine (DPPC, DSPC) and the phospholipid dipalmitoyl-sn-glycero-phosphatidyldiglycerol (DPPG2). The new particles have a hydrodynamic diameter of about 175 nm and a narrow size distribution (PDI 0.02). tSMLPs consist of multiple lipid membranes, which become increasingly closer packed towards the particle center, and have no visible aqueous core. The particles are highly stable due to strong hydrogen bond-based membrane interactions mediated by DPPG2. tSMLPs can be used as carriers for water-soluble drugs (EE 25 %) entrapped within the interlamellar spaces. Based on biophysical (DSC, DLS and ITC) and morphological (cryo-EM) studies, a hypothesis is presented to explain the structural basis underlying the high temperature selectivity, as well as the unusual morphology of the new thermosensitive lipid nanoparticles.

Dual Centrifugation-Based Screening for pH-Responsive Liposomes

In liposomal drug delivery development, the delicate balance of membrane stability is a major challenge to prevent leakage (during shelf-life and blood circulation), and to ensure efficient payload release at the therapeutic destination. Our composite screening approach uses the processing by dual centrifugation technique to speed up the identification of de novo formulations of intermediate membrane stability. By screening binary lipid combinations at systemically varied ratios we highlight liposomal formulations of intermediate stability, what we termed "the edge of stability", requiring moderate stimuli for destabilization. Supplementation with a pH-sensitive cholesterol derivative (to obtain acid labile liposomes) and renewed assessment with cargo load led to the discovery of three formulations with sufficient shelf-life stability, acceptable cargo retention and efficient pH-responsive cargo release in vitro. The "lead candidates" exhibited promising in cellulo uptake with increased intracellular cargo release and revealed in vivo performance advantages compared to a control liposome. Our approach filters lipid compositions on "the edge of stability" that were introduced with a pH-sensitive cholesterol derivate leading pH-responsive liposomes, out of a multidimensional parameter space. Their discovery by rational approaches would have been highly unlikely, thus highlighting the potential of our screening approach.

In vitro and in ovo photodynamic efficacy of nebulized curcumin-loaded tetraether lipid liposomes prepared by DC as stable drug delivery system

Lung cancer is one of the most common causes of high mortality worldwide. Current treatment strategies, e.g., surgery, radiotherapy, chemotherapy, and immunotherapy, insufficiently affect the overall outcome. In this study, we used curcumin as a natural photosensitizer in photodynamic therapy and encapsulated it in liposomes consisting of stabilizing tetraether lipids aiming for a pulmonary drug delivery system against lung cancer. The liposomes with either hydrolyzed glycerol-dialkyl-glycerol tetraether (hGDGT) in different ratios or hydrolyzed glycerol-dialkyl-nonitol tetraether (hGDNT) were prepared by dual centrifugation (DC), an innovative method for liposome preparation. The liposomes' physicochemical characteristics before and after nebulization and other nebulization characteristics confirmed their suitability. Morphological characterization using atomic force and transmission electron microscopy showed proper vesicular structures indicative of liposomes. Qualitative and quantitative uptake of the curcumin-loaded liposomes in lung adenocarcinoma (A549) cells was visualized and proven. Phototoxic effects of the liposomes were detected on A549 cells, showing decreased cell viability. The generation of reactive oxygen species required for PDT and disruption of mitochondrial membrane potential were confirmed. Moreover, the chorioallantoic membrane (CAM) model was used to further evaluate biocompatibility and photodynamic efficacy in a 3D cell culture context. Photodynamic efficacy was assessed by PET/CT after nebulization of the liposomes onto the xenografted tumors on the CAM with subsequent irradiation. The physicochemical properties and the efficacy of tetraether lipid liposomes encapsulating curcumin, especially liposomes containing hGDNT, in 2D and 3D cell cultures seem promising for future PDT usage against lung cancer.

Evaluating the photodynamic efficacy of nebulized curcumin-loaded liposomes prepared by thin-film hydration and dual centrifugation: In vitro and in ovo studies

Lung cancer, one of the most common causes of high mortality worldwide, still lacks appropriate and convenient treatment options. Photodynamic therapy (PDT) has shown promising results against cancer, especially in recent years. However, pulmonary drug delivery of the predominantly hydrophobic photosensitizers still represents a significant obstacle. Nebulizing DPPC/Cholesterol liposomes loaded with the photosensitizer curcumin via a vibrating mesh nebulizer might overcome current restrictions. In this study, the liposomes were prepared by conventional thin-film hydration and two other methods based on dual centrifugation. The liposomes' physicochemical properties were determined before and after nebulization, showing that liposomes do not undergo any changes. However, morphological characterization of the differently prepared liposomes revealed structural differences between the methods in terms of lamellarity. Internalization of curcumin in lung adenocarcinoma (A549) cells was visualized and quantified. The generation of reactive oxygen species because of the photoreaction was also proven. The photodynamic efficacy of the liposomal formulations was tested against A549 cells. They revealed different phototoxic responses at different radiant exposures. Furthermore, the photodynamic efficacy was investigated after nebulizing curcumin-loaded liposomes onto xenografted tumors on the CAM, followed by irradiation, and evaluated using positron emission tomography/computed tomography and histological analysis. A decrease in tumor metabolism could be observed. Based on the efficacy of curcumin-loaded liposomes in 2D and 3D models, liposomes, especially with prior film formation, can be considered a promising approach for PDT against lung cancer.

Dual centrifugation as a novel and efficient method for the preparation of lipodisks

Polyethylene glycol (PEG)-stabilized lipodisks have emerged as innovatiive, promising nanocarriers for several classes of drugs. Prior research underscores the important role of lipid composition and preparation method in determining the lipodisk size, uniformity, and drug loading capacity. In this study, we investigate dual centrifugation (DC) as a novel technique for the production of PEG-stabilized lipodisks. Moreover, we explore the potential use of DC for the encapsulation of two model drugs, curcumin and doxorubicin, within the disks. Our results show that by a considerate choice of experimental conditions, DC can be used as a fast and straightforward means to produce small and homogenous lipodisks with a hydrodynamic diameter of 20-30 nm. Noteworthy, the technique works well for the production of both cholesterol-free and cholesterol-containing disks and does not require pre-mixing of the lipids in organic solvent. Furthermore, our investigations confirm the efficacy of DC in formulating curcumin and doxorubicin within these lipodisks. For doxorubicin, careful control and optimization of the experimental conditions resulted in formulations displaying an encouraging encapsulation efficiency of 84 % and a favourable drug-to-lipid ratio of 0.13 in the disks.

Modern Photodynamic Glioblastoma Therapy Using Curcumin- or Parietin-Loaded Lipid Nanoparticles in a CAM Model Study

Natural photosensitizers, such as curcumin or parietin, play a vital role in photodynamic therapy (PDT), causing a light-mediated reaction that kills cancer cells. PDT is a promising treatment option for glioblastoma, especially when combined with nanoscale drug delivery systems. The curcumin- or parietin-loaded lipid nanoparticles were prepared via dual asymmetric centrifugation and subsequently characterized through physicochemical analyses including dynamic light scattering, laser Doppler velocimetry, and atomic force microscopy. The combination of PDT and lipid nanoparticles has been evaluated in vitro regarding uptake, safety, and efficacy. The extensive and well-vascularized chorioallantois membrane (CAM) of fertilized hen's eggs offers an optimal platform for three-dimensional cell culture, which has been used in this study to evaluate the photodynamic efficacy of lipid nanoparticles against glioblastoma cells. In contrast to other animal models, the CAM model lacks a mature immune system in an early stage, facilitating the growth of xenografts without rejection. Treatment of xenografted U87 glioblastoma cells on CAM was performed to assess the effects on tumor viability, growth, and angiogenesis. The xenografts and the surrounding blood vessels were targeted through topical application, and the effects of photodynamic therapy have been confirmed microscopically and via positron emission tomography and X-ray computed tomography. Finally, the excised xenografts embedded in the CAM were analyzed histologically by hematoxylin and eosin and KI67 staining.

Preparation of Nanosized Pharmaceutical Formulations by Dual Centrifugation

Dual centrifugation (DC) is an innovative in-vial homogenization and in-vial nanomilling technique that has been in use for the preparation of liposomes for more than one decade. Since then, DC has continuously been developed for preparing various liposomes and other lipid nanoparticles including emulsions and solid lipid nanoparticles (SLNs) as well as polymersomes and nanocrystals. Improvements in equipment technology have been achieved over the past decade, so that DC is now on its way to becoming the quasi-standard for the simple, fast, and aseptic production of lipid nanoparticles and nanocrystals in small and medium batch sizes, including the possibility of simple and fast formulation screening or bedside preparations of therapeutic nanoparticles. More than 68 publications in which DC was used to produce nanoparticles have appeared since then, justifying an initial review of the use of DC for pharmaceutical nanotechnology.

Tailoring the Lamellarity of Liposomes Prepared by Dual Centrifugation

Dual centrifugation (DC) is a new and versatile technique for the preparation of liposomes by in-vial homogenization of lipid-water mixtures. Size, size distribution, and entrapping efficiencies are strongly dependent on the lipid concentration during DC-homogenization. In this study, we investigated the detailed structure of DC-made liposomes. To do so, an assay to determine the ratio of inner to total membrane surfaces of liposomes (inaccessible surface) was developed based on either time-resolved or steady-state fluorescence spectroscopy. In addition, cryogenic electron microscopy (cryo-EM) was used to confirm the lamellarity results and learn more about liposome morphology. One striking result leads to the possibility of producing a novel type of liposome-small multilamellar vesicles (SMVs) with low PDI, sizes of the order of 100 nm, and almost completely filled with bilayers. A second particularly important finding is that VPGs can be prepared to contain open bilayer structures that will close spontaneously when, after storage, more aqueous phase is added and liposomes are formed. Through this process, a drug can effectively be entrapped immediately before application. In addition, dual centrifugation at lower lipid concentrations is found to produce predominantly unilamellar vesicles.