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Method Article
A liquid crystal nanoparticle (LCNP) nanocarrier is exploited as a vehicle for the controlled delivery of a hydrophobic cargo to the plasma membrane of living cells.
The controlled delivery of drug/imaging agents to cells is critical for the development of therapeutics and for the study of cellular signaling processes. Recently, nanoparticles (NPs) have shown significant promise in the development of such delivery systems. Here, a liquid crystal NP (LCNP)-based delivery system has been employed for the controlled delivery of a water-insoluble dye, 3,3′-dioctadecyloxacarbocyanine perchlorate (DiO), from within the NP core to the hydrophobic region of a plasma membrane bilayer. During the synthesis of the NPs, the dye was efficiently incorporated into the hydrophobic LCNP core, as confirmed by multiple spectroscopic analyses. Conjugation of a PEGylated cholesterol derivative to the NP surface (DiO-LCNP-PEG-Chol) enabled the binding of the dye-loaded NPs to the plasma membrane in HEK 293T/17 cells. Time-resolved laser scanning confocal microscopy and Förster resonance energy transfer (FRET) imaging confirmed the passive efflux of DiO from the LCNP core and its insertion into the plasma membrane bilayer. Finally, the delivery of DiO as a LCNP-PEG-Chol attenuated the cytotoxicity of DiO; the NP form of DiO exhibited ~30-40% less toxicity compared to DiOfree delivered from bulk solution. This approach demonstrates the utility of the LCNP platform as an efficient modality for the membrane-specific delivery and modulation of hydrophobic molecular cargos.
Since the advent of interfacing nanomaterials (materials ≤100 nm in at least one dimension) with living cells, a continuing goal has been to take advantage of the unique size-dependent properties of nanoparticles (NPs) for various applications. These applications include cell and tissue labeling/imaging (both in vitro and in vivo), real-time sensing, and the controlled delivery of drugs and other cargos1. Examples of such relevant NP properties include the size-dependent emission of semiconductor nanocrystals (quantum dots, QDs); the photothermal properties of gold nanoparticles; the large loading capacity of the aqueous core of liposomes; and the ballistic conductivity of carbon allotropes, such as single-wall carbon nanotubes and graphene.
More recently, significant interest has arisen in the use of NPs for the controlled modulation of drugs and other cargos, such as contrast/imaging agents. Here, the rationale is to significantly enhance/optimize the overall solubility, delivered dose, circulation time, and eventual clearance of the drug cargo by delivering it as an NP formulation. This has come to be known as NP-mediated drug delivery (NMDD), and there are currently seven FDA-approved NP drug formulations for use in the clinic to treat various cancers and hundreds more in various stages of clinical trials. In essence, the goal is to "achieve more with less;" that is, to use the NP as a scaffold to deliver more drug with fewer dosing administrations by taking advantage of the large surface area:volume (e.g., hard particles, such as QDs and metal oxides) of NPs or their large interior volume for loading large cargo payloads (e.g., liposomes or micelles). The purpose here is to reduce the necessity for multiple systemically delivered dosing regimens while at the same time promoting aqueous stability and enhanced circulation, particularly for challenging hydrophobic drug cargos that, while highly effective, are sparingly soluble in aqueous media.
Thus, the goal of the work described herein was to determine the viability of using a novel NP scaffold for the specific and controlled delivery of hydrophobic cargos to the lipophilic plasma membrane bilayer. The motivation for the work was the inherent limited solubility and difficulty in the delivery of hydrophobic molecules to cells from aqueous media. Typically, the delivery of such hydrophobic molecules requires the use of organic solvents (e.g., DMSO) or amphiphilic surfactants (e.g., Poloxamers), which can be toxic and compromise cell and tissue viability2, or micelle carriers, which can have limited internal loading capacities. The NP carrier chosen here was a novel liquid crystal NP (LCNP) formulation developed previously3 and that had been shown previously to achieve a ~40-fold improvement in the efficacy of the anticancer drug doxorubicin in cultured cells4.
In the work described herein, the representative cargo selected was the potentiometric membrane dye, 3,3'-dioctadecyloxacarbocyanine perchlorate (DiO). DiO is a water-insoluble dye that has been used for anterograde and retrograde tracing in living and fixed neurons, membrane potential measurements, and for general membrane labeling5,6,7,8,9. Due to its hydrophobic nature, DiO is typically added directly to cell monolayers or tissues in a crystalline form10, or it is incubated at very high concentrations (~1-20 µM) after dilution from a concentration stock solution11,12.
Here, the approach was use to the LCNP platform, a multifunctional NP whose inner core is completely hydrophobic and whose surface is simultaneously hydrophilic and amenable to bioconjugation, as a delivery vehicle for DiO. DiO is incorporated into the LCNP core during synthesis, and the NP surface is then functionalized with a PEGylated cholesterol moiety to promote the membrane binding of the DiO-LCNP ensemble to the plasma membrane. This approach resulted in a delivery system that partitioned the DiO into the plasma membrane with greater fidelity and membrane residence time than the free form of DiO delivered from bulk solution (DiOfree). Further, this method showed that the LCNP-mediated delivery of DiO substantially modulates and drives the rate of specific partitioning of the dye into the lipophilic plasma membrane bilayer. This is achieved while concomitantly reducing the cytotoxicity of the free drug by ~40% by delivering it as an LCNP formulation.
It is anticipated that the methodology described herein will be a powerful enabling technique for researchers whose work involves or requires the cellular delivery of highly hydrophobic cargos that are sparingly soluble or completely insoluble in aqueous solution.
1. Preparation of DiO-LCNP and DiO-LCNP-PEG-Chol
2. Characterization of DiO-LCNP and DiO-LCNP-PEG-Chol
3. Preparation of Cell Culture Dishes for Delivery Experiments and Imaging
NOTE: DiO-LCNP labeling is performed on HEK 293T/17 human embryonic kidney cells (between passages 5 and 15) that are cultured as described previously4. Perform the delivery experiments and the subsequent cell imaging as described below.
4. Cellular Delivery of DiO and DiO-LCNPs and Imaging of Fixed Cells
5. Cellular Delivery of DiO and DiO-LCNPs and FRET Imaging in Live Cells
NOTE: In this method, cells are colabeled with 6 µM each DiO-LCNP-PEG-Chol (where DiO is a FRET donor) and 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiIfree, where DiI is a FRET acceptor). The release of DiO from DiO-LCNP-PEG-Chol and its incorporation into the plasma membrane is confirmed by an observed increase in energy transfer from the DiO donor to the DiI acceptor.
6. Cytotoxicity Assay of DiO and DiO-LCNPs to the HEK 293T/17 Cells
NOTE: The cytotoxicity of the DiO-LCNP materials is assessed using a tetrazolium dye-based proliferation assay17. Cells are cultured in a multiwell plate in the presence of varying concentrations of the materials under conditions that emulate delivery/labeling. The cells are then cultured for 72 hr to allow for proliferation. A dye (MTS, (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium) is then added to the wells, and metabolically active cells convert the dye into a blue formazan product. The amount of color formation is directly proportional to the number of viable cells.
7. Data Analysis
LCNPs were prepared in which the hydrophobic core of the NP was loaded with a representative membrane-labeling probe to demonstrate the utility of the LCNP as an efficient delivery vehicle for hydrophobic cargos. For this purpose, the cargo chosen was the highly water-insoluble potentiometric membrane-labeling dye, DiO. DiO-loaded LCNPs (DiO-LCNPs) were synthesized using a two-phase mini-emulsion technique with the chemical components DACTP11, AC10COONa, and DiO, as shown in Figure 1
A continuing goal of NMDD is the controlled targeting and delivery of drug formulations to cells and tissues, combined with simultaneous improved drug efficacy. One specific class of drug molecules for which this has posed a significant challenge is hydrophobic drugs/imaging agents that have sparingly to no solubility in aqueous media. This problem has plagued the transition of potent drugs from in vitro cell culture systems to the clinical setting and has resulted in a number of promising drug molecules being &...
The authors declare that they have no competing financial interests.
This work was supported by the NRL Base Funding Program (Work Unit MA041-06-41-4943). ON is supported by a National Research Council Postdoctoral Research Associateship.
Name | Company | Catalog Number | Comments |
1-ethyl-3-(3-(dimethylamino)-propyl)carbodiimide hydrochloride (EDCA) | ThermoFisher | E2247 | |
3,3′-dioctadecyloxacarbocyanine perchlorate (DiO) | Sigma Aldrich | D4292-20MG | Hazardous; make stock solution in DMSO |
Cholesterol poly(ethylene glycol) amine hydrochloride | Nanocs, Inc. | PG2-AMCS-2k | |
Countess automated cell counter | ThermoFisher | C10227 | |
Dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate (DiI) | Sigma Aldrich | 468495-100MG | Hazardous; make stock solution in DMSO |
Dulbecco's Modified Eagle's Medium (DMEM) | ThermoFisher | 21063045 | Warm in 37 °C before use |
Dulbecco's Phosphate Buffered Saline (DPBS) | ThermoFisher | 14040182 | Warm in 37 °C before use |
Dynamic light scattering instrument | ZetaSizer NanoSeries (Malvern Instruments Ltd., Worcestershire, UK) | ||
Fibronectin Bovine Protein, Plasma | ThermoFisher | 33010018 | Make stock solution 1 mg/ml using DPBS. Use 20-30 µg/ml for coating MetTek dish, 2 hr at 37 °C |
Formaldehyde (16%, W/V) | ThermoFisher | 28906 | Hazardous; dilute to 4% using DPBS |
Human embryonic kidney cells (HEK 293T/17) | American Type Culture Collection | ATCC® CRL-11268™ | |
Live cell imaging solution (LCIS) | ThermoFisher | A14291DJ | Warm in 37 °C before use |
MatTek 14 mm # 1.0 coverglass insert cell culture dish | MatTek corporation | P35G-1.0-14-C | |
Modified Eagle Medium (DMEM) containing 25 mM HEPES | ThermoFisher | 21063045 | Warm in 37 °C before use |
N-hydroxysulfosuccinimide sodium salt (NHSS) | ThermoFisher | 24510 | |
Nikon A1si spectral confocal microscope | Nikon Instruments | ||
Trypan Blue Stain (0.4%) | ThermoFisher | T10282 | mix as a 50% to the cell suspension before counting the cells |
Zeta potential instrument | ZetaSizer NanoSeries (Malvern Instruments Ltd., Worcestershire, UK) | ||
Ultrasonic Processor | Sonics and Materials Inc | GEX 600-5 | |
Mini Cetntrifuge | Benchmark | Mini-fuge-04477 | |
PD-10 Sephadex™ G-25 Medium | GE Healthcare | 17-0851-01 | |
Bio-Rad ChemiDoc XRS Imaging System | Bio-RAD | 76S/07434 | |
Trypsin-EDTA (0.25%), phenol red | ThermoFisher | 25200056 |
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