Name: models and methods to evaluate transport of drug delivery systems across cellular barriers
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Description: Watch this Scientific Journal Video about Models and Methods to Evaluate Transport of Drug Delivery Systems Across Cellular Barriers at JoVE.com

This work was supported by a fellowship of the Howard Hughes Medical Institute and National Science Foundation to R.G, and funds awarded to S.M. by the National Institutes of Health (Grant R01-HL98416) and the American Heart Association (Grant 09BGIA2450014).

1. Culturing a Cell Monolayer in Transwell Inserts
<ol>
	<li>In a sterile, biosafety level 2 cell culture hood, place 0.8 mm&#160;pore PET transwell inserts into a 24-well plate (4 wells per condition, for statistical significance) with forceps. All materials entering the hood should be sterilized with ethanol.</li>
</ol>
Note: The pore size of the filter needs to be selected in accord to the mean size of the NC used, to allow transport across the membrane. Also, for statistically significan...

<ol>
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Using the methods discussed above, a cell model for studying transport of targeted NCs across cellular barriers can be established, such as the example provided for Caco-2 epithelial cells, which is relevant to evaluating transport from the GI lumen into the blood in the case of oral drug delivery systems. Culturing of GI epithelial cell monolayers in transwell inserts enabled measurement of TEER and fluorescence immunostaining of tight junctions to confirm formation of a cell permeability barrier. Subsequently, radiolab...

Cellular barriers in the body act as a gateway between the external environment and internal compartments. This is the case for the epithelial lining separating the externally-exposed surface of the gastrointestinal (GI) tract and the bloodstream1-3. Cellular barriers also represent the interface between the bloodstream and the parenchyma and cellular components of tissues and organs. This is the case for the inner endothelial lining in blood vessels, such as the blood-lung barrier, the blood-brain barrier, etc.1&#160;The ability to traverse these cellular barriers in the body is crucial for efficient delivery of therapeutic and diagnostic agents into the circulation and tissues/organs where intervention is needed.
To improve delivery of therapeutic or diagnostic agents, these compounds can be loaded into sub-micrometer nanocarriers (NCs). These drug delivery vehicles can be formulated with a variety of chemistries and structures to optimize drug solubility, protection, pharmacokinetics, release, and metabolism4,5. NCs can also be functionalized with affinity or targeting moieties (e.g.&#160;antibodies, peptides sugars, aptamers, etc.) to facilitate adhesion to areas of the body where the therapeutic action is required2,6. Targeting of NCs to determinants expressed on the surface of cellular barriers can further facilitate transport into and/or across these linings2,6.
The role of selectively transporting substances between two environments requires certain unique features among cell layers. One such feature is cell polarity, whereby the apical membrane facing the lumen of cavities varies from the basolateral membrane oriented towards the tissue interstitium, with respect to membrane morphology and composition of lipids, transporters, and receptors2. Another feature involves intercellular junctions connecting adjacent cells. Regulation of the proteins that form tight junctions, particularly junctional adhesion molecules (JAMs), occludins, and claudins, modulate the barrier function to selectively allow or not transport of substances between cells, known as paracellular transport, allowing passage of materials from the lumen to the basolateral space3. Binding of many natural and synthetic elements (leukocytes, molecules, particles, and drug delivery systems) to cellular barriers in the body can induce cell-junction opening, which may be transient and relatively innocuous or more prolonged and, therefore, unsafe with access of undesired substances across the barrier2,5,7-9. Consequently, this pathway can be assessed by measuring the transepithelial electrical resistance (TEER) and passive paracellular diffusion of molecules (herein called paracellular leakage), whereby decreased resistance to an electrical current or increased paracellular leakage of an inert compound into the basolateral space indicate opening of cell junctions, respectively5,10,11. To complement these methods, any of the tight junction proteins listed above can be stained to assess their integrity, where staining should appear concentrated at the cell-cell borders all around the cell periphery5,10,12.
Alternatively, drug delivery systems that target specific cell surface determinants, such as those associated to clathrin-coated pits or flask-shaped membrane invaginations called caveolae, may trigger vesicular uptake into cells by endocytosis, providing an avenue for drug delivery to intracellular compartments5,13. In addition, endocytosis may lead to trafficking of vesicles across the cell body for release at the basolateral side, a phenomenon known as transyctosis, or transcellular transport14. Therefore, knowledge of the kinetics and mechanism of endocytosis may be used to exploit intracellular and transcellular drug delivery, which offers a relatively safe and controlled mode of delivery compared to the paracellular route. The mechanism of endocytosis may be evaluated with modulators of classical pathways (clathrin- and caveolin-mediated endocytosis, and macropinocytosis) or non-classical routes (such as the case of cell adhesion molecule (CAM)-mediated endocytosis)5,13,15.
Whereas intracellular trafficking is often studied in standard wells or coverslips, the absence of a basolateral compartment precludes cell polarization and the ability to study transport across cell layers. To overcome this obstacle, transport across cell monolayers has been long studied using transwell inserts10,11,16,17, which consist of an upper (apical) chamber, a porous permeable membrane where cells attach and form a tight monolayer, and a lower (basolateral) chamber (Figure 1). In this configuration, transport can be measured in the apical-to-basolateral direction by administering a treatment into the upper chamber, following transport through the cell monolayer and the underlying porous membrane, and finally collecting the medium in the lower chamber for quantification of transported material. Transport in the basolateral-to-apical direction can also be measured by initial administration to the lower chamber and subsequent collection from the upper chamber5,10,12,16. Various techniques exist to verify the formation of permeability barrier on transwells, including TEER and paracellular transport assays, as described above. In addition, the permeable filter on which cells are cultured can be removed for imaging analysis (e.g.&#160;by fluorescence, confocal, electron microscopy), as further validation of the cell monolayer model as well as the mechanism of transport. Selection of the membrane type, which is available in different pore sizes, materials, and surface areas, depends on various factors such as the size of substances or objects to be transported, cell type, and imaging method16,18-20. Transwell inserts also facilitate controlled and accurate quantification of transport compared to complex mammalian systems, as volumes of the chambers and cell surface area are known constants. While many factors involved in in vivo delivery are eliminated, including the presence of intestinal mucus, shear stress, digestive enzymes, immune cells, etc., this small scale in vitro model provides useful preliminary information regarding transport.
As an example to illustrate the adaptation of these methods to study NC transport across cellular barriers10,11,16,17, we describe here a case where the potential for NC transport across the GI epithelium was modeled by assessing passage of a model drug delivery system through a monolayer of human epithelial colorectal adenocarcinoma (Caco-2) cells. For this purpose, cells were cultured in transwell inserts, on a 0.8 &#956;m&#160;pore polyethylene terephthalate (PET) filter (6.4 mm&#160;diameter), which is transparent and can be used for microscopy imaging. The status of the permeability barrier is validated by measuring TEER, apical-to-basolateral transport of a control substance, albumin, and fluorescence microscopy visualization of an element of the tight junctions, occludin protein. A model of targeted polymer NC is used, consisting of 100&#160;nm, nonbiodegradable polystyrene nanoparticles. NCs are coated by surface adsorption with a targeting antibody alone or a combination of a targeting antibody and a therapeutic cargo, where either component can be labeled with 125I for radioisotope tracing. In the selected example, the antibody recognizes intercellular adhesion molecule-1 (ICAM-1), a protein expressed on the surface of GI epithelial (and other) cells, which has been shown to facilitate intracellular and transcellular transport of drug carriers and their cargoes21. The cargo is alpha-Galactosidase (&#945;-Gal), a therapeutic enzyme used for treatment of Fabry disease, a genetic lysosomal storage disorder22.
The coated NCs, of about 200&#160;nm in size, are added to the apical chamber over the cell monolayer and incubated at 37 &#176;C for varying periods of time, after which 125I on NCs can be detected associated to the cell monolayer and/or transported to the basolateral chamber below the cells. Additional determination of free 125I allows subtraction of the degraded fraction and estimation of coated NC transport. The mechanism of transport is further assessed by examining changes in the permeability barrier pertaining to the paracellular route, through the parameters described above, while transcellular transport is determined by examining changes in transport when modulating pathways of endocytosis and transcytosis.
These methods provide valuable information regarding cellular barrier models, the extent and rate of transport of a drug delivery system, and the mechanism of such transport, altogether allowing evaluation of the potential for drug delivery across cellular barriers.

<table border="1">
	<tbody>
		<tr>
			<td>Transwell inserts</td>
			<td>BD Falcon</td>
			<td>353095</td>
			<td></td>
		</tr>
		<tr>
			<td>Dulbecco&#39;s Modified Eagle&#39;s Medium (DMEM), 1x</td>
			<td>Cellgro</td>
			<td>10-013-CM</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum (FBS)</td>
			<td>Cellgro</td>
			<td>35-015-CV</td>
			<td></td>
		</tr>
		<tr>
			<td>Pen Strep</td>
			<td>Gibco</td>
			<td>15140</td>
			<td></td>
		</tr>
		<tr>
			<td>Human epithelial colorectal adenocarcinoma (Caco-2) cells</td>
			<td>ATCC</td>
			<td>HTB-37TM</td>
			<td></td>
		</tr>
		<tr>
			<td>125Iodine</td>
			<td>Perkin Elmer</td>
			<td>NEZ033H002MC</td>
			<td>Radioactive hazard</td>
		</tr>
		<tr>
			<td>Phosphate Buffer Saline (PBS)</td>
			<td>Gibco</td>
			<td>14190-235</td>
			<td></td>
		</tr>
		<tr>
			<td>Bovine Serum Albumin (BSA)</td>
			<td>Equitech Bio</td>
			<td>BAH-66</td>
			<td></td>
		</tr>
		<tr>
			<td>Paraformaldehyde (16%)</td>
			<td>Fisher Scientific</td>
			<td>15710</td>
			<td></td>
		</tr>
		<tr>
			<td>Mouse Immunoglobulin G (IgG)</td>
			<td>Jackson ImmunoResearch</td>
			<td>015-000-003</td>
			<td></td>
		</tr>
		<tr>
			<td>Mouse monoclonal antibodies to human ICAM-1 (anti-ICAM)</td>
			<td>Marlin 1987</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>&#945;-Galactosidase, from green coffee beans</td>
			<td>Sigma</td>
			<td>G8507-25UN</td>
			<td></td>
		</tr>
		<tr>
			<td>FITC latex beads, 100 nm</td>
			<td>Polysciences, Inc.</td>
			<td>17150</td>
			<td></td>
		</tr>
		<tr>
			<td>Triton X-100</td>
			<td>Sigma</td>
			<td>234729-500ML</td>
			<td></td>
		</tr>
		<tr>
			<td>Trichloroacetic acid (TCA)</td>
			<td>Fisher Scientific</td>
			<td>SA433-500</td>
			<td></td>
		</tr>
		<tr>
			<td>Occludin antibody (Y-12), goat polyclonal anti-human</td>
			<td>Santa Cruz Biotechnology</td>
			<td>Sc-27151</td>
			<td></td>
		</tr>
		<tr>
			<td>Monodansylcadaverine (MDC)</td>
			<td>Sigma</td>
			<td>D4008</td>
			<td></td>
		</tr>
		<tr>
			<td>Filipin</td>
			<td>Sigma</td>
			<td>F9765</td>
			<td></td>
		</tr>
		<tr>
			<td>5-(N-ethyl-N-isopropyl) amiloride (EIPA)</td>
			<td>Sigma</td>
			<td>A3085</td>
			<td></td>
		</tr>
		<tr>
			<td>Wortmannin</td>
			<td>Sigma</td>
			<td>W1628</td>
			<td></td>
		</tr>
		<tr>
			<td>Gamma counter</td>
			<td>Perkin Elmer</td>
			<td>Wizard2</td>
			<td></td>
		</tr>
		<tr>
			<td>Volt-ohm meter</td>
			<td>World Precision Instruments</td>
			<td>EVOM2</td>
			<td></td>
		</tr>
		<tr>
			<td>TEER electrodes</td>
			<td>World Precision Instruments</td>
			<td>STX100</td>
			<td>Electrodes available for different well-plates</td>
		</tr>
		<tr>
			<td>Dynamic Light Scattering (DLS)</td>
			<td>Malvern</td>
			<td>Nano-ZS90</td>
			<td></td>
		</tr>
	</tbody>
</table>

models and methods to evaluate transport of drug delivery systems across cellular barriers

Sub-micrometer carriers (nanocarriers; NCs) enhance efficacy of drugs by improving solubility, stability, circulation time, targeting, and release. Additionally, traversing cellular barriers in the body is crucial for both oral delivery of therapeutic NCs into the circulation and transport from the blood into tissues, where intervention is needed. NC transport across cellular barriers is achieved by: (i) the paracellular route, via transient disruption of the junctions that interlock adjacent cells, or (ii) the transcellular route, where materials are internalized by endocytosis, transported across the cell body, and secreted at the opposite cell surface (transyctosis). Delivery across cellular barriers can be facilitated by coupling therapeutics or their carriers with targeting agents that bind specifically to cell-surface markers involved in transport. Here, we provide methods to measure the extent and mechanism of NC transport across a model cell barrier, which consists of a monolayer of gastrointestinal (GI) epithelial cells grown on a porous membrane located in a transwell insert. Formation of a permeability barrier is confirmed by measuring transepithelial electrical resistance (TEER), transepithelial transport of a control substance, and immunostaining of tight junctions. As an example, ~200&#160;nm polymer NCs are used, which carry a therapeutic cargo and are coated with an antibody that targets a cell-surface determinant. The antibody or therapeutic cargo is labeled with 125I for radioisotope tracing and labeled NCs are added to the upper chamber over the cell monolayer for varying periods of time. NCs associated to the cells and/or transported to the underlying chamber can be detected. Measurement of free 125I allows subtraction of the degraded fraction. The paracellular route is assessed by determining potential changes caused by NC transport to the barrier parameters described above. Transcellular transport is determined by addressing the effect of modulating endocytosis and transcytosis pathways.

As validation of our cell model to study transepithelial transport of targeted NCs, Figure 2 shows that Caco-2 cell monolayers plated at a density of 1.5 &#215; 105 cells/cm2 reached confluence ~Day 12 and maintained monolayer integrity up to Day 18, indicated by TEER (Figure 2A). This was validated by the presence of occludin-positive tight junctions (Figure 2B) in monolayers with high TEER (390 &#937;&#215;cm2, Day 14), compared to poor...

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Models and Methods to Evaluate Transport of Drug Delivery Systems Across Cellular Barriers

Many therapeutic applications require safe and efficient transport of drug carriers and their cargoes across cellular barriers in the body. This article describes an adaptation of established methods to evaluate the rate and mechanism of transport of drug nanocarriers (NCs) across cellular barriers, such as the gastrointestinal (GI) epithelium.

Sub-micrometer carriers (nanocarriers; NCs) enhance efficacy of drugs by improving solubility, stability, circulation time, targeting, and release. ...

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Determination of the Transport Rate of Xenobiotics and Nanomaterials Across the Placenta using the ex vivo Human Placental Perfusion Model

Decades ago the human placenta was thought to be an impenetrable barrier between mother and unborn child. However, the discovery of thalidomide-induced birth defects and many later studies afterwards proved the opposite. Today several harmful xenobiotics like nicotine, heroin, methadone or drugs as well as environmental pollutants were described to overcome this barrier. With the growing use of nanotechnology, the placenta is likely to come into contact with novel nanoparticles either accidentally through exposure or intentionally in the case of potential nanomedical applications. Data from animal experiments cannot be extrapolated to humans because the placenta is the most species-specific mammalian organ 1. Therefore, the ex vivo dual recirculating human placental perfusion, developed by Panigel et al. in 1967 2 and continuously modified by Schneider et al. in 1972 3, can serve as an excellent model to study the transfer of xenobiotics or particles.
Here, we focus on the ex vivo dual recirculating human placental perfusion protocol and its further development to acquire reproducible results.
The placentae were obtained after informed consent of the mothers from uncomplicated term pregnancies undergoing caesarean delivery. The fetal and maternal vessels of an intact cotyledon were cannulated and perfused at least for five hours. As a model particle fluorescently labelled polystyrene particles with sizes of 80 and 500 nm in diameter were added to the maternal circuit. The 80 nm particles were able to cross the placental barrier and provide a perfect example for a substance which is transferred across the placenta to the fetus while the 500 nm particles were retained in the placental tissue or maternal circuit. The ex vivo human placental perfusion model is one of few models providing reliable information about the transport behavior of xenobiotics at an important tissue barrier which delivers predictive and clinical relevant data.

Determination of the Transport Rate of Xenobiotics and Nanomaterials Across the Placenta using the ex vivo Human Placental Perfusion Model

The ex vivo dual recirculating human placental perfusion model can be used to investigate the transfer of xenobiotics and nanoparticles across the human placenta. In this video protocol we describe the equipment and techniques required for a successful execution of a placenta perfusion.

Decades ago the human placenta was thought to be an impenetrable barrier between mother and unborn child. However, the discovery of thalidomide-induced ...

Self-reporting Scaffolds for 3-Dimensional Cell Culture

Culturing cells in 3D on appropriate scaffolds is thought to better mimic the in vivo microenvironment and increase cell-cell interactions. The resulting 3D cellular construct can often be more relevant to studying the molecular events and cell-cell interactions than similar experiments studied in 2D. To create effective 3D cultures with high cell viability throughout the scaffold the culture conditions such as oxygen and pH need to be carefully controlled as gradients in analyte concentration can exist throughout the 3D construct. Here we describe the methods of preparing biocompatible pH responsive sol-gel nanosensors and their incorporation into poly(lactic-co-glycolic acid) (PLGA) electrospun scaffolds along with their subsequent preparation for the culture of mammalian cells. The pH responsive scaffolds can be used as tools to determine microenvironmental pH within a 3D cellular construct. Furthermore, we detail the delivery of pH responsive nanosensors to the intracellular environment of mammalian cells whose growth was supported by electrospun PLGA scaffolds. The cytoplasmic location of the pH responsive nanosensors can be utilized to monitor intracellular pH (pHi) during ongoing experimentation.

Biocompatible pH responsive sol-gel nanosensors can be incorporated into poly(lactic-co-glycolic acid) (PLGA) electrospun scaffolds. The produced self-reporting scaffolds can be used for in&#160;situ monitoring of microenvironmental conditions whilst culturing cells upon the scaffold. This is beneficial as the 3D cellular construct can be monitored in real-time without disturbing the experiment.

Culturing cells in 3D on appropriate scaffolds is thought to better mimic the in vivo microenvironment and increase cell-cell interactions. The resulting ...

Manufacture and Drug Delivery Applications of Silk Nanoparticles

Silk is a promising biopolymer for biomedical and pharmaceutical applications due to its outstanding mechanical properties, biocompatibility and biodegradability, as well its ability to protect and subsequently release its payload in response to a trigger. While silk can be formulated into various material formats, silk nanoparticles are emerging as promising drug delivery systems. Therefore, this article covers the procedures for reverse engineering silk cocoons to yield a regenerated silk solution that can be used to generate stable silk nanoparticles. These nanoparticles are subsequently characterized, drug loaded and explored as a potential anticancer drug delivery system. Briefly, silk cocoons are reverse engineered first by degumming the cocoons, followed by silk dissolution and clean up, to yield an aqueous silk solution. Next, the regenerated silk solution is subjected to nanoprecipitation to yield silk nanoparticles &#8211; a simple but powerful method that generates uniform nanoparticles. The silk nanoparticles are characterized according to their size, zeta potential, morphology and stability in aqueous media, as well as their ability to entrap a chemotherapeutic payload and kill human breast cancer cells. Overall, the described methodology yields uniform silk nanoparticles that can be readily explored for a myriad of applications, including their use as a potential nanomedicine.

Nanoparticles are emerging as promising drug delivery systems for a broad range of indications. Here, we describe a simple yet powerful method to manufacture silk nanoparticles using reverse engineered Bombyx mori silk. These silk nanoparticles can be readily loaded with a therapeutic payload and subsequently explored for drug delivery applications.

Silk is a promising biopolymer for biomedical and pharmaceutical applications due to its outstanding mechanical properties, biocompatibility and ...

An Experimental and Finite Element Protocol to Investigate the Transport of Neutral and Charged Solutes across Articular Cartilage

Osteoarthritis (OA) is a debilitating disease that is associated with degeneration of articular cartilage and subchondral bone. Degeneration of articular cartilage impairs its load-bearing function substantially as it experiences tremendous chemical degradation, i.e. proteoglycan loss and collagen fibril disruption. One promising way to investigate chemical damage mechanisms during OA is to expose the cartilage specimens to an external solute and monitor the diffusion of the molecules. The degree of cartilage damage (i.e. concentration and configuration of essential macromolecules) is associated with collisional energy loss of external solutes while moving across articular cartilage creates different diffusion characteristics compared to healthy cartilage. In this study, we introduce a protocol, which consists of several steps and is based on previously developed experimental micro-Computed Tomography (micro-CT) and finite element modeling. The transport of charged and uncharged iodinated molecules is first recorded using micro-CT, which is followed by applying biphasic-solute and multiphasic finite element models to obtain diffusion coefficients and fixed charge densities across cartilage zones.

We propose a protocol to investigate the transport of charged and uncharged molecules across articular cartilage with the aid of recently developed experimental and numerical methods.

Osteoarthritis (OA) is a debilitating disease that is associated with degeneration of articular cartilage and subchondral bone. Degeneration of articular ...

Surface Functionalization of Hepatitis E Virus Nanoparticles Using Chemical Conjugation Methods

Virus-like particles (VLPs) have been used as nanocarriers to display foreign epitopes and/or deliver small molecules in the detection and treatment of various diseases. This application relies on genetic modification, self-assembly, and cysteine conjugation to fulfill the tumor-targeting application of recombinant VLPs. Compared with genetic modification alone, chemical conjugation of foreign peptides to VLPs offers a significant advantage because it allows a variety of entities, such as synthetic peptides or oligosaccharides, to be conjugated to the surface of VLPs in a modulated and flexible manner without alteration of the VLP assembly.
Here, we demonstrate how to use the hepatitis E virus nanoparticle (HEVNP), a modularized theranostic capsule, as a multifunctional delivery carrier. Functions of HEVNPs include tissue-targeting, imaging, and therapeutic delivery. Based on the well-established structural research of HEVNP, the structurally independent and surface-exposed residues were selected for cysteine replacement as conjugation sites for maleimide-linked chemical groups via thiol-selective linkages. One particular cysteine-modified HEVNP (a Cys replacement of the asparagine at 573 aa (HEVNP-573C)) was conjugated to a breast cancer cell-specific ligand, LXY30 and labeled with near-infrared (NIR) fluorescence dye (Cy5.5), rendering the tumor-targeted HEVNPs as effective diagnostic capsules (LXY30-HEVNP-Cy5.5). Similar engineering strategies can be employed with other macromolecular complexes with well-known atomic structures to explore potential applications in theranostic delivery.

We have engineered the capsid protein of hepatitis E virus as a theranostic nanoparticle (HEVNP). HEVNP self-assembles into a stable icosahedral cage in mucosal delivery. Here, we describe the modification of HEVNPs for tumor targeting by mutating surface-exposed residues to cysteines, which conjugate synthetic ligands that specifically bind tumor cells.

Virus-like particles (VLPs) have been used as nanocarriers to display foreign epitopes and/or deliver small molecules in the detection and treatment of ...

Comprehensive Evaluation of the Effectiveness and Safety of Placenta-Targeted Drug Delivery Using Three Complementary Methods

No effective treatments currently exist for placenta-associated pregnancy complications, and developing strategies for the targeted delivery of drugs to the placenta while minimizing fetal and maternal side effects remains challenging. Targeted nanoparticle carriers provide new opportunities to treat placental disorders. We recently demonstrated that a synthetic placental chondroitin sulfate A binding peptide (plCSA-BP) could be used to guide nanoparticles to deliver drugs to the placenta. In this protocol, we describe in detail a system for assessing the efficiency of drug delivery to the placenta by plCSA-BP that employs three separate methods used in combination: in vivo imaging, high-frequency ultrasound (HFUS), and high-performance liquid chromatography (HPLC). Using in vivo imaging, plCSA-BP-guided nanoparticles were visualized in the placentas of live animals, while HFUS and HPLC demonstrated that plCSA-BP-conjugated nanoparticles efficiently and specifically delivered methotrexate to the placenta. Thus, a combination of these methods can be used as an effective tool for the targeted delivery of drugs to the placenta and development of new treatment strategies for several pregnancy complications.

We describe a system that utilizes three methods to evaluate the safety and effectiveness of placenta-targeted drug delivery: in vivo imaging to monitor nanoparticle accumulation, high-frequency ultrasound to monitor placental and fetal development, and HPLC to quantify drug delivery to tissue.

No effective treatments currently exist for placenta-associated pregnancy complications, and developing strategies for the targeted delivery of drugs to ...

Repressing Gene Transcription by Redirecting Cellular Machinery with Chemical Epigenetic Modifiers

Regulation of chromatin compaction is an important process that governs gene expression in higher eukaryotes. Although chromatin compaction and gene expression regulation are commonly disrupted in many diseases, a locus-specific, endogenous, and reversible method to study and control these mechanisms of action has been lacking. To address this issue, we have developed and characterized novel gene-regulating bifunctional molecules. One component of the bifunctional molecule binds to a DNA-protein anchor so that it will be recruited to an allele-specific locus. The other component engages endogenous cellular chromatin-modifying machinery, recruiting these proteins to a gene of interest. These small molecules, called chemical epigenetic modifiers (CEMs), are capable of controlling gene expression and the chromatin environment in a dose-dependent and reversible manner. Here, we detail a CEM approach and its application to decrease gene expression and histone tail acetylation at a Green Fluorescent Protein (GFP) reporter located at the Oct4 locus in mouse embryonic stem cells (mESCs). We characterize the lead CEM (CEM23) using fluorescent microscopy, flow cytometry, and chromatin immunoprecipitation (ChIP), followed by a quantitative polymerase chain reaction (qPCR). While the power of this system is demonstrated at the Oct4 locus, conceptually, the CEM technology is modular and can be applied in other cell types and at other genomic loci.

Regulation of the chromatin environment is an essential process required for proper gene expression. Here, we describe a method for controlling gene expression through the recruitment of chromatin-modifying machinery in a gene-specific and reversible manner.

Regulation of chromatin compaction is an important process that governs gene expression in higher eukaryotes. Although chromatin compaction and gene ...

3D Analysis of Multi-cellular Responses to Chemoattractant Gradients

Various limitations of 2D cell culture systems have sparked interest in 3D cell culture and analysis platforms, which would better mimic the spatial and chemical complexity of living tissues and mimic in vivo tissue functions. Recent advances in microfabrication technologies have facilitated the development of 3D in vitro environments in which cells can be integrated into a well-defined extracellular matrix (ECM) and a defined set of soluble or matrix associated biomolecules. However, technological barriers have limited their widespread use in research laboratories. Here, we describe a method to construct simple devices for 3D culture and experimentation with cells and multicellular organoids in 3D microenvironments with a defined chemoattractant gradient. We illustrate the use of this platform for analysis of the response of epithelial cells and organoids to gradients of growth factors, such as epidermal growth factor (EGF). EGF gradients were stable in the devices for several days leading to directed branch formation in breast organoids. This analysis allowed us to conclude that collective gradient sensing by groups of cells is more sensitive vs. single cells. We also describe the fabrication method, which does not require photolithography facilities nor advanced soft lithography techniques. This method will be helpful to study 3D cellular behaviors in the context of the analysis of development and pathological states, including cancer.

We describe a method to construct devices for 3D culture and experimentation with cells and multicellular organoids. This device allows analysis of cellular responses to soluble signals in 3D microenvironments with defined chemoattractant gradients. Organoids are better than single cells at detection of weak noisy inputs.

Various limitations of 2D cell culture systems have sparked interest in 3D cell culture and analysis platforms, which would better mimic the spatial and ...

Formulating and Characterizing Lipid Nanoparticles for Gene Delivery using a Microfluidic Mixing Platform

Lipid-based drug carriers have been used for clinically and commercially available delivery systems due to their small size, biocompatibility, and high encapsulation efficiency. Use of lipid nanoparticles (LNPs) to encapsulate nucleic acids is advantageous to protect the RNA or DNA from degradation, while also promoting cellular uptake. LNPs often contain multiple lipid components including an ionizable lipid, helper lipid, cholesterol, and polyethylene glycol (PEG) conjugated lipid. LNPs can readily encapsulate nucleic acids due to the ionizable lipid presence, which at low pH is cationic and allows for complexation with negatively charged RNA or DNA. Here LNPs are formed by encapsulating messenger RNA (mRNA) or plasmid DNA (pDNA) using rapid mixing of the lipid components in an organic phase and the nucleic acid component in an aqueous phase. This mixing is performed using a precise microfluidic mixing platform, allowing for nanoparticle self-assembly while maintaining laminar flow. The hydrodynamic size and polydispersity are measured using dynamic light scattering (DLS). The effective surface charge on the LNP is determined by measuring the zeta potential. The encapsulation efficiency is characterized using a fluorescent dye to quantify entrapped nucleic acid. Representative results demonstrate the reproducibility of this method and the influence that different formulation and process parameters have on the developed LNPs.

Lipid nanoparticles are developed using a microfluidic mixing platform approach for mRNA and DNA encapsulation.

Lipid-based drug carriers have been used for clinically and commercially available delivery systems due to their small size, biocompatibility, and high ...

Spatio-Temporal In Vivo Imaging of Ocular Drug Delivery Systems using Fiberoptic Confocal Laser Microendoscopy

Subconjunctival injection is an attractive route to administer ocular drugs due to easy trans-scleral access that bypasses anterior ocular barriers, such as the cornea and conjunctiva. While therapeutic effects and pharmacokinetics of the drugs upon subconjunctival injection have been described in some studies, very few assess the ocular distribution of drugs or drug delivery systems (DDS). The latter is critical for the optimization of intraocular DDS design and drug bioavailability to achieve the desired ocular localization and duration of action (e.g., acute versus. prolonged). This study establishes the use of fiberoptic confocal laser microendoscopy (CLM) to qualitatively study the ocular distribution of fluorescent liposomes in real-time in live mice after sub-conjunctival injection. Being designed for in vivo visual inspection of tissues at the microscopic level, this is also the first full description of the CLM imaging method to study spatio-temporal distribution of injectables in the eye after subconjunctival injection.

Spatio-Temporal In Vivo Imaging of Ocular Drug Delivery Systems using Fiberoptic Confocal Laser Microendoscopy

We present a protocol for the use of fiberoptic confocal laser microendoscopy (CLM) to non-invasively study the spatio-temporal distribution of liposomes in the eye after subconjunctival injection.

Subconjunctival injection is an attractive route to administer ocular drugs due to easy trans-scleral access that bypasses anterior ocular barriers, such ...