Determining the Cytosolic Stability of Small DNA Nanostructures In Cellula.

DNA nanostructures have proven potential in biomedicine. However, their intracellular interactions─especially cytosolic stability─remain mostly unknown and attempts to discern this are confounded by the complexities of endocytic uptake and entrapment. Here, we bypass the endocytic uptake and evaluate the DNA structural stability directly in live cells. Commonly used DNA structures─crosshairs and a tetrahedron─were labeled with a multistep Förster resonance energy transfer dye cascade and microinjected into the cytosol of transformed and primary cells. Energy transfer loss, as monitored by fluorescence microscopy, reported the structure's direct time-resolved breakdown in cellula. The results showed rapid degradation of the DNA crosshair within 20 min, while the tetrahedron remained consistently intact for at least 1 h postinjection. Nuclease assays in conjunction with a current understanding of the tetrahedron's torsional rigidity confirmed its higher stability. Such studies can inform design parameters for future DNA nanostructures where programmable degradation rates may be required.

A Quantum Dot-Protein Bioconjugate That Provides for Extracellular Control of Intracellular Drug Release.

The ability to control the intracellular release of drug cargos from nanobioconjugate delivery scaffolds is critical for the successful implementation of nanoparticle (NP)-mediated drug delivery. This is particularly true for hard NP carriers such as semiconductor quantum dots (QDs) and gold NPs. Here, we report the development of a QD-based multicomponent drug release system that, when delivered to the cytosol of mammalian cells, is triggered to release its drug cargo by the simple addition of a competitive ligand to the extracellular medium. The ensemble construct consists of the central QD scaffold that is decorated with a fixed number of maltose binding proteins (MBPs). The MBP binding site is loaded with dye or drug conjugates of the maltose analogue beta-cyclodextrin (ßCD) to yield a QD-MBP-ßCD ensemble conjugate. The fidelity of conjugate assembly is monitored by Förster resonance energy transfer (FRET) from the QD donor to the dye/drug acceptor. Microplate-based FRET assays demonstrated that the ßCD conjugate was released from the MBP binding pocket by maltose addition with an affinity that matched native MBP-maltose binding interactions. In COS-1 cells, the microinjected assembled conjugates remained stably intact in the cytosol until the addition of maltose to the extracellular medium, which underwent facilitated uptake into the cell. Live cell FRET-based confocal microscopy imaging captured the kinetics of realtime release of the ßCD ligand as a function of extracellular maltose concentration. Our results demonstrate the utility of the self-assembled QD-MBP-ßCD system to facilitate intracellular drug release that is triggered extracellularly through the simple addition of a well-tolerated nutrient and is not dependent on the use of light, magnetic field, ultrasound, or other traditional methods of stimulated drug release. We expect this extracellularly triggered drug release modality to be useful for the in vitro characterization of new drug candidates intended for systemic delivery/actuation and potentially for on-demand drug release in vivo.

Peptides for specifically targeting nanoparticles to cellular organelles: quo vadis?

The interfacing of nanomaterials and especially nanoparticles within all aspects of biological research continues to grow at a nearly unabated pace with projected applications focusing on powerful new tools for cellular labeling, imaging, and sensing, theranostic materials, and drug delivery. At the most fundamental level, many of these nanoparticles are meant to target not only very specific cell-types, regardless of whether they are in a culture, tissue, an animal model, or ultimately a patient, but also in many cases a specific subcellular organelle. During this process, these materials will undergo a complex journey that must first find the target cell of interest, then be taken up by those cells across the extracellular membrane, and ultimately localize to a desired subcellular organelle, which may include the nucleus, plasma membrane, endolysosomal system, mitochondria, cytosol, or endoplasmic reticulum. To accomplish these complex tasks in the correct sequence, researchers are increasingly interested in selecting for and exploiting targeting peptides that can impart the requisite capabilities to a given nanoparticle construct. There are also a number of related criteria that need careful consideration for this undertaking centering on the nature and properties of the peptide vector itself, the peptide-nanoparticle conjugate characteristics, and the target cell. Here, we highlight some important issues and key research areas related to this burgeoning field. We begin by providing a brief overview of some criteria for optimal attachment of peptides to nanoparticles, the predominant methods by which nanoparticles enter cells, and some of the peptide sequences that have been utilized to facilitate nanoparticle delivery to cells focusing on those that engender the initial targeting and uptake. Because almost all materials delivered to cells by peptides utilize the endosomal system of vesicular transport and in many cases remain sequestered within the vesicles, we critically evaluate the issue of endosomal escape in the context of some recently reported successes in this regard. Following from this, peptides that have been reported to deliver nanoparticles to specific subcellular compartments are examined with a focus on what they delivered and the putative mechanisms by which they were able to accomplish this. The last section focuses on two areas that are critical to realizing this overall approach in the long term. The first is how to select for peptidyl sequences capable of improved or more specific cellular or subcellular targeting based upon principles commonly associated with drug discovery. The second looks at what has been done to create modular peptides that incorporate multiple desirable functionalities within a single, contiguous sequence. This provides a viable alternative to either the almost insurmountable challenge of finding one sequence capable of all functions or, alternatively, attaching different peptides with different functionalities to the same nanoparticle in different ratios when trying to orchestrate their net effects. Finally, we conclude with a brief perspective on the future evolution and broader impact of this growing area of bionanoscience.

Modulation of Intracellular Quantum Dot to Fluorescent Protein Förster Resonance Energy Transfer via Customized Ligands and Spatial Control of Donor-Acceptor Assembly.

Understanding how to controllably modulate the efficiency of energy transfer in Förster resonance energy transfer (FRET)-based assemblies is critical to their implementation as sensing modalities. This is particularly true for sensing assemblies that are to be used as the basis for real time intracellular sensing of intracellular processes and events. We use a quantum dot (QD) donor -mCherry acceptor platform that is engineered to self-assemble in situ wherein the protein acceptor is expressed via transient transfection and the QD donor is microinjected into the cell. QD-protein assembly is driven by metal-affinity interactions where a terminal polyhistidine tag on the protein binds to the QD surface. Using this system, we show the ability to modulate the efficiency of the donor-acceptor energy transfer process by controllably altering either the ligand coating on the QD surface or the precise location where the QD-protein assembly process occurs. Intracellularly, a short, zwitterionic ligand mediates more efficient FRET relative to longer ligand species that are based on the solubilizing polymer, poly(ethylene glycol). We further show that a greater FRET efficiency is achieved when the QD-protein assembly occurs free in the cytosol compared to when the mCherry acceptor is expressed tethered to the inner leaflet of the plasma membrane. In the latter case, the lower FRET efficiency is likely attributable to a lower expression level of the mCherry acceptor at the membrane combined with steric hindrance. Our work points to some of the design considerations that one must be mindful of when developing FRET-based sensing schemes for use in intracellular sensing.

Cassiosomes are stinging-cell structures in the mucus of the upside-down jellyfish Cassiopea xamachana.

Snorkelers in mangrove forest waters inhabited by the upside-down jellyfish Cassiopea xamachana report discomfort due to a sensation known as stinging water, the cause of which is unknown. Using a combination of histology, microscopy, microfluidics, videography, molecular biology, and mass spectrometry-based proteomics, we describe C. xamachana stinging-cell structures that we term cassiosomes. These structures are released within C. xamachana mucus and are capable of killing prey. Cassiosomes consist of an outer epithelial layer mainly composed of nematocytes surrounding a core filled by endosymbiotic dinoflagellates hosted within amoebocytes and presumptive mesoglea. Furthermore, we report cassiosome structures in four additional jellyfish species in the same taxonomic group as C. xamachana (Class Scyphozoa; Order Rhizostomeae), categorized as either motile (ciliated) or nonmotile types. This inaugural study provides a qualitative assessment of the stinging contents of C. xamachana mucus and implicates mucus containing cassiosomes and free intact nematocytes as the cause of stinging water.

The role of nanoparticles in the improvement of systemic anticancer drug delivery.

The systemic delivery of drugs to the body via circulation after oral administration is a preferred method of drug administration during cancer treatment given its ease of implementation. However, the physicochemical properties of many current anticancer drugs limit their effectiveness when delivered by systemic routes. The use of nanoparticles (NPs) has emerged as an effective means of overcoming the inherent limitations of systemic drug delivery. We provide herein an overview of various NP formulations that facilitate improvements in the efficacy of various anticancer drugs compared with the free drug. This review will be useful to the reader who is interested in the role NP technology is playing in shaping the future of chemotherapeutic drug delivery and disease treatment.

Multifunctional nanoparticle composites: progress in the use of soft and hard nanoparticles for drug delivery and imaging.

With continued advancements in nanoparticle (NP) synthesis and in the interfacing of NPs with biological systems has come the exponential growth in the use of NPs for therapeutic drug delivery and imaging applications. In recent years, the advent of NP multifunctionality-the ability to perform multiple, disparate functions on a single NP platform-has garnered much excitement for the potential realization of highly functional NP-mediated drug delivery for use in the clinical setting. This Overview will survey the current state of the art (reports published within the last 5 years) of multifunctional NPs for therapeutic drug delivery, imaging or a combination thereof. We provide extensive examples of both soft (micelles, liposomes, polymeric NPs) and hard (noble metals, quantum dots, metal oxides) NP formulations that have been used for multimodal drug delivery and imaging. The criteria for inclusion, herein, is that there must be at least two therapeutic drug cargos or imaging agents or a combination of the two. We next offer an assessment of the cytotoxicity of therapeutic NP constructs in biological systems. We then conclude with a forward-looking perspective on how we expect this field to develop in the coming years. WIREs Nanomed Nanobiotechnol 2017, 9:e1466. doi: 10.1002/wnan.1466 For further resources related to this article, please visit the WIREs website.

Nanoparticle cellular uptake by dendritic wedge peptides: achieving single peptide facilitated delivery.

Significant efforts are being undertaken to optimize the cargo carrying capacity and especially the cellular delivery efficiency of functionalized nanoparticles for applications in biological research and pharmacological delivery. One approach to increasing nanoparticle surface cargo display capacity is to decrease the number of moieties required for mediating cellular delivery by improving their efficiency. We describe a series of multivalent cell penetrating peptide (CPP) dendrimers that facilitate rapid cellular delivery of prototypical nanoparticle-semiconductor quantum dots (QDs). The modular CPP dendrimers were assembled through an innovative convergent oxime ligation strategy between (Arg9)n motifs and a dendritic QD-coordination scaffold. Dendrimeric peptides sequentially incorporate a terminal (His)6 motif for metal-affinity QD coordination, a Pro9 spacer, a branching poly-lysine scaffold, and wedged display of (Arg9)n binding motifs with n = 1×, 2×, 4×, 8×, 16× multivalency. QD dendrimer display capacity was estimated using structural simulations and QD-(Arg9)1-16 conjugates characterized by dynamic light scattering along with surface plasmon resonance-based binding assays to heparan sulfate proteoglycan surfaces. Cellular uptake via endocytosis was confirmed and peptide delivery kinetics investigated as a function of QD-(Arg9)1-16 conjugate exposure time and QD assembly ratio where cellular viability assays reflected no overt cytotoxicity. The ability of single dendrimer conjugates to facilitate cellular uptake was confirmed for QD-(Arg9)2-16 repeats along with the ability to deliver >850 kDa of protein cargo per QD. Minimizing the number of CPPs required for cellular uptake is critical for expanding nanoparticle cargo carrying capacity and can allow for inclusion of additional sensors, therapeutics and contrast agents on their surface.

Elucidating Surface Ligand-Dependent Kinetic Enhancement of Proteolytic Activity at Surface-Modified Quantum Dots.

Combining biomolecules such as enzymes with nanoparticles has much to offer for creating next generation synergistically functional bionanomaterials. However, almost nothing is known about how these two disparate components interact at this critical biomolecular-materials interface to give rise to improved activity and emergent properties. Here we examine how the nanoparticle surface can influence and increase localized enzyme activity using a designer experimental system consisting of trypsin proteolysis acting on peptide-substrates displayed around semiconductor quantum dots (QDs). To minimize the complexity of analyzing this system, only the chemical nature of the QD surface functionalizing ligands were modified. This was accomplished by synthesizing a series of QD ligands that were either positively or negatively charged, zwitterionic, neutral, and with differing lengths. The QDs were then assembled with different ratios of dye-labeled peptide substrates and exposed to trypsin giving rise to progress curves that were monitored by Förster resonance energy transfer (FRET). The resulting trypsin activity profiles were analyzed in the context of detailed molecular dynamics simulations of key interactions occurring at this interface. Overall, we find that a combination of factors can give rise to a localized activity that was 35-fold higher than comparable freely diffusing enzyme-substrate interactions. Contributing factors include the peptide substrate being prominently displayed extending from the QD surface and not sterically hindered by the longer surface ligands in conjunction with the presence of electrostatic and other productive attractive forces between the enzyme and the QD surface. An intimate understanding of such critical interactions at this interface can produce a set of guidelines that will allow the rational design of next generation high-activity bionanocomposites and theranostics.

Quantum Dot-Peptide-Fullerene Bioconjugates for Visualization of in Vitro and in Vivo Cellular Membrane Potential.

We report the development of a quantum dot (QD)-peptide-fullerene (C60) electron transfer (ET)-based nanobioconjugate for the visualization of membrane potential in living cells. The bioconjugate is composed of (1) a central QD electron donor, (2) a membrane-inserting peptidyl linker, and (3) a C60 electron acceptor. The photoexcited QD donor engages in ET with the C60 acceptor, resulting in quenching of QD photoluminescence (PL) that tracks positively with the number of C60 moieties arrayed around the QD. The nature of the QD-capping ligand also modulates the quenching efficiency; a neutral ligand coating facilitates greater QD quenching than a negatively charged carboxylated ligand. Steady-state photophysical characterization confirms an ET-driven process between the donor-acceptor pair. When introduced to cells, the amphiphilic QD-peptide-C60 bioconjugate labels the plasma membrane by insertion of the peptide-C60 portion into the hydrophobic bilayer, while the hydrophilic QD sits on the exofacial side of the membrane. Depolarization of cellular membrane potential augments the ET process, which is manifested as further quenching of QD PL. We demonstrate in HeLa cells, PC12 cells, and primary cortical neurons significant QD PL quenching (ΔF/F0 of 2-20% depending on the QD-C60 separation distance) in response to membrane depolarization with KCl. Further, we show the ability to use the QD-peptide-C60 probe in combination with conventional voltage-sensitive dyes (VSDs) for simultaneous two-channel imaging of membrane potential. In in vivo imaging of cortical electrical stimulation, the optical response of the optimal QD-peptide-C60 configuration exhibits temporal responsivity to electrical stimulation similar to that of VSDs. Notably, however, the QD-peptide-C60 construct displays 20- to 40-fold greater ΔF/F0 than VSDs. The tractable nature of the QD-peptide-C60 system offers the advantages of ease of assembly, large ΔF/F0, enhanced photostability, and high throughput without the need for complicated organic synthesis or genetic engineering, respectively, that is required of traditional VSDs and fluorescent protein constructs.

Controlled actuation of therapeutic nanoparticles: an update on recent progress.

A primary envisioned use for nanoparticles (NPs) in a cellular context is for controlled drug delivery where the full benefit of NP attributes (small size, large drug cargo loading capacity) can improve the pharmacokinetics of the drug cargo. This requires the ability to controllably manipulate the release of the drug cargo from the NP vehicle or 'controlled actuation'. In this review, we highlight new developments in this field from 2013 to 2015. The number and breadth of reports are a testament to the significant advancements made in this field over this time period. We conclude with a perspective of how we envision this field to continue to develop in the years to come.