Understanding nonviral nucleic acid delivery with quantum dot-FRET nanosensors

Eco-Friendly Intracellular Biosynthesis of CdS Quantum Dots Using Pseudomonas aeruginosa: Evaluation of Antimicrobial Effects and DNA Cleavage Activities

BACKGROUND

Intracellular biosynthesis of Quantum Dots (QDs) based on microorganisms offers a green alternative and eco-friendly for the production of nanocrystals with superior properties. This study focused on the production of intracellular CdS QDs by stimulating the detoxification metabolism of Pseudomonas aeruginosa.

METHODS

For this aim, Pseudomonas aeruginosa ATCC 27853 strain was incubated in a solution of 1mM cadmium sulphate (CdSO4) to manipulate the detoxification mechanism. The intracellularly formed Cd-based material was extracted, and its characterization was carried out by Transmission Electron Microscopy (TEM), X-Ray Diffraction (XRD), Energy Dispersive X-ray (EDX) and dynamic light scattering (DLS) analyses and absorption-emission spectra.

RESULTS

The obtained material showed absorption peaks at 385 nm and a luminescence peak at 411 nm, and the particle sizes were measured in the range 4.63-17.54 nm. It was determined that the material was sphere-shaped, with a cubic crystalline structure, including Cd and S elements. The antibacterial and antifungal activities of CdS QDs against patent eleven bacterial (four Grampositive and seven Gram-negative) and one fungal strains were investigated by the agar disk diffusion method. It was revealed that the obtained material has antibacterial effects on both Grampositive and Gram-negative bacteria. However, cleavage activity of CdS QDs on pBR322 DNA was not detected.

CONCLUSION

As a result, it has been proposed that the stimulation of the detoxification mechanism can be an easy and effective way of producing green and cheap luminescent QDs or nanomaterial.

Interaction kinetics of peptide lipids-mediated gene delivery

BACKGROUND

During the course of gene transfection, the interaction kinetics between liposomes and DNA is speculated to play very important role for blood stability, cellular uptake, DNA release and finally transfection efficiency.

RESULTS

As cationic peptide liposomes exhibited great gene transfer activities both in vitro and in vivo, two peptide lipids, containing a tri-ornithine head (LOrn3) and a mono-ornithine head (LOrn1), were chosen to further clarify the process of liposome-mediated gene delivery in this study. The results show that the electrostatically-driven binding between DNA and liposomes reached nearly 100% at equilibrium, and high affinity of LOrn3 to DNA led to fast binding rate between them. The binding process between LOrn3 and DNA conformed to the kinetics equation: y = 1.663631 × exp (- 0.003427x) + 6.278163. Compared to liposome LOrn1, the liposome LOrn3/DNA lipoplex exhibited a faster and more uniform uptake in HeLa cells, as LOrn3 with a tri-ornithine peptide headgroup had a stronger interaction with the negatively charged cell membrane than LOrn1. The efficient endosomal escape of DNA from LOrn3 lipoplex was facilitated by the acidity in late endosomes, resulting in broken carbamate bonds, as well as the "proton sponge effect" of the lipid.

CONCLUSIONS

The interaction kinetics is a key factor for DNA transfection efficiency. This work provided insights into peptide lipid-mediated DNA delivery that could guide the development of the next generation of delivery systems for gene therapeutics.

The cell-penetrating YopM protein-functionalized quantum dot-plasmid DNA conjugate as a novel gene delivery vector

Non-viral gene delivery systems have great potential for safe and efficient gene therapy, while inefficient cellular and nuclear uptake remain as the major hurdles. Novel approaches are needed to enhance the transfection efficiency of non-viral vectors. In accordance with this need, the objective of this study was to construct a non-viral vector that could achieve gene delivery without using additional lipid-based transfection agent. We aimed to impart self-delivery property to a non-viral vector by using the cell and nucleus penetrating properties of YopM proteins from the three Yersinia spp. (Y. pestis, Y. enterocolotica and Y. pseudotuberculosis). Plasmid DNA (pDNA) encoding green fluorescent protein (GFP) was labeled with quantum dots (QDs) via peptide-nucleic acid (PNA) recognition site. Recombinant YopM protein was then attached to the conjugate via a second PNA recognition site. The YopM ̶ QDs ̶ pDNA conjugate was transfected into HeLa cells without using additional transfection reagent. All three conjugates produced GFP fluorescence, indicating that the plasmid was successfully delivered to the nucleus. As control, naked pDNA was transfected into the cells by using a commercial transfection reagent. The Y. pseudotuberculosis YopM-functionalized conjugate achieved the highest GFP expression, compared to other two YopM proteins and the transfection reagent. To the best of our knowledge, YopM protein was used for the first time in a non-viral gene delivery vector.

Dual-responsive polyplexes with enhanced disassembly and endosomal escape for efficient delivery of siRNA

Despite the extracellular barriers for siRNA delivery have been overcome by utilizing advanced nanoparticle delivery systems, the key intracellular barriers after internalization including efficient disassembly of siRNA and endosomal escape still remains challenging. To address the issues, we developed a unique pH- and redox potential-responsive polyplex delivery system based on the copolymer of mPEG-b-PLA-PHis-ssPEI1.8 k, which is composed of a pH-responsive copolymer of PEG-b-PLA-PHis (Mw 5 k) and a branched PEI (Mw1.8 k) linked with redox cleavable disulfide bond. The copolymer showed excellent siRNA complexation and protection abilities against endogenous substances at the relatively low N/P ratio of 6. The siRNA release from the polyplexes (N/P 6) was markedly increased from 13.62% to 58.67% under conditions simulating the endosomal microenvironment. Fluorescence resonance energy transfer (FRET) test also indicated a higher disassembly extent of siRNA from the copolymer. The accelerated siRNA release from the polyplexes was markedly restrained when the N/P ratio was raised above 10 due to the increasing of electrostatic interactions. The efficient endosomal escape of siRNA after internalization was confirmed by confocal microscopy, which was attributed to the cleavaged PEI chains inducing membrane destabilization, the "proton sponge effect" of PHis and PEI as well as the relative small size of after disassembly. The enhanced disassembly and endosomal escape were elucidated as the leading cause for polyplexes (N/P 6) showed more efficient Bcl-2 silencing (85.45%) than those polyplexes with higher N/P ratios (N/P 10 and 15). In vivo results further demonstrated that polyplexes (N/P 6) delivery of siBcl-2 significantly inhibited the MCF-7 breast tumor growth as compared to its counterparts. The incorporation of convertible non-electrical interactions at a balance with electrostatic interactions in complexation siRNA has been demonstrated as an effective strategy to achieve efficient disassembly from stable polyplexes. Moreover, polyplexes equipped with the enhanced disassembly and endosomal escape provides a new potential way to tackle the intracellular delivery bottleneck for siRNA delivery.

Specific Systems for Imaging

Microscopy allows for the characterization of small objects invisible to the naked eye, a technique that, since its conception, has played a key role in the development across nearly every field of science and technology. Given the nanometer size of the materials explored in the field of nanotechnology, the contributions of modern microscopes that can visualize these materials are indispensable, and the ever-improving technology is paramount to the future success of the field. This chapter will focus on four fundamental areas of microscopy used in the field of nanotechnology including fluorescence microscopy (Sect. 3.1), particle tracking and photoactivated localization microscopy (Sect. 3.2), quantum dots and fluorescence resonance energy transfer (Sect. 3.3), and cellular MRI and PET labeling (Sect. 3.4). The functionality, as well as the current and recommended usage of each given imaging system, will be discussed.

Block copolymer conjugated Au-coated Fe3O4 nanoparticles as vectors for enhancing colloidal stability and cellular uptake

BACKGROUND

Polymer surface-modified inorganic nanoparticles (NPs) provide a multifunctional platform for assisting gene delivery. Rational structure design for enhancing colloidal stability and cellular uptake is an important strategy in the development of safe and highly efficient gene vectors.

RESULTS

Heterogeneous Au-coated Fe3O4 (Fe3O4@Au) NPs capped by polyethylene glycol-b-poly1-(3-aminopropyl)-3-(2-methacryloyloxy propylimidazolium bromine) (PEG-b-PAMPImB-Fe3O4@Au) were prepared for DNA loading and magnetofection assays. The Au outer shell of the NPs is an effective platform for maintaining the superparamagnetism of Fe3O4 and for PEG-b-PAMPImB binding via Au-S covalent bonds. By forming an electrostatic complex with DNA at the inner PAMPImB shell, the magnetic nanoplexes offer steric protection from the outer corona PEG, thereby promoting high colloidal stability. Transfection efficiency assays in human esophageal cancer cells (EC109) show that the nanoplexes have high transfection efficiency at a short incubation time in the presence of an external magnetic field, due to increased cellular internalization via magnetic acceleration. Finally, after transfection with the magnetic nanoplexes EC109 cells acquire magnetic properties, thus allowing for selective separation of transfected cells.

CONCLUSION

Precisely engineered architectures based on neutral-cationic block copolymer-conjugated heterogeneous NPs provide a valuable strategy for improving the applicability and efficacy of synthesized vectors.

A gene delivery system containing nuclear localization signal: Increased nucleus import and transfection efficiency with the assistance of RanGAP1

In the present report, a degradable gene delivery system (PAMS/DNA/10NLS) containing nucleus location signal peptide (NLS) was prepared. The agarose gel electrophoresis, particle size and zeta potential of PAMS/DNA/10NLS were similar to those of PAMS/DNA, which proved that NLS did not affect the interaction between PAMS and DNA. PAMS/DNA/10NLS exhibited marked extracellular and intracellular degradation under acidic conditions. The degradation was believed to allow NLS to come into contact with importins easily, which was able to mediate the nucleus import. With the help of NLS, PAMS/DNA/10NLS exhibited a higher transfection capability than PAMS/DNA. Moreover, the transfection of PAMS/DNA/10NLS was less dependent on the breakdown of the nucleus envelope than PAMS/DNA. Considering that GTPase-activating protein 1 (RanGAP1) was able to activate the endogenous GTPase, which was necessary for NLS-mediated nucleus import, RanGAP1 overexpressed cells (RanGAP1 cells) were produced. This result showed that RanGAP1 cells had higher GTPase activities than normal cells. Both the nucleus import and transfection efficiency of PAMS/DNA/10NLS were markedly higher in RanGAP1 cells than that in normal cells. The in vivo transfection results also showed that the transfection efficiency of PAMS/DNA/10NLS was higher in RanGAP1 pre-treated mice than that in normal mice. These findings showed that PAMS/DNA/10NLS is a promising gene delivery system with the assistance of RanGAP1.

STATEMENT OF SIGNIFICANCE

The present report describes the increased transfection efficiency of a degradable gene delivery system (PAMS/DNA/10NLS) containing nuclear location signal (NLS) with the assistance of GTPase-activating protein 1 (RanGAP1). The physicochemical properties of PAMS/DNA/10NLS were similar to those of PAMS/DNA. PAMS/DNA/10NLS exhibited great extracellular and intracellular degradations, which might allow NLS to contact with importins easily. With the help of NLS, PAMS/DNA/10NLS exhibited a higher transfection capability than PAMS/DNA. The transfection of PAMS/DNA/10NLS had less dependence on the breakdown of nuclear envelope. Both the nuclear import and transfection efficiency of PAMS/DNA/10NLS were higher in RanGAP1 overexpressed cells than that in normal cells. Moreover, the transfection efficiency of PAMS/DNA/10NLS was higher in RanGAP1 pre-treated mice than that in normal mice.

Insight of In Vitro Small-Interfering RNA Release From Chitosan Nanoparticles Under Enzymolysis With Förster Resonance Energy Transfer Analysis

Small-interfering RNA (siRNA)-mediated gene silencing with the aid of chitosan (CS)-based carriers has shown efficient and reliable outcome in vitro, but the gene silencing efficiency in vivo is still limited. It is of great importance to balance the protection and release of siRNA from nanoparticles (NPs) so as to achieve high efficiency. However, siRNA release profile from CS/siRNA NPs has been rarely concerned. Here, Förster resonance energy transfer technique was adopted for in vitro investigation of siRNA release from CS NPs in lysozyme-contained buffer. The results clearly showed that siRNA molecules experienced a fast and short release phase under lysozyme competition to both CS and siRNA, and then a slow and long release under lysozyme degradation on CS. Moreover, lysozyme competition played more important role than enzymolysis on trigging siRNA release. This preliminary study of siRNA release is the first step to get insight of in vivo siRNA release mechanism from CS/siRNA NPs, which will be helpful to adjust the design of CS/siRNA NPs for balancing the protection and release of siRNA molecules.

A new trend to determine biochemical parameters by quantitative FRET assays

Förster resonance energy transfer (FRET) has been widely used in biological and biomedical research because it can determine molecule or particle interactions within a range of 1-10 nm. The sensitivity and efficiency of FRET strongly depend on the distance between the FRET donor and acceptor. Historically, FRET assays have been used to quantitatively deduce molecular distances. However, another major potential application of the FRET assay has not been fully exploited, that is, the use of FRET signals to quantitatively describe molecular interactive events. In this review, we discuss the use of quantitative FRET assays for the determination of biochemical parameters, such as the protein interaction dissociation constant (K(d)), enzymatic velocity (k(cat)) and K(m). We also describe fluorescent microscopy-based quantitative FRET assays for protein interaction affinity determination in cells as well as fluorimeter-based quantitative FRET assays for protein interaction and enzymatic parameter determination in solution.

Intracellular FRET-based probes: a review

Probes that exploit Förster resonance energy transfer (FRET) in their feedback mechanism are touted for their sensitivity, robustness, and low background, and thanks to the exceptional distance dependence of the energy transfer process, they provide a means of probing lengthscales well below the resolution of light. These attributes make FRET-based probes superbly suited to an intracellular environment, and recent developments in biofunctionalization and expansion of imaging capabilities have put them at the forefront of intracellular studies. Here, we present an overview of the engineering and execution of a variety of recent intracellular FRET probes, highlighting the diversity of this class of materials and the breadth of application they have found in the intracellular environment.

Spectroscopic investigation of alloyed quantum dot-based FRET to cresyl violet dye

Quantum dots (QDs), bright luminescent semiconductor nanoparticles, have found numerous applications ranging from optoelectronics to bioimaging. Here, we present a systematic investigation of fluorescence resonance energy transfer (FRET) from hydrophilic ternary alloyed quantum dots (CdSeS/ZnS) to cresyl violet dye with a view to explore the effect of composition of QD donors on FRET efficiency. Fluorescence emission of QD is controlled by varying the composition of QD without altering the particle size. The results show that quantum yield of the QDs increases with increase in the emission wavelength. The FRET parameters such as spectral overlap J(λ), Förster distance R0, intermolecular distance (r), rate of energy transfer k(T)(r), and transfer efficiency (E) are determined by employing both steady-state and time-resolved fluorescence spectroscopy. Additionally, dynamic quenching is noticed to occur in the present FRET system. Stern-Volmer (K(D)) and bimolecular quenching constants (k(q)) are determined from the Stern-Volmer plot. It is observed that the transfer efficiency follows a linear dependence on the spectral overlap and the quantum yield of the donor as predicted by the Förster theory upon changing the composition of the QD.

Engineering mesenchymal stem cells for regenerative medicine and drug delivery

Researchers have applied mesenchymal stem cells (MSC) to a variety of therapeutic scenarios by harnessing their multipotent, regenerative, and immunosuppressive properties with tropisms toward inflamed, hypoxic, and cancerous sites. Although MSC-based therapies have been shown to be safe and effective to a certain degree, the efficacy remains low in most cases when MSC are applied alone. To enhance their therapeutic efficacy, researchers have equipped MSC with targeted delivery functions using genetic engineering, therapeutic agent incorporation, and cell surface modification. MSC can be genetically modified virally or non-virally to overexpress therapeutic proteins that complement their innate properties. MSC can also be primed with non-peptidic drugs or magnetic nanoparticles for enhanced efficacy and externally regulated targeting, respectively. Furthermore, MSC can be functionalized with targeting moieties to augment their homing toward therapeutic sites using enzymatic modification, chemical conjugation, or non-covalent interactions. These engineering techniques are still works in progress, requiring optimization to improve the therapeutic efficacy and targeting effectiveness while minimizing any loss of MSC function. In this review, we will highlight the advanced techniques of engineering MSC, describe their promise and the challenges of translation into clinical settings, and suggest future perspectives on realizing their full potential for MSC-based therapy.

Quantum dots in nanomedicine: recent trends, advances and unresolved issues

The review addresses the current state of progress in the use of ultra-small nanoparticles from the category of quantum dots (QDs), which presently embraces a widening range of nanomaterials of different nature, including "classical" semiconductor groups III-V and II-VI nanocrystals, along with more recently emerged carbon, silicon, gold and other types of nanoparticles falling into this class of nanomaterials due to their similar physical characteristics such as small size and associated quantum confinement effects. A diverse range of QDs applications in nanomedicine has been extensively summarised previously in numerous publications. Therefore, this review is not intended to provide an all-embracing survey of the well documented QDs uses, but is rather focused on the most recent emerging developments, concepts and outstanding unresolved problematic and sometimes controversial issues. Over 125 publications are overviewed and discussed here in the context of major nanomedicine domains, i.e. medical imaging, diagnostics, therapeutic applications and combination of them in multifunctional theranostic systems.

Integration of drug, protein, and gene delivery systems with regenerative medicine

Regenerative medicine has the potential to drastically change the field of health care from reactive to preventative and restorative. Exciting advances in stem cell biology and cellular reprogramming have fueled the progress of this field. Biochemical cues in the form of small molecule drugs, growth factors, zinc finger protein transcription factors and nucleases, transcription activator-like effector nucleases, monoclonal antibodies, plasmid DNA, aptamers, or RNA interference agents can play an important role to influence stem cell differentiation and the outcome of tissue regeneration. Many of these biochemical factors are fragile and must act intracellularly at the molecular level. They require an effective delivery system, which can take the form of a scaffold (e.g., hydrogels and electrospun fibers), carrier (viral and nonviral), nano- and microparticle, or genetically modified cell. In this review, we will discuss the history and current technologies of drug, protein, and gene delivery in the context of regenerative medicine. Next, we will present case examples of how delivery technologies are being applied to promote angiogenesis in nonhealing wounds or prevent angiogenesis in age related macular degeneration. Finally, we will conclude with a brief discussion of the regulatory pathway from bench to bedside for the clinical translation of these novel therapeutics.

Location deterministic biosensing from quantum-dot-nanowire assemblies

Semiconductor quantum dots (QDs) with high fluorescent brightness, stability, and tunable sizes, have received considerable interest for imaging, sensing, and delivery of biomolecules. In this research, we demonstrate location deterministic biochemical detection from arrays of QD-nanowire hybrid assemblies. QDs with diameters less than 10 nm are manipulated and precisely positioned on the tips of the assembled Gold (Au) nanowires. The manipulation mechanisms are quantitatively understood as the synergetic effects of dielectrophoretic (DEP) and alternating current electroosmosis (ACEO) due to AC electric fields. The QD-nanowire hybrid sensors operate uniquely by concentrating bioanalytes to QDs on the tips of nanowires before detection, offering much enhanced efficiency and sensitivity, in addition to the position-predictable rationality. This research could result in advances in QD-based biomedical detection and inspires an innovative approach for fabricating various QD-based nanodevices.

Microfluidic preparation of polymer-nucleic acid nanocomplexes improves nonviral gene transfer

As the designs of polymer systems used to deliver nucleic acids continue to evolve, it is becoming increasingly apparent that the basic bulk manufacturing techniques of the past will be insufficient to produce polymer-nucleic acid nanocomplexes that possess the uniformity, stability, and potency required for their successful clinical translation and widespread commercialization. Traditional bulk-prepared products are often physicochemically heterogeneous and may vary significantly from one batch to the next. Here we show that preparation of bioreducible nanocomplexes with an emulsion-based droplet microfluidic system produces significantly improved nanoparticles that are up to fifty percent smaller, more uniform, and are less prone to aggregation. The intracellular integrity of nanocomplexes prepared with this microfluidic method is significantly prolonged, as detected using a high-throughput flow cytometric quantum dot Förster resonance energy transfer nanosensor system. These physical attributes conspire to consistently enhance the delivery of both plasmid DNA and messenger RNA payloads in stem cells, primary cells, and human cell lines. Innovation in processing is necessary to move the field toward the broader clinical implementation of safe and effective nonviral nucleic acid therapeutics, and preparation with droplet microfluidics represents a step forward in addressing the critical barrier of robust and reproducible nanocomplex production.

Development of siRNA-probes for studying intracellular trafficking of siRNA nanoparticles

One important barrier facing the delivery of short interfering RNAs (siRNAs) via synthetic nanoparticles is the rate of nanoparticle disassembly. However, our ability to optimize the release kinetics of siRNAs from nanoparticles for maximum efficacy is limited by the lack of methods to track their intracellular disassembly. Towards this end, we describe the design of two different siRNA-based fluorescent probes whose fluorescence emission changes in response to the assembly state of the nanoparticle. The first probe design involves a redox-sensitive fluorescence-quenched probe that fluoresces only when the nanoparticle is disassembled in a reductive environment. The second probe design is based on a FRET-labeled siRNA pair that fluoresces due to the proximity of the siRNA pair when the nanoparticle is intact. In both approaches, the delivery vehicle need not be labeled. The utility of these probes was investigated with a lipidoid nanoparticle (LNP) as proof-of-concept in both extracellular and intracellular environments. Fluorescence kinetic data from both probes were fit to a two-phase release and decay curve and subsequently quantified to give intracellular disassembly rate constants. Quantitative analysis revealed that the rate constant of siRNA release measured via the fluorescence-quenched probe was almost identical to the rate constant for nanoparticle disassembly measured via the FRET-labeled probes. Furthermore, these probes were utilized to determine subcellular localization of LNPs with the use of automated high-resolution microscopy as they undergo dissociation. Interestingly, this work shows that large amounts of siRNA remain inside vesicular compartments. Altogether, we have developed new siRNA probes that can be utilized with multiple nanocarriers for quantitative and qualitative analysis of nanoparticle dissociation that may serve as a design tool for future delivery systems.