Controlled DNA delivery systems

Polymeric Vehicles for Nucleic Acid Delivery: Enhancing the Therapeutic Efficacy and Cellular Uptake

BACKGROUND

Therapeutic gene delivery may be facilitated by the use of polymeric carriers. When combined with nucleic acids to form nanoparticles or polyplexes, a variety of polymers may shield the cargo from in vivo breakdown and clearance while also making it easier for it to enter intracellular compartments.

AIM AND OBJECTIVES

Polymer synthesis design choices result in a wide variety of compounds and vehicle compositions. Depending on the application, these characteristics may be changed to provide enhanced endosomal escape, longer-lasting distribution, or stronger connection with nucleic acid cargo and cells. Here, we outline current methods for delivering genes in preclinical and clinical settings using polymers.

METHODOLOGY

Significant therapeutic outcomes have previously been attained using genetic material- delivering polymer vehicles in both in-vitro and animal models. When combined with nucleic acids to form nanoparticles or polyplexes, a variety of polymers may shield the cargo from in vivo breakdown and clearance while also making it easier for it to enter intracellular compartments. Many innovative diagnoses for nucleic acids have been investigated and put through clinical assessment in the past 20 years.

RESULTS

Polymer-based carriers have additional delivery issues due to their changes in method and place of biological action, as well as variances in biophysical characteristics. We cover recent custom polymeric carrier architectures that were tuned for nucleic acid payloads such genomemodifying nucleic acids, siRNA, microRNA, and plasmid DNA.

CONCLUSION

In conclusion, the development of polymeric carriers for gene delivery holds promise for therapeutic applications. Through careful design and optimization, these carriers can overcome various challenges associated with nucleic acid delivery, offering new avenues for treating a wide range of diseases.

PLGA-Nanoparticles for Intracellular Delivery of the CRISPR-Complex to Elevate Fetal Globin Expression in Erythroid Cells

Ex vivo gene editing of CD34⁺ hematopoietic stem and progenitor cells (HSPCs) offers great opportunities to develop new treatments for a number of malignant and non-malignant diseases. Efficient gene-editing in HSPCs has been achieved using electroporation and/or viral transduction to deliver the CRISPR-complex, but cellular toxicity is a drawback of currently used methods. Nanoparticle (NP)-based gene-editing strategies can further enhance the gene-editing potential of HSPCs and provide a delivery system for in vivo application. Here, we developed CRISPR/Cas9-PLGA-NPs efficiently encapsulating Cas9 protein, single gRNA and a fluorescent probe. The initial 'burst' of Cas9 and gRNA release was followed by a sustained release pattern. CRISPR/Cas9-PLGA-NPs were taken up and processed by human HSPCs, without inducing cellular cytotoxicity. Upon escape from the lysosomal compartment, CRISPR/Cas9-PLGA-NPs-mediated gene editing of the γ-globin gene locus resulted in elevated expression of fetal hemoglobin (HbF) in primary erythroid cells. The development of CRISPR/Cas9-PLGA-NPs provides an attractive tool for the delivery of the CRISPR components to target HSPCs, and could provide the basis for in vivo treatment of hemoglobinopathies and other genetic diseases.

Polymeric vehicles for nucleic acid delivery

Polymeric vehicles are versatile tools for therapeutic gene delivery. Many polymers-when assembled with nucleic acids into vehicles-can protect the cargo from degradation and clearance in vivo, and facilitate its transport into intracellular compartments. Design options in polymer synthesis yield a comprehensive range of molecules and resulting vehicle formulations. These properties can be manipulated to achieve stronger association with nucleic acid cargo and cells, improved endosomal escape, or sustained delivery depending on the application. Here, we describe current approaches for polymer use and related strategies for gene delivery in preclinical and clinical applications. Polymer vehicles delivering genetic material have already achieved significant therapeutic endpoints in vitro and in animal models. From our perspective, with preclincal assays that better mimic the in vivo environment, improved strategies for target specificity, and scalable techniques for polymer synthesis, the impact of this therapeutic approach will continue to expand.

Poly(Lactic-co-Glycolic Acid) Nanoparticle Delivery of Peptide Nucleic Acids In Vivo

Many important biological applications of peptide nucleic acids (PNAs) target nucleic acid binding in eukaryotic cells, which requires PNA translocation across at least one membrane barrier. The delivery challenge is further exacerbated for applications in whole organisms, where clearance mechanisms rapidly deplete and/or deactivate exogenous agents. We have demonstrated that nanoparticles (NPs) composed of biodegradable polymers can encapsulate and release PNAs (alone or with co-reagents) in amounts sufficient to mediate desired effects in vitro and in vivo without deleterious reactions in the recipient cell or organism. For example, poly(lactic-co-glycolic acid) (PLGA) NPs can encapsulate and deliver PNAs and accompanying reagents to mediate gene editing outcomes in cells and animals, or PNAs alone to target oncogenic drivers in cells and correct cancer phenotypes in animal models. In this chapter, we provide a primer on PNA-induced gene editing and microRNA targeting-the two PNA-based biotechnological applications where NPs have enhanced and/or enabled in vivo demonstrations-as well as an introduction to the PLGA material and detailed protocols for formulation and robust characterization of PNA/DNA-laden PLGA NPs.

Recent development of synthetic nonviral systems for sustained gene delivery

Sustained gene delivery is of particular importance today because it circumvents the need for repeated therapeutic administration and provides spatial and temporal control of the release profile. Better understanding of the genetic basis of diseases and advances in gene therapy have propelled significant research on biocompatible gene carriers for therapeutic purposes. Varied biodegradable polymer-based architectures have been used to create new compositions with unique properties suitable for sustained gene delivery. This review presents the most recent advances in various polymeric systems: hydrogels, microspheres, nanospheres and scaffolds, having complex architectures to encapsulate and deliver functional genes. Through the recombination of different existing polymer systems, the multicomplex systems can be further endowed with new properties for better-targeted biomedical applications.

Nanocarrier-based co-delivery of small molecules and siRNA/miRNA for treatment of cancer

Aberrant gene expression can trigger several vital molecular events that not only result in carcinogenesis but also cause chemoresistance, metastasis and relapse. Gene-based therapies using siRNA/miRNA have been suggested as new treatment method to improve the current regimen. Although these agents can restore the normal molecular cascade thereby resensitizing the cancer cells, delivering a standard regimen (either subsequently or simultaneously) is necessary to achieve the therapeutic benefit. However, co-delivery using a single carrier could give an additional advantage of similar biodistribution profile of the loaded agents. While much research has been carried out in this field in recent years, challenges involved in designing combination formulations including efficient coloading, stability, appropriate biodistribution and target specificity have hampered their clinical translation. This article highlights current aspects of nano-carriers used for co-delivery of small molecules and genes to treat cancer.

Targeted genome modification via triple helix formation

Triplex-forming oligonucleotides (TFOs) are capable of coordinating genome modification in a targeted, site-specific manner, causing mutagenesis or even coordinating homologous recombination events. Here, we describe the use of TFOs such as peptide nucleic acids for targeted genome modification. We discuss this method and its applications and describe protocols for TFO design, delivery, and evaluation of activity in vitro and in vivo.

miRNAs in pancreatic cancer: therapeutic potential, delivery challenges and strategies

Pancreatic ductal adenocarcinoma (PDAC) is a severe pancreatic malignancy and is predicted to victimize 1.5% of men and women during their lifetime (Cancer statistics: SEER stat fact sheet, National Cancer Institute, 2014). miRNAs have emerged as a promising prognostic, diagnostic and therapeutic tool to fight against pancreatic cancer. miRNAs could modulate gene expression by imperfect base-pairing with target mRNA and hence provide means to fine-tune multiple genes simultaneously and alter various signaling pathways associated with the disease. This exceptional miRNA feature has provided a paradigm shift from the conventional one drug one target concept to one drug multiple target theory. However, in vivo miRNA delivery is not fully realized due to challenges posed by this special class of therapeutic molecules, which involves thorough understanding of the biogenesis and physicochemical properties of miRNA and delivery carriers along with the pathophysiology of the PDAC. This review highlights the delivery strategies of miRNA modulators (mimic/inhibitor) in cancer with special emphasis on PDAC since successful delivery of miRNA in vivo constitutes the major challenge in clinical translation of this promising class of therapeutics.

Multi-layered nanoparticles for combination gene and drug delivery to tumors

Drug resistance and toxicity are major obstacles in cancer chemotherapy. Combination therapies can overcome resistance, and synergies can minimize dosing. Polymer nanocarriers are interesting vehicles for cancer therapeutics for their delivery and tumor targeting abilities. We synthesized a multi-layered polymer nanoparticle (MLNP), comprising of poly(lactic-co-glycolic acid) with surface polyethyleneimine and functional peptides, for targeted drug and gene delivery. We confirmed the particle's ability to inhibit tumor growth through synergistic action of the drug and gene product. MLNPs achieved transfection levels similar to lipofectamine, while maintaining minimal cytotoxicity. The particles delivered camptothecin (CPT), and plasmid encoding TNF related apoptosis inducing ligand (pTRAIL) (CT MLNPs), and synergistically inhibited growth of multiple cancer cells in vitro. The synergy of co-delivering CPT and pTRAIL via CT MLNPs was confirmed using the Chou-Talalay method: the combination index (CI) values at 50% inhibition ranged between 0.31 and 0.53 for all cell lines. Further, co-delivery with MLNPs resulted in a 3.1-15 fold reduction in CPT and 4.7-8.0 fold reduction in pTRAIL dosing. CT MLNPs obtained significant HCT116 growth inhibition in vivo compared to monotherapy. These results support our hypothesis that MLNPs can deliver both small molecules and genetic agents towards synergistically inhibiting tumor growth.

Adenovirus-Based Vectors for the Development of Prophylactic and Therapeutic Vaccines

Emerging and reemerging infectious diseases as well as cancer pose great global health impacts on the society. Vaccines have emerged as effective treatments to prevent or reduce the burdens of already developed diseases. This is achieved by means of activating various components of the immune system to generate systemic inflammatory reactions targeting infectious agents or diseased cells for control/elimination. DNA virus-based genetic vaccines gained significant attention in the past decades owing to the development of DNA manipulation technologies, which allowed engineering of recombinant viral vectors encoding sequences for foreign antigens or their immunogenic epitopes as well as various immunomodulatory molecules. Despite tremendous progress in the past 50 years, many hurdles still remain for achieving the full clinical potential of viral-vectored vaccines. This chapter will present the evolution of vaccines from “live” or “attenuated” first-generation agents to recombinant DNA and viral-vectored vaccines. Particular emphasis will be given to human adenovirus (Ad) for the development of prophylactic and therapeutic vaccines. Ad biological properties related to vaccine development will be highlighted along with their advantages and potential hurdles to be overcome. In particular, we will discuss (1) genetic modifications in the Ad capsid protein to reduce the intrinsic viral immunogenicity, (2) antigen capsid incorporation for effective presentation of foreign antigens to the immune system, (3) modification of the hexon and fiber capsid proteins for Ad liver de-targeting and selective retargeting to cancer cells, (4) Ad-based vaccines carrying “arming” transgenes with immunostimulatory functions as immune adjuvants, and (5) oncolytic Ad vectors as a new therapeutic approach against cancer. Finally, the combination of adenoviral vectors with other non-adenoviral vector systems, the prime/boost strategy of immunization, clinical trials involving Ad-based vaccines, and the perspectives for the field development will be discussed.

Functional recovery of urethra by plasmid DNA-loaded injectable agent for the treatment of urinary incontinence

Stress urinary incontinence (SUI) is an embarrassing problem affecting a large number of women and interfering with their quality of life. The injury or weakness of urethral supporting tissues by childbirth and aging has been considered as key factors in the development of the SUI. In this study, plasmid DNA (pDNA; encoding for bFGF) complex-loaded poly(DL-lactic-co-glycolic acid) (PLGA)/Pluronic F127 mixture dispersed with polycaprolactone (PCL) microspheres was prepared as an injectable bioactive bulking agent that may provide bulking effect (by PCL microspheres) and allow stimulation of the defect tissues around urethra (by synthesis of bFGF from cells or tissues transfected by the pDNA complex) for the effective treatment of SUI. From in vitro experiments, the pDNA complex incorporated in the bulking agent was released in a sustained manner over 84 days (≥80% of the initial loading amount). The pDNA complex was effectively transfected into fibroblasts and the cells were continuously producing the target protein, bFGF. From the in vivo study using hairless mice and Sprague-Dawley rats, it was confirmed that the pDNA complex released from the bulking agent is transfected into surrounding cells/tissue, and the cells/tissues synthesize sufficient bFGF to regenerate smooth muscle with biological function around the urethra. Basis on these results, the pDNA (encoding for bFGF) complex-loaded PLGA/Pluronic F127 mixture dispersed with PCL microspheres can be a promising bioactive bulking agent system for the fundamental cure of SUI.

Polymeric Nanomedicines Based on Poly(lactide) and Poly(lactide-co-glycolide)

Small molecule chemotherapeutics often have undesired physiochemical and pharmacological properties, such as low solubility, severe side effect and narrow therapeutic index. To address these challenges, polymeric nanomedicine drug delivery technology has been routinely employed, in particular with the use of biodegradable and biocompatible polyesters, such as poly(lactide) (PLA) and poly(lactide-co-glycolide) (PLGA). Here we review the development and use of PLA and PLGA for the delivery of chemotherapeutic agents in the forms of polymer-drug conjugates and nanoconjugates.

In vitro chondrogenesis by BMP6 gene therapy

In this study, the promotion of in vitro chondrogenesis was investigated by using chitosan scaffolds and rat bone marrow-derived mesenchymal stem cells (rBMSCs) which are transfected by BMP6 (bone morphogenetic protein-6) encoding gene. For this purpose, plasmid DNA (pShuttle-rBMP6), the expression vector consisting of the coding sequence of the BMP6 was obtained, and then, it was entrapped in chitosan scaffolds to obtain a gene-activated matrix (GAM). The chitosan scaffolds performed the controlled and sustained release of plasmid DNA, thus they continuously provided the modification of rBMSCs to induce chondrogenic differentiation. In addition, the cells were transfected by lipid-based agent (Lipofectamine) and then, these modified cells were inoculated into the chitosan scaffolds. Furthermore, a group of chitosan scaffolds with nontransfected rBMSCs with recombinant BMP6 free in culture medium was used as control. Comparative results showed that, mitochondrial activities of modified rBMSCs by Lipofectamine and chitosan GAM were significantly higher than those of nontransfected rBMSCs. The observations from scanning electron microscopy analysis confirmed that BMP6 gene-modified rBMSCs differentiated to the chondrogenic phenotype. Highest amount of glycosaminoglycan contents of rBMSCs on GAM concluded that BMP6 gene-activated chitosan scaffold has a potential in the application of cartilage regeneration.

Surface modified poly(β amino ester)-containing nanoparticles for plasmid DNA delivery

The use of biodegradable polymers provides a potentially safe and effective alternative to viral and liposomal vectors for the delivery of plasmid DNA to cells for gene therapy applications. In this work we describe the formulation of a novel nanoparticle (NP) system containing a blend of poly(lactic-co-glycolic acid) and a representative poly(beta-amino) ester (PLGA and PBAE respectively) for use as gene delivery vehicles. Particles of different weight/weight (wt/wt) ratios of the two polymers were characterized for size, morphology, plasmid DNA (pDNA) loading and surface charge. NPs containing PBAE were more effective at cellular internalization and transfection (COS-7 and CFBE41o-) than NPs lacking the PBAE polymer. However, along with these delivery benefits, PBAE exhibited cytotoxic effects that presented an engineering challenge. Surface coating of these blended particles with the cell-penetrating peptides (CPPs) mTAT, bPrPp and MPG via a PEGylated phospholipid linker (DSPE-PEG2000) resulted in NPs that reduced surface charge and cellular toxicity to levels comparable with NPs formulated with only PLGA. Additionally, these coated nanoparticles showed an improvement in pDNA loading, intracellular uptake and transfection efficiency, when compared to NPs lacking the surface coating. Although all particles with a CPP coating outperformed unmodified NPs, respectively, bPrPp and MPG coating resulted in 3 and 4.5× more pDNA loading than unmodified particles and approximately an order of magnitude improvement on transfection efficiency in CFBE41o- cells. These results demonstrate that surface-modified PBAE containing NPs are a highly effective and minimally toxic platform for pDNA delivery.

Hydrological tracers using nanobiotechnology: proof of concept

In order to answer questions that involve differentiating among multiple and potentially interacting hydrological flowpaths, it would be ideal to use multiple tracers with identical transport properties that can nonetheless be distinguished from each other. This paper describes the development and proof of concept of a new kind of engineered tracer system that allows a large number of individual tracers to be simultaneously distinguished from one another. This new tracer is composed of polylactic acid (PLA) microspheres into which short strands of synthetic DNA and paramagnetic iron oxide nanoparticles are incorporated. The synthetic DNA serves as the "label" or "tag" in our tracers that allow us to distinguish one tracer from another, and paramagnetic iron oxide nanoparticles are included in the tracer to facilitate magnetic concentration of the tracers in potentially dilute water samples. Some potential advantages of this tracer concept include: virtually limitless uniquely labeled tracers, highly sensitive detection, and relatively moderate expense. Three proof-of-concept experiments at scales ranging from orders of 10 cm to 100 m demonstrated the use of the tracer system.

Controlling the stability and size of double-emulsion-templated poly(lactic-co-glycolic) acid microcapsules

The stability and size of poly(lactic-co-glycolic)acid (PLGA)-containing double emulsions and the resulting PLGA microcapsules are controlled by varying the composition of highly monodisperse water-in-oil-in-water (W/O/W) double emulsions. We propose that the basic inner phase of W/O/W double emulsions catalyzes the hydrolysis of PLGA and the ionization of carboxylic acid end groups, which enhances the surface activity of PLGA and facilitates the stabilization of the double emulsions. The size of PLGA-containing double emulsions and that of resulting microcapsules can be readily tuned by osmotic annealing, which depends on the concentration ratio of a solute in the inner and outer phases of double emulsions. The internal volume of PLGA microcapsules can be changed by more than 3 orders of magnitude using this method. This approach also overcomes the difficulty in generating monodisperse double emulsions and microcapsules over a wide range of dimensions using a single microfluidic device. The osmotic annealing method can also be used to concentrate encapsulated species such as colloidal suspensions and biomacromolecules.

Octa-functional PLGA nanoparticles for targeted and efficient siRNA delivery to tumors

Therapies based on RNA interference, using agents such as siRNA, are limited by the absence of safe, efficient vehicles for targeted delivery in vivo. The barriers to siRNA delivery are well known and can be individually overcome by addition of functional modules, such as conjugation of moieties for cell penetration or targeting. But, so far, it has been impossible to engineer multiple modules into a single unit. Here, we describe the synthesis of degradable nanoparticles that carry eight synergistic functions: 1) polymer matrix for stabilization/controlled release; 2) siRNA for gene knockdown; 3) agent to enhance endosomal escape; 4) agent to enhance siRNA potency; 5) surface-bound PEG for enhancing circulatory time; and surface-bound peptides for 6) cell penetration; 7) endosomal escape; and 8) tumor targeting. Further, we demonstrate that this approach can provide prolonged knockdown of PLK1 and control of tumor growth in vivo. Importantly, all elements in these octa-functional nanoparticles are known to be safe for human use and each function can be individually controlled, giving this approach to synthetic RNA-loaded nanoparticles potential in a variety of clinical applications.

Polymer delivery systems for site-specific genome editing

Triplex-forming peptide nucleic acids (PNAs) can be used to coordinate the recombination of short 50-60bp "donor DNA" fragments into genomic DNA, resulting in site-specific correction of genetic mutations or the introduction of advantageous genetic modifications. Site-specific gene editing in hematopoietic stem and progenitor cells (HSPCs) could result in the treatment or cure of inherited disorders of the blood such as β-thalassemia or sickle cell anemia. Gene editing in HSPCs and differentiated T cells could also help combat HIV infection by modifying the HIV co-receptor CCR5, which is necessary for R5-tropic HIV entry. However, translation of genome modification technologies to clinical practice is limited by challenges in intracellular delivery, especially in difficult-to-transfect hematolymphoid cells. Here, we review the use of engineered biodegradable polymer nanoparticles for site-specific genome editing in human hematopoietic cells, which represent a promising approach for ex vivo and in vivo gene therapy.

Hydrophilized 3D porous scaffold for effective plasmid DNA delivery

In this study, hydrophilic PLGA/Pluronic F127 scaffolds loaded with a pDNA/PEI-PEG complex were prepared to estimate their potential use as a polymeric matrix for pDNA delivery. The scaffold was fabricated by a novel precipitation/particulate leaching method. The prepared pDNA/PEI-PEG complex-loaded PLGA/Pluronic F127 scaffold exhibited a highly porous (porosity, 93-95%) and open pore structure, as well as hydrophilicity, which can provide the good environment for cell adhesion and growth. The pDNA/PEI-PEG complexes were efficiently loaded into the PLGA/Pluronic F127 scaffold and continuously released from the scaffolds up to ~90% of the initial loading amount over a period of 8 wk, which may lead to continuous gene transfection into human bone marrow mesenchymal stem cells (hBMMSCs). From the in vitro cell culture in the scaffolds for transfection, it was observed that the pDNA/PEI-PEG complex-loaded hydrophilic PLGA/Pluronic F127 scaffold has a higher transfection efficiency of the pDNA/PEI-PEG complexes into hBMMSCs than the hydrophobic PLGA ones. The cell viability associated with the pDNA/PEI-PEG complexes released from the PLGA/Pluronic F127 scaffold was not significantly different from that of the PLGA/Pluronic F127 scaffold without pDNA, indicating its low cytotoxicity, probably due to the sustained release of the pDNA/PEI-PEG complex from the scaffolds. From these results, we could suggest that the pDNA/PEI-PEG complex-loaded hydrophilic PLGA/Pluronic F127 scaffold can be an effective gene delivery system for 3D tissue formation.

A reliable method for detecting complexed DNA in vitro

Quantification of eluted nucleic acids is a critical parameter in characterizing biomaterial based gene-delivery systems. The most commonly used method is to assay samples with an intercalating fluorescent dye such as PicoGreen®. However, this technique was developed for unbound DNA and the current trend in gene delivery is to condense DNA with transfection reagents, which interfere with intercalation. Here, for the first time, the DNA was permanently labeled with the fluorescent dye Cy5 prior to complexation, an alternative technique hypothesized to allow quantification of both bound and unbound DNA. A comparison of the two methods was performed by quantifying the elution of six different varieties of DNA complexes from a model biomaterial (collagen) scaffold. After seven days of elution, the PicoGreen® assay only allowed detection of three types of complexes (those formed using Lipofectin™ and two synthesised copolymers). However, the Cy5 fluorescent labeling technique enabled detection of all six varieties including those formed via common transfection agents poly(ethylene imine), poly-L-lysine and SuperFect™. This allowed reliable quantification of the elution of all these complexes from the collagen scaffold. Thus, while intercalating dyes may be effective and reliable for detecting double-stranded, unbound DNA, the technique described in this work allowed reliable quantification of DNA independent of complexation state.

Electrostatic surface modifications to improve gene delivery

IMPORTANCE OF THE FIELD

Gene therapy has the potential to treat a wide variety of diseases, including genetic diseases and cancer.

AREAS COVERED IN THIS REVIEW

This review introduces biomaterials used for gene delivery and then focuses on the use of electrostatic surface modifications to improve gene delivery materials. These modifications have been used to stabilize therapeutics in vivo, add cell-specific targeting ligands, and promote controlled release. Coatings of nanoparticles and microparticles as well as non-particulate surface coatings are covered in this review. Electrostatic principles are crucial for the development of multilayer delivery structures fabricated by the layer-by-layer method.

WHAT THE READER WILL GAIN

The reader will gain knowledge about the composition of biomaterials used for surface modifications and how these coatings and multilayers can be utilized to improve spatial control and efficiency of delivery. Examples are shown for the delivery of nucleic acids, including DNA and siRNA, to in vitro and in vivo systems.

TAKE HOME MESSAGE

The versatile and powerful approach of electrostatic coatings and multilayers will lead to the development of enhanced gene therapies.

Central nervous system delivery of large molecules: challenges and new frontiers for intrathecally administered therapeutics

IMPORTANCE OF THE FIELD

Therapeutic proteins and DNA constructs offer promise for the treatment of central nervous system disorders, yet significant biological barriers limit the ability of these molecules to reach the central nervous system from the bloodstream. Direct administrations to the cerebrospinal fluid (intrathecal administration) comprise an emerging field to facilitate the efficient delivery of these biological macromolecules to central nervous system tissues.

AREAS COVERED IN THIS REVIEW

Previous reports from 1990 to the present time describing the interactions and turnover of the cerebrospinal fluid within the intrathecal space, characterizations of the effects that therapeutic proteins and DNA have shown after intrathecal delivery through a lumbar route, and reports of emerging technologies to address the limitations of intrathecally administered macromolecules are reviewed.

WHAT THE READER WILL GAIN

This review provides an overview of the limitations that must be overcome for intrathecally administered biological macromolecules and the recent advances and promising approaches for surmounting these limitations.

TAKE HOME MESSAGE

Emerging approaches that stabilize and sustain the delivery of intrathecally administered biological macromolecules may enhance substantially the clinical relevance of promising therapeutic proteins and DNA constructs for the treatment of various central nervous system disorders.

DNA nanomedicine: Engineering DNA as a polymer for therapeutic and diagnostic applications

Nanomedicine, the application of nanotechnology to medicine, encompasses a broad spectrum of fields including molecular detection, diagnostics, drug delivery, gene regulation and protein production. In recent decades, DNA has received considerable attention for its functionality and versatility, allowing it to help bridge the gap between materials science and biological systems. The use of DNA as a structural nanoscale material has opened a new avenue towards the rational design of DNA nanostructures with different polymeric topologies. These topologies, in turn, possess unique characteristics that translate to specific therapeutic and diagnostic strategies within nanomedicine.

Comparison of post-emulsification freeze drying or spray drying processes for the microencapsulation of plasmid DNA

In this work, methods used to microencapsulate plasmid DNA in a biodegradable polymer were compared for their effects on the physicochemical characteristics of DNA-loaded microparticles and on the release and integrity of encapsulated DNA. Microparticles were formulated by either w/o/w emulsification and freeze-drying (EFD) or by w/o/w emulsification and spray-drying (ESD). The influence of both manufacturing processes on particle morphology, charge, release characteristics and biological activity of encapsulated DNA was evaluated. Particles produced by emulsification/spray-drying exhibited more diversity in shape and size than those produced by emulsification/freeze-drying. These particles also exhibited higher plasmid DNA encapsulation efficiency than particles produced by emulsification/freeze-drying. The fractional DNA release rates were similar over the first 25 days for both formulations, release rate declining more rapidly at later times for the ESD product. Mammalian cell transfection assays confirmed the biological activity of encapsulated DNA extracted from both types of particles, with significantly higher transfection levels being observed for ESD particles. Application of a double emulsion (w/o/w) before spray drying resulted in higher encapsulation levels (> 90%) relative to previous literature values, which used single (w/o) emulsions before spray drying. The emulsification/spray-drying technique described here appears to be a rapid and efficient method for the preparation of PLGA microparticles loaded with plasmid DNA.

Regulated non-viral gene delivery from coaxial electrospun fiber mesh scaffolds

In an effort to add to the versatility of three-dimensional scaffolds for tissue engineering applications, recent experimental designs are incorporating biological molecules such as plasmids and proteins within the scaffold structure. Such scaffolds act as reservoirs for the biological molecules of interest while regulating their release over various durations of time. Here, we describe the use of coaxial electrospinning as a means for the fabrication of fiber mesh scaffolds and the encapsulation and subsequent release of a non-viral gene delivery vector over a period of up to 60 days. Various fiber mesh scaffolds containing plasmid DNA (pDNA) within the core and the non-viral gene delivery vector poly(ethylenimine)-hyaluronic acid (PEI-HA) within the sheath of coaxial fibers were fabricated based on a fractional factorial design that investigated the effects of four processing parameters at two levels. Poly(epsilon-caprolactone) sheath polymer concentration, poly(ethylene glycol) core polymer molecular weight and concentration, and the concentration of pDNA were investigated for their effects on average fiber diameter, release kinetics of PEI-HA, and transfection efficiency. It was determined that increasing the values of each of the investigated parameters caused an increase in the average diameter of the fibers. The release kinetics of PEI-HA from the fibers were affected by the loading concentration of pDNA (with PEI-HA concentration adjusted accordingly to maintain a constant nitrogen to phosphorous (N:P) ratio within the complexes). Two-dimensional cell culture experiments with model fibroblast-like cells demonstrated that complexes of pDNA with PEI-HA released from fiber mesh scaffolds could successfully transfect cells and induce expression of enhanced green fluorescent protein (EGFP). Peak EGFP expression varied with the investigated processing parameters, and the average transfection observed was a function of poly(ethylene glycol) (core) molecular weight and concentration. Furthermore, fibroblast-like cells seeded directly onto coaxial fiber mesh scaffolds containing PEI-HA and pDNA showed EGFP expression over 60 days, which was significantly greater than the EGFP expression observed with scaffolds containing pDNA alone. Hence, variable transfection activity can be achieved over extended periods of time upon release of pDNA and non-viral gene delivery vectors from electrospun coaxial fiber mesh scaffolds, with release and subsequent transfection controlled by tunable coaxial fiber mesh fabrication parameters.

PLGA microsphere-mediated growth hormone release hormone expression induces intergenerational growth

To improve animal growth, growth hormone-releasing hormone (GHRH) expression vectors that maintain constant GHRH expression can be directly injected into muscles. To deliver the GHRH expression vectors, biodegradable microspheres have been used as a sustained release system. Although administering GHRH through microspheres is a common practice, the intergenerational effects of this delivery system are unknown. To investigate the intergenerational effects of polylactic-co-glycolic acid (PLGA) encapsulated plasmid-mediated GHRH supplements, pCMV-Rep-GHRH microspheres were injected into pregnant mice. Growth and expression of GHRH were measured in the offspring. RT-PCR and immunohistochemistry reveal GHRH expression 3-21 days post-injection. The proportion of GH-positive cells in the GHRH treated offspring was 48.2% higher than in the control group (P < 0.01). The GHRH treated offspring were 6.15% (P < 0.05) larger than the control offspring. At day 49 post-injection, IGF-I serum levels were significantly higher in the treatment group than in the control group. This study confirms that intramuscular expression of GHRH mediated by PLGA microspheres significantly enhances intergenerational growth.

Modular Cre/lox system and genetic therapeutics for colorectal cancer

The Cre/lox system is a powerful tool for targeting therapeutic effectors in a wide variety of human disorders. I review a Cre/lox Wnt-targeted system that has shown promise against Wnt-positive colorectal cancer cell lines. In addition to Wnt-specific targeting of cell death inducers, the modular nature of this gene therapy model system can be exploited by designing positive and negative feedback loops to either amplify or inhibit Wnt activity for experimental or therapeutic benefit. I discuss the structural components and performance parameters of the system, the implication of these findings with respect to cancer stem cells, as well as the general applicability of this system to any disorder characterized by differential gene expression. I also consider the issue of gene delivery as well as in vivo testing requirements necessary for the further characterization and development of this system.

Drug releasing systems in cardiovascular tissue engineering

Heart disease and atherosclerosis are the leading causes of morbidity and mortality worldwide. The lack of suitable autologous grafts has produced a need for artificial grafts; however, current artificial grafts carry significant limitations, including thrombosis, infection, limited durability and the inability to grow. Tissue engineering of blood vessels, cardiovascular structures and whole organs is a promising approach for creating replacement tissues to repair congenital defects and/or diseased tissues. In an attempt to surmount the shortcomings of artificial grafts, tissue-engineered cardiovascular graft (TECVG), constructs obtained using cultured autologous vascular cells seeded onto a synthetic biodegradable polymer scaffold, have been developed. Autologous TECVGs have the potential advantages of growth, durability, resistance to infection, and freedom from problems of rejection, thrombogenicity and donor scarcity. Moreover polymers engrafted with growth factors, cytokines, drugs have been developed allowing drug-releasing systems capable of focused and localized delivery of molecules depending on the environmental requirements and the milieu in which the scaffold is placed. A broad range of applications for compound-releasing, tissue-engineered grafts have been suggested ranging from drug delivery to gene therapy. This review will describe advances in the development of drug-delivery systems for cardiovascular applications focusing on the manufacturing techniques and on the compounds delivered by these systems to date.

Gene delivery systems for gene therapy in tissue engineering and central nervous system applications

The present review aims to describe the potential applications of gene delivery systems to tissue engineering and central nervous system diseases. Some key experimental work has been done with interesting results, but the subject is far from being fully explored. The combined approach of gene therapy and material science has a huge potential to improve the therapeutic approaches now available for a wide range of medical applications. Focus is given to this multidisciplinary strategy in neurodegenerative pathologies, where the use of polymeric matrices as gene carriers might make a crucial difference.

Targeted cationic poly(D,L-lactic-co-glycolic acid) nanoparticles for gene delivery to cultured cells

We developed a new targeted cationic nanoparticulate system composed of poly(D,L-lactic-co-glycolic acid) (PLGA), 1,2-dioleoyl-3-(trimethylammonium) propane (DOTAP) and asialofetuin (AF), and found it to be a highly effective formulation for gene delivery to liver tumor cells. The nanoparticles (NP) were prepared by a modified solvent evaporation process that used two protocols in order to encapsulate (NP1 particles) or adsorb (NP2 particles) plasmid DNA. The final particles are in the nanoscale range. pDNA loaded in PLGA/DOTAP/AF particles with high loading efficiency showed a positive surface charge. Targeted asialofetuin-nanoparticles (AF-NP) carrying genes encoding for luciferase and interleukin-12 (IL-12) resulted in increased transfection efficiencies compared to free DNA and to plain (non-targeted) systems, even in the presence of 60% fetal bovine serum (FBS). The results of transfections performed on HeLa cells, defective in asialoglycoprotein receptors (ASGPr-), confirmed the receptor-mediated endocytosis mechanism. In summary, this is the first time that asialoglycoprotein receptor targeting by PLGA/DOTAP/DNA nanoparticles carrying the therapeutic gene IL-12 has been shown to be efficient in gene delivery to liver cancer cells in the presence of a very high concentration of serum, and this could be a potential system for in vivo application.

Nanoparticles as protein and gene carriers to mucosal surfaces

One of the most exciting and challenging applications of nanotechnology in medicine is the development of nanocarriers for the intraepithelial delivery of biomacromolecules through mucosal surfaces. These biomacromolecules represent an increasingly important segment of the therapeutic arsenal; however, their potential is still limited by their instability and inability to cross biological barriers. Nanoparticle carriers have emerged as one of the most promising technologies to overcome this limitation, owing mainly to their demonstrated capacity to interact with biological barriers. In this review, we summarize the current advances made on nanoparticles designed for transmucosal delivery. Supported by the examples of a variety of therapeutic macromolecules – peptides and proteins, gene medicines and vaccines – we review the lessons learned from the past and we offer a future perspective for this field.

Formulating poly(lactide-co-glycolide) particles for plasmid DNA delivery

Biodegradable poly(lactide-co-glycolide) (PLGA) particles have shown significant potential for sustained and targeted delivery of several pharmaceutical agents, including plasmid DNA (pDNA). Here, we survey current approaches to PLGA particle preparation for pDNA delivery and discuss recent progress on optimizing formulation development.

High loading efficiency and tunable release of plasmid DNA encapsulated in submicron particles fabricated from PLGA conjugated with poly-L-lysine

Poly(lactic-co-glycolic acid) (PLGA) particles have been widely explored as vehicles for delivery of plasmid DNA to mammalian cells both in vitro and in vivo. Achieving high incorporation efficiencies and control over release kinetics are significant challenges in encapsulating hydrophilic molecules such as DNA within submicron particles fabricated from PLGA. This study explored two modifications in the preparation of submicron particles to specifically address these challenges. Firstly, we compared homogenization and sonication as energy sources for emulsification. It was demonstrated that particles prepared with homogenization resulted in higher encapsulation efficiency and a linear release profile of DNA as compared to particles prepared with sonication, which exhibited lower encapsulation efficiency and a burst release. Also investigated was conjugation of poly-L-lysine to PLGA (PLGA-PLL) to create an electrostatically favorable interaction between the carrier material and the DNA. Particles fabricated with high weight percentages of PLGA-PLL/PLGA resulted in remarkably increased loading (>90%). Additionally, the release profile could be dictated by the quantity of PLGA-PLL incorporated into the particles. Particles incubated in vitro on COS-7 cells were able to transfect cells. These results demonstrated that DNA encapsulation and release were modulated by the method of fabrication.