Biodegradable DNA Nanoparticles that Provide Widespread Gene Delivery in the Brain

Furan-rich, biobased transfection agents as potential oligomeric candidates for intracellular plasmid DNA delivery

Biobased, DNA delivery vectors have been synthesized with a core motif composed of 2,5-bishydroxymethylfuran (BHMF) readily available from an important biomass feedstock 5-hydroxymethyl furfural (HMF). To generate the product, BHMF was first converted to 2,5-furan bishydroxymethyl diacrylate (2,5-FDA), which was later conjugated with different types of secondary amines. Rich in tertiary nitrogen, these oligomeric FDA-amino esters demonstrated stable electrostatic interactions with negatively charged plasmid DNA in an aqueous environment. We evaluated synthetic routes toward these plasmid DNA-binding amino esters (pFASTs), identified their nanoscale features, and attempted to establish their structure-property relationship in the context of the DNA delivery. Our preliminary studies show that the pFASTs formed stable complexes with the plasmid DNA. Dynamic light scattering indicated that the DNA polyplexes of pFASTs have hydrodynamic diameters within the size range of 100-150 nm with a surface charge (ζ-potential) ranging from -10 to +33 mV, depending on pFAST type. These oligomeric amino esters rich in furan motif were also found to successfully transfect the GFP-expressing plasmid DNA intracellularly. Collectively, this study establishes a new route to produce DNA transfection agents from sustainable resources that can be used for transferring genetic materials for humans, veterinary, and agrochemical purposes.

PEGylated-liposomal astaxanthin ameliorates Aβ neurotoxicity and Alzheimer-related phenotypes by scavenging formaldehyde

Alzheimer's disease (AD), which is a prevailing type of dementia, presents a significant global health concern. The current therapies do not meet clinical expectations. Amyloid-beta (Aβ) has been found to induce endogenous formaldehyde (FA) accumulation by inactivating FA dehydrogenase (FDH); in turn, excessive FA triggers Aβ aggregation that eventually leads to AD onset. Hence, scavenging FA by astaxanthin (ATX, a strong exogenous antioxidant) may be pursued as a promising disease-modifying approach. Here, we report that liposomal nanoparticles coupled with PEG (PEG-ATX@NPs) could enhance water-solubility of ATX and alleviate cognitive impairments by scavenging FA and reducing Aβ deposition. To enable drug delivery to the brain, liposomes were used to encapsulate ATX and then coupled with PEG, which produced liposomal nanoparticles (PEGATX@NPs) with a diameter of <100 nm. The PEG-ATX@NPs reduced Aβ neurotoxicity by both degrading FA and reducing FA-induced Aβ assembly in vitro. Intraperitoneal administration of PEG-ATX@NPs in APPswe/PS1dE9 mice (APP/PS1, a familial model of AD), not only decreased the levels of brain FA and malondialdehyde (MDA, a typical product of oxidative stress), but also attenuated both intracellular Aβ oligomerization and extracellular Aβ-related senile plaque (SP) formation. These pathological changes were accompanied by rescued ability of spatial learning and memory. Collectively, PEG-ATX@NPs improved the water-solubility, bioavailability, and effectiveness of ATX. Thus, it has the potential to be developed as a safe and effective strategy for treating AD.

Poly(β-amino ester)s-based nanovehicles: Structural regulation and gene delivery

The first poly(β-amino) esters (PβAEs) were synthesized more than 40 years ago. Since 2000, PβAEs have been found to have excellent biocompatibility and the capability of ferrying gene molecules. Moreover, the synthesis process of PβAEs is simple, the monomers are readily available, and the polymer structure can be tailored to meet different gene delivery needs by adjusting the monomer type, monomer ratio, reaction time, etc. Therefore, PβAEs are a promising class of non-viral gene vector materials. This review paper presents a comprehensive overview of the synthesis and correlated properties of PβAEs and summarizes the progress of each type of PβAE for gene delivery. The review focuses in particular on the rational design of PβAE structures, thoroughly discusses the correlations between intrinsic structure and effect, and then finishes with the applications and perspectives of PβAEs.

A Highly Translatable Dual-arm Local Delivery Strategy To Achieve Widespread Therapeutic Coverage in Healthy and Tumor-bearing Brain Tissues

Drug delivery nanoparticles (NPs) based entirely on materials generally recognized as safe that provide widespread parenchymal distribution following intracranial administration via convection-enhanced delivery (CED) are introduced. Poly(lactic-co-glycolic acid) (PLGA) NPs are coated with various poloxamers, including F68, F98, or F127, via physical adsorption to render particle surfaces non-adhesive, thereby resisting interactions with brain extracellular matrix. F127-coated PLGA (F127/PLGA) NPs provide markedly greater distribution in healthy rat brains compared to uncoated NPs and widespread coverage in orthotopically-established brain tumors. Distribution analysis of variously-sized F127/PLGA NPs determines the average rat brain tissue porosity to be between 135 and 170 nm while revealing unprecedented brain coverage of larger F127/PLGA NPs with an aid of hydraulic pressure provided by CED. Importantly, F127/PLGA NPs can be lyophilized for long-term storage without compromising their ability to penetrate the brain tissue. Further, 65- and 200-nm F127/PLGA NPs lyophilized-reconstituted and administered in a moderately hyperosmolar infusate solution show further enhance particle dissemination in the brain via osmotically-driven enlargement of the brain tissue porosity. Combination of F127/PLGA NPs and osmotic tissue modulation provides a means with a clear regulatory path to maximize the brain distribution of large NPs that enable greater drug loading and prolong drug release.

Nucleic acid drug vectors for diagnosis and treatment of brain diseases

Nucleic acid drugs have the advantages of rich target selection, simple in design, good and enduring effect. They have been demonstrated to have irreplaceable superiority in brain disease treatment, while vectors are a decisive factor in therapeutic efficacy. Strict physiological barriers, such as degradation and clearance in circulation, blood-brain barrier, cellular uptake, endosome/lysosome barriers, release, obstruct the delivery of nucleic acid drugs to the brain by the vectors. Nucleic acid drugs against a single target are inefficient in treating brain diseases of complex pathogenesis. Differences between individual patients lead to severe uncertainties in brain disease treatment with nucleic acid drugs. In this Review, we briefly summarize the classification of nucleic acid drugs. Next, we discuss physiological barriers during drug delivery and universal coping strategies and introduce the application methods of these universal strategies to nucleic acid drug vectors. Subsequently, we explore nucleic acid drug-based multidrug regimens for the combination treatment of brain diseases and the construction of the corresponding vectors. In the following, we address the feasibility of patient stratification and personalized therapy through diagnostic information from medical imaging and the manner of introducing contrast agents into vectors. Finally, we take a perspective on the future feasibility and remaining challenges of vector-based integrated diagnosis and gene therapy for brain diseases.

Nanoparticle Mediated Gene Therapy: A Trailblazer Armament to Fight CNS Disorders

Central nervous system (CNS) disorders account for boundless socioeconomic burdens with devastating effects among the population, especially the elderly. The major symptoms of these disorders are neurodegeneration, neuroinflammation, and cognitive dysfunction caused by inherited genetic mutations or by genetic and epigenetic changes due to injury, environmental factors, and disease-related events. Currently available clinical treatments for CNS diseases, i.e., Alzheimer's disease, Parkinson's disease, stroke, and brain tumor, have significant side effects and are largely unable to halt the clinical progression. So gene therapy displays a new paradigm in the treatment of these disorders with some modalities, varying from the suppression of endogenous genes to the expression of exogenous genes. Both viral and non-viral vectors are commonly used for gene therapy. Viral vectors are quite effective but associated with severe side effects, like immunogenicity and carcinogenicity, and poor target cell specificity. Thus, non-viral vectors, mainly nanotherapeutics like nanoparticles (NPs), turn out to be a realistic approach in gene therapy, achieving higher efficacy. NPs demonstrate a new avenue in pharmacotherapy for the delivery of drugs or genes to their selective cells or tissue, thus providing concentrated and constant drug delivery to targeted tissues, minimizing systemic toxicity and side effects. The current review will emphasize the role of NPs in mediating gene therapy for CNS disorders treatment. Moreover, the challenges and perspectives of NPs in gene therapy will be summarized.

Design and development of Branched Poly(ß-aminoester) nanoparticles for Interleukin-10 gene delivery in a mouse model of atherosclerosis

Atherosclerosis progression is a result of chronic and non-resolving inflammation, effective treatments for which still remain to be developed. We designed and developed branched poly(ß-amino ester) nanoparticles (NPs) containing plasmid DNA encoding IL-10, a potent anti-inflammatory cytokine to atherosclerosis. The NPs (NP-VHPK) are functionalized with a targeting peptide (VHPK) specific for VCAM-1, which is overexpressed by endothelial cells at sites of atherosclerotic plaque. The anionic coating affords NP-VHPK with significantly lower toxicity than uncoated NPs in both endothelial cells and red blood cells (RBCs). Following injection of NP-VHPK in ApoE^-/- mice, Cy5-labelled IL-10 significantly accumulates in both whole aortas and aortic sinus sections containing plaque compared to injection with a non-targeted control. Furthermore, IL-10 gene delivery results in an attenuation of inflammation locally at the plaque site. NP-VHPK may thus have the potential to reduce the inflammatory component of atherosclerosis in a safe and effective manner. STATEMENT OF SIGNIFICANCE: Atherosclerosis is a chronic inflammatory disease that results in the formation of lipid-laden plaques within vascular walls. Although treatments using drugs and antibodies are now beginning to address the inflammation in atherosclerosis, neither is sufficient for long-term therapy. In this paper, we introduce a strategy to deliver genes encoding the anti-inflammatory protein interleukin-10 (IL-10) in vivo. We showed that Branched Poly(ß-aminoester) carrying the IL-10 gene are able to localize specifically at the plaque via surface-functionalized targeting moieties against inflamed VCAM-1 and/or ICAM-1 and to facilitate gene transcription by ECs to increase the local concentration of the IL-10 within the plaque. To date, there is no report involving non-viral nanotechnology to provide gene-based therapies for atherosclerosis.

Overcoming barriers in non-viral gene delivery for neurological applications

Gene therapy for neurological disorders has attracted significant interest as a way to reverse or stop various disease pathologies. Typical gene therapies involving the central and peripheral nervous system make use of adeno-associated viral vectors whose questionable safety and limitations in manufacturing has given rise to extensive research into non-viral vectors. While early research studies have demonstrated limited efficacy with these non-viral vectors, investigation into various vector materials and functionalization methods has provided insight into ways to optimize these non-viral vectors to improve desired characteristics such as improved blood-brain barrier transcytosis, improved perfusion in brain region, enhanced cellular uptake and endosomal escape in neural cells, and nuclear transport of genetic material post- intracellular delivery. Using a combination of various strategies to enhance non-viral vectors, research groups have designed multi-functional vectors that have been successfully used in a variety of pre-clinical applications for the treatment of Parkinson's disease, brain cancers, and cellular reprogramming for neuron replacement. While more work is needed in the design of these multi-functional non-viral vectors for neural applications, much of the groundwork has been done and is reviewed here.

Poly (β amino esters) copolymers: Novel potential vectors for delivery of genes and related therapeutics

The unique properties of polymers have performed an essential contribution to the drug delivery system by providing an outstanding platform for the delivery of macromolecules and genes. However, the block copolymers have been the subject of many recently published works whose results have demonstrated excellent performance in drug targeting. Poly(β-amino esters) (PβAEs) copolymers are the synthetic cationic polymers that are tailored by chemically joining PβAEs with other additives to demonstrate extraordinary efficiency in designing pre-defined and pre-programmed nanostructures, site-specific delivery, andovercoming the distinct cellular barriers. Different compositional and structural libraries could be generated by combinatorial chemistry and by the addition of various novel functional additives that fulfill the multiple requirements of targeted delivery. These intriguing attributes allow PβAE-copolymers to have customized therapeutic functions such as excellent encapsulation capacity, high stability, and stimuli-responsive release. Here, we give an overview of PβAE copolymers-based formulations along with focusing on most notable improvements such as structural modifications, bio-conjugations, and stimuli-responsive approaches, for safe and effective nucleic acids delivery.

Constructing a passive targeting and long retention therapeutic nanoplatform based on water-soluble, non-toxic and highly-stable core-shell poly(amino acid) nanocomplexes

Drug delivery nanoplatforms have been applied in bioimaging, medical diagnosis, drug delivery and medical therapy. However, insolubility, toxicity, instability, nonspecific targeting and short retention of many hydrophobic drugs limit their extensive applications. Herein, we have constructed a passive targeting and long retention therapeutic nanoplatform of core-shell gefitinib/poly (ethylene glycol)-polytyrosine nanocomplexes (Gef-PY NCs). The Gef-PY NCs have good water-solubility, non-toxicity (correspond to 1/10 dosage of effective gefitinib (hydrochloride) (Gef·HCl) (normal drug administration and slow-release) and high stability (120 days, 80% drug retention at 4 or 25 °C). The core-shell Gef-PY NCs present unexpected kidney targeting and drug slow-release capacity (ca. 72 h). The good water-solubility, non-toxicity and high stability of Gef-PY NCs effectively solve the bottleneck question that Gef-based therapy could be used only in intraperitoneal injection due to its insolubility and severe toxicity. Such excellent properties (e.g., water-solubility, non-toxicity, high stability, kidney targeting and long retention) of Gef-PY NCs create their prominent anti-fibrosis capabilities, such as decreasing approximately 40% tubulointerstitial fibrosis area and 68% expression of collagen I within 7 days. This therapeutic efficacy is well-matched with that of 10 times the dosage of toxic Gef·HCl. It is very hopeful that Gef-PY NCs could realize clinical applications and such a strategy offers an effective route to design high-efficiency treatments for kidney- and tumor-related diseases.

Microenvironment-responsive DNA-conjugated albumin nanocarriers for targeted therapy

Drug delivery with accurate targeting and efficient treatment has become an essential strategy for cancer therapy. Two nanocarriers based on bovine serum albumin (BSA) and DNA were synthesized via click chemistry and DNA hybridization reactions (DNA-BSA1 and DNA-BSA2). One of the hybridized oligonucleotides, Linker1, in DNA-BSA1 included a pH-sensitive i-motif sequence and a cancer cell-targeted guanine-quadruplex-structured AS1411 aptamer sequence, and the other, Linker2, in DNA-BSA2 had only the same pH-sensitive i-motif sequence. Doxorubicin (DOX) molecules could be quickly and preferentially intercalated into double-stranded DNA via non-covalent interactions, and the encapsulation efficiency of DNA-BSA1 and DNA-BSA2 was almost 100% and 87.5%, respectively. As a mimic of the cancer cell microenvironment, a pH-trigger and a deoxyribonuclease I (DNase I)-trigger release mechanism was individually proposed to explain the dynamic release of the DNA-BSA@DOX under acidic conditions and the presence of DNase I in vitro. Intracellular uptake and cytotoxicity experiments confirmed that the nanocarrier DNA-BSA1@DOX had accurate targeting and efficient treatment towards cancer cells due to the high affinity and specificity of AS1411 to nucleolin, which is overexpressed in cancer cells. Furthermore, in vivo studies showed that the nanocarrier system could efficiently inhibit tumor growth. Therefore, the entire bio-based nanocarrier DNA-BSA is a promising candidate for the loading and release of anti-cancer drugs for accurate delivery and efficient treatment.

Non-adhesive and highly stable biodegradable nanoparticles that provide widespread and safe transgene expression in orthotopic brain tumors

Several generations of poly(β-amino ester) (PBAE) polymers have been developed for efficient cellular transfection. However, PBAE-based gene vectors, similar to other cationic materials, cannot readily provide widespread gene transfer in the brain due to adhesive interactions with the extracellular matrix (ECM). We thus engineered eight vector candidates using previously identified lead PBAE polymer variants but endowed them with non-adhesive surface coatings to facilitate their spread through brain ECM. Specifically, we screened for the ability to provide widespread gene transfer in tumor spheroids and healthy mouse brains. We then confirmed that a lead formulation provided widespread transgene expression in orthotopically established brain tumor models with an excellent in vivo safety profile. Lastly, we developed a method to store it long-term while fully retaining its brain-penetrating property. This new platform provides a broad utility in evaluating novel genetic targets for gene therapy of brain tumors and neurological disorders in preclinical and clinical settings. Graphical abstract We engineered biodegradable DNA-loaded brain-penetrating nanoparticles (DNA-BPN) possessing small particle diameters (< 70 nm) and non-adhesive surface coatings to facilitate their spread through brain tumor extracellular matrix (ECM). These DNA-BPN provide widespread gene transfer in models recapitulating the ECM barrier, including three-dimensional multicellular tumor spheroids and mice with orthotopically established brain tumor.

Method for Measuring Mucociliary Clearance and Cilia-generated Flow in Mice by ex vivo Imaging

Ex vivo biophysical measurements provide valuable insights into understanding both physiological and pathogenic processes. One critical physiological mechanism that is regulated by these biophysical properties is cilia-generated flow that mediates mucociliary clearance, which is known to provide protection against foreign particles and pathogens in the upper airway. To measure ciliary clearance, several techniques have been implemented, including the use of radiolabeled particles and imaging with single-photon emission computerized tomography (SPECT) methods. Although non-invasive, these tests require the use of specialized equipment, limiting widespread use. Here we describe a method of ex vivo imaging of cilia-generated flow, adapted from previously reported methods, to make it more accessible and higher throughput for researchers. We excise trachea from mice quickly after euthanasia, cut it longitudinally and place it in an inhouse made slide. We apply fluorescent particles to measure particle movement under a fluorescent microscope, followed by analysis with ImageJ, allowing calculation of fluid flow generated by cilia under different conditions. This method enables ex vivo measurements in tissue with minimal investment or special equipment, giving opportunity to investigate and discover important biophysical properties associated with ciliary movement of the trachea in physiology and disease.

Facile Construction of i-Motif DNA-Conjugated Gold Nanostars as Near-Infrared and pH Dual-Responsive Targeted Drug Delivery Systems for Combined Cancer Therapy

Stimuli-responsive DNA-based nanostructures have emerged as promising vehicles for intelligent drug delivery. In this study, i-motif DNA-conjugated gold nanostars (GNSs) were fabricated in a facile manner as stimuli-responsive drug delivery systems (denoted as A-GNS/DNA/DOX) for the treatment of cancer via combined chemo-photothermal therapy. The i-motif DNA is sensitive to the environmental pH and can switch from a single-stranded structure to a C-tetrad (i-motif) structure as the environmental pH decreases from neutral (∼7.4) to acidic (<6.0). The loaded drug can then be released along with the conformational changes. To enhance cellular uptake and improve cancer cell selectivity, the aptamer AS1411, which recognizes nucleolins, was employed as a targeting moiety. The A-GNS/DNA/DOX nanocomposites were found to be highly capable of photothermal conversion and exhibited photostability under near-infrared (NIR) irradiation, and the pH and NIR irradiation effectively triggered the drug-release behaviors. In addition, the A-GNS/DNA/DOX nanocomposites exhibited good biocompatibility. The targeting recognition enabled the A-GNS/DNA/DOX to exhibit higher cellular uptake and therapeutic efficiency than the GNS/DNA/DOX. Notably, under NIR irradiation, a synergistic effect between chemotherapy and photothermal therapy can be achieved with the proposed delivery system, which exhibits much higher therapeutic efficiency both in monolayer cancer cells and tumor spheroids as compared with a single therapeutic method. This study highlights the potential of GNS/DNA nanoassemblies for intelligent anticancer drug delivery and combined cancer therapy.

Biodegradable microneedle patch for transdermal gene delivery

A gelatin methacryloyl based microneedle patch has been developed for transdermal gene delivery both in vitro and in vivo.

Focused Ultrasound Preconditioning for Augmented Nanoparticle Penetration and Efficacy in the Central Nervous System

Microbubble activation with focused ultrasound (FUS) facilitates the noninvasive and spatially-targeted delivery of systemically administered therapeutics across the blood-brain barrier (BBB). FUS also augments the penetration of nanoscale therapeutics through brain tissue; however, this secondary effect has not been leveraged. Here, 1 MHz FUS sequences that increase the volume of transfected brain tissue after convection-enhanced delivery of gene-vector "brain-penetrating" nanoparticles were first identified. Next, FUS preconditioning is applied prior to trans-BBB nanoparticle delivery, yielding up to a fivefold increase in subsequent transgene expression. Magnetic resonance imaging (MRI) analyses of tissue temperature and Ktrans confirm that augmented transfection occurs through modulation of parenchymal tissue with FUS. FUS preconditioning represents a simple and effective strategy for markedly improving the efficacy of gene vector nanoparticles in the central nervous system.

A Role for Nanoparticles in Treating Traumatic Brain Injury

Traumatic brain injury (TBI) is one of the main causes of disability in children and young adults, as well as a significant concern for elderly individuals. Depending on the severity, TBI can have a long-term impact on the quality of life for survivors of all ages. The primary brain injury can result in severe disability or fatality, and secondary brain damage can increase the complexities in cellular, inflammatory, neurochemical, and metabolic changes in the brain, which can last decades post-injury. Thus, survival from a TBI is often accompanied by lifelong disabilities. Despite the significant morbidity, mortality, and economic loss, there are still no effective treatment options demonstrating an improved outcome in a large multi-center Phase III trial, which can be partially attributed to poor target engagement of delivered therapeutics. Thus, there is a significant unmet need to develop more effective delivery strategies to overcome the biological barriers that would otherwise inhibit transport of materials into the brain to prevent the secondary long-term damage associated with TBI. The complex pathology of TBI involving the blood-brain barrier (BBB) has limited the development of effective therapeutics and diagnostics. Therefore, it is of great importance to develop novel strategies to target the BBB. The leaky BBB caused by a TBI may provide opportunities for therapeutic delivery via nanoparticles (NP). The focus of this review is to provide a survey of NP-based strategies employed in preclinical models of TBI and to provide insights for improved NP based diagnostic or treatment approaches. Both passive and active delivery of various NPs for TBI are discussed. Finally, potential therapeutic targets where improved NP-mediated delivery could increase target engagement are identified with the overall goal of providing insight into open opportunities for NP researchers to begin research in TBI.

Widespread gene transfer to malignant gliomas with In vitro-to-In vivo correlation

Gene therapy of malignant gliomas has shown a lack of clinical success to date due in part to inability of conventional gene vectors to achieve widespread gene transfer throughout highly disseminated tumor areas within the brain. Here, we demonstrate that newly engineered polymer-based DNA-loaded nanoparticles (DNA-NP) possessing small particle diameters (~50 nm) and non-adhesive surface polyethylene glycol (PEG) coatings efficiently penetrate brain tumor tissue as well as healthy brain parenchyma. Specifically, this brain-penetrating nanoparticle (BPN), following intracranial administration via convection enhanced delivery (CED), provides widespread transgene expression in heathy rodent striatum and an aggressive brain tumor tissue established orthotopically in rats. The ability of BPN to efficiently traverse both tissues is of great importance as the highly invasive glioma cells infiltrated into normal brain tissue are responsible for tumor recurrence. Of note, the transgene expression within the orthotopic tumor tissue occurred preferentially in glioma cells over microglial cells. We also show that three-dimensional (3D) multicellular spheroids established with malignant glioma cells, unlike conventional two-dimensional (2D) cell cultures, serve as an excellent in vitro model reliably predicting gene vector behaviors in vivo. Briefly, DNA-NP possessing greater surface PEG coverage exhibited more uniform and higher-level transgene expression both in the 3D model and in vivo, whereas the trend was opposite in 2D culture. The finding here alerts that gene transfer studies based primarily on 2D cultures should be interpreted with caution and underscores the relevance of 3D models for screening newly engineered gene vectors prior to their in vivo evaluation.

Vectors for Glioblastoma Gene Therapy: Viral & Non-Viral Delivery Strategies

Glioblastoma multiforme is the most common and aggressive primary brain tumor. Even with aggressive treatment including surgical resection, radiation, and chemotherapy, patient outcomes remain poor, with five-year survival rates at only 10%. Barriers to treatment include inefficient drug delivery across the blood brain barrier and development of drug resistance. Because gliomas occur due to sequential acquisition of genetic alterations, gene therapy represents a promising alternative to overcome limitations of conventional therapy. Gene or nucleic acid carriers must be used to deliver these therapies successfully into tumor tissue and have been extensively studied. Viral vectors have been evaluated in clinical trials for glioblastoma gene therapy but have not achieved FDA approval due to issues with viral delivery, inefficient tumor penetration, and limited efficacy. Non-viral vectors have been explored for delivery of glioma gene therapy and have shown promise as gene vectors for glioma treatment in preclinical studies and a few non-polymeric vectors have entered clinical trials. In this review, delivery systems including viral, non-polymeric, and polymeric vectors that have been used in glioblastoma multiforme (GBM) gene therapy are discussed. Additionally, advances in glioblastoma gene therapy using viral and non-polymeric vectors in clinical trials and emerging polymeric vectors for glioma gene therapy are discussed.

Poly(β-Amino Esters): Synthesis, Formulations, and Their Biomedical Applications

Poly(β-amino ester) (abbreviated as PBAE or PAE) refers to a polymer synthesized from an acrylate and an amine by Michael addition and has properties inherent to tertiary amines and esters, such as pH responsiveness and biodegradability. The versatility of building blocks provides a library of polymers with miscellaneous physicochemical and mechanical properties. When used alone or together with other materials, PBAEs can be fabricated into different formulations in order to fulfill various requirements in drug delivery (for instance, gene, anticancer drugs, and antimicrobials delivery) and natural complex mimicry (nanochaperones). This progress report discusses the recent developments in design, synthesis, formulations, and applications of PBAEs in biomedical fields and provides a perspective view for the future of the PBAEs.

pH-Sensitive Polymers as Dynamic Mediators of Barriers to Nucleic Acid Delivery

The nonviral delivery of exogenous nucleic acids (NA) into cells for therapeutic purposes has rapidly matured into tangible clinical impact. Synthetic polymers are particularly attractive vectors for NA delivery due to their relatively inexpensive production compared to viral alternatives and their highly tailorable chemical properties; indeed, many preclinical investigations have revealed the primary biological barriers to nonviral NA delivery by systematically varying polymeric material properties. This review focuses on applications of pH-sensitive chemistries that enable polymeric vectors to serially address multiple biological barriers to NA delivery. In particular, we focus on recent innovations with in vivo evaluation that dynamically enable colloidal stability, cellular uptake, endosomal escape, and nucleic acid release. We conclude with a summary of successes to date and projected areas for impactful future research.

Bioreducible Polymeric Nanoparticles Containing Multiplexed Cancer Stem Cell Regulating miRNAs Inhibit Glioblastoma Growth and Prolong Survival

Despite our growing molecular-level understanding of glioblastoma (GBM), treatment modalities remain limited. Recent developments in the mechanisms of cell fate regulation and nanomedicine provide new avenues by which to treat and manage brain tumors via the delivery of molecular therapeutics. Here, we have developed bioreducible poly(β-amino ester) nanoparticles that demonstrate high intracellular delivery efficacy, low cytotoxicity, escape from endosomes, and promotion of cytosol-targeted environmentally triggered cargo release for miRNA delivery to tumor-propagating human cancer stem cells. In this report, we combined this nanobiotechnology with newly discovered cancer stem cell inhibiting miRNAs to develop self-assembled miRNA-containing polymeric nanoparticles (nano-miRs) to treat gliomas. We show that these nano-miRs effectively intracellularly deliver single and combination miRNA mimics that inhibit the stem cell phenotype of human GBM cells in vitro. Following direct intratumoral infusion, these nano-miRs were found to distribute through the tumors, inhibit the growth of established orthotopic human GBM xenografts, and cooperatively enhance the response to standard-of-care γ radiation. Co-delivery of two miRNAs, miR-148a and miR-296-5p, within the bioreducible nano-miR particles enabled long-term survival from GBM in mice.

Lysine-derived, pH-sensitive and biodegradable poly(beta-aminoester urethane) networks and their local drug delivery behaviour

In this study, a series of covalently crosslinked, l-lysine based poly(beta-aminoester urethane) (LPBAEU) networks with good biodegradability and pH sensitivity was reported. The effect of hydrophilic/hydrophobic characteristics and diacrylate/amine molar ratio on the structure, swelling and degradation behaviour of the networks was investigated. The water transport mechanism and dynamic swelling behavior of the LPBAEU networks were strongly affected by medium pH, and swelling amounts up to 252.2% and 148.7% were observed at pH 5.6 and pH 7.4, respectively. It was found that water diffusion within the networks followed a non-Fickian mechanism. The LPBAEU network with the highest diacrylate/amine molar ratio exhibited the highest tensile strength and Young's modulus. In vitro mass losses of networks showed that the degradation rate of LPBAEU networks can be adjusted from 4 to 14 days. LPBAEU networks also supported loading of doxycycline hyclate (DH) and in vitro release studies demonstrated that release of DH from the networks was substantially hindered in the neutral pH environment, with 20.9-56.2% DH release, whereas DH release was accelerated under mild acidic conditions, with a release percentage of 36.6-99.6%. The release data were fitted to different mathematical models and the obtained results confirmed that these networks released DH in a non-Fickian mechanism. The results of this research support the idea that pH-responsive LPBAEU networks may find potential applications in local drug delivery.

Engineering PTEN-L for Cell-Mediated Delivery

The tumor suppressor PTEN is frequently inactivated in glioblastoma. PTEN-L is a long form of PTEN produced by translation from an alternate upstream start codon. Unlike PTEN, PTEN-L has a signal sequence and a tract of six arginine residues that allow PTEN-L to be secreted from cells and be taken up by neighboring cells. This suggests that PTEN-L could be used as a therapeutic to restore PTEN activity. However, effective delivery of therapeutic proteins to treat CNS cancers such as glioblastoma is challenging. One method under evaluation is cell-mediated therapy, where cells with tumor-homing abilities such as neural stem cells are genetically modified to express a therapeutic protein. Here, we have developed a version of PTEN-L that is engineered for enhanced cell-mediated delivery. This was accomplished by replacement of the native leader sequence of PTEN-L with a leader sequence from human light-chain immunoglobulin G (IgG). This version of PTEN-L showed increased secretion and an increased ability to transfer to neighboring cells. Neural stem cells derived from human fibroblasts could be modified to express this version of PTEN-L and were able to deliver catalytically active light-chain leader PTEN-L (lclPTEN-L) to neighboring glioblastoma cells.

Nanomaterials for convection-enhanced delivery of agents to treat brain tumors

Nanomaterials represent a promising and versatile platform for the delivery of therapeutics to the brain. Treatment of brain tumors has been a long-standing challenge in the field of neuro-oncology. The current standard of care - a multimodal approach of surgery, radiation and chemotherapy - yields only a modest therapeutic benefit for patients with malignant gliomas. A major obstacle for treatment is the failure to achieve sufficient delivery of therapeutics at the tumor site. Recent advances in local drug delivery techniques, along with the development of highly effective brain-penetrating nanocarriers, have significantly improved treatment and imaging of brain tumors in preclinical studies. The major advantage of this combined strategy is the ability to optimize local therapy, by maintaining an effective and sustained concentration of therapeutics in the brain with minimal systemic toxicity. This review highlights some of the latest developments, significant advancements and current challenges in local delivery of nanomaterials for the treatment of brain tumors.

Strategies to enhance the distribution of nanotherapeutics in the brain

Convection enhanced delivery (CED) provides a powerful means to bypass the blood-brain barrier and drive widespread distribution of therapeutics in brain parenchyma away from the point of local administration. However, recent studies have detailed that the overall distribution of therapeutic nanoparticles (NP) following CED remains poor due to tissue inhomogeneity and anatomical barriers present in the brain, which has limited its translational applicability. Using probe NP, we first demonstrate that a significantly improved brain distribution is achieved by infusing small, non-adhesive NP via CED in a hyperosmolar infusate solution. This multimodal delivery strategy minimizes the hindrance of NP diffusion imposed by the brain extracellular matrix and reduces NP confinement within the perivascular spaces. We further recapitulate the distributions achieved by CED of this probe NP using a most widely explored biodegradable polymer-based drug delivery NP. These findings provide a strategy to overcome several key limitations of CED that have been previously observed in clinical trials.

Biodegradable brain-penetrating DNA nanocomplexes and their use to treat malignant brain tumors

The discovery of powerful genetic targets has spurred clinical development of gene therapy approaches to treat patients with malignant brain tumors. However, lack of success in the clinic has been attributed to the inability of conventional gene vectors to achieve gene transfer throughout highly disseminated primary brain tumors. Here, we demonstrate ex vivo that small nanocomplexes composed of DNA condensed by a blend of biodegradable polymer, poly(β-amino ester) (PBAE), with PBAE conjugated with 5kDa polyethylene glycol (PEG) molecules (PBAE-PEG) rapidly penetrate healthy brain parenchyma and orthotopic brain tumor tissues in rats. Rapid diffusion of these DNA-loaded nanocomplexes observed in fresh tissues ex vivo demonstrated that they avoided adhesive trapping in the brain owing to their dense PEG coating, which was critical to achieving widespread transgene expression throughout orthotopic rat brain tumors in vivo following administration by convection enhanced delivery. Transgene expression with the PBAE/PBAE-PEG blended nanocomplexes (DNA-loaded brain-penetrating nanocomplexes, or DNA-BPN) was uniform throughout the tumor core compared to nanocomplexes composed of DNA with PBAE only (DNA-loaded conventional nanocomplexes, or DNA-CN), and transgene expression reached beyond the tumor edge, where infiltrative cancer cells are found, only for the DNA-BPN formulation. Finally, DNA-BPN loaded with anti-cancer plasmid DNA provided significantly enhanced survival compared to the same plasmid DNA loaded in DNA-CN in two aggressive orthotopic brain tumor models in rats. These findings underscore the importance of achieving widespread delivery of therapeutic nucleic acids within brain tumors and provide a promising new delivery platform for localized gene therapy in the brain.

NIH workshop report on the trans-agency blood-brain interface workshop 2016: exploring key challenges and opportunities associated with the blood, brain and their interface

A trans-agency workshop on the blood–brain interface (BBI), sponsored by the National Heart, Lung and Blood Institute, the National Cancer Institute and the Combat Casualty Care Research Program at the Department of Defense, was conducted in Bethesda MD on June 7–8, 2016. The workshop was structured into four sessions: (1) blood sciences; (2) exosome therapeutics; (3) next generation in vitro blood–brain barrier (BBB) models; and (4) BBB delivery and targeting. The first day of the workshop focused on the physiology of the blood and neuro-vascular unit, blood or biofluid-based molecular markers, extracellular vesicles associated with brain injury, and how these entities can be employed to better evaluate injury states and/or deliver therapeutics. The second day of the workshop focused on technical advances in in vitro models, BBB manipulations and nanoparticle-based drug carrier designs, with the goal of improving drug delivery to the central nervous system. The presentations and discussions underscored the role of the BBI in brain injury, as well as the role of the BBB as both a limiting factor and a potential conduit for drug delivery to the brain. At the conclusion of the meeting, the participants discussed challenges and opportunities confronting BBI translational researchers. In particular, the participants recommended using BBI translational research to stimulate advances in diagnostics, as well as targeted delivery approaches for detection and therapy of both brain injury and disease.

Gemini-Type Tetraphenylethylene Amphiphiles Containing [12]aneN3 and Long Hydrocarbon Chains as Nonviral Gene Vectors and Gene Delivery Monitors

Four gemini amphiphiles decorated with triazole-[12]aneN₃ as the hydrophilic moiety and various long hydrocarbons as hydrophobic moieties, 1-4, were designed to form micelles possessing the aggregation-induced emission (AIE) property for gene delivery and tracing. All four amphiphiles give ultralow critical micelle concentrations, are pH-/photostable and biocompatible, and completely retard the migration of plasmid DNAs at low concentrations. The DNA-binding abilities of the micelles were fully assessed. The coaggregated nanoparticles of 1-4 with DNAs could convert back into AIE micelles. In vitro transfections indicated that lipids 1 and 2 and their originated liposomes bearing decent delivering abilities have great potentials as nonviral vectors. Finally, on the basis of the transfection and the transitions between condensates and micelles, lipid 2 was singled out as the first example for real-time tracing of the intracellular deliveries of nonlabeled DNA, which provides spatiotemporal messages about the processes of condensate uptake and DNA release.

Convection enhanced delivery of cisplatin-loaded brain penetrating nanoparticles cures malignant glioma in rats

Glioblastoma multiforme (GBM) is highly invasive and uniformly fatal, with median survival<20months after diagnosis even with the most aggressive treatment that includes surgery, radiation, and systemic chemotherapy. Cisplatin is a particularly potent chemotherapeutic agent, but its use to treat GBM is limited by severe systemic toxicity and inefficient penetration of brain tumor tissue even when it is placed directly in the brain within standard delivery systems. We describe the development of cisplatin-loaded nanoparticles that are small enough (70nm in diameter) to move within the porous extracellular matrix between cells and that possess a dense polyethylene glycol (PEG) corona that prevents them from being trapped by adhesion as they move through the brain tumor parenchyma. As a result, these "brain penetrating nanoparticles" penetrate much deeper into brain tumor tissue compared to nanoparticles without a dense PEG corona following local administration by either manual injection or convection enhanced delivery. The nanoparticles also provide controlled release of cisplatin in effective concentrations to kill the tumor cells that they reach without causing toxicity-related deaths that were observed when cisplatin was infused into the brain without a delivery system. Median survival time of rats bearing orthotopic glioma was significantly enhanced when cisplatin was delivered in brain penetrating nanoparticles (median survival not reached; 80% long-term survivors) compared to cisplatin in conventional un-PEGylated particles (median survival=40days), cisplatin alone (median survival=12days) or saline-treated controls (median survival=28days).

Nanoparticles in the clinic

Nanoparticle/microparticle-based drug delivery systems for systemic (i.e., intravenous) applications have significant advantages over their nonformulated and free drug counterparts. For example, nanoparticle systems are capable of delivering therapeutics and treating areas of the body that other delivery systems cannot reach. As such, nanoparticle drug delivery and imaging systems are one of the most investigated systems in preclinical and clinical settings. Here, we will highlight the diversity of nanoparticle types, the key advantages these systems have over their free drug counterparts, and discuss their overall potential in influencing clinical care. In particular, we will focus on current clinical trials for nanoparticle formulations that have yet to be clinically approved. Additional emphasis will be on clinically approved nanoparticle systems, both for their currently approved indications and their use in active clinical trials. Finally, we will discuss many of the often overlooked biological, technological, and study design challenges that impact the clinical success of nanoparticle delivery systems.

PEGylation as a strategy for improving nanoparticle-based drug and gene delivery

Coating the surface of nanoparticles with polyethylene glycol (PEG), or "PEGylation", is a commonly used approach for improving the efficiency of drug and gene delivery to target cells and tissues. Building from the success of PEGylating proteins to improve systemic circulation time and decrease immunogenicity, the impact of PEG coatings on the fate of systemically administered nanoparticle formulations has, and continues to be, widely studied. PEG coatings on nanoparticles shield the surface from aggregation, opsonization, and phagocytosis, prolonging systemic circulation time. Here, we briefly describe the history of the development of PEGylated nanoparticle formulations for systemic administration, including how factors such as PEG molecular weight, PEG surface density, nanoparticle core properties, and repeated administration impact circulation time. A less frequently discussed topic, we then describe how PEG coatings on nanoparticles have also been utilized for overcoming various biological barriers to efficient drug and gene delivery associated with other modes of administration, ranging from gastrointestinal to ocular. Finally, we describe both methods for PEGylating nanoparticles and methods for characterizing PEG surface density, a key factor in the effectiveness of the PEG surface coating for improving drug and gene delivery.