Nicholas J. Boylan

Nanoparticle diffusion in, and microrheology of, the bovine vitreous ex vivo.

Intravitreal injection of biodegradable nanoparticles (NP) holds promise for gene therapy and drug delivery to the back of the eye. In some cases, including gene therapy, NP need to diffuse rapidly from the site of injection in order to reach targeted cell types in the back of the eye, whereas in other cases it may be preferred for the particles to remain at the injection site and slowly release drugs that may then diffuse to the site of action. We studied the movements of polystyrene (PS) NP of various sizes and surface chemistries in fresh bovine vitreous. PS NP as large as 510nm rapidly penetrated the vitreous gel when coated with polyethylene glycol (PEG), whereas the movements of NP 1190nm in diameter or larger were highly restricted regardless of surface chemistry owing to steric obstruction. PS NP coated with primary amine groups (NH2) possessed positively charged surfaces at the pH of bovine vitreous (pH=7.2), and were immobilized within the vitreous gel. In comparison, PS NP coated with COOH (possessing negatively charged surfaces) in the size range of 100-200nm and at particle concentrations below 0.0025% (w/v) readily diffused through the vitreous meshwork; at higher concentrations (~0.1% w/v), these nanoparticles aggregated within vitreous. Based on the mobility of different sized PEGylated PS NP (PS-PEG), we estimated the average mesh size of fresh bovine vitreous to be ~550±50nm. The bovine vitreous behaved as an impermeable elastic barrier to objects sized 1190nm and larger, but as a highly permeable viscoelastic liquid to non-adhesive objects smaller than 510nm in diameter. Guided by these studies, we next sought to examine the transport of drug- and DNA-loaded nanoparticles in bovine vitreous. Biodegradable NP with a diameter of 227nm, composed of a poly(lactic-co-glycolic acid) (PLGA)-based core coated with poly(vinyl alcohol) rapidly penetrated vitreous. Rod-shaped, highly-compacted CK30PEG10k/DNA with PEG coating (neutral surface charge; hydrodynamic diameter ~60nm) also diffused rapidly within vitreous. These findings will help guide the development of nanoparticle-based therapeutics for the treatment of vision-threatening ocular diseases.

Rapid transport of muco-inert nanoparticles in cystic fibrosis sputum treated with N-acetyl cysteine

AIMS Sputum poses a critical diffusional barrier that strongly limits the efficacy of drug and gene carriers in the airways of individuals with cystic fibrosis (CF). Previous attempts to enhance particle penetration of CF sputum have focused on either reducing its barrier properties via mucolytics, or decreasing particle adhesion to sputum constituents by coating the particle surface with non-mucoadhesive polymers, including polyethylene glycol (PEG). Neither approach has enabled particles to penetrate expectorated sputum at rates previously observed for non-mucoadhesive nanoparticles in human cervicovaginal mucus. Here, we sought to investigate whether a common mucolytic, N-acetyl cysteine (NAC), in combination with dense PEG coatings on particles, can synergistically enhance particle penetration across fresh undiluted CF sputum. MATERIALS & METHODS We used high-resolution multiple particle tracking to measure the diffusion of uncoated and PEG-coated nanoparticles in native and NAC-treated CF sputum. RESULTS We discovered that 200 nm particles, if densely coated with PEG, were able to penetrate CF sputum pretreated with NAC with average speeds approaching their theoretical speeds in water. Based on the rapid penetration of PEG-coated particles in NAC-treated sputum, we determined that the average spacing between sputum mesh elements was increased from 145 ± 50 nm to 230 ± 50 nm upon NAC treatment. Mathematical models based on particle transport rates suggest as much as 75 and 30% of 200 and 500 nm PEG-coated particles, respectively, may penetrate a physiologically thick NAC-treated CF sputum layer within 20 min. Uncoated particles were trapped in CF sputum pretreated with NAC nearly to the same extent as in native sputum, suggesting that NAC treatment alone offered little improvement to particle penetration. CONCLUSION NAC facilitated rapid diffusion of PEG-coated, muco-inert nanoparticles in CF sputum. Our results provide a promising strategy to improve drug and gene carrier penetration in CF sputum, offering hope for improved therapies for CF.

Lung gene therapy with highly compacted DNA nanoparticles that overcome the mucus barrier

Inhaled gene carriers must penetrate the highly viscoelastic and adhesive mucus barrier in the airway in order to overcome rapid mucociliary clearance and reach the underlying epithelium; however, even the most widely used viral gene carriers are unable to efficiently do so. We developed two polymeric gene carriers that compact plasmid DNA into small and highly stable nanoparticles with dense polyethylene glycol (PEG) surface coatings. These highly compacted, densely PEG-coated DNA nanoparticles rapidly penetrate human cystic fibrosis (CF) mucus ex vivo and mouse airway mucus ex situ. Intranasal administration of the mucus penetrating DNA nanoparticles greatly enhanced particle distribution, retention and gene transfer in the mouse lung airways compared to conventional gene carriers. Successful delivery of a full-length plasmid encoding the cystic fibrosis transmembrane conductance regulator protein was achieved in the mouse lungs and airway cells, including a primary culture of mucus-covered human airway epithelium grown at air-liquid interface, without causing acute inflammation or toxicity. Highly compacted mucus penetrating DNA nanoparticles hold promise for lung gene therapy.

Highly compacted DNA nanoparticles with low MW PEG coatings: in vitro, ex vivo and in vivo evaluation

Highly compacted DNA nanoparticles, composed of single molecules of plasmid DNA compacted with block copolymers of poly-l-lysine and 10kDa polyethylene glycol (CK(30)PEG(10k)), mediate effective gene delivery to the brain, eyes and lungs in vivo. Nevertheless, we found that CK(30)PEG(10k) DNA nanoparticles are immobilized by mucoadhesive interactions in sputum that lines the lung airways of patients with cystic fibrosis (CF), which would presumably preclude the efficient delivery of cargo DNA to the underlying epithelium. We previously found that nanoparticles can rapidly penetrate human mucus secretions if they are densely coated with low MW PEG (2-5kDa), whereas nanoparticles with 10kDa PEG coatings were immobilized. We thus sought to reduce mucoadhesion of DNA nanoparticles by producing CK(30)PEG DNA nanoparticles with low MW PEG coatings. We examined the morphology, colloidal stability, nuclease resistance, diffusion in human sputum and in vivo gene transfer of CK(30)PEG DNA nanoparticles prepared using various PEG MWs. CK(30)PEG(10k) and CK(30)PEG(5k) formulations did not aggregate in saline, provided partial protection against DNase I digestion and exhibited the highest gene transfer to lung airways following inhalation in BALB/c mice. However, all DNA nanoparticle formulations were immobilized in freshly expectorated human CF sputum, likely due to inadequate PEG surface coverage.

Scalable method to produce biodegradable nanoparticles that rapidly penetrate human mucus.

Mucus typically traps and rapidly removes foreign particles from the airways, gastrointestinal tract, nasopharynx, female reproductive tract and the surface of the eye. Nanoparticles capable of rapid penetration through mucus can potentially avoid rapid clearance, and open significant opportunities for controlled drug delivery at mucosal surfaces. Here, we report an industrially scalable emulsification method to produce biodegradable mucus-penetrating particles (MPP). The emulsification of diblock copolymers of poly(lactic-co-glycolic acid) and polyethylene glycol (PLGA-PEG) using low molecular weight (MW) emulsifiers forms dense brush PEG coatings on nanoparticles that allow rapid nanoparticle penetration through fresh undiluted human mucus. In comparison, conventional high MW emulsifiers, such as polyvinyl alcohol (PVA), interrupts the PEG coating on nanoparticles, resulting in their immobilization in mucus owing to adhesive interactions with mucus mesh elements. PLGA-PEG nanoparticles with a wide range of PEG MW (1, 2, 5, and 10 kDa), prepared by the emulsification method using low MW emulsifiers, all rapidly penetrated mucus. A range of drugs, from hydrophobic small molecules to hydrophilic large biologics, can be efficiently loaded into biodegradable MPP using the method described. This readily scalable method should facilitate the production of MPP products for mucosal drug delivery, as well as potentially longer-circulating particles following intravenous administration.

N-acetylcysteine Enhances Cystic Fibrosis Sputum Penetration and Airway Gene Transfer by Highly Compacted DNA Nanoparticles

For effective airway gene therapy of cystic fibrosis (CF), inhaled gene carriers must first penetrate the hyperviscoelastic sputum covering the epithelium. Whether clinically studied gene carriers can penetrate CF sputum remains unknown. Here, we measured the diffusion of a clinically tested nonviral gene carrier, composed of poly-l-lysine conjugated with a 10 kDa polyethylene glycol segment (CK30PEG10k). We found that CK30PEG10k/DNA nanoparticles were trapped in CF sputum. To improve gene carrier diffusion across sputum, we tested adjuvant regimens consisting of N-acetylcysteine (NAC), recombinant human DNase (rhDNase) or NAC together with rhDNase. While rhDNase alone did not enhance gene carrier diffusion, NAC and NAC + rhDNase increased average effective diffusivities by 6-fold and 13-fold, respectively, leading to markedly greater fractions of gene carriers that may penetrate sputum layers. We further tested the adjuvant effects of NAC in the airways of mice with Pseudomonas aeruginosa lipopolysaccharide (LPS)-induced mucus hypersecretion. Intranasal dosing of NAC prior to CK30PEG10k/DNA nanoparticles enhanced gene expression by up to ~12-fold compared to saline control, reaching levels observed in the lungs of mice without LPS challenge. Our findings suggest that a promising synthetic nanoparticle gene carrier may transfer genes substantially more effectively to lungs of CF patients if administered following adjuvant mucolytic therapy with NAC or NAC + rhDNase.For effective airway gene therapy of cystic fibrosis (CF), inhaled gene carriers must first penetrate the hyperviscoelastic sputum covering the epithelium. Whether clinically studied gene carriers can penetrate CF sputum remains unknown. Here, we measured the diffusion of a clinically tested nonviral gene carrier, composed of poly-l-lysine conjugated with a 10 kDa polyethylene glycol segment (CK(30)PEG(10k)). We found that CK(30)PEG(10k)/DNA nanoparticles were trapped in CF sputum. To improve gene carrier diffusion across sputum, we tested adjuvant regimens consisting of N-acetylcysteine (NAC), recombinant human DNase (rhDNase) or NAC together with rhDNase. While rhDNase alone did not enhance gene carrier diffusion, NAC and NAC + rhDNase increased average effective diffusivities by 6-fold and 13-fold, respectively, leading to markedly greater fractions of gene carriers that may penetrate sputum layers. We further tested the adjuvant effects of NAC in the airways of mice with Pseudomonas aeruginosa lipopolysaccharide (LPS)-induced mucus hypersecretion. Intranasal dosing of NAC prior to CK(30)PEG(10k)/DNA nanoparticles enhanced gene expression by up to ~12-fold compared to saline control, reaching levels observed in the lungs of mice without LPS challenge. Our findings suggest that a promising synthetic nanoparticle gene carrier may transfer genes substantially more effectively to lungs of CF patients if administered following adjuvant mucolytic therapy with NAC or NAC + rhDNase.

Use of Single-Site-Functionalized PEG Dendrons To Prepare Gene Vectors that Penetrate Human Mucus Barriers†

Protective mucus layers serve as the body’s first line of defense at exposed surfaces of the eyes and respiratory, gastrointestinal, and cervicovaginal tracts. These highly viscoelastic and adhesive mucus gels trap most foreign pathogens and environmental ultrafine particles, which are then removed by mucus clearance mechanisms[1] (on the order of seconds to a few hours, depending on anatomical site). However, mucus also immobilizes and rapidly clears therapeutic nanoparticles, including synthetic drug carriers,[2] and clinically tested viral[3] and nonviral gene vectors[4] and, therefore, represents a critical obstacle to localized drug and gene delivery at mucosal surfaces for the treatment of a variety of diseases.[1b]

Enhancement of airway gene transfer by DNA nanoparticles using a pH-responsive block copolymer of polyethylene glycol and poly-l-lysine

Highly compacted DNA nanoparticles, composed of single molecules of plasmid DNA compacted with block copolymers of polyethylene glycol and poly-L-lysine (PEG-CK(30)), have shown considerable promise in human gene therapy clinical trials in the nares, but may be less capable of transfecting cells that lack surface nucleolin. To address this potential shortcoming, we formulated pH-responsive DNA nanoparticles that mediate gene transfer via a nucleolin-independent pathway. Poly-L-histidine was inserted between PEG and poly-L-lysine to form a triblock copolymer system, PEG-CH(12)K(18). Inclusion of poly-L-histidine increased the buffering capacity of PEG-CH(12)K(18) to levels comparable with branched polyethyleneimine. PEG-CH(12)K(18) compacted DNA into rod-shaped DNA nanoparticles with similar morphology and colloidal stability as PEG-CK(30) DNA nanoparticles. PEG-CH(12)K(18) DNA nanoparticles entered human bronchial epithelial cells (BEAS-2B) that lack surface nucleolin by a clathrin-dependent endocytic mechanism followed by endo-lysosomal processing. Despite trafficking through the degradative endo-lysosomal pathway, PEG-CH(12)K(18) DNA nanoparticles improved the in vitro gene transfer by ~20-fold over PEG-CK(30) DNA nanoparticles, and in vivo gene transfer to lung airways in BALB/c mice by ~3-fold, while maintaining a favorable toxicity profile. These results represent an important step toward the rational development of an efficient gene delivery platform for the lungs based on highly compacted DNA nanoparticles.

Non-degradative intracellular trafficking of highly compacted polymeric DNA nanoparticles

Highly compacted DNA nanoparticles (DNPs) composed of polyethylene glycol linked to a 30-mer of poly-l-lysine via a single cysteine residue (CK(30)PEG) have previously been shown to provide efficient gene delivery to the brain, eyes and lungs. In this study, we used a combination of flow cytometry, high-resolution live-cell confocal microscopy, and multiple particle tracking (MPT) to investigate the intracellular trafficking of highly compacted CK(30)PEG DNPs made using two different molecular weights of PEG, CK(30)PEG(10k) and CK(30)PEG(5k). We found that PEG MW did not have a major effect on particle morphology nor nanoparticle intracellular transport. CK(30)PEG(10k) and CK(30)PEG(5k) DNPs both entered human bronchial epithelial (BEAS-2B) cells via a caveolae-mediated pathway, bypassing degradative endolysosomal trafficking. Both nanoparticle formulations were found to rapidly accumulate in the perinuclear region of cells within 2h, 37±19% and 47±8% for CK(30)PEG(10k) and CK(30)PEG(5k), respectively. CK(30)PEG(10k) and CK(30)PEG(5k) DNPs moved within live cells at average velocities of 0.09±0.04μm/s and 0.11±0.04μm/s, respectively, in good agreement with reported values for caveolae. These findings show that highly compacted DNPs employ highly regulated trafficking mechanisms similar to biological pathogens to target specific intracellular compartments.

Corticosteroid-loaded biodegradable nanoparticles for prevention of corneal allograft rejection in rats

Immunologic graft rejection is one of the main causes of short and long-term graft failure in corneal transplantation. Steroids are the most commonly used immunosuppressive agents for postoperative management and prevention of corneal graft rejection. However, steroids delivered in eye drops are rapidly cleared from the surface of the eye, so the required frequency of dosing for corneal graft rejection management can be as high as once every 2h. Additionally, these eye drops are often prescribed for daily use for 1 year or longer, which can result in poor patient compliance and steroid-related side effects. Here, we report a biodegradable nanoparticle system composed of Generally Regarded as Safe (GRAS) materials that can provide sustained release of corticosteroids to prevent corneal graft rejection following subconjunctival injection provided initially during transplant surgery. Poly(lactic-co-glycolic acid) (PLGA) nanoparticles containing dexamethasone sodium phosphate (DSP) exhibited a size of 200 nm, 8 wt.% drug loading, and sustained drug release over 15 days in vitro under sink conditions. DSP-loaded nanoparticles provided sustained ocular drug levels for at least 7 days after subconjunctival administration in rats, and prevented corneal allograft rejection over the entire 9-week study when administered weekly. In contrast, control treatment groups that received weekly injections of either placebo nanoparticles, saline, or DSP in solution demonstrated corneal graft rejection accompanied by severe corneal edema, neovascularization and opacity that occurred in ≤ 4 weeks. Local controlled release of corticosteroids may reduce the rate of corneal graft rejection, perhaps especially in the days immediately following surgery when risk of rejection is highest and when typical steroid eye drop administration requirements are particularly onerous.