Enas Mahmoud

Biocompatible Polymeric Nanoparticles Degrade and Release Cargo in Response to Biologically Relevant Levels of Hydrogen Peroxide

Oxidative stress is caused predominantly by accumulation of hydrogen peroxide and distinguishes inflamed tissue from healthy tissue. Hydrogen peroxide could potentially be useful as a stimulus for targeted drug delivery to diseased tissue. However, current polymeric systems are not sensitive to biologically relevant concentrations of H(2)O(2) (50-100 μM). Here we report a new biocompatible polymeric capsule capable of undergoing backbone degradation and thus release upon exposure to such concentrations of hydrogen peroxide. Two polymeric structures were developed differing with respect to the linkage between the boronic ester group and the polymeric backbone: either direct (1) or via an ether linkage (2). Both polymers are stable in aqueous solution at normal pH, and exposure to peroxide induces the removal of the boronic ester protecting groups at physiological pH and temperature, revealing phenols along the backbone, which undergo quinone methide rearrangement to lead to polymer degradation. Considerably faster backbone degradation was observed for polymer 2 over polymer 1 by NMR and GPC. Nanoparticles were formulated from these novel materials to analyze their oxidation triggered release properties. While nanoparticles formulated from polymer 1 only released 50% of the reporter dye after exposure to 1 mM H(2)O(2) for 26 h, nanoparticles formulated from polymer 2 did so within 10 h and were able to release their cargo selectively in biologically relevant concentrations of H(2)O(2). Nanoparticles formulated from polymer 2 showed a 2-fold enhancement of release upon incubation with activated neutrophils, while controls showed a nonspecific response to ROS producing cells. These polymers represent a novel, biologically relevant, and biocompatible approach to biodegradable H(2)O(2)-triggered release systems that can degrade into small molecules, release their cargo, and should be easily cleared by the body.

Physical and Chemical Strategies for Therapeutic Delivery by Using Polymeric Nanoparticles

A significant challenge that most therapeutic agents face is their inability to be delivered effectively. Nanotechnology offers a solution to allow for safe, high-dose, specific delivery of pharmaceuticals to the target tissue. Nanoparticles composed of biodegradable polymers can be designed and engineered with various layers of complexity to achieve drug targeting that was unimaginable years ago by offering multiple mechanisms to encapsulate and strategically deliver drugs, proteins, nucleic acids, or vaccines while improving their therapeutic index. Targeting of nanoparticles to diseased tissue and cells assumes two strategies: physical and chemical targeting. Physical targeting is a strategy enabled by nanoparticle fabrication techniques. It includes using size, shape, charge, and stiffness among other parameters to influence tissue accumulation, adhesion, and cell uptake. New methods to measure size, shape, and polydispersity will enable this field to grow and more thorough comparisons to be made. Physical targeting can be more economically viable when certain fabrication techniques are used. Chemical targeting can employ molecular recognition units to decorate the surface of particles or molecular units responsive to diseased environments or remote stimuli. In this review, we describe sophisticated nanoparticles designed for tissue-specific chemical targeting that use conjugation chemistry to attach targeting moieties. Furthermore, we describe chemical targeting using stimuli responsive nanoparticles that can respond to changes in pH, heat, and light.

Multiresponse strategies to modulate burst degradation and release from nanoparticles.

Logic gate nanoparticles, where two chemical transformations take place one after the other, were successfully formulated from a newly synthesized random co-polymer. This polymer, poly([2,2′-(propane-2,2-diylbis(oxy))bis(ethane-2,1-diyl) diacrylate ]-co-[hexane-1,6-diyl diacrylate]-4,4′ trimethylene dipiperidine), (poly-β-aminoester ketal-2) contains two pH responsive moieties within its backbone. As nanoparticles they function akin to an AND logic gate. The β-aminoester backbone moiety provides a pH triggered solubility switch, only when this switch is “ON” does the ketal moiety also turn “ON” to undergo rapid acid catalyzed hydrolysis. These AND logic gate polymeric nanoparticles were prepared using an oil in water emulsion method. Their degradation in the pH range of 7.4−5 was monitored by dynamic light scattering and showed excellent stability at pH 7.4 and rapid degradation at pH 5. Our results indicate that the prepared logic gate nanoparticles may prove valuable in delivering therapeutics and diagnostics to cells and diseased tissue.

Inflammation responsive logic gate nanoparticles for the delivery of proteins

Oxidative stress and reduced pH are important stimuli targets for intracellular delivery and for delivery to diseased tissue. However, there is a dearth of materials able to deliver bioactive agents selectively under these conditions. We employed our recently developed dual response strategy to build a polymeric nanoparticle that degrades upon exposure to two stimuli in tandem. Our polythioether ketal based nanoparticles undergo two chemical transformations; the first is the oxidation of the thioether groups along the polymer backbone of the nanoparticles upon exposure to reactive oxygen species (ROS). This transformation switches the polymeric backbone from hydrophobic to hydrophilic and thus allows, in mildly acidic environments, the rapid acid-catalyzed degradation of the ketal groups also along the polymer backbone. Dynamic light scattering and payload release studies showed full particle degradation only in conditions that combined both oxidative stress and acidity, and these conditions led to higher release of encapsulated protein within 24 h. Nanoparticles in neutral pH and under oxidative conditions showed small molecule release and swelling of otherwise intact nanparticles. Notably, cellular studies show absence of toxicity and efficient uptake of nanoparticles by macrophages followed by cytoplasmic release of ovalbumin. Future work will apply this system to inflammatory diseases.

Preparation and Evaluation of Self-nanoemulsifying Tablets of Carvedilol

The purpose of this study was to combine the advantages of self-nanoemulsifying drug delivery systems and tablets as a conventional dosage form emphasizing the excipients’ effect on the development of a new dosage form. Systems composed of HCO-40, Transcutol® HP, and medium-chain triglyceride were prepared. Essential properties of the prepared systems regarding carvedilol solubility, a model drug, and self-emulsification time were determined. In order to optimize self-nanoemulsifying drug delivery systems (SNEDDS), formulation dispersion–drug precipitation test was performed in the absence and presence of cellulosic polymers. Furthermore, SNEDDS was loaded onto liquisolid powders. P-glycoprotein (P-gp) activity of the selected SNEDDS was tested using HCT-116 cells. Carvedilol showed acceptable solubility in the selected excipients. It also demonstrated improvement in the stability upon dilution with aqueous media in the presence of cellulosic polymers. Use of granulated silicon dioxide improved the physical properties of liquisolid powders containing SNEDDS. It improved the compressibility of the selected powders and the tested SNEDDS showed marked P-gp inhibition activity. Prepared self-nanoemulsifying tablet produced acceptable properties of immediate-release dosage forms and expected to increase the bioavailability of carvedilol.

Light-responsive nanoparticle depot to control release of a small molecule angiogenesis inhibitor in the posterior segment of the eye

Therapies for macular degeneration and diabetic retinopathy require intravitreal injections every 4-8 weeks. Injections are uncomfortable, time-consuming, and carry risks of infection and retinal damage. However, drug delivery via noninvasive methods to the posterior segment of the eye has been a major challenge due to the eyes unique anatomy and physiology. Here we present a novel nanoparticle depot platform for on-demand drug delivery using a far ultraviolet (UV) light-degradable polymer, which allows noninvasively triggered drug release using brief, low-power light exposure. Nanoparticles stably retain encapsulated molecules in the vitreous, and can release cargo in response to UV exposure up to 30 weeks post-injection. Light-triggered release of nintedanib (BIBF 1120), a small molecule angiogenesis inhibitor, 10 weeks post-injection suppresses choroidal neovascularization (CNV) in rats. Light-sensitive nanoparticles are biocompatible and cause no adverse effects on the eye as assessed by electroretinograms (ERG), corneal and retinal tomography, and histology.

Metal Chelating Crosslinkers Form Nanogels with High Chelation Stability.

We present a series of hydrogel nanoparticles (nanogels) incorporating either acyclic or cyclic metal chelates as crosslinkers. These crosslinkers are used to formulate polyacrylamide-based nanogels (diameter 50 to 85 nm) yielding contrast agents with enhanced relaxivities (up to 6-fold greater than Dotarem®), because this nanogel structure slows the chelators tumbling frequency and allows fast water exchange. Importantly, these nanogels also stabilize Gd3+ within the chelator thermodynamically and kinetically against metal displacement through transmetallation, which should reduce toxicity associated with release of free Gd3+. This chelation stability suggests that the chelate crosslinker strategy may prove useful for other applications of metal-chelating nanoparticles in medicine, including other imaging modalities and radiotherapy.

Triggered Rapid Degradation of Nanoparticles for Gene Delivery

Effective gene delivery tools offer the possibility of addressing multiple diseases; current strategies rely on viruses or polyplexes. Encapsulation of DNA within nanoparticles is an attractive alternative method for gene delivery. We investigated the use of our recently developed Logic Gate Nanoparticle for gene delivery. The nanoparticles, composed of a dual pH response random copolymer (poly-β-aminoester ketal-2), can undergo a two-step “in series” response to endosomal pH. The first sep is a hydrophobic-hydrophilic switch, which is followed immediately by rapid degradation. Rapid fragmentation is known to increase cytoplasmic delivery from nanoparticles. Therefore, we hypothesized that our Logic Gate Nanoparticles would enable increased gene delivery and expression relative to nanoparticles that degrade more slowly such as PLGA-based nanoparticles. Passive nanoparticle entry into cells was demonstrated by delivering Cy5-labeled pDNA encoding EGFP into HCT116, a colon carcinoma cell line. Flow cytometry analysis showed that cells are positive for Cy5-DNA-nanoparticles and produced EGFP expression superior to PLGA nanoparticles. Inhibition of V-ATPases using bafilomycin A1 demonstrates that expression of EGFP is dependent on low endosomal pH. The advanced Logic Gate Nanoparticles offer new therapeutic possibilities in gene delivery and other applications where rapid release is important.