Featured Article: Chemotherapeutic delivery using pH-responsive, affinity-based release

Polymer Microparticles Prolong Delivery of the 15-PGDH Inhibitor SW033291

As the prevalence of age-related fibrotic diseases continues to increase, novel antifibrotic therapies are emerging to address clinical needs. However, many novel therapeutics for managing chronic fibrosis are small-molecule drugs that require frequent dosing to attain effective concentrations. Although bolus parenteral administrations have become standard clinical practice, an extended delivery platform would achieve steady-state concentrations over a longer time period with fewer administrations. This study lays the foundation for the development of a sustained release platform for the delivery of (+)SW033291, a potent, small-molecule inhibitor of the 15-hydroxyprostaglandin dehydrogenase (15-PGDH) enzyme, which has previously demonstrated efficacy in a murine model of pulmonary fibrosis. Herein, we leverage fine-tuned cyclodextrin microparticles-specifically, β-CD microparticles (β-CD MPs)-to extend the delivery of the 15-PGDH inhibitor, (+)SW033291, to over one week.

Engineering selective molecular tethers to enhance suboptimal drug properties

Small-molecule drugs are utilized in a wide variety of clinical applications, however, many of these drugs suffer from one or more suboptimal properties that can hinder its delivery or cellular action in vivo, or even shelf an otherwise biologically tolerable drug. While high-throughput screening provides a method to discover drugs with altered chemical properties, directly engineering small-molecule bioconjugates provides an opportunity to specifically modulate drug properties rather than sifting through large drug libraries with seemingly 'random' drug properties. Herein, we propose that selectively "tethering" a drug molecule to an additional group with favorable properties will improve the drug conjugate's overall properties, such as solubility. Specifically, we outlined the site-specific chemical conjugation of rapamycin (RAP) to an additional "high-affinity" group to increase the overall affinity the drug has for cyclodextrin-based polymers (pCD). By doing so, we found that RAP's affinity for pCD and RAP's window of delivery from pCD microparticles was tripled without sacrificing RAP's cellular action. This synthesis method was applied to the concept of "affinity" for pCD, but other prosthetic groups can be used similarly. This study displays potential for increasing drug delivery windows of small-molecule drugs in pCD systems for chronic drug therapies and introduces the idea of altering drug properties to tune polymer-drug interactions.

Affinity Effects on the Release of Non-Conventional Antifibrotics from Polymer Depots

For many chronic fibrotic conditions, there is a need for local, sustained antifibrotic drug delivery. A recent trend in the pharmaceutical industry is the repurposing of approved drugs. This paper investigates drugs that are classically used for anthelmintic activity (pyrvinium pamoate (PYR)), inhibition of adrenal steroidgenesis (metyrapone (MTP)), bactericidal effect (rifampicin (RIF), and treating iron/aluminum toxicity (deferoxamine mesylate (DFOA)), but are also under investigation for their potential positive effect in wound healing. In this role, they have not previously been tested in a localized delivery system suitable for obtaining the release for the weeks-to-months timecourse needed for wound resolution. Herein, two cyclodextrin-based polymer systems, disks and microparticles, are demonstrated to provide the long-term release of all four tested non-conventional wound-healing drugs for up to 30 days. Higher drug affinity binding, as determined from PyRx binding simulations and surface plasmon resonance in vitro, corresponded with extended release amounts, while drug molecular weight and solubility correlated with the improved drug loading efficiency of cyclodextrin polymers. These results, combined, demonstrate that leveraging affinity interactions, in combination with drug choice, can extend the sustained release of drugs with an alternative, complimentary action to resolve wound-healing and reduce fibrotic processes.

Serum biomolecules unable to compete with drug refilling into cyclodextrin polymers regardless of the form

Polymers that are refillable and sustain local release will have a great impact in both preventing and treating local cancer recurrence as well as addressing non-resectable diseases. Polymerized cyclodextrin (pCD) disks, which reload drugs into molecular "pockets" in vivo through affinity interactions, have been previously shown to localize doxorubicin (Dox) to treat glioblastoma multiforme. However, one concern is whether drug refilling is influenced by competition from local biomolecules. In addition the impact of the polymer form on drug refilling is unknown. Herein, different pCD formulations were synthesized from γ-cyclodextrin (γ-CD) and were compared in vitro using competitive drug filling/refilling assays. Data reveal that affinity-based drug refilling occurs as a function of both the polymer form and the sustained release polymeric liquid (SRPL) dilution factor, pointing to the surface/volume ratio, as well as the CD pocket density, and the effects of the distance between pocket. In vitro refilling experiments with cholesterol demonstrated no interference with Dox filling of the CD polymer, while the presence of albumin only slightly reduced Dox filling of pCD-γ-MP (microparticle) and pCD-γ-SRPL forms, but not pCD-γ-disks. Moreover, whole serum competition did not inhibit filling or refilling of pCD-γ-MP with Dox at multiple concentrations and filling times, which indicates that this polymer (re)filling is primarily driven by affinity-based interactions that can overcome the physiological conditions which may limit other drug delivery approaches. This was supplemented by isolating variables through docking simulations and affinity measurements. These results attest to the efficiency of in vivo or in situ polymer filling/refilling in the presence of competitive biological molecules achieved partially through high affinity drug to polymer interactions.

Injectable liquid polymers extend the delivery of corticosteroids for the treatment of osteoarthritis

Drug delivery strategies generally use inert materials, such as high molecular weight polymers, to encapsulate and control the release rate of therapeutic drugs. Diffusion governs release and depends on the ease of permeation of the polymer alongside the device thickness. Yet in applications such as osteoarthritis, the physiological constraints and limited intra-articular joint space prevent the use of large, solid drug delivery implants. Other investigators have explored the use of micro- and nanoparticle drug delivery systems. However, the small size of the systems limits the total drug that may be encapsulated and its short diffusion distance causes rapid release. Ordinarily, the extremely low diffusivity of a polymer fluid would make this an unsuitable delivery system. Our technology takes advantage of specific molecular interactions between drug and polymer, which can control the rate of release beyond diffusion. With this "affinity-based drug delivery", we have shown that delivery rates from solid polymer can be prolonged from hours and days, to weeks and months. In this paper, we demonstrate that this affinity-based mechanism also applies to low diffusivity fluid-phase polymers. They show release rates that are substantially slower than chemically similar polymers incapable of forming those inclusion complexes. The similarity of this study's liquid polymers to the viscoelastic fluids used in current clinical practice makes it an ample delivery system for osteoarthritic application. We confirmed the capacity of anti-inflammatory delivery of corticosteroids: hydrocortisone, triamcinolone, and dexamethasone; from both solid implants and polymer fluids. Further, we demonstrated that viscoelastic properties are widely tunable, and within the range of native synovial fluid. Lastly, we determined these polymer fluids have no impact on the differentiation of mesenchymal stem cells to cartilage and are not cytotoxic to a common cell line.

Surface sulfonamide modification of poly(N-isopropylacrylamide)-based block copolymer micelles to alter pH and temperature responsive properties for controlled intracellular uptake

Two different surface sulfonamide-functionalized poly(N-isopropylacrylamide)-based polymeric micelles were designed as pH-/temperature-responsive vehicles. Both sulfadimethoxine- and sulfamethazine-surface functionalized micelles were characterized to determine physicochemical properties, hydrodynamic diameters, zeta potentials, temperature-dependent size changes, and lower critical solution temperatures (LCST) in both pH 7.4 and 6.8 solutions (simulating both physiological and mild low pH conditions), and tested in the incorporation of a proof-of-concept hydrophobic antiproliferative drug, paclitaxel. Cellular uptake studies were conducted using bovine carotid endothelial cells and fluorescently labeled micelles to evaluate if there was enhanced cellular uptake of the micelles in a low pH environment. Both variations of micelles showed enhanced intracellular uptake under mildly acidic (pH 6.8) conditions at temperatures slightly above their LCST and minimal uptake at physiological (pH 7.4) conditions. Due to the less negative zeta potential of the sulfamethazine-surface micelles compared to sulfadimethoxine-surface micelles, and the proximity of their LCST to physiological temperature (37°C), the sulfamethazine variation was deemed more amenable for clinically relevant temperature and pH-stimulated applications. Nevertheless, we believe both polymeric micelle variations have the capacity to be implemented as an intracellular drug or gene delivery system in response to mildly acidic conditions. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1552-1560, 2018.

Erythromycin Modification That Improves Its Acidic Stability while Optimizing It for Local Drug Delivery

The antibiotic erythromycin has limited efficacy and bioavailability due to its instability and conversion under acidic conditions via an intramolecular dehydration reaction. To improve the stability of erythromycin, several analogs have been developed—such as azithromycin and clarithromycin—which decrease the rate of intramolecular dehydration. We set out to build upon this prior work by developing a conjugate of erythromycin with improved pH stability, bioavailability, and preferential release from a drug delivery system directly at the low pH of an infection site. To develop this new drug conjugate, adamantane-1-carbohydrazide was covalently attached to erythromycin via a pH-degradable hydrazone bond. Since Staphylococcus aureus infection sites are slightly acidic, the hydrazone bond will undergo hydrolysis liberating erythromycin directly at the infection site. The adamantane group provides interaction with the drug delivery system. This local delivery strategy has the potential of reducing off-target and systemic side-effects. This work demonstrates the synthesis of a pH-cleavable, erythromycin conjugate that retains the inherent antimicrobial activity of erythromycin, has an increased hydrophobicity, and improved stability in acidic conditions; thereby enhancing erythromycin’s bioavailability while simultaneously reducing its toxicity.