(560a) Polymer-Based Multilayer Coatings for the Rapid Release of DNA From Surfaces: A Weak Polyelectrolyte Approach

Thin films and coatings that promote the release of DNA from surfaces play important roles in the development of new gene delivery systems. These materials have utility as tools for basic biomedical research and they are useful as platforms for the local delivery of DNA in therapeutic contexts. Degradable surface coatings that contain DNA provide straightforward approaches to achieving spatial control over DNA delivery (e.g., release of DNA from the surface of an object results in delivery of DNA to cells in the immediate vicinity of that object). One challenge confronting the development of such coatings, however, is to design materials that degrade or erode on time scales that are appropriate in the context of a broad range of different applications (e.g., to achieve sustained release, rapid release, or to exert tunable temporal control). Another substantial challenge lies in fabricating thin films that do not simply release DNA, but that release it in a form that promotes internalization and fruitful processing by cells. This talk will focus on the design of ultrathin polymer-based multilayer coatings designed to release DNA rapidly in physiological environments.

Our group has used methods for layer-by-layer assembly to fabricate thin polymer multilayers (~100 nm thick) consisting of plasmid DNA and cationic poly(beta-amino ester)s (PBAEs). These films erode gradually and release DNA and DNA/polymer aggregates via hydrolysis of the ester groups in the backbones of the degradable polymer layers. Films having this basic design can be used to coat the surfaces of indwelling devices (e.g., intravascular stents), and can be used to promote localized transgene expression in vitro and in vivo. Although this “degradable polymer/degradable film” approach is useful, it is generally limited to the design of coatings that erode and release DNA for extended periods of time (e.g., ranging from several days to several weeks or months). These coatings are thus not particularly well suited for use in contexts that require rapid or short-term transfer of DNA (e.g., over periods ranging from several seconds to minutes or a few hours). Approaches to achieve accelerated or contact-mediated transfer of DNA will be critical in applied contexts that are inherently time-limited (e.g., balloon-mediated vascular interventions) and in other applications (e.g., transdermal delivery of DNA using microneedles) where short-duration transfer is also desirable.

We recently reported the basis of a new approach to accelerate the release of DNA from polymer multilayers. This approach is based on incorporation of poly(acrylic acid) (PAA; a biocompatible polyanion) to design coatings that disassemble rapidly at physiological pH (through a mechanism that involves pH-dependent ionization of PAA and subsequent disruption of ionic interactions, rather than through a mechanism that involves the hydrolysis of a cationic PBAE). These coatings release DNA up to 24 times faster than films designed using PBAEs and DNA alone (e.g., over 3 hrs vs. 3 days). Here, we demonstrate that this ‘weak polyelectrolyte’ approach can be used to destabilize coatings formed from DNA and non-degradable linear polyethyleneimine (LPEI, a commonly used gene delivery polymer) that are otherwise stable for prolonged periods. Strategic incorporation of nano-layers of PAA during the assembly of LPEI/DNA films yields coatings that release DNA into solution in less than 3 hours (with ~80% released in the first 5 minutes) upon incubation in physiologically relevant media. The results of in vivo experiments also demonstrate (i) that inflatable balloon catheters coated with these LPEI/DNA/PAA films can be used as quick-release coatings for the contact-transfer of DNA to injured vascular tissue in rats (e.g., over periods of 20 minutes), and (ii) that this approach can be used to promote robust and localized expression of reporter genes (e.g., beta-galactosidase) in injured rat arterial tissue in vivo.

In addition to promoting substantially faster release, this weak polyelectrolyte approach is potentially enabling for two other reasons. First, exploiting changes in the ionization of a weak polyelectrolyte as a means to drive film disruption removes the need to include layers of cationic polymers that are hydrolytically degradable. Second, the removal of this constraint provides opportunities to integrate a much broader range of functional polymers – including conventional cationic gene delivery polymers such as LPEI, but also other anionic weak polyelectrolytes – into quick-release coatings. When combined, these attributes suggest a basis for the design of thin, conformal coatings that could promote more rapid release and more effective DNA delivery and transgene expression than other existing PBAE-based multilayer platforms. Results of physicochemical characterization and additional in vitro assays will be presented, and opportunities for the application of this approach to the contact-mediated vascular delivery of therapeutic DNA constructs using film-coated inflatable catheter balloons will be discussed.