(501c) Surface-Mediated Release of Small-Molecule Modulators of Bacterial Quorum Sensing: Toward a New Approach to the Design of Surfaces That Prevent Formation of Bacterial Biofilms

The ability of bacteria to communicate and function as a group is central to the development of many bacterial infections. Over the past 40 years, it has become clear that bacteria communicate by assessing their local population densities through a phenomenon known as ‘quorum sensing’ (QS). Many of the most notorious human pathogens use this sensing mechanism to organize into structured communities called ‘biofilms’ and activate virulence pathways that are the basis for acute and chronic infections. As a result, QS is a relevant target for the development of new anti-infective strategies. In disease-oriented contexts, the development of small molecule-based inhibitors of QS (QSIs) is also particularly attractive because it provides a potential means to avoid evolved-resistance mechanisms that plague currently used bactericidal agents.

One challenge to the application of QSIs as antivirulence agents lies in the development of methods for the administration of these compounds in ways that can be tailored in a range of different clinical and health-oriented contexts. Bacterial colonization and the formation of biofilms on the surfaces of indwelling medical devices, for example, represent two primary points of entry for bacteria into the body. Inhibiting or attenuating QS in bacteria locally (i.e., at or near the surfaces of these objects) presents a significant challenge. In this presentation, we describe an approach that addresses this broad challenge through the design of thin polymer films that provide temporal control over the surface-mediated release of novel small molecules that inhibit bacterial QS. We demonstrate that this approach can be used to control and activate a QS phenotype in a model bacterial system, and that it has several potential advantages relative to methods for the direct (i.e., solution-based) administration of QSIs used in past studies. Although many different approaches have been reported for the design of materials that control the release of antibiotics and other bacteriocidal agents, the controlled release of agents that disrupt bacterial communication represents, to our knowledge, a fundamentally new approach to the localized and surface-mediated prevention of bacterial virulence.

We will present the results of recent proof-of concept studies based on the encapsulation and release of a novel, synthetic N-acylated L-homoserine lactone (AHL) QS modulator from thin films of hydrolytically degradable polymers. We selected N-(3-nitrophenylacetanoyl)-L-homoserine lactone (1) for these studies because past work in our group has shown that this non-native AHL is a potent modulator of QS in bacteria, most notably as an inhibitor in the pathogen Pseudomonas aeruginosa and as a “super-activator” in the bioluminescent symbiont Vibrio fischeri. We selected poly(lactide-co-glycolide) (PLG) as a matrix for encapsulation and surface-mediated release because this polymer is both biocompatible and biodegradable, and it has a well-documented history of use in drug delivery and other biomedical applications. In addition, the environments within matrices of PLG have been demonstrated to be acidic (and could thus serve to stabilize AHL-type inhibitors against hydrolysis upon prolonged exposure to aqueous media).

Our results demonstrate that AHL 1 can be loaded into solvent-cast thin films of PLGA, and that it is released (over periods ranging from several days to several months; depending on the composition of the copolymer) in a form that is active and able to modulate (turn on) QS in the marine symbiont V. fischeri, a bacterial model used widely for fundamental studies of QS. Our results also demonstrate that this polymer-based approach can be used to prolong the activities of the AHL relative to one-time (bolus) treatments with AHL in solution. This result is consistent with the view that the acidic microenvironment inside these films can prevent (or minimize) the hydrolysis, and therefore deactivation, of the AHL prior to release from the film.

The results of this study, when combined, suggest a basis for the design of coatings that intercept bacterial communication in ways that are important in both fundamental and applied contexts (e.g., surfaces that prevent the formation of biofilms). Results of additional physicochemical characterization and bacterial assays will be presented, and opportunities for the application of this approach to prevent bacterial colonization and the formation of biofilms on the surfaces of indwelling devices (e.g., catheters) will be discussed.