(525g) Polyanhydride Nanoparticles Encapsulating Rifampicin Suppress Growth of Pathogenic Acanthamoeba in vitro

Acanthamoeba spp. infections represent a growing problem for developed countries. In immunosuppressed individuals, Acanthamoeba spp. can cause granulomatous amebic encephalitis (GAE), which is often fatal due to a prodromal period, limited diagnostic tools, and a lack of effective antimicrobial treatments. Additionally, Acanthamoeba can cause Acanthamoeba keratitis (AK), a painful corneal infection that can result in vision impairment and can require enucleation if left untreated. AK is associated with corneal trauma and improper cleaning of contact lens. Infections by amoeba demonstrate several challenges to antimicrobial treatment. Delivery of antimicrobial therapeutics to amoebae is limited by the blood-brain barrier in GAE, restricted internalization and rapid efflux of drugs by the amoeba. An effective antimicrobial therapy capable of killing both the metabolically-active trophozoite and cyst forms of Acanthamoeba remains elusive.

Free-living amoeba feed on organic matter including bacteria that are typically 0.5 – 2 microns. Prior research demonstrated that through co-polymerization of hydrophobic and hydrophilic monomers, polyanhydride nanoparticles exhibit bacteria-like properties. By virtue of their hydrolytic degradation and surface erosion, they typically demonstrate a short burst followed by slower, sustained release of their encapsulated payload, which can be tuned by altering the composition of the polymer. Previous research has shown that polyanhydride nanoparticles can encapsulate and stabilize hydrophilic and hydrophobic payloads, enabling a wider selection of therapeutics for delivery. Given that amoebae acquire nutrients through similar phagocytic mechanisms, we hypothesize that polyanhydride nanoparticles could achieve high local concentrations of antimicrobial drugs at intracellular compartments within amoebae using a Trojan horse mechanism.

We report that rifampicin encapsulated in 20:80 1,8-bis(p-carboxyphenoxy)-3,6-dioxaoctane: 1,6-bis(p-carboxyphenoxy)hexane (CPTEG:CPH) nanoparticles shows a burst release over one day followed by a slow, near-zero-order release in aqueous in vitro experiments. We show that rifampicin-encapsulating nanoparticles significantly reduce the growth of two pathogenic Acanthamoeba strains at 72 hours. These results show that 20:80 CPTEG:CPH polyanhydride nanoparticles improve rifampicin efficacy in Acanthamoeba, which we hypothesize is a function of their controlled, local release to the amoebae. By improving the activity of extant antimicrobial therapies, we seek to improve the tool set available to combat amoebae infections.