TONS504 mediated photodynamic antimicrobial chemotherapy inactivation for Acanthamoeba keratitis in rabbits in vivo

Abstract

Purpose : Acanthamoeba keratitis (AK) is a sight-threatening infectious disease. It is difficult to treat and safe medical therapy remains highly debated. The aim of this study is to evaluate TONS504 (a cationic chlorin derivate photosensitizer, Porphyrin Lab, Okayama, Japan) mediated photodynamic antimicrobial chemotherapy (TONS504-PACT) in vivo as a potential treatment for Acanthamoeba keratitis.

Methods : Male Japanese white rabbits were used to establish the AK models. Central corneal epithelial defects with 3.5 mm in diameter were made with n-heptanol in the left eyes of rabbits. Soft contact lenses were incubated with 10⁵/mL Acanthamoeba castellani and placed over the previously debrided corneal surface with temporary tarsorrhaphy. TONS504-PACT was started after the establishment of AK seven days after infectious contact lens exposure. In PACT group with eight eyes, TONS504 was administered at a concentration of 1 mg/mL as eye drops and followed by LED irradiation that delivers light at a single wavelength (660 nm, CCS, Kyoto, Japan) at 60 J/cm² (six 3-min exposures and five 1-min rest periods). The antiamoebic effect was assessed with eight eyes subjected to PACT and three eyes that received no treatment. All subjects were evaluated by a slitlamp microscope daily for three days after the treatment. Clinical score based on corneal epithelial defects detected by fluorescein staining, stromal opacity, edema and vascular infiltration into the cornea was taken. The tested eyes were enucleated for histopathological analysis after three days observation.

Results : Slitlamp examination revealed that all eyes in both control and PACT groups started to manifest signs of infection by seven days after infectious contact lenses exposure. Four of the eight eyes in PACT group were markedly reduced the clinical sign of infection for up to three days after TONS504-PACT. Histopathological analysis showed regular arrangement of stroma fibers and small number of inflammatory cells in four corneas. However, all three corneas in control and the other four corneas in PACT group showed a large number of infiltrating neutrophils and irregular alignment of stromal collagen fibers.

Conclusions : Our TONS504-PACT achieved complete recovery from AK in 50% on experimental rabbit model at this point. Further study should be required to find the better conditions for high effectiveness of our TONS504-PACT for AK.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.