Potential value of cellulose synthesis inhibitors combined with PHMB in the treatment of acanthamoeba keratitis

The aim of this study was to improve the cytopathic effect (CPE) of antiamebic agents by combining with cellulose synthesis inhibitor as an encystation inhibitor. Methods: Cellulose synthesis inhibitors, 2,6-dichlorobenzonitrile (DCB) and isoxaben were used to block encystation of Acanthamoeba during cultivation. Cultured human corneal epithelial (HCE) cells and Acanthamoeba were treated with polyhexamethylene biguanide (PHMB) combined with cellulose synthesis inhibitors to evaluate the CPE as an antiamebic agent. Results: 0.02% PHMB showed a 51.9% CPE on HCE cells within 30 minutes but exhibited significant toxic effects on Acanthamoeba. At a level of 0.00125%, PHMB had no significant CPEs on HCE cells, whereas 100 mM DCB and 10 mM isoxaben significantly inhibited the formation of the inner cyst wall of Acanthamoeba during encystation, and Acanthamoeba trophozoites failed to convert into mature cysts. Although a low concentration (0.00125%) of PHMB was used, the novel combinations with 100 mM DCB or 10 mM isoxaben had 23.4% or 18.7% additional amebicidal effects on Acanthamoeba. However, 100 mM DCB and 10 mM isoxaben had no CPEs on HCE cells. Conclusions: The combination of cellulose synthesis inhibitors with low concentrations of PHMB reduced the CPE on HCE cells and improved the amebicidal effect on Acanthamoeba by inhibition of encystation.