In Vitro Efficacy of Miltefosine Against Clinical Isolates of Acanthamoeba spp. from Patients with Keratitis.

Abstract

Purpose: The US Food and Drug Administration (USFDA) granted the miltefosine orphan drug designation in 2016 for treating Acanthamoeba keratitis. This study evaluates miltefosine's in vitro efficacy against clinical isolates of Acanthamoeba from patients with keratitis and its safety profile in human corneal epithelial cell line to rationalize its localized ocular application.

Methods: Acanthamoeba spp. isolated from corneal scrapings of keratitis patients (n = 17) were cultured axenically, genotyped, and tested for miltefosine's minimal cysticidal and trophozoicidal concentrations (MCC and MTC) by microbroth dilution method. Safer concentrations of miltefosine were determined using human corneal epithelial (HCE) cells at four incubation points. Trophozoites and cysts of one of the isolates, A. castellanii, were challenged on confluent monolayers of HCE in the presence and absence of miltefosine for 24 h. Cytopathic effects were evaluated using microscopic analysis.

Results: The majority of Acanthamoeba isolates tested were T4 genotypes (94.11%). MTC₉₀ and MCC₉₀ of miltefosine were 0.125 and 4 mg/mL, respectively. Miltefosine was found safe on HCE at 0.0625 and 0.125 mg/mL for 4 and 0.25 h, respectively. Microscopical findings showed that A. castellanii trophozoites destroyed the cellular structures of HCE within 24 h without miltefosine. Drug pre-treatment prevented the initiation of infection at both the tested concentrations (0.0625 and 0.125 mg/mL) upto 24 h.

Conclusion: Miltefosine was effective against Acanthamoeba trophozoites and cysts in vitro with >30-fold higher cidal concentration for cysts compared to trophozoites. An effective trophozoicidal concentration of miltefosine (0.125 mg/mL), found to be safe for HCEs, suggests its potential utility as an adjunct treatment for Acanthamoeba keratitis.