In VitroEfficacies of Clinically Available Drugs against Growth and Viability of an Acanthamoeba castellanii Keratitis Isolate Belonging to the T4 Genotype

Abstract

ABSTRACTThe effects of clinically available drugs targeting muscarinic cholinergic, adrenergic, dopaminergic, and serotonergic receptors; intracellular calcium levels and/or the function of calcium-dependent biochemical pathways; ion channels; and cellular pumps were tested against a keratitis isolate ofAcanthamoeba castellaniibelonging to the T4 genotype.In vitrogrowth inhibition (amoebistatic) assays were performed by incubatingA. castellaniiwith various concentrations of drugs in the growth medium for 48 h at 30°C. To determine amoebicidal effects, amoebae were incubated with drugs in phosphate-buffered saline for 24 h, and viability was determined using trypan blue exclusion staining. For controls, amoebae were incubated with the solvent alone. Of the eight drugs tested, amlodipine, prochlorperazine, and loperamide showed potent amoebicidal effects, as no viable trophozoites were observed (>95% kill rate), while amiodarone, procyclidine, digoxin, and apomorphine exhibited up to 50% amoebicidal effects. In contrast, haloperidol did not affect viability, but all the drugs tested inhibitedA. castellaniigrowth. Importantly, amlodipine, prochlorperazine, and loperamide showed compelling cysticidal effects. The cysticidal effects were irreversible, as cysts treated with the aforementioned drugs did not reemerge as viable amoebae upon inoculation in the growth medium. Except for apomorphine and haloperidol, all the tested drugs blocked trophozoite differentiation into cysts in encystation assays. Given the limited availability of effective drugs to treat amoebal infections, the clinically available drugs tested in this study represent potential agents for managing keratitis and granulomatous amoebic encephalitis caused byAcanthamoebaspp. and possibly against other meningoencephalitis-causing amoebae, such asBalamuthia mandrillarisandNaegleria fowleri.