Sensitive, reproducible and convenient fluorometric assay for the in vitro evaluation of anti-cytomegalovirus agents.

Fluorescein diacetate (FDA), a non-fluorescent diacetyl fluorescein ester that becomes fluorescent upon hydrolysis by cytoplasmic esterases, permitted the easy distinction by fluorometry between non-infected and human cytomegalovirus (CMV)-infected HEL cell cultures. As a result of enhanced cytoplasmic esterase activity after CMV infection, FDA-derived fluorescence intensity was brighter for infected than non-infected HEL cells. A similar increase in fluorescence intensity was observed after loading the cells with Indo-1/AM, a non-fluorescent ester of Indo-1 that becomes fluorescent upon cleavage by cytoplasmic esterases. The 50% effective concentrations of a number of anti-CMV agents as determined by the fluorometric assay were very similar to those obtained by the conventional and more time-consuming microscopic evaluation. The fluorometric assay appears very suitable for an automated evaluation of anti-CMV compounds, and also allows rapid determination of the cytotoxicity of potential antiviral compounds.