Ketoconazole inhibits developmental activation of Strongyloides stercoralis iL3 in host-like culture conditions; this inhibition is rescued by Δ7-dafachronic acid.

Frequency of feeding by cultured larvae, as reflected by ingestion of fluorescein isothiocyanate (FITC), was used as an index of developmental activation of infectious third-stage larvae (iL3). Larval mortality was scored as the percentage of larvae classed as non-motile and therefore “dead.” (A) Frequency of iL3 feeding and larval mortality as a function of ketoconazole concentration in Dulbecco’s modified Eagle’s Medium (DMEM), a permissive culture medium. DMEM without ketoconazole was the positive control. M9 buffer, a non-permissive medium, was used without ketoconazole as the negative control. ** Negative correlation of iL3 feeding and ketoconazole concentration (bracketed) is significant (P = 0.0028; Spearman r = -1.000). (B) Frequency of iL3 feeding and larval mortality as a function of Δ7-dafachronic acid (Δ7-DA) concentration in DMEM cultures containing an inhibitory concentration of ketoconazole (35 μM). Cultures of larvae in DMEM alone or in DMEM with 800 nM Δ7-DA were positive controls. Cultures of larvae in M9 buffer constituted the negative control. * Positive correlation of iL3 feeding in 35 μM ketoconazole and Δ7-DA concentration (bracketed) is significant (P = 0.0167; Spearman r = 1.000). In both panels, bar heights represent the mean percentage of iL3 feeding (blue bars) or the mean percentage of dead iL3 (white bars) in four biological replicates. Error bars indicate +1 standard deviation.