Evaluation of the toxicity of substituted benzthioanilides by using in vitro tests

The cytotoxicity of 12 benzthioanilides substituted in the N-aromatic ring, and of two commercial preparations (imaverol and thiuram) for comparison, was studied with clone 81 cat cells, by determining the highest tolerated dose, and by using the neutral red uptake assay and the kenacid blue assay for total protein. The concentrations that induced 20%, 50% and 80% (IC20, IC50 and IC80) inhibition relative to controls were calculated from dose-response curves. For some compounds, rat LD50 values were also determined. All the benzthioanilide preparations showed in vitro toxicities lower than those of the fungicides imaverol and thiuram. It was confirmed that the cytotoxicities of the compounds depend on the type of substituent. The least toxic compound contained a CONHCH(2)CO(2)H substituent in the para position of the N-aromatic ring, and the most toxic compounds contained chloro and fluoro, or three chloro substituents in the anilide moiety. All the benzthioanilides tested showed fungistatic activity for dermatophytes; two of the compounds (compound 5 and compound 12) also inhibited the development of yeasts at concentrations lower than those which caused toxicity in vitro. The LD50 values and the cytotoxic concentrations in vitro were linearly related.