Lack of mutagenicity of diethylstilbestrol metabolite and analog, (±)-indenestrols A and B, in bacterial assays

Indenestrol A (IA), one of metabolites of the indanyl group of diethylstilbestrol, has a stronger binding affinity for the estrogen receptor and also a weaker uterotropic activity than endogenous estradiol. We tested the microbial mutagenicity of structural isomers of indenestrol A and indenestrol B (IB) in Salmonella typhimurium TA100 and TA98 and in Escherichia coli WP2 uvrA to investigate whether the interaction of diethylstilbestrol or IA with genomic DNA has any part in their carcinogenicity and other biological activities. In the absence of S9 mix, (±)-IA was cytotoxic at higher doses (1 and 10 μmmol/plate), and both (±)-IA and (±)-IB were non-mutagenic at lower doses (0.1-100 nmol/plate). In the presence of S9 mix, (±)-IA was cytotoxic at higher doses (0.5 and 1 μmol/plate), and at the other doses, (±)-IA and (±)-IB did not show any distinct increase in revertants. Although (±)-IA and(±)-IB showed a slight increase in the revertants in strain TA100 by the preincubation method without S9 mix, these results were considered to be negative, because no reproducible dose-revertants relationship necessary for a chemical to be determined as mutagenic was obtained. The S9 fraction interacted with (±)-LA or (±)-IB enzymatically or non-enzymatically, and weakened its cytotoxicity, so that the toxic dose was higher in the presence of S9 mix than in its absence. Both the plate incorporation and preincubation methods were used with a wide range of concentrations of (±)-IA and (±)-IB in the present experiment. No clear positive mutagenic data were obtained. These results are the first reports on the mutation assays of (±)-IA and (±)-IB, and suggest that they were non-mutagenic towards the bacterial strains tested. The study revealed that the cytotoxic activity of (±)-IA and (±)-IB did not correlate with DNA interaction, but was the result of a direct effect on microtubule polymerization, although indenestrols are known to have strong binding affinities for estrogen receptors.