Biotransformation of the antiestrogen clomiphene to chemically reactive metabolites in the immature female rat

Novel metabolites of clomiphene (CLO), an antiestrogen effective in experimental breast cancer models, were characterized in studies using immature female rats. After i.p. administration, CLO was eliminated unchanged in feces and as two components which were chromatographically identical to synthetic CLO analogues bearing a m-methoxy-p-hydroxyphenyl (guaiacol) moiety in place of one or the other of its phenyl rings. These components were also found in liver tissue. In the presence of liver microsomal homogenate, CLO underwent p-hydroxylation of either of its phenyl rings, affording 4-hydroxy-CLO and 4'-hydroxy-CLO. These in turn underwent liver microsomal mediated conversion to the respective guaiacol metabolites. 4'-Hydroxy-CLO and its 3'-methoxy analogue, but not positional isomers of these, had arylating ability as shown by chemical and spectral studies, apparently due to spontaneous conversion to electrophilic allene-quinones. Reproductive tract abnormalities produced in neonatal rats by CLO were suggested not to be mediated via such metabolites, since similar such effects were caused by 4'-fluoro-CLO. However, the latent arylating potential of the 4'-hydroxylated metabolites of CLO suggests that these compounds may be useful in biochemical studies of breast cancer cell growth inhibition.