Lack of covalent binding of peroxisome proliferators nafenopin and Wy-14 643 to DNA in vivo and in vitro.

[3H][2-methyl-2-p-(1,2,3,4-tetrahydro-naphthyl)phenoxy] propionic acid (nafenopin), a hepatocarcinogenic peroxisome proliferator, when administered p.o. to normal intact and partially hepatectomized male F344 rats did not show any significant binding to DNA and RNA, but bound to proteins. The in vitro incubation of [3H]nafenopin and [3H]4-chloro-[6-(2,3-xylidino)pyrimidinylthio]acetic acid (Wy-14643), another peroxisome proliferator, with hepatic microsomes and calf thymus DNA also showed no significant binding of these chemicals to DNA.