Initiation of hepatocarcinogenesis in infant male B6C3F1 mice by N-hydroxy-2-aminofluorene or N-hydroxy-2-acetylaminofluorene depends primarily on metabolism to N-sulfooxy-2-aminofluorene and formation of DNA-(deoxyguanosin-8-yl)-2-aminofluorene adducts

Previous work from this laboratory provided strong evidencethat N-sulfooxy-2-aminofluorene is the major ultimate electro-philicand carcinogenic metabolite of N-hydroxy-2-acetyl-aminofluorene(N-hydroxy-AAF) in the livers of infant male B6C3F₁ (C57BL/6Jx C3H/HeJ F₁ mice. Over 90% of the hepatic DNA adducts in thesemice consisted of N-(deoxyguan-osin-8-yl)-2-aminofluorene [N-(dGuo-8-yl)]and<10% were deoxyguanosinyl adducts containing 2-acetylaminofluor-ene(AAF) residues. In the present study hepatic DNA adduct formationand tumor initiation by N-hydroxy-2-aminofluor-ene (N-hydroxy-AF)were examined in these mice. N-(dGuo-8-yl)-AF was the only adductdetected in the hepatic DNA; the level at 9 h after a singlei.p. dose of 0.04 or 0.06 µmol/g body wt of [³H]N-hydroxy-AFwas 1.0 or 1.7 pmol/mg DNA. Pre-treatment with a single i.p.dose (0.04 µmol/g body wt) of the sulfotransferase inhibitorpentachlorophenol (PCP) decreased the DNA adduct level by >80%.Similar levels of this adduct were found by ³²P-postlabelinganalysis of DNA from mice treated with unlabeled N-hydroxy-AF.The liver DNA of in-fant male brachyinorphic B6C3F₂ mice [deficientin 3'-phos-phoadenosine-5'-phosphosulfate (PAPS)] containedonly 0.3 pmol/mg DNA of N-(dGuo-8-yl)-AF after an i.p. doseof 0.06 µmol of N-hydroxy-AF/g body wt, while their phenotypi-callynormal (PAPS-sufficient) male littermates had 1.9 pmol/mg DNA.A single i.p. dose of 0, 0.015, 0.03, 0.06 or 0.12 µmol/body wt of N-hydroxy-AF in infant male B6C3F mice induced by10 months an average of 0.2, 2.5, 7, 11 or 14 hepatomas/mouse.Pretreatment with PCP reduced the liver tumor multiplicity ateach dose level by >80%. Essen-tially the same average tumormultiplicities and inhibitions of tumor formation by PCP pretreatmentwere obtained following injections of N-hydroxy-AF or N-hydroxy-AAFat the three lower dose levels. Collectively these data stronglyindicated that N-sulfooxy-2-aminofluorene is the major ultimate electrophilic and carcinogenic metabolite of N-hydroxyAF in the livers of infant male B6C3F₁ mice. Furthermore, sinceonly N-(dGuo-8-yl)-AF adducts were found in the he atic DNAthese lesions appear to be critical in the initiation of hepatocarcinogenesisin these mice by N-hydroxy-AF.