Tumorigenicity of the dihydrodiols of dibenzo(a,h)anthracene on mouse skin and in newborn mice.

INTRODUCTION Dibenzo(a,h)anthnacene and the three metabolically pos sible trans-dihydrodiols of dibenzo(a,h)anthracene were tested for tumorigenic activity on mouse skin and in new born mice. in the tumorigenicity study on mouse skin, a single topical application of 10 to 160 nmol of compound was followed 7 days later by twice-weekly applications of the tumor promoter 12-O-tetradecanoylphorbol-1 3-acetate for25 weeks.Comparisonsofthepercentageofmicewith tumors and number of tumors per mouse indicated that dibenzo(a,h)anthracene and dibenzo(a,h)anthracene 3,4dihydrodiol were approximately equipotent as tumor initia tors.The 1 2-and 5,6-dihydrodiols of dibenzo(a,h)anthra cene had no significant tumor-initiating activity at the doses tested. Saturation of the double bond at position 1,2 of dibenzo(a,h)anthracene 3,4-dihydrodiol resulted inthefor mation of a tetrahydrodiol with markedly less tumor-initiat ing activity than dibenzo(a,h)anthracene 3,4-dihydrodiol. In the tumorigenicity study in newborn mice, increasing amounts of the compounds were injected i.p. on the 1st, 8th, and 15th days of life to give a total dose of 70 or 420 nmol. The experiment was terminated when the animals were 25 to29 weeks old.Lessthan20% ofcontrolmice or mice treated with the 1,2 or 5,6-dihydrodiol of di benzo(a,h)anthracene developed pulmonary tumors, and the average number of tumors per mouse was less than 0.25. In mice treated with 70 and 420 nmol of dibenzo(a,h)anthracene, 88 and 100%, respectively, devel oped pulmonary tumors with an average of 3.61 and 46.90 tumors/mouse. In mice treated with 70 and 420 nmol of dibenzo(a,h)anthracene 3,4-dihydrodiol, 83 and 99%, re spectively, developed pulmonary tumors, with an average of 1.99 and 28.06 tumors/mouse. Hepatic neoplastic nod uleswere found in42% ofthemale mice treatedwith420 nmol ofthe3,4-dihydrodiol ofdibenzo(a,h)anthracene, but not in female mice or in mice from any of the other treatment groups. The high tumonigenic activity of di benzo(a,h)anthracene 3,4-dihydrodiol on mouse skin and in the lung and liver of newborn mice, together with the lower tumonigenic activity of 3,4-dihydroxy-1 ,2,3,4-tetrahydrodi benzo(a,h)anthracene on mouse skin, provides support for bay-region activation of dibenzo(a,h)anthmacene to an ulti mate carcinogen. 1 To whom requests for reprints should be addressed. 2 Recipient of National Cancer Institute Grant 1 F32 CA05729-01. Received November 9, 1978; accepted January 2, 1979. The polycyclic aromatic hydrocarbon DBA3 is a potent carcinogen (1, 5). The tumorigenic activity of polycyciic hydrocarbons and many other cancer-causing chemicals resultsfrom the formationof highlyreactivemetabolic intermediates, designatedultimatecarcinogens(17,18). Recent studies have shown that certain benzo-ring dihydro diols of the carcinogens benzo(a)pymene, benzo(a)anthra cene, chrysene, and 7-methylbenzo(a)anthracene are car cinogenic in mice (4, 11, 14-16, 22, 29). The unique struc tumal feature of the active dihydrodiols of these hydrocar bons appears to be the presence of a nonaromatic double bond which forms part of the bay region4 of the hydrocar bon and is adjacent to the dihydrodiol. Epoxidation of this double bond forms a diol-epoxide which is the proposed ultimate carcinogenic metabolite (8-10). Bay-region diol epoxides of benzo(a)pyrene and benzo(a)anthracene pos sess high intrinsic mutagenic activity in bacterial and mam malian cells (7, 19, 22, 27, 28, 31), and they are highly carcinogenic in animals (3, 11, 12, 14, 21, 22). The bay region theory predicts that DBA 3,4-dioi-1 ,2-epoxide is an ultimate carcinogenic metabolite of DBA (8-10). Because dihydrodiol formation precedes epoxidation at the adjacent double bond, DBA 3,4-dihydrodiol is the immediate meta bolic precursor of the bay-region diol-epoxide of DBA. DBA 3,4-dihydrodiol isthemajormetabolite formedfromDBA by rat liver microsomes (20)@;it represents 24 to 28% of the total metabolites.5 DBA 1,2and 5,6-dihydrodiols are also metabolites of DBA, and together they represent 10 to 15% 3 The abbreviations used are: DBA, dibenzo(a,h)anthracene; DBA 3,4dihydrodiol, trans-3,4 dihydroxy-3,4-dihydrodibenzo(a,h)anthracene; DBA 1,2-dihydrodiol, trans-l ,2-dihydroxy-l ,2-dihydrodibenzo(a,h)anthracene; DBA 5,6-dihydrodiol, trans-5,6-dihydroxy-5,6-dihydrodibenzo(a,h)anthra cene; DBA H4-3,4-diol., trans-3,4-dihydroxy-l ,2,3,4-tetrahydrodibenzo(a,h)anthracene; TPA, 12-O-tetradecanoylphorbol-1 3-acetate; DMSO, dimethyl sulfoxide.All compoundsare racemicmixtureswhereoptical enantiomers arepossible. 4 A bay region is present in a polycyclic aromatic hydrocarbon when an angularbenzoring is presentin the molecule.Thesimplestexampleof a bay region is the sterically hindered region between positions 4 and 5 of phenanthrene.Benzo(a)pyrenehasa bay region betweenpositions10and 11. and benzo(a)anthracene has a bay region between positions 1 and 12. The bay regions in chrysene are between carbon atoms 4 and 5 and between carbonatoms10 and 11. DBAhasbayregionsbetweencarbonatoms1and 14 and betweencarbon atoms7 and 8 (seeChart 1). Since chryseneand DBAaresymmetricalhydrocarbons,the secondbayregionis identicalto the first. A bay-region diol-epoxide designates the positional isomer in which the epoxide forms part of the bay region. For example, benzo(a)pyrene 7,8-diol 9,10-epoxide and DBA 3,4-dial-i ,2-epoxide are bay-region diol-epoxides, but benzo(a)pyrene 9,lO-diol-7,8-epoxide and DBA 1,2-diol-3,4-epoxide are not bay-region diol-epoxides. S M. Nordqvist, D. R. Thakker, H. Yagi, W. Levin, D. Ryan, P. E. Thomas, A. H.Conney,andD. M.Jerina,manuscriptin preparation. 1310 CANCER RESEARCH VOL. 39 on April 19, 2017. © 1979 American Association for Cancer Research. cancerres.aacrjournals.org Downloaded from Tumorigenicity of DBA dihydrodiols on mouse skinFemale CD-i mice (7 to 8 weeks old) were treated topically withDBA or a derivative of DBA in 200 @tI of acetone:NH4OH (1000:1).TPA (16 nmol/200 @.tI acetone) was applied twice weekly for 25weeks, commencing 7 days after the initiating compound wasapplied.% miceDose withtuTumors/Initiator (nmol) moms mouseNone