trans-3,4-dihydroxy-anti-1,2-epoxy-1,2,3,4-tetrahydrodibenz[a,j]acridine involvement in dibenz[a,j]acridine DNA adduct formation in mouse skin consistent with Ha-ras mutation patterns in tumors
Wl. Xue et al., trans-3,4-dihydroxy-anti-1,2-epoxy-1,2,3,4-tetrahydrodibenz[a,j]acridine involvement in dibenz[a,j]acridine DNA adduct formation in mouse skin consistent with Ha-ras mutation patterns in tumors, CHEM RES T, 14(7), 2001, pp. 871-878
Dibenz[a,j]acridine (DBA), is a N-heteropolycyclic aromatic environmental c
arcinogen found in complex combustion mixtures. The major route of DBA meta
bolic activation is reportedly through the trans-3,4-dihydroxy-3,4-dihydroD
BA (DBA-3,4-DHD). The present studies were undertaken to determine the role
of trans-3,4-dihydroxy-anti-1,2-epoxy-1,2,3,4-tetrahydroDBA (DBADE) in DBA
activation pathway(s), the DNA bases involved in the binding of DBA to DNA
, and whether the adducts produced are consistent with the mutation pattern
in the Ha-ras gene. DBA (300 mug) or 50 mug synthesized (+/-)-DBADE was ap
plied to the back of female Hsd:ICR(Br) mice. The mice were sacrificed 48 h
later, and skin DNA was isolated, hydrolyzed, and analyzed with P-32-postl
abeling. Of the four adducts produced in vivo, adduct 1 was the major adduc
t for DBA (> 50%) and adduct 2 was the major adduct for DBADE (89%). After
the reaction of (+/-)-DBADE with purine nucleotides or calf thymus (CT) DNA
in vitro, 100% of the DBADE-2 ' -dAMP adducts and 94% of DBADE-CT DNA addu
cts were chromatographically identical on TLC with adduct 2 and 86% of the
DBADE-2 ' -dGMP adducts were chromatographically consistent with adduct 1 b
y 32P-postlabeling. Papillomas were induced on the backs of mice by a singl
e application of 0.2 mu mol of DBA followed by twice-weekly application of
12-o-tetra-decanoylphorbol-13-acetate (TPA, 2 mug) for 24-26 weeks. Skin ca
rcinomas were induced by twice weekly applications of DBA (0.1 mu mol) on t
he backs of mice. A to T and G to T transversions were found in codons 12,
13, and 61 of the Ha-ras gene in the treated mouse skin carcinoma and papil
loma DNA, The mutational spectra in the Ha-ras gene are consistent with the
DNA binding of DBA to dG or dA in vivo. Thus, this research has indicated
that DBADE plays an important role in DBA metabolic activation and DNA bind
ing in mouse skin, and an alternative pathway through a bis-dihydrodiol-epo
xide of DBA may also be involved.