MECHANISMS OF CARCINOGENESIS OF DIBENZO(A,1)PYRENE

Although health hazards associated with cigarette smoking are well-known,
the carcinogens that present these hazards have not been quantitatively
determined or in some cases qualitatively identified. Dibenzo[a,l]pyrene
(DB[a,l]P) has been identified in the biologically active fraction of
tobacco smoke condensate. We have recently found this compound to be an
extremely potent carcinogen, much stronger than benzo[a]pyrene (BP),
suggesting that it may represent a significant risk in cigarette smoke
and other environmental pollutants. Therefore, we plan to determine the
potency of DB[a,l]P by comparing its tumorigenic activity in rat mammary
gland by direct application, and in rat lung by direct application to
that of BP, the strongest known environmental polycyclic aromatic
hydrocarbon (PAH), and 7,12-dimethylbenz[a]anthracene (DMBA), the
strongest known carcinogenic PAH. To provide evidence on the mechanism
of carcinogenesis of DB[a,l]P, we propose to investigate 1) whether the
metabolite DB[a,l]P 11,12-dihydrodiol is a proximate tumor-initiator; 2)
whether DBp[a,l[P activates ras oncogenes similarly to DMBA or BP in
mouse skin, rat mammary gland and rat lung tumors by detection of a point
mutated Ha-ras, Ki-ras or N-ras gene using amplification by the
polymerase chain reaction and direct dideoxyribonucleotide DNA
sequencing; 3) the relative reactivity of DB[a,l]P, DB[a,e]P and BP with
nucleophiles in one-electron oxidation with Mn(OAc), and in
electrochemical oxidation; 4) the binding of DB[a,l]P to DNA in vitro
with horseradish peroxidase, prostaglandin H synthase, rat lever
microsomes and rat liver nuclei by determining the level of binding and
identifying the DNA adducts formed; and 5) the binding of DB[a,l]P in
vivo in mouse skin, rat mammary gland and rat lung by determining the
level of binding and identifying the DNA adducts formed. With this
experimental approach we will assess the carcinogenic potency of DB[a,l]P
vs DMBA and BP, and we will also know whether its ability to activate ras
oncogenes resembles that of DMBA and BP, and we will also know whether
its ability to activate ras oncogenes resembles that of DMBA or BP.
Since we expect that the carcinogenicity of DB[a,l]P is similar to that
of DMBA, we think our tumorigenicity studies of DB[a,l]P will demonstrate
that this PAH represents a significant human health hazard in cigarette
smoke and other environmental pollutants. The data obtained from the
chemistry, tumorigenicity, DNA-binding studies and oncogene activation
will provide significant clues concerning the mechanism of carcinogenesis
of DB[a,l]P.