[CANCER RESEARCH 39, 3549-3553, September 1979)
0008-5472 /79/0039-0000$02.00
Tumorigenic Activity of 3-Methyicholanthrene Metabolites on Mouse
Skin and in Newborn Mice
w. Levin,1 M. K. Buening,
A. W. Wood, R. L. Chang, D. R. Thakker,
D. M. Jerina, and A. H. Conney
Department of Biochemistry and Drug Metabolism, Hoffmann-La Roche Inc.. Nutley, New Jersey 071 10 (W. L., M. K. B., A. W. W., R. L. C.. A. H. C.], and
Laboratory of Bioorganic Chemistry, National Institute of Arthritis, Metabolism, and Digestive Diseases, NIH, Bethesda, Maryland 2001 4 ID. R. T., D. M. J.j
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ABSTRACT
INTRODUCTION
3-Methylcholanthrene and eight of its metabolites were
tested for tumonigenic activity in two tumor models. In the
tumonigenicity study on mouse skin, a single topical application
of 3 to 30 nmol of compound was followed 7 days later by
twice weekly applications of the tumor promotor i 2-0-tetra
decanoylphorbol-i 3-acetate for 30 weeks. Comparisons of the
percentage of mice with tumors and the average number of
tumors per mouse indicated that 3-methylcholanthrene, 2-hy
droxy-3- methylcholanthrene, 3-methylcholanthrene- 2-one,
and a i ,9,i 0-tnihydroxy-9,i 0-dihydro-3-methylcholanthrene
diastereomer were approximately equipotent as tumor initia
tons. i -Hydroxy-3-methylcholanthrene had approximately one
fourth the tumor-initiating activity of the most active com
pounds, and 3-methylcholanthrene-i -one and trans-i i ,i 2-di
hydroxy-i 1,i 2-dihydro-3-methylcholanthrene had no signifi
cant tumonigenic activity at the doses tested. In the tumori
genicity study in newborn mice, increasing amounts of the
compounds were injected i.p. on the i st, 8th, and i 5th days of
life to give a total dose of 2i or 49 nmol. The experiment was
terminated when the animals were 35 to 39 weeks old. With
respect to pulmonary tumors, i ,9,i 0-trihydroxy-9,i 0-dihydro
3-methylcholanthrene was the most tumonigenic compound
tested at both doses. 3-Methylcholanthrene and 3-methylchol
anthrene-2-one were the next most active compounds, and
they had approximately one-half to one-third of the activity of
i ,9, 10-tnihydnoxy-9,i 0-dihydro-3-methylcholanthrene
when
the data were expressed as pulmonary tumors per mouse. 2Hydroxy-3-methylcholanthrene was slightly less active than
were 3-methylcholanthrene and 3-methylcholanthrene-2-one.
i -Hydroxy-3-methylcholanthnene had marginal tumorigenic ad
tivity. 3-Methylcholanthrene i i ,i 2-oxide, trans-i i ,i 2-dihy
droxy-i 1,i 2-dihydro-3-methylcholanthrene,
and 3-methyl
cholanthrene-i -one were inactive at the doses tested.
i ,9, i 0-Tnihydroxy-9, i 0-dihydro-3-methylcholanthrene
at
the 2i- and 49-nmol doses also produced hepatic tumors in
50 and 8i % of the male mice, respectively. 3-Methylcholan
threne and 2-hydroxy-3-methylcholanthrene had one-fourth to
one-tenth the activity of i ,9,i 0-tnihydroxy-9,i 0-dihydro-3methylcholanthrene in the liver. The other 3-methylcholan
threne metabolites were essentially inactive in producing he
patic tumors. The high tumorigenic activity of i ,9,i 0-trihy
droxy-9,i 0-dihydno-3-methylcholanthrene on mouse skin and
in newborn mice provides evidence for bay-region activation of
3-methylcholanthrene to an ultimate carcinogen. The data also
indicate that other metabolites of 3-methylcholanthrene may
play a role in the carcinogenicity of this polycyclic aromatic
hydrocarbon.
Previous studies from our laboratories have been concerned
with the identification of ultimate carcinogenic metabolites
of the unsubstituted polycyclic aromatic hydrocarbons
benzo(a)pyrene, benzo(a)anthracene, chrysene, and dibenzo
(a,h)anthnacene (5, i 2, 16). These studies have shown that
dihydrodiols on angular benzo rings with ‘
‘bay-region'
‘
double
bonds are proximate carcinogens and that diol-epoxides
formed from these dihydnodiols, in which the epoxide forms
part of the bay region of the hydrocarbon, are ultimate carci
nogenic metabolites. Among the alternant polycyclic aromatic
hydrocarbons, several alkyl-substituted derivatives of the weak
carcinogen benzo(a)anthnacene, such as MC,2 7-methyl
benzo(a)anthracene, 7,12-dimethylbenzo(a)anthracene, and
F-nor-steranthrene, are potent carcinogens (1 , 7, 15). Recent
studies have suggested that bay-region diol-epoxides of certain
alkyl-substituted polycyclic aromatic hydrocarbons are also
prime candidates as ultimate carcinogenic metabolites (4, 9,
i 3, i 4, i 7—i9, 25, 27, 29, 32). Such alkyl substituents not
only are subject to metabolism themselves but also can dimin
ish the rate at which monooxygenase enzymes form arene
oxides at the formal aromatic double bonds to which they are
attached. The resultant increases or decreases in the formation
of positional isomers of dihydrodiols can thereby modulate the
carcinogenic potency of the parent hydrocarbon (i 0, 1i).
To date, several oxygenated metabolites of the potent car
cinogen MC have been identified (22—26),but the structure(s)
of the ultimate carcinogenic metabolite(s) has yet to be deter
mined. Since MC is an alkyl-substituted derivative of
benzo(a)anthracene, we sought to determine if this polycyclic
aromatic hydrocarbon was metabolically activated to an ulti
mate carcinogenic metabolite in a manner analogous to
benzo(a)anthnacene, i.e. , a bay-region diol-epoxide, which in
the case of MC would be a 9, i 0-diol-7,8-epoxide. Although
our in vitro metabolism studies with rat liver microsomes mdi
dated that dihydrodiol formation was a minor metabolic path
way for MC (24, 25), a major primary oxidative metabolite of
the hydrocarbon, i -hydroxy-MC, was metabolically converted
to at least 4 dihydnodiols to the extent of i 0 to 20% of total
metabolism (25). The 2 major dihydrodiols formed from racemic
To whom requests for reprints should be addressed.
Received January 25. 1979: accepted June 8, 1979.
SEPTEMBER
1979
i -hydroxy-MC
by rat liver microsomes
diastereomerically
2 The
abbreviations
have been identified
related trans-9, 10-dihydrodiols.3
used
are:
MC,
3-methylcholanthrene:
as
These
1 -hydroxy-MC,
1-
hydroxy-3-methylcholanthrene; 1-hydroxy-MC 9, 10-dihydrodiol, 1.9, 10-tnihy
droxy-9, 10-dihydro-3-methylcholanthrene in which the 9- and 10-hydroxyl
groups have the trans configuration: 2-hydroxy-MC, 2-hydroxy-3-methylcholan
threne; 1-keto-MC, 3-methylcholanthrene-1 -one; 2-keto-MC, 3-methylcholan
threne-2-one; MC 11.12-oxide, 3-methylcholanthrene 11.12-oxide; MC-1 1,12dihydrodiol, trans-i 1.12-dihydroxy-1 1.12-dihydro-3-methylcholanthrene; TPA,
12-O-tetradecanoylphorbol-1 3-acetate. Unless stated otherwise, all compounds
are racemic mixtures where optical enantiomers are possible.
Since racemic 1-hydroxy-MC was used as a substrate for metabolism studies
3549
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w.
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Levin
eta!.
Boy
Region
diastereomenic i -hydroxy-MC-9,i 0-dihydrodiols are metabol
ically activated to mutagenic metabolites in Salmonella typhi
murium strains TA98 and TM 00 and Chinese hamster V79
cells to a much greater extent than MC or several other oxy
genated metabolites of MC (32). The present study was under
taken to compare the tumorigenic activity of MC with the
metabolically formed i -hydnoxy-MC 9, i 0-dihydrodiols and
several other known oxidative metabolites of this polycyclic
hydrocarbon.
H3C
Y@
3-METHYLCHOLANTHRENE ( MC)
MATERIALS AND METHODS
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Chemicals. MC was obtained from Eastman Chemicals,
Rochester, N. V., and was purified by recrystallization from
benzene to obtain material homogeneous on analysis by high
pressure liquid chromatography (cf. Ref. 25). i -Hydnoxy-MC,
2-hydroxy-MC, i -keto-MC, 2-keto-MC, MC i i ,i 2-oxide, and
MC i i ,i 2-dihydnodiolwere synthesized as previously de
scnibed (6, 22) except that i - and 2-keto-MC were reduced to
the corresponding alcohols with potassium borohydnide (in
ethanol:tetnahydrofuran, i :3, v/v) instead of lithium aluminum
hydride. The diasteneomenically related i -hydroxy-MC 9, i 0dihydrodiols-@ and -@were obtained biosynthetically as previ
ously described (25). Structures of the MC derivatives are
shown in Chart 1. TPA was purchased from the Department of
Laboratory Medicine and Pathology at the University of Mm
nesota.
Animals. Female CD-i mice (7 to 8 weeks old), obtained
from Charles Riven Breeding Laboratory, North Wilmington,
Mass., were used for the skin tumor model. The mice were
anesthetized with ether and shaved on the dorsal surface with
electric clippers 3 days before treatment with the test com
pounds. Each treatment group consisted of 30 mice. MC and
the MC derivatives were applied once to the dorsal surface of
the mice in 200 @I
acetone:NH4OH (1000:i ). Control mice were
treated with the solvent alone. All mice received twice-weekly
applications of TPA (i 6 nmol/200 @lacetone) beginning 7
days after treatment with the MC derivatives. The development
of skin tumors was recorded every 2 weeks. Papillomas greaten
than 2 mm in diameter were included in the cumulative total if
they persisted for 2 weeks or longer.
Pregnant mice of the Swiss-Webster BLU:Ha (ICR) strain
were obtained from Blue Spruce Farms, Altamont, N. V., i to
8 days before partunition. Eight litters of mice were used in
each treatment group. Within 24 hr of birth, i 0 pups in each
litter were given injections i.p. of the first dose of compound;
additional injections were given on the eighth and i 5th days of
life. A total dose of 2i nmol of compound was divided into 3
injections of 3, 6, and i 2 nmol in 5, i 0, and 20 @iI
dimethyl
sulfoxide:NH4OH (i 000: i ), respectively. A total dose of 49
nmol of compound was divided into 3 injections of 7, i 4, and
28 nmol in 5, i 0, and 20 @I
dimethyl sulfoxide:NH4OH (i 000:
i ), respectively. Control mice were given injections of the
solvent alone. The mice were weaned at 23 days of age. All
with rat liver microsomes, the 2 isolated 1-hydroxy-MC 9, 10-dihydrodiols, des
ignated and @,
are presumed to be diastereomers in which the 1- and 10hydroxyl groups are either cis or trans as shown in Chart 1. At present, nothing
is known about the absolute stereochemistry of these isomers nor is it known
whether the 1- and 10-hydroxyl groups are cis or trans in the major isomer.
Because relatively little of the b isomer was isolated from the incubations, it was
only tested in one tumor model at a single dose.
3550
l-HYDROXY-MC
2-HYDROXY-MC
H3CJI@III@@
l-KETO-MC
2-KETO-MC
l-HYDROXY-MC 9,10DlHYDRODIOL
I - HYDROXY-MC 9,10-
H3C
H3d
DIHYDRODIOL
H3C
xoIoJ@
x@
T
T
@‘OH
OH
MC 11,12-OXIDE
MC 11,12-DIHYDRODIOL
Chart 1. Structures of MC and MC metabolites used in this investigation. The
principal isomer of 1-hydroxy-MC 9, 10-dihydrodiol formed from racemic 1-hy
droxy-MC by rat liver microsomes is referred to as isomer (cf. Footnote 3).
Stereochemistry is relative.
mice were housed in plastic cages with corncob bedding and
were fed Purina laboratory chow (Ralston Purina Co., St. Louis,
Mo.). The mice were killed when they were 35 to 39 weeks
old. At autopsy, the major organs of each animal were exam
med grossly, tumors were counted, and tissues were fixed in
i 0% buffered formalin. A representative number of pulmonary
tumors, all liver samples, and all other tissues with suspected
pathology were examined histologically. Pathology of the lung
tumors was the same as has been described previously (20).
Liver tumors were characterized as neoplastic nodules (31).
These nodules have also been designated as type A (30, 31),
type i or 2 (8), or adenomatous nodules (28) by other investi
gators.
RESULTS
Tumor-initiating Activity of MC Derivatives on Mouse Skin.
The development of skin tumors in CD-i mice after a single
CANCERRESEARCHVOL. 39
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TumorigeniCity of MC Metabolites
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topical application of 3 to 30 nmol of MC or several oxidative
metabolites of MC is summarized in Table i . Comparisons of
the percentage of mice with tumors and the average number of
tumors per mouse indicate that 4 compounds, MC, 2-hydroxy
MC, 2-keto-MC, and i -hydroxy-MC 9,1 0-dihydrodiol-@, had
approximately equipotent tumor-initiating activity and were
considerably more tumonigenic than were the other com
pounds. At 30 weeks of promotion with TPA, 59 to 68% of the
animals treated with 30 nmol of MC, 2-hydroxy-MC, 2-keto
MC, or i -hydroxy-MC 9,i 0-dihydrodioI-@ developed skin tu
mors with an average of i .4 to 2.i tumors per mouse. At the
30-nmol dose, 1- hydroxy-MC had i 6 to 24% of the tumor
initiating activity (papillomas per mouse) of the 4 most active
compounds, and i -keto-MC and MC i i ,i 2-dihydrodiol had
little or no tumorigenic activity. At the 3-nmol initiating dose, 2hydnoxy-MC appeared to be more tumorigenic than was MC.
i -Hydroxy-MC 9, i 0-dihydnodiol-@had little or no tumonigenic
activity at the 3-nmol dose, but at the i 0-nmol dose, it was at
least as active as were 2-hydroxy-MC and MC. Interestingly,
isomer
of i -hydroxy-MC 9,i 0-dihydrodiol had little or no
tumor-initiating activity at the single dose (10 nmol) tested. No
significant differences were observed in the latency period of
tumor development among the highly tumonigenic compounds
MC, 2-hydroxy-MC, 2-keto-MC, and i -hydroxy-MC 9, 10-di
hydrodiol-a.
Tumorigenicity of MC Derivatives in Newborn Mice. i Hydroxy-MC 9, i O-dihydrodiol-@was the most potent MC deny
ative tested for the induction of pulmonary tumors in the new
born mouse (Table 2). In mice treated with 2i or 49 nmol of i hydroxy-MC 9,1O-dihydrodiol-@, 58 and 94% of the animals
developed pulmonary tumors with an average of i .32 and 4.47
tumors per mouse, respectively. MC and 2-keto-MC had ap
1Tumorigenicity
Table
skinFemale
of MC and MC derivatives on mouse
singleinitiating
CD-i mice (7 to 8 weeks old) were treated topically with a
dose of MC or a derivative of MC in acetone:NH4OH (1000:1). Twice
weekly applications of the tumor promotor TPA (16 nmol/application) com
menced 7 days after the initiating compound was applied. At least 27 of 30
micein
each treatment group were alive after 30 weeks of promotion.%
Tumors!Initiator
mouseNone
miceDose of
with
(nmol)
tumors
0MC
0.4610
3
0.7430
2.101-Keto-MC
0.031-Hydroxy-MC
0
14
41
59
30
3
0.0710
3
0.2130
7
17
21
0.1810
3
1.2430
7
45
68
0.192-Keto-MC
-Hydroxy-MC 9, 10-dihydrodiol-b
10
14
1.482-Hydroxy-MC
30
66
0.7010
3
0.8730
43
43
59
0.1730
10
13
14
0.341
-Hydroxy-Md 9, 10-dihydrodioI-@
1.441
proximately one-half to one-third of the tumonigenic activity of
i -hydroxy-MC 9, i 0-dihydrodiol-@ when the data were ex
pressed as the average number of pulmonary tumors per
mouse. 2-Hydroxy-MC appeared to be slightly less active than
were MC and 2-keto-MC, producing tumors in 67% of the
animals with an average of i .03 tumors per mouse. As was
observed in the initiation-promotion experiments on mouse
skin, the compounds with the least tumonigenic activity in
newborn mice were 1-hydroxy-MC, i -keto-MC, and MC i i ,i 2dihydrodiol. The latter 2 compounds and MC i i ,i 2-oxide had
little, if any, activity at the doses tested. Most of the lung tumors
in the various treatment groups were identified as adenomas;
a few were adenocarcinomas. Hepatic tumors were also ob
served in male mice in several treatment groups. Histological
examination of all of the livers from male mice in the various
treatment groups indicated that i -hydroxy-MC 9, i 0-dihydro
dioI-@,2-hydroxy-MC, and MC produced a significant incidence
of hepatic tumors classified as neoplastic nodules (31 ). 1Hydroxy-MC 9, i 0-dihydrodioI-@ produced the highest mci
dence of hepatic tumors (percentage of mice with tumors) and
was also considerably more active than were MC and 2-hy
droxy-MC, based on the average number of neoplastic nodules
per mouse (Table 2).
DISCUSSION
The bay region theory of polycyclic aromatic hydrocarbon
carcinogenesis predicts that a 3-methylcholanthrene 9, i 0-diol
7,8-epoxide, if formed metabolically, would be a prime candi
date as an ultimate carcinogenic metabolite of MC (i 0, i 1).
Pertubational molecular orbital calculations have indicated that
an epoxide on a saturated, angular benzo ring that forms part
of the bay region of the hydrocarbon should have high chemical
reactivity and presumably high biological activity (i i ). Since
the bay region theory makes no attempt to take metabolic
factors into account, the carcmnogenicityof the parent hydno
carbon will also depend on the extent to which these bay
region diol-epoxides are formed metabolically. In the case of
MC, dihydrodiol formation appears to be a minor metabolic
pathway in the tissues and species studied to date (22—25).
However, i -hydnoxy-MC, a major metabolite of MC in rat liver
microsomes, has been shown (25) to be further metabolized to
a pair of diastereomenic 9,i 0-dihydrodiols (9% of total metab
olites).4
When MC and several oxygenated metabolites of the hydro
carbon were tested for their ability to be metabolically activated
to mutagenic metabolites in S. typhimurium strains TA98 and
TAi 00 and in Chinese hamster V79 cells, i -hydroxy-MC-9,i 0dihydrodiol was always activated to a greater extent than was
MC (32). In 4 of 5 different systems utilized, i-hydroxy-MC
9, i 0-dihydrodiol-@ was the most active substrate tested. 5ev
eral other metabolites of MC, including i -hydroxy-MC, 1-keto
4 Tierney
1.68MC
@
11,12-dihydrodiol
SEPTEMBER1979
0.17
et
al.
(26)
have
recently
reported
that
trans-9,i
0-dihydroxy-9,1
0-
dihydro-3-methylcholanthrene is a metabolite of MC as judged by cochromatog
raphy of a radioactive metabolite with trans-9, 10-dihydroxy-9,1 0-dihydro-3methylcholanthrene obtained by autoxidation of MC. However, the amount of this
dihydrodiol formed by rat liver microsomes is extremely small and represents
0.01 pmol/min/mg microsomal protein if one assumes a yield of 20 mg micro
somal protein per g liver and a constant rate of product formation for 30 mm of
incubation. This compares with a rate of formation of 1-hydroxy-MC-9, 10-dihy
drodiol from 1-hydroxy-Md of 206 pmol/min/mg microsomal protein calculated
from data reported by Thakker et al. (25).
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w.
Levin
et
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Table 2
Tumorigenicity of MC and MC metabolites in newborn mice
Swiss-Webster mice (BLU:Ha (ICR)] were given injections p. on the first, eighth, and 15th days of life with one-seventh, two-sevenths, and four-sevenths,
respectively, of the total dose of compound in dimethyl sulfoxide. The mice were weaned at 23 days of age and killed at 36 to 39 weeks of age. Lung and liver tumors
were confirmed by histological examination. Malignant lymphomas were found in 2 female mice treated with dimethyl sulfoxide, 1 female mouse treated with 21 nmol
Md, 2 female mice treated with 21 nmol 1-hydroxy-MC, 1 male and 1 female mouse treated with 49 nmol MC, and 2 female mice treated with 49 nmol 2-hydroxy-Md.
Spleen granulocyte leukemia was observed in 1 male mouse treated with 49 nmol 1-hydroxy-MC 9, 10-dihydrodioI-@.%
% of sun-
mouseDimethyl
Treatment
Total dose
(nmol)
sulfoxide
vival (35—
39 wk)
86
0.11MC
21
50
0.571
-Hydnoxy-MC
21
80
0.24i-Hydroxy-MC
9,iO-dihydnodiol-g
21
46
1.32MC
49
72
1.77i-Keto-MC
49
92
0.081
-Hydroxy-Md
49
80
0.29i
-Hydroxy-MC 9, 10-dihydnodiol-@
49
79
4.472-Keto-Md
49
63
2.082-Hydroxy-Md
49
79
1.03MCii,12-oxide
49
88
0.20MC
11,12-dihydnodiol
@
49
75
MC, and 2-keto-MC, were metabolized to products which had
high mutagenic activity in one or more of the test systems.
These results led us to the conclusions that a i -hydnoxy-MC
9,i 0-dihydrodiol was a prime candidate as a proximate carci
nogenic metabolite of MC and that other metabolites of MC
may also contribute to the high biological activity of this hydro
carbon (32). Additional evidence that MC is activated via the
formation of bay region diol epoxides has been reported from
2 independent studies on the nature of the DNA-bound adducts
of MC (i 3, 29). Both studies indicated the covalently bound
adducts were saturated in positions 7, 8, 9, and 10 of the
hydrocarbon, results consistent with the formation and binding
of a 9,i 0-diol-7,8-epoxide of MC. In further studies, King et a!.
(i 4) have concluded that another DNA-bound metabolite of
MC is a i - or 2-hydroxy derivative of MC saturated in positions
7, 8, 9, and i 0 of the molecule.
3552
Sex
No. of
% of mice
Av. no. of
of male
mice with
mice autopsied
with pulmonary tumors
tumons/
mouse
hepatic tumors
tumors!
Av. no. of
F
20
5
0.05
M
18
17
0.17
6
0.06
Total
38
ii
F
M
13
15
62
27
0.92
0.27
27
0.33
Total
28
43
F
M
Total
17
17
34
12
24
18
0.12
0.35
0
F
M
Total
9
10
19
44
70
58
0.78
1.80
50
1.30
F
M
19
21
84
81
1.79
1.76
19
0.43
Total
40
82
F
M
Total
20
20
40
10
5
8
0.10
0.05
0
0
F
M
Total
15
19
34
27
26
26
0.33
0.26
0
0
F
M
Total
15
21
36
100
90
94
5.27
3.90
81
4.33
F
M
Total
i6
21
37
94
81
86
2.44
1.80
14
0.14
F
M
Total
19
i4
33
68
64
67
1.21
0.79
35
0.35
F
M
Total
15
20
35
7
20
14
0.07
0.30
0
0
F
M
Total
15
15
30
7
20
13
0.07
0.20
0.13
7
0.07
0
Although isomer of 1-hydroxy-9,i 0-dihydrodiol was only
equipotent to MC in the mouse skin initiation-promotion tumor
model, it was 2- to 3-fold more active than was MC in producing
pulmonary tumors and 4- to i 0-fold more active than was MC
in producing hepatic tumors in newborn mice. Other metabo
lites of MC (2-keto-MC and 2-hydroxy-MC) had tumonigenic
activity comparable to MC in both tumor models. Interestingly,
1-keto-MC and i -hydroxy-MC were far less potent than was
MC in the mouse skin model and in newborn mice. Sims (2i)
previously reported that MC, i - and 2-hydroxy-MC, and i - and
2-keto-MC were all highly tumonigenic when injected s.c. in
mice. However, in the absence of a dose-response curve, any
ranking of the relative carcinogenic potency of the compounds
was not possible. Cavalieniet al. (3) ranked MC and 2-hydroxy
MC as the strongest carcinogens followed in order of decreas
ing activity by 2-keto-MC, i -hydroxy-MC, and i -keto-MC (in
CANCERRESEARCHVOL. 39
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Tumorigenicity of MC Metabolites
active) when the compounds were applied chronically on
mouse skin. These observations are consistent with the tumor
igenicity data presented here from initiation-promotion experi
ments on mouse skin and from studies in newborn mice. The
lack of tumorigenic activity of MC 1i ,i 2-oxide in newborn mice
is consistent with previous results showing poor tumorigenic
activity for this K-region oxide on mouse skin (2).
Certain chemical factors may play important roles in deter
mining the relative tumorigenic activity of various oxygenated
derivatives of MC. For example, 1-hydroxy-MC is very prone to
autoxidation to i -keto-MC. The low tumorigenic activity of both
of these compounds may be partially a reflection of the low
activity of 1-keto-MC. For electronic reasons, a 9, 10-diol-7,8epoxide of i -keto-MC would be expected to have reduced
chemical reactivity relative to the corresponding diol epoxide
from MC or i -hydroxy-MC. A 2-keto group would have a similar
deactivating effect but to a lesser extent.
The results of the present study on the tumorigenidity of MC
and several oxygenated metabolites of MC, together with our
previous report (32) on the mutagenicity of these compounds,
indicate that a i-hydroxy-9,iO-diol-7,8-epoxide
may be an
ultimate carcinogenic metabolite of the parent hydrocarbon.
Although it is clear that i -hydroxylation of MC markedly poten
tiates the formation of a 9,i 0-dihydrodiol (cf. Footnote 4), the
relative contribution of the i -hydroxylated versus the unhy
droxylated 9, i 0-dihydrodiol to the carcinogenicity of MC is
presently unknown. Evidence has been presented for high
biological activity of trans-9, i 0-dihydroxy-9, 10-dihydro-3methylcholanthrene (17) as well as the i -hydroxylated deriva
tive (32). However, both mutagenesis and tumorigenesis results
indicate that other oxidative metabolites of MC may contribute
to the carcinogenicity of this polycyclic hydrocarbon.
ACKNOWLEDGMENTS
We thank Nelson Montero and Dennis Tighe for their help in caring for the
animals and Ann Marie Williams for hen assistance in the preparation of this
manuscript. We thank Dr. Gary Williams, C. Q. Wong, and the staff of the Naylor
Dana Institute for Disease Prevention, American Health Foundation, Valhalla,
N. Y. for the histological studies.
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Downloaded from cancerres.aacrjournals.org on June 17, 2017. © 1979 American Association for Cancer Research.
Tumorigenic Activity of 3-Methylcholanthrene Metabolites on
Mouse Skin and in Newborn Mice
W. Levin, M. K. Buening, A. W. Wood, et al.
Cancer Res 1979;39:3549-3553.
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