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Molecular origin of cancer: catechol estrogen-3,4-quinones as endogenous tumor initiators
E L Cavalieri1, D E Stack, P D Devanesan
1Eppley Institute for Research in Cancer, University of Nebraska Medical Center, 600 South 42nd Street, Omaha, NE 68198-6805, USA. ecavalie@unmc.edu
Abstract:
Cancer is a disease that begins with mutation of critical genes: oncogenes and tumor suppressor genes. Our research on carcinogenic aromatic hydrocarbons indicates that depurinating hydrocarbon-DNA adducts generate oncogenic mutations found in mouse skin papillomas (Proc. Natl. Acad. Sci. USA 92:10422, 1995). These mutations arise by mis-replication of unrepaired apurinic sites derived from the loss of depurinating adducts. This relationship led us to postulate that oxidation of the carcinogenic 4-hydroxy catechol estrogens (CE) of estrone (E1) and estradiol (E2) to catechol estrogen-3,4-quinones (CE-3, 4-Q) results in electrophilic intermediates that covalently bind to DNA to form depurinating adducts. The resultant apurinic sites in critical genes can generate mutations that may initiate various human cancers. The noncarcinogenic 2-hydroxy CE are oxidized to CE-2,3-Q and form only stable DNA adducts. As reported here, the CE-3,4-Q were bound to DNA in vitro to form the depurinating adduct 4-OHE1(E2)-1(alpha,beta)-N7Gua at 59-213 micromol/mol DNA-phosphate whereas the level of stable adducts was 0.1 micromol/mol DNA-phosphate. In female Sprague-Dawley rats treated by intramammillary injection of E2-3,4-Q (200 nmol) at four mammary glands, the mammary tissue contained 2.3 micromol 4-OHE2-1(alpha, beta)-N7Gua/molDNA-phosphate. When 4-OHE1(E2) were activated by horseradish peroxidase, lactoperoxidase, or cytochrome P450, 87-440 micromol of 4-OHE1(E2)-1(alpha, beta)-N7Gua was formed. After treatment with 4-OHE2, rat mammary tissue contained 1.4 micromol of adduct/mol DNA-phosphate. In each case, the level of stable adducts was negligible. These results, complemented by other data, strongly support the hypothesis that CE-3,4-Q are endogenous tumor initiators.
Insights
Catechol estrogens (CE) can form DNA adducts that initiate cancer. Our research shows carcinogenic CE-3,4-quinones form depurinating DNA adducts, acting as endogenous tumor initiators.
Area of Science:
- Biochemistry
- Molecular Biology
- Carcinogenesis
Background:
- Cancer initiation involves critical gene mutations.
- Carcinogenic aromatic hydrocarbons form depurinating DNA adducts, leading to mutations.
- Catechol estrogens (CE) are implicated in cancer development.
Purpose of the Study:
- To investigate the hypothesis that oxidized carcinogenic CE-3,4-quinones form depurinating DNA adducts, initiating cancer.
- To compare DNA adduct formation by carcinogenic CE-3,4-quinones versus noncarcinogenic 2-hydroxy CE.
- To assess the in vivo and in vitro formation of depurinating adducts from CE.
Main Methods:
- In vitro binding of CE-3,4-quinones to DNA.
- In vivo administration of estradiol-3,4-quinone to Sprague-Dawley rats.
- Activation of 4-hydroxyestrogens using enzymatic systems (horseradish peroxidase, lactoperoxidase, cytochrome P450).
- Quantification of depurinating and stable DNA adducts.
Main Results:
- CE-3,4-quinones formed significant levels of depurinating adducts (4-OHE1(E2)-1(alpha,beta)-N7Gua) in vitro and in vivo.
- In vitro, depurinating adducts were formed at 59-213 micromol/mol DNA-phosphate, while stable adducts were negligible.
- In vivo, rat mammary tissue showed 2.3 micromol 4-OHE2-1(alpha, beta)-N7Gua/molDNA-phosphate after treatment.
- Enzymatic activation yielded high levels of depurinating adducts (87-440 micromol).
- Stable adducts were formed at negligible levels in all experiments.
Conclusions:
- Oxidation of carcinogenic CE-3,4-quinones generates electrophilic intermediates that form depurinating DNA adducts.
- These depurinating adducts lead to apurinic sites, potentially initiating mutations and cancer.
- CE-3,4-quinones are strongly supported as endogenous tumor initiators.