Induction by estrogen metabolite 16 alpha-hydroxyestrone of genotoxic damage and aberrant proliferation in mouse mammary epithelial cells.
BACKGROUND
Estrogens are potent mammary tumor promoters influencing post-initiation events via epigenetic mechanisms. The upregulation (i.e., induction) of the C16 alpha-hydroxylation pathway during 17 beta-estradiol (E2) biotransformation has been associated with mammary cell transformation. The action of E2 metabolites on tumorigenic transformation, however, is poorly understood.


OBJECTIVE
The newly established mammary epithelial cell line C57/MG, derived from the C57BL mouse strain, was used to examine whether E2 or its metabolites, 16-hydroxyestrone (16 alpha-OHE1) and estriol (E3), function as initiators of mammary cell transformation.


METHODS
DNA repair (hydroxyurea-insensitive thymidine uptake), estrogen metabolism (3H exchange to form 3H2O), hyperproliferation (increased cell number), and acquisition of anchorage-independent growth (soft-agar colonies) were used as quantitative end points to measure the relative extent of transformation.


RESULTS
Treatment of cells with 200 ng/mL 16 alpha-OHE1 resulted in a 55.2% increase in DNA repair synthesis, a 23.09% increase in proliferative activity, and a 18-fold increase in the number of soft-agar colonies, relative to the solvent controls (P less than .0001). The extent of upregulation of the three end points was similar to that induced by the genotoxic mammary carcinogen 7, 12-dimethylbenz[a]anthracene (DMBA, positive control). DMBA treatment also upregulated the ratio of 16 alpha/C2 hydroxylation of E2 leading to increased formation of 16 alpha-OHE1. E2 and E3 were not effective in upregulating these markers for transformation.


CONCLUSIONS
These results demonstrate that in nontransformed C57/MG cells, 16 alpha-OHE1 may function as an initiator, perturbing the intermediate biomarkers for preneoplastic transformation.
Telang
N T
NT
Breast Cancer Research Laboratory, Memorial Sloan-Kettering Cancer Center, New York, NY 10021.
Suto
A
A
Wong
G Y
GY
Osborne
M P
MP
Bradlow
H L
HL
D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002471:Cell Transformation, Neoplastic / Q000139:chemically induced* / Q000235:genetics; D004260:DNA Repair; D004958:Estradiol / Q000378:metabolism* / Q000633:toxicity*; D005260:Female; D006894:Hydroxyestrones / Q000633:toxicity*; D008325:Mammary Neoplasms, Experimental / Q000139:chemically induced* / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D014407:Tumor Cells, Cultured
D006894:Hydroxyestrones; C026702:16-hydroxyestrone; D004958:Estradiol