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Estradiol and its metabolites 4‐hydroxyestradiol and 2‐hydroxyestradiol induce mutations in human breast epithelial cells

An elevated incidence of breast cancer in women has been associated with prolonged exposure to high levels of estrogens. Our laboratory demonstrated that treatment of the immortalized human breast epithelial cells MCF‐10F with 17β‐estradiol (E2), 4‐hydroxyestradiol (4‐OHE2) or 2‐hydroxyestradiol (2‐OHE2) induces phenotypical changes indicative of neoplastic transformation. MCF‐10F cells treated with E2, 4‐OHE2 or 2‐OHE2 formed colonies in agar methocel and lost their ductulogenic capacity in collagen, expressing phenotypes similar to those induced by the carcinogen benzo[a]pyrene. To investigate whether the transformation phenotypes were associated with genomic changes, cells treated with E2, 4‐OHE2 or 2‐OHE2 at different doses were analyzed using microsatellite markers. Since microsatellite instability (MSI) and loss of heterozygosity (LOH) in chromosomes 13 and 17 have been reported in human breast carcinomas, we tested these parameters in MCF‐10F cells treated with E2, 2‐OHE2, or 4‐OHE2 alone or in combination with the antiestrogen ICI182780. MCF‐10F cells treated with E2 or 4‐OHE2, either alone or in combination with ICI182780, exhibited LOH in the region 13q12.3 with the marker D13S893 located at ∼0.8 cM telomeric to BRCA2. Cells treated with E2 or 4‐OHE2 at doses of 0.007 and 70 nM and 2‐OHE2 only at a higher dose (3.6 μM) showed a complete loss of 1 allele with D13S893. For chromosome 17, differences were found using the marker TP53‐Dint located in exon 4 of p53. Cells treated with E2 or 4‐OHE2 at doses of 0.007 nM and 70 nM and 2‐OHE2 only at a higher dose (3.6 μM) exhibited a 5 bp deletion in p53 exon 4. Our results show that E2 and its catechol estrogen metabolites are mutagenic in human breast epithelial cells. ICI182780 did not prevent these mutations, indicating that the carcinogenic effect of E2 is mainly through its reactive metabolites 4‐OHE2 and 2‐OHE2, with 4‐OHE2 and E2 being mutagenic at lower doses than 2‐OHE2. © 2005 Wiley‐Liss, Inc.