Modulation of tumor formation and intestinal cell migration by estrogens in the Apc^Min/+ mouse model of colorectal cancer

Epidemiological studies suggest that post-menopausal hormone replacement therapy (HRT) reduces colorectal cancer (CRC) incidence. Phytoestrogens, including the soy isoflavone genistein and coumestrol, are used by many women as alternatives to HRT. Previous studies showed that ovariectomy induced a 77% increase in intestinal adenoma number in the C57BL/6J-Min/+ (Min/+) mouse, an animal model of adenomatous polyposis coli (APC)-associated CRC. Replacement of estradiol (E₂) in ovariectomized Min/+ mice reduced tumor number to baseline and up-regulated the expression of estrogen receptor β (ERβ). We hypothesized that the phytoestrogens genistein and coumestrol would inhibit intestinal tumorigenesis in ovariectomized Min/+ mice. Min/+ and Apc ^+/+ (WT) mice were ovariectomized and assigned to either a control diet or treatment with E₂, genistein or coumestrol. Treatment of ovariectomized Min/+ (Min/+ OX) mice with genistein resulted in a non-significant reduction in tumor number. Min/+ OX mice treated with coumestrol had significantly fewer tumors than untreated Min/+ OX controls and the same number of tumors as non-ovariectomized Min/+ mice. Bromodeoxyuridine migration assays also demonstrated that treatment with E₂ or coumestrol improved enterocyte migration rate. Immunoprecipitation and immunohistochemistry analyses showed that impaired association of the adherens junction proteins E-cadherin and β-catenin in Min/+ mice was improved by treatment with either E₂ or coumestrol. Immunoblot analyses also showed that expression of ERβ was elevated in enterocytes of Min/+ OX mice treated with E₂ or coumestrol as compared with those of untreated Min/+ OX mice. In conclusion, both coumestrol and E₂ prevent intestinal tumorigenesis and ameliorate enterocyte migration and intercellular adhesion in the Apc^Min/+ mouse model of CRC.