afimoxifene and indole-3-carbinol

Indole-3-carbinol (I3C), a component of Brassica vegetables, is under study as a preventive agent of cancers of the breast and other organs. Following ingestion, I3C is converted to a series of oligomeric products that presumably are responsible for the in vivo effects of I3C. We report the effects of the major trimeric product, 5,6,11,12,17,18-hexahydrocyclonona[1,2-b:4,5-b':7,8-b' ']triindole (CTr), on the estrogen receptor (ER) signaling pathways. Tumor-promoting effects of high doses of I3C may be due to activation of aryl hydrocarbon receptor (AhR)-mediated pathways; therefore, we also examined the effects of CTr on AhR activated processes. We observed that CTr is a strong agonist of ER function. CTr stimulated the proliferation of estrogen-responsive MCF-7 cells to a level similar to that produced by estradiol (E(2)) but did not affect the growth of the estrogen-independent cell line, MDA-MD-231. CTr displaced E(2) in competitive-binding studies and activated ER-binding to an estrogen responsive DNA element in gel mobility shift assays with EC(50)s of about 0.1 microM. CTr activated transcription of an E(2)-responsive endogenous gene and exogenous reporter genes in transfected MCF-7 cells, also with high potency. CTr failed to activate AhR-mediated pathways, consistent with the low-binding affinity of CTr for the AhR reported previously. Comparisons of the conformational characteristics of CTr with other ER ligands indicated a remarkable similarity with tamoxifen, a selective ER antagonist used as a breast cancer therapeutic agent and suggest an excellent fit of CTr into the ligand-binding site of the ER.

Topics: Animals; Binding, Competitive; Cell Division; Electrophoresis, Polyacrylamide Gel; Humans; Indoles; Mice; Models, Molecular; Receptors, Aryl Hydrocarbon; Receptors, Estrogen; Signal Transduction; Tamoxifen; Transcriptional Activation; Tumor Cells, Cultured

The experiments performed in this study were designed to establish that (1) acquisition of anchorage-independent growth, a biological characteristic of tumorigenically transformed phenotype, can be modulated by prototypic tumor-suppressing agents, and (2) modulation of growth is influenced by the metabolic competence of the cells to biotransform estradiol, MCF-7 human breast carcinoma cells exhibited linear cell proliferative kinetics with a 41-hour population doubling time, and a 15% colony-forming efficiency in 0.33% agar. Indole-3-carbinol (13C), a naturally occurring tumor-suppressive agent; tamoxifen (TAM), an antiestrogenic agent; and 4-hydroxytamoxifen (4-OHTAM), a metabolite of TAM, demonstrated 73.7%, 72.5%, and 89.9% suppression in anchorage-independent growth of MCF-7 cells, respectively. At the metabolic level, 13C and 4-OHTAM induced 2.3-fold (P < 0.0001) and 1.3-fold increase (P = 0.001) relative to their own controls in the extent of 2-hydroxylation of estradiol. The results indicate that growth inhibition by 13C, TAM, and 4-OHTAM may in part be due to altered estradiol metabolism in MCF-7 cells. Thus, anchorage-independent growth and altered biotransformation of estradiol may constitute useful cellular and endocrine markers to evaluate the biological response of chemosuppressive agents.

Topics: Antineoplastic Agents; Breast Neoplasms; Cell Division; Estradiol; Humans; Hydroxylation; Indoles; Tamoxifen; Tumor Cells, Cultured