Effects of chemopreventive and antitelomerase agents on the spontaneous immortalization of breast epithelial cells

Background: Activation of telomerase is an early event in the development o f breast and other cancers that may lead to cell immortalization, a critica l and rate-limiting step in cancer progression. Breast epithelial cells fro m women with Li-Fraumeni syndrome (LFS) immortalize spontaneously and repro ducibly in culture. We, therefore, tested whether immortalization of these cells could be prevented by treating them with chemopreventive agents and b y inhibiting telomerase activity, Methods: Noncancerous, preimmortal breast epithelial cells derived from a patient with LFS were treated for 3 months with nontoxic concentrations of the chemopreventive agents oltipraz, diflu oromethylornithine, tamoxifen, and retinoic acid or with two different telo merase inhibitors. The frequency of spontaneous immortalization of LFS-deri ved cells was estimated by an approach based on fluctuation analyses. Stati stical analyses were two-sided. Results: The frequency of spontaneous immor talization events of LFS-derived breast epithelial cells was reduced by lon g-term treatment with retinoic acid (P<.001) or tamoxifen (P<.05) compared with solvent-treated cells. The frequency of immortalization was also reduc ed by treating LFS-derived cells with an antitelomerase antisense oligonucl eotide (P<.001) or by inducing the cells to express a dominant negative mut ant of telomerase (P<.025) compared with cells treated with a control oligo nucleotide or with empty vector, respectively. Conclusions: Treatment of pr eimmortal LFS breast epithelial cells with chemopreventive and antitelomera se agents decreased the frequency of spontaneous immortalization in vitro. These studies validate the application of a new cell culture model system t o screen the effects of novel chemopreventive agents by use of cell immorta lization as an end point. The results also suggest that the telomerase ribo nucleoprotein complex may be an important molecular target for breast cance r prevention.