Over the past few decades there has been dramatic progress in the treatment of cancer. However,for the four most common epithelial malignancies (lung, colon, breast and prostate cancers), the survival of patients with metastatic disease has not changed significantly. Emerging evidence suggest that tumors are driven by a small population of cells, termed cancer stem cells (CSCs), which may be resistant to the current therapeutic approaches. In breast carcinoma, the CSCs have been identified as a CD44+high\CD24-lowcell population that expresses stem cell markers, such as nestin and Oct-4. These rare cells are able to grow as non-adherent sphere-like structures, termed mammospheres.
In this study, we characterized nuclear enzymes in breast CSCs, such as topoisomerases and telomerase that are essential for tumor progression using the MCF7 human breast cancer cell line. We isolated MCF7-CSCs by growing floating cells, from adherent culture, on non-adherent plates, in a serum-free medium supplemented with growth factors. Mammosphere-derived cells were examined for several stem cell markers, compared to the parental adherent cells, and were found to contain a larger CD24-\lowpopulation, as well as higher level of nestin, which suggest that the mammospheres cells possessed stem cell properties. Topoisomerase I activity was decreased in mammospheres, compared to the adherent cells. In contrast, topoisomerase II and telomerase activities increased in mammosphere-derived cells, compared to the adherent cells. The sensitivity of the CSC to topoisomerase anti-cancer drugs was compatible with the activity of these enzymes. In addition, a decrease in nuclear structural proteins, β-actin and lamin B, was observed, compared to the adherent parental cells, probably due to the morphological changes caused by the growing conditions.
Understanding the biological behavior of essential enzymes in CSCs is important for developing new strategies for cancer treatment as well as new therapies for advanced disease.
