Tumor initiating cells: Development and critical characterization of a model derived from the A431 carcinoma cell line forming spheres in suspension

Abstract

To investigate the tumor fraction with cancer stem/tumor initiating cell (CSC/TIC) characteristics, we tested the human cervical carcinoma cell lines A431, Caski and SiHa, by growth as non-adherent spheres in specific media and aldehyde dehydrogenase (ALDH) enzymatic activity. A good correlation between the two parameters was observed and the highest levels were observed in A431 cell line that was selected for characterization of the CSC/TIC fraction. A431 parental cells already displayed characteristics common to CSC/TIC, such as sphere forming efficiency, adherent holoclone formation and high ALDH activity. Non-adherent spheres maintained or increased these properties, and, in particular, ALDH-positive fraction increased from 46 to 65% and a transient induction of stem cell markers such as Nanog, Nestin and Oct4 was observed. Furthermore, a significant increase of paraclone forming cells was observed, suggesting that differentiation took place inside sphere cell populations. As compared to parental cells, spheres were characterized by: (1) a ten-fold higher verapamil-sensitive side population fraction; (2) the appearance of a podoplanin-positive subpopulation characterized by a small cell size; (3) the ability to propagate tumors in nude mice at a lower cell dose. The global gene expression analysis demonstrated a strong and reversible modulation of 'sphere' phenotype in comparison to parental and sphere cells re-induced to adherent conditions. All together our results indicated that the growth of A431 cells as a non-adherent sphere was not sufficient by itself to define a stem-like population, but it was essential for the emergence of a small population of tumor cells with CSC properties.

Clinical significance of Gremlin 1 in cervical cancer and its effects on cancer stem cell maintenance

“…For instance, CD44-or CD133-positive cells are known to be more tumorigenic than negative ones in ovarian cancer (29,30). Similar findings have been suggested for side population (SP) cells in endometrial cancer and ALDH1-positive cells in cervical cancer (31)(32)(33)(34)(35)(36). Gremlin 1 is also reported to be expressed in cervical cancer compared to normal tissues of the cervix (37).…”

Cancer cells in epithelial-to-mesenchymal transition and tumor-propagating–cancer stem cells: distinct, overlapping or same populations

“…As expected from the reversibility concept, in human cervical cancer cell lines, cells with a CSC-TPC-like phenotype, after growth as non-adherent cells in vitro, (stem cell markers, ALDH activity, verapamil resistance) completely revert their phenotype after growth in adherent conditions (Bortolomai et al, 2010). Even the supposedly irreversible senescence allows after long delays the emergence of clones with genetic aberration and sustained proliferation (Gosselin et al, 2009).…”

Involvement of Akt and mTOR in chemotherapeutic- and hormonal-based drug resistance and response to radiation in breast cancer cells

“…PTEN can be mutated or silenced by various mechanisms in human cancer and clearly this pathway plays important roles in breast and other cancers and the generation of cancer stem cells. [105][106][107][108][109][110] Mutations occur which either delete the PTEN gene or alter its activity. Sometimes these mutations actually make the cells sensitive to Akt and mTOR inhibitors as the growth of the cells becomes dependent upon elevated Akt levels and downstream mTOR and p70S6K activities.…”