The major challenge in breast cancer research pertains to tumor heterogeneity being a constant characteristic in the disease process. Although it is recognized that rare cancer cells drive the disease, there is a lack of suitable function-based assays to identify and focus on such cells for therapy development. Based on the hypothesis that only rare but highly adaptable cancer cells succeed in metastasizing, we have recently isolated rare (< 0.01% of population) highly metastatic cells present in an aggressive inflammatory breast cancer cell line SUM149. Using a variety of long-term adaptability assays we have found that such cells have adaptability to survive lack of glutamine, glucose, oxygen, and serum. Unlike the majority of cells, such cells have a high ability to dissociate their metabolic state from regulatory state, thus making them more resistant to chemotherapy drugs. These properties of cancer cells make them suitable for survival as resistant cells in the body, which often use quiescence as a way of surviving unfavorable conditions. As an initial step to optimize our in vitro system for evaluating potential personalized therapies, we compared the efficacy of several experimental targeted therapy drugs on metastatic Gln-independent variants and on parental SUM149 cell line. Since cell proliferation and apoptosis assays after a short exposure to experimental therapies are not good at predicting clinical response, we chose to determine therapeutic efficacy by analyzing residual/resistant cells after a relatively long exposure to therapy. Celecoxib, a COX-2 inhibitor (2-10 micromolar range), failed to inhibit resistant cells in both Gln-ind and parental SUM149 cell lines. At a 50 micromolar concentration, celecoxib eradicated all cells with a proliferative potential in the parental cell line but not in the Gln-ind subpopulation. Metformin, an anti-diabetes drug that activates AMPK and also inhibits “cancer stem cells,” was less effective in inhibiting Gln-ind cells than the parental cell line. BEZ235, a dual PI3K/mTOR inhibitor, sensitized Gln-ind and parental cells to the chemotherapy drugs doxorubicin and paclitaxel. However, Gln-ind cells yielded significantly more clonogenic (10-fold) cells after they were treated sequentially with BAZ235 and doxorubicin/paclitaxel. Salinomycin, a potassium ionophore and an inhibitor of “cancer stem cells,” was also less effective against Gln-ind cells. HDAC inhibitors, valproic acid, and butyrate, which are being evaluated as sensitizers to other therapies in various cancers, sensitized both Gln-ind and parental cell line to doxorubicin and paclitaxel. We conclude that the pair of cell lines used in this study will be useful in discovering strategies (e.g., novel therapies and ways to administer them) for eradicating metastatic breast cancer cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 879. doi:1538-7445.AM2012-879