Breast cancer stem cells (BrCSC) are reported to be responsible for self-replication, treatment resistance, and metastases. Doubly enriched populations of BrCSC have been isolated using combined stem cell markers for CD44+/CD24- and increased levels of ALDEFLUOR® positivity based on aldehyde dehydrogenase enzyme activity. We have examined the sensitivity of doubly enriched populations of BrCSC isolated from basal-like breast cancer cell lines as regards anti-DR5 agonistic monoclonal antibody (TRA-8) mediated cytotoxicity. Methods: BrCSC were isolated and characterized from basal breast cancer cell lines (SUM159, SUM149, HCC38 and 2LMP) based on the intracellular accumulation of ALDEFLUOR® reagent and CD44+/CD24- surface expression by flow cytometry. DR5 expression on the BrCSC subpopulation, in vitro cytotoxicity after 24 h exposure to TRA-8, and caspase activation after TRA-8 exposure were evaluated. The effects of TRA-8 on secondary tumorosphere formation were also investigated. Results: Unsorted basal-like cell lines were highly sensitive to TRA-8 mediated cytotoxicity with IC50 values of 0.7-3.0 ng/ml. Doubly enriched CD44+/CD24/ALDEFLUOR+ BrCSC from these cell lines exhibited comparable DR5 expression and were similarly highly sensitive to TRA-8 induced cytotoxicity with rapid induction of caspase 3 and 8 cleavage. Secondary tumorosphere formation was greater than 90% inhibited by TRA-8 exposure. An agonistic anti-DR4 monoclonal antibody (2E12) had no effect, and TRAIL was only partially inhibitory to secondary tumorosphere formation at equimolar concentrations. TRA-8 effect on BrCSC tumorigenicity will be presented. These studies suggest that TRA-8 may be an effective targeted therapy directed at BrCSC in basal-like breast cancer patients.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr LB-260.