Accumulating evidence indicates that breast cancer is caused by cancer stem cells and cure of breast cancer requires eradication of breast cancer stem cells. Previous studies with leukemia stem cells have shown that NF-κB pathway is important for leukemia stem cell survival. In this study, by using MCF7 sphere cells as model of breast cancer stem-like cells, we evaluated the effect of NF-κB pathway specific inhibitors on human breast cancer MCF7 sphere cells. Three inhibitors including parthenolide (PTL), pyrrolidinedithiocarbamate (PDTC) and its analog diethyldithiocarbamate (DETC) were found to preferentially inhibit MCF7 sphere cell proliferation. These compounds also showed preferential inhibition in term of proliferation and colony formation on MCF7 side population (SP) cells, a small fraction of MCF7 cells known to enrich in breast cancer stem-like cells. The preferential inhibition effect of these compounds was due to inhibition of the NF-κB activity in both MCF7 sphere and MCF7 cells, with higher inhibition effect on MCF7 sphere cells than on MCF7 cells. PDTC was further evaluated in vivo and showed significant tumor growth inhibition alone but had better tumor growth inhibition in combination with paclitaxel in the mouse xenograft model than either PDTC or paclitaxel alone. This study suggests that breast cancer stem-like cells could be selectively inhibited by targeting signaling pathways important for breast cancer stem-like cells.

An assay was developed to study the spontaneous transfer and transbilayer movement (flip-flop) of lipid analogs labeled with the fluorescent fatty acid, 5-(5,7-dimethyl BODIPY)-1-pentanoic acid (C5-DMB-) in large unilamellar lipid vesicles comprised of 1-palmitoyl-2-oleoyl phosphatidylcholine (POPC). The assay is based on the concentration-dependent changes in fluorescence intensity that occur when donor vesicles containing a C5-DMB-lipid are mixed with nonfluorescent acceptor vesicles. A kinetic model was developed to describe the time-dependent changes in concentration of a lipid undergoing both spontaneous transfer between unilamellar vesicles and transbilayer movement within the vesicle membranes, and a mathematical solution was obtained. Data were obtained using C5-DMB-labeled analogs of sphingomyelin (C5-DMB-SM), ceramide (C5-DMB-Cer), phosphatidylcholine (C5-DMB-PC), and diacylglycerol (C5-DMB-DAG), and kinetic parameters for each lipid were determined using a nonlinear least-squares fitting program. The half-times for interbilayer transfer of the lipids were C5-DMB-SM (21 s) < C5-DMB-PC (350 s) approximately C5-DMB-Cer (400 s) << C5-DMB-DAG (100 h). C5-DMB-Cer (t1/2 approximately 22 min) and C5-DMB-DAG (t1/2 approximately 70 ms) exhibited rapid spontaneous transbilayer movement, while C5-DMB-SM (t1/2 approximately 3.3 h) and C5-DMB-PC (t1/2 approximately 7.5 h) moved across the bilayer very slowly. These results provide a basis for interpreting the behavior of these lipid analogs in cells.

Oestrogen-responsive EBP50 may play an important role in tumour progression and might be a potential marker of invasiveness for breast cancer.