NF-kappaB pathway inhibitors preferentially inhibit breast cancer stem-like cells

Abstract

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-kappaB 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-kappaB 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-kappaB 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.

Fig. 1

Growth inhibition of PTL, PDTC, DETC and paclitaxel on MCF7 sphere cells compared with MCF7 bulk cells

Fig. 2

(a) A representative MCF7 SP profile for sorting. MCF7 cells were stained as described in Methods. The MCF7 SP and non-SP regions are indicated by trapezoinds on the left (R5) and right (R8), respectively. (b) Growth inhibition of PTL, PDTC, DETC and paclitaxel on MCF7 SP cells, compared with MCF7 non-SP cells. (c) Inhibition of colony formation by PTL, PDTC, DETC and paclitaxel on MCF7 SP and non-SP cells

Fig. 3

Inhibition of NF-κB activity of MCF7 cells and MCF7 sphere cells after treatment with PTL, PDTC and DETC. Cells were treated with PTL, PDTC and DETC at 5 µM for 24 h. Nuclear extract was prepared from control and treated cells. The quantification of NF-κB activation was performed using Trans-AM NF-κB kit from ActiveMotif

Fig. 4

Antitumor effect of PDTC in vitro and in vivo. (a) Decreasing SP fraction within MCF7 cells by PDTC. (b) Growth inhibition effect of PDTC, paclitaxel and combination on MCF7 sphere cells. (c) In vivo anti-tumor growth effect of PDTC (60 mg/kg) paclitaxel (10 mg/kg) and combination on MCF7 xenograft. Treatment was given twice a week for four weeks. Tumor sizes were measured twice weekly