Figure 1.

Colon cancer stem cells (CSCs) are resistant toward chemotherapy. (a) Spheroid primary cultures were derived from primary human colorectal tumors and transduced with TOP-GFP construct. In these cultures, Wnt pathway activity drives the expression of GFP (TOP-GFP). These spheroid cultures with TOP-GFP (Co100) were treated with chemotherapy, for example, oxaliplatin for 24 h. Subsequently, spheroid cultures were stained with CaspGlow to measure caspase-3 activity. Cells are first gated on TOP-GFP^low (blue bar) and TOP-GFP^high (red bar), differentiated tumor cells and CSCs, respectively. Caspase-3 activity is then separately analyzed for the differentiated tumor cells and CSCs. (b) This method was used to test various chemotherapeutic therapies. Spheroid cultures treated for 24 h with oxaliplatin, cisplatin, 5-FU, etoposide, FOLFIRI and FOLFOX or 4 h with TRAIL are shown. Caspase-3 activity shows more cell death in differentiated cells compared with CSCs. Significance comparing differentiated versus CSCs is indicated (*P<0.05, **P<0.01, ***P<0.001)