Fig. (3) Validation testing with clinically used cancer drugs. To show that CK5Pro-GFP is a selective reporter for the CSC phenotype we utilized the clinically used cancer drugs 5FU and Tamoxifen. MCTS were treated with 100 nM P4 and 1 μM 5FU or Tamoxifen for 72 h. The CK5Pro-GFP activity was quantitated using the sum of A) Fluorescence intensity and B) Area of GFP expression. The mean and SEM were obtained using four MCTS per treatment group and the data were normalized to the control group (100 nM P4 + vehicle). These data indicate that CSC phenotype is not downregulated as a result of cytotoxicity caused by 5FU and the estrogen receptor antagonist Tamoxifen.