Targeted Killing of CSCs by CDF Figure 2. CDF and Curcumin decreased clonogenicity and invasion in AsPC-1, AsPC1-GTR, MIAPaCa-2, and MIAPaCa-2-GTR cells. Clonogenic assay (A) Invasion assay (B). Fluorescence of the invaded cells was read using ULTRA Multifunctional microplate reader (TECAN) at excitation/emission wavelengths of 530/590 nm. Basal level of ABCG2 expression showing relatively higher expression in drug resistant cell lines (C). doi:10.1371/journal.pone.0017850.g002 curcumin, and 20 nmol/L of gemcitabine were used to treat individually as well as in combination with gemcitabine for 72h. The results showed that CDF treatment in combination with gemcitabine caused a remarkable reduction of cell survival in all four cell lines compared to curcumin and gemcitabine combination treatment (Figure 3). Furthermore, analysis of drug combination treatment showed that the combination index after treatment with CDF in combination with gemcitabine was less than 1.00 (Figure 3), suggesting the synergistic effect of CDF combination. In contrast, the combination index with curcumin and gemcitabine was more than 1.00 (Figure 3), showing non-synergistic effect. Overall, these results suggest that CDF caused a much more significant reduction of cell survival in PC cells, compared to gemcitabine/curcumin alone or their combinations compared to CDF and gemcitabine combination. Figure 3. CDF and its combination with gemcitabine inhibited cell viability. MTT assay was conducted in all four cell lines after 72h of treatment with CDF, curcumin, or its combination with gemcitabine. Untreated control has been assigned a value of 100%. The p value shown represents comparisons between single agent and their combinations by using paired t-test. The combination Index (CI) ,1 for CDF and Gemcitabine combination indicates synergism. doi:10.1371/journal.pone.0017850.g003 PLoS ONE | www.plosone.org 4 March 2011 | Volume 6 | Issue 3 | e17850