Does Combination of DNR and Casticin show advantage in favor of apoptosis on AML leukemia stem-like cell lines? A preliminary study

Acute myeloid leukemia (AML) is a form of acute leukemia with the highest incidence and the lowest overall survival rates. Insufficiency of targeting leukemia stem cells (LSC) is the main obstacle that causes drug resistance and relapse in AML. Another important problem is chemotherapeutics' toxicity. Developing a combination, including well-known chemotherapeutics in lower dose and new agent that have capacity to target LSC may be more reliable and practical way to overcome these limitations. Previously, we found that Casticin polyphenol induces apoptosis in AML stem-like (KG1a) and parental (KG1) cell lines without affecting healthy cell. Therefore, for the first time, we aimed to find synergistic combination of Daunorubicin (DNR) and Casticin to target apoptosis in both LSC and leukemic blasts with less toxicity. Synergism of DNR-Casticin combinations on KG1a, KG1, HL-60 cells were determined with MTT viability assay by Chou-Talalay method. The apoptotic/necrotic effects of combinations were evaluated with Annexin V- PI kit by flow cytometry. Synergistic combination of 0.25 mu M DNR + 0.0625 mu M Casticin (combination index, CI<1) decreased cell viability to 45.3% and 63.2% in KG1a, KG1 cell lines, respectively. However, the combination-induced apoptosis (KG1a: 5 %; KG1: 5.8%) were not higher than 0.25 mu M DNR-induced (KG1a: 9.4%; KG1: 8.1%) or 0.0625 mu M Casticin-induced (KG1a: 3.8%; KG1: 5.1%) apoptosis (p>0.05). Our study showed that synergistic combination of DNR-Casticin causes important decrease in cell viability. Although we did not detect increase in apoptosis with the combination, we presume that other cell death pathways may be included. The highest apoptosis was obtained by the treatment of 2 mu M Casticin alone in KG1a (21.7%), KG1 (26.5%), HL-60 (14.6%). Therefore, we think that Casticin polyphenol might be the possible candidate for new targeted therapy studies for AML.