2.7. Cytotoxicity

The cytotoxic assays of curcumin, curcumin liposomes and gemcitabine against normal human bronchial epithelial cells (BEAS-2B, provided by Z. Yang from BIRM) and human lung cancer A549 cells (provided by Chinese Academy of Medical Sciences, China) were performed with CCK-8 kits (Gen-View Scientific Inc., USA). Cells were seeded at a density of 5×10⁵ cells/well and incubated at 37 °C for 24 h. Curcumin was dissolved in a small volume of dimethyl sulphoxide (DMSO) and then diluted with the HLC-8 culture media and the DMEM culture media (Gibco, USA) for use with BEAS-2B and A549 cells, respectively, where DMSO was less than 0.1% in the final dilutions. LCDs and gemcitabine were also dispersed in the above culture media. A series of drug concentrations, including 6.25, 12.5, 25, 50 and 100 μmol/L of curcumin or gemcitabine, were tested for cytotoxicity. The cells were incubated with these dilutions for 24 h. The CCK-8 reagents were added into the wells and then incubated for 4 h. They were measured at 450 nm using a microplate reader (ELX800, BioTek Instrument, Inc, USA). Cell viability was calculated as (absorbance of sample)/(absorbance of control)×100%. The selection index is defined as the viability ratio of A549/BEAS-2B.