1. Isoliquiritigenin (ISL) is a natural pigment with the simple chalcone structure 4,2',4'-trihydroxychalcone. In the present study, we report, for the first time, ISL-induced inhibition of the proliferation of the human non-small cell lung cancer A549 cell line.

2. The results showed that ISL not only inhibited A549 cell proliferation, but also induced apoptosis and blocked cell cycle progression in the G1 phase. An ELISA assay demonstrated that ISL significantly increased the expression of p53 and p21/WAF1 protein, which caused cell cycle arrest.

3. An enhancement in Fas and its two ligands, namely membrane-bound Fas ligand (mFasL) and soluble Fas ligand (sFasL), may be responsible for the apoptotic effect induced by ISL.

4. Taken together, the results indicate that the p53 and Fas/FasL apoptotic system may participate in the antiproliferative activity of ISL in A549 cells.