Abstract: ObjectiveTo investigate the effects and mechanisms of phloretin on the proliferation and apoptosis of human small cell lung cancer H446 cells. 
MethodsH446 cells were treated with 20， 30 or 40 μg／ml phloretin， and cells untreated were set as control. The proliferative rate of H446 cells treated with phloretin for 24， 48 and 72 h was detected by MTT assay； Apoptosis of cells treated with varied doses of phloretin was evaluated by flow cytometry method； The content of cytochrome C in cytosol was assessed by Western blotting method； Besides， mRNA expression of procaspase3， Bax and Bcl2 were examined by realtime PCR（QPCR）. 
ResultsThe dose of 20， 30 or 40 μg／ml phloretin could inhibite the proliferation of H446 cells in a dose and time dependent manner（P＜0.05）. Flow cytometry method showed that the apoptotic ratio of control group was（4.23±0.25）％， much lower than（12.97±0.21）％，（18.48±0.24）％ and（33.61±0.27）％ treated by 20， 30 or 40 μg／ml phloretin. Besides， the protein content of cytochrome C in cytosol was upregulated by phloretin in a dosedependent manner（P＜005）. Phloretin could dosedependently decrease the expression of Bcl2 mRNA（P＜0.05） and increase the mRNA expression of procaspase3 and Bax（P＜005）. 
ConclusionPhloretin can inhibit the proliferation of H446 cells and induce apoptosis by interfering the release of cytochrome C from mitochondria to cytosol and the mRNA expression of procaspase3， Bax and Bcl-2.

Key words: Small cell lung cancer, Phloretin, Proliferation, Apoptosis