Phloretin induces apoptosis of human esophageal cancer via a mitochondria-dependent pathway

2,4,6-trihydroxy-3-(4-hydroxyphenyl) propiophenone (phloretin) is found in apple tree leaves and the Manchurian apricot, and is a potent compound that exhibits antiinflammatory, antioxidant and antitumor activities. However, the effect of phloretin on esophageal cancer cells is not well-defined. The present study aimed to examine whether and how phloretin induced apoptosis in human esophageal cancer cells. EC-109 cells were cultured in Dulbecco's modified Eagle's medium and incubated with 60, 70, 80, 90 and 100 mu g/ml phloretin for 6, 12, 24 and 48 h. Cell proliferation was measured by an MTT assay. Cell apoptosis rate was measured using flow cytometric analysis subsequent to propidium iodide (PI) staining. The protein expression levels were determined by western blot analysis. It was found that phloretin significantly decreased viable cell numbers in a dose- and time-dependent manner and induced apoptosis in EC-109 cells. Additionally, phloretin exhibited potent anticancer activity in vitro, as evidenced by the downregulation of the anti-apoptosis-associated molecule B-cell lymphoma 2 (bcl-2) and an increase in the levels of the apoptosis-associated molecules bcl-2-like protein 4 and tumor protein p53. Phloretin treatment also affected the expression of apoptotic protease activating factor-1, the protein product of the direct binding of the inhibitor of apoptosis protein with low PI to the X-linked inhibitor of apoptosis protein. The present results indicated that phloretin may inhibit EC-109 cell growth by inducing apoptosis, which may be mediated through a mitochondria-dependent pathway.