Effects of Oleuropein on colon cancer progression in vitro. A preliminary report

Introduction. Accumulating evidence highlights that Oleuropein (OLE), one of the main bioactive phenolic compound present in olives, olive oil and olive leaves, appears to exert chemo-preventive effects against several human malignancies including gastrointestinal tumors. As the cellular mechanisms underlying this phenomenon are still not fully elucidated, we have undertaken some in vitro studies to examine the effects of OLE on the growth, adhesion and invasion of HTC116 and SW480 human colon cancer cells and the influence of this molecule on the production of certain proteins that appear to be relevant to cancer progression namely, matrix metalloproteinase-2 (MMP-2), matrix metalloproteinase-9 (MMP-9) and transforming growth factor-β (TGF-β) Methods. The effects of OLE on HTC116 and SW480 colon cancer cells growth, adhesion and invasion were evaluated by i) the colorimetric MTT assay, ii) the fibronectin coated multi-well assay and iii) the Matrigel transwell invasion assay, respectively. The influence of OLE on the rate of MMP-2, MMP-9 and TGF-β secretion by tumor cells during adhesion and invasion were determined by enzyme-linked immunosorbent assay. Results. 1)Exposure of human HCT116 and SW480 cancer cells for 24 or 72h to different concentrations of OLE (10-500 µM) resulted in a dose- and time-dependent inhibition of cell proliferation. The calculated IC50 values were 323.1µM and 186.8µM at 24h and 72h respectively for HCT116 tumor cells and 317.6µM at 24h and 226.8 µM at 72h for SW480 tumor cells. 2) The adhesion of HTC116 tumor cells exposed to non-cytotoxic concentrations of OLE (50-250 µM) up to 4h was reduced by 30% as compared to untreated cells while, a 72h continuous exposure to OLE (10-100 µM) decreased HTC116 cell invasion by 40%. This molecule showed to inhibit also SW480 tumor cell adhesion (-25%) but only at the highest drug concentration (250 µM) while, its effects on SW480 invasion were negligible. 3) The secretion of MMP-2, MMP-9 and TGF-β by OLE-treated HCT116 cells during adhesion experiments was reduced (-39%,-19%,-48% respectively) as compared to unexposed cells while, in invasion experiments, the extracellular release of MMP-2 and MMP-9 resulted increased at 24h (+41% and +23%) and then decreased (~ -25%) after 72h. However, TGF-β secretion was not significantly influenced by drug treatments. Finally, in invasion experiments, MMP-9 and TGF-β secretion by OLE-treated SW480 cells resulted impaired (-32% and-74% respectively) while, MMP-2 levels were only slightly affected ( -10%) Conclusions. These data indicate that OLE might exert its chemo-preventive effects by interfering with some key steps of cancer progression, such as tumor cell proliferation, adhesion and invasion and by modulating the extracellular secretion of proteins that may foster these processes. Further studies to better assess the specific molecular mechanisms underlying these phenomena are warranted by these preliminary observations.