Hydroxytyrosol rich extract from olive leaves modulates cell cycle progression in MCF-7 human breast cancer cells

Throughout the history, olive (Olea europea L.) leaves have been heavily exploited for the prevention or the treatment of hypertension, carcinogenesis, diabetes, atherosclerosis and so many other traditional therapeutic uses. These activities are thought to be the output of olive micronutrients especially polyphenols. Hydroxytyrosol and oleuropein are considered as major polyphenolic compounds in olive leaf. In this work, a hydroxytyrosol rich olive leaves extract was investigated for potential anti-tumoral activities. In vitro cytotoxic effects against MCF-7 breast cancer cells were examined using MTT and neutral red tests. The anti-tumor activities were further investigated by flow cytometry and western blotting. Cytotoxicity assays resulted in a dose dependent growth inhibition of MCF-7 cells. This inhibition was due to the cell cycle arrest in the G0/G1 phase. The understanding of the molecular mechanism by which olive leaves extract arrested cell growth showed a down-expression of the peptidyl-prolyl cis-trans isomerase Pin1 which in turn decreased the level of a G1 key protein; Cyclin D1. Additionally, olive leaves extract treatment up-regulated the AP1 transcription factor member, c-jun. Therefore, olive leaves extract will necessitate further deep investigation for a probable use as a cancer preventive food additive.