Olive Leaf Extract Reduces Myeloid-Derived Suppressor Cells, and Modulates the Function of Residual Cells in Experimental Model of Melanoma

Background: Immunosuppression in melanoma is mediated by increased accumulation of Myeloid Derived Suppressor Cells (MDSCs). Olive Leaf Extract (OLE) has been developed as a natural anti-inflammatory, anti-oxidant, anti-proliferative and antiapoptotic agent on cancer immunotherapy. Objective: To investigate whether OLE could inhibit MDSCs, enhance anti-tumor activities and consequently increase the survival rate of the murine melanoma model. Methods: The C57BL/6 mice were inoculated subcutaneously with B16/F10 melanoma tumor cell lines. Induced mice were orally treated with 500 mgkg-1 of olive extract per kg of body weight for 8 consecutive days. The frequency and function of MDSCs and induction of inflammatory mediators as well as tumor growth and survival rate were assessed in treated and untreated mice. Results: The results of current study revealed that the optimal dose of OLE (500 mgkg-1) reduced the tumor growth (40%), and prolonged mice survival (25%) by significant decreasing (P<0.05) the number (over 50%), and suppressive function of MDSCs (over 60%) (P<0.05). OLE was also significantly (P<0.05) down regulated the induction of inflammatory agents in melanoma-bearing mice (over 50%) at the applied dose (500 mgkg-1). Conclusion: Therefore, these results altogether provided some evidence that regulation of immunosuppression were the possible therapeutic effects of OLE in tumor cells.