PEITC treatment suppresses myeloid derived tumor suppressor cells to inhibit breast tumor growth.

Breast tumors are heterogeneous with a complex etiology. The immune system plays a crucial role in the development of tumors and can facilitate tumor growth pleiotropically. Myeloid derived suppressor cells (MDSCs) generate reactive oxygen species (ROS) and cytokines to suppress T cells, dendritic cells and natural killer (NK) cells. Hence, the inhibition of MDSCs could be an important strategy for anticancer therapeutics. Phenethyl isothiocyanate (PEITC), a bioactive compound present in cruciferous vegetables, is known to have anticancer properties. However, the effects of PEITC administration on the immune system have not been previously reported. In the current study, we evaluated the effects of administering PEITC to immunocompromised NOD-SCID IL2Rγ-/- (SCID/NSG) host mice bearing MDA-MB-231 xenografts on MDSCs in the peripheral blood. Our results reveal that oral administration of 12 μmol PEITC attenuated tumor growth by 76%. This was marked tumor-inhibitory phenotype was associated with a significant reduction in the levels of MDSCs bearing the surface markers CD33, CD34 and CD11b in PEITC treated mice, indicating that overall tumor growth suppression by PEITC correlates with inhibition of MDSCs. To the best of our knowledge, this is the first study showing effects of PEITC on MDSCs.