Antioxidant Reprogram Macrophages from Pro-Tumor M2 to Anti-Tumor M1

Macrophages (Mφ) have high plasticity and can polarize to two extremes, pro-inflammatory M1 Mφ and immuno-suppressive M2 Mφ. In breast cancer, tumor associated Mφ (TAM) have a pro-tumor M2-like phenotype and are associated with decreased survival. Thus, it is vital to develop treatments to reprogram TAM away from pro-tumor M2 Mφ toward anti-tumor M1 Mφ. A recent study reported a lipid peroxide scavenger selectively inhibits M2 Mφ markers and cytokines. However, little is known about the differences in reactive oxygen species (ROS) metabolism between M1 Mφ and M2 Mφ. Our hypothesis is pro-tumorigenic M2 Mφ possess a distinct profile of pro- and anti-oxidant enzymes, as well as a different sensitivity to ROS modulation versus the anti-tumor M1 Mφ. Our results show M2 Mφ, derived from primary human monocytes, have a significant 20-30% reduction in intracellular ROS levels versus M1 Mφ by DCFH and DHE staining. Extracellular ROS synthesis was dramatically reduced by ~70% in M2 Mφ, in part due to reduced mRNA expression of Nox2 and its accessory protein CYBA in M2 Mφ. Another contributing factor to lower ROS levels is that M2 Mφ have significantly increased Cu/ZnSOD and Gpx1 protein and activity, as well as increased Catalase mRNA expression. These data suggest M2 Mφ have increased ROS metabolism versus M1 Mφ, which may provide an advantage in the oxidative tumor microenvironment. Furthermore, EcSOD re-expression in MB231, a triple negative breast cancer cell line, inhibited the MB231-mediated increase in M2 Mφ markers and decrease in M1 Mφ markers. We moved forward utilizing Mn(III) meso-tetrakis(N-ethylpyridinium-2-yl)porphyrin (MnTE), a small molecule SOD mimetic, shown to have anti-tumor effects. MnTE treatment increased M1 Mφ markers, IL-12b and CD86, while concurrently decreasing M2 Mφ markers, IL-10, CD163, and C206. MnTE also inhibited the ability of M2 Mφ to inhibit T cell activation suggesting ROS is required for M2 Mφ polarization and function. These studies provide rationale for antioxidant treatment of breast cancer to reprogram TAM from pro-tumorigenic M2-like TAM phenotype to a more tumoricidal M1-like phenotype.