DIFFERENTIAL PHENOTYPE MODULATION AND MOLECULAR MECHANISMS INDUCED BY LIPOXIN IN TUMOR-ASSOCIATED MACROPHAGES

INTRODUCTION AND OBJECTIVES: Macrophages are cells of the innate immune system and present as a heterogeneous population. Depending on the stimuli present in the inflammatory environment, they acquire two main profiles: M1, with pro-inflammatory characteristics, including high expression of markers such as CD86 and cytokines associated with the immune response, as well as the production of reactive oxygen species (ROS) and nitric oxide (NO), which are important for their cytotoxic capacity; and M2, with anti-inflammatory properties, characterized by an increase in markers such as CD206 and immunosuppressive mediators, playing a role in tissue remodeling. Once in the tumor microenvironment, tumor-associated macrophages (TAMs) exhibit an M2-like phenotype with tumor-promoting characteristics. Our group has shown that lipoxin (LX), a pro-resolving lipid mediator, triggers antitumor effects in melanoma-derived TAMs by selectively shifting M2 cells towards an M1-like profile, thereby restoring cytotoxic activities in vitro and decreasing tumor progression in vivo. In this work, we investigated the signaling mechanisms involved in the effects of LX on the phenotypes of TAMs derived from different tumors and the signaling pathways involved in these effects. MATERIAL AND METHODS: Human monocytes-derived macrophages were isolated and differentiated to TAM by treatment with conditioned medium (CM) from cultures of human melanoma (MV3), glioblastome (U373), and prostate cancer cells (PC-3). After 72 hours, they were treated with lipoxin (10nM) for an additional 72 hours. RESULTS AND CONCLUSION: TAMs derived from all types of tumor cells presented similar phenotype, expressing the M2 marker CD206 and decreased expression of the M1 marker CD86. When treated with lipoxin,TAMs  showed  reduced  expression  of  the  M2  marker  CD206, increased levels of CD86,ROS, and NO. Both MC MV3 and TAMs MV3 secrete high levels of VEGF. Additionally, we observed that, after the treatment with lipoxin, MV3 TAMs polarized in the absence of VEGF maintained their M2 phenotype with high expression of CD206. Thus, demonstrating that the effects of lipoxin on TAMs depends on the presence of VEGF in the CM during the M2/TAM polarization. Since the effect of lipoxin on TAMs depends on the presence of VEGF during the polarization of macrophages towards the M2/TAM profile, we detected that treatment with lipoxin reduced the phosphorylation of the VEGFR1 and increased the expression of SHP-1 in MV3 TAMs in relation to the other phenotypes. Thus, the data indicate that lipoxin negatively modulates the ability of these cells to assume the characteristic M2/TAM phenotype, leading the cell to an M1-like profile. Together, the data support that lipoxin can modulate the phenotypic and functional profile of TAMs from different types of tumors, from an M2 to M1 phenotype, in a manner dependent on the VEGF-VEGFR1 signaling pathway.