Purpose: Macrophages are important components of leukocyte infiltrates in various tumor stroma. Macrophages that infiltrate into tumor tissues are called tumor-associated macrophages (TAMs). TAMs show anti-tumorigenesis(M1) or pro-tumorigenesis (M2) functions depending on the cytokine milieu of the tumor microenvironment. TAMs perform some key homeostatic functions that allow tumor maintenance and growth. However, the signals involved in communication between tumor cells and macrophages are poorly defined. The aim of this study is to explore the macrophage polarization treated with the tumor-conditioned medium.

Methods: Ana-1 macrophages, human THP-1 monocytes, and bone-marrow-derived macrophages (BMDMs) from C57BL/6J mice were incubated with HCT116-conditioned medium, respectively. Then we detected M1/M2 specific molecular markers by flow cytometry, Western blot and Real-time PCR. Flow cytometry was used to quantitatively assess the change of macrophage populations in macrophages treated with conditioned medium or normal medium. CD68(human) and CD11b(human), F4/80(mouse) and CD11b(mouse) were used as total-macrophage markers, CD206 as a marker of M2 macrophage. Secretory cytokine profile of the polarized macrophages was measured by cytokine array. Then, HCT116 cells were treated with conditioned medium of M2-like macrophage and applied to cell growth and colony formation assay.

Results: By Western blot, we found that HCT116-conditioned medium could induce BMDMs and Ana-1 cells to overexpress arginase1(Arg1), but Ana-1 cells to express low inducible nitric oxide synthase(iNOS). Flow cytometry showed high expression level of CD68(human) and CD11b(human), F4/80(mouse) and CD11b(mouse), CD206 in HCT116-conditioned medium induced macrophages. Additionally, mRNA level of Arg1 was higher and M2-related cytokines IL-10,IL13 were also significantly upregulated, while mRNA level of iNOS was lower and M1-related cytokines IL-12,IFN-γwere downregulated in HCT116-conditioned medium induced macrophages. Conditioned medium of M2-like macrophages promoted the HCT116 cell growth and proliferation.

Conclusions: HCT116 can secrete the soluble factors into conditioned medium, which would induce TAM polarization. Subsequently, conditioned medium of M2-like macrophages can promote tumor cells growth.

Citation Format: Weina Zhang. Functional polarization of macrophage triggered by tumor-conditioned medium. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 473. doi:10.1158/1538-7445.AM2015-473