ME-18 * INDUCTION OF M2 TYPE MACROPHAGES BY GBM CELLS

Abstract

Tumor associated macrophages (TAMS) have many roles in the tumor microenvironment. TAMs aid in pro-tumor mechanisms, such as invasion, migration, tumor proliferation, angiogenesis, and immunosupression. The predominant phenotype of TAMs is an M2 or anti-inflammatory phenotype. We utilized an in vitro culture system to investigate GBM cells' induction of M2 polarization in macrophages. THP-1 cells, a human monocytic cell line, were grown in conditioned media from three different GBM cell lines: G48, BTCOE 4795, and BTCOE 4536; the latter two are low passage explant cells. M2 activation markers (CD163, CD163L1, CD204, and CD206) and cytokine secretion profiles were assayed via immunoblotting and cytokine arrays respectively. The conditioned media of all GBM cell induced CD163, CD163L1, and CD204 expression in THP-1 cells. They also expressed prominently MCP-1, TNF-α, IL-3, GM-CSF, IL-8, GRO, IL-10, oncostatin and RANTES. These phenotypic characteristics were similar to our M2 positive controls which were monocytes induced by the classical anti-inflammatory paradigm, phorbol myristate acetate (PMA), IL-4, and IL-13. To further investigate how monocytes were polarized to M2 macrophages by GBM cells, we analyzed the secretomes of all three GBM cell lines using mass spectrometry. We have identified several candidates that play a role in macrophage recruitment and activation. Among a number of such factors, CCL-2 was a candidate protein identified by our proteomic analysis. We have been able to demonstrate M2 activation by CCL-2 in our in vitro monocyte cultures in follow up studies. These results indicate that GBM cells are able to induce monocytes to become M2 macrophages by a direct cross-communication. Further elucidation and understanding of these complex interactions should lead to developing novel therapies to circumvent TAMs pro-tumor mechanisms in the GBM microenvironment.