Introduction: Multiple reports have demonstrated that M2-polarized tumor associated macrophages (TAMs) play a significant role in promoting tumor metastasis, survival and resistance to chemotherapy. Thus, limiting the pro-tumorigenic activity of TAMs may hold great therapeutic promise. Objective: To determine whether targeting the Cluster of Differentiation 206 (CD206) receptor on TAMs with an engineered peptides having both CD206 specificity and apoptotic activity, will limit the protumorigenic effects of TAMs and enhance cancer cells response to chemotherapy. Method: A class of engineered peptides were designed to stimulate phagocytosis via the CD206 receptor, and to initiate apopotic cell death once endocytosed. Primary cells were isolated from C57BL/6J mice from Jackson Laboratory and were polarized to M1 and M2 phenotypes by treating with IL-4 (20ng/ml) and IFN-γ (10ng/ml) respectively from R&D Biosciences for 24 hrs. CD206 targeting peptide was biotin-labeled and utilized to treat M2-polarized cells. Precipitated proteins were analyzed by mass spectrometry analysis, and informatics software. In vitro proliferation and confirmation of apoptosis was assessed using Annexin/PI staining and Western blot analysis for Caspase 8 expression and activity. In xenograft models of triple negative breast cancer (MDA-MB-231), mice were treated with CD206 peptide and gemcitabine, singly or in combination Results: Mass spectrometry analysis of gel bands from the biotin / streptavidin pull down assay confirmed CD206 as a cell surface target. Bioinformatics analysis of the proteomics data from the pull down assay further confirmed that apoptotic proteins were highly expressed in the M2 populations than in the M1 populations. Treatment with CD206 peptide produced a significant decrease in cell proliferation only in M2 macrophages. FACS analysis of Annexin/PI staining and Caspase 8 activity, demonstrated by Western blot, showed that CD206 targeting peptide caused apoptosis specifically in M2 macrophages. In xenograft models of triple negative breast cancer (MDA-MB-231) mice treated with peptide alone (10 mg/kg qD subcu), there was a 39% reduction in tumor growth; gemcitabine @ 40 mg/kg q4D produced a 68% reduction; however, peptide in combination with gemcitabine completely blocked tumor growth. Moreover, immunohistochemistry staining of treated tumors showed a decrease in the expression of CD206 positive M2 macrophages and CD45/CD25 positive Treg cells, and an increase in CD86 positive M1 macrophages. These results were consistent with the in vitro results obtained. Discussion and Conclusion: These results suggest that a targeting CD206 peptide engineered to promote apoptosis, enhances the tumor response to chemotherapy by limiting the pro-tumorigenic activity of TAMs.

Citation Format: Anghesom A. Ghebremedhin, Clayton Yates, Jesse Jaynes, George Martin, Henry Lopez, Charles Garvin. A novel peptide-suppressing M2 polarized tumor-associated macrophages enhances tumor response to chemotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1640. doi:10.1158/1538-7445.AM2017-1640