Disruption of CCL2 in Mesenchymal Stem Cells as an Anti-Tumor Approach against Prostate Cancer

SIMPLE SUMMARY: Cancer cells and mesenchymal stem cells (MSCs) secrete C-C motif chemokine ligand 2 (CCL2), a small protein that attracts tumor-associated macrophages (TAMs), which promotes malignant progression, such as drug resistance and metastasis. In addition, MSCs can also be recruited by CCL2; thus, a local milieu consisting of tumor cells, MSCs, and TAMs can promote tumor progression via a CCL2-dependent paracrine. The aim of the current study was to examine the functions of endogenous CCL2 of MSCs in cancer biology. Using a genetic engineering technique, we blocked the CCL2 expression in murine bone marrow-derived MSCs (CCL2 KO MSCs) and analyzed the effects on cancer progression. We found that CCL2 KO MSCs showed anti-tumor function when injected with murine prostate cancer cells into mice. The inhibitory effect was associated with an increase of CD45(+)CD11b(+) mononuclear myeloid cells in tumors. ABSTRACT: Background: MSCs are known to secrete abundant CCL2, which plays a crucial role in recruiting TAMs, promoting tumor progression. It is important to know whether disrupting MSC-derived CCL2 affects tumor growth. Methods: Murine bone marrow-derived MSCs were characterized by their surface markers and differentiation abilities. Proliferation and migration assays were performed in order to evaluate the functions of MSCs on cancer cells. CCL2 expression in MSCs was reduced by small interfering RNA (siRNA) or completely disrupted by CRISPR/Cas9 knockout (KO) approaches. An immune-competent syngeneic murine model of prostate cancer was applied in order to assess the role of tumor cell- and MSC-derived CCL2. The tumor microenvironment was analyzed to monitor the immune profile. Results: We confirmed that tumor cell-derived CCL2 was crucial for tumor growth and MSCs migration. CCL2 KO MSCs inhibited the migration of the monocyte/macrophage but not the proliferation of tumor cells in vitro. However, the mice co-injected with tumor cells and CCL2 KO MSCs exhibited anti-tumor effects when compared with those given tumor cell alone and with control MSCs, partly due to increased infiltration of CD45(+)CD11b(+)Ly6G(−) mononuclear myeloid cells. Conclusions: Disruption of MSC-derived CCL2 enhances anti-tumor functions in an immune-competent syngeneic mouse model for prostate cancer.