MCP-1 acts as a paracrine and autocrine factor for CaP growth and invasion.

Prostate cancer preferentially metastasizes to bone, resulting in high mortality. Strategies to inhibit prostate cancer metastasis include targeting both tumor-induced osteoblastic lesions and underlying osteoclastic activities. We and others have previously shown that blocking receptor activator of nuclear factor-KB ligand (RANKL) partially blocks tumor establishment and progression in bone in murine models. However, levels of RANKL in the cell lines used in these studies were very low, suggesting that soluble factors other than RANKL may mediate the cancer-induced osteoclast activity. To identify these factors, a human cytokine antibody array was used to measure cytokine expression in conditioned medium collected from primary prostate epithelial cells (PrEC), prostate cancer LNCaP and its derivative C4-2B, and PC3 cells. All prostate cancer cells produced high amounts of monocyte chemotactic protein-1 (MCP-1) compared with PrEC cells. Furthermore, levels of interleukin (IL)-6, IL-8, GROA, ENA-78, and CXCL-16 were higher in PC3 than LNCaP. These results were confirmed by ELISA. Finally, human bone marrow mononuclear cells (HBMC) were cultured with PC3 conditioned medium. Although both recombinant human MCP-1 and IL-8 directly stimulated HBMC differentiation into osteoclast-like cells, IL-8, but not MCP-1, induced bone resorption on dentin slices with 21 days of culture in the absence of RANKL. However, the conditioned mediuminduced bone resorption was inhibited by MCP-1 neutralizing antibody and was further synergistically inhibited with IL-8 antibody, indicating that MCP-1, in addition to IL-8, mediates tumor-induced osteoclastogenesis and bone resorption. MCP-1 may promote preosteoclast cell fusion, forming multinucleated tartrate-resistant acid phosphatase-positive osteoclast-like cells. This study may provide novel therapeutic targets for treatment of prostate cancer skeletal metastasis.

Although the primary role of chemokines and their receptors is controlling the trafficking of leukocytes during inflammatory responses, they also play pleoitropic roles in cancer development. There is emerging evidence that cancer cells produce chemokines that induce tumor cell proliferation or chemotaxis in various cancer types. We have previously reported that MCP-1 acts as a paracrine and autocrine factor for prostate cancer (PCa) growth and invasion. As the cellular effects of MCP-1 are mediated by CC chemokine receptor 2 (CCR2), we hypothesized that CCR2 may contribute PCa progression. Accordingly, we first determined CCR2 mRNA and protein expression in various cancer cell lines, including PCa and other cancer types. All cells expressed CCR2 mRNA and protein, but in PCa, more aggressive cancer cells such as C4-2B, DU145, and PC3 expressed a higher amount of CCR2 compared with the less aggressive cancer cells such as LNCaP or non-neoplastic PrEC and RWPE-1 cells. Further, we found a positive correlation between CCR2 expression and PCa progression by analyzing an ONCOMINE gene array database. We confirmed that CCR2 mRNA was highly expressed in PCa metastatic tissues compared with the localized PCa or benign prostate tissues by real-time RT-PCR. Finally, CCR2 protein expression was examined by immunohistochemical staining on tissue microarray specimens from 96 PCa patients and 31 benign tissue controls. We found that CCR2 expression correlated with Gleason score and clinical pathologic stages, whereas lower levels of CCR2 were expressed in normal prostate tissues. These results suggest that CCR2 may contribute to PCa development.