Background The processes of prostate cancer (PCa) invasion and metastasis are facilitated by proteolytic cascade involving multiple proteases, such as matrix metalloproteinases, serine proteases and cysteine proteases including cathepsin K (CatK). CatK is predominantly secreted by osteoclasts and specifically degrades collagen I leading to bone destruction. PCa and breast cancer preferentially metastasize to the bone. Importantly, CatK expression level is greater in PCa bone metastatic sites compared to primary tumor and normal prostate tissues. However, the underlying mechanism of CatK during PCa metastases into the bone remains to be elucidated. We investigated the functional role of CatK during the PCa establishment and growth process in the murine bone. Methods CatK mRNA expression was validated by RT-PCR, protein expression by immunoblotting in PCa LNCaP, C4-2B, and PC3 cells as well as in PCa tissues. Its protein production was measured using ELISA assay. The effect of both knockdowns via siRNA and CatK inhibitor was compared in regard to PCa cell invasion. We further studied the dose-dependent CatK inhibitor effect on conditioned media-induced bone resorption. In setting up an animal model, C4-2B cells were injected into the tibiae of SCID mice. The animals treated with either vehicle or CatK inhibitor for 8 weeks at the time of tumor cell injection (tumor establishment model; protocol I) or 4 weeks after tumor cell injection (tumor progression model; protocol II) were applied to histological and histomorphometric analyses. Results We confirmed CatK expression in PCa LNCaP, C4-2B, and PC3 cells as well as in PCa tissues. Furthermore, we observed the inhibitory effects of a selective CatK inhibitor on PCa cell invasion. The CatK inhibitor dose-dependently inhibited PCa-conditioned media-induced bone resorption. Upon injection of C4-2B cells into the tibiae of SCID mice, the selective CatK inhibitor significantly prevented the tumor establishment in protocol I, and reduced the tumor growth in bone in protocol II. It also decreased serum PSA levels in both animal models. The inhibitory effects of the CatK inhibitor were enhanced in combination with zoledronic acid (ZA). Conclusion The selective CatK inhibitor may prevent the establishment and progression of PCa in bone, thus making it a novel therapeutic approach for advanced PCa.

Overexpression of the tumor-derived monocyte chemotactic protein-1 (MCP-1) has been suggested to partially promote prostate cancer bone metastasis, but the function for host-derived MCP-1 in these processes is not well established. To understand the function of host-derived MCP-1 on bone metastasis, we developed a mouse model using intracardiac injection and in vivo selection to obtain tumor cell subpopulations with a higher propensity for bone metastasis. Here, we found that a loss of host MCP-1 (MCP-1 knockout) retarded tumor growth in bone and prolonged survival of mice by intracardiac injection of tumor cells in vivo. Moreover, a decrease in osteolytic bone lesion was observed in MCP-1 knockout mice by bone density analysis, as compared to wild-type control. Systemically, MCP-1 deficiency inhibited the proportion of PMN-and M-MDSC populations with immunosuppressive function. Together, this study indicates that the dysregulated immunity resulting from a loss of host MCP-1 signaling is sufficient to drive PCa bone metastasis, and provides a new perspective for targeting the endogenous MCP-1 pathway as an antimetastatic strategy. Supported by NSFC Key Project 81130046; NSFC projects 81773146, 81272415; JCYJ20170412152943794, JCYJ20170412154619484, JCYJ20170307105128101, JCYJ2017030711041760; Guangxi Key Projects 2013GXNSFEA053004. Citation Format: Jie Meng, Weiping Liang, Haibo Tong, Evan T. Keller, Jian Zhang, Yi Lu. Host-derived MCP-1 dictates prostate cancer skeletal metastasis in vivo [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 996.

Metastasis, a major characteristic of malignancy, causes high mortality. Accumulating evidence suggests that cancer intends to metastasize to specific organ, however the molecular mechanisms remain unknown. Others and us have demonstrated that epithelial to mesenchymal transition (EMT) plays key roles in initiation of primary tumor adherent, migration, and invasion, whereas mesenchymal to epithelial transition (MET) revokes “sleeping” disseminated tumor cell (DTC) to colonization at distant metastatic organ sites and facilitates the tumor cell proliferation. We have successfully generated the lung-specific metastatic subclones of human prostate cancer PC3 and murine RM1 cells. Through omic bench work and data analysis and comparison with TCGA database, we, for the first time, identified a preliminary network of “driver genes” that potentially promotes the reversible EMT/MET process We utilized cutting-edge tools of data analysis to identify the selected driver genes (LAMA, SPP1, ITGB3, S100A8, SERPINE, DKK2) and further characterized the gene functions via in vitro bioassay of cell proliferation, migration, invasion, cell cycle, and apoptotic testing etc, and in vivo with our unique cell and animal metastatic models. We observed that the rate of organ-specific metastasis was dramatically reduced when these gene expression levels were changed. Finally, we confirmed our findings using TMA slides, Our results may provide novel mechanisms of metastasis and clinical targets of cancer therapy. Supported by NSFC projects 81773146; Guangdong Provincial Key Laboratory of Cell Microenvironment and Disease Research (2017B030301018); JCYJ20170412152943794, JCYJ20170412154619484, JCYJ20170307105128101, JCYJ2017030711041760 Note: This abstract was not presented at the meeting. Citation Format: Ming Chang, Xin Huang, Songjian Lu, Wei Zhang, Weiping Liang, Evan Keller, Xinghua Lu, Jian Zhang. Driver genes network promotes mesenchymal to epithelial transition and organ-specific metastasis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2784.