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Rationale: Bone is the most frequent site for breast cancer metastasis, which accounts for the leading cause of death in advanced breast cancer patients. Serious skeletal-related events (SREs) caused by bone metastasis have a decisive impact on the life expectancy of breast cancer patients, making breast cancer almost incurable. Metastatic breast cancer cell induced pathological osteoclastogenesis is a key driver of bone metastasis and osteolytic bone lesions. We previously reported that gold clusters can prevent inflammation induced osteoclastogenesis and osteolysis in vivo. In this study, we investigated the effects of a BSA-coated gold cluster on metastatic breast cancer-induced osteoclastogenesis in vitro and tumor-induced osteolysis in vivo, and elucidated its possible mechanism. Methods: Breast cancer cell line MDA-MB-231 was used to evaluate the regulatory effects of gold clusters on breast cancer metastasis and tumor induced osteoclastogenesis in vitro. Cell counting kit-8, transwell, wound-healing and colony formation assays were performed to evaluate the effect of gold clusters on proliferation and metastasis of MDA-MB-231 cells. Tartrate-resistant acid phosphatase (TRAP) staining and filamentous-actin rings analysis were used to detect the regulatory effects of gold clusters on MDA-MB-231 cell-conditioned medium (MDA-MB-231 CM) triggered and receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclastogenesis in mouse bone marrow-derived mononuclear cells (BMMs). A mouse model of breast cancer bone metastasis was used to evaluate the in vivo activity of the gold cluster on the tumor induced osteolysis. Results: The gold clusters suppressed the migration, invasion and colony formation of MDA-MB-231 cells in a dose-dependent manner in vitro. The gold clusters strongly inhibited both MDA-MB-231 CM triggered and RANKL-induced osteoclast formation from BMMs in vitro. Cell studies indicated that the gold clusters suppressed the expression of osteolysis-related factors in MDA-MB-231 cells and inhibited the subsequent activation of NF-κB pathway in BMMs. Treatment with the clusters at a dose of 10 mg Au/kg.bw significantly reduces the breast cancer cell induced osteolysis in vivo. Conclusion: Therefore, the gold clusters may offer new therapeutic agents for preventing breast cancer bone metastasis and secondary osteolysis to improve patient outcomes.

Inflammation-induced bone erosion is a major pathological factor in several chronic inflammatory diseases that often cause severe outcomes, such as rheumatoid arthritis and periodontitis. Plenty of evidences indicated that the inflammatory bone destruction was attributed to an increase in the number of bone-resorbing osteoclasts. However, anti-resorptive therapy alone failed to prevent bone loss in an inflammatory condition. Conventional anti-inflammation treatments are usually intended to suppress inflammation only, but ignore debilitating the subsequent bone destruction. Therefore, inhibition of proinflammatory activation of osteoclastogenesis could be an important strategy for the development of drugs aimed at preventing inflammatory bone destruction. Methods: In this study, we synthesized a peptide coated gold cluster to evaluate its effects on inflammatory osteoclastogenesis in vitro and inflammation-induced bone destruction in vivo. The in vitro anti-inflammation and anti-osteoclastogenesis effects of the cluster were evaluated in LPS-stimulated and receptor activator of nuclear factor κB ligand (RANKL) stimulated macrophages, respectively. The LPS-induced expression of crucial pro-inflammation cytokines and RANKL-induced osteoclastogenesis as well as the activation of NF-κB pathway in both situations were detected. The inflammation-induced RANKL expression and subsequent inflammatory bone destruction in vivo were determined in collagen-immunized mice. Results: The gold cluster strongly suppresses RANKL-induced osteoclast formation via inhibiting the activation of NF-κB pathway in vitro. Moreover, treatment with the clusters at a dose of 5 mg Au/kg.bw significantly reduces the severity of inflammation-induced bone and cartilage destruction in vivo without any significant toxicity effects. Conclusion: Therefore, the gold clusters may offer a novel potent therapeutic stratagem for inhibiting chronic inflammation associated bone destruction.

Sepsis-induced acute kidney injury (AKI) with high incidence and mortality rates remains a great challenge in the clinic, thus, novel therapies need to be developed urgently. This complication is associated with an overwhelming systemic inflammatory response. The aim of this study was to evaluate the potential effects and possible mechanisms of gold clusters on septic AKI in vitro. Rat mesangial HBZY-1 cells were treated with peptide-templated gold clusters under lipopolysaccharide (LPS) stimulation. The LPS-induced expression of pro-inflammatory cytokines was measured, including tumor necrosis factor alpha (TNF-&alpha, ), interleukin-1 beta (IL-1&beta, ) and interleukin-6 (IL-6). Our data showed that the LPS-induced transcription and secretion of these cytokines were suppressed by pretreatment of gold clusters in a dose-dependent manner. Cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) also play key roles in septic AKI and both of them are induced upon LPS-stimulation in mesangial cells. Our results further showed that pretreatment with gold clusters dramatically inhibited the LPS-stimulated transcription and expression of COX2 and iNOS, and the subsequent prostaglandin E2 (PGE2) and nitric oxide (NO) production in HBZY-1 cells. Since these factors are involved in the NF-&kappa, B pathway upon LPS stimulation, the potential roles of gold clusters on the NF-&kappa, B pathway were further determined. We found that LPS-induced NF-&kappa, B activation was suppressed in gold clusters-pretreated HBZY-1 cells. These results demonstrated that gold clusters can attenuate LPS-induced inflammation in mesangial cells, probably via inhibiting the activation of the NF-&kappa, B pathway, suggesting a potential therapeutic approach for septic AKI.