骨转移在转移性前列腺癌（PCa）患者中发生率约为70％，并且是导致PCa患者死亡的主要原因。新兴证据已经证明了淫羊藿苷在调节骨代谢和重构肿瘤微环境（TME）方面的潜在活性。然而，淫羊藿苷是否通过调节TME来抑制PCa骨转移和破坏以及其潜在机制仍不清楚。本研究调查了淫羊藿苷是否能通过调节骨TME以及潜在机制来抑制PCa骨转移和破坏。从小鼠骨髓源性巨噬细胞（BMMs）或Raw264.7细胞诱导成破骨细胞。在体外培养肿瘤相关巨噬细胞（TAMs）的巨噬细胞的条件培养基（CM）或在体内与巨噬细胞共注射PCa细胞以模拟它们在TME中的共存。利用多种分子生物学实验和小鼠RM1-Luc PCa骨转移模型来探索淫羊藿苷对PCa转移和骨破坏的抑制活性和机制。淫羊藿苷处理显著抑制了PCa的生长、骨转移和破坏以及体内破骨细胞发生。此外，淫羊藿苷明显抑制了破骨细胞的分化，即使在肿瘤相关巨噬细胞（TAMs）的CM存在下，对成骨细胞没有明显影响。此外，淫羊藿苷抑制了Raw264.7源性TAMs的M2表型极化，并通过抑制SPI1转录途径在转录水平上减弱了它们的CC基序趋化因子配体5（CCL5）的表达和分泌。此外，CCL5通过与其受体CCR5结合诱导了破骨细胞前体细胞的分化和趋化。临床病理分析进一步验证了PCa患者TME中TAM / CCL5 / CCR5轴与破骨细胞发生之间的正相关。更重要的是，淫羊藿苷通过抑制破骨细胞发生并下调TAM / CCL5途径，在体内显著抑制了PCa转移引起的骨破坏。综上所述，这些结果不仅将淫羊藿苷视为PCa骨转移和破坏的有前途的候选免疫调节剂，还为靶向TAM / CCL5介导的破骨细胞生成作为潜在的骨溶性骨转移治疗策略提供了新的思路。本研究有助于推进对骨TME与骨稳态之间相互作用的理解。版权所有©2023 Elsevier GmbH出版。

Bone metastasis occurs in nearly 70% of patients with metastatic prostate cancer (PCa), and represents the leading cause of death in patients with PCa. Emerging evidence has demonstrated the potential activities of icariin in modulating bone metabolism and remodelling the tumor microenvironment (TME). However, whether icariin could inhibit PCa bone metastasis and destruction by modulating the TME as well as the underlying mechanisms remains unclear.This study investigated whether icariin could inhibit PCa bone metastasis and destruction by modulating the bone TME as well as the underlying mechanisms.Osteoclasts were induced from mouse bone marrow-derived macrophages (BMMs) or Raw264.7 cells. PCa cells were cultured in the conditional medium (CM) of macrophages in vitro or co-injected with macrophages in vivo to simulate their coexistence in the TME. Multiple molecular biology experiments and the mouse RM1-Luc PCa bone metastasis model were used to explore the inhibitory activity and mechanism of icariin on PCa metastasis and bone destruction.Icariin treatment significantly suppressed PCa growth, bone metastasis and destruction as well as osteoclastogenesis in vivo. Furthermore, icariin remarkably inhibited osteoclast differentiation, even in the presence of the CM of tumor-associated macrophages (TAMs), while exhibiting no obvious effect on osteoblasts. Moreover, icariin suppressed the M2 phenotype polarization of Raw264.7-derived TAMs and transcriptionally attenuated their CC motif chemokine ligand 5 (CCL5) expression and secretion via inhibiting SPI1. Additionally, CCL5 induced the differentiation and chemotaxis of osteoclast precursor cells by binding with its receptor CCR5. The clinicopathological analysis further verified the positive correlation between the TAM/CCL5/CCR5 axis and osteoclastogenesis within the TME of PCa patients. More importantly, icariin remarkably suppressed PCa metastasis-induced bone destruction in vivo by inhibiting osteoclastogenesis via downregulating the TAM/CCL5 pathway.Altogether, these results not only implicate icariin as a promising candidate immunomodulator for PCa bone metastasis and destruction but also shed novel insight into targeting TAM/CCL5-mediated osteoclastogenesis as a potential treatment strategy for osteolytic bone metastasis. This study helps to advance the understanding of the crosstalk between bone TME and bone homeostasis.Copyright © 2023. Published by Elsevier GmbH.