Zoledronic Acid Inhibits Thyroid Cancer Stemness and Metastasis by Repressing M2-like Tumor-Associated Macrophages Induced Wnt/β-catenin Pathway

Aims: This study aims to explore the effect and underlying mechanism of zoledronic acid (ZA) on the incidence of thyroid cancer (TC) tumorigenesis. Materials and methods: Human mononuclear cells THP-1 were differentiated into M2-like tumor associated macrophages (TAMs) by incubation with PMA followed by additional incubation of IL-4 and IL-13. TC cells TPC-1 and IHH4 were co-cultured with M2-like TAMs. Identification of M2-like TAMs markers were determined by immunohistochemistry or flow cytometry. Cell proliferation, stemness and migration/invasion ability were measured by colony, sphere formation assay and transwell assay, respectively. The expression levels of cell stemness, EMT and Wnt/beta-catenin pathway-related factors were verified by qRT-PCR, Western blotting, and immunofluorescence. A subcutaneous tumor model was established in nude mice to examine the in vivo effects of ZA. Key findings: M2-like TAMs were enriched in TC tissues, and they promoted the colony/sphere formation, accompanied with a down-regulated expression in E-cadherin and an up-regulated expression in N-cadherin, Vimentin and other stemness-associated markers (CD133, Oct4, c-Myc) in TC cells. The effects were suppressed when ZA co-treatment was given, because ZA inhibited the polarization of M2-like TAMs and beta-catenin entry into the nucleus. Moreover, in agreement with in vitro data, ZA also limited subcutaneous tumor formation and macrophage enrichment in nude mice. Significance: ZA suppressed M2-like TAMs induced TC cell proliferation, stemness and metastasis through inhibiting M2-like TAMs polarization and Wnt/beta-catenin pathway, which sheds light on the mechanisms of TC and provides avenues for the development of clinical therapy to TC.