Background: Zoledronic acid is the most potent osteoclast inhibitor and is widely used for advanced cancer patients with bone metastasis, but its role on cancer stem cells (CSCs) remains unclear. In the present study, we aimed to identify the stemness phenotypic characteristics of CSCs derived from cervical cancer cells and explore the anti-cancer efficiency of zoledronic acid on these cells, as well as the possible molecular mechanisms.
Methods: Stemness phenotypic identification of cervical cancer cells derived CSCs was performed via sphere formation efficiency (SFE), tumorigenesis, immunofluorescence staining, Transwell assay, and western blot. Anti-cancer efficiency of zoledronic acid on these cells (including proliferation, stemness phenotype, apoptosis, and cell cycle) was carried out through MTT assay, SFE, transwell, DAPI staining, flow cytometry, immunofluorescence, TUNEL staining, and western blot, both in vitro and in vivo.
Results: Enhanced self-renewal ability, including SFE and tumorigenesis, was verified in cervical cancer cells derived CSCs compared to parental cervical cancer cells. Specifically, the expression of ALDH1, Sox2, CD49f, Nanog, and Oct4 was significantly up-regulated in cervical cancer cells derived CSCs. Furthermore, enhanced migratory ability was observed in these cells along with up-regulated N-cadherin and Vimentin and down-regulated E-cadherin. Zoledronic acid inhibited cervical cancer cells derived CSCs proliferation in vitro and in vivo. The stemness phenotype of these CSCs including tumor sphere formation, migration, as well as the expression of the aforementioned associated markers was also suppressed. In addition, zoledronic acid significantly induced apoptosis and cell cycle arrest of cervical cancer cells derived CSCs in a dose-dependent manner. Mechanistically, the expression of phosphorylated Erk1/2 and Akt was significantly increased in cervical cancer cells derived CSCs compared to parental cervical cancer cells. Zoledronic acid inhibited phosphorylated Erk1/2 and Akt in cervical cancer cells derived CSCs. IGF-1, a potent stimulator for Erk1/2 and PI3K/Akt, attenuated the aforementioned anti-cancer effect of zoledronic acid.
Conclusions: Zoledronic acid inhibited the growth of cervical cancer cells derived CSCs through attenuating their stemness phenotype, inducing apoptosis, and arresting cell cycle. The suppression of phosphorylated Erk1/2 and Akt was involved in this process.
Keywords: Cancer stem cell; Cervical cancer; Erk1/2; PI3K/Akt; Zoledronic acid.