Bisphosphonates (BPs) are potent anti-resorptive agents that are widely used to treat metastatic bone diseases in cancer patients. BPs target the mevalonate pathway and inhibit cholesterol synthesis and prenylation (e.g., geranylgernaylation and farnesylation) of small GTPases that are important for cell proliferation and survival. Long-term users of BPs are at the higher risk of developing osteonecrosis of the jaw (ONJ), which commonly occurs at the site of previous tooth extraction or other surgical interventions. Although bisphosphonate-related osteonecrosis of the jaw (BRONJ) is clinically defined as exposed necrotic bone with unhealed and open oral mucosa, the exact role of oral mucosa in the pathophysiology of BRONJ is not fully understood. The current study was undertaken to examine direct effects of BPs on the reepithelialization of oral mucosal cells. When normal human oral keratinocytes (NHOK) were treated with pamidronate (PAM), proliferation and migration were inhibited in dose-dependent manner as determined by MTT assay, proliferation assay, Western blotting against PCNA, and the scratch wound healing assay. Cell cycle analysis revealed increased S-phase content in PAM-treated NHOK, and this was associated with decreased mRNA and protein expressions of Cyclin A2 but not Cyclin D. PAM also induced premature senescence in NHOK as determined by increased β-galactosidase positivity, increased p16 expression, and phosphorylated p-38 MAP kinase pathway. PAM-induced premature senescence and proliferation inhibition were partially reversed by geranylgerniol (GGOH), but not farnesol (FOH), which reconstitute geranylgeranylation and farnesylation of the mevalonate pathway, respectively. Finally, using 3-dimensional (3D) raft culture system, we found that PAM-treated oral mucosal tissue constructs showed diminished immunohistochemical staining of PCNA and loss of reepithelialization in the wounded area, indicating that BPs impair proliferation and migration of oral epithelium constructs ex vivo. Our study demonstrates that BPs induce premature senescence and directly impair proliferation and migration of oral mucosal cells, which may explain the pathophysiology of BRONJ in cancer patients undergoing BP-treatment. This study was supported by NIDCR/NIH (DE017121).

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3218.