Bazedoxifene enhances the anti-tumor effects of cisplatin and radiation treatment by blocking IL-6 signaling in head and neck cancer

Recent studies have shown that IL-6 signaling plays an important role in the aggressive and metastatic phenotype of head and neck squamous cell carcinoma (HNSCC). Therefore, we hypothesized that targeting of IL-6 signaling in HNSCC could enhance the therapeutic efficacy of standard chemoradiation treatment. We used both in vitro and in vivo models to test the efficacy of Bazedoxifene (BZA), a drug that was originally developed as a newer-generation selective estrogen receptor modulator (SERM) for the treatment of postmenopausal osteoporosis. Recently, BZA was also shown to exhibit potent anti-cancer effects that were both estrogen receptor (ER)-dependent and ER-independent. Our results suggest that BZA inhibits IL-6 signaling by disrupting IL-6R/gp130 protein-protein interactions. BZA treatment of CAL27-IL-6 (IL-6 overexpressing cells) or UM-SCC-74A (naturally expressing high levels of IL-6) significantly inhibited cell proliferation, migration and colony formation ability in a dose-dependent manner. In addition, BZA significantly decreased IL-6-mediated tumorsphere formation by markedly reducing nanog expression. BZA treatment also markedly reduced chemo and radioresistance in head and neck cancer cells by downregulating ERCC-1, XRCC-1 and survivin expression. In a SCID mouse xenograft model, BZA significantly enhanced the anti-tumor effects of cisplatin and radiation treatment with no added systemic toxicity. Furthermore, combination treatments significantly decreased tumor metastasis, pSTAT3 expression and nanog expression, in vivo. Taken together, our results suggest that targeting IL-6 signaling with bazedoxifene could be an effective treatment strategy for the treatment of HNSCC patients.