Repositioning Bazedoxifene as a novel IL-6/GP130 signaling antagonist for human rhabdomyosarcoma therapy

Interleukins-6 (IL-6)/GP130 signaling pathway represents a promising target for cancer therapy due to its critical role in survival and progression of multiple types of cancer. We have identified Bazedoxifene, a Food and Drug Administration (FDA)-approved drug used for the prevention of postmenopausal osteoporosis, with novel function as inhibitor of IL-6/GP130 interaction. In this study, we investigate the effect of Bazedoxifene in rhabdomyosarcoma and evaluate whether inhibiting IL-6/GP130 signaling is an effective therapeutic strategy for rhabdomyosarcoma. The inhibitory effect of Bazedoxifene was assessed in rhabdomyosarcoma cell lines in vitro and RH30 xenograft model was used to further examine the suppressive efficacy of Bazedoxifene on tumor growth in vivo. Rhabdomyosarcoma cells showed their sensitivity to GP130 inhibition using gene knockdown or neutralized antibody, suggesting IL-6/GP130 as therapeutic target in rhabdomyosarcoma cells. Bazedoxifene decreased the signal transducer and activator of transcription3 (STAT3) phosphorylation, blocked STAT3 DNA binding, and down-regulated the expression of STAT3 downstream genes. Bazedoxifene also induced cell apoptosis, reduced cell viability, and inhibited colony formation in rhabdomyosarcoma cells. The inhibition of colony formation, STAT3 phosphorylation, or cell viability following Bazedoxifene treatment was partially reversed by addition of excess IL-6 or overexpression of constitutive STAT3, respectively, supporting Bazedoxifene acted through IL-6/GP130 signaling. In addition, Bazedoxifene repressed cell invasion and angiogenesis in vitro. Furthermore, oral administration of Bazedoxifene significantly suppressed tumor growth and expression of STAT3 phosphorylation in nude mice bearing established human rhabdomyosarcoma xenograft. Taken together, these findings validate IL-6/GP130 signaling as therapeutic target in rhabdomyosarcoma and provide first evidence that Bazedoxifene may serve as a novel promising drug targeting IL-6/GP130 for treatment of rhabdomyosarcoma.