Honokiol Radiosensitizes Squamous Cell Carcinoma of the Head and Neck by Downregulation of Survivin

Purpose: Previous studies revealed diverging results regarding the role of survivin in squamous cell carcinoma of the head and neck (SCCHN).This study aimed to evaluate the clinical significance of survivin expression in SCCHN; the function of survivin in DNA damage repair following ionizing radiationtherapy (RT) in SCCHN cells; and the potential of honokiol to enhance RT through downregulation of survivin. Experimental Design: Expression of survivin in SCCHN patient primary tumor tissues (n=100) was analyzed and correlated with clinical parameters. SCCHN cell lines were used to evaluate the function of survivin and the effects of honokiol on survivin expression in vitro and in vivo. Results: Overexpression of survivin was significantly associated with lymph nodes metastatic status (p=0.025), worse overall survival (OS) and disease free survival (DFS) in patients receiving RT (n=65, OS: p=0.024, DFS: p=0.006) and in all patients with SCCHN (n=100, OS: p=0.002, DFS: p=0.003). In SCCHN cells, depletion of survivin led to increased DNA damage and cell death following RT, whereas overexpression of survivin increased clonogenic survival. RT induced nuclear accumulation of survivin and its molecular interaction with -H2AX and DNA-PKCs. Survivin specifically bound to DNA DSB sites induced by I-SceI endonuclease. Honokiol (which downregulates survivin expression) in combination with RT significantly augmented cytotoxicity in SCCHN cells with acquired radioresistance and inhibited growth in SCCHN xenograft tumors. Conclusions: Survivin is a negative prognostic factor and is involved in DNA damage repair induced by RT. Targeting survivin using honokiol in combination with RT may provide novel therapeutic opportunities.

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