Activation of microRNA-494-targeting Bmi1 and ADAM10 by silibinin ablates cancer stemness and predicts favourable prognostic value in head and neck squamous cell carcinomas

// Yu-Chao Chang 1,2,4 , Chia-Ing Jan 5,6,* , Chih-Yu Peng 1,2,4,* , Yu-Chi Lai 3 , Fang-Wei Hu 1,2,3,4 and Cheng-Chia Yu 1,2,3,4 1 School of Dentistry, Chung Shan Medical University, Taichung, Taiwan 2 Department of Dentistry, Chung Shan Medical University Hospital, Taichung, Taiwan 3 Institute of Oral Sciences, Chung Shan Medical University, Taichung, Taiwan 4 Oral Medicine Research Center, Chung Shan Medical University, Taichung, Taiwan 5 Department of Pathology, China Medical University Hospital, Taichung, Taiwan 6 Department of Pathology, China Medical University Beigang Hospital, Yunlin, Taiwan * These authors contributed equally to this work Correspondence to: Cheng-Chia Yu, email: // Fang-Wei Hu, email: // Keywords : head and neck squamous cell carcinomas, tumor initiating cells, silibinin, microRNA-494 Received : February 26, 2015 Accepted : May 30, 2015 Published : June 08, 2015 Abstract Tumor initiating cells (TICs) possessing cancer stemness were shown to be enriched after therapy, resulting in the relapse and metastasis of head and neck squamous cell carcinomas (HNC). An effective therapeutic approach suppressing the HNC-TICs would be a potential method to improve the treatments for HNC. We observed that the treatment of silibinin (SB) dose dependently down-regulated the ALDH1 activity, CD133 positivity, stemness signatures expression, self-renewal property, and chemoresistance in ALDH1+CD44+ HNC-TICs. Using miRNA-microarray and mechanistic studies, SB increased the expression of microRNA-494 (miR-494) and both Bmi1 and ADAM10 were identified as the novel targets of miR-494. Moreover, overexpression of miR-494 results in a reduction in cancer stemness. However, knockdown of miR-494 in CD44 − ALDH1 - non-HNC-TICs enhanced cancer stemness and oncogenicity, while co-knockdown of Bmi1 and ADAM10 effectively reversed these phenomena. Mice model showed that SB treatment by oral gavage to xenograft tumors reduced tumor growth and prolonged the survival time of tumor-bearing mice by activation of miR-494-inhibiting Bmi1/ADAM10 expression. Survival analysis indicated that a miR494 high Bmi1 low ADAM10 low phenotype predicted a favourable clinical outcome. We conclude that the inhibition of tumor aggressiveness in HNC-TICs by SB was mediated by up-regulation miR-494, suggesting that SB would be a valuable anti-cancer drug for treatment of HNC.