Identification of sphingosine kinase 1 (SphK1) as a primary target of icaritin in hepatocellular carcinoma cells.

// Pei-Hua Lu 1, 2, * , Min-Bin Chen 3, * , Yuan-Yuan Liu 3, * , Mian-Hua Wu 2 , Wen-Ting Li 2 , Mu-Xin Wei 4 , Chao-Ying Liu 1 , Shu-Kui Qin 5 1 Department of Medical Oncology, Wuxi People’s Hospital Affiliated to Nanjing Medical University, Wuxi, China 2 Jiangsu Collaborative Innovation Center of Traditional Chinese Medicine (TCM) Prevention and Treatment of Tumor of Nanjing University of Chinese Medicine, Nanjing, China 3 Department of Oncology, Kunshan First People’s Hospital Affiliated to Jiangsu University, Kunshan, China 4 Department of Traditional Chinese Medicine, First Affiliated Hospital of Nanjing Medical University, Nanjing, China 5 People’s Liberation Army Cancer Center, 81st Hospital of People’s Liberation Army, Nanjing, China * Co-first authors Correspondence to: Shu-Kui Qin, email: drqinshukuinj@126.com Min-Bin Chen, email: cmb1981@163.com Keywords: hepatocellular carcinoma (HCC), icaritin, sphingosine kinase 1 (SphK1), ceramide Received: September 20, 2016      Accepted: November 08, 2016      Published: February 09, 2017 ABSTRACT Hepatocellular carcinoma (HCC) is a highly aggressive neoplasm. We aim to explore the anti-HCC activity by a natural prenylflavonoid icaritin. Icaritin was cytotoxic and pro-apoptotic when added to established (HepG2, KYN-2 and Huh-7 lines) and primary human HCC cells. At the signaling level, icaritin inhibited sphingosine kinase 1 (SphK1) activity in HCC cells, which led to pro-apoptotic ceramide production and JNK1 activation. SphK1 inhibition or silence (by shRNA/microRNA) mimicked icaritin-mediated cytotoxicity, and almost nullified icaritin’s activity in HepG2 cells. Reversely, exogenous over-expression of SphK1 sensitized icaritin-induced HepG2 cell apoptosis. In vivo , oral administration of icaritin dramatically inhibited HepG2 xenograft growth in SCID mice. Further, SphK1 activity in icaritin-treated tumors was largely inhibited. In summary, icaritin exerts potent anti-HCC activity in vitro and in vivo . SphK1 inhibition could be the primary mechanism of its actions in HCC cells.