Abstract 2125: Flavokawain A, a kava chalcone, inhibits growth and invasion of human osteosarcoma cells by targeting Skp2

Purpose: Osteosarcoma (OS) is the most common primary bone malignancy with a high propensity for local invasion and distant metastasis. Flavokawain A (FKA), a major chalcone from kava extract, has been reported to have antitumor effects on multiple cancer cell lines. The consumption of kava-containing beverage has been associated with a low cancer incidence. In a previous report, mice treated with high-dose FKA did not demonstrate any significant major organ toxicity. However, the efficacy and anticancer mechanisms of FKA in OS is still to be elucidated. Experimental Design: OS cell lines were treated with increasing dosage of FKA and tested for cell motility, proliferation, and invasion by MTT assay and Matrigel invasion assay. Cell cycle analysis was performed using flow cytometry. We examined Skp2 expression in several OS cell lines using western blot and in patient tissue array by immunostaining. Kaplan-meier analysis and log rank test were used to compare overall survival. Both Skp2-dependent cell cycle progression and Skp2-related RhoA expression were also examined after FKA treatment. The effects of FKA on lung metastasis were evaluated after orthotopic injection of OS cells into the tibia. Results: We show that FKA inhibits the growth and motility of multiple OS cell lines in vitro. Flow cytometry analysis confirms cellular apoptosis and arrest in G2/M phase after FKA treatment, whereas cellular invasion is also inhibited in a dose-dependent manner. Skp2 is expressed in several OS cell lines and is associated with a poor prognosis in OS patients. Skp2 levels in OS cell lines decreased after FKA treatment. The expression of cell cycle regulators including p21 and p27, which are downstream of Skp2, was upregulated. Moreover, Skp2-related RhoA expression is inhibited by FKA and confirmed at protein level. Conclusions: Taken together, the evidence suggests FKA exerts anti-invasive effects in association with Skp2-dependent cell cycle progression and Skp2-related RhoA expression. Since Skp2 is a negative prognostic factor for OS patients, FKA should be investigated further as an anti-Skp2 therapeutic strategy for OS. Citation Format: Yidan Zhang, Wendong Zhang, Nikolas Zaphiros, Xiuquan Du, Pratistha Koirala, Michael Roth, Jonathan Gill, Sajida Piperdi, David Geller, Rui Yang, Jinghang Zhang, Richard Gorlick, Xiaolin Zi, Tao Ji, Bang H. Hoang. Flavokawain A, a kava chalcone, inhibits growth and invasion of human osteosarcoma cells by targeting Skp2 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2125. doi:10.1158/1538-7445.AM2017-2125