Abstract 5550: The flavone baicalein increases DDIT4 protein expression and inhibits mTOR activity in platinum-resistant epithelial ovarian cancer cells.
Authors: Han Ernest S. , Wang Yujun , Xing Quanhua , Yan Jin , Yip Richard , Wakabayashi Mark , Yim John 
Published: August 2014

OBJECTIVES: Baicalein is a natural flavone and an active component in traditional Chinese medicine. We have recently found that epithelial ovarian cancer cells treated with baicalein increases DDIT4 gene expression, a mediator of DNA damage response. Our objectives are to compare the effects of baicalein to carboplatin and gemcitabine on platinum sensitive and resistant ovarian cancer cell lines. Specifically we examined DDIT4 protein expression, effect on mTOR activity, and growth inhibition.

METHODS: The ovarian cancer cell line A2780 and the derivative platinum resistant cell line A2780R were treated with carboplatin, gemcitabine, and baicalein with appropriate controls and growth was assessed at 72 hours by MTT assay. Alternatively cells were treated at identical concentrations for 24 hours and western blots were performed for DDIT4 protein expression, mTOR activity as reflected by phosphorylation of S6K1 (pS6K1) and S6 (pS6), as well as unphosphorylated controls and actin.

RESULTS: MTT assay demonstrated that carboplatin and gemcitabine do not inhibit the growth of the A2780R cells at concentrations that inhibit A2780 while baicalein inhibits both cell lines nearly equally (2.5 to 20 μM). DDIT4 protein expression increased in a dose dependent fashion in both cell lines treated with baicalein. Furthermore, the mTOR targets S6K1 and S6 demonstrate a dose dependent decrease in phosphorylation, reflecting inhibition of mTOR activity (Figure 1). In contrast, DDIT4 protein expression was not altered in carboplatin and gemcitabine treated A2780R cells with minimal effect on mTOR activity, whereas A2780 cells displayed increased DDIT4 protein with increasing doses as well as corresponding decreases in the phosphorylation of the mTOR targets.

CONCLUSIONS: Baicalein can inhibit growth of both platinum sensitive and resistant ovarian cancer cells. The inhibitory effects of baicalein correlate with both DDIT4 protein expression and inhibition of mTOR activity as reflected by phosphorylation of the mTOR targets S6K1 and S6. Baicalein may be a novel treatment option for patients with ovarian cancer, especially those that are platinum resistant. DDIT4 may mediate growth inhibition through inhibition of mTOR. Interestingly, DDIT4 expression and inhibition of mTOR activity may also play a role in the antitumor effects of the chemotherapeutics carboplatin and gemcitabine in sensitive ovarian cancer cells.

Citation Format: Ernest S. Han, Yujun Wang, Quanhua Xing, Jin Yan, Richard Yip, Mark Wakabayashi, John Yim. The flavone baicalein increases DDIT4 protein expression and inhibits mTOR activity in platinum-resistant epithelial ovarian cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5550. doi:10.1158/1538-7445.AM2013-5550