Abstract 3614: The anti-tumor effect of antimalarial chloroquine on endometrial cancer cells is dependent on autophagy inhibition

Abstract

Abstract Introduction: Autophagy, which literally means ‘self-eating’, is a major lysosomal degradation system of cytoplasmic materials. Autophagy plays roles in promoting tumor growth by fueling energy and inducing resistance to chemotherapy and/or irradiation in various types of human cancer. However, the roles of autophagy have not been well investigated in endometrial cancer. Chloroquine (CQ) was originally developed as an anti-malarial agent, discovered in 1934. It has also been known as an autophagy inhibitor. In this study, we investigated the anti-tumor effect and inhibition of autophagy by CQ in endometrial cancer cells. Methods: Cell proliferation and cell cycle in response to CQ were assessed in Ishikawa, AN3CA and KLE endometrial cancer cell lines by MTT assay and flow cytometry, respectively. The autophagic activity and autophagosome formation were monitored by LC3 expression in Western blotting and immunofluorescence. The effect of knockdown of either ATG5 or ATG7, both of which are indispensable for induction of autophagy, was also assessed by MTT assay. The sensitivity to CQ was compared between parental and cisplatin-resistant (CP-r) Ishikawa cells. Results: CQ attenuated proliferation of all the three endometrial cancer cell lines in a dose dependent manner. The IC50 values were from 1.5 to 12 uM, which were estimated to be lower than clinical dose of 250 mg daily. CQ induced apoptosis in these cells. Inhibition of autophagy by knocking down either ATG5 or ATG7 decreased the sensitivity to CQ in Ishikawa cells, suggesting that the anti-tumor effect of CQ is dependent on inhibition of autophagy. Exposure to cisplatin increased the level of basal autophagy, and the sensitivity to cisplatin was improved by knocking down ATG5 or ATG7. In addition, CP-r Ishikawa cells acquired higher level of autophagic activity, and the CP-r cells retained the sensitivity to cisplatin by autophagy inhibition by CQ. Conclusions: Our data suggest that autophagy is involved in endometrial tumor growth, and that CQ might be a promising therapeutic agent as an autophagy inhibitor in endometrial cancer. In addition, CQ might retain the sensitivity to cisplatin in cisplatin-resistant endometrial cells, through the suppression of the increased level of autophagy. Citation Format: Tomohiko Fukuda, Katsutoshi Oda, Osamu Wada-Hiraike, Kenbun Sone, Kanako Inaba, Yuji Ikeda, Tomoko Kashiyama, Aki Miyasaka, Chinami Makii, Reiko Kurikawa, Takahide Arimoto, Tetsu Yano, Kei Kawana, Noboru Mizushima, Yutaka Osuga, Tomoyuki Fujii. The anti-tumor effect of antimalarial chloroquine on endometrial cancer cells is dependent on autophagy inhibition. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3614. doi:10.1158/1538-7445.AM2015-3614