Cancer Therapy : Preclinical mTOR Is a Promising Therapeutic Target Both in Cisplatin-Sensitive and Cisplatin-Resistant Clear Cell Carcinoma of the Ovary

Purpose: Mammalian target of rapamycin (mTOR) plays a central role in cell proliferation and is regarded as a promising target in cancer therapy, including for ovarian cancer. This study aimed to examine the role of mTOR as a therapeutic target in clear cell carcinoma of the ovary, which is regarded as an aggressive, chemoresistant histologic subtype. Experimental Design: Using tissue microarrays of 98 primary ovarian cancers (52 clear cell carcinomas and 46 serous adenocarcinomas), the expression of phospho-mTOR was assessed by immunohistochemistry. Then, the growth-inhibitory effect of mTOR inhibition by RAD001 (everolimus) was examined using two pairs of cisplatin-sensitive parental (RMG1 and KOC7C) and cisplatin-resistant human clear cell carcinoma cell lines (RMG1-CR and KOC7C-CR) both in vitro and in vivo. Results: Immunohistochemical analysis showed that mTOR was more frequently activated in clear cell carcinomas than in serous adenocarcinomas (86.6% versus 50%). Treatment with RAD001 markedly inhibited the growth of both RMG1 and KOC7C cells both in vitro and in vivo. Increased expression of phospho-mTOR was observed in cisplatin-resistant RMG1-CR and KOC7C-CR cells, compared with the respective parental cells. This increased expression of phospho-mTOR in cisplatin-resistant cells was associated with increased activation of AKT. RMG1-CR and KOC7C-CR cells showed greater sensitivity to RAD001 than did parental RMG1 and KOC7C cells, respectively, in vitro and in vivo. Conclusion: mTOR is frequently activated in clear cell carcinoma and can be a promising therapeutic target in the management of clear cell carcinoma. Moreover, mTOR inhibition by RAD001 may be efficacious as a second-line treatment of recurrent disease in patients previously treated with cisplatin. (Clin Cancer Res 2009;15(17):5404–13) Ovarian carcinoma is the fourth most common cause of cancer death among women in the United States, with >21,000 new cases each year and an estimated 15,520 deaths in 2008 (1). Cytoreductive surgery followed by platinum-based chemotherapy usually combined with paclitaxel is the standard initial treatment and has improved survival in patients with epithelial ovarian cancer (2). However, there still exists many clinical problems in the treatment of epithelial ovarian cancer. One of the most important problems that needs to be resolved is the management of clear cell carcinoma of the ovary, which was first recognized by the WHO as a distinct histologic subtype in 1973 (3). The precise incidence of clear cell carcinoma is unknown, but it is reported to be 3.7% to 12.1% of all histologic subtypes among epithelial ovarian cancer (4). There have been two major clinical problems in the clinical management of clear cell carcinoma. First is its poor sensitivity to first-line platinum-based chemotherapy and the association with a worse prognosis than themore common serous adenocarcinomas. In the setting of front-line chemotherapy, the response rate to conventional platinum-based chemotherapy, platinum agent alone or in combination with cyclophosphamide and Authors' Affiliations: Department of Obstetrics and Gynecology, Osaka University Graduate School of Medicine, Department of Pathology, Osaka Police Hospital, and Department of Obstetrics and Gynecology, Osaka Medical College, Osaka, Japan; Women's Cancer Program, Cancer Genetics and Signaling Program, and Molecular Medicine Program, Fox Chase Cancer Center, Philadelphia, Pennsylvania; and Department of Obstetrics and Gynecology, Wakayama Rosai Hospital, Wakayama, Japan Received 2/15/09; revised 5/26/09; accepted 5/27/09; published OnlineFirst 8/18/09. Grant support: National Cancer Institute Grants CA83638 (SPORE in Ovarian Cancer), CA77429 and CA06927, Grant-in-aid for Young Scientists, No 19890125 from the Ministry of Education, Culture, Sports, Science and Technology of Japan. D.A. A. is supported in part by the Liz Tilberis Scholar Program, funded by the Ovarian Cancer Research Found, Inc. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Note: S. Mabuchi and C. Kawase contributed equally to this work. Requests for reprints: Seiji Mabuchi, Department of Obstetrics and Gynecology, Osaka University Graduate School of Medicine, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan. Phone: 81-6-6879-3354; Fax: 81-6-68793359; E-mail: smabuchi@gyne.med.osaka-u.ac. jp. F 2009 American Association for Cancer Research. doi:10.1158/1078-0432.CCR-09-0365 5404 Clin Cancer Res 2009;15(17) September 1, 2009 www.aacrjournals. org Research. on June 9, 2017. © 2009 American Association for Cancer clincancerres.aacrjournals. org Downloaded from Published OnlineFirst August 18, 2009; DOI: 10.1158/1078-0432.CCR-09-0365