Therapeutic strategy targeting the mTOR-HIF-1alpha-VEGF pathway in ovarian clear cell adenocarcinoma

Masaki Miyazawa, Masanori Yasuda, Mariko Fujita, Hiroshi Kajiwara, Kenichi Hirabayashi, Susumu Takekoshi, Takeshi Hirasawa, Masaru Murakami, Naoki Ogane, Kazushige Kiguchi, Isamu Ishiwata, Mikio Mikami, R Yoshiyuki Osamura
Pathology International 2009, 59 (1): 19-27
Malignant tumors usually involve a relatively hypoxic state, which induces overexpression of hypoxia-inducible factor-1alpha (HIF-1alpha) to satisfactorily enable the tumor to survive. Thus, inhibition of the mammalian target of rapamycin (mTOR) pathway including HIF-1alpha is expected to play a major role in suppression of tumor cell growth, having recently drawn much attention as an anti-cancer therapeutic strategy for various malignant tumors. In the present study, which compared clear cell adenocarcinoma (CLA) of the ovary with serous adenocarcinoma (SEA), the immunohistochemical expression of mTOR, phosphorylated-mTOR (p-mTOR), HIF-1alpha, and vascular endothelial growth factor (VEGF) was examined in surgically resected specimens of 29 SEA and 47 CLA. There were no significant differences in expression of mTOR, HIF-1alpha and VEGF between SEA and CLA, but it was noted that p-mTOR expression was more prominent in CLA than SEA. Then, using the cell lines of CLA (RMG-1 and W3uF), an experimental study was designed to clarify whether tumor suppression due to downregulation of mTOR activity could represent a promising therapeutic strategy for CLA. After treatment of an analogue of rapamycin (everolimus), expression of mTOR, p-mTOR, HIF-1alpha and VEGF was examined on western blot. As a result, although mTOR expression remained unchangeable, expression of p-mTOR, HIF-1alpha and VEGF was shown to be sharply depressed. The same expression alterations were demonstrated in the xenograft model treated with everolimus. In conclusion, mTOR-targeted therapy through usage of drugs such as everolimus may be more effective for CLA of the ovary because of its significant expression of p-mTOR.

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