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

Malignant tumors usually involve a relatively hypoxic state, which induces overexpression of hypoxia-inducible factor-1α (HIF-1α) to satisfactorily enable the tumor to survive. Thus, inhibition of the mammalian target of rapamycin (mTOR) pathway including HIF-1α 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-1α, 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-1α 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-1α and VEGF was examined on western blot. As a result, although mTOR expression remained unchangeable, expression of p-mTOR, HIF-1α 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.