Abstract 4148: Rapamycin potentiates the effects of paclitaxel in uterine papillary serous carcinoma (UPSC) cells through inhibition of cell proliferation and induction of apoptosis

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC Objectives: Treatment of women with uterine papillary serous carcinoma (UPSC) using cytotoxic chemotherapeutic agents has been met with limited success. This has led to the search for an additional agent that could be used in combination with more traditional therapies to dramatically increase therapeutic efficacy while not increasing toxicities. Among the most promising of these for endometrial cancer are inhibitors of the mammalian target of rapamycin (mTOR). Rapamycin and paclitaxel have been found to be synergistic in type I endometrial cancer cell lines. Thus, our objective was to examine the effects of combined therapy with rapamycin and paclitaxel in a UPSC cell line. Methods: The UPSC cell line, SPEC-2 was used. Cell proliferation was assessed after exposure to rapamycin or paclitaxel alone or in combination, and viable cell densities were determined by measuring conversion of the metabolic dye, MTT. Apoptosis was assessed by flow cytometric analysis of annexin-V expression. hTERT expression, as a marker of telomerase activity, was determined by real-time RT-PCR. Western immunoblotting was performed to determine the expression of the downstream targets of the mTOR pathway, including phosphorylated S6 and 4E-BP-1. Results: Paclitaxel inhibited proliferation in a dose-dependent manner in the SPEC-2 cell line, with an IC50 value of 1-10 nM. Simultaneous exposure of cells to various doses of paclitaxel in combination with rapamycin (1 nM) resulted in a significant synergistic anti-proliferative effect (p=0.0032-0.0059). In addition, rapamycin increased paclitaxel-induced apoptosis over that of paclitaxel alone. Rapamycin decreased hTERT mRNA expression while paclitaxel alone had no effect on telomerase activity. Rapamycin decreased phosphorylation of the S6 and 4E-BP-1 proteins after 24 hrs of exposure. In contrast, paclitaxel had little effect on 4E-BP-1 phosphorylation but did induce phosphorylation of S6 at higher doses (10 nM). Treatment with paclitaxel and rapamycin resulted in overall decreased phosphorylation of both S6 and 4E-BP-1. Conclusions: We demonstrate that rapamycin potentiates the effects of paclitaxel in UPSC cells through inhibition of cell proliferation and induction of apoptosis. This suggests that the combination of rapamycin and paclitaxel may be a promising effective targeted therapy for UPSC, an aggressive and often lethal subtype of endometrial cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4148.