Mammalian Target of Rapamycin Complex 1 and Cyclooxygenase 2 Pathways Cooperatively Exacerbate Endometrial Cancer

The underlying causes of endometrial cancer (EMC) are poorly understood, and treatment options for patients with advanced stages of the disease are limited. Mutations in the phosphatase and tensin homologue gene are frequently detected in EMC. Cyclooxygenase 2 (Cox2) and mammalian target of rapamycin complex 1 (mTORC1) are known downstream targets of the phosphatase and tensin homologue protein, and their activities are up-regulated in EMC. However, it is not clear whether Cox2 and mTORC1 are crucial players in cancer progression or whether they work in parallel or cooperatively. In this study, we used a Cox2 inhibitor, celecoxib, and an mTORC1 inhibitor, rapamycin, in mouse models of EMC and in human EMC cell lines to explore the interactive roles of Cox2 and mTORC1 signaling. We found that a combined treatment with celecoxib and rapamycin markedly reduces EMC progression. We also observed that rapamycin reduces Cox2 expression, whereas celecoxib reduces mTORC1 activity. These results suggest that Cox2 and mTORC1 signaling is cross-regulated and cooperatively exacerbate EMC.Endometrial cancer (EMC) is the most common gynecological malignancy among American women.^1,2 According to National Cancer Institute estimates, about 50,000 women will be diagnosed with EMC in 2013 and approximately 8200 patients are likely to die from it. Underlying causes of EMC are not clearly understood, and treatment options for patients with advanced stages are limited.^1,2 Several genetic alterations are associated with EMC.^1,2 One of the most common mutations is in the phosphatase and tensin homologue gene (PTEN). Mutations of the TP53 gene, which encodes p53, are also found in EMC and primarily occur in poorly differentiated carcinomas.^1,2The loss of PTEN results in increased phosphoinositide 3-kinase (PI3K) activity and thymoma viral proto-oncogene 1 (Akt) activation. Increased levels of phosphorylated (activated) Akt (pAkt) stimulate cyclooxygenase 2 (Cox2) and mammalian target of rapamycin complex 1 (mTORC1) activities.^3–9 Heightened Cox2 and mTORC1 signaling are associated with EMC.^9–14 Cox2 is overexpressed in many solid tumors, and Cox2-derived prostaglandins (PGs), especially PGE₂ via its receptors EP₂/EP₄, significantly contribute to carcinogenesis.^15,16 Interestingly, analogues of rapamycin and related inhibitors of mTORC1 signaling are in phase I to II clinical trials to treat EMC, and the beneficial effects of celecoxib in cancers are also the subject of current clinical trials (http://www.clinicaltrials.gov, last accessed July 22, 2014).Animal models of spontaneously developed cancers are powerful tools for studying the mechanisms underlying cancer initiation and progression and for developing treatment strategies. We previously generated mouse models with conditional uterine deletion of Pten (Pten^d/d) or of Pten and Trp53 (Pten/Trp53^d/d) using the Cre/loxP approach.¹⁷ Female mice with floxed alleles of Pten and/or Trp53 were crossed with males expressing Cre recombinase driven under the progesterone receptor promoter (Pgr-Cre).¹⁸Pten^d/d females spontaneously developed EMC with 100% penetrance by 30 days of age, and Pten/Trp53^d/d females developed a more aggressive form of this disease by 21 days of age. Using these mouse models, we previously showed that pAkt and Cox2 levels are elevated in the uteri of both Pten^d/d and Pten/Trp53^d/d mice.¹⁷Here, we show that a downstream component of the mTORC1 effector pathway is significantly up-regulated in the uteri of these mice. These results suggest that Cox2 and mTORC1 are associated with EMC. We then examined whether the Cox2 and mTORC1 pathways are critical in cancer progression and whether they influence EMC independently or cooperatively. We treated Pten^d/d females and their control littermates (Pten^f/f) with rapamycin (mTORC1 inhibitor) and/or celecoxib (Cox2 inhibitor) by oral gavage on every alternate day for 29 days, beginning at 30 days of age. We found that treatment with rapamycin or celecoxib monotherapy attenuated tumor growth, whereas maximal reductions in tumor growth and progression were noted in Pten^d/d females receiving both rapamycin and celecoxib. We also observed a similar reduction in tumor progression in Pten/Trp53^d/d females after combined treatment with rapamycin and celecoxib. Using a mouse EMC cell line established from Pten/Trp53^d/d uteri and three human EMC cell lines, we also found that rapamycin reduces Cox2 expression at the mRNA and protein levels and that celecoxib reduces mTORC1 activity, suggesting that Cox2 and mTORC1 activities are cross-regulated and cooperatively exacerbate EMC. Thus, a combined treatment with celecoxib and rapamycin could be an effective therapeutic strategy for combating EMC.