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      Phosphorylation of mTOR and S6RP predicts the efficacy of everolimus in patients with metastatic renal cell carcinoma

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          Abstract

          Background

          The incidence of renal cell cancer (RCC) has been increasing for the past decade, and the 5-year survival for patients with metastatic RCC (mRCC) is rather low. Everolimus (RAD001), a new inhibitor for mammalian target of rapamycin (mTOR), is generally well tolerated, and demonstrates clinical benefit to patients with anti-VEGF-refractory mRCC. However, factors for selection of patients who may benefit from everolimus remain largely unknown. Here we aimed to explore potential molecular indicators for mRCC patients who may benefit from everolimus treatment.

          Methods

          Paraffin-embedded tumor tissue specimens derived from 18 mRCC patients before everolimus treatment, who participated the phase 1b trial of everolimus in VEGF receptor (VEGFR)-tyrosine kinase inhibitor (TKI)-refractory Chinese patients with mRCC (clinicaltrials.gov, NCT01152801), were examined for the expression levels of phosphorylated AKT, mTOR, eukaryotic initiation factor 4E (eIF4E) binding protein-1 (4EBP1) and 40S ribosomal protein S6 (S6RP) by immunohistochemistry. Clinical benefit rate (complete response [CR], partial response [PR], plus stable disease [SD] ≥ 6 months) and progression-free survival time (PFS) were correlated with expression levels of these mTOR-associated molecules.

          Results

          In these 18 patients, there were 1 PR, 15 SDs (including 9 SDs ≥ 6 months), and 2 progressive diseases (PD). The clinical benefit rate (CBR) was 55.6% (10/18), and the median PFS time was 8.4 months. Patients with positive expression of phospho-mTOR showed a better CBR (71.4% versus 0%, P = 0.023) and PFS time (11.3 versus 3.7 months, P = 0.001) than those patients with negative expression. The median PFS of patients with positive phospho-S6RP expression was longer (11.3 versus 3.7 months, P = 0.002) than that of patients negative for phospho-S6RP expression. However, expression levels of phospho-4EBP1 and phospho-AKT were unassociated to efficacy of everolimus treatment with respect to CBR and PFS. Co-expression of phosphorylated mTOR, S6RP and/or 4EBP1 may improve the predictive value of the biomarkers for patients treated with everolimus.

          Conclusions

          The expression levels of phospho-mTOR and phospho-S6RP may be potential predictive biomarkers for efficacy of everolimus in patients with mRCC. Combining examinations of phosphorylated mTOR, S6RP and/or 4EBP1 may be a potential strategy to select mRCC patients sensitive to mTOR inhibitor treatment.

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          Most cited references16

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          Interferon-alfa as a comparative treatment for clinical trials of new therapies against advanced renal cell carcinoma.

          To define outcome data and prognostic criteria for patients with metastatic renal cell carcinoma (RCC) treated with interferon-alfa as initial systemic therapy. The data can be applied to design and interpretation of clinical trials of new agents and treatment programs against this refractory malignancy. Four hundred sixty-three patients with advanced RCC administered interferon-alpha as first-line systemic therapy on six prospective clinical trials were the subjects of this retrospective analysis. Three risk categories for predicting survival were identified on the basis of five pretreatment clinical features by a stratified Cox proportional hazards model. The median overall survival time was 13 months. The median time to progression was 4.7 months. Five variables were used as risk factors for short survival: low Karnofsky performance status, high lactate dehydrogenase, low serum hemoglobin, high corrected serum calcium, and time from initial RCC diagnosis to start of interferon-alpha therapy of less than one year. Each patient was assigned to one of three risk groups: those with zero risk factors (favorable risk), those with one or two (intermediate risk), and those with three or more (poor risk). The median time to death of patients deemed favorable risk was 30 months. Median survival time in the intermediate-risk group was 14 months. In contrast, the poor-risk group had a median survival time of 5 months. Progression-free and overall survival with interferon-alpha treatment can be compared with new therapies in phase II and III clinical investigations. The prognostic model is suitable for risk stratification of phase III trials using interferon-alpha as the comparative treatment arm.
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            mTOR signaling and drug development in cancer.

            Mammalian target of rapamycin (mTOR) is a protein kinase of the PI3K/Akt signaling pathway. Activation of mTOR in response to growth, nutrient and energy signals leads to an increase in protein synthesis, which is required for tumor development. This feature makes mTOR an attractive target for cancer therapy. First-generation mTOR inhibitors are sirolimus derivatives (rapalogs), which have been evaluated extensively in cancer patients. Everolimus and temsirolimus are already approved for the treatment of renal-cell carcinoma. Temsirolimus is also approved for the treatment of mantle-cell lymphoma. These drugs, in addition to ridaforolimus (formerly deforolimus) and sirolimus, are currently being evaluated in clinical trials of various cancers. Second-generation mTOR inhibitors are small molecules that target the kinase domain, and have also entered clinical development. Clinical trials are underway to identify additional malignancies that respond to mTOR inhibitors, either alone or in combination with other therapies. Future research should evaluate the optimal drug regimens, schedules, patient populations, and combination strategies for this novel class of agents.
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              S6K1(-/-)/S6K2(-/-) mice exhibit perinatal lethality and rapamycin-sensitive 5'-terminal oligopyrimidine mRNA translation and reveal a mitogen-activated protein kinase-dependent S6 kinase pathway.

              Activation of 40S ribosomal protein S6 kinases (S6Ks) is mediated by anabolic signals triggered by hormones, growth factors, and nutrients. Stimulation by any of these agents is inhibited by the bacterial macrolide rapamycin, which binds to and inactivates the mammalian target of rapamycin, an S6K kinase. In mammals, two genes encoding homologous S6Ks, S6K1 and S6K2, have been identified. Here we show that mice deficient for S6K1 or S6K2 are born at the expected Mendelian ratio. Compared to wild-type mice, S6K1(-/-) mice are significantly smaller, whereas S6K2(-/-) mice tend to be slightly larger. However, mice lacking both genes showed a sharp reduction in viability due to perinatal lethality. Analysis of S6 phosphorylation in the cytoplasm and nucleoli of cells derived from the distinct S6K genotypes suggests that both kinases are required for full S6 phosphorylation but that S6K2 may be more prevalent in contributing to this response. Despite the impairment of S6 phosphorylation in cells from S6K1(-/-)/S6K2(-/-) mice, cell cycle progression and the translation of 5'-terminal oligopyrimidine mRNAs were still modulated by mitogens in a rapamycin-dependent manner. Thus, the absence of S6K1 and S6K2 profoundly impairs animal viability but does not seem to affect the proliferative responses of these cell types. Unexpectedly, in S6K1(-/-)/S6K2(-/-) cells, S6 phosphorylation persisted at serines 235 and 236, the first two sites phosphorylated in response to mitogens. In these cells, as well as in rapamycin-treated wild-type, S6K1(-/-), and S6K2(-/-) cells, this step was catalyzed by a mitogen-activated protein kinase (MAPK)-dependent kinase, most likely p90rsk. These data reveal a redundancy between the S6K and the MAPK pathways in mediating early S6 phosphorylation in response to mitogens.
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                Author and article information

                Contributors
                Journal
                BMC Cancer
                BMC Cancer
                BMC Cancer
                BioMed Central
                1471-2407
                2014
                28 May 2014
                : 14
                : 376
                Affiliations
                [1 ]Department of Renal Cancer and Melanoma, Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education), Peking University Cancer Hospital and Institute, Beijing 100142, China
                Article
                1471-2407-14-376
                10.1186/1471-2407-14-376
                4041340
                24886512
                ff8fc2e2-74b1-45af-88f5-fae06efbb9fe
                Copyright © 2014 Li et al.; licensee BioMed Central Ltd.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.

                History
                : 16 April 2013
                : 20 May 2014
                Categories
                Research Article

                Oncology & Radiotherapy
                metastatic renal cell carcinoma,targeted therapy,mammalian target of rapamycin,clinical response,predictive biomarker

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