Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P42345 (mTOR)
 26,049 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The oncogenic epidermal growth factor receptor (EGFR) pathway triggers downstream phosphatidylinositol 3-kinase (PI3K)/RAS-mediated signaling cascades. In transgenic mice, glioblastoma cannot develop on single but only on simultaneous activation of the EGFR signaling mediators RAS and AKT. However, complete blockade of EGFR activation does not result in apoptosis in human glioblastoma cells, suggesting additional cross-talk between downstream pathways. Based on these observations, we investigated combination therapies using protein kinase inhibitors against EGFR, platelet-derived growth factor receptor, and mammalian target of rapamycin, assessing glioblastoma cell survival. Clinically relevant doses of AEE788, Gleevec (imatinib), and RAD001 (everolimus), alone or in combinations, did not induce glioblastoma cell apoptosis. In contrast, simultaneous inactivation of the EGFR downstream targets mitogen-activated protein/extracellular signal-regulated kinase (ERK) kinase and PI3K by U0126 and wortmannin triggered rapid tumor cell death. Blocking EGFR with AEE788 in combination with sublethal concentrations of the microtubule stabilizer patupilone also induced apoptosis and reduced cell proliferation in glioblastoma cells, accompanied by reduced AKT and ERK activity. These data underline the critical role of the PI3K/AKT and the RAS/RAF/mitogen-activated protein/ERK kinase/ERK signaling cascades in the cell-intrinsic survival program of sensitive glioblastoma cell lines. We conclude that drug combinations, which down-regulate both ERK and protein kinase B/AKT activity, may prove effective in overcoming cell resistance in a subgroup of glioblastoma.
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PMID:Combination of sublethal concentrations of epidermal growth factor receptor inhibitor and microtubule stabilizer induces apoptosis of glioblastoma cells. 1730 73

Specific inhibitors can be designed to inactivate the molecular pathways involved in tumor growth. A compelling example is the use of small molecule drugs, such as imatinib (Gleevec), which inhibit the KIT tyrosine kinase in gastrointestinal stromal tumors (GIST). Assays are needed to determine which inhibitor is most effective at silencing the KIT kinase in each GIST patient. The aim of this study was to develop a robust, cytology-based assay to measure tumor susceptibility to target-specific small molecule inhibitors. We created an immortal GIST cell line (GIST882) that was treated in vitro with several inhibitors of the KIT --> AKT --> mTOR --> S6 signaling pathway. KIT was inhibited with imatinib, and mTOR with RAD001. Treatment response was assessed in cytologic preparations by immunocytochemical staining with antibodies to KIT, phospho-KIT, phospho-AKT, and phospho-S6. Optimization was performed to maximize staining in the absence of inhibitor, and minimize staining in the presence of inhibitor. GIST882 cells demonstrated strong, robust phospho-S6 expression in the absence of inhibitor. This expression was completely inhibited by treatment with upstream signaling pathway inhibitors (imatinib and RAD001). Other phospho-specific antibodies had weaker baseline reactivity in the absence of inhibitor. The accuracy of the immunocytochemical results on the cytologic preparations was validated by immunoblotting studies. Our study demonstrates the feasibility of cytologic methods to monitor labile biochemical responses in tumor cells during drug therapy. Such approaches will be enhanced by the development of additional activation state-specific antibodies, particularly those optimized for use in cytologic preparations.
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PMID:An in vitro cytologic assay for evaluation of the KIT signaling pathway in gastrointestinal stromal tumors. 1739 39

Drug combinations may provide a therapeutic benefit in treating cancer patients. However when considering a drug combination, it is important to assess how the molecular impact of the combination relates to the effects manifested by each drug alone and whether or not it varies depending on the tumor type. In this study, we have analyzed the molecular impact on a human leiomyosarcoma cell line (SK-LMS-1) of a combination consisting of the mTOR inhibitor rapamycin and either the anti-metabolite drug gemcitabine (Gemzar) or the protein tyrosine kinase inhibitor imatinib mesylate (Gleevec, STI571). We show that imatinib mesylate depolarizes the mitochondrial membrane potential (DeltaPhim) and inhibits protein tyrosine phosphorylation, but displays only minor effects on cell proliferation when added alone or in combin-ation with rapamycin. Gemcitabine or rapamycin, when added alone, inhibit protein tyrosine phosphorylation as well as phosphorylation of the MAP kinases ERK1/2. Both drugs also affect the cell cycle, arresting the cells at the S or G1 phase respectively. Rapamycin elevates significantly DeltaPhim but produces only a moderate effect on cell growth. Gemcitabine inhibits considerably cell growth but exerts no effect on DeltaPhim. Combining gemcitabine and rapamycin produces a major effect on the cell cycle, elevates the DeltaPhim even further and maintains the molecular impacts exerted by each single drug. Therefore, consistent with our clinical observation, these results suggest that combining gemcitabine and rapamycin may be beneficial in treating leiomyosarcoma patients.
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PMID:Molecular impacts of rapamycin-based drug combinations: combining rapamycin with gemcitabine or imatinib mesylate (Gleevec) in a human leiomyosarcoma model. 1754 26

Protein kinases catalyse key phosphorylation reactions in signalling cascades that affect every aspect of cell growth, differentiation and metabolism. The kinases have become prime targets for drug intervention in the diseased state, especially in cancer. There are currently 10 drugs that have been approved for clinical use and many more in clinical trials. This review summarises the structural basis for protein kinase inhibition and discusses the mode of action for each of the approved drugs in the light of structural results. All but one of the approved compounds target the ATP binding site on the kinase. Both the active and inactive conformations of protein kinases have been used in strategies to produce potent and selective compounds. Targeting the inactive conformation can give high specificity. Targeting the active conformation is favourable where the diseased state has arisen from activating mutations, but such inhibitors generally target several protein kinases. Drug resistance mutations are a potential risk for both conformational states, where drug-binding regions are not directly involved in catalysis. Imatinib (Glivec), the most successful of protein kinase inhibitors, targets the inactive conformation of ABL tyrosine kinase. Newer compounds, such as dasatinib, which targets the ABL active state, have been developed to increase potency and have proved effective for some, but not all, drug-resistant mutations. The first epidermal growth factor receptor (EGFR) inhibitors in clinical use [gefitinib (Iressa) and erlotinib (Tarceva)] targeted the active form of the kinase, and this proved advantageous for patients whose cancer was caused by mutations that resulted in a constitutively active EGFR kinase domain. Newer approved compounds, such as lapatinib (Tykerb), target the inactive conformation with high potency. A further compound that forms a covalent attachment to the kinase has been found to overcome one of the major drug resistance mutations, where the effectiveness of the drug in vivo is dependent on its ability to compete successfully in the presence of cellular concentrations of ATP. Inhibitors of vascular endothelial growth factor receptor (VEGFR) kinase against cancer angiogenesis show the advantage of some relaxation in specificity. Sorafenib, originally developed as RAF inhibitor, is now in clinical use as a VEGFR inhibitor. Temsirolimus (a derivative of rapamycin) is the only example of a drug in clinical use that does not target the kinase ATP site. Instead rapamycin, when in complex with the protein FKBP12, effectively targets mTOR kinase at a site located on a domain, the FRB domain, that appears to be involved in localisation or substrate docking.
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PMID:Protein kinase inhibitors: contributions from structure to clinical compounds. 1929 66

The mammalian target of rapamycin (mTOR) is one target of BCR-ABL fusion gene of chronic myeloid leukemia (CML). Moreover, it drives a compensatory route to Imatinib mesylate (IM) possibly involved in the progression of leukemic progenitors towards a drug-resistant phenotype. Accordingly, mTOR inhibitors are proposed for combined therapeutic strategies in CML. The major caveat in the use of mTOR inhibitors for cancer therapy comes from the induction of an mTOR-phosphatidylinositol 3 kinase (PI3k) feedback loop driving the retrograde activation of Akt. Here we show that the rapamycin derivative RAD 001 (everolimus, Novartis Institutes for Biomedical Research) inhibits mTOR and, more importantly, revokes mTOR late re-activation in response to IM. RAD 001 interferes with the assembly of both mTOR complexes: mTORC1 and mTORC2. The inhibition of mTORC2 results in the de-phosphorylation of Akt at Ser(473) in the hydrophobic motif of C-terminal tail required for Akt full activation and precludes Akt re-phosphorylation in response to IM. Moreover, RAD 001-induced inhibition of Akt causes the de-phosphorylation of tuberous sclerosis tumor suppressor protein TSC2 at 14-3-3 binding sites, TSC2 release from 14-3-3 sigma (restoring its inhibitory function on mTORC1) and nuclear import (promoting the nuclear translocation of cyclin-dependent kinase [CDK] inhibitor p27(Kip1), the stabilization of p27(Kip1) ligand with CDK2, and the G(0)/G(1) arrest). RAD 001 cytotoxicity on cells not expressing the BCR-ABL fusion gene or its p210 protein tyrosine kinase (TK) activity suggests that the inhibition of normal hematopoiesis may represent a drug side effect.
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PMID:RAD 001 (everolimus) prevents mTOR and Akt late re-activation in response to imatinib in chronic myeloid leukemia. 2001 66

Although a relatively rare malignancy with a national incidence of 3500-4000 annually, Gastrointestinal Stromal Tumor (GIST) is of significance in the realm of clinical and pharmacological research. GIST exhibits remarkable uniformity in its pathogenesis and ultrastructure as 95% of cases are linked to constitutive activation and overexpression of a membrane tyrosine kinase, c-KIT (CD117). Although previously refractory to any course of action but surgery, GIST heralded a triumph in targeted cancer therapy when administration of a specific first-generation tyrosine-kinase inhibitor Imatinib mesylate (STI571) was shown to inhibit c-Kit and demonstrated a significant increase in patient survival. Over the subsequent decade, GIST has become a paradigm for the potency of Imatinib in adjuvant or neoadjuvant therapy, showcasing the clinical relevance and rapidity of translational research in the field of targeted molecular therapy. Subsequent to demonstrating the efficacy of Imatinib as a therapeutic agent, GIST has also exposed the limitations of current targeted therapies. Within two years, 50% of GISTs develop secondary mutations that allow resistance to Imatinib. However, extensive research regarding both primary and secondary c-KIT mutations has illuminated the mechanisms of Imatinib resistance and has the potential to ameliorate this therapeutic setback. Current research to this end lies in two primary directions: the development of tyrosine kinase inhibitors (some of which also inhibit other oncogenic agents such as PDGFR, bcr-abl, and VEGF) that are either generally more potent than Imatinib or less susceptible to specific mechanisms of resistance; and drugs that target the downstream effectors of the mutant c-KIT kinase, including PKC and mTOR. This paper will systematically review current research on second-generation targeted molecular therapy in the treatment of GIST, and expand upon its value as a model for treatment of other solid organ tumors.
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PMID:Gastrointestinal stromal tumors: a paradigm for therapeutic options in solid organ tumors. 2050 Jan 52


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