J Angiogenes Res. 2010 Feb 19;2(1):5.
Methylnaltrexone potentiates the anti-angiogenic effects of mTOR inhibitors.
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Singleton PA,
Mambetsariev N,
Lennon FE,
Mathew B,
Siegler JH,
Moreno-Vinasco L,
Salgia R,
Moss J,
Garcia JG.
Department of Medicine, University of Chicago, 5841 S Maryland Avenue, W604, Chicago, IL 60637, USA.
psinglet@medicine.bsd.uchicago.edu
Abstract
BACKGROUND: Recent cancer therapies include drugs that target both tumor growth and angiogenesis including mammalian target of rapamycin (mTOR) inhibitors. Since mTOR inhibitor therapy is associated with significant side effects, we examined potential agents that can reduce the therapeutic dose. METHODS: Methylnaltrexone (MNTX), a peripheral mu opioid receptor (MOR) antagonist, in combination with the mTOR inhibitors temsirolimus and/or rapamycin, was evaluated for inhibition of VEGF-induced human pulmonary microvascular endothelial cell (EC) proliferation and migration as well as in vivo angiogenesis (mouse Matrigel plug assay). RESULTS: MNTX inhibited VEGF-induced EC proliferation and migration with an IC50 of approximately 100 nM. Adding 10 nM MNTX to EC shifted the IC50 of temsirolimus inhibition of VEGF-induced proliferation and migration from approximately 10 nM to approximately 1 nM and from approximately 50 to approximately 10 nM respectively. We observed similar effects with rapamycin. On a mechanistic level, we observed that MNTX increased EC plasma membrane-associated tyrosine phosphate activity. Inhibition of tyrosine phosphatase activity (3,4-dephostatin) blocked the synergy between MNTX and temsirolimus and increased VEGF-induced tyrosine phosphorylation of Src with enhanced PI3 kinase and mTOR Complex 2-dependent phosphorylation of Akt and subsequent activation of mTOR Complex 1 (rapamycin and temsirolimus target), while silencing Src, Akt or mTOR complex 2 components blocked VEGF-induced angiogenic events. CONCLUSIONS:
Our data indicate that MNTX exerts a synergistic effect with rapamycin and temsirolimus on inhibition of VEGF-induced human EC proliferation and migration and in vivo angiogenesis. Therefore, addition of MNTX could potentially lower the dose of mTOR inhibitors which could improve therapeutic index.
PMID: 20298531 [PubMed]PMCID: PMC2831839Free PMC Article
Transplant Proc. 2008 Dec;40(10 Suppl):S32-5.
The impact of mTOR inhibitors on the development of malignancy.
Geissler EK.
University of Regensburg, Regensburg, Germany.
edward.geissler@klinik.uni-regensburg.de
Abstract
Although continuous improvements have been made in fighting rejection with immunosuppressive drugs in transplant recipients, this success story has been tempered by an associated high incidence of cancer. The latest projections are that cancer might exceed cardiovascular disease as the leading cause of death among transplant recipients. Indeed,
immunosuppression reduces our natural ability to destroy cancer cells and to inhibit viral infections potentially linked to cancer development. Therefore, a strategy to counter the problem of cancer in transplantation is needed. Recently, mammalian target of rapamycin (mTOR) inhibitors have demonstrated potential as both immunosuppressive and anticancer agents.
Although mTOR inhibitors prevent organ transplant rejection, this class of drugs has potential anticancer properties that may be useful in the "balance of effects" toward cancer-free survival in transplant recipients. Mechanisms of mTOR inhibitors' anticancer effects are multiple, affecting processes including angiogenesis, cell proliferation, cell survival, and molecular oncogenic signaling. Importantly, experimental work supports the view that tumor inhibition can be accomplished with mTOR inhibitors while protecting allografts against rejection. Most recently, prospective randomized clinical studies have been initiated to test the concept that mTOR inhibitors reduce cancer while simultaneously inhibiting allograft rejection. One such study, the SiLVER trial, examines hepatocellular carcinoma recurrence in mTOR inhibitor-treated liver transplant patients. More robust evidence as to whether cancer risk can be reduced in transplant recipients with mTOR inhibitors may come from such clinical trials.
PMID: 19100904 [PubMed - indexed for MEDLINE]
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