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      Tuberous sclerosis preclinical studies: timing of treatment, combination of a rapamycin analog (CCI-779) and interferon-gamma, and comparison of rapamycin to CCI-779

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      1 , 1 , 1 , 1 ,
      BMC Pharmacology
      BioMed Central

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          Abstract

          Background

          Tuberous Sclerosis Complex (TSC) is an autosomal dominant hamartoma disorder with variable expression for which treatment options are limited. TSC is caused by a mutation in either the TSC1 or TSC2 genes, whose products, hamartin and tuberin, function as negative regulators in the highly-conserved mammalian target of rapamycin (mTOR) signaling pathway. Rapamycin (also known as sirolimus), an mTOR inhibitor, has been shown to reduce disease severity in rodent models of TSC and is currently being evaluated in clinical trials in human populations. The cytokine interferon-gamma (IFN-γ) is also a potential therapeutic agent for TSC. A high-expressing IFN-γ allele has been associated with reduced disease severity in human TSC patients and it has been shown in mouse models that treatment with exogenous IFN-γ reduces disease severity.

          Results

          Here, we examine the effects of treating Tsc2 +/- mice at different time points with a rapamycin analog (CCI-779) as a single agent or with a combination of CCI-779 and IFN-γ. We observed that administering a short course of CCI-779 or CCI-779 plus IFN-γ reduced the severity of kidney lesions if administered after such lesions develop. As long as treatment is given after lesions arise, altering the time period during which treatment was given did not significantly impact the effect of the treatment on disease severity. We did not observe a significant benefit of combination therapy relative to treatment with a rapamycin analog alone in Tsc2 +/- mice. We also compared timing of treatment and two mTOR inhibitors (rapamycin and CCI-779) in nude mice bearing Tsc2 -/- tumors.

          Conclusion

          Preventing the genesis of TSC-related kidney lesions in Tsc2 +/- mice is not an effective treatment strategy; rather, the presence of growing tumors appears to be the most important factor when determining an appropriate treatment schedule. Treatment with rapamycin was more effective in reducing tumor growth and improving survival in nude mice bearing Tsc2 -/- tumors and also resulted in higher rapamycin levels in blood, brain, and kidney tissue than treatment with an equal milligram dose of CCI-779. We anticipate these results will influence future preclinical and clinical trials for TSC.

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          Most cited references28

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          Dysregulation of the TSC-mTOR pathway in human disease.

          The mammalian target of rapamycin (mTOR) has a central role in the regulation of cell growth. mTOR receives input from multiple signaling pathways, including growth factors and nutrients, to stimulate protein synthesis by phosphorylating key translation regulators such as ribosomal S6 kinase and eukaryote initiation factor 4E binding protein 1. High levels of dysregulated mTOR activity are associated with several hamartoma syndromes, including tuberous sclerosis complex, the PTEN-related hamartoma syndromes and Peutz-Jeghers syndrome. These disorders are all caused by mutations in tumor-suppressor genes that negatively regulate mTOR. Here we discuss the emerging evidence for a functional relationship between the mTOR signaling pathway and several genetic diseases, and we present evidence supporting a model in which dysregulation of mTOR may be a common molecular basis, not only for hamartoma syndromes, but also for other cellular hypertrophic disorders.
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            The biology and clinical relevance of the PTEN tumor suppressor pathway.

            Genetic alterations targeting the PTEN tumor suppressor gene are among the most frequently noted somatic mutations in human cancers. Such lesions have been noted in cancers of the prostate and endometrium and in glioblastoma multiforme, among many others. Moreover, germline mutation of PTEN leads to the development of the related hereditary cancer predisposition syndromes, Cowden disease, and Bannayan-Zonana syndrome, wherein breast and thyroid cancer incidence is elevated. The protein product, PTEN, is a lipid phosphatase, the enzymatic activity of which primarily serves to remove phosphate groups from key intracellular phosphoinositide signaling molecules. This activity normally serves to restrict growth and survival signals by limiting activity of the phosphoinositide-3 kinase (PI3K) pathway. Multiple lines of evidence support the notion that this function is critical to the ability of PTEN to maintain cell homeostasis. Indeed, the absence of functional PTEN in cancer cells leads to constitutive activation of downstream components of the PI3K pathway including the Akt and mTOR kinases. In model organisms, inactivation of these kinases can reverse the effects of PTEN loss. These data raise the possibility that drugs targeting these kinases, or PI3K itself, might have significant therapeutic activity in PTEN-null cancers. Akt kinase inhibitors are still in development; however, as a first test of this hypothesis, phase I and phase II trials of inhibitors of mTOR, namely, rapamycin and rapamycin analogs are underway.
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              Phase II trial of temsirolimus (CCI-779) in recurrent glioblastoma multiforme: a North Central Cancer Treatment Group Study.

              Temsirolimus (CCI-779) is a small-molecule inhibitor of the mammalian target of rapamycin (mTOR) and represents a rational therapeutic target against glioblastoma multiforme (GBM). Recurrent GBM patients with < or = 1 chemotherapy regimen for progressive disease were eligible. Temsirolimus was administered in a 250-mg intravenous dose weekly. Sixty-five patients were treated. The incidence of grade 3 or higher nonhematologic toxicity was 51%, and consisted mostly of hypercholesterolemia (11%), hypertriglyceridemia (8%), and hyperglycemia (8%). Grade 3 hematologic toxicity was observed in 11% of patients. Temsirolimus peak concentration (Cmax), and sirolimus Cmax and area under the concentration-time curve were decreased in patients receiving p450 enzyme-inducing anticonvulsants (EIACs) by 73%, 47%, and 50%, respectively, but were still within the therapeutic range of preclinical models. Twenty patients (36%) had evidence of improvement in neuroimaging, consisting of decrease in T2 signal abnormality +/- decrease in T1 gadolinium enhancement, on stable or reduced steroid doses. Progression-free survival at 6 months was 7.8% and median overall survival was 4.4 months. Median time to progression (TTP) for all patients was 2.3 months and was significantly longer for responders (5.4 months) versus nonresponders (1.9 months). Development of grade 2 or higher hyperlipidemia in the first two treatment cycles was associated with a higher percentage of radiographic response (71% v 31%; P = .04). Significant correlation was observed between radiographic improvement and high levels of phosphorylated p70s6 kinase in baseline tumor samples (P = .04). Temsirolimus is well tolerated in recurrent GBM patients. Despite the effect of EIACs on temsirolimus metabolism, therapeutic levels were achieved. Radiographic improvement was observed in 36% of temsirolimus-treated patients, and was associated with significantly longer TTP. High levels of phosphorylated p70s6 kinase in baseline tumor samples appear to predict a patient population more likely to derive benefit from treatment. These findings should be validated in other studies of mTOR inhibitors.
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                Author and article information

                Journal
                BMC Pharmacol
                BMC Pharmacology
                BioMed Central
                1471-2210
                2007
                6 November 2007
                : 7
                : 14
                Affiliations
                [1 ]Translational Medicine Division, Department of Medicine, Brigham & Women's Hospital, Karp Family Research Laboratories, Boston, MA, USA
                Article
                1471-2210-7-14
                10.1186/1471-2210-7-14
                2213639
                17986349
                024b8f2c-4367-4e62-a6e1-df3cb8fc4626
                Copyright © 2007 Messina 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 cited.

                History
                : 8 June 2007
                : 6 November 2007
                Categories
                Research Article

                Pharmacology & Pharmaceutical medicine
                Pharmacology & Pharmaceutical medicine

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