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Abstract 3745: The dual PI3K/mTOR inhibitor NVP-BEZ235 is a potent inhibitor of ATM- and DNA-PKcs-mediated DNA damage responses

Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
Neoplasia (New York, N.Y.) (Impact Factor: 5.4). 06/2012; 14(1):34-43. DOI: 10.1158/1538-7445.AM2012-3745
Source: PubMed

ABSTRACT Inhibitors of PI3K/Akt signaling are being actively developed for tumor therapy owing to the frequent mutational activation of the PI3K-Akt-mTORC1 pathway in many cancers, including glioblastomas (GBMs). NVP-BEZ235 is a novel and potent dual PI3K/mTOR inhibitor that is currently in phase 1/2 clinical trials for advanced solid tumors. Here, we show that NVP-BEZ235 also potently inhibits ATM and DNA-PKcs, the two major kinases responding to ionizing radiation (IR)-induced DNA double-strand breaks (DSBs). Consequently, NVP-BEZ235 blocks both nonhomologous end joining and homologous recombination DNA repair pathways resulting in significant attenuation of DSB repair. In addition, phosphorylation of ATMtargets and implementation of the G(2)/M cell cycle checkpoint are also attenuated by this drug. As a result, NVP-BEZ235 confers an extreme degree of radiosensitization and impairs DSB repair in a panel of GBM cell lines irrespective of their Akt activation status. NVP-BEZ235 also significantly impairs DSB repair in a mouse tumor model thereby validating the efficacy of this drug as a DNA repair inhibitor in vivo. Our results, showing that NVP-BEZ235 is a potent and novel inhibitor of ATM and DNA-PKcs, have important implications for the informed and rational design of clinical trials involving this drug and also reveal the potential utility of NVP-BEZ235 as an effective radiosensitizer for GBMs in the clinic.

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    • "However it is more difficult to determine to what extent alleviation of hypoxia accounts for these results, because these inhibitors also sensitize cells to DNA damage under oxic conditions. Inhibition of PI3K reduces DNA damage repair, but BEZ235 also has off-target effects of inhibition of ATR and DNA-PK [29]. Fokas et al. attempted to separate the effects on tumor oxygenation from cell-specific effects by administering the drug BEZ235 immediately before tumor radiation, when it still altered tumor signaling but before the more prolonged changes of hypoxia associated with extended preincubation had occurred. "
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    ABSTRACT: Background Inhibitors of the phosphatidylinositol 3-kinase (PI3K) and the mammalian target of rapamycin (mTOR) pathway are currently in clinical trials. In addition to antiproliferative and proapoptotic effects, these agents also diminish tumor hypoxia. Since hypoxia is a major cause of resistance to radiotherapy, we sought to understand how it is regulated by PI3K/mTOR inhibition. Methods Whole cell, mitochondrial, coupled and uncoupled oxygen consumption were measured in cancer cells after inhibition of PI3K (Class I) and mTOR by pharmacological means or by RNAi. Mitochondrial composition was assessed by immunoblotting. Hypoxia was measured in spheroids, in tumor xenografts and predicted with mathematical modeling. Results Inhibition of PI3K and mTOR reduced oxygen consumption by cancer cell lines is predominantly due to reduction of mitochondrial respiration coupled to ATP production. Hypoxia in tumor spheroids was reduced, but returned after removal of the drug. Murine tumors had increased oxygenation even in the absence of average perfusion changes or tumor necrosis. Conclusions Targeting the PI3K/mTOR pathway substantially reduces mitochondrial oxygen consumption thereby reducing tumor hypoxia. These alterations in tumor hypoxia should be considered in the design of clinical trials using PI3K/mTOR inhibitors, particularly in conjunction with radiotherapy.
    Radiotherapy and Oncology 04/2014; 111(1). DOI:10.1016/j.radonc.2014.02.007 · 4.86 Impact Factor
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    • "The radiosensitizing effect was independent of the PTEN and p53 status of the cell lines. The enhancement of radiation sensitivity by NVP-BEZ235 under schedule II reported here is consistent with the recent findings that, if added shortly before IR, NVP-BEZ235 radiosensitizes various tumor cell lines [29] [30] [31] [32] [33]. At variance with schedule II, a long-term pretreatment of cells with NVP-BEZ235 (schedule I) completely abolished the radiosensitizing ability in all of tested glioblastoma lines (Figure 2, top row). "
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    ABSTRACT: Previous studies have shown that the dual phosphatidylinositide 3-kinase/mammalian target of rapamycin (PI3K/mTOR) inhibitor NVP-BEZ235 radiosensitizes tumor cells if added shortly before ionizing radiation (IR) and kept in culture medium thereafter. The present study explores the impact of inhibitor and IR schedule on the radiosensitizing ability of NVP-BEZ235 in four human glioblastoma cell lines. Two different drug-IR treatment schedules were compared. In schedule I, cells were treated with NVP-BEZ235 for 24 hours before IR and the drug was removed before IR. In schedule II, the cells were exposed to NVP-BEZ235 1 hour before, during, and up to 48 hours after IR. The cellular response was analyzed by colony counts, expression of marker proteins of the PI3K/AKT/mTOR pathway, cell cycle, and DNA damage. We found that under schedule I, NVP-BEZ235 did not radiosensitize cells, which were mostly arrested in G1 phase during IR exposure. In addition, the drug-pretreated and irradiated cells exhibited less DNA damage but increased expressions of phospho-AKT and phospho-mTOR, compared to controls. In contrast, NVP-BEZ235 strongly enhanced the radiosensitivity of cells treated according to schedule II. Possible reasons of radiosensitization by NVP-BEZ235 under schedule II might be the protracted DNA repair, prolonged G2/M arrest, and, to some extent, apoptosis. In addition, the PI3K pathway was downregulated by the NVP-BEZ235 at the time of irradiation under schedule II, as contrasted with its activation in schedule I. We found that, depending on the drug-IR schedule, the NVP-BEZ235 can act either as a strong radiosensitizer or as a cytostatic agent in glioblastoma cells.
    Translational oncology 04/2013; 6(2):169-79. DOI:10.1593/tlo.12364 · 3.40 Impact Factor
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    ABSTRACT: Modulation of DNA repair pathways in oncology has been an area of intense interest in the last decade, not least as a consequence of the promising clinical activity of poly(ADP-ribose) polymerase (PARP) inhibitors. In this review article, we highlight inhibitors of the phosphatidylinositol 3-kinase related kinase (PIKK) family as of potential interest in the treatment of cancer, both in combination with DNA-damaging therapies and as stand-alone agents.
    Bioorganic & medicinal chemistry letters 07/2012; 22(17):5352-9. DOI:10.1016/j.bmcl.2012.06.053 · 2.33 Impact Factor
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