Pediatric and adult glioblastoma radiosensitization induced by PI3K/mTOR inhibition causes early metabolic alterations detected by nuclear magnetic resonance spectroscopy
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Alice Agliano1, Geetha Balarajah1,4, Daniela M. Ciobota1, Jasmin Sidhu1, Paul A. Clarke2, Chris Jones3, Paul Workman2, Martin O. Leach1 and Nada M.S. Al-Saffar1
1Cancer Research UK Cancer Imaging Centre, Division of Radiotherapy and Imaging, The Institute of Cancer Research, London, United Kingdom
2Cancer Research UK Cancer Therapeutics Unit, The Institute of Cancer Research, London, United Kingdom
3Divisions of Cancer Therapeutics and Molecular Pathology, The Institute of Cancer Research and The Royal Marsden NHS Foundation Trust, London, United Kingdom
4The Centre for Molecular Pathology, Division of Cancer Therapeutics, The Institute of Cancer Research, London, United Kingdom
Martin Leach, email: Martin.Leach@icr.ac.uk
Nada Al-Saffar, email: Nada.Al-Saffar@icr.ac.uk
Keywords: metabolic biomarker, glioblastoma, PI3K/mTOR, nuclear magnetic resonance spectroscopy, irradiation
Received: October 19, 2016 Accepted: April 29, 2017 Published: May 24, 2017
Poor outcome for patients with glioblastomas is often associated with radioresistance. PI3K/mTOR pathway deregulation has been correlated with radioresistance; therefore, PI3K/mTOR inhibition could render tumors radiosensitive. In this study, we show that NVP-BEZ235, a dual PI3K/mTOR inhibitor, potentiates the effects of irradiation in both adult and pediatric glioblastoma cell lines, resulting in early metabolic changes detected by nuclear magnetic resonance (NMR) spectroscopy. NVP-BEZ235 radiosensitises cells to X ray exposure, inducing cell death through the inhibition of CDC25A and the activation of p21cip1(CDKN1A). Lactate and phosphocholine levels, increased with radiation, are decreased after NVP-BEZ235 and combination treatment, suggesting that inhibiting the PI3K/mTOR pathway reverses radiation induced metabolic changes. Importantly, NVP-BEZ235 potentiates the effects of irradiation in a xenograft model of adult glioblastoma, where we observed a decrease in lactate and phosphocholine levels after seven days of combination treatment. Although tumor size was not affected due to the short length of the treatment, a significant increase in CASP3 mRNA was observed in the combination group. Taken together, our data suggest that NMR metabolites could be used as biomarkers to detect an early response to combination therapy with PI3K/mTOR inhibitors and radiotherapy in adult and pediatric glioblastoma patients.
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