Phosphatidylinositide 3-kinase (PI3K) and PI3K-related kinase (PIKK) activity contributes to radioresistance in thyroid carcinomas
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Natalie Burrows1,7, Joseph Williams1, Brian A Telfer1, Julia Resch2, Helen R Valentine3, Richard J Fitzmaurice4, Amanda Eustace3, Joely Irlam3, Emily J Rowling1, Cuong Hoang-Vu5, Catharine M West3,6, Georg Brabant2, Kaye J Williams1,6
1Hypoxia and Therapeutics Group, Manchester Pharmacy School, University of Manchester, Manchester, UK
2Experimental and Clinical Endocrinology, Medizinische Klinik I, Lubeck, Germany
3Translational Radiobiology Group, University of Manchester, Christie Hospital, NHS Trust, Manchester Academic Health Science Centre, Manchester, UK
4Department of Histopathology, CSB1, Manchester Royal Infirmary, Manchester, UK
5Martin Luther University of Halle-Wittenberg, Halle, Salle, Germany
6Radiotherapy Related Research Group, Manchester Cancer Research Centre, Manchester, UK
7Current address: School of Clinical Medicine, Cambridge Institute for Medical Research, University of Cambridge, Cambridge Biomedical Campus, Cambridge, UK
Natalie Burrows, email: [email protected]
Keywords: radioresistance, ATM, ATR, DNA-PKcs, PI3K
Received: March 21, 2016 Accepted: July 09, 2016 Published: August 04, 2016
Anaplastic (ATC) and certain follicular thyroid-carcinomas (FTCs) are radioresistant. The Phosphatidylinositide 3-kinase (PI3K) pathway is commonly hyperactivated in thyroid-carcinomas. PI3K can modify the PI3K-related kinases (PIKKs) in response to radiation: How PIKKs interact with PI3K and contribute to radioresistance in thyroid-carcinomas is unknown. Further uncertainties exist in how these interactions function under the radioresistant hypoxic microenvironment.
Under normoxia/anoxia, ATC (8505c) and FTC (FTC-133) cells were irradiated, with PI3K-inhibition (via GDC-0941 and PTEN-reconstitution into PTEN-null FTC-133s) and effects on PIKK-activation, DNA-damage, clonogenic-survival and cell cycle, assessed. FTC-xenografts were treated with 5 × 2 Gy, ± 50 mg/kg GDC-0941 (twice-daily; orally) for 14 days and PIKK-activation and tumour-growth assessed. PIKK-expression was additionally assessed in 12 human papillary thyroid-carcinomas, 13 FTCs and 12 ATCs.
GDC-0941 inhibited radiation-induced activation of Ataxia-telangiectasia mutated (ATM), ATM-and Rad3-related (ATR) and DNA-dependent protein kinase catalytic subunit (DNA-PKcs). Inhibition of ATM and DNA-PKcs was PI3K-dependent, since activation was reduced in PTEN-reconstituted FTC-133s. Inhibition of PIKK-activation was greater under anoxia: Consequently, whilst DNA-damage was increased and prolonged under both normoxia and anoxia, PI3K-inhibition only reduced clonogenic-survival under anoxia. GDC-0941 abrogated radiation-induced cell cycle arrest, an effect most likely linked to the marked inhibition of ATR-activation. Importantly, GDC-0941 inhibited radiation-induced PIKK-activation in FTC-xenografts leading to a significant increase in time taken for tumours to triple in size: 26.5 ± 5 days (radiation-alone) versus 31.5 ± 5 days (dual-treatment). PIKKs were highly expressed across human thyroid-carcinoma classifications, with ATM scoring consistently lower. Interestingly, some loss of ATM and DNA-PKcs was observed. These data provide new insight into the mechanisms of hypoxia-associated radioresistance in thyroid-carcinoma.
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