Glucose requirement for hypoxic accumulation of hypoxia-inducible factor-1a (HIF-1a) Dirk Vordermark * , Peter Kraft, Astrid Katzer, Tobias Bo ¨lling, Jochen Willner, Michael Flentje Department of Radiation Oncology, University of Wu ¨rzburg, Josef-Schneider-Str. 11, 97080 Wu ¨rzburg, Germany Received 9 February 2004; received in revised form 23 November 2004; accepted 23 December 2004 Abstract Hypoxia-inducible factor-1a (HIF-1a) is both a potential endogenous marker of tumor hypoxia and therapeutic target, and elevated HIF-1a protein levels have been shown to be associated with increased hypoxic radiation resistance in FaDu human pharyngeal carcinoma cells in vitro. Here, we found that in FaDu xenografts, no significant HIF-1a protein accumulation was detectable by either flow cytometry or Western blot, despite the presence of hypoxic (pimonidazole-positive, radiation resistant) cells. To investigate the effect of different tumor microenvironment conditions on hypoxic HIF-1a accumulation, we performed in vitro hypoxia experiments (0.1% O 2 , 24 h) with manipulation of pH (7.4 vs. 6.7), glucose (0–5.5 mM) and serum (0 or 10%) availability in FaDu and HT 1080 human fibrosarcoma cells. Hypoxic induction of HIF-1a protein was strongly dependent on glucose availability and largely abolished at 0.55 mM glucose or less in both cell lines. This glucose effect was confirmed in a hypoxia-responsive-element (HRE)/enhanced-green-fluorescent-protein (EGFP) reporter assay in transfected HT 1080 cells and possibly explains a lack of HIF-1a protein in hypoxic tumor cells. q 2005 Elsevier Ireland Ltd. All rights reserved. Keywords: Tumor microenvironment; Tumor hypoxia; Radiosensitivity; Hypoxia markers; Hypoxia-inducible factor-1a 1. Introduction Tumor hypoxia is an established adverse prognostic factor in the radiotherapy of solid human tumors and the identification of patients with poorly oxygenated tumors is essential for the introduction of novel treatment strategies aimed at overcoming or exploiting tumor hypoxia. Measurements of intratumoral pO 2 with the Eppendorf electrode have defined the significance of tumor hypoxia in tumor sites accessible to measurement, in particular cervix and head and neck cancer as well as soft tissue sarcomas [1–3]. This method, however, is an invasive procedure and has several limitations, among them the difficult appli- cation in deep-seated lesions. Alternatively, injectable 2-nitroimidazole derivatives, among them pimonida- zole and EF5, are currently evaluated as exogenous hypoxia markers in immunohistochemical sections or nuclear medicine studies [4,5]. Recently, proteins Cancer Letters 230 (2005) 122–133 www.elsevier.com/locate/canlet 0304-3835/$ - see front matter q 2005 Elsevier Ireland Ltd. All rights reserved. doi:10.1016/j.canlet.2004.12.040 * Corresponding author. Tel.: C49 931 20128891; fax: C49 931 20128221. E-mail address: vordermark_d@klinik.uni-wuerzburg.de (D. Vordermark).