Activation of AKT by hypoxia: a potential target for hypoxic tumors of the head and neck

• Main Authors: Stegeman Hanneke, Kaanders Johannes H, Wheeler Deric L, van der Kogel Albert J, Verheijen Marieke M, Waaijer Stijn J, Iida Mari, Grénman Reidar, Span Paul N, Bussink Johan
• Format: Article
• Language: English
• Published: BMC 2012-10-01
• Series: BMC Cancer
• Subjects: Head and neck cancer; Tumor microenvironment; Hypoxia; pAKT; EGFR
• Online Access: http://www.biomedcentral.com/1471-2407/12/463

<p>Abstract</p> <p>Background</p> <p>Only a minority of cancer patients benefits from the combination of EGFR-inhibition and radiotherapy in head and neck squamous cell carcinoma (HNSCC). A potential resistance mechanism is activation of EGFR and/or downstream pathways by stimuli in the microenvironment. The aim of this study was to find molecular targets induced by the microenvironment by determining the <it>in vitro</it> and <it>in vivo</it> expression of proteins of the EGFR-signaling network in 6 HNSCC lines. As hypoxia is an important microenvironmental parameter associated with poor outcome in solid tumors after radiotherapy, we investigated the relationship with hypoxia <it>in vitro</it> and <it>in vivo</it>.</p> <p>Methods</p> <p>Six human HNSCC cell lines were both cultured as cell lines (<it>in vitro</it>) and grown as xenograft tumors (<it>in vivo)</it>. Expression levels were determined via western blot analysis and localization of markers was assessed via immunofluorescent staining. To determine the effect of hypoxia and pAKT-inhibition on cell survival, cells were incubated at 0.5% O₂ and treated with MK-2206.</p> <p>Results</p> <p>We observed strong <it>in vitro</it>-<it>in vivo</it> correlations for EGFR, pEGFR and HER2 (r_s=0.77, p=0.10, r_s=0.89, p=0.03) and r_s=0.93, p=0.02, respectively), but not for pAKT, pERK1/2 or pSTAT3 (all r_s<0.55 and p>0.30). <it>In vivo,</it> pAKT expression was present in hypoxic cells and pAKT and hypoxia were significantly correlated (r_s=0.51, p=0.04). We confirmed <it>in vitro</it> that hypoxia induces activation of AKT. Further, pAKT-inhibition via MK-2206 caused a significant decrease in survival in hypoxic cells (p<0.01), but not in normoxic cells.</p> <p>Conclusions</p> <p>These data suggest that (p)EGFR and HER2 expression is mostly determined by intrinsic features of the tumor cell, while the activation of downstream kinases is highly influenced by the tumor microenvironment. We show that hypoxia induces activation of AKT both <it>in vitro</it> and <it>in vivo,</it> and that hypoxic cells can be specifically targeted by pAKT-inhibition. Targeting pAKT is thus a potential way to overcome therapy resistance induced by hypoxia and improve patient outcome.</p>