Abstract
Tumor associated macrophages (TAMs) constitute a substantial mass in gliomas. The activated macrophages secrete various cytokines that affect diverse functions of tumors. The aim of this study was to elucidate the role of Akt and NF‐κB pathways in resistance to TNF‐α mediated cell death in human gliomas using monolayers and multicellular spheroids (MCS) as in vitro models. Akt and NF‐κB are constitutively expressed and intimately involved in progression of gliomas. The activation of these pathways also renders the tumors resistant to conventional treatments including chemotherapy. While PI3K/Akt is shown to regulate the NF‐κB activation in diverse systems, other studies place NF‐κB upstream of Akt activation. Using a stable IκBα mutant LN‐18 cell line and pharmacological inhibitors to PI3K/Akt (LY294002) and Akt (Akt2), we provide evidence that Akt and NF‐κB are activated independently on stimulation with TNF‐α and both the pathways contribute towards resistance to TNF‐α mediated cell death. TNF‐α‐induced NF‐κB activation independent of PI3K/Akt pathway was also confirmed in human glioma cell lines‐LN‐229 and U373MG. We also show that NF‐κB and Akt are activated during spheroidogenesis and their expression is further enhanced on stimulation with TNF‐α implicating their involvement in resistance to cell death. The findings thus underscore the relevance of spheroids as appropriate in vitro models for studying the signaling pathways in drug induced resistance. © 2007 Wiley‐Liss, Inc.