ORIGINAL ARTICLE Cellular membranes function as a storage compartment for celecoxib Thorsten J. Maier & Susanne Schiffmann & Ivonne Wobst & Kerstin Birod & Carlo Angioni & Marika Hoffmann & Jakob J. Lopez & Clemens Glaubitz & Dieter Steinhilber & Gerd Geisslinger & Sabine Grösch Received: 13 February 2009 / Revised: 13 July 2009 / Accepted: 15 July 2009 / Published online: 30 July 2009 # Springer-Verlag 2009 Abstract Celecoxib is a selective cyclooxygenase-2- (COX-2)-inhibitor used to treat inflammation and pain and prevents colorectal cancer in patients at high doses by affecting several non-COX-2 proteins. However, celecoxib concentrations appropriate to inhibit proliferation or to induce apoptosis in cell culture (up to 100 μM) clearly exceed those in human plasma (up to 10 μM). Therefore, we speculated that celecoxib might accumulate in human cells, which may facilitate the drug’ s interaction with non- COX-2 proteins. Determination of intracellular celecoxib concentrations by liquid chromatography tandem mass spectrometry gave five- to tenfold higher levels as compared to other coxibs (etoricoxib, valdecoxib, lumira- coxib, and rofecoxib) in different tumor cell types, including human HCA-7 and HCT-116 colon carcinoma cells, BL-41 B lymphocytes, Mono Mac 6 monocytes, and in mouse NIH-3T3 non-tumor fibroblasts. This intracellular accumulation of celecoxib was due to an integration of the drug into cellular phospholipid membranes as demonstrated by nuclear Overhauser spectroscopy/nuclear magnetic resonance. Consequently, celecoxib disturbed the plasma membrane integrity of HCT-116 cells and displayed an increased COX-2-inhibitory potency in HCA-7 cells. The use of other coxibs demonstrated that intracellular accumu- lation is peculiar of celecoxib. Accumulation of celecoxib in human cells may provide a novel molecular basis for the ability of the drug to interact with non-COX-2 targets in vivo despite comparatively low plasma concentrations. Keywords NSAIDs . Intracellular accumulation . Non-COX-2 targets . NOESY-NMR . Cyclooxygenase . Colon cancer Abbreviations BSA Bovine serum albumin COX-2 Cyclooxygenase-2 EDTA Ethylenediaminetetraacetate ELISA Enzyme-linked immunoassay FAP Familial adenomatous polyposis FCS Fetal calf serum HPLC High-performance liquid chromatography HUVEC Human umbilical vein endothelial cell LC-MS/MS Liquid chromatography coupled with tandem mass spectrometry MAS NOESY Magic angle spinning assisted nuclear Overhauser spectroscopy NMR Nuclear magnetic resonance NSAID Nonsteroidal anti-inflammatory drug T. J. Maier and S. Schiffmann contributed equally. Electronic supplementary material The online version of this article (doi:10.1007/s00109-009-0506-8) contains supplementary material, which is available to authorized users. T. J. Maier : S. Schiffmann (*) : I. Wobst : K. Birod : C. Angioni : G. Geisslinger : S. Grösch pharmazentrum frankfurt/ZAFES, Institute of Clinical Pharmacology, Goethe-University, Theodor-Stern-Kai 7, 60590 Frankfurt am Main, Germany e-mail: susanne.schiffmann@med.uni-frankfurt.de T. J. Maier : M. Hoffmann : D. Steinhilber Institute of Pharmaceutical Chemistry/ZAFES, Goethe-University, Max-von-Laue Str. 9, 60438 Frankfurt am Main, Germany J. J. Lopez : C. Glaubitz Centre for Biomolecular Magnetic Resonance and Institute for Biophysical Chemistry, Goethe-University, Max-von-Laue Str. 9, 60438 Frankfurt am Main, Germany J Mol Med (2009) 87:981–993 DOI 10.1007/s00109-009-0506-8