Understanding of the physiological role of peroxisome proliferator-activated receptor gamma (PPARgamma) offers new opportunities for the treatment of cancers, immune disorders and inflammatory diseases. In contrast to PPARgamma agonists, few PPARgamma antagonists have been studied, though they do exert immunomodulatory effects. Currently, no therapeutically useful PPARgamma antagonist is commercially available. The aim of this study was to identify and kinetically characterise a new competitive PPARgamma antagonist for therapeutic use. A PPARgamma-dependent transactivation assay was used to kinetically characterise (E)-2-(5-((4-methoxy-2-(trifluoromethyl)quinolin-6-yl)methoxy)-2-((4-(trifluorome thyl)benzyl)oxy)-benzylidene)-hexanoic acid (MTTB) in kidney, T and monocytic cell lines. Cytotoxic effects were analysed and intracellular accumulation of MTTB was assessed by tandem mass spectrometry (LC-MS/MS). Potential interactions of MTTB with the PPARgamma protein were suggested by molecular docking analysis. In contrast to non-competitive, irreversible inhibition caused by 2-chloro-5-nitrobenzanilide (GW9662), MTTB exhibited competitive antagonism against rosiglitazone in HEK293T and Jurkat T cells, with IC50 values in HEK293T cells of 4.3microM and 1.6microM, using the PPARgamma ligand binding domain (PPARgamma-LBD) and the full PPARgamma protein, respectively. In all cell lines used, however, MTTB showed much higher intracellular accumulation than GW9662. MTTB alone exhibited weak partial agonistic effects and low cytotoxicity. Molecular docking of MTTB with the PPARgamma-LBD supported direct interaction with the nuclear receptor. MTTB is a promising prototype for a new class of competitive PPARgamma antagonists. It has weak partial agonistic and clear competitive antagonistic characteristics associated with rapid cellular uptake. Compared to commercially available PPARgamma modulators, this offers the possibility of dose regulation of PPARgamma and immune responses.