Rhodanine derivatives as novel peroxisome proliferator-activated receptor γ agonists
Aim: To characterize the in vitro bioactivities of rhodanine derivatives as novel peroxisome proliferator-activated receptor (PPAR) γ modulators, based on a hit (SH00012671) identified during high-throughput screening (HTS) of a diverse synthetic compound library, and to preliminarily elucidate the structure-activity relationship of this class of PPARγ agonists. 
 Methods: Full-length PPARγ and retinoid X receptor α (RXRα), biotinylated PPAR response element (PPRE), [3H]BRL49653 (rosiglitazone), and streptavidin-coated FlashPlate or microbeads were used to measure the receptor-binding properties of various compounds based on the scintillation proximity assay (SPA) technology. A recombinant PPRE vector was transiently cotransfected with PPARγ and RXRα plasmids into the African green monkey kidney (CV-1) cells, and the effects of BRL49653 and test compounds on transcription mediated by PPARγ were determined by examining luciferase (reporter) responses. 3T3-L1 cells were employed to determine whether the compounds facilitated adipogenesis upon PPARγ activation. 
 Results: Of the 16 000 samples screened with the SPA method, only 1 compound (SH00012671) displayed a similar binding affinity ( K i =186.7 nmol/L) to PPARγ as BRL49653, but it was inactive in the cell-based assays. A series of rhodanine derivatives were synthesized based on the core structure of SH00012671 and 8 of them showed agonist activities in both cotransfection and pre-adipocyte differentiation assays. To reduce intrinsic cytotoxicities, the sulphur on the rhodanine was changed to oxygen. This alteration led to a decrease in receptor-binding affinities while modified analogues generally maintained agonist efficacies in the cell-based assays. Of the analogues studied, compound 31 exhibited about 70% the efficacy exerted by BRL49653 in both cotransfection and pre-adipocyte differentiation assays. 
 Conclusion: Through minor chemical modifications on the core structure of the initial HTS hit, SH00012671 was transformed to possess both molecular (PPARγ binding) and cellular (adipogenesis) activities. The rhodanine derivatives reported here may represent a new scaffold in further understanding the molecular mechanism of agonism at PPARγ.