The synthetic retinoid AGN-193109 is a potent pan retinoic acid receptor (RAR) antagonist. It has been shown to block the antiproliferative effect of retinoids in cultured human cervical cancer cells. AGN-193109 is a potent RAR antagonist and a potential antidote of retinoid intoxication in vivo. In addition to potential clinical applications in the prevention and treatment of retinoid toxicity, AGN-193109 should provide a powerful experimental tool for the elucidation of retinoid biology.

6-(4-chlorophenyl)imidazo(2,1-b)(1,3)thiazole-5-carbaldehyde O-(3,4-dichlorobenzyl)oxime (CITCO) is a novel potent and selective agonist for the human orphan nuclear receptor CAR (constitutive androstane receptor). CITCO displayed an EC50 of 49 nM in a CAR FRET assay and showed 50-fold selectivity for CAR over PXR. CITCO displayed no activity against a panel of 15 other nuclear receptors at a concentration of 10 µM. In hepatocytes CITCO induced CAR nuclear translocation and induced the CAR target gene CYP2B6. The cell proliferation of several ovarian cell lines expressing CAR significantly increased when CITCO was combined with anticancer agents compared with any anticancer agent alone. The up-regulation of MDR1 and UGT1A1 by anticancer agents was further enhanced in the presence of CITCO. Combination of CITCO with any anticancer agents significantly enhanced CAR-mediated transcription compared with any anticancer agents alone and CAR down-regulation completely inhibited the transcription in the presence of CITCO and/or anticancer agents. Inhibition of CAR pathway could be a novel therapeutic approach for the augmentation of sensitivity to anticancer agents, or to overcome resistance, in the treatment of ovarian cancer. CITCO has being shown to inhibit growth and expansion of brain tumour stem cells. CITCO induced a dose-dependent decrease in growth and expansion of CD133(+) BTSCs as gliospheres in culture. Cell cycle arrest and apoptosis in BTSCs were induced by CITCO, but not in normal astrocytes. Growth of s.c BTSC xenograft in nude mice was also inhibited by CITCO. CITCO inhibits the growth and expansion of BTSCs, suggesting the use of CAR agonists for the treatment of brain tumour.