Effect of several analogs of 2,4,6-triphenyldioxane-1,3 on constitutive androstane receptor activation

2,4,6-Triphenyldioxane-1,3 (TPD) is a highly effective species-specific inducer of CYP2В in rats. Several analogs of TPD were synthesized to verify a hypothesis that minor changes in the inducer structure can cause changes in induction abilities (R = H, cisTPD and transTPD; R = N(CH3)2, transpDMA; R = NO2, transpNO2; R = F, transpF; R = OCH3, transpMeO). Five of six compounds were able to activate CAR in rat liver. Results of Western-blot and ChIP showed that cisTPD and transTPD, transpDMA, transpNO2, transpF treatment stimulated nuclear accumulation of CAR and evoked CAR receptor PBREM-binding activity in rat liver. cisTPD, transTPD, transpDMA, transpNO2 and transpF administration significantly increased total CYP content (1.3-2.5 fold) and the level of PROD (12-20 fold), CYP2B specific activity, whereas transpMeO did not have any effects. Western blot and real-time RT-PCR showed that the increase of PROD in liver is related to the high content of CYP2B proteins and paralleled the increase of CYP2B1 (10-43 fold) and CYP2B2 (8-26 fold) mRNAs. At the same time content of CYP2B proteins and CYP2B1 and CYP2B2 mRNA levels were unchanged in rat liver after transpMeO treatment. The dose-response studies have shown that cisTPD, transpDMA, transpF and transpNO2 have similar potency, and transTPD is less potent derivative. Moreover, it is likely transTPD act as a partial CAR activator. Thus, our results provide evidence to support the conclusion that the differences of TPD analogs ability to activate CYP2B gene expression can be explained by various interactions with CAR.