Abstract C76: A novel small molecule inhibitor of constitutive androstane receptor (CAR) that resensitizes doxorubicin-resistant neuroblastoma cells

Abstract

Abstract This study aims to identify new specific small molecule inhibitors of the xenobiotic receptor CAR (constitutive androstane receptor) which could be used to increase sensitivity of resistant cancer cells to chemotherapeutics. CAR and PXR are xenobiotic sensors that respond to drugs and endobiotics by modulating the expression of metabolic genes that enhance detoxification and elimination. Elevated levels of drug metabolizing enzymes and efflux transporters resulting from CAR activation promote the elimination of chemotherapeutic agents leading to reduced therapeutic effectiveness. Interestingly, all previously reported CAR inverse-agonists are also activators of PXR thus rendering them mechanistically counterproductive in tissues expressing both receptors. Using a directed screening approach, we discovered a potent small molecule, CINPA1, capable of reducing CAR-mediated transcription with an IC50 of ∼70 nM, without activating PXR. CINPA1 is a specific xenobiotic inhibitor and has no general cytotoxic effects up to 25 μM. CINPA1 effectively inhibits CAR-mediated gene expression in all donors of human hepatocytes that express CAR endogenously. The mechanisms by which CINPA1 inhibits CAR function were extensively examined. We show that CINPA1 association with the CAR ligand binding domain results in increased corepressor interaction and reduced recruitment of coactivators. In addition, chromatin immunoprecipitation in the presence of CINPA1 illustrates reduced CAR binding to the promoter regions of target genes. Multidrug resistance in tumors after chemotherapy can be associated with errant CAR activity, as in the case of neuroblastoma. Treatment of doxorubicin-resistant neuroblastoma cells with CINPA1 resulted in reduced CAR activity and subsequent decrease in drug-transporter levels. In doxorubicin-resistant UKF-NB3 (neuroblastoma) cells, CINPA1 treatment increased doxorubicin sensitivity and decreased cell growth. This suggests that CAR inhibitors used in combination with existing chemotherapeutics could potentially be utilized to attenuate multidrug resistance and resensitize chemo-resistant cancer cells. Citation Format: Milu T. Cherian, Apana A. Takwi, Wenwei Lin, Taosheng Chen. A novel small molecule inhibitor of constitutive androstane receptor (CAR) that resensitizes doxorubicin-resistant neuroblastoma cells. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C76.