Flavonoids Kaempferol and Quercetin are Nuclear Receptor 4A1 (NR4A1, Nur77) Ligands and inhibit Rhabdomyosarcoma Cell and Tumor Growth

Abstract

BackgroundFlavonoid’s exhibit both chemopreventive and chemotherapeutic activity for multiple tumor types, however, their mechanisms of action are not well defined. Based on some of their functional and gene modifying activities as anticancer agents, we hypothesized that kaempferol and quercetin were nuclear receptor 4A1 (NR4A1, Nur77) ligands and confirmed that both compounds directly bound NR4A1 with KD values of 3.1 and 0.93 µM, respectively. MethodsThe activities of kaempferol and quercetin were determined in direct binding to NR4A1 and in NR4A1-dependent transactivation assays in Rh30 and Rh41 rhabdomyosarcoma (RMS) cells, flavonoid-dependent effects as inhibitors of cell growth, survival and invasion were determined in XTT, Annexin V and Boyden chamber assays respectively and changes in protein levels were determined by western blots. Tumor growth inhibition studies were carried out in athymic nude mice bearing Rh30 cells. ResultsKaempferol and quercetin bind NR4A1 protein and inhibit NR4A1-dependent transactivation in RMS cells. NR4A1 also regulates RMS cell growth, survival, and invasion and pro-oncogenic PAX3-FOX01 and G9a gene expression, mTOR signaling and gene products and, these pathways and genes are inhibited by kaempferol and quercetin. Moreover, at a dose of 50 mg/kg/d kaempferol and quercetin inhibited tumor growth in athymic nude mouse xenograft model bearing Rh30 cells. ConclusionThese results demonstrate the clinical potential for repurposing these flavonoids for clinical applications as precision medicine for treating RMS patients that express NR4A1 in order to increase the efficacy and decrease dosages of currently used cytotoxic drugs.