Oxidized Analogs of Di(1-indol-3-yl)methyl-4-substituted Benzenes Are NR4A1-dependent UPR Inducers with Potent and Safe Anti-cancer Activity

Di(1-indol-3-yl)(4-trifluoromethylphenyl)methane (DIM-Ph-4-CF) is an analog of orphan nuclear receptor 4A1 (NR4A1) ligand cytosporone B. We have synthesized several oxidation products of DIM-Ph-4-CF, focusing on analogs with electron-withdrawing or donating groups at their phenyl ring 4-positions, and examined their anti-cancer activity and mechanism-of-action. Mesylates (DIM-Ph-4-X OMss) having CF, COMe and Cl groups were more effective inhibitors of cancer cell viability than their precursors. F NMR spectroscopy and differential scanning calorimetry strongly indicated interactions of DIM-Ph-4-CF OMs with the NR4A1 ligand binding domain, and compound-induced apoptosis of prostate cancer cells was dependent on NR4A1. DIM-Ph-4-CF3 OMs showed robust inhibition of LNCaP prostate cancer xenografts with no apparent toxicity. and , DIM-Ph-4-CF3 OMs activated proapoptotic unfolded protein response (UPR) signaling in prostate cancer cells. Independently of DIM-Ph-4-CF OMs, the bulk of NR4A1 localized to the cytoplasm in various cancer cell lines, suggesting a cytoplasmic mechanism-of-action of DIM-Ph-4-CF OMs in UPR induction and cell death. In summary, the data suggest that oxidized analogs of DIM-Ph-4-CF3 possess potent and safe anti-cancer activity which is mediated through UPR signaling downstream of NR4A1 binding.