The Role Of TR4 On Enzalutamide Resistance In Castration Resistant Prostate Cancer

Background:Prostate cancer(PCa)is one of the most common malignant tumors in male genitourinary system and attributed to over 29,000 deaths in 2014 in America,and represented as the second leading cancer related deaths in men.While enzalutamide(MDV3100)has led to improvement in the treatment of castration-resistant prostate cancer(CRPC)with extended 4.8 months survival,patients who have a response to MDV3100 would eventually become secondary resistance.Early studies indicated that the NR2C2,esticular orphan nuclear receptor 4(TR4),may play a key role to modulate the prostate cancer chemo-resistance.The TR4 nuclear receptor 4(TR4)belongs to the nuclear receptor superfamily and was first cloned from human prostate and testis cDNA libraries.Early studies suggested that TR4 might play important roles to alter several key signaling pathways via interacting with selective nuclear receptors including:thyroid receptor,androgen receptor,estrogen receptor,vitamin D receptor,retinoic acid receptor/retinoid X receptor and PPAR.TR4 could influence the oxidative stress-and ionizing radiation-induced damage,and altered TR4 could also lead to change the sensitivity of chemotherapy in PCa.The potential linkage of TR4 to the ADT-Enz,however,remains unclear.Objective:The aim of this study was to validate the role of TR4 in the enzalutamide treatment of CRPC,and explore the mechanism of TR4-induced enzalutamide resistance to provide some guidance for clinical rational drugs use and improvement of efficacy.Methods:Prostate cancer cell lines C4-2 and 22Rvl were used as experimental materials,and the concentration of enzalutamide was gradually increased to culture C4-2 enzalutamide-resistant cells.MTS was used to detect the resistance.The expression of TR4,Malatl and AR-v7 in rostate cancer cells was detected by Western blot or/and qPCR.The expression of TR4 in different levels of prostate cells was established by using lentivirus infection technique.The expression of Malatl and AR-v7 was detected by Western blot or/and qPCR.MTS assay was used to detect the effect of TR4 on the susceptibility and resistance of enzalutamide of prostate cancer cell lines.Transfection of TR4-overexpressing C4-2 and 22Rvl cells with Malatl siRNA confirmed TR4 regulates AR-v7 expression by Malatl to affect the sensitivity of prostate cancer cells to enzalutamide.Chip and double luciferase reporter gene analysis of TR4 on the expression of Malatl regulation.Results:TR4 and AR-v7 expression are increased in enzalutamide-treated PCa cell lines and established enzalutamide-resistant PCa cell lines.Altered TR4 expression culminated in changes of AR-v7 expression,inducing the resistance of PCa cells against enzalutamide-therapy.Higher TR4 expression in PCa cells might reduce the efficacy of enzalutamide to better suppress the PCa progression.Knocked-down TR4 with TR4-siRNA in PCa cells increased enzalutamide sensitivity and overexpression TR4 with TR4-cDNA in PCa cells increased enzalutamide resistance.Mechanism dissection revealed that TR4 might function through altering the IncRNA Malatl expression at the transcriptional level to enhance AR-v7 expression,and interrupted Malatl expression via malatl-siRNA reversed TR4-enhanced enzalutamide resistance in PCa cells.Conclusion:These results provided a potential therapeutic approach via TR4/Malatl/AR-v7 signals to increase the efficacy of enzalutamide to better suppress the CRPC progression.