HZ08 suppresses RelB-activated MnSOD expression and enhances Radiosensitivity of prostate Cancer cells

Yanyan Zhang,Yunman Li,Yong Xu,Wenlong Huang,Weizi Hu,Chunli Tan,Zhi Xu,Jiaji Ding

doi:10.1186/s13046-018-0849-5

Abstract

BackgroundThe development of radioresistance is one of main causes for therapeutic failure of prostate cancer (PCa). The present study aims to investigate the function and the related mechanism by which HZ08 sensitizes radiotherapeutic efficiency to treat aggressive PCa cells.MethodsPCa cells were pretreated with HZ08 (6,7-dimethoxy-1-(3,4-dimethoxy) benzyl-2-(N-n-octyl-N′-cyano) guanyl-1,2,3,4-tetrahydroisoquinoline) and followed by ionizing radiation (IR) treatment. Cytotoxicity in the treated cells was analyzed to assess the radiosensitization capacity of HZ08 by flow cytometry, MTT and colony survival assays. The cellular levels of reactive oxygen species (ROS) and oxygen consumption rates (OCR) were measured using specific ROS detection probes and a Seahorse XF96 Analyzer, respectively. RelB binding to the NF-κB intronic enhancer region of the human SOD2 gene was determined using a ChIP assay. The levels of phosphorylation of PI3K, Akt and IKKα were quantified and further confirmed using a PI3K inhibitor. Finally, the synergistic effect of HZ08 on radiosensitization of PCa cells was validated using a mouse xenograft tumor model.ResultsHZ08 enhanced radiosensitivity of PCa cells through increasing ROS and declining mitochondrial respiration due to suppression of mitochondrial antioxidant enzyme MnSOD. Mechanistically, HZ08 appeared to inhibit PI3K/Akt/IKKα signaling axis, resulting in transcriptional repression of MnSOD expression by preventing RelB nuclear translocation.ConclusionsHZ08 can serve as a useful radiosensitizing agent to improve radiotherapy for treating aggressive PCa cells with high level of constitutive RelB. The present study suggests a promising approach for enhancing radiotherapeutic efficiency to treat advanced PCa by inhibiting antioxidant defense function.

Highlights

The development of radioresistance is one of main causes for therapeutic failure of prostate cancer (PCa)
Downregulation of RelB enhances the radiosensitivity of PC-3 cells Our previous studies reported that the high levels of nuclear RelB in PCa contribute to tumor metastatic progression and resistance to radiation [26, 28]
To test whether the downregulation of RelB enhances the radiosensitivity, the RelB-silenced PC-3 cells were treated with different doses of ionizing radiation (IR) and cytotoxicity in the cells was analyzed by MTT assay

Summary

Introduction

The development of radioresistance is one of main causes for therapeutic failure of prostate cancer (PCa). The present study aims to investigate the function and the related mechanism by which HZ08 sensitizes radiotherapeutic efficiency to treat aggressive PCa cells. PCa is the second most common malignancy and a major leading cause of cancer death among men worldwide [1]. Several studies had been conducted to identify radiosensitizing agents that were able to sensitize PCa cells to radiation. Only three such trials had been reported with the eliminated effects, including two targeted agents and one natural compound.

Methods

Results

Discussion

Conclusion