Targeting HR Repair as a Synthetic Lethal Approach to Increase DNA Damage Sensitivity by a RAD52 Inhibitor in BRCA2-Deficient Cancer Cells.

Wei-Che Tseng,Shih-Ting Tseng,Chi-Yuan Chen,Ya-Chen Chiu,Yi-Chen Li,Shou-Jhen Liou,Ying-Chih Chi,Chin-Chuan Chen,Yi-Tsen Kuo,Chu-An Wang,Shu-Fang Cheng,Ching-Yuh Chern,Pei-Ya Lin,Wen-Chih Lee

doi:10.3390/ijms22094422

Abstract

BRCA mutation, one of the most common types of mutations in breast and ovarian cancer, has been suggested to be synthetically lethal with depletion of RAD52. Pharmacologically inhibiting RAD52 specifically eradicates BRCA-deficient cancer cells. In this study, we demonstrated that curcumin, a plant polyphenol, sensitizes BRCA2-deficient cells to CPT-11 by impairing RAD52 recombinase in MCF7 cells. More specifically, in MCF7-siBRCA2 cells, curcumin reduced homologous recombination, resulting in tumor growth suppression. Furthermore, a BRCA2-deficient cell line, Capan1, became resistant to CPT-11 when BRCA2 was reintroduced. In vivo, xenograft model studies showed that curcumin combined with CPT-11 reduced the growth of BRCA2-knockout MCF7 tumors but not MCF7 tumors. In conclusion, our data indicate that curcumin, which has RAD52 inhibitor activity, is a promising candidate for sensitizing BRCA2-deficient cells to DNA damage-based cancer therapies.

Highlights

Double-strand breaks (DSBs) are the most severe type of DNA damage
On the basis of immunoblot analysis, we found curcumin to impair the CPT-11-induced upregulation of RAD52 expression in a dose- and time-dependent manner, whereas the expression of MRE11 was not affected by curcumin (Figure 1A,B)
We noticed that curcumin per se did not affect MCF siCcontrol cells in the clonogenic assay at low concentrations; curcumin per se still reduced tumor growth in mice

Summary

Introduction

Double-strand breaks (DSBs) are the most severe type of DNA damage. Chromosome rearrangement and cell death are thought to be consequences of a failure to accurately repair DSBs [1]. The repair of DSBs is mediated via the homologous recombination (HR) or nonhomologous end joining (NHEJ) pathway. NHEJ occurs mainly in the G1 phase of the cell cycle, while HR is the major DNA repair mechanism occurring in the S and G2/M phases. Since most normal cells stop dividing in the G1 phase and cancer cells are more often in the S phase, the HR pathway is more frequently used to repair DNA damage [2]. HR-mediated repair begins with the recognition and binding of DSB ends by the MRN complex, which consists of the MRE11, RAD50, and NBS1 proteins. Subsequent binding of the RPA protein to single-stranded DNA (RPA-ssDNA) attracts additional repair proteins such as BRCA1 and BRCA2. BRCA1 and BRCA2 help load RAD51 onto the RPA–ssDNA complex to identify homologous sequences of sister chromatids and initiate HR repair [3,4,5]

Methods

Results

Conclusion