Defective base excision repair in the response to DNA damaging agents in triple negative breast cancer

Abstract

21 22 23DNA repair defects have been increasingly focused on as therapeutic targets. In hormone 24 positive breast cancer, XRCC1-deficient tumors have been identified and proposed as 25 targets for combination therapies that damage DNA and inhibit DNA repair pathways. 26XRCC1 is a scaffold protein that functions in base excision repair (BER) by mediating 27 essential interactions between DNA glycosylases, AP endonuclease, poly(ADP-ribose) 28 polymerase 1, DNA polymerase β (POL β), and DNA ligases. Loss of XRCC1 confers 29 BER defects and hypersensitivity to DNA damaging agents. BER defects have not been 30 evaluated in triple negative breast cancer (TNBC), for which new therapeutic targets and 31 therapies are needed. To evaluate the potential of XRCC1 as an indicator of BER defects 32 in TNBC, we examined XRCC1 expression and localization in the TCGA database and in 33 TNBC cell lines. High XRCC1 expression was observed for TNBC tumors in the TCGA 34 database and expression of XRCC1 varied between TNBC cell lines. We also observed 35 changes in XRCC1 subcellular localization in TNBCs that alter the ability to repair base 36 lesions and single-strand breaks. Subcellular localization changes were also observed for 37 POL β that did not correlate with XRCC1 localization. Basal levels of DNA damage were 38 also measured in the TNBC cell lines, and damage levels correlated with observed 39 changes in XRCC1 expression, localization, and repair functions. The results confirmed 40 that XRCC1 expression changes may indicate DNA repair capacity changes but 41 emphasize that basal DNA damage levels along with expression and localization are 42 better indicators of DNA repair defects. Given the observed over-expression of XRCC1 in 43 TNBC preclinical models and the TCGA database, XRCC1 expression levels should be 44 considered when evaluating treatment responses of TNBC preclinical model cells. 45 3 Keywords: triple negative breast cancer, base excision repair, XRCC1, PARP1, DNA 46 repair, DNA damage, nuclear localization 47 48 Defects in DNA damage response and repair are driving factors in carcinogenesis 49and key determinants in the response to chemotherapy. Breast cancers may display 50 defects in DNA repair such as mutations in key DNA damage response and repair 51 proteins such as breast cancer-susceptibility (BRCA1/2) and tumor suppressor protein 52 p53 (TP53), and altered expression levels of DNA repair proteins thymine-DNA 53 glycosylase (TDG) and poly(ADP-ribose) polymerase 1 (PARP1) [1-3]. Therapeutic 54 outcomes may be improved by exploiting DNA repair defects present in cancer cells but 55 absent in normal cells, as in the use of PARP-inhibitors (PARPi) in cancers that have 56 BRCA1/2 deficiencies. However, characterization of DNA repair pathways often is lacking 57 in preclinical models and cell lines. Examining DNA repair defects in preclinical models 58 and patients is essential for evaluating the efficacy of therapeutic agents. 59 In breast cancer, DNA repair defects often extend beyond homologous 60 re...

Exploiting DNA repair defects in triple negative breast cancer to improve cell killing

“…MDA-468 showed high expression levels of BER factors, including APE1, FEN1, PARP1, POLβ, and XRCC1, consistent with the high BER capacity and resistance to alkylating DNA damage observed previously. 13 Low oxidative DNA damage repair capacity was reported previously for several TNBC cell lines, including the four cell lines in this study, consistent with the low expression of OGG1 and NEIL family proteins in these cell lines. 17 We next evaluated repair by the NER pathway.…”

“…We previously used the flow cytometric host cell reactivation assay (FM-HCR) to characterize the BER repair capacity of a panel of commonly used TNBC cell line models, MDA-157, MDA-231, HCC1806, and MDA-468. 13 From this analysis, we observed that MDA-468 cells were the most BER competent of the four cell lines. 13 The previous BER analysis primarily evaluated lesion recognition by DNA glycosylases.…”

“…13 From this analysis, we observed that MDA-468 cells were the most BER competent of the four cell lines. 13 The previous BER analysis primarily evaluated lesion recognition by DNA glycosylases. Although glycosylase activity determines the rate at which BER is initiated, apurinic/apyrimidinic endonuclease 1 (APE1) also is important in BER initiation.…”

“…11 Evaluation of the efficiency of THF repair by APE1 between the TNBC cell lines showed efficient processing of THF lesions in all TNBC cell lines, unlike the glycosylase substrates (Figure 1). 13 The highest level of expression for the THF reporter was observed in HCC1806 cells. MDA157 and HCC1806 also showed the highest levels of THF activity and lowest amounts of APE1 at the protein and mRNA levels in the cell lines (Figure 1).…”

Relapse‐related molecular signature in early‐stage lung adenocarcinomas based on base excision repair, stimulator of interferon genes pathway and tumor‐infiltrating lymphocytes

“…High expression of APE1 in tumors was associated with the resistance to platinum and radiotherapy 39,40 . XRCC1 downregulated in gastric cancer, lung cancer and cervical cancer was associated with tumor invasion and poor prognosis 41‐43 . Furthermore, polβ mutations were found to be associated with tumor susceptibility 44,45 …”