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

Germline BRCA1/2 mutations account for about 10% of all breast cancer. BRCA1/2 proteins are involved in homologous recombination - DNA double-strand break repair mechanism. Poly-(ADP ribose) polymerases (PARP) are required to repair DNA single-strand breaks through base excision repair. PARP inhibitors represent a modern option of treatment of metastatic HER2 negative breast cancer with germline BRCA1/2 mutations. Mechanism of action of PARP inhibitors is based on the concept of synthetic lethality under conditions of BRCA dysfunction, when both DNA repair mechanisms, homologous recombination and base excision repair, are impaired. This leads to the apoptosis of cancer cells. Currently two PARP inhibitors are registered in Russia for the treatment of BRCA-associated metastatic HER2 negative breast cancer – olaparib and talazoparib. Efficacy of PARP inhibitors olaparib and talazoparib versus standard chemotherapy has been studied in very similarly designed phase III trials OlympiAD и EMBRACA. Benefit in the progression free survival, acceptable toxicity profile and positive impact on quality of life support inclusion of PARP inhibitors in treatment schemes of metastatic BRCAassociated breast cancer. Very important is the role of PARP inhibitors in treatment of very aggressive triple negative breast cancer with limited number of effective therapy options. We represent here a clinical case of treatment of metastatic triple negative breast cancer with talazoparib in 4th line of therapy.

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

10.1101/685271 ◽

2019 ◽

Author(s):

Kevin J. Lee ◽

Cortt G. Piett ◽

Joel F Andrews ◽

Elise Mann ◽

Zachary D. Nagel ◽

...

Keyword(s):

Breast Cancer ◽

Dna Damage ◽

Dna Repair ◽

Cell Lines ◽

Base Excision Repair ◽

Triple Negative ◽

Excision Repair ◽

Dna Damaging Agents ◽

Tnbc Cell ◽

Base Excision

AbstractDNA repair defects have been increasingly focused on as therapeutic targets. In hormone positive breast cancer, XRCC1-deficient tumors have been identified and proposed as targets for combination therapies that damage DNA and inhibit DNA repair pathways. XRCC1 is a scaffold protein that functions in base excision repair (BER) by mediating essential interactions between DNA glycosylases, AP endonuclease, poly(ADP-ribose) polymerase 1, DNA polymerase β (POL β), and DNA ligases. Loss of XRCC1 confers BER defects and hypersensitivity to DNA damaging agents. BER defects have not been evaluated in triple negative breast cancer (TNBC), for which new therapeutic targets and therapies are needed. To evaluate the potential of XRCC1 as an indicator of BER defects in TNBC, we examined XRCC1 expression and localization in the TCGA database and in TNBC cell lines. High XRCC1 expression was observed for TNBC tumors in the TCGA database and expression of XRCC1 varied between TNBC cell lines. We also observed changes in XRCC1 subcellular localization in TNBCs that alter the ability to repair base lesions and single-strand breaks. Subcellular localization changes were also observed for POL β that did not correlate with XRCC1 localization. Basal levels of DNA damage were also measured in the TNBC cell lines, and damage levels correlated with observed changes in XRCC1 expression, localization, and repair functions. The results confirmed that XRCC1 expression changes may indicate DNA repair capacity changes but emphasize that basal DNA damage levels along with expression and localization are better indicators of DNA repair defects. Given the observed over-expression of XRCC1 in TNBC preclinical models and the TCGA database, XRCC1 expression levels should be considered when evaluating treatment responses of TNBC preclinical model cells.

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Activated STAT3 Is a Novel Regulator of the XRCC1 Promoter and Selectively Increases XRCC1 Protein Levels in Triple Negative Breast Cancer

International Journal of Molecular Sciences ◽

10.3390/ijms22115475 ◽

2021 ◽

Vol 22 (11) ◽

pp. 5475

Author(s):

Griffin Wright ◽

Manoj Sonavane ◽

Natalie R. Gassman

Keyword(s):

Breast Cancer ◽

Triple Negative Breast Cancer ◽

Triple Negative ◽

Excision Repair ◽

Strand Break ◽

Xrcc1 Gene ◽

Single Strand Break ◽

Expression Levels ◽

Constitutive Activation ◽

Gene And Protein Expression

Base Excision Repair (BER) addresses base lesions and abasic sites induced by exogenous and endogenous stressors. X-ray cross complementing group 1 (XRCC1) functions as a scaffold protein in BER and single-strand break repair (SSBR), facilitating and coordinating repair through its interaction with a host of critical repair proteins. Alterations of XRCC1 protein and gene expression levels are observed in many cancers, including colorectal, ovarian, and breast cancer. While increases in the expression level of XRCC1 are reported, the transcription factors responsible for this up-regulation are not known. In this study, we identify the signal transducer and activator of transcription 3 (STAT3) as a novel regulator of XRCC1 through chromatin immunoprecipitation. Activation of STAT3 through phosphorylation at Y705 by cytokine (IL-6) signaling increases the expression of XRCC1 and the occupancy of STAT3 within the XRCC1 promoter. In triple negative breast cancer, the constitutive activation of STAT3 upregulates XRCC1 gene and protein expression levels. Increased expression of XRCC1 is associated with aggressiveness and resistance to DNA damaging chemotherapeutics. Thus, we propose that activated STAT3 regulates XRCC1 under stress and growth conditions, but constitutive activation in cancers results in dysregulation of XRCC1 and subsequently BER and SSBR.

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