Abstract
BackgroundTriple negative breast cancer (TNBC) is a breast cancer subgroup characterized by a lack of hormone receptors’ expression and no HER2 overexpression. These molecular features both drastically reduce treatment options and confer poor prognosis. Platinum (Pt)-salts are being investigated as a new therapeutic strategy. The base excision repair (BER) pathway is important for resistance to Pt-based therapies. Overexpression of APE1, a pivotal enzyme of the BER pathway, as well as the expression of NPM1, a functional regulator of APE1, are associated with poor outcome and resistance to Pt-based therapies.MethodsWe evaluated the role of NPM1, APE1 and altered NPM1/APE1 interaction in the response to Pt-salts treatment in different cell lines: APE1 knockout (KO) cells, NPM1 KO cells, cell line models having an altered APE1/NPM1 interaction and HCC70 and HCC1937 TNBC cell lines, having different levels of APE1/NPM1. We evaluated the TNBC cells response to new chemotherapeutic small molecules targeting the endonuclease activity of APE1 or the APE1/NPM1 interaction, in combination with Pt-salts treatments. Expression levels’ correlation between APE1 and NPM1 and their impact on prognosis was analyzed in a cohort of TNBC patients through immunohistochemistry. Bioinformatics analysis, using TCGA datasets, was performed to predict a molecular signature of cancers based on APE1 and NPM1 expression.ResultsAPE1 and NPM1, and their interaction as well, protect from the cytotoxicity induced by Pt-salts treatment. HCC1937 cells, having higher levels of APE1/NPM1 proteins, are more resistant to Pt-salts treatment compared to the HCC70 cells. A sensitization effect by APE1 inhibitors to Pt-compounds was observed. The association of NPM1/APE1 with cancer gene signatures highlighted alterations concerning cell-cycle dependent proteins.ConclusionsAPE1 and NPM1 protect cancer cells from Pt-compounds cytotoxicity, suggesting a possible improvement of the activity of Pt-based therapy for TNBC, using the NPM1 and APE1 proteins as secondary therapeutic targets. Based on positive or negative correlation with APE1 and NPM1 gene expression levels, we finally propose several TNBC gene signatures that should deserve further attention for their potential impact on TNBC precision medicine approaches.
Highlights
Triple negative breast cancer (TNBC) is a breast cancer subgroup characterized by a lack of hormone receptors’ expression and no HER2 overexpression
Based on the above mentioned evidences, we deemed fundamental to investigate the cytotoxicity induced by the combined treatment of Pt-compounds and APE1inhibitors, which may have synergistic therapeutic effects in the treatment of cancers such as TNBC [69, 70]. For this reason, starting from the emerging importance of Pt-salts for the treatment of TNBC patients and, in parallel, from the continuously evolving knowledge on Apurinic/apyrimidinic endonuclease 1 (APE1) functions, the purpose of this study was to understand the role of APE1, and of its interactor NPM1, in TNBC cell lines treated with Pt-compounds, including CDDP and CBDCA
Compound #3 and APE1/NPM1 inhibitors [61] were dissolved in dimethyl sulfoxide (DMSO) as 10 mM stock, cisplatin was dissolved in dimethylformamide (DMF) as 33.3 mM stock and carboplatin was dissolved in water as 13.45 mM stock (SIGMA, Milan, Italy)
Summary
Triple negative breast cancer (TNBC) is a breast cancer subgroup characterized by a lack of hormone receptors’ expression and no HER2 overexpression. Overexpression of APE1, a pivotal enzyme of the BER pathway, as well as the expression of NPM1, a functional regulator of APE1, are associated with poor outcome and resistance to Pt-based therapies. Among the therapeutic options already employed in the clinical practice of several tumors including TNBC, platinum (Pt)-based compounds emerge for their ability to interfere with several cellular processes, including DNA replication and transcription [13,14,15]. The pivotal role of APE1 is demonstrated by its function in cellular viability and embryonic development [24], due to its role in DNA repair activity and other recently characterized non-canonical functions. NPM1 is an important functional regulator of BER factors, controlling levels and localization of BER proteins, including APE1 [43].
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