A DNA repair BRCA1 estrogen receptor and targeted therapy in breast cancer

BRCA1 Promotes Repair of DNA Damage in Cochlear Hair Cells and Prevents Hearing Loss

Cochlear hair cells (HCs) sense sound waves and allow us to hear. Loss of HCs will cause irreversible sensorineural hearing loss. It is well known that DNA damage repair plays a critical role in protecting cells in many organs. However, how HCs respond to DNA damage and how defective DNA damage repair contributes to hearing loss remain elusive. In this study, we showed that cisplatin induced DNA damage in outer hair cells (OHCs) and promoted OHC loss, leading to hearing loss in mice of either sex. Cisplatin induced the expression of Brca1, a DNA damage repair factor, in OHCs. Deficiency of Brca1 induced OHC and hearing loss, and further promoted cisplatin-induced DNA damage in OHCs, accelerating OHC loss. This study provides the first in vivo evidence demonstrating that cisplatin mainly induces DNA damage in OHCs and that BRCA1 promotes repair of DNA damage in OHCs and prevents hearing loss. Our findings not only demonstrate that DNA damage-inducing agent generates DNA damage in postmitotic HCs but also suggest that DNA repair factors, like BRCA1, protect postmitotic HCs from DNA damage-induced cell death and hearing loss.

Homologous repair deficiency-associated genes in invasive breast cancer revealed by WGCNA co-expression network analysis and genetic perturbation similarity analysis

BACKGROUND

Homologous repair deficiency (HRD) causes double-strand break repair to be impeded, which is a common driver of carcinogenesis. However, the therapeutic and prognostic potential of HRD in invasive breast cancer (BRCA) has not been fully explored using comprehensive bioinformatics analysis.

MATERIALS AND METHODS

HRD score was defined as the unweighted sum of LOH, TAI, and LST scores and obtained from the previous study according to Theo A et al. To characterize BRCA tumor microenvironment (TME) subtypes, "ConsensusClusterPlus" R package was used to conduct unsupervised clustering. The xCell algorithm was utilized for tumor composition analysis to estimate the TME in TCGA-BRCA. A WGCNA analysis was conducted to uncover the gene coexpression modules and hub genes in the HRD-related gene module of BRCA. The functional enrichment study was carried out using Metascape. A novel analysis pipeline, Genetic Perturbation Similarity Analysis (GPSA), was used to explore the single-gene perturbation closely related to HRD based on 3048 stable knockdown/knockout cell lines. The prognostic variables were evaluated using univariate COX analysis. Kaplan-Meier (KM) survival analysis was performed to assess the prognostic potential of HRD score. Receiver operator characteristic (ROC) curve was utilized to judge the diagnostic utility. Drug sensitivity was estimated through the R package "oncoPredict" and Genomics of Drug Sensitivity in Cancer (GDSC) database. XSum algorithm was performed to screen the candidate small molecule drugs based on the connectivity map (CMAP) database.

RESULTS

Low HRD score suggested a better prognosis in BRCA patients. The tumor with low HRD score had considerably greater degree of infiltration of stromal cells and infiltration of immunocytes was significantly enhanced in the high HRD score group. Using WGCNA, ten co-expression modules were obtained. The turquoise module and 25 hub genes were identified as the most correlated with HRD in BRCA. Functional enrichment analysis revealed that the turquoise gene module was mainly concentrated in the "cell cycle" pathways. Candidate HRD-related gene signatures (MELK) were screened out through WGCNA and GPSA analysis pipeline and then validated on independent validation sets. A small molecule drug (Clofibrate) that has the potential to reverse the increase of high HRD score was screened out to improve oncological outcomes in BRCA. Molecular docking suggested MELK to be one of possible molecular targets in the Clofibrate treatment of BRCA.

CONCLUSION

Based on bioinformatic analysis, we fully explored the therapeutic and prognostic potential of HRD in BRCA. A novel HRD-related gene signature (MELK) were identified through the combination of WGCNA and GPSA analysis. In addition, we detailed the TME landscape in BRCA and identified four unique TME subtypes in group with high or low HRD score group. Moreover, Clofibrate were screened out to improve oncological outcomes in BRCA by reversing the increase of high HRD score. Thus, our study contributes to the development of personalized clinical management and treatment regimens of BRCA.

Mass spectrometric determination of N7-HPTE-dG and N7-HPTE-Gua in mammalian cells and mice exposed to methoxychlor, an emergent persistent organic pollutant

Methoxychlor (MXC) is an organopesticide classified as a "Proposed Persistent Organic Pollutant" in the Stockholm Convention, and recent studies revealed that MXC could induce DNA strand breaks, whereas its underlying mechanisms were underinvestigated. Here, we first reported that hydroxymethoxychlor (HPTE), one of MXC's active metabolites, could be oxidized in vivo to form quinone intermediate, which attacked N7 position of 2'-deoxyguanosine to form N7-HPTE-deoxyguanosine (N7-HPTE-dG), followed by depurination to produce N7-HPTE-guanine (N7-HPTE-Gua) in MXC-treated mammalian cells and tissues from mice fed with MXC, employing an ultra-performance liquid chromatography-electrospray ionization-tandem mass spectrometry (UPLC-ESI-MS/MS) method. We observed a positive correlation between the doses of MXC exposure and the levels of N7-HPTE-Gua and N7-HPTE-dG in cytoplasm and genomic DNA, respectively. Furthermore, after removal of exogenous MXC, the amount of genomic N7-HPTE-dG was significantly decreased during 24 h, while the level of cytoplasmic N7-HPTE-Gua was elevated during first 12 h, indicating the accumulation of the N7-HPTE-Gua in cells. Additionally, for animal experiment, genomic N7-HPTE-dG was observed in livers and cortexes from female C57BL/6 mice fed with MXC, suggesting a potential mechanism of its hepatoxicity and neurotoxicity. Overall, our study provides new understanding about the formation of MXC-induced DNA adducts in mammalian cells and animal models.

Platinum-based adjuvant therapy was efficient for triple-negative breast cancer: a meta-analysis from randomized controlled trials

Triple-negative breast cancer (TNBC) is the most aggressive breast cancer. Neoadjuvant chemotherapy was widely accepted for treating TNBC. This systematic review and meta-analysis aimed to evaluate the efficacy, safety, and survival benefit of platinum-based adjuvant therapy (PBAT) in treating TNBC. The keywords were searched in Medline, Embase, Pubmed, and Cochrane Library database up to July 24, 2022. All the randomized control trials (RCTs) comparing PBAT and non-PBAT in treating TNBC were included in our study. The pathological complete remission (pCR) and complications were compared by odds ratio (OR) and 95% confidence intervals (CIs). The overall survival (OS) and relapse-free survival (RFS) were compared by hazard ratio (HR) and 95% CIs. A total of 19 RCTs were included in our meta-analysis, among which 2,501 patients were treated with PBAT and 2,290 with non-PBAT. The patients treated with PBAT combined a significantly higher pCR rate compared to those patients treated with non-PBAT (49.8% versus 36.4%, OR = 1.27, 95%CI = 1.14-1.43, P < 0.001). Besides, patients treated with PBAT had a significantly better RFS (HR = 0.78, 95%CI = 0.63-0.95, P = 0.016), but not in OS (HR = 0.84, P = 0.304). Although the occurrence of neutropenia and nausea were slightly different between the PBAT group (51.5% and 24.4%) and the non-PBAT group (47.0% and 29.4%), the complications were acceptable in the two treatments groups. Our results demonstrated that TNBC patients treated with PBAT could achieve a higher pCR rate and better RFS benefit without a higher complication rate.Highlights Platinum-based adjuvant therapy provided a higher pCR rate for TNBC.Platinum-based adjuvant therapy prolonged the RFS but without prolongingthe OS.Neutropenia and nausea rate was different between group PBAT and non-PBAT.

DNA binding and cleavage, BRCA1 gene interaction, antiglycation and anticancer studies of transition metal complexes of sulfonamides

A series of 4-((4-methylphenylsulfonamido)methyl)cyclohexanecarboxylic acid (NaMSCCA) transition metal complexes [Cu(II), Zn(II), Ni(II), Mn(II), and Co(II)] have been synthesized by precipitation method. The characterization was done by physical techniques, FT-IR spectroscopy, mass spectrometry, and NMR spectroscopy. The molecular structures of nickel (II) AZ-3 and cobalt (II) AZ-5 complexes were determined by the X-ray diffraction technique and found to crystallize in the triclinic space group P-1. The coordination geometry around the central nickel (AZ-3) and cobalt (AZ-5) atoms was square planar bipyramidal. Molecular docking was performed with duplex DNA of sequence d(CGCGAATTCGCG)₂ DNA to determine the probable binding mode of compounds. Then these synthesized compounds were used to perform DNA cleavage activity through the agarose gel electrophoresis method. Among the compounds, compounds AZ-1 and AZ-2 exhibited good nuclease activity. The DNA sequence of breast-cancer suppressor gene 1 (BRCA1) was amplified through PCR and interaction studies of compounds AZ-1 and AZ-2 were performed through gel electrophoresis and fluorescence emission spectroscopy. The expression analysis of the BRCA1 gene was also performed to quantify the expression relative fold change (2^-(∆∆CT)) after treatment with compounds. All synthesized compounds were evaluated for their antioxidant and antiglycation activities and AZ-2 exhibited excellent results. The molecular docking study of these compounds was performed against the protein structure of advanced glycation end products to support the experimental results. Anticancer activity of compounds was performed through MTT assay. Copper and zinc complexes depicted the highest anticancer activity against human breast adenocarcinoma (MCF7) and human corneal epithelial cell (HCEC) cell lines.

Modulation of BRCA1 mediated DNA damage repair by deregulated ER-α signaling in breast cancers

BRCA1 mutation carriers have a greater risk of developing cancers in hormone-responsive tissues like breasts and ovaries. However, this tissue-specific incidence of BRCA1 related cancers remains elusive. The majority of the BRCA1 mutated breast cancers exhibit typical histopathological features of high-grade tumors, with basal epithelial phenotype, classified as triple-negative molecular subtype and have a higher percentage of DNA damage and chromosomal abnormality. Though there are many studies relating BRCA1 with ER-α (Estrogen receptor-α), it has not been reported whether E2 (Estrogen) -ER-α signaling can modulate the DNA repair activities of BRCA1. The present study analyzes whether deregulation of ER-α signaling, arising as a result of E2/ER-α deficiency, could impact the BRCA1 dependent DDR (DNA Damage Response) pathways, predominantly those of DNA-DSB (Double Strand break) repair and oxidative damage response. We demonstrate that E2/E2-stimulated ER-α can augment BRCA1 mediated high fidelity repairs like HRR (Homologous Recombination Repair) and BER (Base Excision Repair) in breast cancer cells. Conversely, a condition of ER-α deficiency itself or any interruption in ligand-dependent ER-α transactivation resulted in delayed DNA damage repair, leading to persistent activation of γH2AX and retention of unrepaired DNA lesions, thereby triggering tumor progression. ER-α deficiency not only limited the HRR in cells but also facilitated the DSB repair through error prone pathways like NHEJ (Non Homologous End Joining). ER-α deficiency associated persistence of DNA lesions and reduced expression of DDR proteins were validated in human mammary tumors.

FEN1 is a prognostic biomarker for ER+ breast cancer and associated with tamoxifen resistance through the ERα/cyclin D1/Rb axis

Background

Tamoxifen is an important choice in endocrine therapy for patients with oestrogen receptor-positive (ER+) breast cancer, and disease progression-associated resistance to tamoxifen therapy is still challenging. Flap endonuclease-1 (FEN1) is used as a prognostic biomarker and is considered to participate in proliferation, migration, and drug resistance in multiple cancers, especially breast cancer, but the prognostic function of FEN1 in ER+ breast cancer, and whether FEN1 is related to tamoxifen resistance or not, remain to be explored.

Methods

On-line database Kaplan-Meier (KM) plotter, GEO datasets, and immunohistochemistry were used to analyse the prognostic value of FEN1 in ER+ breast cancer from mRNA and protein levels. Cell viability assay and colony formation assays showed the response of tamoxifen in MCF-7 and T47D cells. Microarray data with FEN1 siRNA versus control group in MCF-7 cells were analysed by Gene Set Enrichment Analysis (GSEA). The protein levels downstream of FEN1 were detected by western blot assay.

Results

ER+ breast cancer patients who received tamoxifen for adjuvant endocrine therapy with poor prognosis showed a high expression of FEN1. MCF-7 and T47D appeared resistant to tamoxifen after FEN1 over-expression and increased sensitivity to tamoxifen after FEN1 knockdown. Importantly, FEN1 over-expression could activate tamoxifen resistance through the ERα/cyclin D1/Rb axis.

Conclusions

As a biomarker of tamoxifen effectiveness, FEN1 participates in tamoxifen resistance through ERα/cyclin D1/Rb axis. In the future, reversing tamoxifen resistance by knocking-down FEN1 or by way of action as a small molecular inhibitor of FEN1 warrants further investigation.

Deregulated estrogen receptor signaling and DNA damage response in breast tumorigenesis

Carriers of BRCA1 mutations have a higher chance of developing cancers in hormone-responsive tissues like the breast, ovary and prostate, compared to other tissues. These tumors generally exhibit basal-like characters and do not express estrogen receptor (ER) or progesterone receptor (PR). Intriguingly, BRCA1 mutated breast cancers have a less favorable clinical outcome, as they will not respond to hormone therapy. BRCA1 has been reported to exhibit ligand dependent and independent transcriptional inhibition of ER-α; however, there exists a controversy on whether BRCA1 induces or inhibits ER-α expression. The mechanisms associated with resistance of BRCA1 mutated cancers to hormone therapy, as well as the tissue restriction exhibited by BRCA1 mutated tumors are still largely unknown. BRCA1 mutated tumors possess increased DNA damages and decreased genomic integrity, as BRCA1 plays a cardinal role in high fidelity DNA damage repair pathways, like homologous recombination (HR). The existence of cross regulatory signaling networks between ER-α and BRCA1 speculates a role of ER on BRCA1 dependent DDR pathways. Thus, the loss or haploinsufficiency of BRCA1 and the consequential deregulation of ER-α signaling may result in persistence of unrepaired DNA damages, eventually leading to tumorigenesis. Therefore, understanding of this cross-talk between ER-α and BRCA1, with regard to DDR, will provide critical insights to steer drug development and therapy for breast/ovarian cancers. This review discusses the mechanisms by which estrogen and ER signaling influence BRCA1 mediated DNA damage response and repair pathways in the mammalian system.

The inhibitory effects of cisplatin-radiation combination treatment on malignant osteosarcoma MG-63 cells and BRCA1-p53 pathways are more efficient than single treatments

The poor prognosis of patients with osteosarcoma remains a persistent problem, in particular for patients with unresectable tumors or metastasis. Therefore, combination of radiotherapy and chemotherapy has been considered for patients with metastasis or recurrence, patients unsuitable for surgery and patients refusing surgery. The present study aimed to investigate the effect of the combined treatment with cisplatin and radiation therapy on the biological characteristics of the osteosarcoma cell line MG-63 and the breast cancer 1 (BRCA1)-associated signaling pathways. Cell proliferation was determined using Cell Counting kit-8 assay, and cell apoptosis and cell cycle were assessed by flow cytometry. Cell migration was examined by Transwell assay. The mRNA and protein expression levels of candidate genes, including BRCA1 and p53, were determined by reverse transcription-quantitative PCR and western blotting, respectively. The results demonstrated that combined treatment with radiation and cisplatin significantly inhibited MG-63 cell proliferation compared with radiation or cisplatin treatment alone. Furthermore, radiation, cisplatin or the combined treatment with radiation and cisplatin increased the apoptosis rate of MG-63 cells, which resulted in G₂ phase arrest, and significantly decreased the migratory capacity of MG-63 cells. In addition, the apoptosis rate of MG-63 cells following combined radiation and cisplatin treatment was higher compared with the cisplatin group, but lower compared with the radiation group. Furthermore, combined treatment with radiation and cisplatin decreased the mRNA and protein expression levels of BRCA1 and p53. Additionally, combined treatment with radiation and cisplatin had a more potent inhibitory effect on p53 expression than on BRCA1 expression. In addition, combination of radiation and cisplatin had a higher inhibitory effect on Bax protein level and a higher inductive effect on Bcl-2 protein level compared with treatments with radiation and cisplatin alone. The results demonstrated that combined treatment of radiation and cisplatin exhibited superior therapeutic effects on osteosarcoma MG-63 cells compared with radiation or cisplatin treatment alone, which may be mediated by the BRCA1-p53 signaling pathway.

Analysis of the TP53 Deleterious Single Nucleotide Polymorphisms Impact on Estrogen Receptor Alpha-p53 Interaction: A Machine Learning Approach

Breast cancer is a leading cancer type and one of the major health issues faced by women around the world. Some of its major risk factors include body mass index, hormone replacement therapy, family history and germline mutations. Of these risk factors, estrogen levels play a crucial role. Among the estrogen receptors, estrogen receptor alpha (ERα) is known to interact with tumor suppressor protein p53 directly thereby repressing its function. Previously, we have studied the impact of deleterious breast cancer-associated non-synonymous single nucleotide polymorphisms (nsnps) rs11540654 (R110P), rs17849781 (P278A) and rs28934874 (P151T) in TP53 gene on the p53 DNA-binding core domain. In the present study, we aimed to analyze the impact of these mutations on p53–ERα interaction. To this end, we, have modelled the full-length structure of human p53 and validated its quality using PROCHECK and subjected it to energy minimization using NOMAD-Ref web server. Three-dimensional structure of ERα activation function-2 (AF-2) domain was downloaded from the protein data bank. Interactions between the modelled native and mutant (R110P, P278A, P151T) p53 with ERα was studied using ZDOCK. Machine learning predictions on the interactions were performed using Weka software. Results from the protein–protein docking showed that the atoms, residues and solvent accessibility surface area (SASA) at the interface was increased in both p53 and ERα for R110P mutation compared to the native complexes indicating that the mutation R110P has more impact on the p53–ERα interaction compared to the other two mutants. Mutations P151T and P278A, on the other hand, showed a large deviation from the native p53-ERα complex in atoms and residues at the surface. Further, results from artificial neural network analysis showed that these structural features are important for predicting the impact of these three mutations on p53–ERα interaction. Overall, these three mutations showed a large deviation in total SASA in both p53 and ERα. In conclusion, results from our study will be crucial in making the decisions for hormone-based therapies against breast cancer.

Overview on Epigenetic Re-programming: A Potential Therapeutic Intervention in Triple Negative Breast Cancers

Breast cancer treatments leads to variable responses. Hormonal therapy is beneficial to receptor positive breast cancer subtypes and display better clinical outcome than triple negative breast cancers (TNBCs) with FEC (5-Fluorouracil, Epirubicin and Cyclophosphamide) the mainstay chemotherapy regiment. Owning to their negative expressions of estrogen (ER), progesterone (PR) and HER2 receptors, disease recurrence and metastasis befalls some patients indicating resistance to FEC. Involvement of epigenetic silencing through DNA methylation, histone methylation, acetylation and sumoylation may be the key player in FEC chemoresistance. Epigenetic and molecular profiling successfully classified breast cancer subtypes, indicating potential driver mechanisms to the progression of TNBCs but functional mechanisms behind chemoresistance of these molecular markers are not well defined. Several epigenetic inhibitors and drugs have been used in the management of cancers but these attempts are mainly beneficial in hematopoietic cancers and not specifically favourable in solid tumours. Hypothetically, upon administration of epigenetic drugs, recovery of tumour suppressor genes is expected. However, high tendency of switching on global metastatic genes is predicted. Polycomb repressive complex (PRC) such as EZH2, SETD1A, DNMT, is known to have repressive effects in gene regulation and shown to inhibit cell proliferation and invasion in breast cancers. Individual epigenetic regulators may be an option to improve chemo-drug delivery in cancers. This review discussed on molecular signatures of various breast cancer subtypes and on-going attempts in understanding underlying molecular mechanisms of epigenetic regulators as well as providing insights on possible ways to utilize epigenetic enzymes/inhibitors with responses to chemotherapeutic drugs to re-program cellular and biological outcome in TNBCs.

Germline mutations in DNA repair genes may predict neoadjuvant therapy response in triple negative breast patients

Triple negative breast cancers (TNBCs) represent about 15-20% of all breast cancer cases and are characterized by a complex molecular heterogeneity. Some TNBCs exhibit clinical and pathological properties similar to BRCA-mutated tumors, without actually bearing a mutation in BRCA genes. This "BRCAness" phenotype may be explained by germline mutations in other genes involved in DNA repair. Although respond to chemotherapy with alkylating agents, they have a high risk of recurrence and progression. Some studies have shown the efficacy of neoadjuvant therapy in TNBC patients with DNA repair defects, but proper biomarkers of DNA repair deficiency are still needed. Here, we investigated if mutations in DNA repair genes may be correlated with anthracyclines/taxanes neoadjuvant therapy response. DNA from 19 TNBC patients undergoing neoadjuvant therapy were subjected to next generation sequencing of a panel of 24 genes in DNA repair and breast cancer predisposition. In this study, 5 of 19 patients (26%) carried a pathogenic mutation in BRCA1, PALB2, RAD51C and two patients carried a probable pathogenic missense variant. Moreover, VUS (Variants of Unknown Significance) in other genes, predicted to be deleterious by in silico tools, were detected in five patients. Germline mutations in DNA repair genes were found to be associated with the group of TNBC patients who responded to therapy. We conclude that a subgroup of TNBC patients have defects in DNA repair genes, other than BRCA1, and such patients respond favourably to neoadjuvant anthracyclines/taxanes therapy. © 2016 Wiley Periodicals, Inc.

Predicting chemoinsensitivity in breast cancer with 'omics/digital pathology data fusion

Predicting response to treatment and disease-specific deaths are key tasks in cancer research yet there is a lack of methodologies to achieve these. Large-scale 'omics and digital pathology technologies have led to the need for effective statistical methods for data fusion to extract the most useful patterns from these diverse data types. We present FusionGP, a method for combining heterogeneous data types designed specifically for predicting outcome of treatment and disease. FusionGP is a Gaussian process model that includes a generalization of feature selection for biomarker discovery, allowing for simultaneous, sparse feature selection across multiple data types. Importantly, it can accommodate highly nonlinear structure in the data, and automatically infers the optimal contribution from each input data type. FusionGP compares favourably to several popular classification methods, including the Random Forest classifier, a stepwise logistic regression model and the Support Vector Machine on single data types. By combining gene expression, copy number alteration and digital pathology image data in 119 estrogen receptor (ER)-negative and 345 ER-positive breast tumours, we aim to predict two important clinical outcomes: death and chemoinsensitivity. While gene expression data give the best predictive performance in the majority of cases, the digital pathology data are much better for predicting death in ER cases. Thus, FusionGP is a new tool for selecting informative features from heterogeneous data types and predicting treatment response and prognosis.

Silencing of CXCR4 sensitizes triple-negative breast cancer cells to cisplatin

Triple-negative breast cancer (TNBC) is an aggressive form of breast cancer for which there is no effective treatment. Previously, we and others demonstrated that CXCR4 surface expression is an independent prognostic factor for disease relapse and survival in breast cancer. In this study, we investigated the effects of CXCR4 gene silencing on cisplatin chemosensitivity in human triple-negative breast cancer cell lines. We found that CXCR4 silencing significantly inhibited cell growth, decreased colony formation, and enhanced cisplatin sensitivity while overexpression of CXCR4 rendered cells more resistant to cisplatin. Moreover, the percentage of apoptosis and cell cycle arrest at the G2/M phase of cisplatin-treated CXCR4 knockdown cells was significantly higher than control cells. Furthermore, we demonstrated CXCR4 knockdown cells showed lower levels of mutant p53 and Bcl-2 protein than the control group, while also having higher levels of caspase-3 and Bax. However overexpression of CXCR4 had the reverse effect. In vivo experiments confirmed that downregulation of CXCR4 enhanced cisplatin anticancer activity in tumor-bearing mice, and that this enhanced anticancer activity is attributable to tumor cell apoptosis. Thus, this study indicates that CXCR4 can modulate cisplatin sensitivity in TNBC cells and suggests that CXCR4 may be a therapeutic target for TNBC.

Cellular responses of BRCA1-defective and triple-negative breast cancer cells and in vitro BRCA1 interactions induced by metallo-intercalator ruthenium(II) complexes containing chloro-substituted phenylazopyridine

BACKGROUND

Triple-negative breast cancer (TNBC) is defined by the absence of expression of estrogen receptor, progesterone receptor and human epidermal growth factor receptor 2. Breast cancers with a BRCA1 mutation are also frequently triple-negative. Currently, there is a lack of effective therapies and known specific molecular targets for this aggressive breast cancer subtype. To address this concern, we have explored the cellular responses of BRCA1-defective and triple-negative breast cancer cells, and in vitro BRCA1 interactions induced by the ruthenium(II) complexes containing the bidentate ligand, 5-chloro-2-(phenylazo)pyridine.

METHODS

Triple-negative MDA-MB-231, BRCA1-defective HCC1937 and BRCA1-competent MCF-7 breast cancer cell lines were treated with ruthenium(II) complexes. The cytoxoxicity of ruthenium-induced breast cancer cells was evaluated by a real time cellular analyzer (RTCA). Cellular uptake of ruthenium complexes was determined by ICP-MS. Cell cycle progression and apoptosis were assessed using propidium iodide and Annexin V flow cytometry. The N-terminal BRCA1 RING protein was used for conformational and functional studies using circular dichroism and in vitro ubiquitination.

RESULTS

HCC1937 cells were significantly more sensitive to the ruthenium complexes than the MDA-MB-231 and MCF-7 cells. Treatment demonstrated a higher degree of cytotoxicity than cisplatin against all three cell lines. Most ruthenium atoms were retained in the nuclear compartment, particularly in HCC1937 cells, after 24 h of incubation, and produced a significant block at the G2/M phase. An increased induction of apoptotic cells as well as an upregulation of p53 mRNA was observed in all tested breast cancer cells. It was of interest that BRCA1 mRNA and replication of BRCA1-defective cells were downregulated. Changes in the conformation and binding constants of ruthenium-BRCA1 adducts were observed, causing inactivation of the RING heterodimer BRCA1/BARD1-mediated E3 ubiquitin ligase activity.

CONCLUSIONS

This study has revealed the ability of ruthenium complexes to inhibit cell proliferation, induce cell cycle progression and apoptosis. Ruthenium treatment upregulated the marker genes involved in apoptosis and cell cycle progression while it downregulated BRCA1 mRNA and replication of HCC1937 cells. Our results could provide an alternative approach to finding effective therapeutic ruthenium-based agents with promising anticancer activity, and demonstrated that the BRCA1 RING domain protein was a promising therapeutic target for breast cancers.

Polymorphism of UBC9 gene encoding the SUMO-E2-conjugating enzyme and breast cancer risk

UBC9 protein (E2-conjugating enzyme) plays a key role in post-translation modification named sumoylation. Proteins, which are sumoylated take part in many cellular processes including cell growth, maintaining the genome integrity and stability and cancer development. The aim of this study was to investigate an association between three polymorphisms of the UBC9 gene: c.73G>A (rs11553473), c.430T>G (rs75020906) and g.1289209T>C (rs7187167) and a risk of ductal breast cancer occurrence. We performed a case-control study in 181 breast cancer cases and 277 controls using PCR-RLFP and ASO-PCR. In the case of the 430T>G polymorphism of the UBC9 gene lack of variability suggests that there is not a polymorphic site in polish population. We observed that a risk of breast cancer occurrence is elevated in patients with the G/A genotype (OR 5.03; 95 % Cl 3.05–8.28), the A/A genotype (OR 11.3; 95 % Cl 4.24–30.3) and the A allele (OR 6.86; 95 % Cl 4.43–10.6) of the c.73G>A polymorphism. In the case of the g.1289209T>C polymorphism we found a correlation between estrogen receptor (ER) expression and the T/T genotype (OR 0.22; 95 % Cl 0.07–0.64) and the T allele (OR 0.53; 95 % Cl 0.32–0.88). We also found a correlation between the T/T genotype (OR 4.13; 95 % Cl 1.21–14.1) and the T allele (OR 2.09; 95 % Cl 1.07–4.08) of the g.1289209T>C polymorphism with triple negative breast cancer. Our results suggest that the variability of the UBC9 gene can play a role in breast cancer occurrence.