Critical role for BRCA1 expression as a marker of chemosensitivity response and prognosis

Radiosensitizing effect of a novel CTSS inhibitor by enhancing BRCA1 protein stability in triple-negative breast cancer cells

Triple-negative breast cancer (TNBC) patients harboring wild-type breast cancer susceptibility gene 1 (BRCA1) account for most TNBC patients but lack adequate targeted therapeutic options. Although radiotherapy (RT) is the primary treatment modality for TNBC patients, radioresistance is one of the major challenges. RT-induced increase in cathepsin S (CTSS) causes radioresistance through suppressing BRCA1-mediated apoptosis of tumor cells, which was induced by CTSS-mediated degradation of BRCA1. Targeting CTSS may provide a novel therapeutic opportunity for TNBC patients. Publicly available data and human tissue microarray slides were analyzed to investigate the relationship between CTSS and BRCA1 in breast cancer patients. A CTSS enzyme assay and in silico docking analysis were conducted to identify a novel CTSS inhibitor. RO5461111 was used first to confirm the concept of targeting CTSS for radiosensitizing effects. The MDA-MB-231 TNBC cell line was used for in vitro and in vivo assays. Western blotting, promoter assay, cell death assay, clonogenic survival assay, and immunohistochemistry staining were conducted to evaluate novel CTSS inhibitors. CTSS inhibitors were further evaluated for their additional benefit of inhibiting cell migration. A novel CTSS inhibitor, TS-24, increased BRCA1 protein levels and showed radiosensitization in TNBC cells with wild-type BRCA1 and in vivo in a TNBC xenograft mouse model. These effects were attributed by BRCA1-mediated apoptosis facilitated by TS-24. Furthermore, TS-24 demonstrated the additional effect of inhibiting cell migration. Our study suggests that employing CTSS inhibitors for the functional restoration of BRCA1 to enhance RT-induced apoptosis may provide a novel therapeutic opportunity for TNBC patients harboring wild-type BRCA1.

Mechanistic insights into the survival curve of HeLa cells with a short shoulder and their S phase-specific sensitivity†

HeLa cells are a cell line with two unique cellular features: a short-shouldered survival curve and two peaks of radioresistance during the cell cycle phase, while their underlying mechanisms remain unclear. We herein proposed that these radiobiological features are due to a common mechanism by which radiation suppresses homologous recombination repair (HRR) in a dose-dependent manner. This radio-suppression of HRR is mediated by an intra-S checkpoint and reduces survivals of cells in S phase, especially early S phase, resulting in both short shoulder and radioresistance with two peaks in the cell cycle. This new explanation may not be limited to HeLa cells since a similar close association of these features is also observed in other type of cells.

Potential diagnostic and prognostic biomarkers for breast cancer: A compiled review

Breast cancer is one of the major reason for death of women worldwide. As per the International Agency for Research on Cancer (IARC) statistics, the number of cases of breast cancer is increasing year by year in many parts of the world. As per the recent global cancer burden figures, in 2020, there were 2.26 million incidences of breast cancer cases and it is one of the main causes of mortality due to cancer in women in the world. Biomarkers of breast cancer would prove to be very beneficial to screen women who are at higher risk and for detection of disease recurrence. Here, studies carried out on biomarkers of breast cancer and susceptibility to the disease have been reviewed. Various databases like Google Scholar, ScienceDirect and PubMed have been used for searching and majorly literature from the last 10 years have been considered. Potential biomarkers of breast cancer including blood based angiogenic factors, glycoprotein-based biomarkers, hormone receptor biomarkers and other biomarkers that were identified from various studies have been summarized.

Inhibition of c-MET increases the antitumour activity of PARP inhibitors in gastric cancer models

Gastric cancer is the fifth most common malignancy and the third leading cause of cancer‐related death worldwide. Activation of c‐MET increases tumour cell survival through the initiation of the DNA damage repair pathway. PARP is an essential key in the DNA damage repair pathway. The primary role of PARP is to detect and initiate an immediate cellular response to single‐strand DNA breaks. Tumours suppressor genes such as BRCA1/2 are closely associated with the DNA repair pathway. In BRCA1/2 mutations or deficiency status, cells are more likely to develop additional genetic alterations and chromosomal instability and can lead to cancer. In this study, we investigate the role of c‐MET and PARP inhibition in a gastric cancer model. We exploited functional in vitro and in vivo experiments to assess the antitumour potential of co‐inhibition of c‐MET (SU11274) and PARP (NU1025). This leads to a reduction of gastric cancer cells viability, especially after knockdown of BRCA1/2 through apoptosis and induction of γ‐Η2ΑΧ. Moreover, in AGS xenograft models, the combinatorial treatment of NU1025 plus SU11274 reduced tumour growth and triggers apoptosis. Collectively, our data may represent a new therapeutic approach for GC thought co‐inhibition of c‐MET and PARP, especially for patients with BRCA1/2 deficiency tumours.

Oxidative DNA Damage Modulates DNA Methylation Pattern in Human Breast Cancer 1 (BRCA1) Gene via the Crosstalk between DNA Polymerase β and a de novo DNA Methyltransferase

DNA damage and base excision repair (BER) are actively involved in the modulation of DNA methylation and demethylation. However, the underlying molecular mechanisms remain unclear. In this study, we seek to understand the mechanisms by exploring the effects of oxidative DNA damage on the DNA methylation pattern of the tumor suppressor breast cancer 1 (BRCA1) gene in the human embryonic kidney (HEK) HEK293H cells. We found that oxidative DNA damage simultaneously induced DNA demethylation and generation of new methylation sites at the CpGs located at the promoter and transcribed regions of the gene ranging from -189 to +27 in human cells. We demonstrated that DNA damage-induced demethylation was mediated by nucleotide misincorporation by DNA polymerase β (pol β). Surprisingly, we found that the generation of new DNA methylation sites was mediated by coordination between pol β and the de novo DNA methyltransferase, DNA methyltransferase 3b (DNMT3b), through the interaction between the two enzymes in the promoter and encoding regions of the BRCA1 gene. Our study provides the first evidence that oxidative DNA damage can cause dynamic changes in DNA methylation in the BRCA1 gene through the crosstalk between BER and de novo DNA methylation.

Somatic aberrations of BRCA1 gene are associated with ALDH1, EGFR, and tumor progression in prostate cancer

BRCA1 is a pivotal tumor suppressor. Its dysfunction is known to play a role in different tumors. Among others, BRCA1 germline mutations account for higher risk and more aggressive course of prostate cancer (PCa). In addition, somatic BRCA1 gene loss was demonstrated to be a signature of PCa dissemination to lymph nodes and peripheral blood, and indicate worse clinical outcome. In order to substantiate the data for BRCA1 gene loss in PCa and reveal its phenotypical background, BRCA1 gene status was assessed in a large cohort of PCa patients and compared to different molecular factors. BRCA1 gene dosage was assessed in 2398 tumor samples from 1,199 PCa patients using fluorescent in situ hybridization. It was compared to clinico-pathological parameters, patients' outcome as well as selected proteins (Ki-67, apoptosis marker, cytokeratins, vimentin, E- and N-cadherin, ALDH1 and EGFR) examined immunohistochemically. BRCA1 losses were found in 10%, whereas gains appeared in 7% of 603 informative PCa patients. BRCA1 losses correlated to higher T stage (p = 0.027), Gleason score (p = 0.039), shorter time to biochemical recurrence in patients with Gleason score > 7 independently of other factors (multivariate analysis, p = 0.005) as well as expression of proteins regulating stemness and epithelial-mesenchymal transition, that is, ALDH1 (p = 0.021) and EGFR (p = 0.011), respectively. BRCA1 gains correlated to shorter time to metastasis (p = 0.012) and expression of ALDH1 (p = 0.014). These results support the assumption that BRCA1 gene losses contribute to a progressive and stem cell-like phenotype of PCa. Furthermore, they reveal that also BRCA1 gain conceivably representing loss-of-function might mark more invasive tumors.

Impact of Etoposide on BRCA1 Expression in Various Breast Cancer Cell Lines

Breast cancer 1 (BRCA1), as a tumor suppressor, exerts an effective influence on protecting DNA integrity to suppress the development of breast cancer (BC). BRCA1 expression is induced in response to DNA-damaging agents such as etoposide. Germline BRCA1 gene mutations are associated with development of hereditary BC. However, besides BRCA-mutated BCs, some sporadic cancers may also exhibit a BRCA-like phenotype, displaying so-called ‘BRCAness’. This common phenotype may respond to similar therapeutic approaches as BRCA-mutated tumors and may thus have important implications for the clinical management of these cancers. In order to determine whether and how etoposide regulates the protein levels of BRCA1 in BC cells, we exposed a panel of five selected cell lines to etoposide, compared the results to untreated control cells, and then stained the cells with the specific, reliable, and reproducible MS110 antibody directed against phosphorylated Ser1423 BRCA1. By evaluating cytoplasmic BRCA1 protein levels, we were able to distinguish three aggressive BC subtypes with BRCAness characteristics. In addition, determination of early and late apoptosis helped to complete the analysis of BRCA1 functions in the DNA damage pathway of aggressive BC. In conclusion, our study suggested that high cytoplasmic BRCA1 protein levels could be considered as a potential predictive marker for response to chemotherapy in both sporadic and hereditary BC. Tumors with either BRCAness phenotype or germline BRCA1 mutation are both aggressive BCs associated with poor prognosis and could both be subjected to targeted therapies against BRCA1-mutated BC in future clinical management strategies.

Prediction of therapy response in ovarian cancer: Where are we now?

Therapy resistance is a major challenge in the management of ovarian cancer (OC). Advances in detection and new technology validation have led to the emergence of biomarkers that can predict responses to available therapies. It is important to identify predictive biomarkers to select resistant and sensitive patients in order to reduce important toxicities, to reduce costs and to increase survival. The discovery of predictive and prognostic biomarkers for monitoring therapy is a developing field and provides promising perspectives in the era of personalized medicine. This review article will discuss the biology of OC with a focus on targetable pathways; current therapies; mechanisms of resistance; predictive biomarkers for chemotherapy, antiangiogenic and DNA-targeted therapies, and optimal cytoreductive surgery; and the emergence of liquid biopsy using recent studies from the Medline database and ClinicalTrials.gov.