High RAD51 mRNA expression characterize estrogen receptor-positive/progesteron receptor-negative breast cancer and is associated with patient's outcome

PG545 sensitizes ovarian cancer cells to PARP inhibitors through modulation of RAD51-DEK interaction

PG545 (Pixatimod) is a highly sulfated small molecule known for its ability to inhibit heparanase and disrupt signaling mediated by heparan-binding-growth factors (HB-GF). Previous studies indicated that PG545 inhibits growth factor-mediated signaling in ovarian cancer (OC) to enhance response to chemotherapy. Here we investigated the previously unidentified mechanisms by which PG545 induces DNA damage in OC cells and found that PG545 induces DNA single- and double-strand breaks, reduces RAD51 expression in an autophagy-dependent manner and inhibits homologous recombination repair (HRR). These changes accompanied the ability of PG545 to inhibit endocytosis of the heparan-sulfate proteoglycan interacting DNA repair protein, DEK, leading to DEK sequestration in the tumor microenvironment (TME) and loss of nuclear DEK needed for HRR. As a result, PG545 synergized with poly (ADP-ribose) polymerase inhibitors (PARPis) in OC cell lines in vitro and in 55% of primary cultures of patient-derived ascites samples ex vivo. Moreover, PG545/PARPi synergy was observed in OC cells exhibiting either de novo or acquired resistance to PARPi monotherapy. PG545 in combination with rucaparib also generated increased DNA damage, increased antitumor effects and increased survival of mice bearing HRR proficient OVCAR5 xenografts compared to monotherapy treatment in vivo. Synergistic antitumor activity of the PG545/rucaparib combination was likewise observed in an immunocompetent syngeneic ID8F3 OC model. Collectively, these results suggest that targeting DEK-HSPG interactions in the TME through the use of PG545 may be a novel method of inhibiting DNA repair and sensitizing cells to PARPis.

Identification of Nanog as a novel inhibitor of Rad51

To develop inhibitors targeting DNA damage repair pathways is important to improve the effectiveness of chemo- and radiotherapy for cancer patients. Rad51 mediates homologous recombination (HR) repair of DNA damages. It is widely overexpressed in human cancers and overwhelms chemo- and radiotherapy-generated DNA damages through enhancing HR repair signaling, preventing damage-caused cancer cell death. Therefore, to identify inhibitors of Rad51 is important to achieve effective treatment of cancers. Transcription factor Nanog is a core regulator of embryonic stem (ES) cells for its indispensable role in stemness maintenance. In this study, we identified Nanog as a novel inhibitor of Rad51. It interacts with Rad51 and inhibits Rad51-mediated HR repair of DNA damage through its C/CD2 domain. Moreover, Rad51 inhibition can be achieved by nanoscale material- or cell-penetrating peptide (CPP)-mediated direct delivery of Nanog-C/CD2 peptides into somatic cancer cells. Furthermore, we revealed that Nanog suppresses the binding of Rad51 to single-stranded DNAs to stall the HR repair signaling. This study provides explanation for the high γH2AX level in unperturbed ES cells and early embryos, and suggests Nanog-C/CD2 as a promising drug candidate applied to Rad51-related basic research and therapeutic application studies.

Molecular Determinant of DIDS Analogs Targeting RAD51 Activity

RAD51 is the central protein in DNA repair by homologous recombination (HR), involved in several steps of this process. It is shown that overexpression of the RAD51 protein is correlated with increased survival of cancer cells to cancer treatments. For the past decade, RAD51 overexpression-mediated resistance has justified the development of targeted inhibitors. One of the first molecules described to inhibit RAD51 was the 4,4′-diisothiocyanato-stilbene-2,2′-disulfonic acid (DIDS) molecule. This small molecule is effective in inhibiting different functions of RAD51, however its mode of action and the chemical functions involved in this inhibition have not been identified. In this work, we used several commercial molecules derived from DIDS to characterize the structural determinants involved in modulating the activity of RAD51. By combining biochemical and biophysical approaches, we have shown that DIDS and two analogs were able to inhibit the binding of RAD51 to ssDNA and prevent the formation of D-loop by RAD51. Both isothiocyanate substituents of DIDS appear to be essential in the inhibition of RAD51. These results open the way to the synthesis of new molecules derived from DIDS that should be greater modulators of RAD51 and more efficient for HR inhibition.

Homologous Recombination Deficiency: Cancer Predispositions and Treatment Implications

Homologous recombination (HR) is a highly accurate DNA repair mechanism. Several HR genes are established cancer susceptibility genes with clinically actionable pathogenic variants (PVs). Classically, BRCA1 and BRCA2 germline PVs are associated with significant breast and ovarian cancer risks. Patients with BRCA1 or BRCA2 PVs display worse clinical outcomes but respond better to platinum-based chemotherapies and poly-ADP ribose polymerase inhibitors, a trait termed "BRCAness." With the advent of whole-exome sequencing and multigene panels, PVs in other HR genes are increasingly identified among familial cancers. As such, several genes such as PALB2 are reclassified as cancer predisposition genes. But evidence for cancer risks remains unclear for many others. In this review, we will discuss cancer predispositions and treatment implications beyond BRCA1 and BRCA2, with a focus on 24 HR genes: 53BP1, ATM, ATR, ATRIP, BARD1, BLM, BRIP1, DMC1, MRE11A, NBN, PALB2, RAD50, RAD51, RAD51B, RAD51C, RAD51D, RIF1, RMI1, RMI2, RPA1, TOP3A, TOPBP1, XRCC2, and XRCC3. IMPLICATIONS FOR PRACTICE: This review provides a comprehensive reference for readers to quickly identify potential cancer predisposing homologous recombination (HR) genes, and to generate research questions for genes with inconclusive evidence. This review also evaluates the "BRCAness" of each HR member. Clinicians can refer to these discussions to identify potential candidates for future clinical trials.

MUC3A promotes non-small cell lung cancer progression via activating the NFκB pathway and attenuates radiosensitivity

Mucin 3A (MUC3A) is highly expressed in non-small cell lung cancer (NSCLC), but its functions and effects on clinical outcomes are not well understood. Tissue microarray of 92 NSCLC samples indicated that high levels of MUC3A were associated with poor prognosis, advanced staging, and low differentiation. MUC3A knockdown significantly suppressed NSCLC cell proliferation and induced G1/S accumulation via downregulating cell cycle checkpoints. MUC3A knockdown also inhibited tumor growth in vivo and had synergistic effects with radiation. MUC3A knockdown increased radiation-induced DNA double strain breaks and γ-H2AX phosphorylation in NSCLC cells. MUC3A downregulation inhibited the BRCA-1/RAD51 pathway and nucleus translocation of P53 and XCRR6, suggesting that MUC3A promoted DNA damage repair and attenuated radiation sensitivity. MUC3A knockdown also resulted in less nucleus translocation of RELA and P53 in vivo. Immunoprecipitation revealed that MUC3A interacted with RELA and activated the NFκB pathway via promoting RELA phosphorylation and interfering the binding of RELA to IκB. Our studies indicated that MUC3A was a potential oncogene and associated with unfavorable clinical outcomes. NSCLC patients with a high MUC3A level, who should be more frequent follow-up and might benefit less from radiotherapy.

New RAD51 Inhibitors to Target Homologous Recombination in Human Cells

Targeting DNA repair proteins with small-molecule inhibitors became a proven anti-cancer strategy. Previously, we identified an inhibitor of a major protein of homologous recombination (HR) RAD51, named B02. B02 inhibited HR in human cells and sensitized them to chemotherapeutic drugs in vitro and in vivo. Here, using a medicinal chemistry approach, we aimed to improve the potency of B02. We identified the B02 analog, B02-isomer, which inhibits HR in human cells with significantly higher efficiency. We also show that B02-iso sensitizes triple-negative breast cancer MDA-MB-231 cells to the PARP inhibitor (PARPi) olaparib.

Luminal A Breast Cancer Co-expression Network: Structural and Functional Alterations

Luminal A is the most common breast cancer molecular subtype in women worldwide. These tumors have characteristic yet heterogeneous alterations at the genomic and transcriptomic level. Gene co-expression networks (GCNs) have contributed to better characterize the cancerous phenotype. We have previously shown an imbalance in the proportion of intra-chromosomal (cis-) over inter-chromosomal (trans-) interactions when comparing cancer and healthy tissue GCNs. In particular, for breast cancer molecular subtypes (Luminal A included), the majority of high co-expression interactions connect gene-pairs in the same chromosome, a phenomenon that we have called loss of trans- co-expression. Despite this phenomenon has been described, the functional implication of this specific network topology has not been studied yet. To understand the biological role that communities of co-expressed genes may have, we constructed GCNs for healthy and Luminal A phenotypes. Network modules were obtained based on their connectivity patterns and they were classified according to their chromosomal homophily (proportion of cis-/trans- interactions). A functional overrepresentation analysis was performed on communities in both networks to observe the significantly enriched processes for each community. We also investigated possible mechanisms for which the loss of trans- co-expression emerges in cancer GCN. To this end we evaluated transcription factor binding sites, CTCF binding sites, differential gene expression and copy number alterations (CNAs) in the cancer GCN. We found that trans- communities in Luminal A present more significantly enriched categories than cis- ones. Processes, such as angiogenesis, cell proliferation, or cell adhesion were found in trans- modules. The differential expression analysis showed that FOXM1, CENPA, and CIITA transcription factors, exert a major regulatory role on their communities by regulating expression of their target genes in other chromosomes. Finally, identification of CNAs, displayed a high enrichment of deletion peaks in cis- communities. With this approach, we demonstrate that network topology determine, to at certain extent, the function in Luminal A breast cancer network. Furthermore, several mechanisms seem to be acting together to avoid trans- co-expression. Since this phenomenon has been observed in other cancer tissues, a remaining question is whether the loss of long distance co-expression is a novel hallmark of cancer.

Polymorphic Variants in 5'-UTR Regions of the RAD51 Gene are Associated With RAD51 Expression and Triple-Negative Breast Cancer (TNBC): A Case-Control Study

Breast cancer is a heterogeneous disease at morphologic and molecular levels, which is considered the most commonly occurring cancer in women. RAD51, a DNA-repairing protein, involves homologous recombination and has a vital role in genome stability. Polymorphism of the RAD51 gene, and its overexpression, has been proposed to be associated with the development of breast cancer. Overexpression of RAD51 in many types of human cancer including metastatic breast cancer may signify its potential use as a biomarker. Considering the numerous reports on the role of the 5'-UTR-RAD51 polymorphism in breast cancer, this study aimed to investigate the utility of RAD51 gene expression and its variants G135C and G172T as a possible foretelling factor of breast cancer development. DNA sequencing and immunohistochemistry of RAD51 were conducted on 103 samples from patients diagnosed with sporadic breast cancer and 80 samples from a control group. The results demonstrated that the RAD51 variants, G135C and G172T, were significantly presented in the breast cancer tissue compared with the control group. RAD51 expression was mainly shown in the cytoplasm of malignant cells (56% of cases) and significantly correlated with p53 and G135C, C135C variants. Moreover, the occurrence of the G172T variant was significantly associated with the expression of estrogen receptor. Interestingly, 21/26 (81%) of the triple-negative breast cancer showed G135C and C135C genotypes that were significantly associated with the expression of RAD51 (73%). In conclusion, the G135C and C135C variants together with the cytoplasmic expression of RAD51 may have clinical potential as a prognostic predictor for breast cancer development and aggressiveness.

Regulation and pharmacological targeting of RAD51 in cancer

Regulation of homologous recombination (HR) is central for cancer prevention. However, too little HR can increase cancer incidence, whereas too much HR can drive cancer resistance to therapy. Importantly, therapeutics targeting HR deficiency have demonstrated a profound efficacy in the clinic improving patient outcomes, particularly for breast and ovarian cancer. RAD51 is central to DNA damage repair in the HR pathway. As such, understanding the function and regulation of RAD51 is essential for cancer biology. This review will focus on the role of RAD51 in cancer and beyond and how modulation of its function can be exploited as a cancer therapeutic.

Cytokines, JAK-STAT Signaling and Radiation-Induced DNA Repair in Solid Tumors: Novel Opportunities for Radiation Therapy

A number of solid tumors are treated with radiation therapy (RT) as a curative modality. At the same time, for certain types of cancers the applicable doses of RT are not high enough to result in a successful eradication of cancer cells. This is often caused by limited pharmacological tools and strategies to selectively sensitize tumors to RT while simultaneously sparing normal tissues from RT. We present an outline of a novel strategy for RT sensitization of solid tumors utilizing Jak inhibitors. Here, recently published pre-clinical data are reviewed which demonstrate the promising role of Jak inhibition in sensitization of tumors to RT. A wide number of currently approved Jak inhibitors for non-malignant conditions are summarized including Jak inhibitors currently in clinical development. Finally, intersection between Jak/Stat and the levels of serum cytokines are presented and discussed as they relate to susceptibility to RT.

Role of Rad51 and DNA repair in cancer: A molecular perspective

The maintenance of genome integrity is essential for any organism survival and for the inheritance of traits to offspring. To the purpose, cells have developed a complex DNA repair system to defend the genetic information against both endogenous and exogenous sources of damage. Accordingly, multiple repair pathways can be aroused from the diverse forms of DNA lesions, which can be effective per se or via crosstalk with others to complete the whole DNA repair process. Deficiencies in DNA healing resulting in faulty repair and/or prolonged DNA damage can lead to genes mutations, chromosome rearrangements, genomic instability, and finally carcinogenesis and/or cancer progression. Although it might seem paradoxical, at the same time such defects in DNA repair pathways may have therapeutic implications for potential clinical practice. Here we provide an overview of the main DNA repair pathways, with special focus on the role played by homologous repair and the RAD51 recombinase protein in the cellular DNA damage response. We next discuss the recombinase structure and function per se and in combination with all its principal mediators and regulators. Finally, we conclude with an analysis of the manifold roles that RAD51 plays in carcinogenesis, cancer progression and anticancer drug resistance, and conclude this work with a survey of the most promising therapeutic strategies aimed at targeting RAD51 in experimental oncology.

Targeting RAD51 enhances chemosensitivity of adult T‑cell leukemia‑lymphoma cells by reducing DNA double‑strand break repair

RAD51, is a key homologous recombination protein that repairs DNA damage and maintains gene diversity and stability. Previous studies have demonstrated that the over‑expression of RAD51 is associated with chemotherapy resistance of tumor cells to chemotherapy, and enhanced activity of DNA damage repair (DDR) systems contributes to resistance of adult T‑cell leukemia‑lymphoma (ATL) resistance to chemotherapy. Thus, targeting RAD51 is a potential strategy for the sensitization of ATL cells to chemotherapeutic drugs by inducing DNA damage. In general, cells can repair minor DNA damage through DDR; however, serious DNA damage may cause cell toxicity in cells which cannot be restored. In the present, down regulation of RAD51 by shRNA and imatinib sensitized Jurkat cells to etoposide by decreasing the activity of homologous recombination (HR). We found that the suppression of RAD51 by shRNA inhibited tumor cells proliferation and enhanced apoptosis of Jurkat cells after etoposide treatment. Importantly, downregulation of RAD51 by imatinib obviously increased the apoptosis of Jurkat cell after etoposide treatment. These results demonstrated that RAD51 may be of great value to as a novel target for the clinical treatment of adult T‑cell leukemia‑lymphoma (ATL), and it may improve the survival of leukemia patients.

Recent advances of therapeutic targets based on the molecular signature in breast cancer: genetic mutations and implications for current treatment paradigms

Breast cancer is the most common malignancy in women all over the world. Genetic background of women contributes to her risk of having breast cancer. Certain inherited DNA mutations can dramatically increase the risk of developing certain cancers and are responsible for many of the cancers that run in some families. Regarding the widespread multigene panels, whole exome sequencing is capable of providing the evaluation of genetic function mutations for development novel strategy in clinical trials. Targeting the mutant proteins involved in breast cancer can be an effective therapeutic approach for developing novel drugs. This systematic review discusses gene mutations linked to breast cancer, focusing on signaling pathways that are being targeted with investigational therapeutic strategies, where clinical trials could be potentially initiated in the future are being highlighted.

Studies of lncRNAs in DNA double strand break repair: what is new?

The ‘junk DNA’ that has haunted human genetics for a long time now turns out to hold enormous hidden treasures. As species had their genomes and transcriptomes sequenced, there are an overwhelming number of lncRNA transcripts being reported, however, less than 100 of them have been functionally characterized. DNA damage is recognized and quickly repaired by the cell, with increased expression of numerous genes involved in DNA repair. Most of the time the studies have focused only on proteins involved in these signaling pathways. However, recent studies have implied that lncRNAs can be broadly induced by DNA damage and regulate DNA repair processes by various mechanisms. In this paper, we focus on recent advances in the identification and functional characterization of novel lncRNAs participating in DNA double strand break repair.

Nuclear phosphoinositide regulation of chromatin

Phospholipid signaling has clear connections to a wide array of cellular processes, particularly in gene expression and in controlling the chromatin biology of cells. However, most of the work elucidating how phospholipid signaling pathways contribute to cellular physiology have studied cytoplasmic membranes, while relatively little attention has been paid to the role of phospholipid signaling in the nucleus. Recent work from several labs has shown that nuclear phospholipid signaling can have important roles that are specific to this cellular compartment. This review focuses on the nuclear phospholipid functions and the activities of phospholipid signaling enzymes that regulate metazoan chromatin and gene expression. In particular, we highlight the roles that nuclear phosphoinositides play in several nuclear-driven physiological processes, such as differentiation, proliferation, and gene expression. Taken together, the recent discovery of several specifically nuclear phospholipid functions could have dramatic impact on our understanding of the fundamental mechanisms that enable tight control of cellular physiology.

High RAD54B expression: an independent predictor of postoperative distant recurrence in colorectal cancer patients

We recently reported a specific mechanism that RAD54B, an important factor in homologous recombination, promotes genomic instability via the degradation of p53 protein in vitro. However, clinical significance of RAD54Bin colorectal cancer (CRC) remains unclear. Thus we analyzed RAD54B geneexpression in CRC patients. Using the training set (n = 123), the optimal cut-off value for stratification was determined, and validated in another cohort (n = 89). Kaplan-Meier plots showed that distant recurrence free survival was significantly lesser in high RAD54B expression group compared with that of low expression group in both training (P = 0.0013) and validation (P = 0.024) set. Multivariate analysis using Cox proportional-hazards model showed that high RAD54B expression was an independent predictor in both training (hazard ratio, 4.31; 95% CI, 1.53-13.1; P = 0.0060) and validation (hazard ratio, 3.63; 95% CI, 1.23-10.7; P = 0.021) set. In addition, a negative significant correlation between RAD54B and CDKN1A, a target gene of p53, was partially confirmed, suggesting that RAD54B functions via the degradation of p53 protein even in clinical samples. This study first demonstrated RAD54B expression has potential to serve as a novel prognostic biomarker, particularly for distant recurrence in CRC patients.

HDAC Inhibition Induces MicroRNA-182, which Targets RAD51 and Impairs HR Repair to Sensitize Cells to Sapacitabine in Acute Myelogenous Leukemia

PURPOSE

The double-strand breaks elicited by sapacitabine, a clinically active nucleoside analogue prodrug, are repaired by RAD51 and the homologous recombination repair (HR) pathway, which could potentially limit its toxicity. We investigated the mechanism by which histone deacetylase (HDAC) inhibitors targeted RAD51 and HR to sensitize acute myelogenous leukemia (AML) cells to sapacitabine.

EXPERIMENTAL DESIGN

Chromatin immunoprecipitation identified the role of HDACs in silencing miR-182 in AML. Immunoblotting, gene expression, overexpression, or inhibition of miR-182 and luciferase assays established that miR-182 directly targeted RAD51. HR reporter assays, apoptotic assays, and colony-forming assays established that the miR-182, as well as the HDAC inhibition-mediated decreases in RAD51 inhibited HR repair and sensitized cells to sapacitabine.

RESULTS

The gene repressors, HDAC1 and HDAC2, became recruited to the promoter of miR-182 to silence its expression in AML. HDAC inhibition induced miR-182 in AML cell lines and primary AML blasts. miR-182 targeted RAD51 protein both in luciferase assays and in AML cells. Overexpression of miR-182, as well as HDAC inhibition-mediated induction of miR-182 were linked to time- and dose-dependent decreases in the levels of RAD51, an inhibition of HR, increased levels of residual damage, and decreased survival after exposure to double-strand damage-inducing agents.

CONCLUSIONS

Our findings define the mechanism by which HDAC inhibition induces miR-182 to target RAD51 and highlights a novel pharmacologic strategy that compromises the ability of AML cells to conduct HR, thereby sensitizing AML cells to DNA-damaging agents that activate HR as a repair and potential resistance mechanism. Clin Cancer Res; 22(14); 3537-49. ©2016 AACR.

Identification of RECQ1-regulated transcriptome uncovers a role of RECQ1 in regulation of cancer cell migration and invasion

The RECQ protein family of helicases has critical roles in protecting and stabilizing the genome. Three of the 5 known members of the human RecQ family are genetically linked with cancer susceptibility syndromes, but the association of the most abundant human RecQ homolog, RECQ1, with cellular transformation is yet unclear. RECQ1 is overexpressed in a variety of human cancers, indicating oncogenic functions. Here, we assessed genome-wide changes in gene expression upon knockdown of RECQ1 in HeLa and MDA-MB-231 cells. Pathway analysis suggested that RECQ1 enhances the expression of multiple genes that play key roles in cell migration, invasion, and metastasis, including EZR, ITGA2, ITGA3, ITGB4, SMAD3, and TGFBR2. Consistent with these results, silencing RECQ1 significantly reduced cell migration and invasion. In comparison to genome-wide annotated promoter regions, the promoters of genes downregulated upon RECQ1 silencing were significantly enriched for a potential G4 DNA forming sequence motif. Chromatin immunoprecipitation assays demonstrated binding of RECQ1 to the G4 motifs in the promoters of select genes downregulated upon RECQ1 silencing. In breast cancer patients, the expression of a subset of RECQ1-activated genes positively correlated with RECQ1 expression. Moreover, high RECQ1 expression was associated with poor prognosis in breast cancer. Collectively, our findings identify a novel function of RECQ1 in gene regulation and indicate that RECQ1 contributes to tumor development and progression, in part, by regulating the expression of key genes that promote cancer cell migration, invasion and metastasis.

An integrated approach to reveal miRNAs' impacts on the functional consequence of copy number alterations in cancer

Copy number alteration (CNA) is known to induce gene expression changes mainly through dosage effect, and therefore affect the initiation and progression of tumor. However, tumor samples exhibit heterogeneity in gene dosage sensitivity due to the complicated mechanisms of transcriptional regulation. Currently, no high-throughput method has been available for identifying the regulatory factors affecting the functional consequences of CNA, and determining their effects on cancer. In view of the important regulatory role of miRNA, we investigated the influence of miRNAs on the dosage sensitivities of genes within the CNA regions. By integrating copy number, mRNA expression, miRNA expression profiles of three kinds of cancer, we observed a tendency for high dosage-sensitivity genes to be more targeted by miRNAs in cancer, and identified the miRNAs regulating the dosage sensitivity of amplified/deleted target genes. The results show that miRNAs can modulate oncogenic biological functions by regulating the genes within the CNA regions, and thus play a role as a trigger or balancer in cancer, affecting cancer processes, even survival. This work provided a framework for analyzing the regulation of dosage effect, which will shed a light on understanding the oncogenic and tumor suppressive mechanisms of CNA. Besides, new cancer-related miRNAs were identified.

Regulation of DNA Damage Response by Estrogen Receptor β-Mediated Inhibition of Breast Cancer Associated Gene 2

Accumulating evidence suggests that ubiquitin E3 ligases are involved in cancer development as their mutations correlate with genomic instability and genetic susceptibility to cancer. Despite significant findings of cancer-driving mutations in the BRCA1 gene, estrogen receptor (ER)-positive breast cancers progress upon treatment with DNA damaging-cytotoxic therapies. In order to understand the underlying mechanism by which ER-positive breast cancer cells develop resistance to DNA damaging agents, we employed an estrogen receptor agonist, Erb-041, to increase the activity of ERβ and negatively regulate the expression and function of the estrogen receptor α (ERα) in MCF-7 breast cancer cells. Upon Erb-041-mediated ERα down-regulation, the transcription of an ERα downstream effector, BCA2 (Breast Cancer Associated gene 2), correspondingly decreased. The ubiquitination of chromatin-bound BCA2 was induced by ultraviolet C (UVC) irradiation but suppressed by Erb-041 pretreatment, resulting in a blunted DNA damage response. Upon BCA2 silencing, DNA double-stranded breaks increased with Rad51 up-regulation and ataxia telangiectasia mutated (ATM) activation. Mechanistically, UV-induced BCA2 ubiquitination and chromatin binding were found to promote DNA damage response and repair via the interaction of BCA2 with ATM, γH2AX and Rad51. Taken together, this study suggests that Erb-041 potentiates BCA2 dissociation from chromatin and co-localization with Rad51, resulting in inhibition of homologous recombination repair.

MicroRNAs Used in Combination with Anti-Cancer Treatments Can Enhance Therapy Efficacy

MicroRNAs (miRNAs), a recently discovered class of small non-coding RNAs, constitute a promising approach to anti-cancer treatments when they are used in combination with other agents. MiRNAs are evolutionarily conserved non-coding RNAs that negatively regulate gene expression by binding to the complementary sequence in the 3'-untranslated region (UTR) of target genes. MiRNAs typically suppress gene expression by direct association with target transcripts, thus decreasing the expression levels of target proteins. The delivery to cells of synthetic miRNAs that mimic endogenous miRNA targeting genes involved in the DNA-Damage Response (DDR) can perturb the process, making cells more sensitive to chemotherapy or radiotherapy. This review examines how cells respond to combined therapy and it provides insights into the role of miRNAs in targeting the DDR repair pathway when they are used in combination with chemical compounds or ionizing radiation to enhance cellular sensitivity to treatments.

An appraisal of RECQ1 expression in cancer progression

RECQ1 is the most abundant member of the human RecQ family of DNA helicases genetically linked with cancer predisposition syndromes and well known for their functions in genome stability maintenance through DNA repair. Despite being the first discovered RecQ homolog in humans, biological functions of RECQ1 have remained largely underappreciated and its relevance to cellular transformation is yet unclear. RECQ1 is overexpressed and amplified in many clinical cancer samples. In silico evaluation of RECQ1 mRNA expression across the NCI-60 cancer cell lines predicts an association of RECQ1 with cancer cell migration, invasion, and metastasis. Consistent with this, latest work implicates RECQ1 in regulation of gene expression, especially of those associated with cancer progression. Functionally, silencing RECQ1 expression significantly reduces cell proliferation, migration, and invasion. Collectively, these results propose that discerning the role of RECQ1 in conferring proliferative and invasive phenotype to cancer cells could be useful in developing therapeutic strategies to block primary tumor progression and metastasis.

Targeting homologous recombination, new pre-clinical and clinical therapeutic combinations inhibiting RAD51

The DNA damage response (DDR) is essential for maintaining genomic stability and cell survival. However, when tumour cells with deficiencies in HR are faced with radio- and chemotherapies they are forced to rely on error-prone, alternative repair pathways or aberrant HR for survival; threatening genome integrity and driving further mutation. Accurate therapeutic targeting of the key drivers of DNA repair can circumvent survival pathways and avoid aggressive therapy resistant mutants. Several studies have identified that stabilization of the cancer genome in HR deficient cells can be achieved by overexpression of the recombinase RAD51. Radio- and chemotherapeutic resistance is associated with overactive HR repair mechanisms. However no clinical trials have directly targeted RAD51, despite RAD51 displaying synergy in several drug screens against multiple cancer types. Currently synthetic lethality targeting the DDR pathways and HR deficiency has had clinical success with BRCA1 functional loss and PARP inhibition. In this review we suggest that clinical outcomes could be improved by additionally targeting RAD51. We examine the latest developments in directly and indirectly targeting RAD51. We scrutinize the potential treatment efficacy and future clinical applications of RAD51 inhibitors as single agents and in combination with other therapies and consider the best therapeutic options.

A Small-Molecule Inhibitor of RAD51 Reduces Homologous Recombination and Sensitizes Multiple Myeloma Cells to Doxorubicin

We previously reported high expression of RAD51 and increased homologous recombination (HR) rates in multiple myeloma (MM) cells, and showed that genomic instability and disease progression are commensurate with HR levels. Moreover, high RAD51 expression in vivo is associated with chemoresistance and poor patient survival. Doxorubicin (DOX) is one of the most widely used drug treatments in MM chemotherapy. DOX is cytotoxic because it induces DNA double-strand breaks, which can be repaired by RAD51-mediated HR; activation of this pathway thus contributes to resistance. To investigate the role of RAD51 in MM drug resistance, we assessed the ability of B02, a small-molecule inhibitor of RAD51, to enhance DOX sensitivity of MM cells. Combining low-toxicity doses of DOX and B02 resulted in significant synthetic lethality, observed as increased apoptosis and reduced viability compared to either agent alone, or to the product of their individual effects. In contrast, the combination did not produce significant synergy against normal human CD19⁺ B cells from peripheral blood. DOX induced RAD51 at both mRNA and protein levels, while arresting cells in S and G2. DOX treatment also increased the number of RAD51 foci, a marker of HR repair, so that the fraction of cells with ≥5 foci rose fourfold, whereas γH2AX foci rose far less, implying that most new breaks are repaired. When B02 treatment preceded DOX exposure, the induction of RAD51 foci was severely blunted, whereas, γH2AX foci rose significantly relative to basal levels or either agent alone. In MM cells carrying a chromosomally integrated reporter of HR repair, DOX increased HR events while B02 inhibition of RAD51 blocked the HR response. These studies demonstrate the crucial role of RAD51 in protecting MM cells from genotoxic agents such as DOX, and suggest that specific inhibition of RAD51 may be an effective means to block DNA repair in MM cells and thus to enhance the efficacy of chemotherapy.

Evaluation of microRNA-10b prognostic significance in a prospective cohort of breast cancer patients

Background

MicroRNA-10b (miR-10b) has a prominent role in regulating tumor invasion and metastasis by targeting the HOXD10 transcriptional repressor and has been found up-regulated in several tumor types.

Methods

We evaluated the expression of miR-10b in paired tumor and normal specimens obtained from a prospective cohort of breast cancer patients with at least 36 months follow-up enrolled according to the REMARK guidelines (n = 150). RNA quality was measured and only samples with RNA Integrity Number (RIN) ≥7.0 were analyzed.

Results

The relative expression of miR-10b in tumor as compared to its normal counterpart (RER) was determined by RT-qPCR. miR-10b RERs were higher in the subgroup of patients with synchronous metastases (n = 11, Median 0.25; IQR 0.11-1.02) as compared with patients without metastases (n = 90, Median 0.09; IQR 0.04-0.29) (p = 0.028). In the subgroup of patients without synchronous metastases (n = 90), higher miR-10b RERs were associated with increased risk of disease progression and death in both univariable (HR 1.16, p = 0.021 and HR 1.20, p = 0.015 respectively for 0.10 unitary increase of miR-10b RERs levels) and multivariable (HR1.30, p < 0.001, and HR 1.31, p = 0.003 respectively for 0.10 unitary increase of miR-10b RERs levels) Cox regression models. The addition of miR-10b RERs to the Nottingham Prognostic Index (NPI) provided an improvement in discrimination power and risk reclassification abilities for the clinical outcomes at 36 months. Survival C-indices significantly increased from 0.849 to 0.889 (p = 0.009) for OS and from 0.735 to 0.767 (p = 0.050) for DFS.

Conclusions

Our results provide evidences that the addition of miR-10b RERs to the prognostic factors used in clinical routine could improve the prediction abilities for both overall mortality and disease progression in breast cancer patients.

Rad51 supports triple negative breast cancer metastasis

In contrast to extensive studies on familial breast cancer, it is currently unclear whether defects in DNA double strand break (DSB) repair genes play a role in sporadic breast cancer development and progression. We performed analysis of immunohistochemistry in an independent cohort of 235 were sporadic breast tumours. This analysis suggested that RAD51 expression is increased during breast cancer progression and metastasis and an oncogenic role for RAD51 when deregulated. Subsequent knockdown of RAD51 repressed cancer cell migration in vitro and reduced primary tumor growth in a syngeneic mouse model in vivo. Loss of RAD51 also inhibited associated metastasis not only in syngeneic mice but human xenografts and changed the metastatic gene expression profile of cancer cells, consistent with inhibition of distant metastasis. This demonstrates for the first time a new function of RAD51 that may underlie the proclivity of patients with RAD51 overexpression to develop distant metastasis. RAD51 is a potential biomarker and attractive drug target for metastatic triple negative breast cancer, with the capability to extend the survival of patients, which is less than 6 months.

Regulation of Rad51 promoter

The DNA double-strand break repair and homologous recombination protein Rad51 is overexpressed in the majority of human cancers. This correlates with therapy resistance and decreased patient survival. We previously showed that constructs containing Rad51 promoter fused to a reporter gene are, on average, 850-fold more active in cancer cells than in normal cells. It is not well understood what factors and sequences regulate the Rad51 promoter and cause its high activity in cancerous cells. Here we characterized regulatory regions and examined genetic requirements for oncogenic stimulation of the Rad51 promoter. We identified specific regions responsible for up- and downregulation of the Rad51 promoter in cancerous cells. Furthermore, we show that Rad51 expression is positively regulated by EGR1 transcription factor. We then modeled the malignant transformation process by expressing a set of oncoproteins in normal human fibroblasts. Expression of different combinations of SV40 large T antigen, oncogenic Ras and SV40 small T antigen resulted in step-wise increase in Rad51 promoter activity, with all the 3 oncoproteins together leading to a 47-fold increase in expression. Cumulatively, these results suggest that Rad51 promoter is regulated by multiple factors, and that its expression is gradually activated as cells progress toward malignancy.

Gene expression profiling reveals activation of the FA/BRCA pathway in advanced squamous cervical cancer with intrinsic resistance and therapy failure

Background

Advanced squamous cervical cancer, one of the most commonly diagnosed cancers in women, still remains a major problem in oncology due to treatment failure and distant metastasis. Antitumor therapy failure is due to both intrinsic and acquired resistance; intrinsic resistance is often decisive for treatment response. In this study, we investigated the specific pathways and molecules responsible for baseline therapy failure in locally advanced squamous cervical cancer.

Methods

Twenty-one patients with locally advanced squamous cell carcinoma were enrolled in this study. Primary biopsies harvested prior to therapy were analyzed for whole human gene expression (Agilent) based on the patient’s 6 months clinical response. Ingenuity Pathway Analysis was used to investigate the altered molecular function and canonical pathways between the responding and non-responding patients. The microarray results were validated by qRT-PCR and immunohistochemistry. An additional set of 24 formalin-fixed paraffin-embedded cervical cancer samples was used for independent validation of the proteins of interest.

Results

A 2859-gene signature was identified to distinguish between responder and non-responder patients. ‘DNA Replication, Recombination and Repair’ represented one of the most important mechanisms activated in non-responsive cervical tumors, and the ‘Role of BRCA1 in DNA Damage Response’ was predicted to be the most significantly altered canonical pathway involved in intrinsic resistance (p = 1.86E-04, ratio = 0.262). Immunohistological staining confirmed increased expression of BRCA1, BRIP1, FANCD2 and RAD51 in non-responsive compared with responsive advanced squamous cervical cancer, both in the initial set of 21 cervical cancer samples and the second set of 24 samples.

Conclusions

Our findings suggest that FA/BRCA pathway plays an important role in treatment failure in advanced cervical cancer. The assessment of FANCD2, RAD51, BRCA1 and BRIP1 nuclear proteins could provide important information about the patients at risk for treatment failure.

Protective role of miR-155 in breast cancer through RAD51 targeting impairs homologous recombination after irradiation

Cell survival after DNA damage relies on DNA repair, the abrogation of which causes genomic instability and development of cancer. However, defective DNA repair in cancer cells can be exploited for cancer therapy using DNA-damaging agents. DNA double-strand breaks are the major lethal lesions induced by ionizing radiation (IR) and can be efficiently repaired by DNA homologous recombination, a system that requires numerous factors including the recombinase RAD51 (RAD51). Therapies combined with adjuvant radiotherapy have been demonstrated to improve the survival of triple-negative breast cancer patients; however, such therapy is challenged by the emergence of resistance in tumor cells. It is, therefore, essential to develop novel therapeutic strategies to overcome radioresistance and improve radiosensitivity. In this study we show that overexpression of microRNA 155 (miR-155) in human breast cancer cells reduces the levels of RAD51 and affects the cellular response to IR. miR-155 directly targets the 3'-untranslated region of RAD51. Overexpression of miR-155 decreased the efficiency of homologous recombination repair and enhanced sensitivity to IR in vitro and in vivo. High miR-155 levels were associated with lower RAD51 expression and with better overall survival of patients in a large series of triple-negative breast cancers. Taken together, our findings indicate that miR-155 regulates DNA repair activity and sensitivity to IR by repressing RAD51 in breast cancer. Testing for expression levels of miR-155 may be useful in the identification of breast cancer patients who will benefit from an IR-based therapeutic approach.

Targeting homologous recombination-mediated DNA repair in cancer

INTRODUCTION

DNA is the target of many traditional non-specific chemotherapeutic drugs. New drugs or therapeutic approaches with a more rational and targeted component are mandatory to improve the success of cancer therapy. The homologous recombination (HR) pathway is an attractive target for the development of inhibitors because cancer cells rely heavily on HR for repair of DNA double-strand breaks resulting from chemotherapeutic treatments. Additionally, the discovery that poly(ADP)ribose polymerase-1 inhibitors selectively kill cells with genetic defects in HR has spurned an even greater interest in inhibitors of HR.

AREAS COVERED

HR drives the repair of broken DNA via numerous protein-mediated sequential DNA manipulations. Due to extensive number of steps and proteins involved, the HR pathway provides a rich pool of potential drug targets. This review discusses the latest developments concerning the strategies being explored to inhibit HR. Particular attention is given to the identification of small molecule inhibitors of key HR proteins, including the BRCA proteins and RAD51.

EXPERT OPINION

Current HR inhibitors are providing the basis for pharmaceutical development of more potent and specific inhibitors to be applied in mono- or combinatorial therapy regimes, while novel targets will be uncovered by experiments aimed to gain a deeper mechanistic understanding of HR and its subpathways.

Slug/β-catenin-dependent proinflammatory phenotype in hypoxic breast cancer stem cells

Cancer stem cell survival relies on the activation of inflammatory pathways, which is speculatively triggered by cell autonomous mechanisms or by microenvironmental stimuli. Here, we observed that hypoxic bone marrow stroma-derived transforming growth factor-β 1 promotes the growth of human breast cancer stem cells as mammospheres. The ensuing Slug-dependent serine 139 phosphorylation of the DNA damage sensor H2AX in breast cancer stem cells induces tumor necrosis factor-α and IL-8 mRNAs, whose stability is enhanced by cytoplasmic β-catenin. β-Catenin also up-regulates and binds miR-221, reducing the stability of the miR-221 targets Rad51 and ERα mRNAs. Our data show that the Slug/β-catenin-dependent activation of DNA damage signaling triggered by the hypoxic microenvironment sustains the proinflammatory phenotype of breast cancer stem cells.

XRCC3 and RAD51 expression are associated with clinical factors in breast cancer

AIMS

XRCC3 and RAD51 are two important members in homologous recombination repair pathway. This study was performed to detect the expressions of these two molecules in breast cancer and explore their correlations with clinicopathological factors.

METHODS AND RESULTS

Immunohistochemistry was used to detect protein expressions of XRCC3 and RAD51 in 248 cases of breast cancer tissue and 78 cases of adjacent non-cancerous tissue. Data showed that expressions for both XRCC3 and RAD51 were significantly increased in breast cancer. High XRCC3 expression was associated with large tumor size and positive PR and HER2 status, while high RAD51 expression was associated with axillary lymph node metastasis and positive PR and HER2 status. The result of multivariate analysis demonstrated that HER2, PR and RAD51 were significantly association with XRCC3. And besides XRCC3, axillary lymph node metastasis and PR were significantly correlated with RAD51.

CONCLUSIONS

XRCC3 and RAD51 were significantly associated with clinicopathological factors and they might play important roles in the development and progress of breast cancer.

BLM and RAD51 genes polymorphism and susceptibility to breast cancer

DNA repair by homologous recombination is one of the main processes of DNA double strand breaks repair. In the present work we performed a case-control study (304 cases and 319 controls) to check an association between the genotypes of the c.-61 G>T and the g.38922 C>G polymorphisms of the RAD51 gene and the g.96267 A>C and the g.85394 A>G polymorphisms of the BLM gene and breast cancer occurrence. Genotypes were determined in DNA from peripheral blood by PCR-RLFP and by PCR-CTPP. We observed an association between breast cancer occurrence and the T/G genotype (OR 4.41) of the c.-61 G>T-RAD51 polymorphism, the A/A genotype (OR 1.69) of the g.85394 A>G-BLM polymorphism and the A/A genotype (OR 2.49) of the g.96267 A>C-BLM polymorphism. Moreover, we demonstrated a correlation between intra- and intergenes genotypes combinations and breast cancer occurrence. We found a correlation between progesterone receptor expression and the T/G genotype (OR 0.57) of the c.-61 G>T- RAD51 polymorphism. We also found a correlation between the T/G genotype (OR 1.86) and the T/T genotype (OR 0.56) of the c.-61 G>T- RAD51 polymorphism and the lymph node metastasis. We showed an association between the A/A genotype (OR 2.45) and the A/C genotype (OR 0.41) of the g.96267 A>C-BLM polymorphism and G3 grade of tumor. Our results suggest that the variability of the RAD51 and BLM genes may play a role in breast cancer occurrence. This role may be underlined by a common interaction between these genes.

HSF4 is involved in DNA damage repair through regulation of Rad51

Heat shock factor protein 4 (HSF4) is expressed exclusively in the ocular lens and plays a critical role in the lens formation and differentiation. Mutations in the HSF4 gene lead to congenital and senile cataract. However, the molecular mechanisms causing this disease have not been well characterized. DNA damage in lens is a crucial risk factor in senile cataract formation, and its timely repair is essential for maintaining the lens' transparency. Our study firstly found evidence that HSF4 contributes to the repair of DNA strand breaks. Yet, this does not occur with cataract causative mutations in HSF4. We verify that DNA damage repair is mediated by the binding of HSF4 to a heat shock element in the Rad51 promoter, a gene which assists in the homologous recombination (HR) repair of DNA strand breaks. HSF4 up-regulates Rad51 expression while mutations in HSF4 fail, and DNA does not get repaired. Camptothecin, which interrupts the regulation of Rad51 by HSF4, also affects DNA damage repair. Additionally, with HSF4 knockdown in the lens of Zebrafish, DNA damage was observed and the protein level of Rad51 was significantly lower. Our study presents the first evidence demonstrating that HSF4 plays a role in DNA damage repair and may contribute a better understanding of congenital cataract formation.

Shortening of 3'UTRs correlates with poor prognosis in breast and lung cancer

A major part of the post-transcriptional regulation of gene expression is affected by trans-acting elements, such as microRNAs, binding the 3' untraslated region (UTR) of their target mRNAs. Proliferating cells partly escape this type of negative regulation by expressing shorter 3' UTRs, depleted of microRNA binding sites, compared to non-proliferating cells. Using large-scale gene expression datasets, we show that a similar phenomenon takes place in breast and lung cancer: tumors expressing shorter 3' UTRs tend to be more aggressive and to result in shorter patient survival. Moreover, we show that a gene expression signature based only on the expression ratio of alternative 3' UTRs is a strong predictor of survival in both tumors. Genes undergoing 3'UTR shortening in aggressive tumors of the two tissues significantly overlap, and several of them are known to be involved in tumor progression. However the pattern of 3' UTR shortening in aggressive tumors in vivo is clearly distinct from analogous patterns involved in proliferation and transformation.

Adenoviral vector driven by a minimal Rad51 promoter is selective for p53-deficient tumor cells

BACKGROUND

The full length Rad51 promoter is highly active in cancer cells but not in normal cells. We therefore set out to assess whether we could confer this tumor-selectivity to an adenovirus vector.

METHODOLOGY/PRINCIPAL FINDINGS

Expression of an adenovirally-vectored luciferase reporter gene from the Rad51 promoter was up to 50 fold higher in cancer cells than in normal cells. Further evaluations of a panel of truncated promoter mutants identified a 447 bp minimal core promoter element that retained the full tumor selectivity and transcriptional activity of the original promoter, in the context of an adenovirus vector. This core Rad51 promoter was highly active in cancer cells that lack functional p53, but less active in normal cells and in cancer cell lines with intact p53 function. Exogenous expression of p53 in a p53 null cell line strongly suppressed activity of the Rad51 core promoter, underscoring the selectivity of this promoter for p53-deficient cells. Follow-up experiments showed that the p53-dependent suppression of the Rad51 core promoter was mediated via an indirect, p300 coactivator dependent mechanism. Finally, transduction of target cells with an adenovirus vector encoding the thymidine kinase gene under transcriptional control of the Rad51 core promoter resulted in efficient killing of p53 defective cancer cells, but not of normal cells, upon addition of ganciclovir.

CONCLUSIONS/SIGNIFICANCE

Overall, these experiments demonstrated that a small core domain of the Rad51 promoter can be used to target selective transgene expression from adenoviral vectors to tumor cells lacking functional p53.

Phenotype-genotype correlation in familial breast cancer

Familial breast cancer accounts for a small but significant proportion of breast cancer cases worldwide. Identification of the candidate genes is always challenging specifically in patients with little or no family history. Therefore, a multidisciplinary team is required for the proper detection and further management of these patients. Pathologists have played a pivotal role in the cataloguing of genotypic-phenotypic correlations in families with hereditary cancer syndromes. These efforts have led to the identification of histological and phenotypic characteristics that can help predict the presence or absence of germline mutations of specific cancer predisposition genes. However, the panoply of cancer phenotypes associated with mutations of genes other than in BRCA1 is yet to be fully characterised; in fact, many cancer syndromes, germline mutations and gene sequence variants are under investigation for their possible morphological associations. Here we review the current understanding of phenotype-genotype correlation in familial breast cancer.