Targeting DNA repair in breast cancer: A clinical and translational update

KHSRP has oncogenic functions and regulates the expression and alternative splicing of DNA repair genes in breast cancer MDA-MB-231 cells

Breast cancer has become the most common type of cancers worldwide. Its high prevalence and malignant features are associated with various environmental factors and molecules. The KH-type splicing regulatory protein (KHSRP) participates in the development of breast cancer, while the underlying mechanisms are largely unknown. In this study, we silenced KHSRP expression in MDA-MB-231 cells by small interfering RNA (siKHSRP), and then assessed its effects on cellular features. Finally, we performed whole transcriptome sequencing (RNA-seq) experiments to explore the downstream targets of KHSRP, and validated their changed pattern using quantitative polymerase chain reaction. We found KHSRP showed higher expression level and was associated with worse prognosis in breast cancer patients. In siKHSRP samples, the proliferation, invasion, and migration abilities were significantly repressed compared with negative control (NC) samples, while the apoptosis level was increased. By investigating the RNA-seq data, we found KHSRP globally regulates the expression and alternative splicing profiles of MDA-MB-231 cells by identifying 1632 differentially expressed genes (DEGs) and 1630 HKSRP-regulated AS events (RASEs). Functional enriched analysis of DEGs demonstrated that cilium assembly and movement and extracellular matrix organization pathways were specifically enriched in up DEGs, consistent with the repressed migration and invasion abilities in siKHSRP cells. Interestingly, the cell cycle and DNA damage and repair associated pathways were enriched in both down DEGs and RASE genes, suggesting that KHSRP may modulate cell proliferation by regulating genes in these pathways. Finally, we validated the changed expression and AS patterns of genes in cell cycle and DNA damage/repair pathways. Expression levels of BIRC5, CCNA2, CDK1, FEN1, FOXM1, PTTG1, and UHRF1 were downregulated in siKHSRP samples. The AS patterns of PARK7, ERCC1, CENPX, and UBE2A were also dysregulated in siKHSRP samples and confirmed PCR experiments. In summary, our study comprehensively explored the downstream targets and their functions of KHSRP in breast cancer cells, highlighting the molecular mechanisms of KHSRP on the oncogenic features of breast cancer. The identified molecular targets could be served as potential therapeutic targets for breast cancer in future.

Ubiquitin-specific peptidase 11 promotes development of keloid derived fibroblasts by de-ubiquitinating TGF-β receptorII

BACKGROUND

Keloid scars occur as a result of abnormal wound healing caused by trauma or inflammation of the skin. The progression of keloids is dependent on genetic and environmental influences. The incidence is more prevalent in people with darker skin tones (African, Asian and Hispanic origin). Studies have demonstrated that transforming growth factor (TGF) β/Smad signalling has an essential function in keloid as well as that USP11 could modulate the activation of TGFβ/Smad signalling and impact the progression of the fibrotic disease. Nonetheless, the potential mechanisms of USP11 in keloid were still unclear. The authors postulated that USP11 up-regulates and augments the ability of proliferation, invasion, migration and collagen deposition of keloid-derived fibroblasts (KFBs) through deubiquitinating TGF-β receptor II (TβRII).

METHODS

Fibroblast cells were isolated from keloid scars in vitro. Lentivirus infection was utilized to knockdown and over-express the USP11 in KFBs. Influence of USP11 on proliferation, invasion and migration of KFBs, and expression level of TβRII, Smad2, Smad3, α-SMA, collagen1 and collagen3 were assayed by CCK8, scratching, transwell, Western blot and real-time quantitative polymerase chain reaction. The interactions between USP11 and TβRII were examined using ubiquitination assays and co-immunoprecipitation. To further confirm the role of USP11 in keloid growth, we performed animal experiments.

RESULTS

Results show that down-regulated USP11 markedly suppressed the ability of proliferation, invasion and migration of keloid derived-fibroblasts in vitro and reduce the expression of TβRII, Smad2, Smad3, αSMA, collagen1 and collagen3. In addition, over-expression of USP11 demonstrated the contrary tendency. Ubiquitination experiments and co-immunoprecipitation demonstrated that USP11 was interacting with TβRII and deubiquitinated TβRII. Interferences with USP11 inhibited growth of keloid in vivo. Additionally, we have verified that knockdown of USP11 has no significant effect on normal skin fibroblasts.

CONCLUSION

USP11 elevates the ability of proliferation, collagen deposition, invasion and migration of keloid-derived fibroblasts by deubiquitinating TβRII.

PRIMA-1 synergizes olaparib-induced cell death in p53 mutant triple negative human breast cancer cell line via restoring p53 function, arresting cell cycle, and inducing apoptosis

This study concerned with assessing the effect of restoring p53 using PRIMA-1 on the anti-cancer activity of olaparib against TP53-mutant triple negative breast cancer (TNBC) cells and exploring the optimum synergistic concentrations and the underlying mechanism. Human BC cell lines, MDA-MB-231 with mutated TP53 gene, and MCF-7 with wild-type TP53 gene were treated with olaparib and/or PRIMA-1. The IC50 value for olaparib was significantly decreased by PRIMA-1 in MDA-MB-231 cells compared to MCF-7 cells. Contrary to MCF-7 cells, co-treatment with olaparib and PRIMA-1 had a synergistic anti-proliferative effect in MDA-MB-231 at all tested concentrations with the best synergistic combination at 45 and 8.5 µM, respectively, and furthermore PRIMA-1 enhanced olaparib-induced apoptosis. This synergistic apoptotic effect was associated with a significant boost in mRNA expression of TP53 gene, cell cycle arrest at G2/M phase, modulation of BRCA-1, BAX and Bcl2 proteins expressions, and induction of active caspase-3. These results present a clue for the utility of combined olaparib and PRIMA-1 in treatment of TP53-mutant TNBC invitro. PRIMA-1 triggers olaparib-induced MDA-MB-231 cell death in a synergistic manner via restoring TP53, decreasing BRCA-1 expression, cell cycle arrest, and enhancement of apoptosis via p53/BAX/Bcl2/caspase 3 pathway.

Enhancing the anti-tumor response by combining DNA damage repair inhibitors in the treatment of solid tumors

The anti-cancer efficacy of anti-malignancy therapies is related to DNA damage. However, DNA damage-response mechanisms can repair DNA damage, failing anti-tumor therapy. The resistance to chemotherapy, radiotherapy, and immunotherapy remains a clinical challenge. Thus, new strategies to overcome these therapeutic resistance mechanisms are needed. DNA damage repair inhibitors (DDRis) continue to be investigated, with polyadenosine diphosphate ribose polymerase inhibitors being the most studied inhibitors. Evidence of their clinical benefits and therapeutic potential in preclinical studies is growing. In addition to their potential as a monotherapy, DDRis may play an important synergistic role with other anti-cancer therapies or in reversing acquired treatment resistance. Here we review the impact of DDRis on solid tumors and the potential value of combinations of different treatment modalities with DDRis for solid tumors.

Enhanced Antitumoral Activity of Encapsulated BET Inhibitors When Combined with PARP Inhibitors for the Treatment of Triple-Negative Breast and Ovarian Cancers

Simple Summary

Poly (adenosine diphosphate ribose) polymerase inhibitors (PARPis) have demonstrated antitumoral activity in several cancers harbouring germline and somatic BRCA1/2 mutations. The widespread use of these agents in clinical practice is restricted by the development of acquired resistance due to the presence of compensatory pathways. A strategy to deal with this is the use of combination therapies with drugs that act synergistically against the tumour. BETis can completely disrupt the HR pathway by repressing the expression of BRCA1 and could be aimed at generation combination regimes to overcome PARPi resistance and enhance PARPi efficacy. However, this strategy is hampered by the poor pharmacokinetic profile and short half-life of BETis. In this work and as a proof of concept, we discuss the potential preclinical benefit provided by the combination of the PARPi olaparib and the BET inhibitor JQ1 encapsulated into nanoparticles for the treatment of BRCAness tumours.

Abstract

BRCA1/2 protein-deficient or mutated cancers comprise a group of aggressive malignancies. Although PARPis have shown considerably efficacy in their treatment, the widespread use of these agents in clinical practice is restricted by various factors, including the development of acquired resistance due to the presence of compensatory pathways. BETis can completely disrupt the HR pathway by repressing the expression of BRCA1 and could be aimed at generation combination regimes to overcome PARPi resistance and enhance PARPi efficacy. Due to the poor pharmacokinetic profile and short half-life, the first-in-class BETi JQ1 was loaded into newly developed nanocarrier formulations to improve the effectivity of olaparib for the treatment of BRCAness cancers. First, polylactide polymeric nanoparticles were generated by double emulsion. Moreover, liposomes were prepared by ethanol injection and evaporation solvent method. JQ1-loaded drug delivery systems display optimal hydrodynamic radii between 60 and 120 nm, with a very low polydispersity index (PdI), and encapsulation efficiencies of 92 and 16% for lipid- and polymeric-based formulations, respectively. Formulations show high stability and sustained release. We confirmed that all assayed JQ1 formulations improved antiproliferative activity compared to the free JQ1 in models of ovarian and breast cancers. In addition, synergistic interaction between JQ1 and JQ1-loaded nanocarriers and olaparib evidenced the ability of encapsulated JQ1 to enhance antitumoral activity of PARPis.

Genomic Correlates of DNA Damage in Breast Cancer Subtypes

Simple Summary

Breast cancer (BC) is the most common invasive tumor in women and the second leading cause of cancer-related death. Therefore, identification of druggable targets to improve current therapies and overcome resistance is a major goal. In this work, we performed an in silico analysis of transcriptomic datasets in breast cancer, and focused on those involved in DNA damage, as were clearly upregulated using gene set enrichment analyses (GSEA), particular the following pathways: ATM/ATR, BARD1 and Fanconi Anemia. BHLHE40, RFWD2, BRIP1, PRKDC, NBN, RNF8, FANCD2, RAD1, BLM, DCLRE1C, UBE2T, CSTF1, MCM7, RFC4, YWHAB, YWHAZ, CDC6, CCNE1, and FANCI genes were amplified/overexpressed in BC, and correlated with detrimental prognosis. Finally, we selected the best transcriptomic signature of genes within this function that associated with clinical outcome to identify functional genomic correlates of outcome.

Abstract

Among the described druggable vulnerabilities, acting on the DNA repair mechanism has gained momentum, with the approval of PARP inhibitors in several indications, including breast cancer. However, beyond the mere presence of BRCA1/BRCA2 mutations, the identification of additional biomarkers that would help to select tumors with an extreme dependence on DNA repair machinery would help to stratify therapeutic decisions. Gene set enrichment analyses (GSEA) using public datasets evaluating expression values between normal breast tissue and breast cancer identified a set of upregulated genes. Genes included in different pathways, such as ATM/ATR, BARD1, and Fanconi Anemia, which are involved in the DNA damage response, were selected and confirmed using molecular alterations data contained at cBioportal. Nineteen genes from these gene sets were identified to be amplified and upregulated in breast cancer but only five of them NBN, PRKDC, RFWD2, UBE2T, and YWHAZ meet criteria in all breast cancer molecular subtypes. Correlation of the selected genes with prognosis (relapse free survival, RFS, and overall survival, OS) was performed using the KM Plotter Online Tool. In last place, we selected the best signature of genes within this process whose upregulation can be indicative of a more aggressive phenotype and linked with worse outcome. In summary, we identify genomic correlates within DNA damage pathway associated with prognosis in breast cancer.

DNA damage response and breast cancer development: Possible therapeutic applications of ATR, ATM, PARP, BRCA1 inhibition

Breast cancer is the most common and significant cancers in females regarding the loss of life quality. Similar to other cancers, one of the etiologic factors in breast cancer is DNA damage. A plethora of molecules are responsible for sensing DNA damage and mediating actions which lead to DNA repair, senescence, cell cycle arrest and if damage is unbearable to apoptosis. In each of these, aberrations leading to unrepaired damage was resulted in uncontrolled proliferation and cancer. Another cellular function is autophagy defined as a process eliminating of unnecessary proteins in stress cases involved in pathogenesis of cancer. Knowing their role in cancer, scholars have tried to develop strategies in order to target DDR and autophagy. Further, the interactions of DDR and autophagy plus their regulatory role on each other have been focused simultaneously. The present review study has aimed to illustrate the importance of DDR and autophagy in breast cancer according to the related studies and uncover the relation between DDR and autophagy and its significance in breast cancer therapy.

LncRNA XIST promotes chemoresistance of breast cancer cells to doxorubicin by sponging miR-200c-3p to upregulate ANLN

The resistance of breast cancer cells to drugs is a major obstacle to effective cancer chemotherapy. Here, we study the function mechanisms of long non-coding RNA XIST in chemoresistance of breast cancer to doxorubicin. We examined the 50% inhibitive concentration of doxorubicin to MDA-MB-231 and MDA-MB-231/ADM cells, showing that the doxorubicin resistance of MDA-MB-231/ADM cells was much higher than MDA-MB-231 cells. The gene or protein expression of XIST and ANLN were also higher in MDA-MB-231/ADM cells than that in MDA-MB-231 cells. Moreover, XIST overexpression promoted cell proliferation and inhibited apoptosis of doxorubicin-treated MDA-MB-231 cells by promoting ANLN expression. XIST silencing inhibited cell proliferation and promoted apoptosis of doxorubicin-treated MDA-MB-231/ADM cells by inhibiting ANLN expression. Luciferase reporter assay showed that XIST functioned as a competing endogenous RNA to repress miR-200c-3p, which controlled its downstream target ANLN. In conclusion, these data reveal that XIST promotes chemoresistance of breast cancer cells to doxorubicin by sponging miR-200c-3p to upregulate ANLN. This work explores the relationship between lncRNA XIST and doxorubicin resistance in breast cancer cells and highlights a novel therapeutic target for the treatment of breast cancer.

Enhance PARPi Application beyond BRCA-Mutant Breast Cancer (BC): Facts Are Facts

Breast cancer (BC) represents one of the three most common neoplasia and the principal worldwide leading cause of death among women [...].

Pharmacological screening and transcriptomic functional analyses identify a synergistic interaction between dasatinib and olaparib in triple-negative breast cancer

Identification of druggable vulnerabilities is a main objective in triple‐negative breast cancer (TNBC), where no curative therapies exist. Gene set enrichment analyses (GSEA) and a pharmacological evaluation using a library of compounds were used to select potential druggable combinations. MTT and studies with semi‐solid media were performed to explore the activity of the combinations. TNBC cell lines (MDAMB‐231, BT549, HS‐578T and HCC3153) and an additional panel of 16 cell lines were used to assess the activity of the two compounds. Flow cytometry experiments and biochemical studies were also performed to explore the mechanism of action. GSEA were performed using several data sets (GSE21422, GSE26910, GSE3744, GSE65194 and GSE42568), and more than 35 compounds against the identified functions were evaluated to discover druggable opportunities. Analyses done with the Chou and Talalay algorithm confirmed the synergy of dasatinib and olaparib. The combination of both agents significantly induced apoptosis in a caspase‐dependent manner and revealed a pleotropic effect on cell cycle: Dasatinib arrested cells in G0/G1 and olaparib in G2/M. Dasatinib inhibited pChk1 and induced DNA damage measured by pH2AX, and olaparib increased pH3. Finally, the effect of the combination was also evaluated in a panel of 18 cell lines representative of the most frequent solid tumours, observing a particularly synergism in ovarian cancer. Breast cancer, triple negative, dasatinib, olaparib, screening.

DNA damage repair functions and targeted treatment in breast cancer

Cell DNA is continuously attacked by endogenous and exogenous agents, which causes DNA damage. During long-term evolution, complex defense systems for DNA damage repair are formed by cells to maintain genome stability. Defects in the DNA damage repair process may lead to various diseases, including tumors. Therefore, DNA damage repair systems have become a new anti-tumor drug target. To date, a number of inhibitors related to DNA damage repair systems have been developed, particularly for tumors with BRCA1 and BRCA2 mutations. Poly (ADP-ribose) polymerase inhibitors developed by synthetic lethality are widely used in individualized tumor therapy. In this review, we briefly introduce the mechanisms underlying DNA damage repair, particularly in breast cancer, and mainly focus on new treatments targeting the DNA damage repair pathway in breast cancer.

Advances and perspectives of PARP inhibitors

DNA damage repair deficiency leads to the increased risk of genome instability and oncogenic transformation. In the meanwhile, this deficiency could be exploited for cancer treatment by inducing excessive genome instability and catastrophic DNA damage. Continuous DNA replication in cancer cells leads to higher demand of DNA repair components. Due to the oncogenic loss of some DNA repair effectors (e.g. BRCA) and incomplete DNA repair repertoire, some cancer cells are addicted to certain DNA repair pathways such as Poly (ADP-ribose) polymerase (PARP)-related single-strand break repair pathway. The interaction between BRCA and PARP is a form of synthetic lethal effect which means the simultaneously functional loss of two genes lead to cell death, while defect in any single gene has a slight effect on cell viability. Based on synthetic lethal theory, Poly (ADP-ribose) polymerase inhibitor (PARPi) was developed aiming to selectively target cancer cells harboring BRCA1/2 mutations. Recently, a growing body of evidence indicated that a broader population of patients could benefit from PARPi therapy far beyond those with germline BRCA1/2 mutated tumors. Numerous biomarkers including homologous recombination deficiency and high level of replication pressure also herald high sensitivity to PARPi treatment. Besides, a series of studies indicated that PARPi-involved combination therapy such as PARPi with additional chemotherapy therapy, immune checkpoint inhibitor, as well as targeted agent had a great advantage in overcoming PARPi resistance and enhancing PARPi efficacy. In this review, we summarized the advances of PARPi in clinical application. Besides, we highlighted multiple promising PARPi-based combination strategies in preclinical and clinical studies.

Discovery of potent 2,4-difluoro-linker poly(ADP-ribose) polymerase 1 inhibitors with enhanced water solubility and in vivo anticancer efficacy

Poly (ADP-ribose) polymerase 1 (PARP1) is overexpressed in a variety of cancers, especially in breast and ovarian cancers; tumor cells that are deficient in breast cancer gene 1/2 (BRCA1/2) are highly sensitive to PARP1 inhibition. In this study, we identified a series of 2,4-difluorophenyl-linker analogs (15-55) derived from olaparib as novel PARP1 inhibitors. Four potent analogs 17, 43, 47, and 50 (IC₅₀=2.2-4.4 nmol/L) effectively inhibited the proliferation of Chinese hamster lung fibroblast V-C8 cells (IC₅₀=3.2-37.6 nmol/L) in vitro, and showed specificity toward BRCA-deficient cells (SI=40-510). The corresponding hydrochloride salts 56 and 57 (based on 43 and 47) were highly water soluble in pH=1.0 buffered salt solutions (1628.2 μg/mL, 2652.5 μg/mL). In a BRCA1-mutated xenograft model, oral administration of compound 56 (30 mg·kg^-1·d^-1, for 21 d) exhibited more prominent tumor growth inhibition (96.6%) compared with the same dose of olaparib (56.3%); in a BRCA2-mutated xenograft model, oral administration of analog 43 (10 mg·kg^-1·d^-1, for 28 d) significantly inhibited tumor growth (69.0%) and had no negative effects on the body weights. Additionally, compound 56 exhibited good oral bioavailability (F=32.2%), similar to that of olaparib (F=45.4%). Furthermore, the free base 43 of the hydrochloride salt 56 exhibited minimal hERG inhibition activity (IC₅₀=6.64 μmol/L). Collectively, these data demonstrate that compound 56 may be an excellent drug candidate for the treatment of cancer, particularly BRCA-deficient tumors.

Novel tricyclic poly (ADP-ribose) polymerase-1/2 inhibitors with potent anticancer chemopotentiating activity: Design, synthesis and biological evaluation

8,9-Dihydro-2,4,7,9a-tetraazabenzo[cd]azulen-6(7H)-ones were designed and synthesized as a new class of PARP-1/2 inhibitors. The compounds displayed a variable pattern of PARP-1/2 enzymes inhibition profile that, in part, paralleled the antiproliferative activity in cell lines. Among them, compound 9e exhibited not only the significant IC50 value of 28nM in the PARP-1 and 7.7nM in PARP-2 enzyme assay, but also a profound synergic efficacy combined with temozolomide with PF50 values of 2.6, 2.5, and 6.5 against MDA-MB-468, SW-620 and A549 and cell line, respectively.

BRCA testing, treatment patterns and survival in platinum-sensitive recurrent ovarian cancer - an observational cohort study

Background

Breast cancer associated (BRCA) genes are critical for DNA repair. Mutations in BRCA1 and BRCA2 (BRCAm) result in loss of these repair mechanisms and potential carcinogenesis. Germline BRCAm are common in ovarian carcinomas, particularly in platinum-sensitive disease. The increased prevalence of BRCAm in platinum-sensitive disease is likely due to enhanced responsiveness to platinum chemotherapy from homologous recombination repair deficiency. The purpose of this study was to explore BRCA testing, treatment patterns and survival in platinum-sensitive recurrent (PSR) ovarian cancer.

Methods

This was an observational cohort analysis of PSR ovarian cancer treated at the Huntsman Cancer Institute from 1995 to 2012. Germline BRCA status was ascertained through chart review and categorized as BRCAm (BRCA1/2 positive), BRCAwt (BRCA wild type or variant of uncertain significance), and untested. Treatment patterns and survival were assessed from recurrence until death or last follow-up. The Kaplan-Meier method was used to evaluate survival from recurrence by BRCA status. Logistic regression and COX proportional hazard model was used to estimate predictors of BRCA testing and survival, respectively.

Results

Of the 168 PSR patients, 15 (9 %) were BRCAm, 25 (15 %) were BRCAwt, and 128 (76 %) were untested. Median age at PSR was 56 years for BRCAm and BRCAwt (p = 0.90) and 63 years for those untested (p = 0.033 vs BRCAm). Overall survival was similar between BRCAm and BRCAwt (median 50.4 vs 67.5 months, p = 0.86) and was 24.9 months in untested patients. Significant predictors for the likelihood of BRCA testing were age (OR = 0.93, 95 % CI 0.89, 0.97, p = 0.002), family history of breast or ovarian cancer (OR = 8.33, 95 % CI: 3.08, 22.59, p < 0.001), and cancer diagnosis year (OR = 10.02, 95 % CI: 3.22, 31.21, p < 0.001). BRCA-tested patients had a lower risk of death versus untested (HR 0.35, 95 % CI 0.17, 0.68, p = 0.001).

Conclusions

BRCAwt patients had similar outcomes to BRCAm patients, potentially owing to similar age at diagnosis, representing a BRCA testing channeling bias. Younger patients, those with a family history of breast or ovarian cancer, and those diagnosed more recently were more likely to be BRCA tested. BRCA tested patients had a lower risk of death.

Electronic supplementary material

The online version of this article (doi:10.1186/s13048-016-0227-x) contains supplementary material, which is available to authorized users.

Advances in small-molecule drug discovery for triple-negative breast cancer

Triple-negative breast cancer (TNBC) is a subtype of poor prognosis, highly invasive and difficult-to-treat breast cancers accounting for approximately 15% of clinical cases. Given the poor outlook and lack of sustained response to conventional therapies, TNBC has been the subject of intense studies on new therapeutic approaches in recent years. The development of targeted cancer therapies, often in combination with established chemotherapy, has been applied to a number of new clinical studies in this setting in recent years. This review will highlight recent therapeutic advances in TNBC, focusing on small-molecule drugs and their associated biological mechanisms of action, and offering the possibility of improved prospects for this patient group in the near future.

Mitoxantrone, More than Just Another Topoisomerase II Poison

Mitoxantrone is a synthetic anthracenedione originally developed to improve the therapeutic profile of the anthracyclines and is commonly applied in the treatment of breast and prostate cancers, lymphomas, and leukemias. A comprehensive overview of the drug's molecular, biochemical, and cellular pharmacology is presented here, beginning with the cardiotoxic nature of its predecessor doxorubicin and how these properties shaped the pharmacology of mitoxantrone itself. Although mitoxantrone is firmly established as a DNA topoisomerase II poison within mammalian cells, it is now clear that the drug interacts with a much broader range of biological macromolecules both covalently and noncovalently. Here, we consider each of these interactions in the context of their wider biological relevance to cancer therapy and highlight how they may be exploited to further enhance the therapeutic value of mitoxantrone. In doing so, it is now clear that mitoxantrone is more than just another topoisomerase II poison.

Discovery of biomarkers predictive of GSI response in triple-negative breast cancer and adenoid cystic carcinoma

Next-generation sequencing was used to identify Notch mutations in a large collection of diverse solid tumors. NOTCH1 and NOTCH2 rearrangements leading to constitutive receptor activation were confined to triple-negative breast cancers (TNBC; 6 of 66 tumors). TNBC cell lines with NOTCH1 rearrangements associated with high levels of activated NOTCH1 (N1-ICD) were sensitive to the gamma-secretase inhibitor (GSI) MRK-003, both alone and in combination with paclitaxel, in vitro and in vivo, whereas cell lines with NOTCH2 rearrangements were resistant to GSI. Immunohistochemical staining of N1-ICD in TNBC xenografts correlated with responsiveness, and expression levels of the direct Notch target gene HES4 correlated with outcome in patients with TNBC. Activating NOTCH1 point mutations were also identified in other solid tumors, including adenoid cystic carcinoma (ACC). Notably, ACC primary tumor xenografts with activating NOTCH1 mutations and high N1-ICD levels were sensitive to GSI, whereas N1-ICD-low tumors without NOTCH1 mutations were resistant.

SIGNIFICANCE

NOTCH1 mutations, immunohistochemical staining for activated NOTCH1, and HES4 expression are biomarkers that can be used to identify solid tumors that are likely to respond to GSI-based therapies.

Host Cell Reactivation and Transcriptional Activation of Carboplatin-Modified BRCA1

The breast cancer susceptibility gene 1 (BRCA1) has been shown to maintain genomic stability through multiple functions in the regulation of DNA damage repair and transcription. Its translated BRCT (BRCA1 C-terminal domain) acts as a strong transcriptional activator. BRCA1 damaged by carboplatin treatment may lead to a loss of such functions. To address the possibility of the BRCA1 gene as a therapeutic target for carboplatin, we investigated the functional consequences of the 3′-terminal region of human BRCA1 following in vitro platination with carboplatin. A reduction in cellular BRCA1 repair of carboplatin-treated plasmid DNA, using a host cell reactivation assay, was dependent on the platination levels on the reporter gene. The transcriptional transactivation activity of the drug-modified BRCA1, assessed using a one-hybrid GAL4 transcriptional assay, was inversely proportional to the carboplatin doses. The data emphasized the potential of the BRCA1 gene to be a target for carboplatin treatment.

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.

The evolution of personalized cancer genetic counseling in the era of personalized medicine

Practice changes in cancer genetic counseling have occurred to meet the demand for cancer genetic services. As cancer genetics continues to impact not only prevention strategies but also treatment decisions, current cancer genetic counseling models will need to be tailored to accommodate emerging clinical indications. These clinical indications include: surgical prophylactic bilateral mastectomy candidates, PARP-inhibitor candidates, patients with abnormal tumor screening results for Lynch syndrome, and post-test counseling patients (after genetic testing is ordered by another healthcare provider). A more personalized, multidisciplinary approach to selecting the best framework, for a given clinical indication, may become increasingly necessary in this era of personalized medicine.

Targeted therapies of metastatic breast cancer: relationships with cancer stem cells

In the last years, many targeted agents have been developed for metastatic breast cancer (MBC) treatment and are being tested in clinical trials. In spite of this, apart from epidermal growth factor receptor 2 (HER2) positive subset, no significant increase in the median overall survival (OS) has been reported. Similarly to conventional chemo- and radiotherapy, the cancer stem cell theory has been evoked to explain the frustrating results often obtained with this emerging category of drugs. This review examines the results in MBC of the approved targeted therapies or those currently under evaluation in experimental studies or in clinical trials, in the light of their relationships with breast CSCs and of the efforts to circumvent the development of resistance. In the next, there is the principal need to investigate if the effects on CSCs may be used to overcome cancer resistance and it will be opportune to consider whether molecular targeted therapies should be used alone or combined with conventional therapy, or with a different target drug specific for CSCs.

Treating breast cancer in the 21st century: emerging biological therapies

For many years, the medical treatment of breast cancer was reliant solely on cytotoxic chemotherapy. However, over the past twenty years, treatment has evolved to a more target-directed approach. We now employ tailored therapy based on the presence or absence of receptors for estrogen, progesterone, and human epidermal growth factor 2 (HER2). We expect this trend to continue, as agents that use novel approaches to target HER2, as well as targeting different portions of the HER signaling pathway, are in various stages of development. Notably, pertuzumab, a humanized monoclonal antibody that binds to a different domain of the extracellular portion of the HER2 receptor than trastuzumab, was recently approved for use, as was lapatinib, a small-molecule tyrosine kinase inhibitor. Patients with triple negative breast cancer, particularly those with the BRCA mutation, have more limited treatment options and carry a worse prognosis than those who are hormone receptor positive. However, recent data has shown that PARP inhibitors may have significant anti-tumor effect in those with this subtype of breast cancer. Novel agents that inhibit mTOR, PI3K, the insulin-like growth factor, heat shock protein 90, and histone deacetylase have shown promise in phase I-III trials and offer exciting new possibilities for the treatment of this often fatal disease. As we are presented with an ever increasing number of treatment options, the timing and combinations of therapeutic agents used becomes ever more complex in the age of personalized care, but we are hopeful that ultimately this will lead to improved patient outcomes.

Targeted therapy for triple-negative breast cancer: where are we?

Breast cancers that are negative for estrogen receptor (ER), progesterone receptors (PR) and HER2, using standard clinical assays, have been dubbed triple-negative (TN). Unlike other molecular subtypes of invasive breast cancer, validated targeted therapies are currently unavailable for patients with TN breast cancer. Preclinical studies however, have identified several potential targets such as epidermal growth factor receptor (EGFR), SRC, MET and poly ADP ribose polymerase 1/2 (PARP1/2). Because of tumor heterogeneity, it is unlikely that any single targeted therapy will be efficacious in all patients with TN breast cancer. The rational way forward for treating these patients is likely to be biomarker-driven, combination targeted therapies or combination of targeted therapy with cytotoxic chemotherapy.

Increased expression of Rab25 in breast cancer correlates with lymphatic metastasis

Breast cancer is the most common cancer in women worldwide. Studies have suggested that Ras-related protein 25 (Rab25), a member of Rab small GTPase family, is involved in the pathogenesis of breast cancer. In this study, we investigated whether the expression of Rab25 correlated with lymphatic metastasis in breast cancer and whether the expression of Rab25 was positively correlated with oestrogen receptor (ER) and progesterone receptor (PR) expression in breast cancer. Breast cancer tissues from 42 invasive ductal breast cancer patients with or without lymphatic metastasis were collected and the levels of Rab25 mRNA and protein measured by quantitative real-time PCR and immunohistochemistry, respectively. The mRNA level of Rab25 was significantly increased in invasive ductal breast cancer with lymphatic metastasis compared to that in invasive ductal breast cancer without lymphatic metastasis. Immunohistochemical analysis demonstrated that Rab25 and vascular endothelial growth factor (VEGF) were highly expressed in invasive ductal breast cancer with lymphatic metastasis regardless of whether the cancer is ER and PR positive or negative. Higher expression of Rab25 positively correlated with VEGF expression. However, the expressions of Rab25 in ER and PR-positive cancers were much higher than ER and PR-negative cancers regardless of whether lymphatic metastasis occurred. These data suggest that higher level of Rab25 was associated with lymphatic metastasis, specifically in ER and PR-positive breast cancer. The better understanding of the mechanism of Rab25 may provide a basis for the development of a novel therapeutic target in breast cancer.

Therapeutic potential of PARP inhibitors for metastatic breast cancer

Increasing understanding of the cellular aberrations inherent to cancer cells has allowed the development of therapies to target biological pathways, an important step towards individualization of breast cancer therapy. The clinical development of poly(ADP-ribose) polymerase (PARP) inhibitors, with their novel and selective mechanism of action, are an example of this strategy. PARP plays a key role in DNA repair mechanisms, particularly the base excision repair pathway. Initially developed as inhibitors able to enhance the cytotoxicity of radiation and certain DNA-damaging agents, they have more recently been shown to have single-agent activity in certain tumors. Inhibition of PARP in a DNA repair-defective tumor can lead to gross genomic instability and cell death by exploiting the paradigm of synthetic lethality. Several studies have evaluated the role of PARP inhibitors for treatment of breast cancer, particularly in the context of BRCA-mutated and triple-negative breast cancers. In addition, inhibition of PARPs repair functions for chemotherapy-induced DNA lesions has been shown to potentiate the effect of some chemotherapy regimens. This article discusses the current understanding of PARP inhibition as a treatment for metastatic breast cancer, evidence from clinical trials and addresses its future implications.

Triple negative breast cancer: proposals for a pragmatic definition and implications for patient management and trial design

In trials in triple negative breast cancer (TNBC), oestrogen and progesterone receptor negativity should be defined as < 1% positive cells. Negativity is a ratio of <2 between Her2 gene copy number and centromere of chromosome 17 or a copy number of 4 or less. In routine practice, immunohistochemistry is acceptable given stringent quality assurance. Triple negativity emerging after neoadjuvant treatment differs from primary TN and such patients should not enter TNBC trials. Patients relapsing with TN metastases should be eligible even if their primary was positive. Rare TN subtypes such as apocrine, adenoid-cystic and low-grade metaplastic tumours should be excluded. TN and basal-like (BL) signatures overlap but are not equivalent. Since the significance of basal cytokeratin or EGFR overexpression is not known and we lack validated assays, these features should not be used to subclassify TN tumours. Tissue collection in trials is mandatory so the effect on outcome of different tumour phenotypes and BRCA mutation can be explored. No prospective studies have established that TN tumours have particular sensitivity or resistance to any specific chemotherapy agent or radiation. TNBC patients should be treated according to tumour and clinical characteristics.

Complexes of mismatched and complementary DNA with minor groove binders. Structures at nucleotide resolution via an improved hydroxyl radical cleavage methodology

Tumor cell lines can replicate faster than normal cells and many also have defective DNA repair pathways. This has lead to the investigation of the inhibition of DNA repair proteins as a means of therapeutic intervention. An alternative approach is to hide or mask damaged DNA from the repair systems. We have developed a protocol to investigate the structures of the complexes of damaged DNA with drug like molecules. Nucleotide resolution structural information can be obtained using an improved hydroxyl radical cleavage protocol. The use of a dT(n) tail increases the length of the smallest fragments of interest and allows efficient co-precipitation of the fragments with poly(A). The use of a fluorescent label, on the 5' end of the dT(n) tail, in conjunction with modified cleavage reaction conditions, avoids the lifetime and other problems with (32)P labeling. The structures of duplex DNAs containing AC and CC mismatches in the presence and absence of minor groove binders have been investigated as have those of the fully complementary DNA. The results indicate that the structural perturbations of the mismatches are localized, are sequence dependent and that the presence of a mismatch can alter the binding of drug like molecules.

Expression of poly (adenosine diphosphate-ribose) polymerase and p53 in epithelial ovarian cancer and their role in prognosis and disease outcome

PARP, poly (adenosine diphosphate-ribose) polymerase, is a damage-sensing protein, which is essential for the repair of DNA single-strand breaks. PARP and p53 function synergistically in repairing DNA damage and suppressing chromosomal rearrangements. The aim of this study was to determine the expression of PARP and p53 in epithelial ovarian cancer (EOC) and to correlate their expression with clinicopathologic characteristics. PARP and p53 were evaluated using immunohistochemistry applied on a tissue microarray of 189 EOC and their expressions were correlated to clinicopathologic variables, including the age of diagnosis, stage, grade, histologic type, optimal debulking, progression-free survival, and overall survival (OS). PARP and p53 expressions were shown in 61% and 54% of cases, respectively. PARP-positive tumors are more likely to have higher grade (P=0.03) and complete response to initial first-line chemotherapy (P=0.009). Patients with positive p53 staining are more likely to be at the advanced stage disease (P=0.004). Finally, there were no significant associations between PARP and p53 expression and no differences in progression-free survival and OS for PARP or p53 expressions. The overexpression of PARP and p53 in high grade, and advanced stage tumors indicated that these 2 markers might serve as an indicator of aggressive disease behavior. Additional studies are warranted to evaluate the role of PARP and PARP inhibitors in the setting of adjuvant chemotherapy.

Poly(ADP-ribose) polymerase-1 inhibition: preclinical and clinical development of synthetic lethality

The hereditary forms of breast cancer identified by BRCA1 and BRCA2 genes have a defect in homologous DNA repair and demonstrate a dependence on alternate DNA repair processes by base excision repair, which requires poly(ADP-ribose) polymerase 1 (PARP-1). siRNA and deletion mutations demonstrate that interference with PARP-1 function results in enhanced cell death when the malignancy has a defect in homologous recombination. These findings resulted in a plethora of agents in clinical trials that interfere with DNA repair, and these agents offer the potential of being more selective in their effects than classic chemotherapeutic drugs. An electronic search of the National Library of Medicine for published articles written in English used the terms "PARP inhibitors" and "breast cancer" to find prospective, retrospective and review articles. Additional searches were done for articles dealing with mechanism of action. A total of 152 articles dealing with breast cancer and PARP inhibition were identified. PARP inhibition not only affects nonhomologous repair, but also has several other nongenomic functions. Mutational resistance to these agents was seen in preclinical studies. To date, PARP-1 inhibitors were shown to enhance cytotoxic effects of some chemotherapy agents. This new class of agents may offer more therapeutic specificity by exploiting a DNA repair defect seen in some human tumors with initial clinical trials demonstrating antitumor activity. Although PARP inhibitors may offer a therapeutic option for selected malignancies, the long-term effects of these agents have not yet been defined.

Identification of a regulatory segment of poly(ADP-ribose) glycohydrolase

Coordinate regulation of PARP-1 and -2 and PARG is required for cellular responses to genotoxic stress. While PARP-1 and -2 are regulated by DNA breaks and covalent modifications, mechanisms of PARG regulation are poorly understood. We report here discovery of a PARG regulatory segment far removed linearly from residues involved in catalysis. Expression and analysis of human PARG segments identified a minimal catalytically active C-terminal PARG (hPARG59) containing a 16-residue N-terminal mitochondrial targeting sequence (MTS). Deletion analysis and site-directed mutagenesis revealed that the MTS, specifically hydrophobic residues L473 and L474, was required for PARG activity. This region of PARG was termed the "regulatory segment/MTS" (REG/MTS). The overall alpha-helical composition of hPARG59, determined by circular dichroism (CD), was unaffected by mutation of the REG/MTS leucine residues, suggesting that activity loss was not due to incorrect protein folding. REG/MTS was predicted to be in a loop conformation because the CD spectra of mutant Delta1-16 lacking the REG/MTS showed a higher alpha-helical content than hPARG59, indicating a secondary structure other than alpha-helix for this segment. Deletion of the REG/MTS from full-length hPARG111 also resulted in a complete loss of activity, indicating that all PARG isoforms are subject to regulation at this site. The presence of the REG/MTS raises the possibility that PARG activity is regulated by interactions of PARP-1 and -2 and other proteins at this site, raises interesting questions concerning mitochondrial PARG because MTS residues are often removed after transport, and offers a potentially novel site for drug targeting of PARG.

The RING heterodimer BRCA1-BARD1 is a ubiquitin ligase inactivated by the platinum-based anticancer drugs

The breast cancer susceptibility protein 1 (BRCA1) participates in the maintenance of cells genomic integrity through DNA repair, cell cycle checkpoint, protein ubiquitination, and transcriptional regulation. The N-terminus of BRCA1 contains a RING domain that preferentially forms a heterodimeric complex with BARD1. The BRCA1-BARD1 RING complex has an E3 ubiquitin ligase activity that plays an essential role in response to DNA damage. Preclinical and clinical studies have recently revealed that structural changes to the heterodimer result in alterations to the BRCA1-mediated DNA repair pathways in cancer cells, and lead to hypersensitivity to several chemotherapeutic agents. It is of interest to approach the BRCA1 RING domain as a potentially molecular target for platinum-based drugs for cancer therapy. A previous study has shown that the anticancer drug cisplatin formed intramolecular and intermolecular BRCA1 adducts in which His117 was the primary platinum-binding site, and conferred conformational changes and induced thermostability. Here, we have studied the functional consequence of the in vitro platination of the BRCA1 RING domain by a number of platinum complexes. The BRCA1 ubiquitin ligase activity was inhibited by transplatin > cisplatin > oxaliplatin > carboplatin in that order. The consequences of the binding of the platinum complexes on the reactivity of the BRCA1 were also discussed. The data raised the possibility of selectively targeting the BRCA1 DNA repair for cancer therapy.