Update on PARP Inhibitors in Breast Cancer

Enhanced Anti-Cancer Effect of Folate-Conjugated Olaparib Nanoparticles Combined with Radiotherapy in Cervical Carcinoma

BACKGROUND

Radiotherapy (RT), one of the main treatments for cervical cancer, has tremendous potential for improvement in the efficacy. Poly (ADP-ribose) polymerase (PARP) is a key enzyme in the repair of DNA strand breaks (DSB). Olaparib (Ola) is a PARP inhibitor that is involved in preventing the release of PARP from RT-induced damaged DNA to potentiate the effect of RT. Although the basic mechanism of Ola's radiosensitization is well known, the radiosensitization mechanism of its nanomedicine is still unclear. In addition, the lack of tumor tissue targeting is a major obstacle for the clinical success of Ola.

MATERIALS AND METHODS

In this study, we developed folate-conjugated active targeting olaparib nanoparticles (ATO) and investigated the anti-tumor effect of ATO combined with radiotherapy (RT) in nude mice using cervical cancer xenograft models. We used folate (FA)-conjugated poly (ε-caprolactone)-poly (ethyleneglycol)-poly (e-caprolactone) (PCEC) copolymer to prepare ATO via emulsification/solvent diffusion. Further, we evaluated ATO particle size, potential, encapsulation efficiency, and in vitro release characteristics, and evaluated the shape of ATO via transmission electron microscopy (TEM). We then performed MTT and cell uptake assays to detect cytotoxicity and targeting uptake in vitro. We investigated the anti-tumor properties of ATO in vivo by apoptosis test, 18 F-FDG PET/CT, and immunohistochemical analysis. Finally, the xenografted tumor in nude mice was subjected to RT and/or ATO treatment.

RESULTS

The results confirmed that ATO in combination with RT significantly inhibited tumor growth and prolonged survival time of tumor-bearing mice. This may be related to the inhibition of tumor proliferation and DNA damage repair and induction of cell apoptosis in vivo.

CONCLUSION

The ATO developed in this study may represent a novel formulation for olaparib delivery and have promising potential for treating tumors with an over-expression of folate receptors.

Heritability of Low ER Staining/HER2-Breast Tumors: Are We Missing an Opportunity for Germline Testing?

In 2010, the genetic testing criteria was changed to allow women diagnosed ≤ 60 years old with triple negative breast cancer (TNBC) to undergo germline testing. In the same year, estrogen receptor (ER) positivity was defined as having ≥1% ER staining cells. While tumors with 1–10% ER staining cells and HER2 negative (HER2-) status share characteristics with TNBC, the utility of germline testing in women with ER low positive/HER2- (ERLP/HER2-) tumors is not well-understood. To this end, all patients with hormone receptor positive staining cells ≤ 10% and negative HER2 status were identified. Clinical genetic test results were extracted for patients who underwent testing. Panel testing was performed for those women who had genomic DNA available for research purposes. ERLP/HER2-tumors constituted 2.7% of all tumors in the database. Patients did not differ significantly from those with TNBC by age at diagnosis, ethnicity, family history or tumor size, stage or grade (p > 0.05). Mutation frequency did not differ significantly (p = 0.757) between groups (ERLP/HER2- 16.1%; TNBC 16.7%). Hereditary forms of breast cancer were similar in both ERLP/HER2- and TNBC, thus current guidelines may result in the under testing of women with low ER tumors, resulting in missed opportunities to improve patient management.

New Perspectives for Resistance to PARP Inhibitors in Triple-Negative Breast Cancer

Poly (ADP-ribose) polymerase (PARP) inhibitors are a therapeutic milestone exerting a synthetic lethal effect in the treatment of cancer involving BRCA1/2 mutation. Theoretically, PARP inhibitors (PARPi) eliminate tumor cells by disrupting DNA damage repair through either PARylation or the homologous recombination (HR) pathway. However, resistance to PARPi greatly hinders therapeutic effectiveness in triple-negative breast cancer (TNBC). Owing to the high heterogeneity and few genetic targets in TNBC, there has been limited therapeutic progress in the past decades. In view of this, there is a need to circumvent resistance to PARPi and develop potential treatment strategies for TNBC. We present, herein, a review of the scientific progress and explore the mechanisms underlying PARPi resistance in TNBC. The complicated mechanisms of PARPi resistance, including drug exporter formation, loss of poly (ADP-ribose) glycohydrolase (PARG), HR reactivation, and restoration of replication fork stability, are discussed in detail in this review. Additionally, we also discuss new combination therapies with PARPi that can improve the clinical response in TNBC. The new perspectives for PARPi bring novel challenges and opportunities to overcome PARPi resistance in breast cancer.

Poly (ADP-ribose) Polymerase Inhibition in Patients with Breast Cancer and BRCA 1 and 2 Mutations

The poly-(ADP-ribose) polymerase (PARP) inhibitors olaparib and talazoparib, have recently been approved for use in patients with metastatic breast cancer (BC) and germline BRCA 1 or 2 mutations due to improved progression-free survival compared to chemotherapy. An increasing number of clinical trials are evaluating the role of PARP inhibitors (PARPi) in BC, alone and in combination with other therapies (including immunotherapy), as well as in earlier stages of the disease. This review describes the unique mechanism of action of these drugs and puts into clinical context the results of pivotal clinical trials. We also discuss the future development of PARPi in BC, their potential combination with other strategies, including chemotherapy and immune-checkpoint inhibitors, and the impact of these treatments in current genetic counselling.

TACC3 expression as a prognostic factor in aggressive types of adult T-cell leukemia/lymphoma patients

INTRODUCTION

Adult T-cell leukemia/lymphoma (ATLL) is a malignant peripheral T-cell neoplasm associated with human T-cell leukemia virus type-1 (HTLV-1). The acute and lymphoma subtypes are regarded as aggressive ATLLs, and the overall survival (OS) of patients remains poor. Transforming acidic coiled-coil-containing protein 3 (TACC3) regulates microtubules, which are associated with cancer-related proteins overexpressed in various cancers. Such a relationship has not been reported in hematopoietic tumors, including ATLL.

METHODS

We examined tissue microarrays of histological samples from 92 cases of aggressive ATLL and assessed clinical features, including TACC3 protein expression levels.

RESULTS

Compared with TACC3-low, TACC3-high ATLL patients were significantly older (P < .001), with a tendency toward pleomorphic variant over other morphological classifications (P = .019). TACC3-high patients (median survival time [MST] 10.6 months, confidence interval [CI] [6.27-15.6]) had poorer OS compared to TACC3-low patients (MST 20 months, CI [9.43-38.5]) (P = .0168). Moreover, multivariate analysis on TACC3 expression levels suggests that TACC3-high is an independent significant prognostic factor (HR, 1.700; 95% CI, 1.037-2.753; P = .0355).

CONCLUSION

Certain drugs that inhibit TACC3-overexpressing neoplastic cells are used clinically. Further studies might highlight a key role for TACC3 in the oncogenesis and progression of ATLL.

BRCA testing in a genomic diagnostics referral center during the COVID-19 pandemic

The first person-to-person transmission of the 2019-novel coronavirus in Italy on 21 February 2020 led to an infection chain that represents one of the largest known COVID-19 outbreaks outside Asia. Hospitals have been forced to reorganized their units in response to prepare for an unforeseen healthcare emergency. In this context, our laboratory (Molecular and Genomic Diagnostics Unit, Fondazione Policlinico Universitario Agostino Gemelli IRCCS) re-modulated its priorities by temporarily interrupting most of the molecular tests guaranteeing only those considered “urgent” and not postponable. In particular, this paper details changes regarding the execution of germline BRCA (gBRCA) testing in our laboratory. A substantial reduction in gBRCA testing (about 60%) compared to the first 2 months of the current year was registered, but the requests have not been reset. The requesting physicians were mainly gynaecologists and oncologists. These evidences further emphasize the new era of gBRCA testing in the management of cancer patients and confirms definitively the integration of gBRCA testing/Next Generation Sequencing (NGS) into clinical oncology. Finally, a re-organization of gBRCA testing in our Unit, mainly related to delayed and reduced arrival of tests was necessary, ensuring, however, a high-quality standard and reliability, mandatory for gBRCA testing in a clinical setting.

Modeling of the Enzyme-Substrate Complexes of Human Poly(ADP-Ribose) Polymerase 1

Poly(ADP-ribose) polymerase 1 (PARP-1) is a key DNA repair enzyme and an important target in cancer treatment. Conventional methods of studying the reaction mechanism of PARP-1 have limitations because of the complex structure of PARP-1 substrates; however, the necessary data can be obtained by molecular modeling. In this work, a molecular dynamics model for the PARP-1 enzyme-substrate complex containing NAD+ molecule and the end of the poly(ADP-ribose) chain in the form of ADP molecule was obtained for the first time. Interactions with the active site residues have been characterized where Gly863, Lys903, Glu988 play a crucial role, and the S_N1-like mechanism for the enzymatic ADP-ribosylation reaction has been proposed. Models of PARP-1 complexes with more sophisticated two-unit fragments of the growing polymer chain as well as competitive inhibitors 3-aminobenzamide and 7-methylguanine have been obtained by molecular docking.

Molecular Mechanisms of PARP-1 Inhibitor 7-Methylguanine

7-Methylguanine (7-MG), a natural compound that inhibits DNA repair enzyme poly(ADP-ribose) polymerase 1 (PARP-1), can be considered as a potential anticancer drug candidate. Here we describe a study of 7-MG inhibition mechanism using molecular dynamics, fluorescence anisotropy and single-particle Förster resonance energy transfer (spFRET) microscopy approaches to elucidate intermolecular interactions between 7-MG, PARP-1 and nucleosomal DNA. It is shown that 7-MG competes with substrate NAD⁺ and its binding in the PARP-1 active site is mediated by hydrogen bonds and nonpolar interactions with the Gly863, Ala898, Ser904, and Tyr907 residues. 7-MG promotes formation of the PARP-1–nucleosome complexes and suppresses DNA-dependent PARP-1 automodification. This results in nonproductive trapping of PARP-1 on nucleosomes and likely prevents the removal of genotoxic DNA lesions.

BRCA1/BRCA2 Pathogenic Variant Breast Cancer: Treatment and Prevention Strategies

Hereditary breast cancer is known for its strong tendency of inheritance. Most hereditary breast cancers are related to BRCA1/BRCA2 pathogenic variants. The lifelong risk of breast cancer in pathogenic BRCA1 and BRCA2 variant carriers is approximately 65% and 45%, respectively, whereas that of ovarian cancer is estimated to be 39% and 11%, respectively. Therefore, understanding these variants and clinical knowledge on their occurrence in breast cancers and carriers are important. BRCA1 pathogenic variant breast cancer shows more aggressive clinicopathological features than the BRCA2 pathogenic variant breast cancer. Compared with sporadic breast cancer, their prognosis is still debated. Treatments of BRCA1/BRCA2 pathogenic variant breast cancer are similar to those for BRCA-negative breast cancer, mainly including surgery, radiotherapy, and chemotherapy. Recently, various clinical trials have investigated poly (adenosine diphosphate [ADP]-ribose) polymerase (PARP) inhibitor treatment for advanced-stage BRCA1/BRCA2 pathogenic variant breast cancer. Among the various PARP inhibitors, olaparib and talazoparib, which reached phase III clinical trials, showed improvement of median progression-free survival around three months. Preventive and surveillance strategies for BRCA pathogenic variant breast cancer to reduce cancer recurrence and improve treatment outcomes have recently received increasing attention. In this review, we provide an information on the clinical features of BRCA1/BRCA2 pathogenic variant breast cancer and clinical recommendations for BRCA pathogenic variant carriers, with a focus on treatment and prevention strategies. With this knowledge, clinicians could manage the BRCA1/BRCA2 pathogenic variant breast cancer patients more effectively.

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.

Targeting DNA repair in gliomas

PURPOSE OF REVIEW

Gliomas represent a disparate group of malignancies with varying clinical outcomes despite a tremendous amount of time, effort, and resources dedicated to their management and understanding. The most aggressive entity, glioblastoma, has a dismal prognosis with poor local control despite intense local and systemic treatment, including radiation therapy.

RECENT FINDINGS

Given the heterogeneity in genotype, phenotype, and patient outcomes, researchers and clinicians have turned their attention toward attacking DNA damage response and repair mechanisms in gliomas in an effort to develop novel chemo and radiosensitizers. However, despite extensive work in both the laboratory and the clinic, no sensitizers have yet to emerge as clear options in the treatment of glioma, often because of meager preclinical data or an inability to penetrate the blood-brain barrier.

SUMMARY

This review will examine current understanding of molecular DNA repair targets in glioma and their potential exploitation to improve local control and, ultimately, overall survival of patients afflicted with these diseases.

Catching HPV in the Homologous Recombination Cookie Jar

To replicate, the human papillomaviruses (HPVs) that cause anogenital and oropharyngeal malignancies must simultaneously activate DNA repair pathways and avoid the cell cycle arrest that normally accompanies DNA repair. For years it seemed that HPV oncogenes activated the homologous recombination pathway to facilitate the HPV lifecycle. However, recent developments show that, although homologous recombination gene expression and markers of pathway activation are increased, homologous recombination itself is attenuated. This review provides an overview of the diverse ways that HPV oncogenes manipulate homologous recombination and ideas on how the resulting dysregulation and inhibition offer opportunities for improved therapies and biomarkers.

Depletion of DNA damage binding protein 2 sensitizes triple-negative breast cancer cells to poly ADP-ribose polymerase inhibition by destabilizing Rad51

Poly ADP‐ribose polymerase inhibitors (PARPi) have shown promising therapeutic efficacy in triple‐negative breast cancer (TNBC) patients. However, resistance ultimately develops, preventing a curative effect from being attained. Extensive investigations have indicated the diversity in the mechanisms underlying the PARPi sensitivity of breast cancer. In this study, we found that DNA damage binding protein 2 (DDB2), a DNA damage‐recognition factor, could protect TNBC cells from PARPi by regulating DNA double‐strand break repair through the homologous recombination pathway, whereas the depletion of DDB2 sensitizes TNBC cells to PARPi. Furthermore, we found that DDB2 was able to stabilize Rad51 by physical association and disrupting its ubiquitination pathway‐induced proteasomal degradation. These findings highlight an essential role of DDB2 in modulating homologous recombination pathway activity and suggest a promising therapeutic target for TNBC.

PARP-1 activity (PAR) determines the sensitivity of cervical cancer to olaparib

OBJECTIVES

Cervical cancer (CC) remains a major health problem worldwide. Poly (adenosine diphosphate [ADP]-ribose) polymerase (PARP) inhibitors (PARPi) have emerged as a promising class of chemotherapeutics in ovarian cancer. We explored the preclinical in vitro and in vivo activity of olaparib against multiple primary whole exome sequenced (WES) CC cells lines and xenografts.

METHODS

Olaparib cell-cycle, apoptosis, homologous-recombination-deficiency (HRD), PARP trapping and cytotoxicity activity was evaluated against 9 primary CC cell lines in vitro. PARP and PAR expression were analyzed by Western blot assays. Finally, olaparib in vivo antitumor activity was tested against CC xenografts.

RESULTS

While none of the cell lines demonstrated HRD, three out of 9 (33.3%) primary CC cell lines showed strong PARylation activity and demonstrated high sensitivity to olaparib in vitro treatment (cutoff IC50 values < 2 μM, p = 0.0012). Olaparib suppressed CC cell growth through cell cycle arrest in the G2/M phase and caused apoptosis (p < 0.0001). Olaparib activity in CC involved both PARP enzyme inhibition and trapping. In vivo, olaparib significantly impaired CC xenografts tumor growth (p = 0.0017) and increased overall animal survival (p = 0.008).

CONCLUSIONS

A subset of CC primary cell lines is highly responsive to olaparib treatment in vitro and in vivo. High level of PARylation correlated with olaparib preclinical activity and may represent a useful biomarker for the identification of CC patients benefitting the most from PARPi.

Pyridoxine for prevention and treatment of PARP inhibitor induced nausea and vomiting

Poly-ADP ribose polymerase inhibitors (PARPi) are a promising new treatment option for patients with ovarian cancer and are moderately emetogenic. Tolerance of therapy is paramount, and uncontrolled nausea and vomiting may limit use. Although most patients will experience improvement in nausea and vomiting after one to two months, approximately one in twenty patients will discontinue therapy due to unrelieved symptom burden. Three cases of olaparib-related nausea and vomiting mitigated by primary pyridoxine use are reported. Case 1 demonstrates successful use of pyridoxine in breakthrough nausea. Case 2 details the use of pyridoxine following refractory nausea and vomiting requiring hospitalization. Case 3 describes a prophylactic approach for a patient with significant anticipatory nausea. All three patients tolerated olaparib after starting and continuing pyridoxine. Vitamin B6, or pyridoxine, was successful as both a therapeutic and prophylactic option for significant treatment-related nausea and vomiting with PARPi use.

Combined poly-ADP ribose polymerase and ataxia-telangiectasia mutated/Rad3-related inhibition targets ataxia-telangiectasia mutated-deficient lung cancer cells

Background

Up to 40% of lung adenocarcinoma have been reported to lack ataxia-telangiectasia mutated (ATM) protein expression. We asked whether ATM-deficient lung cancer cell lines are sensitive to poly-ADP ribose polymerase (PARP) inhibitors and determined the mechanism of action of olaparib in ATM-deficient A549 cells.

Methods

We analysed drug sensitivity data for olaparib and talazoparib in lung adenocarcinoma cell lines from the Genomics of Drug Sensitivity in Cancer (GDSC) project. We deleted ATM from A549 lung adenocarcinoma cells using CRISPR/Cas9 and determined the effects of olaparib and the ATM/Rad3-related (ATR) inhibitor VE-821 on cell viability.

Results

IC₅₀ values for both olaparib and talazoparib positively correlated with ATM mRNA levels and gene amplification status in lung adenocarcinoma cell lines. ATM mutation was associated with a significant decrease in the IC₅₀ for olaparib while a similar trend was observed for talazoparib. A549 cells with deletion of ATM were sensitive to ionising radiation and olaparib. Olaparib induced phosphorylation of DNA damage markers and reversible G2 arrest in ATM-deficient cells, while the combination of olaparib and VE-821 induced cell death.

Conclusions

Patients with tumours characterised by ATM-deficiency may benefit from treatment with a PARP inhibitor in combination with an ATR inhibitor.

UPLC-MS/MS method for the determination of talazoparib in rat plasma and its pharmacokinetic study

In the present study, an accurate and sensitive ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method for the determination of plasma talazoparib concentration in rats was developed and established. The purpose of chromatographic separation of talazoparib and the internal standard (bosutinib) was achieved on an Acquity BEH C18 (2.1 mm × 50 mm, 1.7 μm) column with a flow rate of 0.40 mL/min, using a gradient elution with acetonitrile and 0.1% formic acid in water as the mobile phase. The detection was performed on a XEVO TQ-S triple quadrupole tandem mass spectrometer coupled with electrospray ionization interface under positive-ion multiple reaction monitoring (MRM) mode with the precursor-to-product ion transitions of m/z 381.3 → 285.2 for talazoparib and m/z 530.2 → 141.2 for bosutinib (IS), respectively. The method was linear over the range of 0.5-200 ng/mL for talazoparib. The accuracies and precisions of intra- and inter-day were all within the acceptance limits, and no matrix effect was observed in this method. The validated method was further employed to a pharmacokinetic study of talazoparib after oral treatment with 0.2 mg/kg talazoparib to rats.

Mechanism of Action and Clinical Efficacy of CDK4/6 Inhibitors in BRCA-Mutated, Estrogen Receptor-Positive Breast Cancers: Case Report and Literature Review

Sensitivity to endocrine therapy of patients with estrogen receptor (ER)-positive metastatic breast cancer and germline BRCA1/2 mutations is not yet fully elucidated. Furthermore, the registration trials of CDK 4/6 inhibitors in combination with endocrine therapy lacked of a pre-specified subgroup analysis in BRCA1/2 mutation carriers. We report clinical history of two patients with BRCA-mutated, ER-positive metastatic breast cancer treated with letrozole plus the CDK 4/6 inhibitor palbociclib. Biological and clinical implications of the treatment outcome observed in the two cases are discussed with the knowledge of scientific evidence to date available. Overall, biological rationale, preclinical, and clinical data support the prominent role of CDK 4/6 inhibitors plus endocrine therapy, even in combination with PARP inhibitors, in the treatment of BRCA-mutated, ER-positive breast cancers. However, the interaction between Cyclin/CDK pathway, ER and BRCA is complex and evidences reported so far, albeit reliable, await confirmation in the context of future randomized clinical trials.

Genomics applied to the treatment of breast cancer

Breast cancer remains a major health issue in the world with 1.7 million new cases in 2012 worldwide. It is the second cause of death from cancer in western countries. Genomics have started to modify the treatment of breast cancer, and the developments should become more and more significant, especially in the present era of treatment personalization and with the implementation of new technologies. With molecular signatures, genomics enabled a de-escalation of chemotherapy and personalized treatments of localized forms of estrogen-dependent breast cancers. Genomics can also make a real contribution to constitutional genetics, so as to identify mutations in a panel of candidate genes. In this review, we will discuss the contributions of genomics applied to the treatment of breast cancer, whether already validated contributions or possible future applications linked to research data.

Targeting autophagy potentiates the anti-tumor effect of PARP inhibitor in pediatric chronic myeloid leukemia

Due to its potent cytotoxicity in BRCA-mutated tumors, synthetic lethality elicited by poly (ADP-ribose) polymerase (PARP) inhibitor gives renewed enthusiasm to researching and developing anti-cancer therapies. Chronic myeloid leukemia (CML) is a type of cancers that starts in certain blood-forming cells of the bone marrow. Here, we showed that poly (ADP-ribose) polymerase (PARP) inhibitor talazoparib could induce a concentration-dependent cytotoxicity in CML cells derived from pediatric patients. During talazoparib treatment, autophagy was markedly activated, which was confirmed by the accumulation of autophagosomes, decrease of SQSTM1 and up-regulation of LC3-II. Inhibition of autophagy by pharmaceutical inhibitor chloroquine or small-interfering RNA siATG5 significantly increased the cytotoxicity of talazoparib in pediatric CML cells and elicited synergistic anti-tumor effect in patient-derived xenograft model. Our data demonstrated that autophagy played a cyto-protective role in talazoparib-treated pediatric CML and co-treatment with talazoparib and autophagy inhibitor could induce synergetic anti-tumor effect, providing novel insights for pediatric CML treatment.

A Review of the Hereditary Component of Triple Negative Breast Cancer: High- and Moderate-Penetrance Breast Cancer Genes, Low-Penetrance Loci, and the Role of Nontraditional Genetic Elements

Triple negative breast cancer (TNBC), representing 10-15% of breast tumors diagnosed each year, is a clinically defined subtype of breast cancer associated with poor prognosis. The higher incidence of TNBC in certain populations such as young women and/or women of African ancestry and a unique pathological phenotype shared between TNBC and BRCA1-deficient tumors suggest that TNBC may be inherited through germline mutations. In this article, we describe genes and genetic elements, beyond BRCA1 and BRCA2, which have been associated with increased risk of TNBC. Multigene panel testing has identified high- and moderate-penetrance cancer predisposition genes associated with increased risk for TNBC. Development of large-scale genome-wide SNP assays coupled with genome-wide association studies (GWAS) has led to the discovery of low-penetrance TNBC-associated loci. Next-generation sequencing has identified variants in noncoding RNAs, viral integration sites, and genes in underexplored regions of the human genome that may contribute to the genetic underpinnings of TNBC. Advances in our understanding of the genetics of TNBC are driving improvements in risk assessment and patient management.

BRCA Genes: The Role in Genome Stability, Cancer Stemness and Therapy Resistance

Carcinogenesis is a multistep process, and tumors frequently harbor multiple mutations regulating genome integrity, cell division and death. The integrity of cellular genome is closely controlled by the mechanisms of DNA damage signaling and DNA repair. The association of breast cancer susceptibility genes BRCA1 and BRCA2 with breast and ovarian cancer development was first demonstrated over 20 years ago. Since then the germline mutations within these genes were linked to genomic instability and increased risk of many other cancer types. Genomic instability is an engine of the oncogenic transformation of non-tumorigenic cells into tumor-initiating cells and further tumor evolution. In this review we discuss the biological functions of BRCA1 and BRCA2 genes and the role of BRCA mutations in tumor initiation, regulation of cancer stemness, therapy resistance and tumor progression.

Mild antagonistic effect of Valproic acid in combination with AZD2461 in MCF-7 breast cancer cells

Background: Breast cancer (BC) is a complex disease, but current treatments are not efficient enough considering increased relapse and decreased survival rate among patients. Poly (ADP-ribose) polymerase inhibitors are recently developed anticancer agents which target cells with defects in homologous recombination (HR) pathway. This study wishes to assess whether the combination of AZD2461 as a newly developed PARP1 inhibitor and valproic acid (VPA), a histone deacetylase inhibitor could effectively reduce the growth of MCF-7 cells with no fundamental DNA repair defect.

Methods: Both trypan blue dye exclusion assay and MTT viability test were used to evaluate cell death. γ-H2AX levels, as a marker of DNA repair, were measured using in cell ELISA method. The Student's t-test and non-parametric analysis of variance (ANOVA) were applied for our data analyses where p-value <0.05 was considered statistically significant.

Results: As calculated by CompuSyn software, IC50 values for VPA and AZD2461 were 4.89 mM and 42.83 µM respectively following 48 hours treatment. Also, the trypan blue exclusion assay results showed a concentration- and time-dependent decrease when MCF-7 cells were treated with both agents (p<0.05). Combination analysis showed a mild antagonism (CI>1.1) while γ-H2AX levels found not to be significantly increased in MCF-7 cells co-treated with VPA+AZD2461 compared to each agent alone (p=0.29).

Conclusion: Our findings revealed that the combination of VPA and AZD2461 could decrease cell viability of MCF-7 cells, but it was not able to significantly increase unrepaired DNA damage sites. The mechanism responsible for drugs combination was not of synergism or addition. Determining the type of involved cell death mechanisms might be followed in further studies.

Therapeutic advances in hormone-dependent cancers: focus on prostate, breast and ovarian cancers

Hormonal cancers affect over 400,000 men and women and contribute collectively to over 100,000 deaths in the United States alone. Thanks to advances in the understanding of these cancers at the molecular level and to the discovery of several disease-modifying therapeutics, the last decade has seen a plateauing or even a decreasing trend in the number of deaths from these cancers. These advanced therapeutics not only effectively slow the growth of hormonal cancers, but also provide an insight on how these cancers become refractory and evolve as an altogether distinct subset. This review summarizes the current therapeutic trends in hormonal cancers, with focus on prostate, breast and ovarian cancers. The review discusses the clinical drugs being used now, promising molecules that are going through various stages of development and makes some predictions on how the therapeutic landscape will shift in the next decade.

BRD4 and Cancer: going beyond transcriptional regulation

BRD4, member of the Bromodomain and Extraterminal (BET) protein family, is largely acknowledged in cancer for its role in super-enhancers (SEs) organization and oncogenes expression regulation. Inhibition of BRD4 shortcuts the communication between SEs and target promoters with a subsequent cell-specific repression of oncogenes to which cancer cells are addicted and cell death. To date, this is the most credited mechanism of action of BET inhibitors, a class of small molecules targeting BET proteins which are currently in clinical trials in several cancer settings.

However, recent evidence indicates that BRD4 relevance in cancer goes beyond its role in transcription regulation and identifies this protein as a keeper of genome stability.

Indeed, a non-transcriptional role of BRD4 in controlling DNA damage checkpoint activation and repair as well as telomere maintenance has been proposed, throwing new lights into the multiple functions of this protein and opening new perspectives on the use of BETi in cancer. Here we discuss the current available information on non-canonical, non-transcriptional functions of BRD4 and on their implications in cancer biology. Integrating this information with the already known BRD4 role in gene expression regulation, we propose a “common” model to explain BRD4 genomic function. Furthermore, in light of the transversal function of BRD4, we provide new interpretation for the cytotoxic activity of BETi and we discuss new possibilities for a wide and focused employment of these drugs in clinical settings.

Implications of nestin in breast cancer pathogenesis (Review)

The aim of the present review was to summarize the current knowledge of the involvement of nestin in breast cancer (BC) pathogenesis. Nestin is a member of the class VI family of intermediate filament proteins, originally identified as a marker of neural stem cells and subsequently demonstrated to be expressed in BC and other cancer types. In normal breast tissue, nestin is expressed in the basal/myoepithelial cells of the mammary gland. In BC, nestin identifies basal-like tumours and predicts aggressive behaviour and poor prognosis. Nestin expression has also been detected in BC stem cells and newly-formed tumour vessels, being a factor in promoting invasion and metastasis. The present review provides an up-to-date overview of the involvement of nestin in processes facilitating BC pathogenesis and progression.

Emerging therapeutic modalities of PARP inhibitors in breast cancer

Inhibition of Poly (ADP-ribose) polymerase (PARP) has shown marked benefit for breast cancer with homologous recombination deficiency, whether driven by defects in BRCA1, BRCA2, or other pathway components. Since the initial approval of olaparib, a mostly investigated PARP inhibitor (PARPi), the clinical development of PARPi in breast cancer treatment has been a major emphasis. Researches in investigating platinum-PARPi combination use compared with platinum monotherapy demonstrated promising benefit in metastatic BRCA mutated breast cancer or TNBC, while no such superiority was observed in the neoadjuvant setting of TNBC. Moreover, the utility of PARP inhibition in BRCA1/2 mutated breast cancer with different platinum-free interval was investigated. There was a clear association between clinical benefit with PARPi and platinum sensitivity, whereas partial efficacy of PARPi still occurs in platinum-resistant patients. In addition, proof-of-principle studies of immunotherapy combined with PARPi in breast cancer have obtained promising results, indicating the potential benefit of the combination therapy in patients with breast cancer. These efforts, contributing to maximize the utility of PARPi, may drive a new era of this agent after its first routine use. In this review, we summarized the utility of combining platinum-PARPi in BRCA mutated breast cancer or TNBC compared with platinum monotherapy and provided promising prospects of PARPi as maintenance therapy in breast cancer, as well as providing a strong rationale for testing immunotherapy combined with PARPi in breast cancer to expand the clinical utility of PARPi.