Cells redox environment modulates BRCA1 expression and DNA homologous recombination repair

NADPH Oxidases: From Molecular Mechanisms to Current Inhibitors

NADPH oxidases (NOXs) form a family of electron-transporting membrane enzymes whose main function is reactive oxygen species (ROS) generation. Strong evidence suggests that ROS produced by NOX enzymes are major contributors to oxidative damage under pathologic conditions. Therefore, blocking the undesirable actions of these enzymes is a therapeutic strategy for treating various pathological disorders, such as cardiovascular diseases, inflammation, and cancer. To date, identification of selective NOX inhibitors is quite challenging, precluding a pharmacologic demonstration of NOX as therapeutic targets in vivo. The aim of this Perspective is to furnish an updated outlook about the small-molecule NOX inhibitors described over the last two decades. Structures, activities, and in vitro/in vivo specificity are discussed, as well as the main biological assays used.

Distribution of copy number variations and rearrangement endpoints in human cancers with a review of literature

Copy number variations (CNVs) which include deletions, duplications, inversions, translocations, and other forms of chromosomal re-arrangements are common to human cancers. In this report we investigated the pattern of these variations with the goal of understanding whether there exist specific cancer signatures. We used re-arrangement endpoint data deposited on the Catalogue of Somatic Mutations in Cancers (COSMIC) for our analysis. Indeed, we find that human cancers are characterized by specific patterns of chromosome rearrangements endpoints which in turn result in cancer specific CNVs. A review of the literature reveals tissue specific mutations which either drive these CNVs or appear as a consequence of CNVs because they confer an advantage to the cancer cell. We also identify several rearrangement endpoints hotspots that were not previously reported. Our analysis suggests that in addition to local chromosomal architecture, CNVs are driven by the internal cellular or nuclear physiology of each cancer tissue.

Novel mechanisms in alcohol neurodevelopmental disorders via BRCA1 depletion and BRCA1-dependent NADPH oxidase regulation

The breast cancer 1 protein (BRCA1) facilitates DNA repair, preventing embryolethality and protecting the fetus from reactive oxygen species (ROS)-induced developmental disorders mediated by oxidatively damaged DNA. Alcohol (ethanol, EtOH) exposure during pregnancy causes fetal alcohol spectrum disorders (FASD), characterized by aberrant behaviour and enhanced ROS formation and proteasomal protein degradation. Herein, ROS-producing NADPH oxidase (NOX) activity was higher in Brca1 +/- vs. +/+ fetal and adult brains, and further enhanced by a single EtOH exposure. EtOH also enhanced catalase and proteasomal activities, while conversely reducing BRCA1 protein levels without affecting Brca1 gene expression. EtOH-initiated adaptive postnatal freezing behaviour was lost in Brca1 +/- progeny. Pretreatment with the free radical spin trap and ROS inhibitor phenylbutylnitrone blocked all EtOH effects, suggesting ROS-dependent mechanisms. This is the first in vivo evidence of NOX regulation by BRCA1, and of EtOH-induced, ROS-mediated depletion of BRCA1, revealing novel mechanisms of BRCA1 protection in FASD.

Estrogen enhances the cytotoxicity of PARP inhibitors on breast cancer cells through stimulating nitric oxide production

Inhibition of Poly(ADP-ribose) polymerase (PARP) is effective for breast cancer susceptibility genes 1 (BRCA1)-deficient breast cancers. Although hormones play critical roles on the occurrence as well as being used in conventional therapies of breast cancer, their impacts on PARP-targeted therapy have been poorly addressed. Here, we showed that addition of estrogen could enhance the cytotoxicity of PARP inhibitors on estrogen receptor (ER)-positive breast cancer cells, causing significant suppression of cell growth. Further analysis revealed that the impact was due to estrogen's stimulating the production of nitric oxide (NO), which could be abrogated when blocking NO formation. Moreover, the effect of estrogen can be resembled by two exogenous nitric oxide donors (SNAP and GSNO). Using ER-negative cell line MDA-MB231, estrogen could not enhance the cell killing of PARP inhibitors any more, but addition of NO donors re-established the enhancing effects. The increased NO level led to accumulation of DNA double strand breaks (DSBs) based on the formation of H2AX foci. Consistent with earlier studies, we demonstrated that NO suppressed the expression of BRCA1, a key player involved in DSB recombination repair. Taken together, these data reveal an important role of estrogen on the treatment of PARP inhibitors, which may affect its clinical treatment and should be considered in precision therapies for ER-positive and negative cancers.

Molecular insights of NADPH oxidases and its pathological consequences

Reactive oxygen species (ROS), formed by the partial reduction of oxygen, were for a long time considered to be a byproduct of cellular metabolism. Since, increase in cellular levels of ROS results in oxidative stress leading to damage of nucleic acids, proteins, and lipids resulting in numerous pathological conditions; ROS was considered a bane for aerobic species. Hence, the discovery of NADPH oxidases (NOX), an enzyme family that specifically generates ROS as its prime product came as a surprise to redox biologists. NOX family proteins participate in various cellular functions including cell proliferation and differentiation, regulation of genes and protein expression, apoptosis, and host defence immunological response. Balanced expression and activation of NOX with subsequent production of ROS are critically important to regulate various genes and proteins to maintain homeostasis of the cell. However, dysregulation of NOX activation leading to enhanced ROS levels is associated with various pathophysiologies including diabetes, cardiovascular diseases, neurodegenerative diseases, ageing, atherosclerosis, and cancer. Although our current knowledge on NOX signifies its importance in the normal functioning of various cellular pathways; yet the choice of ROS producing enzymes which can tip the scale from homeostasis toward damage, as mediators of biological functions remain an oddity. Though the role of NOX in maintaining normal cellular functions is now deemed essential, yet its dysregulation leading to catastrophic events cannot be denied. Hence, this review focuses on the involvement of NOX enzymes in various pathological conditions imploring them as possible targets for therapies. SIGNIFICANCE OF THE STUDY: The NOXs are multi-subunit enzymes that generate ROS as a prime product. NOX generated ROS are usually regulated by various molecular factors and play a vital role in different physiological processes. The dysregulation of NOX activity is associated with pathological consequences. Recently, the dynamic proximity of NOX enzymes with different molecular signatures of pathologies has been studied extensively. It is essential to identify the precise role of NOX machinery in its niche during the progression of pathology. Although inhibition of NOX could be a promising approach for therapeutic interventions, it is critical to expand the current understanding of NOX's dynamicity and shed light on their molecular partners and regulators.

Clinical potential of ATM inhibitors

The protein defective in the human genetic disorder ataxia-telangiectasia, ATM, plays a central role in responding to DNA double strand breaks and other lesions to protect the genome against DNA damage and in this way minimize the risk of mutations that can lead to abnormal cellular behaviour. Its function in normal cells is to protect the cell against genotoxic stress but inadvertently it can assist cancer cells by providing resistance against chemotherapeutic agents and thus favouring tumour growth and survival. However, it is now evident that ATM also functions in a DNA damage-independent fashion to protect the cell against other forms of stress such as oxidative and nutrient stress and this non-canonical mechanism may also be relevant to cancer susceptibility in individuals who lack a functional ATM gene. Thus the use of ATM inhibitors to combat resistance in tumours may extend beyond a role for this protein in the DNA damage response. Here, we provide some background on ATM and its activation and investigate the efficacy of ATM inhibitors in treating cancer.

Slowly Repaired Bulky DNA Damages Modulate Cellular Redox Environment Leading to Premature Senescence

Treatments on neoplastic diseases and cancer using genotoxic drugs often cause long-term health problems related to premature aging. The underlying mechanism is poorly understood. Based on the study of a long-lasting senescence-like growth arrest (10-12 weeks) of human dermal fibroblasts induced by psoralen plus UVA (PUVA) treatment, we here revealed that slowly repaired bulky DNA damages can serve as a “molecular scar” leading to reduced cell proliferation through persistent endogenous production of reactive oxygen species (ROS) that caused accelerated telomere erosion. The elevated levels of ROS were the results of mitochondrial dysfunction and the activation of NADPH oxidase (NOX). A combined inhibition of DNA-PK and PARP1 could suppress the level of ROS. Together with a reduced expression level of BRCA1 as well as the upregulation of PP2A and 53BP1, these data suggest that the NHEJ repair of DNA double-strand breaks may be the initial trigger of metabolic changes leading to ROS production. Further study showed that stimulation of the pentose phosphate pathway played an important role for NOX activation, and ROS could be efficiently suppressed by modulating the NADP/NADPH ratio. Interestingly, feeding cells with ribose-5-phosphate, a precursor for nucleotide biosynthesis that produced through the PPP, could evidently suppress the ROS level and prevent the cell enlargement related to mitochondrial biogenesis. Taken together, these results revealed an important signaling pathway between DNA damage repair and the cell metabolism, which contributed to the premature aging effects of PUVA, and may be generally applicable for a large category of chemotherapeutic reagents including many cancer drugs.

Nitric oxide-donor/PARP-inhibitor combination: A new approach for sensitization to ionizing radiation

Recently, clinical development of PARP inhibitors (PARPi) expanded from using them as a single agent to combining them with DNA-damaging therapy to derive additional therapeutic benefit from stimulated DNA damage. Furthermore, inhibiting PARP in cancers with BRCA1/2 mutations has been shown to be an effective synthetic lethality approach either as a single agent or in combination with the different DNA damaging agents: chemotherapy or ionizing radiation (IR). However, inherited BRCA1/2 mutations account only for 5–10% of breast cancers, 10–15% of ovarian cancers, and lesser for the other cancers. Hence, for most of the cancer patients with BRCA1/2-proficient tumors, sensitization to DNA-damaging agents with PARPi is significantly less effective. We recently demonstrated that moderate, non-toxic concentrations of NO-donors inhibited BRCA1 expression, with subsequent inhibition of error-free HRR and increase of error-prone non-homologous end joining (NHEJ). We also demonstrated that the effect of NO-dependent block of BRCA1 expression can only be achieved in the presence of oxidative stress, a condition that characterizes the tumor microenvironment and is also a potential effect of IR. Hence, NO-donors in combination with PARPi, with effects limited by tumor microenvironment and irradiated area, suggest a precise tumor-targeted approach for radio-sensitization of BRCA1/2-proficient tumors. The combination with NO-donors allows PARPi to be successfully applied to a wider variety of tumors. The present work demonstrates a new drug combination (NO-donors and PARP-inhibitors) which demonstrated a high potency in sensitization of wide variety of tumors to ionizing radiation treatment.

Yulangsan polysaccharide inhibits 4T1 breast cancer cell proliferation and induces apoptosis in vitro and in vivo

Yulangsan polysaccharide (YLSPS) is derived from the root of Millettia pulchra (Benth.) Kurz var. Recent studies have postulated YLSPS as a regimen for cancer treatment. However, the underlying mechanism anti-breast cancer is still poorly unknown. The aim of this study was to examine the suppressive and apoptosis effect of YLSPS on the growth of breast cancer cell 4T1 and its possible underlying mechanism. In this study, breast cancer cell 4T1 viability and apoptosis were assessed by CCK-8 and flow cytometry, relative quantitative real-time PCR and western blot after treated with drug-serum of YLSPS. Furthermore, therapy experiments were conducted using a Balb/c mouse transplanted tumor model of breast cancer. The number of apoptotic cells and microvascular density (MVD) in the tumor tissues were assessed by TUNEL and CD34 immunostaining. Immunohistochemical assays and ELISA were used to detect the expression of VEGF, Bcl-2, Bax and Caspase-3 in the tissues. The in vitro studies showed that the drug-serum of YLSPS significantly inhibition of proliferation and effectively induced apoptosis of 4T1 cells. Oral administration of YLSPS in the breast cancer models significantly reduced the tumor volume and weight. The enhanced antitumor efficacy was associated with decreased angiogenesis, an enhanced antioxidant capacity, an increased induction of apoptosis and an inhibition of lung metastasis. These findings indicate that YLSPS significantly inhibited mouse breast cancer growth in vitro and in vivo. These data suggest that YLSPS may serve as a potential therapeutic agent for breast cancer.

NO control of mitochondrial function in normal and transformed cells

Nitric oxide (NO) is a signaling molecule with multiple facets and involved in numerous pathological process, including cancer. Among the different pathways where NO has a functionally relevant participation, is the control of mitochondrial respiration and biogenesis. NO is able to inhibit the electron transport chain, mainly at Complex IV, regulating oxygen consumption and ATP generation, but at the same time, can also induce increase in reactive oxygen and nitrogen species. The presence of reactive species can induce oxidative damage or participate in redox signaling. In this review, we discuss how NO affects mitochondrial respiration and mitochondrial biogenesis, and how it influences the development of mitochondrial deficiency and cancer. This article is part of a Special Issue entitled Mitochondria in Cancer, edited by Giuseppe Gasparre, Rodrigue Rossignol and Pierre Sonveaux.

Repair of DNA Double-Strand Breaks in Heterochromatin

DNA double-strand breaks (DSBs) are among the most damaging lesions in DNA, since, if not identified and repaired, they can lead to insertions, deletions or chromosomal rearrangements. DSBs can be in the form of simple or complex breaks, and may be repaired by one of a number of processes, the nature of which depends on the complexity of the break or the position of the break within the chromatin. In eukaryotic cells, nuclear DNA is maintained as either euchromatin (EC) which is loosely packed, or in a denser form, much of which is heterochromatin (HC). Due to the less accessible nature of the DNA in HC as compared to that in EC, repair of damage in HC is not as straightforward as repair in EC. Here we review the literature on how cells deal with DSBs in HC.