Ouabain, a cardiac glycoside, inhibits the Fanconi anemia/BRCA pathway activated by DNA interstrand cross-linking agents

A Novel 3D High-Throughput Phenotypic Drug Screening Pipeline to Identify Drugs with Repurposing Potential for the Treatment of Ovarian Cancer

Ovarian cancer (OC) poses a significant clinical challenge due to its high recurrence rates and resistance to standard therapies, particularly in advanced stages where recurrence is common, and treatment is predominantly palliative. Personalized treatments, while effective in other cancers, remain underutilized in OC due to a lack of reliable biomarkers predicting clinical outcomes. Accordingly, precision medicine approaches are limited, with PARP inhibitors showing efficacy only in specific genetic contexts. Drug repurposing offers a promising, rapidly translatable strategy by leveraging existing pharmacological data to identify new treatments for OC. Patient-derived polyclonal spheroids, isolated from ascites fluid closely mimic the clinical behavior of OC, providing a valuable model for drug testing. Using these spheroids, a high-throughput drug screening pipeline capable of evaluating both cytotoxicity and anti-migratory properties of a diverse drug library, including FDA-approved, investigational, and newly approved compounds is developed. The findings highlight the importance of 3D culture systems, revealing a poor correlation between drug efficacy in traditional 2D models and more clinically relevant 3D spheroids. This approach has expedited the identification of promising candidates, such as rapamycin, which demonstrated limited activity as a monotherapy but synergized effectively with standard treatments like cisplatin and paclitaxel in vitro. In combination with platinum-based therapy, Rapamycin led to significant in vitro cytotoxicity and a marked reduction in tumor burden in a syngeneic in vivo model. This proof-of-concept study underscores the potential of drug repurposing to rapidly advance new treatments into clinical trials for OC, offering renewed hope for patients with advanced disease.

A high-throughput approach to identify BRCA1-downregulating compounds to enhance PARP inhibitor sensitivity

PARP inhibitors (PARPi) are efficacious in BRCA1-null tumors; however, their utility is limited in tumors with functional BRCA1. We hypothesized that pharmacologically reducing BRCA1 protein levels could enhance PARPi effectiveness in BRCA1 wild-type tumors. To identify BRCA1 downregulating agents, we generated reporter cell lines using CRISPR-mediated editing to tag endogenous BRCA1 protein with HiBiT. These reporter lines enable the sensitive measurement of BRCA1 protein levels by luminescence. Validated reporter cells were used in a pilot screen of epigenetic-modifying probes and a larger screen of more than 6,000 compounds. We identified 7 compounds that could downregulate BRCA1-HiBiT expression and synergize with olaparib. Three compounds, N-acetyl-N-acetoxy chlorobenzenesulfonamide (NANAC), A-443654, and CHIR-124, were validated to reduce BRCA1 protein levels and sensitize breast cancer cells to the toxic effects of olaparib. These results suggest that BRCA1-HiBiT reporter cells hold promise in developing agents to improve the clinical utility of PARPi.

The mechanistic role of cardiac glycosides in DNA damage response and repair signaling

Cardiac glycosides (CGs) are a class of bioactive organic compounds well-known for their application in treating heart disease despite a narrow therapeutic window. Considerable evidence has demonstrated the potential to repurpose CGs for cancer treatment. Chemical modification of these CGs has been utilized in attempts to increase their anti-cancer properties; however, this has met limited success as their mechanism of action is still speculative. Recent studies have identified the DNA damage response (DDR) pathway as a target of CGs. DDR serves to coordinate numerous cellular pathways to initiate cell cycle arrest, promote DNA repair, regulate replication fork firing and protection, or induce apoptosis to avoid the survival of cells with DNA damage or cells carrying mutations. Understanding the modus operandi of cardiac glycosides will provide critical information to better address improvements in potency, reduced toxicity, and the potential to overcome drug resistance. This review summarizes recent scientific findings of the molecular mechanisms of cardiac glycosides affecting the DDR signaling pathway in cancer therapeutics from 2010 to 2022. We focus on the structural and functional differences of CGs toward identifying the critical features for DDR targeting of these agents.

Drug repurposing against galectin-3 using simulation-based studies

The protein galectin, which binds to carbohydrates and is involved in a number of therapeutic processes including cell proliferation, inflammatory responses, apoptosis, etc., has been discovered as a potential therapeutic target. Galectin-3 is a stable biomarker that exhibits both increased and decreased expression in a variety of illnesses and infections, regardless of sex, age, or body mass index. The goal of the current study is to apply bioinformatics techniques to examine the possibility of cardiovascular medications to inhibit Galectin-3-related biological activities. Unsupervised clustering techniques, molecular docking, and guided molecular dynamics (MD) simulation were used to create a computational pipeline that was used to screen potential chemical compounds from a library of chemical compounds with related molecular fingerprints. Utilizing input factors such as gene expression, mode of action, and chemical descriptors, clustering enables prioritization of medicinal molecules. Twenty-four compounds were screened and repurposed against Galectin-3 utilizing molecular docking as part of the cluster-facilitated virtual screening technique. The polar interactions that Arg144, Glu184, Arg162, His158, and Asn174 have with Bufalin, Cymarin, and Ouabalin have the highest binding affinities, according to docking studies. Studies using MD simulations confirm the tested compounds' ability to inhibit Galectin-3. Galactin-3 targeted experimental and in vivo animal model-based validation studies using Bufalin, Cymarin, and Ouabalin are also necessary.Communicated by Ramaswamy H. Sarma.

Cardiac glycoside neriifolin exerts anti-cancer activity in prostate cancer cells by attenuating DNA damage repair through endoplasmic reticulum stress

Prostate cancer (PCa) is one of the most common cancers in men. Patients with recurrent disease initially respond to androgen-deprivation therapy, but the tumor eventually progresses into castration-resistant PCa. Thus, new therapeutic approaches for PCa resistance to current treatments are urgently needed. Here, we report that cardiac glycoside neriifolin suppresses the malignancy of cancer cells via increasing DNA damage and apoptosis through activation of endoplasmic reticulum stress (ERS) in prostate cancers. We found that cardiac glycoside neriifolin markedly inhibited the cell growth and induced apoptosis in prostate cancer cells. Transcriptome sequence analysis revealed that neriifolin significantly induced DNA damage and double strand breaks (DSBs), validated with attenuation expression of genes in DSBs repair and increasing phosphorylated histone H2AX (γ-H2AX) foci formation, a quantitative marker of DSBs. Moreover, we found that neriifolin also activated ERS, evidenced by upregulation and activation of ERS related proteins, including eukaryotic initiation factor 2α (eIF2α), protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK) and C/EBP homologous protein (CHOP) as well as downregulation of CCAATenhancerbinding protein alpha (C/EBP-α), a transcriptional factor that forms heterodimers with CHOP. In addition, neriifolin treatment dramatically inhibited the by tumor growth, which were reversed by CHOP loss or overexpression of C/EBP-α in nude mice. Mechanistically, neriifolin suppressed the tumor growth by increasing DNA damage and apoptosis through CHOP-C/EBP-α signaling axis of ERS in prostate cancers. Taken together, these results suggest that cardiac glycoside neriifolin may be a potential tumor-specific chemotherapeutic agent in prostate cancer treatment.

The botanical drug PBI-05204, a supercritical CO2 extract of Nerium oleander, sensitizes alveolar and embryonal rhabdomyosarcoma to radiotherapy in vitro and in vivo

Treatment of rhabdomyosarcoma (RMS), the most common a soft tissue sarcoma in childhood, provides intensive multimodal therapy, with radiotherapy (RT) playing a critical role for local tumor control. However, since RMS efficiently activates mechanisms of resistance to therapies, despite improvements, the prognosis remains still largely unsatisfactory, mainly in RMS expressing chimeric oncoproteins PAX3/PAX7-FOXO1, and fusion-positive (FP)-RMS. Cardiac glycosides (CGs), plant-derived steroid-like compounds with a selective inhibitory activity of the Na+/K+-ATPase pump (NKA), have shown antitumor and radio-sensitizing properties. Herein, the therapeutic properties of PBI-05204, an extract from Nerium oleander containing the CG oleandrin already studied in phase I and II clinical trials for cancer patients, were investigated, in vitro and in vivo, against FN- and FP-RMS cancer models. PBI-05204 induced growth arrest in a concentration dependent manner, with FP-RMS being more sensitive than FN-RMS, by differently regulating cell cycle regulators and commonly upregulating cell cycle inhibitors p21Waf1/Cip1 and p27Cip1/Kip1. Furthermore, PBI-05204 concomitantly induced cell death on both RMS types and senescence in FN-RMS. Notably, PBI-05204 counteracted in vitro migration and invasion abilities and suppressed the formation of spheroids enriched in CD133+ cancer stem cells (CSCs). PBI-05204 sensitized both cell types to RT by improving the ability of RT to induce G2 growth arrest and counteracting the RT-induced activation of both Non‐Homologous End‐Joining and homologous recombination DSBs repair pathways. Finally, the antitumor and radio-sensitizing proprieties of PBI-05204 were confirmed in vivo. Notably, both in vitro and in vivo evidence confirmed the higher sensitivity to PBI-05204 of FP-RMS. Thus, PBI-05204 represents a valid radio-sensitizing agent for the treatment of RMS, including the intrinsically radio-resistant FP-RMS.

Procyanidin C1 from Viola odorata L. inhibits Na+,K+-ATPase

Members of the Viola genus play important roles in traditional Asian herbal medicine. This study investigates the ability of Viola odorata L. extracts to inhibit Na⁺,K⁺-ATPase, an essential animal enzyme responsible for membrane potential maintenance. The root extract of V. odorata strongly inhibited Na⁺,K⁺-ATPase, while leaf and seeds extracts were basically inactive. A UHPLC-QTOF-MS/MS metabolomic approach was used to identify the chemical principle of the root extract’s activity, resulting in the detection of 35,292 features. Candidate active compounds were selected by correlating feature area with inhibitory activity in 14 isolated fractions. This yielded a set of 15 candidate compounds, of which 14 were preliminarily identified as procyanidins. Commercially available procyanidins (B1, B2, B3 and C1) were therefore purchased and their ability to inhibit Na⁺,K⁺-ATPase was investigated. Dimeric procyanidins B1, B2 and B3 were found to be inactive, but the trimeric procyanidin C1 strongly inhibited Na⁺,K⁺-ATPase with an IC₅₀ of 4.5 µM. This newly discovered inhibitor was docked into crystal structures mimicking the Na₃E₁∼P·ADP and K₂E₂·P_i states to identify potential interaction sites within Na⁺,K⁺-ATPase. Possible binding mechanisms and the principle responsible for the observed root extract activity are discussed.

Cardiac Glycoside Ouabain Exerts Anticancer Activity via Downregulation of STAT3

Cardiac glycosides are plant-derived steroid-like compounds which have been used for the treatment of cardiovascular diseases. Ouabain, a cardiotonic steroid and specific Na⁺/K⁺-ATPase inhibitor, has been rediscovered for its potential use in the treatment of cancer. However, the cellular targets and anticancer mechanism of ouabain in various cancers remain largely unexplored. In this study, we confirmed the cytotoxic effects of ouabain on several cancer cell lines. Further examination revealed the increase of apoptosis, intracellular ROS generation and DNA double-strand breaks induced by ouabain treatment. Besides, ouabain effectively suppressed STAT3 expression as well as phosphorylation in addition to block STAT3-mediated transcription and downstream target proteins. Interestingly, these inhibitory activities seemed to be independent of the Na⁺/K⁺-ATPase. Furthermore, we found that ouabain inhibited protein synthesis through regulation of the eukaryotic initiation factor 4E (eIF4E) and eIF4E binding protein 1 (4EBP1). Taken together, our study provided a novel molecular insight of anticancer activities of ouabain in human cancer cells, which could raise the hope of using cardiac glycosides for cancer therapeutics more rational.

Ouabain and Digoxin Activate the Proteasome and the Degradation of the ERα in Cells Modeling Primary and Metastatic Breast Cancer

Simple Summary

Breast cancer (BC) treatment relies on the detection of the estrogen receptor α (ERα). ERα-expressing BC patients are treated with anti-estrogen drugs (i.e., tamoxifen and fulvestrant). Despite their proven efficacy, these drugs cause serious side effects in a significant fraction of the patients, including both tumor insurgence in secondary organs, and resistant phenotypes, which result in a relapsing disease with scarce treatment options. Thus, new drugs for treatment of primary and metastatic BC (MBC) are needed. Here, we report the characterization of two cardiac glycosides (CGs) (i.e., ouabain and digoxin), approved by the FDA for treatment of heart disease, as novel ‘anti-estrogen’-like drugs. We found that these drugs induce ERα degradation, and prevent the proliferation of cellular models of primary and metastatic BC cells. Remarkably, we discovered that these CGs are activators of the proteasome, and therefore may be repurposed for treatment not only of BC, but also for other proteasome-based diseases.

Abstract

Estrogen receptor α expressing breast cancers (BC) are classically treated with endocrine therapy. Prolonged endocrine therapy often results in a metastatic disease (MBC), for which a standardized effective therapy is still lacking. Thus, new drugs are required for primary and metastatic BC treatment. Here, we report that the Food and Drug Administration (FDA)-approved drugs, ouabain and digoxin, induce ERα degradation and prevent proliferation in cells modeling primary and metastatic BC. Ouabain and digoxin activate the cellular proteasome, instigating ERα degradation, which causes the inhibition of 17β-estradiol signaling, induces the cell cycle blockade in the G2 phase, and triggers apoptosis. Remarkably, these effects are independent of the inhibition of the Na/K pump. The antiproliferative effects of ouabain and digoxin occur also in diverse cancer models (i.e., tumor spheroids and xenografts). Additionally, gene profiling analysis reveals that these drugs downregulate the expression of genes related to endocrine therapy resistance. Therefore, ouabain and digoxin behave as ‘anti-estrogen’-like drugs, and are appealing candidates for the treatment of primary and metastatic BCs.

Inhibitors of the Fanconi anaemia pathway as potential antitumour agents for ovarian cancer

The Fanconi anaemia (FA) pathway is an important mechanism for cellular DNA damage repair, which functions to remove toxic DNA interstrand crosslinks. This is particularly relevant in the context of ovarian and other cancers which rely extensively on interstrand cross-link generating platinum chemotherapy as standard of care treatment. These cancers often respond well to initial treatment, but reoccur with resistant disease and upregulation of DNA damage repair pathways. The FA pathway is therefore of great interest as a target for therapies that aim to improve the efficacy of platinum chemotherapies, and reverse tumour resistance to these. In this review, we discuss recent advances in understanding the mechanism of interstrand cross-link repair by the FA pathway, and the potential of the component parts as targets for therapeutic agents. We then focus on the current state of play of inhibitor development, covering both the characterisation of broad spectrum inhibitors and high throughput screening approaches to identify novel small molecule inhibitors. We also consider synthetic lethality between the FA pathway and other DNA damage repair pathways as a therapeutic approach.

Ouabain induces apoptotic cell death in human prostate DU 145 cancer cells through DNA damage and TRAIL pathways

Ouabain, a cardiotonic steroid and specific Na⁺ /K⁺ -ATPase inhibitor, has a potential to induce cancer cell apoptosis but the mechanisms of apoptosis induced by ouabain are not fully understand. The aim of this study was to investigate the cytotoxic effects of ouabain on human prostate cancer DU 145 cells in vitro. Cell morphological changes were examined by phase contrast microscopy. Cell viability, cell cycle distribution, cell apoptosis, DNA damage, the production of ROS and Ca²⁺ , and mitochondrial membrane potential (ΔΨ_m ) were measured by flow cytometry assay. Results indicated that ouabain induced cell morphological changes, decreased total cell viability, induced G0/G1 phase arrest, DNA damage, and cell apoptosis, increased ROS and Ca²⁺ production, but decreased the levels of ΔΨ_m in DU 145 cells. Ouabain also increased the activities of caspase-3, -8, and -9. Western blotting was used for measuring the alterations of apoptosis-associated protein expressions in DU 145 cells and results indicated that ouabain increased the expression of DNA damage associated proteins (pATM^Ser1981 , p-H2A.X^Ser139 , and p-p53^Ser15 ) and ER-stress-associated proteins (Grp78, ATF6β, p-PERK^Thr981 , PERK, eIF2A, GADD153, CaMKIIβ, and caspase-4) in time-dependently. Furthermore, ouabain increased apoptosis-associated proteins (DR4, DR5, Fas, Fas Ligand, and FADD), TRAIL pathway, which related to extrinsic pathway, promoted the pro-apoptotic protein Bax, increased apoptotic-associated proteins, such as cytochrome c, AIF, Endo G, caspase-3, -8, and -9, but reduced anti-apoptotic protein Bcl-2 and Bcl-x in DU 145 cells. In conclusion, we may suggest that ouabain decreased cell viability and induced apoptotic cell death may via caspase-dependent and mitochondria-dependent pathways in human prostate cancer DU 145 cells.

Effects of Sepantronium Bromide (YM-155) on the Whole Transcriptome of MDA-MB-231 Cells: Highlight on Impaired ATR/ATM Fanconi Anemia DNA Damage Response

Sepantronium bromide (YM-155) is believed to elicit apoptosis and mitotic arrest in tumor cells by reducing (BIRC5, survivin) mRNA. In this study, we monitored changes in survivin mRNA and protein after treating MDA-MB-231 cells with YM-155 concurrent with evaluation of whole transcriptomic (WT) mRNA and long intergenic non-coding RNA at 2 time points: 8 h sub-lethal (83 ng/mL) and 20 h at the LC50 (14.6 ng/mL). The data show a tight association between cell death and the precipitating loss of survivin protein and mRNA (-2.67 fold-change (FC), p<0.001) at 20 h, questioning if the decline in survivin is attributed to cell death or drug impact. The meager loss of survivin mRNA was overshadowed by enormous differential change to the WT in both magnitude and significance for over 2000 differentially up/down-regulated transcripts: (+22 FC to -12 FC, p<0.001). The data show YM-155 to up-regulate transcripts in control of circadian rhythm (NOCT, PER, BHLHe40, NFIL3), tumor suppression (SIK1, FOSB), histone methylation (KDM6B) and negative feedback of NF-kappa B signaling (TNFAIP3). Down-regulated transcripts by YM-155 include glucuronidase (GUSBP3), numerous micro-RNAs, DNA damage repair elements (CENPI, POLQ, RAD54B) and the most affected system was the ataxia-telangiectasia mutated (ATM)/Fanconi anemia E3 monoubiquitin ligase core complexes (FANC transcripts - A/B/E/F/G/M), FANC2, FANCI, BRCA1, BRCA2, RAD51, PALB2 gene and ATR (ATM- and Rad3-Related) pathway. In conclusion, these findings suggest that a primary target of YM-155 is the loss of replicative DNA repair systems.

A systems biology approach for elucidating the interaction of curcumin with Fanconi anemia FANC G protein and the key disease targets of leukemia

Fanconi anemia (FA) is an autosomal recessive disorder with a high risk of malignancies including acute myeloid leukemia and squamous cell carcinoma. There is a constant search out of new potential therapeutic molecule to combat this disorder. In most cases, patients with FA develop haematological malignancies with acute myeloid leukemia and acute lymphoblastic leukemia. Identifying drugs which can efficiently block the pathways of both these disorders can be an ideal and novel strategy to treat FA. The curcumin, a natural compound obtained from turmeric is an interesting therapeutic molecule as it has been reported in the literature to combat both FA as well as leukemia. However, its complete mechanism is not elucidated. Herein, a systems biology approach for elucidating the therapeutic potential of curcumin against FA and leukemia is investigated by analyzing the computational molecular interactions of curcumin ligand with FANC G of FA and seven other key disease targets of leukemia. The proteins namely DOT1L, farnesyl transferase (FDPS), histone decetylase (EP3000), Polo-like kinase (PLK-2), aurora-like kinase (AUKRB), tyrosine kinase (ABL1), and retinoic acid receptor alpha (RARA) were chosen as disease targets for leukemia and modeled structure of FANC G protein as the disease target for FA. The docking investigations showed that curcumin had a very high binding affinity of -8.1 kcal/mol with FANC G protein. The key disease targets of leukemia namely tyrosine kinase (ABL1), aurora-like kinase (AUKRB), and polo-like kinase (PLK-2) showed that they had the comparable binding affinities of -9.7 k cal/mol, -8.7 k cal/mol, and -8.6 k cal/mol, respectively with curcumin. Further, the percentage similarity scores obtained from PAM50 using EMBOSS MATCHER was shown to provide a clue to understand the structural relationships to an extent and to predict the binding affinity. This investigation shows that curcumin effectively interacts with the disease targets of both FA and leukemia.

FANCD2 re-expression is associated with glioma grade and chemical inhibition of the Fanconi Anaemia pathway sensitises gliomas to chemotherapeutic agents

Brain tumours kill more children and adults under 40 than any other cancer. Around half of primary brain tumours are glioblastoma multiforme (GBMs) where treatment remains a significant challenge. GBM survival rates have improved little over the last 40 years, thus highlighting an unmet need for the identification/development of novel therapeutic targets and agents to improve GBM treatment. Using archived and fresh glioma tissue, we show that in contrast to normal brain or benign schwannomas GBMs exhibit re-expression of FANCD2, a key protein of the Fanconi Anaemia (FA) DNA repair pathway, and possess an active FA pathway. Importantly, FANCD2 expression levels are strongly associated with tumour grade, revealing a potential exploitable therapeutic window to allow inhibition of the FA pathway in tumour cells, whilst sparing normal brain tissue. Using several small molecule inhibitors of the FA pathway in combination with isogenic FA-proficient/deficient glioma cell lines as well as primary GBM cultures, we demonstrate that inhibition of the FA pathway sensitises gliomas to the chemotherapeutic agents Temozolomide and Carmustine. Our findings therefore provide a strong rationale for the development of novel and potent inhibitors of the FA pathway to improve the treatment of GBMs, which may ultimately impact on patient outcome.

Digoxin use and the risk for colorectal cancer

PURPOSE

Cardiac glycosides affect several pathways central for tumor formation. We sought to evaluate the association between digoxin use and colorectal cancer (CRC) risk.

METHODS

We conducted a nested case-control study using The Health Improvement Network (THIN), a medical record database representative of the broader UK population. Study cases were defined as those with a diagnostic code for CRC. Each case was matched to up to four eligible controls on age, sex, practice site, and duration of follow-up before index date using incidence density sampling. Exposure of interest was digoxin therapy before index date. The odds ratios (ORs) and 95% confidence intervals (CIs) for CRC associated with digoxin use were estimated using conditional logistic regression analysis, adjusted for BMI, alcoholism, smoking history, diabetes mellitus, heart disease, chronic NSAIDs use and previous screening colonoscopies.

RESULTS

The case-control analysis included 20 990 CRC patients and 82 054 controls whose mean follow-up time before index date was 6.5 years (SD 4.0). The adjusted OR for CRC among current digoxin users was increased compared with non-users with an adjusted ORs of 1.41 (95%CI 1.25-1.59, p < 0.0001), 1.45 (95%CI 1.22-1.72, p < 0.0001) and 1.41 (95%CI 1.00-1.99, p = 0.049) for first prescriptions 1-5 years, 5-10 years and more than 10 years before index date respectively. Similar results were observed when cumulative duration and number of digoxin prescriptions were analyzed. The risk was not elevated for past digoxin users.

CONCLUSIONS

Current digoxin use is associated with increased CRC risk.

Elaeodendron orientale as a source of cytotoxic cardenolides

In the present study, we report six cardiac glycosides (1-6) along with four known ones (7-10) isolated from the leaves and fruits of Elaeodendron orientale. Their stereostructures were elucidated on the basis of spectroscopic analysis, including 1D and 2D NMR, and the absolute configuration of 1 was determined by X-ray diffraction analysis. The compounds were evaluated for growth inhibitory activity against a panel of human cancer cell lines, HeLa, A-549, MCF-7 and HL-60, and normal Vero cells. Four compounds from this series (5 and 7-9, IC50 values ranging from 0.01 to 0.07μM) exhibited cytotoxicity against three of the cancer cell lines assayed that was similar to or higher than the well-known therapies digoxin and digitoxigenin. Taking into account the narrow safety range of cardiac glycosides used in clinic, this series shows a selectivity index higher than 3 for three of the cancer cell lines assayed, increasing their interest for further study.

The Fanconi anemia/BRCA pathway is involved in DNA interstrand cross-link repair of adriamycin-resistant leukemia cells

The Fanconi anemia/BRCA (FA/BRCA) pathway plays a vital role in DNA damage repair induced by DNA cross-linking agents and is closely related to drug response in cancer treatment. Here we demonstrate that the FA/BRCA pathway contributes to acquired drug resistance in adriamycin (ADR)-resistant leukemia cell lines, and disruption of this pathway partially reverses the drug resistance. We observed that ADR-resistant cells have reduced DNA interstrand cross-links (ICL) compared with ADR-sensitive cells. Western blot studies demonstrated enhanced FA protein expression in ADR-resistant cells. Using siRNA to knock down FANCF in K562/R drug-resistant cells showed increases in sensitivity to ADR and ADR-induced DNA damage, and demonstrated a direct relationship between the FA/BRCA pathway and drug sensitivity. Overexpression of FANCF in K562 drug-sensitive cells partially reproduced the drug-resistant phenotype. These results show that the FA/BRCA pathway is involved in acquired ADR resistance of leukemia cells. The FA/BRCA pathway may be a new target to reverse ADR resistance in leukemia treatment.

Damaged mitochondria in Fanconi anemia - an isolated event or a general phenomenon?

Fanconi anemia (FA) is known as an inherited bone marrow failure syndrome associated with cancer predisposition and susceptibility to a number of DNA damaging stimuli, along with a number of clinical features such as upper limb malformations, increased diabetes incidence and typical anomalies in skin pigmentation. The proteins encoded by FA-defective genes (FANC proteins) display well-established roles in DNA damage and repair pathways. Moreover, some independent studies have revealed that mitochondrial dysfunction (MDF) is also involved in FA phenotype. Unconfined to FA, we have shown that other syndromes featuring DNA damage and repair (such as ataxia-telangiectasia, AT, and Werner syndrome, WS) display MDF-related phenotypes, along with oxidative stress (OS) that, altogether, may play major roles in these diseases. Experimental and clinical studies are warranted in the prospect of future therapies to be focused on compounds scavenging reactive oxygen species (ROS) as well as protecting mitochondrial functions.

Targeting homologous recombination-mediated DNA repair in cancer

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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