Topoisomerase poisons: harnessing the dark side of enzyme mechanism

H2AX: A key player in DNA damage response and a promising target for cancer therapy

Cancer is caused by a complex interaction of factors that interrupt the normal growth and division of cells. At the center of this process is the intricate relationship between DNA damage and the cellular mechanisms responsible for maintaining genomic stability. When DNA damage is not repaired, it can cause genetic mutations that contribute to the initiation and progression of cancer. On the other hand, the DNA damage response system, which involves the phosphorylation of the histone variant H2AX (γH2AX), is crucial in preserving genomic integrity by signaling and facilitating the repair of DNA double-strand breaks. This review provides an explanation of the molecular dynamics of H2AX in the context of DNA damage response. It emphasizes the crucial role of H2AX in recruiting and localizing repair machinery at sites of chromatin damage. The review explains how H2AX phosphorylation, facilitated by the master kinases ATM and ATR, acts as a signal for DNA damage, triggering downstream pathways that govern cell cycle checkpoints, apoptosis, and the cellular fate decision between repair and cell death. The phosphorylation of H2AX is a critical regulatory point, ensuring cell survival by promoting repair or steering cells towards apoptosis in cases of catastrophic genomic damage. Moreover, we explore the therapeutic potential of targeting H2AX in cancer treatment, leveraging its dual function as a biomarker of DNA integrity and a therapeutic target. By delineating the pathways that lead to H2AX phosphorylation and its roles in apoptosis and cell cycle control, we highlight the significance of H2AX as both a prognostic tool and a focal point for therapeutic intervention, offering insights into its utility in enhancing the efficacy of cancer treatments.

Identification of potential anti-hyperglycemic compounds in Cordyceps militaris ethyl acetate extract: in vitro and in silico studies

Cordyceps militaris has been long known for valuable health benefits by folk experience and was recently reported with diabetes-tackling evidences, thus deserving extending efforts on screening for component-activity relationship. In this study, experiments were carried out to find the evidence, justification, and input for computations on the potential against diabetes-related protein structures: PDB-4W93, PDB-3W37, and PDB-4A3A. Liquid chromatography identified 14 bioactive compounds in the ethyl acetate extract (1-14) and quantified the contents of cordycepin (0.11%) and adenosine (0.01%). Bioassays revealed the overall potential of the extract against α-amylase (IC50 = 6.443 ± 0.364 mg.mL-1) and α-glucosidase (IC50 = 2.580 ± 0.194 mg.mL-1). A combination of different computational platforms was used to select the most promising candidates for applications as anti-diabetic bio-inhibitors, i.e. 1 (ground state: -888.49715 a.u.; dipole moment 3.779 Debye; DS ¯ -12.3 kcal.mol-1; polarizability 34.7 Å3; logP - 1.30), 10 (ground state: -688.52406 a.u.; dipole moment 5.487 Debye; DS ¯ -12.6 kcal.mol-1; polarizability 24.9 Å3; logP - 3.39), and 12 (ground state: -1460.07276 a.u.; dipole moment 3.976 Debye; DS ¯ -12.5 kcal.mol-1; polarizability 52.4 Å3; logP - 4.39). The results encourage further experimental tests on cordycepin (1), mannitol (10), and adenosylribose (12) to validate their in-practice diabetes-related activities, thus conducive to hypoglycemic applications.Communicated by Ramaswamy H. Sarma.

Combined Treatment of Dendrosomal-Curcumin and Daunorubicin Synergistically Inhibit Cell Proliferation, Migration and Induce Apoptosis in A549 Lung Cancer Cells

Purpose

Chemotherapy drugs used to treat lung cancer are associated with drug resistance and severe side effects. There have been rising demands for new therapeutic candidates and novel approaches, including combination therapy. Here, we aimed to investigate the combinatorial effect of a dendrosomal formulation of curcumin (DNC) and daunorubicin (DNR) on the A549 lung cancer cell line.

Methods

We performed cytotoxicity, apoptosis, cell migration, colony-formation capacity, and gene expression analysis to interpret the mechanism of action for a combination of DNC and DNR on A549 cells.

Results

Our results revealed that the combination of DNC and DNR could synergistically inhibit the A549 cells' growth. This synergistic cytotoxicity was further approved by flow cytometry, migration assessment, colony-forming capacity and gene expression analysis. DNR combination with DNC resulted in increased apoptosis to necrosis ratio compared to DNR alone. In addition, the migration and colony-forming capacity were at the minimal range when DNC was combined with DNR. Combined treatment decreased the expression level of MDR-1, hTERT and Bcl-2 genes significantly. In addition, the ratio of Bax/Bcl2 gene expression significantly increased. Our analysis by free curcumin, dendrosomes and DNC also showed that dendrosomes do not have any significant cytotoxic effect on the A549 cells, suggesting that this carrier has a high potential for enhancing the curcumin's biological effects.

Conclusion

Our observations suggest that the DNC formulation of curcumin synergistically enhances the antineoplastic effect of DNR on the A549 cell line through the modulation of apoptosis/necrosis ratio, as well as Bax/Bcl2 ratio, MDR-1 and hTERT gene expression.

Therapeutic Targeting of DNA Replication Stress in Cancer

This article reviews the currently used therapeutic strategies to target DNA replication stress for cancer treatment in the clinic, highlighting their effectiveness and limitations due to toxicity and drug resistance. Cancer cells experience enhanced spontaneous DNA damage due to compromised DNA replication machinery, elevated levels of reactive oxygen species, loss of tumor suppressor genes, and/or constitutive activation of oncogenes. Consequently, these cells are addicted to DNA damage response signaling pathways and repair machinery to maintain genome stability and support survival and proliferation. Chemotherapeutic drugs exploit this genetic instability by inducing additional DNA damage to overwhelm the repair system in cancer cells. However, the clinical use of DNA-damaging agents is limited by their toxicity and drug resistance often arises. To address these issues, the article discusses a potential strategy to target the cancer-associated isoform of proliferating cell nuclear antigen (caPCNA), which plays a central role in the DNA replication and damage response network. Small molecule and peptide agents that specifically target caPCNA can selectively target cancer cells without significant toxicity to normal cells or experimental animals.

Recent development of multi-targeted inhibitors of human topoisomerase II enzyme as potent cancer therapeutics

Multi-target therapies have been considered one of the viable options to overcome the challenges to eradicate intrinsic and acquired drug-resistant cancer cells. While to increase the efficacy of therapeutics, the use of a single drug against multiple structurally similar sites, which noncommittedly modulate several vital cellular pathways proposed as a potential alternative to a 'single drug single target'. Besides, it reduces the usage of a number of drugs and their side effects. Topoisomerase II enzyme plays a very significant role in DNA replication and thus served as an important target for numerous anti-cancer agents. However, in spite of promising clinical results, in several cases, it was found that cancer cells have developed resistance against the anti-cancer agents targeting this enzyme. Therefore, multi-target therapies have been proposed as an alternative to overcome different drug resistance mechanisms while topoisomerases II are a primary target site. In this review, we have tried to discuss the characteristics of the binding cavity available for interactions of drugs, and potent inhibitors concurrently modulate the functions of topoisomerases II as well as other structurally related target sites. Additionally, the mechanism of drug resistance by considering molecular and cellular insights by including various types of cancers.

Topoisomerases in Immune Cell Development and Function

DNA topoisomerases (TOPs) are complex enzymatic machines with extraordinary capacity to maintain DNA topology during torsion-intensive steps of replication and transcription. Recently, TOPs have gained significant attention for their tissue-specific function, and the vital role of TOPs in immune homeostasis and dysfunction is beginning to emerge. TOPs have been implicated in various immunological disorders such as autoimmunity, B cell immunodeficiencies, and sepsis, underscoring their importance in immune regulation. However, much remains unknown about immunological underpinnings of TOPs, and a deeper understanding of the role of TOPs in the immune system will be critical for yielding significant insights into the etiology of immunological disorders. In this review, we first discuss the recent literature highlighting the contribution of TOPs in the development of immune cells, and we further provide an overview of their importance in immune cell responses.

Inhibition of DNA synthesis and cancer therapies

Cancer is a worldwide problem afflicting 19 million people. Inhibition of DNA synthesis has been a cornerstone of anticancer therapy. A variety of chemotherapy drugs have been developed and many of these are aimed at inhibiting DNA synthesis, as they damage DNA, form DNA adduct and interfere with DNA synthesis. Another type of chemotherapy interferes with the synthesis of nucleotide pools. There are also other types of drugs that inhibit topoisomerases resulting in the interference with DNA replication and transcription. Significant progress has been made regarding radiation therapy that includes X-ray (and γ-ray), proton therapy and heavy ion therapy. The Auger therapy is a type of radiation therapy that differs from X-ray, proton or heavy ion therapy. The method relies on the use of high Z elements such as gadolinium, iodine, gold or silver. Irradiation of these elements results in the release of electrons including the Auger electrons that have strong DNA damaging effect. Tamanoi et al. developed novel nanoparticles containing gadolinium or iodine to place high Z elements at the periphery of the nucleus thus localizing them close to DNA. Irradiation with monochromatic X-ray resulted in the formation of double-strand DNA breaks leading to the destruction of tumor mass. Comparison of conventional X-ray therapy and the Auger therapy is discussed.

DNA damage to β cells in culture recapitulates features of senescent β cells that accumulate in type 1 diabetes

OBJECTIVE

Type 1 Diabetes (T1D) is characterized by progressive loss of insulin-producing pancreatic β cells as a result of autoimmune destruction. In addition to β cell death, recent work has shown that subpopulations of β cells acquire dysfunction during T1D. We previously reported that β cells undergoing a DNA damage response (DDR) and senescence accumulate during the pathogenesis of T1D. However, the question of how senescence develops in β cells has not been investigated.

METHODS

Here, we tested the hypothesis that unrepaired DNA damage in the context of genetic susceptibility triggers β cell senescence using culture models including the mouse NIT1 β cell line derived from the T1D-susceptible nonobese diabetic (NOD) strain, human donor islets and EndoC β cells. DNA damage was chemically induced using etoposide or bleomycin and cells or islets were analyzed by a combination of molecular assays for senescence phenotypes including Western blotting, qRT-PCR, Luminex assays, flow cytometry and histochemical staining. RNA-seq was carried out to profile global transcriptomic changes in human islets undergoing DDR and senescence. Insulin ELISAs were used to quantify glucose-stimulated insulin secretion from chemically-induced senescent human islets, EndoC β cells and mouse β cell lines in culture.

RESULTS

Sub-lethal DNA damage in NIT1 cells led to several classical hallmarks of senescence including sustained DDR activation, growth arrest, enlarged flattened morphology and a senescence-associated secretory phenotype (SASP) resembling what occurs in primary β cells during T1D in NOD mice. These phenotypes differed between NIT1 cells and the MIN6 β cell line derived from a non-T1D susceptible mouse strain. RNA-seq analysis of DNA damage-induced senescence in human islets from two different donors revealed a p53 transcriptional program and upregulation of prosurvival and SASP genes, with inter-donor variability in this response. Inter-donor variability in human islets was also apparent in the extent of persistent DDR activation and SASP at the protein level. Notably, chemically induced DNA damage also led to DDR activation and senescent phenotypes in EndoC-βH5 human β cells, confirming that this response can occur directly in a human β cell line. Finally, DNA damage led to different effects on glucose-stimulated insulin secretion in mouse β cell lines as compared with human islets and EndoC β cells.

CONCLUSIONS

Taken together, these findings suggest that some of the phenotypes of senescent β cells that accumulate during the development of T1D in the NOD mouse and humans can be modeled by chemically induced DNA damage to mouse β cell lines, human islets and EndoC β cells in culture. The differences between β cells from different mouse strains and different human islet donors and EndoC β cells highlights species differences and the role for genetic background in modifying the β cell response to DNA damage and its effects on insulin secretion. These culture models will be useful tools to understand some of the mechanisms of β cell senescence in T1D.

Casticin and chrysosplenol D from Artemisia annua L. induce apoptosis by inhibiting topoisomerase IIα in human non-small-cell lung cancer cells

BACKGROUND

Artemisia annua L. (A. annua) and its active components exhibit antitumour effects in many cancer cells. However, the biological processes and mechanisms involved are not well understood, especially for the treatment of non-small-cell lung cancer (NSCLC).

PURPOSE

This study aimed to comprehensively explore the biological processes of A. annua and its active components in NSCLC cells and to identify the mechanism by which these compounds induce apoptosis.

STUDY DESIGNS/METHODS

Cell viability and flow cytometry assays were used to evaluate the cytotoxicity of A. annua active components casticin (CAS) and chrysosplenol D (CHD) in A. annua in NSCLC cells. After treatment with CAS and CHD, A549 cells were subjected to RNA sequencing (RNA-seq) analysis, differentially expressed genes (DEGs) were screened and subjected to functional enrichment analysis (KEGG and GO analysis) as well as protein interaction network analysis. The key targets associated with apoptosis induction in A549 cells were screened by Cytoscape, and the screened DEGs were validated by qRT-PCR. Immunoblotting, immunofluorescence, and molecular docking assays were used to determine whether CAS and/or CHD could induce apoptosis in NSCLC cells by inducing DNA damage through down-regulation of topoisomerase IIα (topo IIα) expression. The same experiments were verified again in the H1299 lung cancer cell line.

RESULTS

CAS and CHD inhibited NSCLC cells proliferation in a time- and dose-dependent manner, and significantly induced apoptosis. A total of 115 co-upregulated DEGs and 277 co-downregulated DEGs were identified in A549 cells following treatment with CAS and CHD. Comprehensive and systematic data about biological processes and mechanisms were obtained. DNA damage pathways and topo IIα targets were screened to study the apoptosis effects of CAS and CHD on NSCLC cells. CAS and CHD may be able to induce DNA damage by binding to topo IIα-DNA and reducing topo IIα activity.

CONCLUSION

This study suggested that CAS and CHD may reduce topo IIα activity by binding to topo IIα-DNA, affecting the replication of DNA, triggering DNA damage, and inducing apoptosis. It described a novel mechanism associated with topo IIα inhibition to reveal a novel role for CAS and CHD in A. annua as potential anticancer agents and/or adjuvants in NSCLC cells.

Proteomic Assessment of Extracellular Vesicles from Canine Tissue Explants as a Pipeline to Identify Molecular Targets in Osteosarcoma: PSMD14/Rpn11 as a Proof of Principle

Osteosarcoma (OS) is a highly malignant bone tumour that has seen little improvement in treatment modalities in the past 30 years. Understanding what molecules contribute to OS biology could aid in the discovery of novel therapies. Extracellular vesicles (EVs) serve as a mode of cell-to-cell communication and have the potential to uncover novel protein signatures. In our research, we developed a novel pipeline to isolate, characterize, and profile EVs from normal bone and osteosarcoma tissue explants from canine OS patients. Proteomic analysis of vesicle preparations revealed a protein signature related to protein metabolism. One molecule of interest, PSMD14/Rpn11, was explored further given its prognostic potential in human and canine OS, and its targetability with the drug capzimin. In vitro experiments demonstrated that capzimin induces apoptosis and reduces clonogenic survival, proliferation, and migration in two metastatic canine OS cell lines. Capzimin also reduces the viability of metastatic human OS cells cultured under 3D conditions that mimic the growth of OS cells at secondary sites. This unique pipeline can improve our understanding of OS biology and identify new prognostic markers and molecular targets for both canine and human OS patients.

Endophytic Fungi: Key Insights, Emerging Prospects, and Challenges in Natural Product Drug Discovery

Plant-associated endophytes define an important symbiotic association in nature and are established bio-reservoirs of plant-derived natural products. Endophytes colonize the internal tissues of a plant without causing any disease symptoms or apparent changes. Recently, there has been a growing interest in endophytes because of their beneficial effects on the production of novel metabolites of pharmacological significance. Studies have highlighted the socio-economic implications of endophytic fungi in agriculture, medicine, and the environment, with considerable success. Endophytic fungi-mediated biosynthesis of well-known metabolites includes taxol from Taxomyces andreanae, azadirachtin A and B from Eupenicillium parvum, vincristine from Fusarium oxysporum, and quinine from Phomopsis sp. The discovery of the billion-dollar anticancer drug taxol was a landmark in endophyte biology/research and established new paradigms for the metabolic potential of plant-associated endophytes. In addition, endophytic fungi have emerged as potential prolific producers of antimicrobials, antiseptics, and antibiotics of plant origin. Although extensively studied as a “production platform” of novel pharmacological metabolites, the molecular mechanisms of plant–endophyte dynamics remain less understood/explored for their efficient utilization in drug discovery. The emerging trends in endophytic fungi-mediated biosynthesis of novel bioactive metabolites, success stories of key pharmacological metabolites, strategies to overcome the existing challenges in endophyte biology, and future direction in endophytic fungi-based drug discovery forms the underlying theme of this article.

The Role of DNA Topoisomerase Binding Protein 1 (TopBP1) in Genome Stability in Arabidopsis

DNA topoisomerase II (TOPII) plays a very important role in DNA topology and in different biological processes such as DNA replication, transcription, repair, and chromosome condensation in higher eukaryotes. TOPII has been found to interact directly with a protein called topoisomerase II binding protein 1 (TopBP1) which also seems to have important roles in DNA replication and repair. In this study, we conducted different experiments to assess the roles of TopBP1 in DNA repair, mitosis, and meiosis, exploring the relationship between TOPII activity and TopBP1. We found that topbp1 mutant seedlings of Arabidopsis thaliana were hypersensitive to cisplatin treatment and the inhibition of TOPII with etoposide produced similar hypersensitivity levels. Furthermore, we recognised that there were no significant differences between the WT and topbp1 seedlings treated with cisplatin and etoposide together, suggesting that the hypersensitivity to cisplatin in the topbp1 mutant could be related to the functional interaction between TOPII and TopBP1. Somatic and meiotic anaphase bridges appeared in the topbp1 mutant at similar frequencies to those when TOPII was inhibited with merbarone, etoposide, or ICFR-187. The effects on meiosis of TOPII inhibition were produced at S phase/G2 stage, suggesting that catenanes could be produced at the onset of meiosis. Thus, if the processing of the catenanes is impaired, some anaphase bridges can be formed. Also, the appearance of anaphase bridges at first and second division is discussed.

Trapped topoisomerase-DNA covalent complexes in the mitochondria and their role in human diseases

Topoisomerases regulate DNA topology, organization of the intracellular DNA, the transmission of genetic materials, and gene expressions. Other than the nuclear genome, mitochondria also harbor the small, circular DNA (mtDNA) that encodes a critical subset of proteins for the production of cellular ATP; however, mitochondria are solely dependent on the nucleus for all the mitochondrial proteins necessary for mtDNA replication, repair, and maintenance. Mitochondrial genome compiles topological stress from bidirectional transcription and replication, therefore imports four nuclear encoded topoisomerases (Top1mt, Top2α, Top2β, and Top3α) in the mitochondria to relax mtDNA supercoiling generated during these processes. Trapping of topoisomerase on DNA results in the formation of protein-linked DNA adducts (PDAs), which are widely exploited by topoisomerase-targeting anticancer drugs. Intriguingly mtDNA is potentially exposed to DNA damage that has been attributed to a variety of human diseases, including neurodegeneration, cancer, and premature aging. In this review, we focus on the role of different topoisomerases in the mitochondria and our current understanding of the mitochondrial DNA damage through trapped protein-DNA complexes, and the progress in the molecular mechanisms of the repair for trapped topoisomerase covalent complexes (Topcc). Finally, we have discussed how the pathological DNA lesions that cause mtDNA damage,trigger mitochondrial fission and mitophagy, which serve as quality control events for clearing damaged mtDNA.

Drugging the 'undruggable'. Therapeutic targeting of protein-DNA interactions with the use of computer-aided drug discovery methods

Transcription factors (TFs) act as major oncodrivers in many cancers and are frequently regarded as high-value therapeutic targets. The functionality of TFs relies on direct protein-DNA interactions, which are notoriously difficult to target with small molecules. However, this prior view of the 'undruggability' of protein-DNA interfaces has shifted substantially in recent years, in part because of significant advances in computer-aided drug discovery (CADD). In this review, we highlight recent examples of successful CADD campaigns resulting in drug candidates that directly interfere with protein-DNA interactions of several key cancer TFs, including androgen receptor (AR), ETS-related gene (ERG), MYC, thymocyte selection-associated high mobility group box protein (TOX), topoisomerase II (TOP2), and signal transducer and activator of transcription 3 (STAT3). Importantly, these findings open novel and compelling avenues for therapeutic targeting of over 1600 human TFs implicated in many conditions including and beyond cancer.

In Vitro Antiplasmodial, Heme Polymerization, and Cytotoxicity of Hydroxyxanthone Derivatives

The previous study showed that xanthone had antiplasmodial activity. Xanthone, with additional hydroxyl groups, was synthesized to increase its antiplasmodial activity. One of the strategies to evaluate a compound that can be developed into an antimalarial drug is by testing its mechanism in inhibiting heme polymerization. In acidic condition, hematin can be polymerized to β-hematin in vitro, which is analog with hemozoin in Plasmodium. This study was conducted to evaluate the antiplasmodial activity of hydroxyxanthone derivative compounds on two strains of Plasmodium falciparum 3D-7 and FCR-3, to assess inhibition of heme polymerization activity and determine the selectivity of hydroxyxanthone derivative compounds. The antiplasmodial activity of each compound was tested on Plasmodium falciparum 3D-7 and FCR-3 with 72 hours incubation period, triplicated in three replications with the microscopic method. The compound that showed the best antiplasmodial activity underwent flow cytometry assay. Heme polymerization inhibition test was performed using the in vitro heme polymerization inhibition activity (HPIA) assay. The antiplasmodial activity and heme polymerization inhibition activity were expressed as the 50% inhibitory concentration (IC50). In vitro cytotoxicity was tested using the MTT assay method on Vero cell lines to determine its selectivity index. The results showed that among 5-hydroxyxanthone derivative compounds, the 1,6,8-trihydroxyxanthone had the best in vitro antiplasmodial activity on both 3D-7 and FCR-3 Plasmodium falciparum strains with IC50 values of 6.10 ± 2.01 and 6.76 ± 2.38 μM, respectively. The 1,6,8-trihydroxyxanthone showed inhibition activity of heme polymerization with IC50 value of 2.854 mM and showed the high selectivity with selectivity index of 502.2-556.54. In conclusion, among 5-hydroxyxanthone derivatives tested, the 1,6,8-trihydroxyxantone showed the best antiplasmodial activity and has heme polymerization inhibition activity and high selectivity.

Ca2+ Signaling as the Untact Mode during Signaling in Metastatic Breast Cancer

Metastatic features of breast cancer in the brain are considered a common pathology in female patients with late-stage breast cancer. Ca2+ signaling and the overexpression pattern of Ca2+ channels have been regarded as oncogenic markers of breast cancer. In other words, breast tumor development can be mediated by inhibiting Ca2+ channels. Although the therapeutic potential of inhibiting Ca2+ channels against breast cancer has been demonstrated, the relationship between breast cancer metastasis and Ca2+ channels is not yet understood. Thus, we focused on the metastatic features of breast cancer and summarized the basic mechanisms of Ca2+-related proteins and channels during the stages of metastatic breast cancer by evaluating Ca2+ signaling. In particular, we highlighted the metastasis of breast tumors to the brain. Thus, modulating Ca2+ channels with Ca2+ channel inhibitors and combined applications will advance treatment strategies for breast cancer metastasis to the brain.

Modular and Divergent Syntheses of Protoberberine and Protonitidine Alkaloids

A modularly convergent and divergent strategy was established for the family synthesis of both protoberberine and protonitidine alkaloids. The robust, scalable, and flexible synthetic route featured a collective preparation of protoberberine and protonitidine alkaloids from a common isoquinoline assembled from pyridyne as the key synthon, which was based on the selective N-C or C-C cyclization via distinct processes. Through the strategy, 20 protoberberine alkaloids, 5 protonitidine alkaloids, and 11 analogues with diverse substituents were comprehensively aquired.

Molecular docking analysis of α-Topoisomerase II with δ-Carboline derivatives as potential anticancer agents

The enzyme, α-topoisomerase II (α-Topo II), is known to regulate efficiently the topology of DNA. It is highly expressed in rapidly proliferating cells and plays an important role in replication, transcription and chromosome organisation. This has prompted several investigators to pursue α-Topo II inhibitors as anticancer agents. δ-Carboline, a natural product, and its synthetic derivatives are known to exert potent anticancer activity by selectively targeting α-Topo II. Therefore, it is of interest to design carboline derivatives fused with pyrrolidine-2,5-dione in this context. δ-Carbolines fused with pyrrolidine-2,5-dione are of interest because the succinimide part of fused heteroaromatic molecule can interact with the ATP binding pocket via the hydrogen bond network with selectivity towards α-Topo II. The 300 derivatives designed were subjected to the Lipinski rule of 5, ADMET and toxicity prediction. The designed compounds were further analysed using molecular docking analysis on the active sites of the α-Topo II crystal structure (PDB ID:1ZXM). Molecular dynamic simulations were also performed to compare the binding mode and stability of the protein-ligand complexes. Compounds with ID numbers AS89, AS104, AS119, AS209, AS239, AS269, and AS299 show good binding activity compared to the co-crystal ligand. Molecular Dynamics simulation studies show that the ligand binding to α-Topo II in the ATP domain is stableand the protein-ligand conformation remains unchanged. Binding free energy calculations suggest that seven molecules designed are potential inhibitors for α-Topo II for further consideration as anticancer agents.

A new look at 9-substituted acridines with various biological activities

Heterocycles have long been the focus of intensive study in attempts to develop novel therapeutic compounds, and acridine, a polynuclear nitrogen molecule containing a heterocycle, has attracted a considerable amount of scientific attention. Acridine derivatives have been studied in detail and have been found to possess multitarget properties, which inhibit topoisomerase enzymes that regulate topological changes in DNA and interfere with the essential biological function of DNA. This article describes some recent advancements in the field of new 9-substituted acridine heterocyclic agents and describes both the structure and the structure-activity relationship of the most promising molecules. The article will also present the IC₅₀ values of the novel derivatives against various human cancer cell lines. The mini review also investigates the topoisomerase inhibition and antibacterial and antimalarial activity of these polycyclic aromatic derivatives.

An assay for DNA polymerase β lyase inhibitors that engage the catalytic nucleophile for binding

DNA polymerase β (Pol β) repairs cellular DNA damage. When such damage is inflicted upon the DNA in tumor cells treated with DNA targeted antitumor agents, Pol β thus diminishes their efficacy. Accordingly, this enzyme has long been a target for antitumor therapy. Although numerous inhibitors of the lyase activity of the enzyme have been reported, none has yet proven adequate for development as a therapeutic agent. In the present study, we developed a new strategy to identify lyase inhibitors that critically engage the lyase active site primary nucleophile Lys72 as part of the binding interface. This involves a parallel evaluation of the effect of the inhibitors on the wild-type DNA polymerase β (Pol β) and Pol β modified with a lysine analogue at position 72. A model panel of five structurally diverse lyase inhibitors identified in our previous studies (only one of which has been published) with unknown modes of binding were used for testing, and one compound, cis-9,10-epoxyoctadecanoic acid, was found to have the desired characteristics. This finding was further corroborated by in silico docking, demonstrating that the predominant mode of binding of the inhibitor involves an important electrostatic interaction between the oxygen atom of the epoxy group and N^ε of the main catalytic nucleophile, Lys72. The strategy, which is designed to identify compounds that engage certain structural elements of the target enzyme, could find broader application for identification of ligands with predetermined sites of binding.

DNA Damage-Inducing Anticancer Therapies: From Global to Precision Damage

DNA damage-inducing therapies are of tremendous value for cancer treatment and function by the direct or indirect formation of DNA lesions and subsequent inhibition of cellular proliferation. Of central importance in the cellular response to therapy-induced DNA damage is the DNA damage response (DDR), a protein network guiding both DNA damage repair and the induction of cancer-eradicating mechanisms such as apoptosis. A detailed understanding of DNA damage induction and the DDR has greatly improved our knowledge of the classical DNA damage-inducing therapies, radiotherapy and cytotoxic chemotherapy, and has paved the way for rational improvement of these treatments. Moreover, compounds targeting specific DDR proteins, selectively impairing DNA damage repair in cancer cells, form a promising novel therapy class that is now entering the clinic. In this review, we give an overview of the current state and ongoing developments, and discuss potential avenues for improvement for DNA damage-inducing therapies, with a central focus on the role of the DDR in therapy response, toxicity and resistance. Furthermore, we describe the relevance of using combination regimens containing DNA damage-inducing therapies and how they can be utilized to potentiate other anticancer strategies such as immunotherapy.

Irinotecan-Still an Important Player in Cancer Chemotherapy: A Comprehensive Overview

Irinotecan has been used in the treatment of various malignancies for many years. Still, the knowledge regarding this drug is expanding. The pharmacogenetics of the drug is the crucial component of response to irinotecan. Furthermore, new formulations of the drug are introduced in order to better deliver the drug and avoid potentially life-threatening side effects. Here, we give a comprehensive overview on irinotecan’s molecular mode of action, metabolism, pharmacogenetics, and toxicity. Moreover, this article features clinically used combinations of the drug with other anticancer agents and introduces novel formulations of drugs (e.g., liposomal formulations, dendrimers, and nanoparticles). It also outlines crucial mechanisms of tumor cells’ resistance to the active metabolite, ethyl-10-hydroxy-camptothecin (SN-38). We are sure that the article will constitute an important source of information for both new researchers in the field of irinotecan chemotherapy and professionals or clinicians who are interested in the topic.

A dual PI3 kinase/mTOR inhibitor BEZ235 reverses doxorubicin resistance in ABCB1 overexpressing ovarian and pancreatic cancer cell lines

BACKGROUND

Multi-drug resistance (MDR) develops because cancer cells evade toxicity of several structurally unrelated drugs. Besides other mechanisms, MDR is linked to the overexpression of ATP Binding Cassette (ABC), transporters, among which ABCB1 is the best characterized one. Since overactivation of PI3K/Akt/mTOR plays a pivotal role in the growth of human cancers, we hypothesized whether dual PI3K and mTOR inhibitor, BEZ235 (BEZ, dactolisib) reverses resistance to doxorubicin (DOX).

METHODS

Ovarian (A2780) and pancreatic (MiaPaca2) cancer cells were used to generate DOX-resistant clones by overexpressing ABCB1 or stepwise treatment of DOX. Intracellular accumulation of DOX was measured by flow cytometry after treatment with BEZ.

RESULTS

BEZ treatment caused an increase in intracellular levels of DOX which was almost identical to the naïve parental cell lines. BEZ was found to be a weak substrate for ABCB1 as demonstrated by minimal increase in ATPase activity. BEZ treatment caused a dose-dependent decrease in cell viability in combination with DOX, which was associated with an increase in cleaved PARP expression in the drug resistant clones.

CONCLUSIONS

These results suggest that BEZ is a non-substrate inhibitor of ABCB1 and is able to effectively re-sensitize cells overexpressing ABCB1 to the effects of DOX.

GENERAL SIGNIFICANCE

Dual PI3 Kinase/mTOR inhibitor, BEZ, has the potential to reverse MDR in cancer patients.

Design, Synthesis, Dynamic Docking, Biochemical Characterization, and in Vivo Pharmacokinetics Studies of Novel Topoisomerase II Poisons with Promising Antiproliferative Activity

We previously reported a first set of hybrid topoisomerase II (topoII) poisons whose chemical core merges key pharmacophoric elements of etoposide and merbarone, which are two well-known topoII blockers. Here, we report on the expansion of this hybrid molecular scaffold and present 16 more hybrid derivatives that have been designed, synthesized, and characterized for their ability to block topoII and for their overall drug-like profile. Some of these compounds act as topoII poison and exhibit good solubility, metabolic (microsomal) stability, and promising cytotoxicity in three cancer cell lines (DU145, HeLa, A549). Compound 3f (ARN24139) is the most promising drug-like candidate, with a good pharmacokinetics profile in vivo. Our results indicate that this hybrid new chemical class of topoII poisons deserves further exploration and that 3f is a favorable lead candidate as a topoII poison, meriting future studies to test its efficacy in in vivo tumor models.

Smoothed Potential MD Simulations for Dissociation Kinetics of Etoposide To Unravel Isoform Specificity in Targeting Human Topoisomerase II

Human type II topoisomerases (TopoII) are essential for controlling DNA topology within the cell. For this reason, there are a number of TopoII-targeted anticancer drugs that act by inducing DNA cleavage mediated by both TopoII isoforms (TopoIIα and TopoIIβ) in cells. However, recent studies suggest that specific poisoning of TopoIIα may be a safer strategy for treating cancer. This is because poisoning of TopoIIβ appears to be linked to the generation of secondary leukemia in patients. We recently reported that enzyme-mediated DNA cleavage complexes (in which TopoII is covalently linked to the cleaved DNA during catalysis) formed in the presence of the anticancer drug etoposide persisted approximately 3-fold longer with TopoIIα than TopoIIβ. Notably, enhanced drug-target residence time may reduce the adverse effects of specific TopoIIα poisons. However, it is still not clear how to design drugs that are specific for the α isoform. In this study, we report the results of classical molecular dynamics (MD) simulations to comparatively analyze the molecular interactions formed within the TopoII/DNA/etoposide complex with both isoforms. We also used smoothed potential MD to estimate etoposide dissociation kinetics from the two isoform complexes. These extensive classical and enhanced sampling simulations revealed stabilizing interactions of etoposide with two serine residues (Ser763 and Ser800) in TopoIIα. These interactions are missing in TopoIIβ, where both amino acids are alanine residues. This may explain the greater persistence of etoposide-stabilized cleavage complexes formed with Topo TopoIIα. These findings could be useful for the rational design of specific TopoIIα poisons.

DIVERSet JAG Compounds Inhibit Topoisomerase II and Are Effective Against Adult and Pediatric High-Grade Gliomas

High-grade gliomas (HGGs) are aggressive primary brain tumors with local invasive growth and poor clinical prognosis in both adult and pediatric patients. Clinical response is compounded by resistance to standard frontline antineoplastic agents, an absence of novel therapeutics, and poor in vitro models to evaluate these. We screened a range of recently identified anticancer compounds in conventional adult, pediatric, and new biopsy-derived HGG models. These in vitro lines showed a range of sensitivity to standard chemotherapeutics, with varying expression levels of the prognostic markers hypoxia-induced factor (HIF) 1α and p53. Our evaluation of lead DIVERSet library compounds identified that JAG-6A, a compound that was significantly more potent than temozolomide or etoposide, was effective against HGG models in two-dimensional and three-dimensional systems; mediated this response by the potent inhibition of topoisomerase Iiα; remained effective under normoxic and hypoxic conditions; and displayed limited toxicity to non-neoplastic astrocytes. These data suggest that JAG-6A could be an alternative topoisomerase IIα inhibitor and used for the treatment of HGG.

Helping the Released Guardian: Drug Combinations for Supporting the Anticancer Activity of HDM2 (MDM2) Antagonists

The protein p53, known as the "Guardian of the Genome", plays an important role in maintaining DNA integrity, providing protection against cancer-promoting mutations. Dysfunction of p53 is observed in almost every cancer, with 50% of cases bearing loss-of-function mutations/deletions in the TP53 gene. In the remaining 50% of cases the overexpression of HDM2 (mouse double minute 2, human homolog) protein, which is a natural inhibitor of p53, is the most common way of keeping p53 inactive. Disruption of HDM2-p53 interaction with the use of HDM2 antagonists leads to the release of p53 and expression of its target genes, engaged in the induction of cell cycle arrest, DNA repair, senescence, and apoptosis. The induction of apoptosis, however, is restricted to only a handful of p53wt cells, and, generally, cancer cells treated with HDM2 antagonists are not efficiently eliminated. For this reason, HDM2 antagonists were tested in combinations with multiple other therapeutics in a search for synergy that would enhance the cancer eradication. This manuscript aims at reviewing the recent progress in developing strategies of combined cancer treatment with the use of HDM2 antagonists.

PPEF: A bisbenzimdazole potent antimicrobial agent interacts at acidic triad of catalytic domain of E. coli topoisomerase IA

BACKGROUND

Topoisomerase is a well known target to develop effective antibacterial agents. In pursuance of searching novel antibacterial agents, we have established a novel bisbenzimidazole (PPEF) as potent E. coli topoisomerase IA poison inhibitor.

METHODS

In order to gain insights into the mechanism of action of PPEF and understanding protein-ligand interactions, we have produced wild type EcTopo 67 N-terminal domain (catalytic domain) and its six mutant proteins at acidic triad (D111, D113, E115). The DDE motif is replaced by alanine (A) to create three single mutants: D111A, D113A, E115A and three double mutants: D111A-D113A, D113A-E115A and D111A-E115A.

RESULTS

Calorimetric study of PPEF with single mutants showed 10 fold lower affinity than that of wild type EcTopo 67 (7.32 × 10⁶ M^-1for wild type, 0.89 × 10⁶ M^-1for D111A) and 100 fold lower binding with double mutant D113A-E115A (0.02 × 10⁶ M^-1) was observed. The mutated proteins showed different CD signature as compared to wild type protein. CD and fluorescence titrations were done to study the interaction between EcTopo 67 and ligands. Molecular docking study validated that PPEF has decreased binding affinity towards mutated enzymes as compared to wild type.

CONCLUSION

The overall study reveals that PPEF binds to D113 and E115 of acidic triad of EcTopo 67. Point mutations decrease binding affinity of PPEF towards DDE motif of topoisomerase.

GENERAL SIGNIFICANCE

This study concludes PPEF as poison inhibitor of E. coli Topoisomerase IA, which binds to acidic triad of topoisomerase IA, responsible for its function. PPEF can be considered as therapeutic agent against bacteria.

Comparison of the effect of three different topoisomerase II inhibitors combined with cisplatin in human glioblastoma cells sensitized with double strand break repair inhibitors

Topoisomerase II (Topo2) inhibitors in combination with cisplatin represent a common treatment modality used for glioma patients. The main mechanism of their action involves induction of DNA double-strand breaks (DSBs). DSBs are repaired via the homology-dependent DNA repair (HRR) and non-homologous end-joining (NHEJ). Inhibition of the NHEJ or HRR pathway sensitizes cancer cells to the treatment. In this work, we investigated the effect of three Topo2 inhibitors-etoposide, NK314, or HU-331 in combination with cisplatin in the U-87 human glioblastoma cell line. Etoposide as well as NK314 inhibited Topo2 activity by stabilizing Topo2-DNA cleavable complexes whereas HU-331 inhibited the ATPase activity of Topo2 using a noncompetitive mechanism. To increase the effectiveness of the treatment, we combined cisplatin and Topo2 inhibitor treatment with DSB repair inhibitors (DRIs). The cells were sensitized with NHEJ inhibitor, NU7441, or the novel HRR inhibitor, YU238259, prior to drug treatment. All of the investigated Topo2 inhibitors in combination with cisplatin efficiently killed the U-87 cells. The most cytotoxic effect was observed for the cisplatin + HU331 treatment scheme and this effect was significantly increased when a DRI pretreatment was used; however, we did not observed DSBs. Therefore, the molecular mechanism of cytotoxicity caused by the cisplatin + HU331 treatment scheme is yet to be evaluated. We observed a concentration-dependent change in DSB levels and accumulation at the G2/M checkpoint and S-phase in glioma cells incubated with NK314/cisplatin and etoposide/cisplatin. In conclusion, in combination with cisplatin, HU331 is the most potent Topo2 inhibitor of human glioblastoma cells.

Protective role of N-acetylcysteine (NAC) on human sperm exposed to etoposide

Background

Although recent progress in cancer treatment has increased patient survival and improved quality of life, reproductive side effects are still for concern. One way to decrease gonadal impairment is to use cytoprotectors. In testicular cancer, etoposide is generally used in combination with other agents, but there are no in-vitro studies of sperm exposure to etoposide and cytoprotectors, namely N-acetylcysteine (NAC).

Methods

Twenty semen samples were individually divided into five groups: control, incubation with NAC alone, incubation with etoposide alone, sequential exposure of NAC followed by etoposide (pre-treatment) and sequential exposure of etoposide followed by NAC (post-treatment). Sperm characteristics, chromatin condensation (aniline blue), DNA fragmentation (TUNEL), oxidative stress (OxyDNA labelling) and glutathione quantification were used to evaluate the capabilities of NAC as a prophylactic (pre-treatment) or ameliorator (post-treatment) agent over the effects caused in sperm during in-vitro exposure to etoposide.

Results

No deleterious effects were observed on sperm motility or sperm membrane integrity. Results revealed that prophylactic use of NAC (pre-treatment) increased rates of immature sperm chromatin as compared to ameliorator use of NAC (post-treatment), and increased rates of sperm DNA fragmentation in relation to controls. Pre and post-treatment with NAC increased oxidative levels in comparison to controls, but also increased levels of cellular antioxidant glutathione.

Conclusions

The results indicate that NAC has the ability to counteract etoposide-induced toxicity rather than preventing the etoposide cytotoxic effects over sperm DNA, suggesting that the administration of NAC to cells formerly exposed to etoposide is preferable to its prophylactic use. As the results evidenced that NAC seems to be more efficient in attenuating sperm etoposide cytotoxic effects instead of being used as a chemoprophylactic agent, this reinforces the idea that there might be a new NAC mechanism over DNA.

Computational screening of chalcones acting against topoisomerase IIα and their cytotoxicity towards cancer cell lines

Targeted cancer therapy has become one of the high potential cancer treatments. Human topoisomerase II (hTopoII), which catalyzes the cleavage and rejoining of double-stranded DNA, is an important molecular target for the development of novel cancer therapeutics. In order to diversify the pharmacological activity of chalcones and to extend the scaffold of topoisomerase inhibitors, a series of chalcones was screened against hTopoIIα by computational techniques, and subsequently tested for their in vitro cytotoxicity. From the experimental IC₅₀ values, chalcone 3d showed a high cytotoxicity with IC₅₀ values of 10.8, 3.2 and 21.1 µM against the HT-1376, HeLa and MCF-7 cancer-derived cell lines, respectively, and also exhibited an inhibitory activity against hTopoIIα-ATPase that was better than the known inhibitor, salvicine. The observed ligand-protein interactions from a molecular dynamics study affirmed that 3d strongly interacts with the ATP-binding pocket residues. Altogether, the newly synthesised chalcone 3d has a high potential to serve as a lead compound for topoisomerase inhibitors.

Antileishmanial activity of new hybrid tetrahydroquinoline and quinoline derivatives with phosphorus substituents

Heterocyclic compounds, such as hybrid tetrahydroquinoline and quinoline derivatives with phosphorated groups, have been prepared by multicomponent cycloaddition reaction between phosphorus-substituted anilines, aldehydes and styrenes. The antileishmanial activity of these compounds has been evaluated on both promastigotes and intramacrophagic amastigotes of Leishmania infantum. Good antileishmanial activity of functionalized tetrahydroquinolines 4a, 5a, 6b and quinoline 8b has been observed with similar activity than the standard drug amphotericin B and close selective index (SI between 43 and 57) towards L. infantum amastigotes to amphotericin B. Special interest shows tetrahydroquinolylphosphine sulfide 5a with an EC₅₀ value (0.61 ± 0.18 μM) similar to the standard drug amphotericin B (0.32 ± 0.05 μM) and selective index (SI = 56.87). In addition, compound 4c shows remarkable inhibition on Leishmania topoisomerase IB. Parallel theoretical study of stereoelectronic properties, application of docking-based virtual screening methods, along with molecular electrostatic potential and predictive druggability analyses are also reported.

Endophytic Fungi-Alternative Sources of Cytotoxic Compounds: A Review

Cancer is a major cause of death worldwide, with an increasing number of cases being reported annually. The elevated rate of mortality necessitates a global challenge to explore newer sources of anticancer drugs. Recent advancements in cancer treatment involve the discovery and development of new and improved chemotherapeutics derived from natural or synthetic sources. Natural sources offer the potential of finding new structural classes with unique bioactivities for cancer therapy. Endophytic fungi represent a rich source of bioactive metabolites that can be manipulated to produce desirable novel analogs for chemotherapy. This review offers a current and integrative account of clinically used anticancer drugs such as taxol, podophyllotoxin, camptothecin, and vinca alkaloids in terms of their mechanism of action, isolation from endophytic fungi and their characterization, yield obtained, and fungal strain improvement strategies. It also covers recent literature on endophytic fungal metabolites from terrestrial, mangrove, and marine sources as potential anticancer agents and emphasizes the findings for cytotoxic bioactive compounds tested against specific cancer cell lines.

Chemotherapeutic-Induced Cardiovascular Dysfunction: Physiological Effects, Early Detection-The Role of Telomerase to Counteract Mitochondrial Defects and Oxidative Stress

Although chemotherapeutics can be highly effective at targeting malignancies, their ability to trigger cardiovascular morbidity is clinically significant. Chemotherapy can adversely affect cardiovascular physiology, resulting in the development of cardiomyopathy, heart failure and microvascular defects. Specifically, anthracyclines are known to cause an excessive buildup of free radical species and mitochondrial DNA damage (_mtDNA) that can lead to oxidative stress-induced cardiovascular apoptosis. Therefore, oncologists and cardiologists maintain a network of communication when dealing with patients during treatment in order to treat and prevent chemotherapy-induced cardiovascular damage; however, there is a need to discover more accurate biomarkers and therapeutics to combat and predict the onset of cardiovascular side effects. Telomerase, originally discovered to promote cellular proliferation, has recently emerged as a potential mechanism to counteract mitochondrial defects and restore healthy mitochondrial vascular phenotypes. This review details mechanisms currently used to assess cardiovascular damage, such as C-reactive protein (CRP) and troponin levels, while also unearthing recently researched biomarkers, including circulating _mtDNA, telomere length and telomerase activity. Further, we explore a potential role of telomerase in the mitigation of mitochondrial reactive oxygen species and maintenance of _mtDNA integrity. Telomerase activity presents a promising indicator for the early detection and treatment of chemotherapy-derived cardiac damage.

Synergistic enhancement of topotecan-induced cell death by ascorbic acid in human breast MCF-7 tumor cells

Topotecan, a derivative of camptothecin, is an important anticancer drug for the treatment of various human cancers in the clinic. While the principal mechanism of tumor cell killing by topotecan is due to its interactions with topoisomerase I, other mechanisms, e.g., oxidative stress induced by reactive free radicals, have also been proposed. However, very little is known about how topotecan induces free radical-dependent oxidative stress in tumor cells. In this report we describe the formation of a topotecan radical, catalyzed by a peroxidase-hydrogen peroxide system. While this topotecan radical did not undergo oxidation-reduction with molecular O₂, it rapidly reacted with reduced glutathione and cysteine, regenerating topotecan and forming the corresponding glutathiyl and cysteinyl radicals. Ascorbic acid, which produces hydrogen peroxide in tumor cells, significantly increased topotecan cytotoxicity in MCF-7 tumor cells. The presence of ascorbic acid also increased both topoisomerase I-dependent topotecan-induced DNA cleavage complex formation and topotecan-induced DNA double-strand breaks, suggesting that ascorbic acid participated in enhancing DNA damage induced by topotecan and that the enhanced DNA damage is responsible for the synergistic interactions of topotecan and ascorbic acid. Cell death by topotecan and the combination of topotecan and ascorbic acid was predominantly due to necrosis of MCF-7 breast tumor cells.

3EZ, 20Ac-ingenol induces cell-specific apoptosis in cyclin D1 over-expression through the activation of ATR and downregulation of p-Akt

Acute lymphoblastic leukemia (ALL) samples exhibit an activated PI3K/Akt pathway, which suggests a general role of Akt in the development of leukemia. We have previously used western blot analysis to show that the catalytic topoisomerase (topo) inhibitor, 3EZ, 20Ac-ingenol, induced DNA damage response (DDR), which activated ATR, downregulated p-Akt through upregulation of PTEN level, and led to cell cycle arrest or apoptosis. In this study, we used ATR or PTEN siRNA and observed that the specific cell arrest and apoptosis of BALL-1 cells in DDR caused by 3EZ, 20Ac-ingenol was dependant on activation of ATR and downregulation of nuclear p-Akt through upregulation of PTEN. Moreover, some B cell lymphomas among ALLs overexpress cyclin D1. The DDR induced during the S-phase with 3EZ, 20Ac-ingenol treatment was increased by the intra S-phase checkpoint response that was triggered by the loss of nuclear cyclin D1 regulation in BALL-1 cells overexpressing cyclin D1. Although topo 1 catalytic inhibitors induce a decatenation checkpoint and subsequent G2/M phase arrest, the decatenation checkpoint caused by 3EZ, 20Ac-ingenol induced apoptosis only in the BALL-1 cells that accumulated cyclin D1.

Functions of SUMO in the Maintenance of Genome Stability

Like in most other areas of cellular metabolism, the functions of the ubiquitin-like modifier SUMO in the maintenance of genome stability are manifold and varied. Perturbations of global sumoylation causes a wide spectrum of phenotypes associated with defects in DNA maintenance, such as hypersensitivity to DNA-damaging agents, gross chromosomal rearrangements and loss of entire chromosomes. Consistent with these observations, many key factors involved in various DNA repair pathways have been identified as SUMO substrates. However, establishing a functional connection between a given SUMO target, the cognate SUMO ligase and a relevant phenotype has remained a challenge, mainly because of the difficulties involved in identifying important modification sites and downstream effectors that specifically recognize the target in its sumoylated state. This review will give an overview over the major pathways of DNA repair and genome maintenance influenced by the SUMO system and discuss selected examples of SUMO's actions in these pathways where the biological consequences of the modification have been elucidated.

Nitric oxide inhibits ATPase activity and induces resistance to topoisomerase II-poisons in human MCF-7 breast tumor cells

Background

Topoisomerase poisons are important drugs for the management of human malignancies. Nitric oxide (^•NO), a physiological signaling molecule, induces nitrosylation (or nitrosation) of many cellular proteins containing cysteine thiol groups, altering their cellular functions. Topoisomerases contain several thiol groups which are important for their activity and are also targets for nitrosation by nitric oxide.

Methods

Here, we have evaluated the roles of ^•NO/^•NO-derived species in the stability and activity of topo II (α and β) both in vitro and in human MCF-7 breast tumor cells. Furthermore, we have examined the effects of ^•NO on the ATPase activity of topo II.

Results

Treatment of purified topo IIα and β with propylamine propylamine nonoate (PPNO), an NO donor, resulted in inhibition of the catalytic activity of topo II. Furthermore, PPNO significantly inhibited topo II-dependent ATP hydrolysis. ^•NO-induced inhibition of these topo II (α and β) functions resulted in a decrease in cleavable complex formation in MCF-7 cells in the presence of m-AMSA and XK469 and induced significant resistance to both drugs in MCF-7 cells.

Conclusion

PPNO treatment resulted in the nitrosation of the topo II protein in MCF-7 cancer cells and inhibited both catalytic-, and ATPase activities of topo II. Furthermore, PPNO significantly affected the DNA damage and cytotoxicity of m-AMSA and XK469 in MCF-7 tumor cells.

General significance

As tumors express nitric oxide synthase and generate ^•NO, inhibition of topo II functions by ^•NO/^•NO-derived species could render tumors resistant to certain topo II-poisons in the clinic.

•

Nitric oxide (^•NO) induces nitrosylation of many proteins, including topoisomerases.

•

Nitrosation of topo II inhibited catalytic-, and ATPase activities of topo II.

•

Inhibition of topo II activity resulted in resistance to topoisomerase II poisons.

Erythro-austrobailignan-6 down-regulates HER2/EGFR/integrinβ3 expression via p38 activation in breast cancer

BACKGROUND

Despite the benefits from different options of therapy for breast cancer, resistance of the disease to these therapies is rising and a novel agent is needed. Erythro-austrobailignan-6 (EA6) exhibits anti-cancer activity. However, the detailed anti-tumor mechanisms by which EA6 inhibits 4T-1 and MCF-7 cell growth have not been well studied.

PURPOSE

In this study, we investigated the anti-proliferative and anti-tumor properties of EA6 on breast carcinoma and its accompanying mechanisms.

METHODS

The cytotoxic and apoptotic effect of EA6 were measured in breast cancer cell lines of 4T-1 and MCF-7. The role of EA6 on cell proliferation and migration was examined by immunoblotting. The anti-tumor activity of EA6 was assessed in mice inoculated with 4T-1 breast cancer cells.

RESULTS

EA6 increased the number of Annexin V-positive apoptotic bodies and cleaved form of caspase-3 in a dose-dependent manner and phosphorylated JNK and p38 in both cells. Moreover, EA6 down-regulated cell cycle dependent proteins of CDK-4 and cyclin D1, and increased G0/G1 population in both cells. EA6-induced apoptosis is mediated by p38 MAPK and caspase-3 activation in both cells. EA6 significantly reduced HER2/EGFR/integrin β3 expression and Src phosphorylation, which was dependent on p38 MAPK activation in 4T-1 and MCF-7 cells. Furthermore, we confirmed the down-regulation of topoisomerases by EA6 treatment, but the overall effects of EA6 on topoisomerase isotype were cell type specific. Finally, EA6 (20mg/kg/day) significantly reduced mammary tumor volume in 4T-1 bearing mice by down-regulating HER2/EGFR/integrin β3 expression in tumor tissues.

CONCLUSIONS

Our results offer a novel insight into the mechanism of EA6-induced apoptosis in breast cancer cells. We propose that EA6 treatment resulted in the activation of p38 MAPK and caspase-3, which eventually participated in regulating apoptosis in 4T-1 and MCF-7 cells.

Nitric oxide: Friend or Foe in Cancer Chemotherapy and Drug Resistance: A Perspective

A successful treatment of cancers in the clinic has been difficult to achieve because of the emergence of drug resistant tumor cells. While various approaches have been tried to overcome multi-drug resistance, it has remained a major road block in achieving complete success in the clinic. Extensive research has identified various mechanisms, including overexpression of P-glycoprotein 170, modifications in activating or detoxification enzymes (phase I and II enzymes), and mutation and/or decreases in target enzymes in cancer cells. However, nitric oxide and/or nitric oxide-related species have not been considered an important player in cancer treatment and or drug resistance. Here, we examine the significance of nitric oxide in the treatment and resistance mechanisms of various anticancer drugs. Furthermore, we describe the significance of recently reported effects of nitric oxide on topoisomerases and the development of resistance to topoisomerase-poisons in tumor cells.

The ascidian natural product eusynstyelamide B is a novel topoisomerase II poison that induces DNA damage and growth arrest in prostate and breast cancer cells

As part of an anti-cancer natural product drug discovery program, we recently identified eusynstyelamide B (EB), which displayed cytotoxicity against MDA-MB-231 breast cancer cells (IC₅₀ = 5 μM) and induced apoptosis. Here, we investigated the mechanism of action of EB in cancer cell lines of the prostate (LNCaP) and breast (MDA-MB-231). EB inhibited cell growth (IC₅₀ = 5 μM) and induced a G2 cell cycle arrest, as shown by a significant increase in the G2/M cell population in the absence of elevated levels of the mitotic marker phospho-histone H3. In contrast to MDA-MB-231 cells, EB did not induce cell death in LNCaP cells when treated for up to 10 days. Transcript profiling and Ingenuity Pathway Analysis suggested that EB activated DNA damage pathways in LNCaP cells. Consistent with this, CHK2 phosphorylation was increased, p21^CIP1/WAF1 was up-regulated and CDC2 expression strongly reduced by EB. Importantly, EB caused DNA double-strand breaks, yet did not directly interact with DNA. Analysis of topoisomerase II-mediated decatenation discovered that EB is a novel topoisomerase II poison.