Enzyme Topoisomerase Research Articles

Pharmacophore modeling, 3D-QSAR, docking, and molecular dynamics simulation on topoisomerase IV inhibitors of wild type Staphylococcus aureus

Staphylococcus aureus is a gram-positive bacterium. It is a foremost cause of skin and respiratory infections, endocarditis, osteomyelitis, Ritter’s disease, and bacteraemia. Topoisomerase enzyme is involved in preventing or correcting topological problems of overwinding or underwinding occurring in DNA before replication process. An exhaustive molecular modeling studies that includes pharmacophore modeling, ligand-based three-dimensional quantitative structure-activity relationship (3D-QSAR), molecular docking, molecular dynamics simulation, and ADME calculations were performed on isothiazoloquinolones derivatives which are reported as effective inhibitors against topoisomerase IV of wild type S. aureus. In pharmacophore modeling by using pharmacophore alignment and scoring engine (PHASE) a five-point model (AHHRR.3) was generated with existing compounds having statistical significant as correlation coefficient (R 2 = 0.954), cross-validation coefficient (Q 2 = 0.650), and F value of 130.5. Ligand-based 3D-QSAR study was applied using comparative molecular field analysis (CoMFA) with Q 2 = 0.616, R 2 = 0.989, and comparative molecular similarity indices analysis (CoMSIA) with Q 2 = 0.510, R 2 = 0.995. The predictive ability of this model was determined using a test set of molecules that gave acceptable predictive correlation (R 2 Pred) values 0.55 and 0.56 for CoMFA and CoMSIA, respectively. Docking and molecular dynamic simulations were employed to position the inhibitors into protein active site to find out the most probable binding mode and most reliable conformations. Developed pharmacophore models and docking methods provide guidance to design enhanced activity molecules.

Topoisomerase IIβ Selectively Regulates Motor Neuron Identity and Peripheral Connectivity through Hox/Pbx-Dependent Transcriptional Programs.

Vital motor functions, such as respiration and locomotion, rely on the ability of spinal motor neurons (MNs) to acquire stereotypical positions in the ventral spinal cord and to project with high precision to their peripheral targets. These key properties of MNs emerge during development through transcriptional programs that dictate their subtype identity and connectivity; however, the molecular mechanisms that establish the transcriptional landscape necessary for MN specification are not fully understood. Here, we show that the enzyme topoisomerase IIβ (Top2β) controls MN migration and connectivity. Surprisingly, Top2β is not required for MN generation or survival but has a selective role in columnar specification. In the absence of Top2β, phrenic MN identity is eroded, while other motor columns are partially preserved but fail to cluster to their proper position. In Top2β-/- mice, peripheral connectivity is impaired as MNs exhibit a profound deficit in terminal branching. These defects likely result from the insufficient activation of Hox/Pbx-dependent transcriptional programs as Hox and Pbx genes are downregulated in the absence of Top2β. Top2β mutants recapitulate many aspects of Pbx mutant mice, such as MN disorganization and defects in medial motor column (MMC) specification. Our findings indicate that Top2β, a gene implicated in neurodevelopmental diseases such as autism spectrum disorders, plays a critical, cell-specific role in the assembly of motor circuits.

The Global Regulatory Cyclic AMP Receptor Protein (CRP) Controls Multifactorial Fluoroquinolone Susceptibility in Salmonella enterica Serovar Typhimurium

Fluoroquinolone antibiotics are prescribed for the treatment of Salmonella enterica infections, but resistance to this family of antibiotics is growing. Here we report that loss of the global regulatory protein cyclic AMP (cAMP) receptor protein (CRP) or its allosteric effector, cAMP, reduces susceptibility to fluoroquinolones. A Δcrp mutation was synergistic with the primary fluoroquinolone resistance allele gyrA83, thus able to contribute to clinically relevant resistance. Decreased susceptibility to fluoroquinolones could be partly explained by decreased expression of the outer membrane porin genes ompA and ompF with a concomitant increase in the expression of the ciprofloxacin resistance efflux pump gene acrB in Δcrp cells. Expression of gyrAB, which encode the DNA supercoiling enzyme GyrAB, which is blocked by fluoroquinolones, and expression of topA, which encodes the dominant supercoiling-relaxing enzyme topoisomerase I, were unchanged in Δcrp cells. Yet Δcrp cells maintained a more relaxed state of DNA supercoiling, correlating with an observed increase in topoisomerase IV (parCE) expression. Surprisingly, the Δcrp mutation had the unanticipated effect of enhancing fitness in the presence of fluoroquinolone antibiotics, which can be explained by the observation that exposure of Δcrp cells to ciprofloxacin had the counterintuitive effect of restoring wild-type levels of DNA supercoiling. Consistent with this, Δcrp cells did not become elongated or induce the SOS response when challenged with ciprofloxacin. These findings implicate the combined action of multiple drug resistance mechanisms in Δcrp cells: reduced permeability and elevated efflux of fluoroquinolones coupled with a relaxed DNA supercoiling state that buffers cells against GyrAB inhibition by fluoroquinolones.

New Mutations in Ciprofloxacin Resistant Strains of Pseudomonas aeruginosa Isolated from Guilan Province, Northern Iran

Pseudomonas aeruginosa (P. aeruginosa) is a gram-negative bacterium that continues to be a major cause of opportunistic nosocomial infections. In P. aeruginosa, several fluoroquinolones resistance mechanisms have been proposed such as mutations in the target enzymes GyrA and ParC and upregulation of efflux pump MexAB-OprM. Fluoroquinolones inhibit the target enzymes DNA gyrase and topoisomerase IV, each comprised of two subunits: GyrA and GyrB, and ParC and ParE, respectively. In addition, fluoroquinolones were blocked by overexpression of MexAB-OprM induced through mutations in the regulatory genes mexR and nalC. In this study, 44 P. aeruginosa strains were isolated from different clinical samples of burn and infection from patients in some hospitals and laboratories in Guilan, which were identified by biochemical tests. The antibiotic resistance and susceptibility of strains was determined by Kirby Bauer method and microdilution method, and then PCR-sequencing was carried out to assess mutation in several genes involved in ciprofloxacin resistance. Of 44 isolates, 14 isolates were fluoroquinolone resistant. All 14 strains were nalidixic acid resistant with MIC = 1024 μg/mL. While ciprofloxacin resistance was showed in resistant isolates with MIC to be 32–1024 μg/mL. PCR-sequencing analysis showed that all 14 fluoroquinolone resistant isolates had one or two mutations in gyrA mutation. Mutations in parC, mexR and nalC were shown in some ciprofloxacin resistant isolates. Moreover, three strains had new mutation in mexR gene (111InsC and 262-263delAG). It seems that high resistance to ciprofloxacin can simultaneously be the result of mutation in several genes such as topoisomerase enzymes and negative regulatory genes implicated in the expression of efflux pump systems in Guilan Province.

The MukB–topoisomerase IV interaction is required for proper chromosome compaction

The bacterial condensin MukB and the cellular decatenating enzyme topoisomerase IV interact. This interaction stimulates intramolecular reactions catalyzed by topoisomerase IV, supercoiled DNA relaxation, and DNA knotting but not intermolecular reactions such as decatenation of linked DNAs. We have demonstrated previously that MukB condenses DNA by sequestering negative supercoils and stabilizing topologically isolated loops in the DNA. We show here that the MukB-topoisomerase IV interaction stabilizes MukB on DNA, increasing the extent of DNA condensation without increasing the amount of MukB bound to the DNA. This effect does not require the catalytic activity of topoisomerase IV. Cells carrying a mukB mutant allele that encodes a protein that does not interact with topoisomerase IV exhibit severe nucleoid decompaction leading to chromosome segregation defects. These findings suggest that the MukB-topoisomerase IV complex may provide a scaffold for DNA condensation.

Expression and inhibition of BRD4, EZH2 and TOP2A in neurofibromas and malignant peripheral nerve sheath tumors.

Malignant peripheral nerve sheath tumors (MPNST) are rare, highly aggressive sarcomas that can occur spontaneously or from pre-existing plexiform neurofibromas in neurofibromatosis type1 (NF1) patients. MPNSTs have high local recurrence rates, metastasize easily, are generally resistant to therapeutic intervention and frequently fatal for the patient. Novel targeted therapeutic strategies are urgently needed. Standard treatment for patients presenting with advanced disease is doxorubicin based chemotherapy which inhibits the actions of the enzyme topoisomerase IIα (TOP2A). Recent molecular studies using murine models and cell lines identified the bromodomain containing protein 4 (BRD4) and enhancer of zeste homolog 2 (EZH2) as novel targets for MPNST treatment. We investigated the expression and potential use of BRD4, EZH2 and TOP2A as therapeutic targets in human NF1-derived MPNSTs. The transcript levels of BRD4, EZH2 and TOP2A were determined in paired formalin-fixed paraffin-embedded (FFPE) neurofibroma/MPNST samples derived from the same NF1 patient and in a set of plexiform neurofibromas, atypical neurofibromas and MPNST. We further examined the effect on cell viability of genetic or pharmacological inhibition of BRD4, EZH2 and TOP2A in an MPNST cell line panel. Our results indicated that in MPNST samples BRD4 mRNA levels were not upregulated and that MPNST cell lines were relatively insensitive to the bromodomain inhibitor JQ1. We corroborated that EZH2 mRNA expression is increased in MPNST but failed to confirm its reported pivotal role in MPNST pathogenesis as EZH2 knockdown by siRNA did not interfere with cellular proliferation and viability. Finally, the relation between TOP2A levels and sensitivity for doxorubicin was examined, confirming reports that TOP2A mRNA levels were overexpressed in MPNST and showing that MPNST cell lines exhibited relatively high TOP2A protein levels and sensitivity to doxorubicin. We tentatively conclude that the potential for effective therapeutic intervention in MPNST by targeting BRD4, EZH2 and TOP2A individually, may be limited. Clinical studies are necessary to ultimately prove the relevance of BRD4 and EZH2 inhibition as novel therapeutic strategies for MPNST.

Molecular docking studies on thirteen fluoroquinolines with human topoisomerase II a and b

DNA relaxation is an important step in DNA replication. DNA topoisomerases play a major role in DNA relaxation. Hence these enzymes are important targets for cancer drugs. DNA topoisomerase inhibitors bind to the transient enzyme–DNA complex and inhibit DNA replication. Various inhibitors of topoisomerase I and II are prescribed as drugs. Topoisomerase II is considered as an important target for the development of anticancer drugs. In this study we have demonstrated molecular docking of thirteen fluoroquinolines with human DNA topoisomerase II alpha (a) and beta (b). Fluoroquinolines are broad spectrum antibacterial antibiotics and it is highly effective against various bacterial infections. Some of the fluoroquinolines like moxifloxacin exert antifungal as well as anti-cancer activity. It forms complexes with topoisomerase II a and are responsible for stoppage DNA replication. Molecular docking studies showed that fluoroquinolines has shown formation of hydrogen bond and good binding affinity with human Topo2a and Topo2b. Hence FQs may inhibit the activity of enzyme topoisomerase by binding at its active site. Ofloxacin, sparafloxacin, ciprofloxacin and moxifloxacin are predicted to be the most potent inhibitors among the thirteen FQs docked. GLN773, ASN770, LYS723 and TRP931 amino acid residues of Topo2a are involved in binding with FQs while ASP479, SER480, ARG820, ARG503, LYS456 and GLN778 amino acid residues of Topo2b are involved in binding with FQs. Our in silico study suggests that fluoroquinolines could be repositioned as DNA topoisomerase II inhibitors hence can be used as anticancer drugs. In vitro and in vivo experiments need to be done to confirm their efficacy.

Efficient Sampling of Knotting-Unknotting Pathways for Semiflexible Gaussian Chains.

We propose a stochastic method to generate exactly the overdamped Langevin dynamics of semi-flexible Gaussian chains, conditioned to evolve between given initial and final conformations in a preassigned time. The initial and final conformations have no restrictions, and hence can be in any knotted state. Our method allows the generation of statistically independent paths in a computationally efficient manner. We show that these conditioned paths can be exactly generated by a set of local stochastic differential equations. The method is used to analyze the transition routes between various knots in crossable filamentous structures, thus mimicking topological reconnections occurring in soft matter systems or those introduced in DNA by topoisomerase enzymes. We find that the average number of crossings, writhe and unknotting number are not necessarily monotonic in time and that more complex topologies than the initial and final ones can be visited along the route.

Investigation of nuclear enzyme topoisomerase as a putative molecular target of monohaloacetonitrile disinfection by-products

Disinfection by-products occur widely as the unintended effect of water disinfection and are associated with toxicity and adverse human health effects. Yet the molecular mechanisms of their toxicity are not well understood. To investigate the molecular basis of hyperploidy induction by monohaloacetonitriles, the interaction of monohaloacetonitriles with topoisomerase II in Chinese hamster ovary cells was examined. We showed a concentration-dependent inhibition of DNA decatenation activity of topoisomerase under acellular conditions while in vitro monohaloacetonitrile treatment expressed mixed results. The working hypothesis, that topoisomerase II is a molecular target of monohaloacetonitriles, was only partially supported. Nevertheless, this research serves as a starting point toward molecular mechanisms of toxic action of monohaloacetonitriles.

Topoisomerase I and II Inhibitors: A Patent Review.

Topoisomerases are a set of nuclear enzymes that play a vital role in handling of topological consequences of DNA during various genetic activities necessary for vitality of cell. Inhibition of these enzymes consequently leads to the blockage of ligation step of the cell cycle which generates single and double strand breakage in DNA strand. Introduction of these breaks subsequently leads to programmed cell death (Apoptosis). In the past several years, topoisomerases have become one of the most expedient and strategic molecular targets for anticancer drugs and numerous patents have been filed and published on topoisomerase inhibitors. This review compiles the patent literature up to 2016 embracing topo I and II inhibitors as well as dual inhibitors which are structurally adjacent to camptothecin (CPT), natural products such as lamellarins and synthetic trisubstituted pyridines. The present assemblage can be extremely advantageous for the medicinal chemists who are in crave for the development of potential anticancer agents targeting topoisomerases. Recent patents indicated that some of the nitrogen containing heteroaromatic compounds have immense potential to inhibit topoisomerase enzyme. In particular, fused N-Heterocycles can be anticipated for their promising therapeutic potential alone or in combination with other anticancer agents. Naphthyridinone and indenoisoquinoline derivatives, described in the preceding sections of this review, are endowed with significant potency against topoisomerase I which clearly indicates the need of preclinical and clinical studies to place them in forefront as potential future drug candidates.

Discovery of Camptothecin Based Topoisomerase I Inhibitors: Identification Using an Atom Based 3D-QSAR, Pharmacophore Modeling, Virtual Screening and Molecular Docking Approach

Camptothecin is a quinoline alkaloid, isolated from the Chinese tree Camptotheca acuminate which exhibits its cytotoxic activity by the inhibition of nuclear enzyme Topoisomerase I (topo I). Camptothecin and its analogues forms a covalent bond with DNA which can arrest the tumor growth by slowing the religation step of the enzyme and stabilize the covalent adduct between topo I and DNA. Besides its strong anticancer potential, the limited solubility as well as instability of the hydroxylactone ring (Ring E) limits the clinical application of Camptothecin. This study was undertaken to identify novel compounds having anticancer activity with mechanism of action similar to that of Camptothecin using scaffold perception technique. We developed a common pharmacophore hypothesis using 32 camptothecin analogues, which was used for preliminary screening of large databases (ZINC "drug-like" database) to make sure, to include only compounds containing the key structural features needed to be Topoisomerase I inhibitors. In terms of a structure based approach, we systematically investigated various types of docking protocols to identify the most active compounds from the identified hit molecules. A post docking energy calculation was also carried out by MM/GBSA method. From the selected series of camptothecin analogs, a 3D-QSAR pharmacophore model was developed. The model consists of one acceptor site, one donor site, one hydrophobic site and two aromatic functions (ADHRR). Then, the pharmacophore model was employed as 3D search query to screen compounds from ZINC database which followed by molecular docking study and MM/GBSA calculation identified 2 lead molecules which, however, were not biologically validated. In silico studies reveals that the identified lead molecules have a better binding affinity than the co crystallized ligand. The identified molecules were able to bind to the active site of Topo-I enzyme similar to that of Camptothecin and the ADME properties were within the acceptable range defined for human use. The new molecules identified by virtual screening as such or on further optimization can be used as potential leads in designing Topoisomerase I inhibitors.

Supercoiling Effects on Short-Range DNA Looping in E. coli

DNA-protein loops can be essential for gene regulation. The Escherichia coli lactose (lac) operon is controlled by DNA-protein loops that have been studied for decades. Here we adapt this model to test the hypothesis that negative superhelical strain facilitates the formation of short-range (6–8 DNA turns) repression loops in E. coli. The natural negative superhelicity of E. coli DNA is regulated by the interplay of gyrase and topoisomerase enzymes, adding or removing negative supercoils, respectively. Here, we measured quantitatively DNA looping in three different E. coli strains characterized by different levels of global supercoiling: wild type, gyrase mutant (gyrB226), and topoisomerase mutant (ΔtopA10). DNA looping in each strain was measured by assaying repression of the endogenous lac operon, and repression of ten reporter constructs with DNA loop sizes between 70–85 base pairs. Our data are most simply interpreted as supporting the hypothesis that negative supercoiling facilitates gene repression by small DNA-protein loops in living bacteria.

Synthesis and topoisomerases inhibitory activity of heteroaromatic chalcones

The critical role of nuclear topoisomerase enzymes during cell proliferation process guided topoisomerases to be one of the major targets for anticancer drug development. We have designed and synthesized 22 heteroaromatic ring incorporated chalcone derivatives substituted with epoxide or thioepoxide. Topoisomerase enzyme inhibitory activity and cytotoxic tests were also conducted to evaluate compounds’ pharmacological efficacy. In the topoisomerase I inhibitory test, compound 1 was most active one, 24% of inhibition at 20μM, among all the compounds but it was lower than camptothecin. Compounds 9, 11, and 13 inhibited the function of topoisomerase II more strongly than etoposide with almost same magnitude (around 90% and 30% inhibition at 100 and 20μM, respectively) which were higher than those of etoposide (72% and 18% inhibition). In the cytotoxicity test, compound 9 inhibited T47D cancer cell growth with the IC50 value of 6.61±0.21μM. On the other hand, compound 13 (IC50: 4.32±0.18μM) effectively suppressed MDA-MB468 cancer cell growth.

Synthesis and biological evaluation of imidazopyridinyl-1,3,4-oxadiazole conjugates as apoptosis inducers and topoisomerase IIα inhibitors

A series of imidazopyridinyl-1,3,4-oxadiazole conjugates were synthesized and investigated for their cytotoxic activity and some compounds showed promising cytotoxic activity. Compound 8q (NSC: 763639) exhibited notable growth inhibition that satisfies threshold criteria at single dose (10μM) on all human cancer cell lines. This compound was further evaluated at five dose levels (0.01, 0.1, 1, 10 and 100μM) to obtain GI50 values ranging from 1.30 to 5.64μM. Flow cytometric analysis revealed that compound 8q arrests the A549 cells in sub G1 phase followed by induction of apoptosis which was further confirmed by Annexin-V-FITC, Hoechst nuclear staining, caspase 3 activation, measurement of mitochondrial membrane potential and ROS generation. Topo II mediated DNA relaxation assay results showed that conjugate 8q could significantly inhibit the activity of topo II. Moreover, molecular docking studies also indicated binding to the topoisomerase enzyme (PDBID 1ZXN).

Unwinding DNA and unleasing inflammation

Inflammation Fighting infections often comes with collateral damage, which sometimes can be deadly. For instance, in septic shock, the overwhelming release of inflammatory mediators drives multi-organ failure. Rialdi et al. now report a potential new therapeutic target for controlling excessive inflammation: the DNA unwinding enzyme topoisomerase I (Top1) (see the Perspective by Pope and Medzhitov). Upon infection, Top1 specifically localizes to the promoters of pathogen-induced genes and promotes their transcription by helping to recruit RNA polymerase II. Pharmacological inhibition of Top1 in a therapeutic setting increased survival in several mouse models of severe microbially induced inflammation. Science , this issue p. [10.1126/science.aad7993][1]; see also p. [1058][2] [1]: /lookup/doi/10.1126/science.aad7993 [2]: /lookup/doi/10.1126/science.aag0365

A simplified protocol for high-yield expression and purification of bacterial topoisomerase I

Type IA topoisomerases represent promising antibacterial drug targets. Data exists suggesting that the two bacterial type IA topoisomerase enzymes—topoisomerase I and topoisomerase III—share an overlapping biological role. Furthermore, topoisomerase I has been shown to be essential for the survival of certain organisms lacking topoisomerase III. With this in mind, it is plausible that topoisomerase I may represent a potential target for selective antibacterial drug development. As many reported bacterial topoisomerase I purification protocols have either suffered from relatively low yield, numerous steps, or a simple failure to report target protein yield altogether, a high-yield and high-purity bacterial topoisomerase I expression and purification protocol is highly desirable. The goal of this study was therefore to optimize the expression and purification of topoisomerase I from Streptococcus mutans, a clinically relevant organism that plays a significant role in oral and extra-oral infection, in order to quickly and easily attain the requisite quantities of pure target enzyme suitable for use in assay development, compound library screening, and carrying out further structural and biochemical characterization analyses. Herein we report the systematic implementation and analysis of various expression and purification techniques leading to the development and optimization of a rapid and straightforward protocol for the auto-induced expression and two-step, affinity tag purification of Streptococcus mutans topoisomerase I yielding >20 mg/L of enzyme at over 95% purity.

(3E)-5-Chloro-3-(2-phenylhydrazinylidene)-1H-indol-2(3H)-one

The reaction between 5-cholroisatin and phenylhydrazine yields the title compound, C14H10ClN3O. The molecular structure deviates slightly from the ideal planarity, with an r.m.s. deviation of 0.1372 (12) Å for the non-H atoms. An N—H...O intramolecular interaction is observed, which supports anEconformation with respect to the C=N bond. In the crystal, molecules are linked by a pair of N—H...O interactions into an inversion dimer. The dimers are linked by weak C—H...Cl interactions, formng a tape structure along [101]. The tapes are also linked through a weak π–π interaction [centroid–centroid distance = 3.5773 (8) Å] into a layer parallel to (-111). Anin silicoevaluation of the title compound with a topoisomerase enzyme was performed and the global free energy of −26.59 kJ mol−1was found.

Interactions of Non-Phosphorous Glycerolipids with DNA: Energetics, Molecular Docking and Topoisomerase I Attenuation.

The phosphorus-containing glycerolipid based antitumor drugs (edelfosine as a prototype) are currently in clinical trials. To avoid the use of potentially harmful phosphoric reagents in the preparation of biologically active glycerolipids, and to obtain the compounds without the phosphoester bond cleavable inside the cells, we developed the synthesis of non-phosphorous glycerolipids (NPGLs) with neutral or cationic polar 'heads'. In this study, we analyzed the ability of novel NPGLs L1-L5 to interact with duplex DNA and interfere with the DNA modifying enzyme topoisomerase I (topo I). In cell-free systems, NPGLs formed highly affine complexes with DNA. Molecular docking revealed that NPGLs fitted very well into the DNA minor groove. Compounds L2 (with two long hydrophobic 'tails') and L4 (with ethylimidazolium cationic group), the most affine DNA binders, showed the best calculated energies of complex formation with DNA and topo I. The models demonstrated the binding of NPGLs to the topo I site known for interaction with conventional inhibitors. Each NPGL attenuated the topo I mediated unwinding of supercoiled DNA. Again, L2 and, to a lesser extent, L4 were the most potent topo I inhibitors. Thus, NPGLs with polar 'heads' emerge as a new class of DNA ligands and interfacial topo I antagonists.

Isolation and characterization of 2-hydroxy-9,10-anthraquinone from Streptomyces olivochromogenes (ERINLG-261) with antimicrobial and antiproliferative properties

Currently Streptomyces is one of the most important antibiotic producing microorganisms against several diseases. In the present study Streptomyces olivochromogenes ERINLG-261 was isolated from the soil samples of the Mudumalai hills, Western Ghats, India. Morphological, physiological, biochemical and 16S rRNA studies strongly suggested that this isolate belonged to the genus Streptomyces. ERINLG-261 showed good antimicrobial activity against different bacteria and fungi in Micromonospora fermentation medium. The active ethyl acetate extract was packed in column chromatography over silica gel which led to the isolation of 2-hydroxy-9,10-anthraquinone as the active principle. The isolated compound showed good antimicrobial activity against tested bacteria and fungi in minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) studies. The compound showed moderate in vitro antiproliferative activity against A549 and COLO320 cells. The compound was subjected to molecular docking studies for the inhibition of Topoisomerase, TtgR and Beta-lactamase enzymes which are targets for antimicrobials. Docking results of the compound showed low docking energy with these enzymes indicating its usefulness as antimicrobial agent. This is the first report of antimicrobial and antiproliferative activity of 2-hydroxy-9,10-anthraquinone isolated from Streptomyces olivochromogenes along with molecular docking studies.

The combined effects of proteasome inhibitor bortezomib with topoisomerase I and II inhibitors on topoisomerase enzymes.

DNA topoisomerases are ubiquitous enzymes that regulate conformational changes in DNA topology during essential cellular processes, and, for this reason, have been characterized as the cellular targets of a number of anticancer drugs. Bortezomib is a powerful proteasome inhibitor used in the treatment of hematological malignancies. In this study, we investigated the inhibitory effects of bortezomib on human topoisomerase I and II enzymes both alone and in combination modes with camptothecin and etoposide. The interactions of these drugs with topoisomerase enzymes were evaluated by relaxation assay in cell-free systems. IC50 values of the drugs on topoisomerase enzymes were calculated using the S probit analysis program. Bortezomib showed a very weak inhibition effect on topoisomerase I (IC50 = 87.11 mM). On the other hand, it had a strong inhibitory effect on topoisomerase II (IC50 = 1.41 mM). Our results indicated that bortezomib is effective not only on proteasome but also on topoisomerase II. In addition, bortezomib possesses an increased synergistic effect when used in combination with camptothecin and etoposide than when used alone. The results of this study point out that these data may build a framework for combination studies with bortezomib, camptothecin, and etoposide in the treatment of cancer.