DNA Binding Behavior Research Articles

Characterization of DNA binding and pairing activities associated with the native SFPQ·NONO DNA repair protein complex

Nonhomologous end joining (NHEJ) is a major pathway for repair of DNA double-strand breaks. We have previously shown that a complex of SFPQ (PSF) and NONO (p54nrb) cooperates with Ku protein at an early step of NHEJ, forming a committed preligation complex and stimulating end-joining activity by 10-fold or more. SFPQ and NONO show no resemblance to other repair factors, and their mechanism of action is uncertain. Here, we use an optimized microwell-based assay to characterize the in vitro DNA binding behavior of the native SFPQ·NONO complex purified from human (HeLa) cells. SFPQ·NONO and Ku protein bind independently to DNA, with little evidence of cooperativity and only slight mutual interference at high concentration. Whereas Ku protein requires free DNA ends for binding, SFPQ·NONO does not. Both Ku and SFPQ·NONO have pairing activity, as measured by the ability of DNA-bound protein to capture a second DNA fragment in a microwell-based assay. Additionally, SFPQ·NONO stimulates DNA-dependent protein kinase autophosphorylation, consistent with the ability to promote formation of a synaptic complex formation without occluding the DNA termini proper. These findings suggest that SFPQ·NONO promotes end joining by binding to internal DNA sequences and cooperating with other repair proteins to stabilize a synaptic pre-ligation complex.

Study on DNA binding behavior and light switch effect of new coumarin-derived Ru(II) complexes

A new ligand mhcip (mhcip=2-(4-methyl-7-hydroxyl-8-coumarinyl)imidazo[4,5-f]-[1,10]phenanthroline) and its ruthenium complexes, [Ru(L)2mhcip]2+ (L=bpy (2,2′-bipyridine), phen (1,10-phenanthroline)), have been synthesized and characterized. The introduction of coumarin ring may play an important role in the strong fluorescence of the complexes. Intercalative binding mode between both complexes and CT-DNA was determined by UV–visible spectroscopy, fluorescence spectroscopy and viscosity measurements. The two complexes show efficient DNA photocleavage under irradiation at 365nm. The cycling of light switch off and on has been achieved for both complexes through the introduction of Cu2+ and EDTA in the absence or presence of DNA.

Exploration of DNA binding mode, chemical nuclease, cytotoxic and apoptotic potentials of diketone based oxovanadium(IV) complexes

Two diketone based oxovanadium complexes, viz., bis(4,4,4-trifluoro-1-phenylbutane-1,3-dionato)oxovanadium(IV) (1) and bis(1,1,1-trifluoropentane-2,4-dionato)oxovanadium(IV) (2), have been synthesized and characterized by spectroscopic and analytical techniques. The DNA binding and the cleaving ability of the complexes is assessed by UV–vis spectroscopy, fluorescence spectroscopy, viscometry and gel electrophoretic studies. The DNA binding constant values (Kb) are found to be 1.95±0.16×103M−1 for complex 1 and 1.064±0.17×103M−1 for complex 2, respectively. Based on the results of the spectral and viscosity studies, it is observed that the complexes, interestingly, have preferred minor groove binding with DNA. Further, the concentration-dependent oxidative cleavage pattern of pBR322 in the presence of the activating reagent, hydrogen peroxide, has also been discussed. In addition, the complexes have shown moderate cytotoxic activity by inducing apoptosis against the cervical cancer cell line, HeLa. The results of in silico analysis and logP predictions are found to be in good agreement with the experimental observations. Thus, synthesized oxovanadium complexes have displayed promising DNA binding behavior and DNA cleavage activity with moderately cytotoxic nature.

Unexpected DNA binding properties with correlated downstream biological applications in mono vs. bis-1,8-naphthalimide Ru(II)-polypyridyl conjugates.

The synthesis, spectroscopic characterisation and biological evaluation of mono- and bis-1,8-naphthalimide-conjugated ruthenium(ii)-polypyridyl complexes is presented. Spectroscopic DNA titrations, together with denaturation studies, show strong binding of both species to DNA through the naphthalimide arms. Linear and circular dichroism (LD and CD) spectroscopy reveal close association of the Ru(bpy)3(2+) core with DNA in the case of the mono-naphthalamide complex, [Ru(bpy)2(bpy-NAP)](2+). Significantly, binding by the second naphthalimide arm in the [Ru(bpy)2(bpy-NAP2)](2+) complex is found to displace the Ru(bpy)3(2+) centre from the DNA backbone. This 'negative allosteric effect' is found to have a dramatic influence on the photoinduced damage of plasmid DNA, and the viability of HeLa cancer cells upon photoactivation. Overall the study clearly maps and correlates the relationship between molecular structure, in vitro binding and activity, and in cellulo function.

Synthesis, DNA interactions and antibacterial PDT of Cu(II) complexes of phenanthroline based photosensitizers via singlet oxygen generation

Cu(II) complexes [Cu(mqt)(B)H2O]ClO4(1–3) of 2-thiol 4-methylquinoline and phenanthroline bases (B), viz 1,10-phenanthroline (phen in 1), Dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq in 2) and Dipyrido[3,2-a:2′,3′-c]phenazine (dppz in 3) have been prepared and characterized by elemental analysis, IR, UV–Vis, magnetic moment values, EPR spectra and conductivity measurements. The spectral data reveal that all the complexes exhibit square-pyramidal geometry. The DNA-binding behaviors of the three complexes were investigated by absorption spectra, viscosity measurements and thermal denaturation studies. The DNA binding constants for complexes (1), (2) and (3) were determined to 2.2×103, 1.3×104 and 8.6×104M−1 respectively. The experimental results suggest that these complexes interact with DNA through groove-binding mode. The photo induced cleavage studies shows that the complexes possess photonuclease property against pUC19 DNA under UV–Visible irradiation via a mechanistic pathway involving formation of singlet oxygen as the reactive species. Antimicrobial photodynamic therapy was studied using photodynamic antimicrobial chemotherapy (PACT) assay against Escherichiacoli and all complexes exhibited significant reduction in bacterial growth on photoirradiation.

Antitumor platinum(II) complexes of N-cyclobutyl-1R,2R-diaminocyclohexane with dicarboxylates as leaving groups

Four platinum(II) complexes of N-cyclobutyl-1R,2R-diaminocyclohexane with different bidentate dicarboxylates (1 oxalate, 2 malonate, 3 1,1-cyclobutanedicarboxylate and 4 3-hydroxy-1,1-cyclobutanedicarboxylate) as leaving groups were synthesized and characterized by elemental analyses, IR and 1HNMR spectra together with ESI-MS spectroscopy. All complexes showed considerable cytotoxicity against the tested four human tumor cell lines including A549, HCT-116, HepG-2 and MCF-7. Especially, complex 4 showed good cytotoxicity against A549 (IC50=3.5μM) and HCT-116 (IC50=0.9μM) cancer cell lines. Moreover, complex 3 is the most effective agent among the tested compounds against MCF-7 cell line (IC50=1.1μM). The DNA binding behavior of both complexes 3 and 4, studied by agarose gel electrophoresis, revealed that they bound to DNA in almost the same way as cisplatin.

Water soluble {2-[3-(diethylamino)phenoxy]ethoxy} substituted zinc(II) phthalocyanine photosensitizers

The new peripherally and non-peripherally tetra-{2-[3-(diethylamino)phenoxy] ethoxy} substituted zinc phthalocyanines (2a and 3a) were synthesized by cyclotetramerization of phthalonitrile derivatives (2 and 3). 2-[3-(diethylamino)phenoxy] ethoxy group was chosen as substituent because the quaternization of the diethylamino functionality on the structure of this group produced water soluble zinc phthalocyanines (2b and 3b). The water solubility is very important for many different applications such as photosensitizers in the photodynamic therapy of cancer because the water soluble photosensitizers can be injected directly to the body and they can transport to cancer cells through blood stream. The new compounds were characterized by using elemental analysis, UV–vis, IR, 1H NMR, 13C NMR and mass spectroscopies. The photophysical and photochemical properties of these novel photosensitizer compounds were examined in DMSO (both non-ionic and ionic complexes) and in PBS (for ionic complexes) solutions. The investigation of these properties is very important for the usage of the compounds as photosensitizers for PDT because determination of these properties is the first stage of potential of the compounds as photosensitizers. The bovine serum albumin (BSA) and DNA binding behaviour of the studied water soluble zinc (II) phthalocyanines were also investigated in PBS solutions for the determination of biological activity of these compounds.

Dual inhibition of topoisomerases I and IIα by ruthenium(II) complexes containing asymmetric tridentate ligands.

Five novel ruthenium(II) complexes, [Ru(dtzp)(dppt)](2+) (1), [Ru(dtzp)(pti)](2+) (2), [Ru(dtzp)(ptn)](2+) (3), [Ru(dtzp)(pta)](2+) (4) and [Ru(dtzp)(ptp)](2+) (5) (where dtzp = 2,6-di(thiazol-2-yl)pyridine, dppt = 3-(1,10-phenanthroline-2-yl)-5,6-diphenyl-as-triazine), pti = 3-(1,10-phenanthroline-2-yl)-as-triazino-[5,6-f]isatin, ptn = 3-(1,10-phenanthroline-2-yl)-as-triazino[5,6-f]naphthalene, pta = 3-(1,10-phenanthroline-2-yl)-as-triazino[5,6-f]acenaphthylene, and ptp = 3-(1,10-phenanthroline-2-yl)-as-triazino[5,6-f]-phenanthrene), were synthesised and characterised. The structures of complexes 3-5 were determined by X-ray diffraction. The DNA binding behaviours of the complexes were studied by spectroscopic and viscosity measurements. The results suggested that the Ru(II) complexes, except for complex 1, bind to DNA in an intercalative mode. Topoisomerase inhibition and DNA strand passage assay confirmed that Ru(II) complexes 3, 4, and 5 acted as efficient dual inhibitors of topoisomerases I and IIα. In vitro cytotoxicity assays indicated that these complexes exhibited anticancer activity against various cancer cell lines. Ruthenium(ii) complexes were confirmed to preferentially accumulate in the nucleus of cancer cells and induced DNA damage. Flow cytometric analysis and AO/EB staining assays indicated that these complexes induced cell apoptosis. With the loss of the mitochondrial membrane potential, the Ru(ii) complexes induce apoptosis via the mitochondrial pathway.

Ruthenium(II) polypyridyl complexes induce BEL-7402 cell apoptosis by ROS-mediated mitochondrial pathway

A new ligand dmdppz and its four ruthenium(II) polypyridyl complexes [Ru(dmb)2(dmdppz)](ClO4)2 (1), [Ru(bpy)2(dmdppz)](ClO4)2 (2), [Ru(phen)2(dmdppz)](ClO4)2 (3) and [Ru(dmp)2(dmdppz)](ClO4)2 (4) (where dmb, bpy, phen, dmp and dmdppz stand for 4,4′-dimethyl-2,2′-bipyridine, 2,2′-bipyridine, 1,10-phenanthroline, 2,9-dimethyl-1,10-phenanthroline and 5,8-dimethoxylpyrido[3,2-a:2′,3′-c]phenazine, respectively) have been synthesized and characterized. Their DNA binding behaviors show that the complexes bind to calf thymus DNA by intercalation. The complexes exhibit efficient photocleavage of pBR322 DNA on irradiation. The cytotoxicity of the ligand and the complexes toward HepG-2, HeLa, MG-63, A549 and BEL-7402 were assayed by MTT ((3-(4,5-dimethylthiazo-2-yl)-2,5-diphenyltetrazolium bromide)) method. The IC50 values of the complexes 1, 2, 3 and 4 toward BEL-7402 cells are 14.6, 16.8, 18.0 and 16.7μM, respectively. Dmdppz shows no cytotoxic activity against selected cell lines. The cellular uptake, apoptosis, comet assay, reactive oxygen species (ROS), mitochondrial membrane potential and western blot analysis were investigated. These results indicate that complexes 1–4 exert their toxicity through the intrinsic ROS-mediated mitochondrial pathway, which is accompanied by the regulation of Bcl-2 family proteins.

Novel ruthenium (II) polypyridyl complexes containing carbazole with flexible substituents: Crystal structure, nonlinear optical properties and DNA-binding interaction

Five novel ruthenium (II) polypyridyl (N∧N∧N or N∧N∧C) complexes (1–5) containing carbazole with flexible substituents have been synthesized, and fully characterized. The crystal structure of complex 5 was determined by X-ray diffraction analysis. The photophysical properties of them were systematic studied. The complexes exhibited ligand-centered π–π∗ transition in the range of 290–350 nm and metal-to-ligand charge transition bands in the range of 450–650 nm. The third-order nonlinear optical response was measured by Z-scan technique for the complexes. The results revealed that cyclometalated (N∧N∧C) complexes 1 and 2 possess a stronger third-order nonlinear optical response than those of noncyclometalated (N∧N∧N) complexes 3, 4 and 5. The DNA binding behaviors of the complexes have been investigated by spectroscopic and viscosity measurements. It was found that the complexes can interact with DNA in different modes, including classical intercalation for complexes 1–3 and partial intercalation for complexes 4–5.

DNA interaction, antioxidant activity, and bioactivity studies of two ruthenium(II) complexes

Two new ruthenium(II) polypyridyl complexes [Ru(dmb)2(dcdppz)](ClO4)2 (1) and [Ru(bpy)2(dcdppz)](ClO4)2 (2) were prepared and characterized. The crystal structure of the complex 2 was solved by single crystal X-ray diffraction. The complex crystallizes in the monoclinic system, space group P21/n with a=12.9622(14)Å, b=17.1619(19)Å, c=22.7210(3)Å, β=100.930(2)°, R=0.0536, Rω=0.1111. The DNA-binding constants for complexes 1 and 2 were determined to be 1.92×105 (s=1.72) and 2.24×105 (s=1.86)M−1, respectively. The DNA-binding behaviors showed that complexes 1 and 2 interact with DNA by intercalative mode. The antioxidant activities of the ligand and the complexes were performed. Ligand, dcdppz, has no cytotoxicity against the selected cell lines. Complex 1 shows higher cytotoxicity than complex 2, but lower than cisplatin toward selected cell lines. The apoptosis and cell cycle arrest were investigated, and the apoptotic mechanism of BEL-7402 cells was studied by reactive oxygen species (ROS), mitochondrial membrane potential and western blot analysis. Complex 1 induces apoptosis in BEL-7402 cells through ROS-mediated mitochondrial dysfunction pathway and by regulating the expression of Bcl-2 family proteins.

Spectroscopic and molecular modeling based approaches to study on the binding behavior of DNA with a copper (II) complex.

Blocking the division of tumor cells by small-molecules is currently of great interest for the design of new antitumor drugs. The interaction of a new metal complex with DNA was investigated through several techniques. Absorption spectroscopy and gel electrophoresis studies on the interaction of the Cu-complex of (2a-4mpyH)2 [Cu(pyzdc)2 (H2O)2].6 H2O with DNA have shown that this complex can bind to CT-DNA with binding constant 3.99 × 10(5) M(-1). The cyclic voltammetry (CV) responses of the metal complex in the presence of CT-DNA have shown that the metal complex can bind to CT-DNA through partial intercalation mode and this is consistent with molecular docking analysis, quenching process and thermal denaturation experiments. The cytotoxicity of this complex has been evaluated by MTT assay. The results of cell viability assay on DU145 cell line revealed that the metal complex had cytotoxic effects.

DNA binding behaviors and nuclease activities of novel mixed-ligand ruthenium(II) complexes

Two types of ruthenium(II) complexes cis-[Ru(bpy)2ClL]+ and cis-[Ru(bpy)2L2]2+ (L=1,6-diaminohexane (1,6-dahx), 1-aminohexane (1-ahx)) were synthesized, and the interactions of these complexes with DNA were investigated. Importantly, cis-[Ru(bpy)2(1,6-dahx)2]2+ possessed hydrogen-bonding to DNA, preferentially binds at adenine and/or thymine residues, and exhibits more efficient nuclease activity.

Synthesis, characterization, crystal structure and theoretical study of a compound with benzodiazole ring: Antimicrobial activity and DNA binding

2-(Thiophen-2-yl)-1-((thiophen-2-yl)methyl)-1H-1,3-benzodiazole (HL) is synthesized and characterized by elemental analysis, UV–Vis, FT-IR, 1H, 13C NMR, mass spectra, scanning electron microscope (SEM) and single crystal X-ray diffraction. The crystal structure is stabilized by intermolecular CH⋯N and CH⋯π interactions. The molecular structure is also optimized at the B3LYP/6-31G level using density functional theory (DFT). The structural parameters from the theory are nearer to those of crystal, the calculated total energy of coordination is −1522.814a.u. The energy of HOMO–LUMO and the energy gap are −0.20718, −0.04314, 0.16404a.u, respectively. All data obtained from the spectral studies support the structural properties of the compound HL. The benzimidazole ring is essentially planar. The in vitro biological screening effects of the synthesized compound is tested against four bacterial and four fungal strains by well diffusion method. Antioxidant property and DNA binding behaviour of the compound has been investigated using spectrophotometric method.

Cellular uptake, cytotoxicity, apoptosis, DNA-binding, photocleavage and molecular docking studies of ruthenium(II) polypyridyl complexes

Three new mononuclear [Ru (phen)2 ptip]2+ (1), [Ru (bpy)2 ptip]2+ (2) and [Ru (dmb)2 ptip]2+ (3) [ptip=(2-(5-phenylthiophen-2-yl)-1H-imidazo[4, 5-f][1,10 phenanthroline, phen=1, 10 phenanthroline, bpy=2, 2′ bipyridine, dmb=4, 4′-dimethyl 2, 2′ bipyridine] complexes were synthesized and characterised by elemental analysis, IR, NMR and Mass spectra. The DNA-binding behaviours were investigated by electronic absorption titration, luminescence spectra, viscosity measurements and photo-activated cleavage. The DNA-binding constants Kb of complexes 1, 2 and 3 were determined to be 7.0 (±0.06)×105, 3.87 (±0.04)×105, 2.79 (±0.07)×105 respectively. The results showed that these complexes interact with CT-DNA by intercalative mode. Cell viability experiments indicated that the Ru(II) complex showed significant dose-dependent cytotoxicity to HeLa tumour cell lines. Further flow cytometry experiments showed that the cytotoxic Ru(II) complex induced apoptosis of HeLa tumour cell lines. Our data demonstrated that the Ru(II) polypyridyl complex binds to DNA and thereby induces apoptosis in tumor cells, suggesting that anti-tumor activity of the Ru(II) complex could be related to its interaction with DNA. The molecular dynamic simulations and docking methods were used to predict the DNA binding affinity of ruthenium complexes and with good visualisation images supporting with experimental results.

Synthesis, spectroscopic characterization, pH dependent redox mechanism and DNA binding behavior of chlorohydroxyaniline derivatives

Three new chlorohydroxyanilines were synthesized and characterized. The results revealed these compounds to have strong antioxidant activity and DNA binding propensity.

Arene ruthenium(ii) complexes induce S-phase arrest in MG-63 cells through stabilization of c-Myc G-quadruplex DNA

A series of arene ruthenium(II) complexes coordinated by phenanthroimidazole derivatives have been synthesized and evaluated for their in vitro anticancer activities. It has been found that these types of arene Ru(II) complexes, especially [(C6H6)Ru(o-ClPIP)Cl]Cl·2H2O (2a), exhibited acceptable antiproliferative activity against several human cancer cell lines but with low toxicity towards normal HK-2 human cells. Mechanistic studies revealed that 2a-induced growth inhibition against osteosarcoma MG-63 cells was mainly caused by S-phase cell cycle arrest, which was confirmed by the down-regulation of cyclin A and CDK2 using western blot analysis of protein levels. Furthermore, studies using comet assay at single cell level indicated that 2a triggered DNA damage in MG-63 cells, and subsequently initiated S-phase arrest, as shown by the up-regulation of phosphorylated p53 and histone. Moreover, exposure of MG-63 cells to 2a resulted in the down-regulation of c-Myc protein expression. The in vitro DNA-binding behaviors also indicated that 2a could stabilize c-Myc G-quadruplex DNA (G4-DNA) by affecting its conformation. In conclusion, these results suggest that arene Ru(II) complexes coordinated by phenanthroimidazole derivatives serve as c-Myc G4-DNA stabilizers that could induce S-phase arrest in cancer cells by triggering DNA damage, which suggest that these complexes may act as potential candidates for the treatment of human malignant osteosarcoma.

V-shaped ligand bis(2-benzimidazolylmethyl)amine containing three copper(ii) ternary complexes: synthesis, structure, DNA-binding properties and antioxidant activity

Three copper(II) ternary complexes with the V-shaped ligand bis(2-benzimidazolylmethyl)amine (bba), with composition [Cu(bba)(crotonate)]·ClO4 (1), [Cu(bba)(methacrylate)]·ClO4 (2) and [Cu(bba)(acrylate)(CH3OH)]·NO3·H2O (3), have been synthesized and characterized by elemental analyses, molecular conductivities, IR, UV spectra and X-ray single crystal diffraction. The copper ions in these three complexes have a similar coordination mode, which can be described as a five-coordinated tetragonal pyramid geometry. The interaction of the ligand bba and copper(II) complexes with calf thymus DNA was investigated by electronic absorption, fluorescence spectroscopy and viscosity measurements. The experimental results suggest that the ligand bba and copper(II) complexes bind to DNA in an intercalation mode, and their binding affinity for DNA follows the order 2 > 1 > 3 > bba. The main reason for the DNA-binding behaviors can be attributed to the large coplanar aromatic rings in the V-shaped ligand. Such a trend in the DNA-binding affinities of the bba ligand and copper(II) complexes binding to DNA can be reasonably explained by the change of the electron density, the V-shaped angle (αV) and the value of τ. Moreover, the antioxidant assay in vitro also shows that the copper(II) complexes possess significant antioxidant activities.

Interaction of two new mixed ligand copper(II) complexes with DNA probed by thermodynamic and spectroscopic studies

The DNA binding behavior of [Cu(4,7-dmp)(phen-dione)Cl]Cl (1) and [Cu(2,9-dmp)(phen-dione)Cl]Cl (2) where dmp and phen-dion stand for dimethyl-1,10-phenanthroline and 1,10-phenanthroline-5,6-dion, respectively, was studied with a series of techniques including Viscometry, UV-Vis absorption, circular dichroism and fluorescence spectroscopy. Cytotoxicity effect was also investigated. Thermodynamic parameters, enthalpy and entropy changes were calculated according to Van't Hoff equation, which indicated that both reactions are predominantly enthalpically driven. However, these two complexes show different behavior in fluorescence, circular dichroism and viscometry methods which indicate the Cu(II) complexes interact with calf-thymus DNA by different mode of binding. These have further been verified by competition studies using Hoechst as a distinct groove binder. All these results indicate that these two complexes (1) and (2) interact with CT-DNA via groove binding and partially intercalative mode, respectively and the binding affinity of the complex 1 is higher than that of complex 2. Finally, our findings suggest that the type of ligands and structure of complexes have marked effect on the binding affinity of complexes involving CT-DNA. Also, these new complexes showed excellent antitumor activity against human T lymphocyte carcinoma-Jurkat cell line.

Dual topoisomerase I and II poisoning by chiral Ru(II) complexes containing 2-thiophenylimidazo[4,5-f][1,10]phenanthroline derivatives

A series of chiral Ru(II) complexes bearing thiophene ligands were synthesized and characterized. Both Ru(II) complexes Δ/Λ-[Ru(bpy)2(pscl)]2+ (Δ/Λ-1) and Δ/Λ-[Ru(bpy)2(psbr)]2+ (Δ/Λ-2) (bpy=2,2′-bipyridine, pscl=2-(5-chlorothiophen-2-yl)imidazo[4,5-f][1,10]phenanthroline, psbr=2-(5-bromothiophen-2-yl)imidazo[4,5-f][1,10]phenanthroline) showed antitumor activities against A549, HepG2 and BEL-7402 tumor cell lines, especially HeLa tumor cell line. Moreover, Δ enantiomers were more active than Λ enantiomers, accounting for the different cellular uptake. In addition, with the extension of time, these enantiomers could finally accumulate in the nucleus, suggesting that nucleic acids were the cellular target of these enantiomers. The DNA-binding behaviors of complexes were studied using spectroscopic and viscosity measurements. Results suggested that four complexes could bind to DNA in an intercalative mode but no obvious DNA-binding selectivity between the enantiomers was observed. Topoisomerase inhibition and DNA religation assay confirmed that four complexes acted as efficient dual topoisomerase I and II poisons, DNA strand breaks had also been observed from alkaline single cell gel electrophoresis (comet assay). Δ-1 and Δ-2 inhibited the growth of HeLa cells through the induction of apoptotic cell death, as evidenced by the Alexa Fluor® 488 annexin V staining assays and flow cytometry analysis. The results demonstrated that Δ/Λ-1 and Δ/Λ-2 acted as dual topoisomerase I and II poisons and caused DNA damage that could lead to cell cycle arrest by apoptosis.